github__gh-stack/cmd/rebase_test.go

package cmd

import (
	"encoding/json"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"testing"

	"github.com/github/gh-stack/internal/config"
	"github.com/github/gh-stack/internal/git"
	"github.com/github/gh-stack/internal/github"
	"github.com/github/gh-stack/internal/stack"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// rebaseCall records arguments passed to RebaseOnto or Rebase.
type rebaseCall struct {
	newBase string
	oldBase string
	branch  string
}

// resetCall records arguments passed to CheckoutBranch + ResetHard.
type resetCall struct {
	branch string
	sha    string
}

// newRebaseMock creates a MockOps pre-configured for rebase tests.
// It returns stable SHAs based on ref name, tracks checkout, and allows
// callers to override specific function fields after creation.
func newRebaseMock(tmpDir string, currentBranch string) *git.MockOps {
	return &git.MockOps{
		GitDirFn:        func() (string, error) { return tmpDir, nil },
		CurrentBranchFn: func() (string, error) { return currentBranch, nil },
		RevParseFn: func(ref string) (string, error) {
			// Default: origin/<branch> returns same SHA as <branch> (no FF needed)
			if strings.HasPrefix(ref, "origin/") {
				return "sha-" + strings.TrimPrefix(ref, "origin/"), nil
			}
			return "sha-" + ref, nil
		},
		IsAncestorFn:    func(a, d string) (bool, error) { return true, nil },
		FetchFn:         func(string) error { return nil },
		EnableRerereFn:  func() error { return nil },
		IsRebaseInProgressFn: func() bool { return false },
	}
}

// TestRebase_CascadeRebase verifies that a stack [b1, b2, b3] with all active
// branches triggers the correct cascade: b1 rebased onto trunk, b2 onto b1,
// b3 onto b2.
func TestRebase_CascadeRebase(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var allRebaseCalls []rebaseCall
	var currentCheckedOut string

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(name string) error {
		currentCheckedOut = name
		return nil
	}
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase: base, oldBase: "", branch: currentCheckedOut})
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)

	// All branches should be rebased in order: b1 onto main, b2 onto b1, b3 onto b2
	require.Len(t, allRebaseCalls, 3)
	assert.Equal(t, "main", allRebaseCalls[0].newBase, "b1 should be rebased onto trunk")
	assert.Equal(t, "b1", allRebaseCalls[1].newBase, "b2 should be rebased onto b1")
	assert.Equal(t, "b2", allRebaseCalls[2].newBase, "b3 should be rebased onto b2")

	assert.Contains(t, output, "rebased locally")
}

// TestRebase_MergedBranch_UsesOnto verifies that when b1 has a merged PR,
// it is skipped and b2 uses RebaseOnto with trunk as newBase and b1's original
// SHA as oldBase. b3 also uses --onto (propagation).
func TestRebase_MergedBranch_UsesOnto(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10, Merged: true}},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var rebaseCalls []rebaseCall

	// Use explicit SHAs so assertions are self-documenting
	branchSHAs := map[string]string{
		"main": "main-sha-aaa",
		"b1":   "b1-orig-sha",
		"b2":   "b2-orig-sha",
		"b3":   "b3-orig-sha",
	}

	mock := newRebaseMock(tmpDir, "b2")
	mock.BranchExistsFn = func(name string) bool { return true }
	mock.RevParseFn = func(ref string) (string, error) {
		if sha, ok := branchSHAs[ref]; ok {
			return sha, nil
		}
		return "default-sha", nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "Skipping b1")

	// b2: onto trunk, oldBase = b1's original SHA
	// b3: onto b2, oldBase = b2's original SHA (propagation)
	require.Len(t, rebaseCalls, 2)
	assert.Equal(t, rebaseCall{"main", "b1-orig-sha", "b2"}, rebaseCalls[0],
		"b2 should rebase --onto main using b1's original SHA as oldBase")
	assert.Equal(t, rebaseCall{"b2", "b2-orig-sha", "b3"}, rebaseCalls[1],
		"b3 should propagate --onto mode with b2's original SHA as oldBase")
}

// TestRebase_OntoPropagatesToSubsequentBranches verifies that when multiple
// branches are merged, --onto propagates correctly through the chain.
func TestRebase_OntoPropagatesToSubsequentBranches(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10, Merged: true}},
			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11, Merged: true}},
			{Branch: "b3"},
			{Branch: "b4"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var rebaseCalls []rebaseCall

	// Use explicit SHAs so assertions are self-documenting
	branchSHAs := map[string]string{
		"main": "main-sha-aaa",
		"b1":   "b1-orig-sha",
		"b2":   "b2-orig-sha",
		"b3":   "b3-orig-sha",
		"b4":   "b4-orig-sha",
	}

	mock := newRebaseMock(tmpDir, "b3")
	mock.BranchExistsFn = func(name string) bool { return true }
	mock.RevParseFn = func(ref string) (string, error) {
		if sha, ok := branchSHAs[ref]; ok {
			return sha, nil
		}
		return "default-sha", nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "Skipping b1")
	assert.Contains(t, output, "Skipping b2")

	// b1 merged → ontoOldBase = b1-orig-sha
	// b2 merged → ontoOldBase = b2-orig-sha
	// b3: first non-merged ancestor search finds none → newBase = trunk
	//   RebaseOnto("main", "b2-orig-sha", "b3")
	// b4: first non-merged ancestor = b3 → newBase = b3
	//   RebaseOnto("b3", "b3-orig-sha", "b4")
	require.Len(t, rebaseCalls, 2)
	assert.Equal(t, rebaseCall{"main", "b2-orig-sha", "b3"}, rebaseCalls[0],
		"b3 should rebase --onto main with b2's SHA as oldBase")
	assert.Equal(t, rebaseCall{"b3", "b3-orig-sha", "b4"}, rebaseCalls[1],
		"b4 should rebase --onto b3 with b3's original SHA as oldBase")
}

// TestRebase_StaleOntoOldBase_FallsBackToMergeBase verifies that when a branch
// was already rebased past the merged branch's tip (e.g. by a previous run),
// the stale ontoOldBase is detected via IsAncestor and replaced with
// merge-base(newBase, branch) to avoid replaying already-applied commits.
func TestRebase_StaleOntoOldBase_FallsBackToMergeBase(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10, Merged: true}},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var rebaseCalls []rebaseCall

	// b1's local ref is the stale pre-squash tip from before a previous rebase.
	// b2 was already rebased onto main by a previous run, so b1's old tip
	// is NOT an ancestor of b2.
	branchSHAs := map[string]string{
		"main": "main-sha",
		"b1":   "b1-stale-presquash-sha",
		"b2":   "b2-on-main-sha",
		"b3":   "b3-on-b2-sha",
	}

	mock := newRebaseMock(tmpDir, "b2")
	mock.BranchExistsFn = func(name string) bool { return true }
	mock.RevParseFn = func(ref string) (string, error) {
		if sha, ok := branchSHAs[ref]; ok {
			return sha, nil
		}
		return "default-sha", nil
	}
	mock.IsAncestorFn = func(ancestor, descendant string) (bool, error) {
		// b1's stale SHA is NOT an ancestor of b2 (b2 was already rebased onto main)
		if ancestor == "b1-stale-presquash-sha" {
			return false, nil
		}
		return true, nil
	}
	mock.MergeBaseFn = func(a, b string) (string, error) {
		if a == "main" && b == "b2" {
			return "main-b2-mergebase", nil
		}
		return "default-mergebase", nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Out.Close()
	cfg.Err.Close()

	assert.NoError(t, err)
	require.Len(t, rebaseCalls, 2)

	// b2: stale ontoOldBase detected → falls back to merge-base(main, b2)
	assert.Equal(t, rebaseCall{"main", "main-b2-mergebase", "b2"}, rebaseCalls[0],
		"b2 should use merge-base as oldBase when ontoOldBase is stale")

	// b3: b2's SHA is a valid ancestor → uses it directly
	assert.Equal(t, rebaseCall{"b2", "b2-on-main-sha", "b3"}, rebaseCalls[1],
		"b3 should use b2's original SHA as oldBase (not stale)")
}

// TestRebase_ConflictSavesState verifies that when a rebase conflict occurs,
// the state is saved with the conflict branch and remaining branches.
func TestRebase_ConflictSavesState(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	mock := newRebaseMock(tmpDir, "b1")
	mock.CheckoutBranchFn = func(string) error { return nil }
	mock.RebaseFn = func(string, git.RebaseOpts) error { return nil } // b1 succeeds
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		if branch == "b2" {
			return assert.AnError // conflict on b2
		}
		return nil
	}
	mock.ConflictedFilesFn = func() ([]string, error) { return nil, nil }

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.Error(t, err)
	assert.ErrorIs(t, err, ErrConflict)
	assert.Contains(t, output, "--continue")

	// Verify state file was saved
	stateData, readErr := os.ReadFile(filepath.Join(tmpDir, "gh-stack-rebase-state"))
	require.NoError(t, readErr, "rebase state file should be saved")

	var state rebaseState
	require.NoError(t, json.Unmarshal(stateData, &state))
	assert.Equal(t, "b2", state.ConflictBranch)
	assert.Equal(t, []string{"b3"}, state.RemainingBranches)
	assert.Equal(t, "b1", state.OriginalBranch)
	assert.Contains(t, state.OriginalRefs, "b1")
	assert.Contains(t, state.OriginalRefs, "b2")
	assert.Contains(t, state.OriginalRefs, "b3")
}

// TestRebase_Continue_NoState verifies that --continue without a state file
// produces a "no rebase in progress" message.
func TestRebase_Continue_NoState(t *testing.T) {
	tmpDir := t.TempDir()

	mock := newRebaseMock(tmpDir, "b1")
	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--continue"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.ErrorIs(t, err, ErrSilent)
	assert.Contains(t, output, "no rebase in progress")
}

// TestRebase_Abort_RestoresBranches verifies that --abort restores all branches
// to their original SHAs and removes the state file.
func TestRebase_Abort_RestoresBranches(t *testing.T) {
	tmpDir := t.TempDir()

	// Pre-create rebase state
	state := &rebaseState{
		CurrentBranchIndex: 1,
		ConflictBranch:     "b2",
		RemainingBranches:  []string{"b3"},
		OriginalBranch:     "b1",
		OriginalRefs: map[string]string{
			"b1": "orig-sha-b1",
			"b2": "orig-sha-b2",
			"b3": "orig-sha-b3",
		},
	}
	stateData, _ := json.MarshalIndent(state, "", "  ")
	require.NoError(t, os.WriteFile(filepath.Join(tmpDir, "gh-stack-rebase-state"), stateData, 0644))

	var resets []resetCall
	var checkouts []string
	currentBranch := "b2" // simulating we're on the conflict branch

	mock := newRebaseMock(tmpDir, currentBranch)
	mock.CheckoutBranchFn = func(name string) error {
		checkouts = append(checkouts, name)
		currentBranch = name
		return nil
	}
	mock.ResetHardFn = func(ref string) error {
		resets = append(resets, resetCall{currentBranch, ref})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--abort"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "Rebase aborted and branches restored")

	// Verify each branch was reset to its original SHA.
	// Map iteration order is non-deterministic, so collect into a map.
	resetMap := make(map[string]string)
	for _, r := range resets {
		resetMap[r.branch] = r.sha
	}
	assert.Equal(t, "orig-sha-b1", resetMap["b1"])
	assert.Equal(t, "orig-sha-b2", resetMap["b2"])
	assert.Equal(t, "orig-sha-b3", resetMap["b3"])

	// State file should be removed
	_, err = os.Stat(filepath.Join(tmpDir, "gh-stack-rebase-state"))
	assert.True(t, os.IsNotExist(err), "state file should be removed after abort")

	// Should return to original branch
	assert.Contains(t, checkouts, "b1", "should checkout original branch at end")
}

// TestRebase_DownstackOnly verifies that --downstack only rebases branches
// from trunk to the current branch (inclusive).
func TestRebase_DownstackOnly(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var allRebaseCalls []rebaseCall
	var currentCheckedOut string

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(name string) error {
		currentCheckedOut = name
		return nil
	}
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase: base, oldBase: "", branch: currentCheckedOut})
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--downstack"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Out.Close()
	cfg.Err.Close()

	assert.NoError(t, err)
	// b2 is at index 1, so downstack = [b1, b2] (indices 0..1)
	require.Len(t, allRebaseCalls, 2, "downstack should rebase b1 and b2 only")
	assert.Equal(t, "main", allRebaseCalls[0].newBase, "b1 should be rebased onto trunk")
	assert.Equal(t, "b1", allRebaseCalls[1].newBase, "b2 should be rebased onto b1")
}

// TestRebase_UpstackOnly verifies that --upstack only rebases branches
// from the current branch to the top.
func TestRebase_UpstackOnly(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var allRebaseCalls []rebaseCall
	var currentCheckedOut string

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(name string) error {
		currentCheckedOut = name
		return nil
	}
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase: base, oldBase: "", branch: currentCheckedOut})
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--upstack"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Out.Close()
	cfg.Err.Close()

	assert.NoError(t, err)
	// b2 is at index 1, upstack = [b2, b3] (indices 1..2)
	require.Len(t, allRebaseCalls, 2, "upstack should rebase b2 and b3")
	assert.Equal(t, "b1", allRebaseCalls[0].newBase, "b2 should be rebased onto b1")
	assert.Equal(t, "b2", allRebaseCalls[1].newBase, "b3 should be rebased onto b2")
}

// TestRebase_UpstackWithMergedBranchBelow verifies that --upstack pre-seeds
// --onto state when a merged branch exists immediately below the rebase range.
func TestRebase_UpstackWithMergedBranchBelow(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10, Merged: true}},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var allRebaseCalls []rebaseCall
	var currentCheckedOut string

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(name string) error {
		currentCheckedOut = name
		return nil
	}
	mock.BranchExistsFn = func(name string) bool { return true }
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase: base, oldBase: "", branch: currentCheckedOut})
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--upstack"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Out.Close()
	cfg.Err.Close()

	assert.NoError(t, err)
	// b2 is at index 1, upstack = [b2, b3]. b1 is merged below.
	// b2 should use --onto because b1 was merged.
	require.Len(t, allRebaseCalls, 2, "upstack should rebase b2 and b3")

	// b2: --onto rebase with b1's old SHA as old base
	assert.Equal(t, "main", allRebaseCalls[0].newBase, "b2 should be rebased onto main (first non-merged ancestor)")
	assert.Equal(t, "sha-b1", allRebaseCalls[0].oldBase, "b2 should use b1's original SHA as old base")
	assert.Equal(t, "b2", allRebaseCalls[0].branch, "b2 should be the branch being rebased")

	// b3: --onto continues to propagate
	assert.Equal(t, "b2", allRebaseCalls[1].newBase, "b3 should be rebased onto b2")
	assert.NotEmpty(t, allRebaseCalls[1].oldBase, "b3 should also use --onto")
}

// TestRebase_SkipsMergedBranches verifies that merged branches are skipped
// with an appropriate message.
func TestRebase_SkipsMergedBranches(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 42, Merged: true}},
			{Branch: "b2"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var rebaseCalls []rebaseCall

	mock := newRebaseMock(tmpDir, "b2")
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "Skipping b1")
	assert.Contains(t, output, "PR #42 merged")

	// Only b2 should be rebased
	require.Len(t, rebaseCalls, 1)
	assert.Equal(t, "b2", rebaseCalls[0].branch)
}

// queuedPRClient returns a MockClient whose FindPRByNumber reports the given PR
// numbers as queued (in a merge queue, open, not merged) and finds no PR by
// branch name. Used to drive the transient Queued state through syncStackPRs in
// rebase/sync tests.
func queuedPRClient(headByNumber map[int]string) *github.MockClient {
	return &github.MockClient{
		FindPRByNumberFn: func(n int) (*github.PullRequest, error) {
			head, ok := headByNumber[n]
			if !ok {
				return nil, nil
			}
			return &github.PullRequest{
				Number:          n,
				HeadRefName:     head,
				State:           "OPEN",
				Merged:          false,
				MergeQueueEntry: &github.MergeQueueEntry{ID: fmt.Sprintf("MQ_%d", n)},
			}, nil
		},
		FindPRForBranchFn: func(string) (*github.PullRequest, error) { return nil, nil },
	}
}

// TestRebase_QueuedBranch_DownstreamStaysStacked verifies the #144 fix: a queued
// PR is NOT treated as merged. Its branch is skipped (frozen in the merge queue),
// but downstream branches stay stacked on top of it — they rebase onto the queued
// branch, not --onto trunk with the queued commits dropped.
func TestRebase_QueuedBranch_DownstreamStaysStacked(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10}},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var rebaseCalls []rebaseCall

	mock := newRebaseMock(tmpDir, "b2")
	mock.BranchExistsFn = func(name string) bool { return true }
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cfg.GitHubClientOverride = queuedPRClient(map[int]string{10: "b1"})
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "Skipping b1")
	assert.Contains(t, output, "queued")
	assert.NotContains(t, output, "adjusted for merged PR",
		"queued branches must not trigger the merged --onto path")

	// b2 stays stacked on the queued b1 (not rebased --onto main); b3 onto b2.
	require.Len(t, rebaseCalls, 2)
	assert.Equal(t, rebaseCall{"b1", "sha-b1", "b2"}, rebaseCalls[0],
		"b2 should rebase onto the queued branch b1, keeping its commits")
	assert.Equal(t, rebaseCall{"b2", "sha-b2", "b3"}, rebaseCalls[1],
		"b3 should rebase onto b2")
}

// TestRebase_MergedBelowQueued_KeepsStackedOnQueued verifies that when a merged
// branch sits below a queued branch, the branch above the queued one stays
// stacked on the queued branch. The queued branch is frozen and still carries the
// merged branch's commits, so downstream cannot drop them via --onto.
func TestRebase_MergedBelowQueued_KeepsStackedOnQueued(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10, Merged: true}},
			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11}},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var rebaseCalls []rebaseCall

	mock := newRebaseMock(tmpDir, "b3")
	mock.BranchExistsFn = func(name string) bool { return true }
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cfg.GitHubClientOverride = queuedPRClient(map[int]string{11: "b2"})
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "Skipping b1")
	assert.Contains(t, output, "PR #10 merged")
	assert.Contains(t, output, "Skipping b2")
	assert.Contains(t, output, "queued")

	// b1 merged and b2 queued are both skipped. b3 stays stacked on the queued
	// b2 — it must NOT be rebased --onto main (which would drop b2's + b1's
	// commits while b2 is frozen).
	require.Len(t, rebaseCalls, 1)
	assert.Equal(t, rebaseCall{"b2", "sha-b2", "b3"}, rebaseCalls[0],
		"b3 should rebase onto the queued b2, not --onto main")
	assert.NotContains(t, output, "adjusted for merged PR")
}

// TestRebase_UpstackAboveQueuedBranch verifies the onto-seed fix: with --upstack
// starting just above a queued branch, the first in-range branch rebases normally
// onto the queued predecessor rather than dropping its commits via --onto.
func TestRebase_UpstackAboveQueuedBranch(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10}},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var rebaseCalls []rebaseCall

	mock := newRebaseMock(tmpDir, "b2")
	mock.BranchExistsFn = func(name string) bool { return true }
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cfg.GitHubClientOverride = queuedPRClient(map[int]string{10: "b1"})
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--upstack"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	// upstack from b2 = [b2, b3]; b1 (queued) is below the range.
	require.Len(t, rebaseCalls, 2)
	assert.Equal(t, rebaseCall{"b1", "sha-b1", "b2"}, rebaseCalls[0],
		"b2 should rebase onto the queued predecessor b1, not --onto main")
	assert.Equal(t, rebaseCall{"b2", "sha-b2", "b3"}, rebaseCalls[1],
		"b3 should rebase onto b2")
	assert.NotContains(t, output, "adjusted for merged PR")
}

// TestRebase_StateRoundTrip verifies that rebase state can be saved and loaded
// back with all fields preserved, including the --onto fields.
func TestRebase_StateRoundTrip(t *testing.T) {
	tmpDir := t.TempDir()

	original := &rebaseState{
		CurrentBranchIndex: 2,
		ConflictBranch:     "feature-b",
		RemainingBranches:  []string{"feature-c", "feature-d"},
		OriginalBranch:     "feature-a",
		OriginalRefs: map[string]string{
			"feature-a": "aaa111",
			"feature-b": "bbb222",
			"feature-c": "ccc333",
			"feature-d": "ddd444",
		},
		UseOnto:     true,
		OntoOldBase: "bbb222",
	}

	err := saveRebaseState(tmpDir, original)
	require.NoError(t, err)

	loaded, err := loadRebaseState(tmpDir)
	require.NoError(t, err)

	assert.Equal(t, original.CurrentBranchIndex, loaded.CurrentBranchIndex)
	assert.Equal(t, original.ConflictBranch, loaded.ConflictBranch)
	assert.Equal(t, original.RemainingBranches, loaded.RemainingBranches)
	assert.Equal(t, original.OriginalBranch, loaded.OriginalBranch)
	assert.Equal(t, original.OriginalRefs, loaded.OriginalRefs)
	assert.Equal(t, original.UseOnto, loaded.UseOnto)
	assert.Equal(t, original.OntoOldBase, loaded.OntoOldBase)
}

// TestRebase_Continue_RebasesRemainingBranches verifies the --continue success
// path: RebaseContinue is called, remaining branches are rebased via RebaseOnto,
// the state file is cleaned up, and the original branch is restored.
func TestRebase_Continue_RebasesRemainingBranches(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	// State: b2 had a conflict (index 1), b3 remains to be rebased.
	state := &rebaseState{
		CurrentBranchIndex: 1,
		ConflictBranch:     "b2",
		RemainingBranches:  []string{"b3"},
		OriginalBranch:     "b1",
		OriginalRefs: map[string]string{
			"main": "main-orig-sha",
			"b1":   "b1-orig-sha",
			"b2":   "b2-orig-sha",
			"b3":   "b3-orig-sha",
		},
	}
	stateData, _ := json.MarshalIndent(state, "", "  ")
	require.NoError(t, os.WriteFile(filepath.Join(tmpDir, "gh-stack-rebase-state"), stateData, 0644))

	var rebaseContinueCalled bool
	var rebaseCalls []rebaseCall
	var checkouts []string

	mock := newRebaseMock(tmpDir, "b2")
	mock.IsRebaseInProgressFn = func() bool { return true }
	mock.RebaseContinueFn = func(opts git.RebaseOpts) error {
		rebaseContinueCalled = true
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}
	mock.CheckoutBranchFn = func(name string) error {
		checkouts = append(checkouts, name)
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--continue"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	assert.NoError(t, err)
	assert.True(t, rebaseContinueCalled, "RebaseContinue should be called")

	// b3 is at idx 2 (idx > 0, not UseOnto) → RebaseOnto(base=b2, originalRefs[b2], b3)
	require.Len(t, rebaseCalls, 1)
	assert.Equal(t, rebaseCall{"b2", "b2-orig-sha", "b3"}, rebaseCalls[0])

	// State file should be removed after success
	_, statErr := os.Stat(filepath.Join(tmpDir, "gh-stack-rebase-state"))
	assert.True(t, os.IsNotExist(statErr), "state file should be removed after success")

	// Original branch should be checked out at the end
	assert.Contains(t, checkouts, "b1", "should checkout original branch")
}

// TestRebase_Continue_QueuedBranchBelowConflict verifies that a queued branch is
// still skipped when the cascade resumes via --continue after a conflict below
// it. The Queued flag is transient and lost when continueRebase reloads the
// stack from disk, so it must be refreshed before the remaining cascade — else
// the frozen merge-queue branch would be rebased.
func TestRebase_Continue_QueuedBranchBelowConflict(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 20}},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	// State: b1 (below the queued b2) conflicted; b2 and b3 remain.
	state := &rebaseState{
		CurrentBranchIndex: 0,
		ConflictBranch:     "b1",
		RemainingBranches:  []string{"b2", "b3"},
		OriginalBranch:     "b3",
		OriginalRefs: map[string]string{
			"main": "main-orig-sha",
			"b1":   "sha-b1",
			"b2":   "sha-b2",
			"b3":   "sha-b3",
		},
	}
	stateData, _ := json.MarshalIndent(state, "", "  ")
	require.NoError(t, os.WriteFile(filepath.Join(tmpDir, "gh-stack-rebase-state"), stateData, 0644))

	var rebaseCalls []rebaseCall

	mock := newRebaseMock(tmpDir, "b1")
	mock.BranchExistsFn = func(name string) bool { return true }
	mock.IsRebaseInProgressFn = func() bool { return true }
	mock.RebaseContinueFn = func(opts git.RebaseOpts) error { return nil }
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}
	mock.CheckoutBranchFn = func(string) error { return nil }

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cfg.GitHubClientOverride = queuedPRClient(map[int]string{20: "b2"})
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--continue"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "Skipping b2")
	assert.Contains(t, output, "queued")

	// Only b3 is rebased, onto the queued b2. The queued b2 itself must not be
	// rebased (its branch is frozen in the merge queue).
	require.Len(t, rebaseCalls, 1)
	assert.Equal(t, rebaseCall{"b2", "sha-b2", "b3"}, rebaseCalls[0])
	for _, c := range rebaseCalls {
		assert.NotEqual(t, "b2", c.branch, "the frozen queued branch must not be rebased")
	}
}

// TestRebase_Continue_OntoMode verifies the --continue path when UseOnto is
// set (merged branches upstream). With no remaining branches, only
// RebaseContinue runs and the state is cleaned up.
func TestRebase_Continue_OntoMode(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", PullRequest: &stack.PullRequestRef{Number: 10, Merged: true}},
			{Branch: "b2", PullRequest: &stack.PullRequestRef{Number: 11, Merged: true}},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	// b3 was the conflict branch; no remaining branches after it.
	state := &rebaseState{
		CurrentBranchIndex: 2,
		ConflictBranch:     "b3",
		RemainingBranches:  []string{},
		OriginalBranch:     "b1",
		OriginalRefs: map[string]string{
			"main": "sha-main",
			"b1":   "sha-b1",
			"b2":   "sha-b2",
			"b3":   "sha-b3",
		},
		UseOnto:     true,
		OntoOldBase: "sha-b2",
	}
	stateData, _ := json.MarshalIndent(state, "", "  ")
	require.NoError(t, os.WriteFile(filepath.Join(tmpDir, "gh-stack-rebase-state"), stateData, 0644))

	var rebaseContinueCalled bool

	mock := newRebaseMock(tmpDir, "b3")
	mock.IsRebaseInProgressFn = func() bool { return true }
	mock.RebaseContinueFn = func(opts git.RebaseOpts) error {
		rebaseContinueCalled = true
		return nil
	}
	mock.CheckoutBranchFn = func(string) error { return nil }

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--continue"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	assert.NoError(t, err)
	assert.True(t, rebaseContinueCalled, "RebaseContinue should be called")

	// State file should be removed after success
	_, statErr := os.Stat(filepath.Join(tmpDir, "gh-stack-rebase-state"))
	assert.True(t, os.IsNotExist(statErr), "state file should be removed after success")
}

// TestRebase_Continue_ConflictOnRemaining verifies that when --continue
// successfully resolves the first conflict but hits a new conflict on a
// remaining branch, the state is updated and ErrConflict is returned.
func TestRebase_Continue_ConflictOnRemaining(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
			{Branch: "b4"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	state := &rebaseState{
		CurrentBranchIndex: 1,
		ConflictBranch:     "b2",
		RemainingBranches:  []string{"b3", "b4"},
		OriginalBranch:     "b1",
		OriginalRefs: map[string]string{
			"main": "sha-main",
			"b1":   "sha-b1",
			"b2":   "sha-b2",
			"b3":   "sha-b3",
			"b4":   "sha-b4",
		},
	}
	stateData, _ := json.MarshalIndent(state, "", "  ")
	require.NoError(t, os.WriteFile(filepath.Join(tmpDir, "gh-stack-rebase-state"), stateData, 0644))

	mock := newRebaseMock(tmpDir, "b2")
	mock.IsRebaseInProgressFn = func() bool { return true }
	mock.RebaseContinueFn = func(opts git.RebaseOpts) error { return nil }
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		if branch == "b3" {
			return assert.AnError // conflict on b3
		}
		return nil
	}
	mock.ConflictedFilesFn = func() ([]string, error) { return nil, nil }
	mock.CheckoutBranchFn = func(string) error { return nil }

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--continue"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.Error(t, err)
	assert.ErrorIs(t, err, ErrConflict)
	assert.Contains(t, output, "--continue")

	// State file should still exist with updated conflict info
	updatedData, readErr := os.ReadFile(filepath.Join(tmpDir, "gh-stack-rebase-state"))
	require.NoError(t, readErr, "state file should still exist after new conflict")

	var updatedState rebaseState
	require.NoError(t, json.Unmarshal(updatedData, &updatedState))
	assert.Equal(t, "b3", updatedState.ConflictBranch)
	assert.Equal(t, []string{"b4"}, updatedState.RemainingBranches)
}

// TestRebase_Abort_WithActiveRebase verifies that --abort calls RebaseAbort
// when a git rebase is in progress, restores branches, and cleans up the state.
func TestRebase_Abort_WithActiveRebase(t *testing.T) {
	tmpDir := t.TempDir()

	state := &rebaseState{
		CurrentBranchIndex: 1,
		ConflictBranch:     "b2",
		RemainingBranches:  []string{},
		OriginalBranch:     "b1",
		OriginalRefs: map[string]string{
			"b1": "orig-sha-b1",
			"b2": "orig-sha-b2",
		},
	}
	stateData, _ := json.MarshalIndent(state, "", "  ")
	require.NoError(t, os.WriteFile(filepath.Join(tmpDir, "gh-stack-rebase-state"), stateData, 0644))

	var rebaseAbortCalled bool
	var resets []resetCall
	var checkouts []string
	currentBranch := "b2"

	mock := newRebaseMock(tmpDir, currentBranch)
	mock.IsRebaseInProgressFn = func() bool { return true }
	mock.RebaseAbortFn = func() error {
		rebaseAbortCalled = true
		return nil
	}
	mock.CheckoutBranchFn = func(name string) error {
		checkouts = append(checkouts, name)
		currentBranch = name
		return nil
	}
	mock.ResetHardFn = func(ref string) error {
		resets = append(resets, resetCall{currentBranch, ref})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--abort"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.True(t, rebaseAbortCalled, "RebaseAbort should be called when rebase is in progress")
	assert.Contains(t, output, "Rebase aborted and branches restored")

	// Verify branches restored to original SHAs
	resetMap := make(map[string]string)
	for _, r := range resets {
		resetMap[r.branch] = r.sha
	}
	assert.Equal(t, "orig-sha-b1", resetMap["b1"])
	assert.Equal(t, "orig-sha-b2", resetMap["b2"])

	// State file should be removed
	_, statErr := os.Stat(filepath.Join(tmpDir, "gh-stack-rebase-state"))
	assert.True(t, os.IsNotExist(statErr), "state file should be removed after abort")

	// Should return to original branch
	assert.Contains(t, checkouts, "b1", "should checkout original branch at end")
}

// TestRebase_FastForwardsBranchFromRemote verifies that when origin/b1 is ahead
// of local b1 (someone pushed a new commit), the branch is fast-forwarded before
// the cascade rebase so downstream branches include the new commits.
func TestRebase_FastForwardsBranchFromRemote(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var allRebaseCalls []rebaseCall
	var updateBranchRefCalls []struct{ branch, sha string }

	mock := newRebaseMock(tmpDir, "b2")
	// b1 is behind origin/b1 (remote has new commit)
	mock.RevParseFn = func(ref string) (string, error) {
		if ref == "b1" {
			return "b1-local-sha", nil
		}
		if ref == "origin/b1" {
			return "b1-remote-sha", nil
		}
		// trunk and origin/trunk same — trunk already up to date
		if ref == "main" || ref == "origin/main" {
			return "main-sha", nil
		}
		if strings.HasPrefix(ref, "origin/") {
			return "sha-" + strings.TrimPrefix(ref, "origin/"), nil
		}
		return "sha-" + ref, nil
	}
	mock.IsAncestorFn = func(a, d string) (bool, error) {
		// b1-local is ancestor of b1-remote → can fast-forward
		if a == "b1-local-sha" && d == "b1-remote-sha" {
			return true, nil
		}
		return false, nil
	}
	mock.UpdateBranchRefFn = func(branch, sha string) error {
		updateBranchRefCalls = append(updateBranchRefCalls, struct{ branch, sha string }{branch, sha})
		return nil
	}
	mock.CheckoutBranchFn = func(string) error { return nil }
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase: base})
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	// b1 should be fast-forwarded to remote SHA
	require.Len(t, updateBranchRefCalls, 1, "should fast-forward b1 via UpdateBranchRef")
	assert.Equal(t, "b1", updateBranchRefCalls[0].branch)
	assert.Equal(t, "b1-remote-sha", updateBranchRefCalls[0].sha)

	assert.Contains(t, output, "Fast-forwarded b1")

	// Cascade rebase should still occur
	assert.NotEmpty(t, allRebaseCalls, "cascade rebase should still happen")
}

// TestRebase_BranchAlreadyUpToDate_NoFF verifies that when a branch's local
// and remote SHAs match, no fast-forward occurs.
func TestRebase_BranchAlreadyUpToDate_NoFF(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var updateBranchRefCalls int
	var mergeFFCalls int

	mock := newRebaseMock(tmpDir, "b1")
	// Same SHA for b1 and origin/b1 — already up to date (default mock handles this)
	mock.UpdateBranchRefFn = func(string, string) error {
		updateBranchRefCalls++
		return nil
	}
	mock.MergeFFFn = func(string) error {
		mergeFFCalls++
		return nil
	}
	mock.CheckoutBranchFn = func(string) error { return nil }
	mock.RebaseFn = func(string, git.RebaseOpts) error { return nil }

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Out.Close()
	cfg.Err.Close()

	assert.NoError(t, err)
	assert.Equal(t, 0, updateBranchRefCalls, "no UpdateBranchRef for branches already up to date")
	assert.Equal(t, 0, mergeFFCalls, "no MergeFF for branches already up to date")
}

// TestRebase_BranchDiverged_NoFF verifies that when local and remote branches
// have diverged (e.g., after a previous local rebase), no fast-forward occurs.
func TestRebase_BranchDiverged_NoFF(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var updateBranchRefCalls int

	mock := newRebaseMock(tmpDir, "b1")
	// Different SHAs for b1 and origin/b1
	mock.RevParseFn = func(ref string) (string, error) {
		if ref == "b1" {
			return "b1-local-sha", nil
		}
		if ref == "origin/b1" {
			return "b1-remote-sha", nil
		}
		if ref == "main" || ref == "origin/main" {
			return "main-sha", nil
		}
		return "sha-" + ref, nil
	}
	// Neither is ancestor of the other — diverged
	mock.IsAncestorFn = func(a, d string) (bool, error) {
		return false, nil
	}
	mock.UpdateBranchRefFn = func(string, string) error {
		updateBranchRefCalls++
		return nil
	}
	mock.CheckoutBranchFn = func(string) error { return nil }
	mock.RebaseFn = func(string, git.RebaseOpts) error { return nil }

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Out.Close()
	cfg.Err.Close()

	assert.NoError(t, err)
	assert.Equal(t, 0, updateBranchRefCalls, "no FF when branches have diverged")
}

func TestRebase_SkipsMergedBranchesNotExistingLocally(t *testing.T) {
	// Simulates a stack where b1 is merged and its branch was auto-deleted
	// from the remote, so it doesn't exist locally. The stored Head SHA is
	// used as ontoOldBase for the next branch's --onto rebase.
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1", Head: "b1-stored-head-sha", PullRequest: &stack.PullRequestRef{Number: 42, Merged: true}},
			{Branch: "b2"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var rebaseCalls []rebaseCall

	mock := newRebaseMock(tmpDir, "b2")
	mock.BranchExistsFn = func(name string) bool {
		// b1 does not exist locally (deleted from remote after merge)
		return name != "b1"
	}
	mock.RevParseMultiFn = func(refs []string) ([]string, error) {
		// Only resolve refs that exist — b1 should not be in the list
		shas := make([]string, len(refs))
		for i, r := range refs {
			if r == "b1" {
				t.Fatalf("RevParseMulti should not be called with non-existent branch b1")
			}
			shas[i] = "sha-" + r
		}
		return shas, nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseCalls = append(rebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "Skipping b1")

	// Only b2 should be rebased, and the rebase should use b1's stored
	// Head SHA as oldBase so `git rebase --onto` receives valid arguments.
	require.Len(t, rebaseCalls, 1)
	assert.Equal(t, "b2", rebaseCalls[0].branch)
	assert.Equal(t, "main", rebaseCalls[0].newBase)
	assert.Equal(t, "b1-stored-head-sha", rebaseCalls[0].oldBase)
}

// TestRebase_CommitterDateIsAuthorDate verifies that when
// --committer-date-is-author-date is passed, it is forwarded to all rebase
// calls in the cascade.
func TestRebase_CommitterDateIsAuthorDate(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var receivedOpts []git.RebaseOpts
	var currentCheckedOut string

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(name string) error {
		currentCheckedOut = name
		return nil
	}
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		receivedOpts = append(receivedOpts, opts)
		_ = currentCheckedOut
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		receivedOpts = append(receivedOpts, opts)
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	cmd.SetArgs([]string{"--committer-date-is-author-date"})
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "rebased locally")

	// All 3 rebase calls should have CommitterDateIsAuthorDate set.
	require.Len(t, receivedOpts, 3)
	for i, opts := range receivedOpts {
		assert.True(t, opts.CommitterDateIsAuthorDate,
			"rebase call %d should have CommitterDateIsAuthorDate=true", i)
	}
}

// TestRebase_PreserveDatesAlias verifies that --preserve-dates is an alias
// for --committer-date-is-author-date.
func TestRebase_PreserveDatesAlias(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var receivedOpts []git.RebaseOpts

	mock := newRebaseMock(tmpDir, "b1")
	mock.CheckoutBranchFn = func(string) error { return nil }
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		receivedOpts = append(receivedOpts, opts)
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	cmd.SetArgs([]string{"--preserve-dates"})
	err := cmd.Execute()

	assert.NoError(t, err)
	require.Len(t, receivedOpts, 1)
	assert.True(t, receivedOpts[0].CommitterDateIsAuthorDate,
		"--preserve-dates should set CommitterDateIsAuthorDate=true")
}

// TestRebase_StateRoundTrip_CommitterDateIsAuthorDate verifies that
// CommitterDateIsAuthorDate is persisted and restored in rebase state.
func TestRebase_StateRoundTrip_CommitterDateIsAuthorDate(t *testing.T) {
	tmpDir := t.TempDir()

	original := &rebaseState{
		CurrentBranchIndex: 1,
		ConflictBranch:     "b2",
		RemainingBranches:  []string{"b3"},
		OriginalBranch:     "b1",
		OriginalRefs: map[string]string{
			"b1": "sha-b1",
			"b2": "sha-b2",
			"b3": "sha-b3",
		},
		CommitterDateIsAuthorDate: true,
	}

	err := saveRebaseState(tmpDir, original)
	require.NoError(t, err)

	loaded, err := loadRebaseState(tmpDir)
	require.NoError(t, err)

	assert.Equal(t, true, loaded.CommitterDateIsAuthorDate)
}

// TestRebase_Continue_PreservesCommitterDateFlag verifies that --continue
// restores the committer-date-is-author-date flag from saved state and
// passes it to subsequent rebase calls.
func TestRebase_Continue_PreservesCommitterDateFlag(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	// State: b2 had a conflict, b3 remains. Flag was set.
	state := &rebaseState{
		CurrentBranchIndex: 1,
		ConflictBranch:     "b2",
		RemainingBranches:  []string{"b3"},
		OriginalBranch:     "b1",
		OriginalRefs: map[string]string{
			"main": "main-orig-sha",
			"b1":   "b1-orig-sha",
			"b2":   "b2-orig-sha",
			"b3":   "b3-orig-sha",
		},
		CommitterDateIsAuthorDate: true,
	}
	require.NoError(t, saveRebaseState(tmpDir, state))

	var continueCalled bool
	var continueOpts git.RebaseOpts
	var rebaseOntoOpts []git.RebaseOpts

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(string) error { return nil }
	mock.IsRebaseInProgressFn = func() bool { return continueCalled == false }
	mock.RebaseContinueFn = func(opts git.RebaseOpts) error {
		continueCalled = true
		continueOpts = opts
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		rebaseOntoOpts = append(rebaseOntoOpts, opts)
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	cmd.SetArgs([]string{"--continue"})
	err := cmd.Execute()

	assert.NoError(t, err)
	assert.True(t, continueCalled)
	assert.True(t, continueOpts.CommitterDateIsAuthorDate,
		"RebaseContinue should receive CommitterDateIsAuthorDate=true from saved state")
	require.Len(t, rebaseOntoOpts, 1)
	assert.True(t, rebaseOntoOpts[0].CommitterDateIsAuthorDate,
		"remaining cascade rebase should receive CommitterDateIsAuthorDate=true from saved state")
}

// TestRebase_ConflictSavesCommitterDateFlag verifies that when a conflict
// occurs with --committer-date-is-author-date active, the flag is persisted
// in the saved state.
func TestRebase_ConflictSavesCommitterDateFlag(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	mock := newRebaseMock(tmpDir, "b1")
	mock.CheckoutBranchFn = func(string) error { return nil }
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		return nil // b1 succeeds
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		if branch == "b2" {
			return fmt.Errorf("conflict")
		}
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	cmd.SetArgs([]string{"--committer-date-is-author-date"})
	_ = cmd.Execute()

	// Load the saved state and verify the flag is persisted.
	loaded, err := loadRebaseState(tmpDir)
	require.NoError(t, err)
	assert.True(t, loaded.CommitterDateIsAuthorDate,
		"saved rebase state should preserve CommitterDateIsAuthorDate flag")
}

// TestRebase_NoTrunk_SkipsTrunkRebase verifies that --no-trunk skips rebasing
// branch 1 onto trunk but still cascades inter-branch rebases.
func TestRebase_NoTrunk_SkipsTrunkRebase(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var allRebaseCalls []rebaseCall
	var currentCheckedOut string

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(name string) error {
		currentCheckedOut = name
		return nil
	}
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase: base, oldBase: "", branch: currentCheckedOut})
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--no-trunk"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)

	// Only b2 onto b1 and b3 onto b2 — no rebase onto trunk (main).
	require.Len(t, allRebaseCalls, 2, "should only rebase b2 and b3 (skip b1 onto trunk)")
	assert.Equal(t, "b1", allRebaseCalls[0].newBase, "b2 should be rebased onto b1")
	assert.Equal(t, "b2", allRebaseCalls[1].newBase, "b3 should be rebased onto b2")

	assert.Contains(t, output, "without trunk")
}

// TestRebase_NoTrunk_SkipsFetch verifies that --no-trunk does not call Fetch.
func TestRebase_NoTrunk_SkipsFetch(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	fetchCalled := false

	mock := newRebaseMock(tmpDir, "b1")
	mock.CheckoutBranchFn = func(name string) error { return nil }
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error { return nil }
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error { return nil }
	mock.FetchFn = func(remote string) error {
		fetchCalled = true
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--no-trunk"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Out.Close()
	cfg.Err.Close()

	assert.NoError(t, err)
	assert.False(t, fetchCalled, "Fetch should not be called with --no-trunk")
}

// TestRebase_NoTrunk_SingleBranch verifies that --no-trunk with a single-branch
// stack has no branches to rebase (since branch 1 onto trunk is skipped).
func TestRebase_NoTrunk_SingleBranch(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	mock := newRebaseMock(tmpDir, "b1")
	mock.CheckoutBranchFn = func(name string) error { return nil }

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, errR := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--no-trunk"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Err.Close()
	errOut, _ := io.ReadAll(errR)
	output := string(errOut)

	assert.NoError(t, err)
	assert.Contains(t, output, "No branches to rebase")
}

// TestRebase_NoTrunk_WithUpstack verifies --no-trunk combined with --upstack
// when the current branch is above index 0. The --no-trunk should not change
// behavior since --upstack already starts from a non-trunk branch.
func TestRebase_NoTrunk_WithUpstack(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	var allRebaseCalls []rebaseCall
	var currentCheckedOut string

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(name string) error {
		currentCheckedOut = name
		return nil
	}
	mock.RebaseFn = func(base string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase: base, oldBase: "", branch: currentCheckedOut})
		return nil
	}
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		allRebaseCalls = append(allRebaseCalls, rebaseCall{newBase, oldBase, branch})
		return nil
	}

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--no-trunk", "--upstack"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	err := cmd.Execute()

	cfg.Out.Close()
	cfg.Err.Close()

	assert.NoError(t, err)
	// --upstack from b2 = [b2, b3], --no-trunk doesn't change this since startIdx is already 1
	require.Len(t, allRebaseCalls, 2, "upstack should rebase b2 and b3")
	assert.Equal(t, "b1", allRebaseCalls[0].newBase, "b2 should be rebased onto b1")
	assert.Equal(t, "b2", allRebaseCalls[1].newBase, "b3 should be rebased onto b2")
}

// TestRebase_NoTrunk_ConflictSavesState verifies that --no-trunk persists the
// NoTrunk flag in the rebase state when a conflict occurs.
func TestRebase_NoTrunk_ConflictSavesState(t *testing.T) {
	s := stack.Stack{
		Trunk: stack.BranchRef{Branch: "main"},
		Branches: []stack.BranchRef{
			{Branch: "b1"},
			{Branch: "b2"},
			{Branch: "b3"},
		},
	}

	tmpDir := t.TempDir()
	writeStackFile(t, tmpDir, s)

	mock := newRebaseMock(tmpDir, "b2")
	mock.CheckoutBranchFn = func(name string) error { return nil }
	mock.RebaseOntoFn = func(newBase, oldBase, branch string, opts git.RebaseOpts) error {
		if branch == "b2" {
			return fmt.Errorf("conflict")
		}
		return nil
	}
	mock.ConflictedFilesFn = func() ([]string, error) { return nil, nil }

	restore := git.SetOps(mock)
	defer restore()

	cfg, _, _ := config.NewTestConfig()
	cmd := RebaseCmd(cfg)
	cmd.SetArgs([]string{"--no-trunk"})
	cmd.SetOut(io.Discard)
	cmd.SetErr(io.Discard)
	_ = cmd.Execute()

	// Load the saved state and verify the NoTrunk flag is persisted.
	loaded, err := loadRebaseState(tmpDir)
	require.NoError(t, err)
	assert.True(t, loaded.NoTrunk,
		"saved rebase state should preserve NoTrunk flag")
}