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package stack
import (
"bytes"
"crypto/sha256"
"encoding/json"
"errors"
"fmt"
"os"
"path/filepath"
"strings"
)
const (
schemaVersion = 1
stackFileName = "gh-stack"
)
// PullRequestRef holds relatively immutable metadata about an associated PR.
type PullRequestRef struct {
Number int `json:"number"`
ID string `json:"id,omitempty"`
URL string `json:"url,omitempty"`
Merged bool `json:"merged,omitempty"`
}
// BranchRef represents a branch and its associated commit hash.
// For the trunk, Head stores the HEAD commit SHA.
// For stacked branches, Base stores the parent branch's HEAD SHA
// at the time of last sync/rebase, used to identify unique commits.
type BranchRef struct {
Branch string `json:"branch"`
Head string `json:"head,omitempty"`
Base string `json:"base,omitempty"`
PullRequest *PullRequestRef `json:"pullRequest,omitempty"`
// Queued is a transient (not persisted) flag indicating the branch's
// PR is currently in a merge queue. It is populated by syncStackPRs
// from the GitHub API on each command run.
Queued bool `json:"-"`
}
// Stack represents a single stack of branches.
type Stack struct {
ID string `json:"id,omitempty"`
Prefix string `json:"prefix,omitempty"`
Numbered bool `json:"numbered,omitempty"`
Trunk BranchRef `json:"trunk"`
Branches []BranchRef `json:"branches"`
}
// DisplayChain returns a human-readable chain representation of the stack.
// Format: (trunk) <- branch1 <- branch2 <- branch3
func (s *Stack) DisplayChain() string {
parts := []string{"(" + s.Trunk.Branch + ")"}
for _, b := range s.Branches {
parts = append(parts, b.Branch)
}
return strings.Join(parts, " <- ")
}
// BranchNames returns the list of branch names in order.
func (s *Stack) BranchNames() []string {
names := make([]string, len(s.Branches))
for i, b := range s.Branches {
names[i] = b.Branch
}
return names
}
// IndexOf returns the index of the given branch in the stack, or -1 if not found.
func (s *Stack) IndexOf(branch string) int {
for i, b := range s.Branches {
if b.Branch == branch {
return i
}
}
return -1
}
// Contains returns true if the branch is part of this stack (including trunk).
func (s *Stack) Contains(branch string) bool {
if s.Trunk.Branch == branch {
return true
}
return s.IndexOf(branch) >= 0
}
// BaseBranch returns the base branch for the given branch in the stack.
// For the first branch, this is the trunk. For others, it's the previous branch.
func (s *Stack) BaseBranch(branch string) string {
idx := s.IndexOf(branch)
if idx <= 0 {
return s.Trunk.Branch
}
return s.Branches[idx-1].Branch
}
// IsMerged returns whether a branch's PR has been merged.
func (b *BranchRef) IsMerged() bool {
return b.PullRequest != nil && b.PullRequest.Merged
}
// IsQueued returns whether a branch's PR is currently in a merge queue.
// This is a transient state populated from the GitHub API on each run.
func (b *BranchRef) IsQueued() bool {
return b.Queued
}
// IsSkipped returns whether a branch should be skipped during push/sync/submit.
// A branch is skipped if its PR has been merged or is currently queued.
func (b *BranchRef) IsSkipped() bool {
return b.IsMerged() || b.IsQueued()
}
// ActiveBranches returns only branches that are pushable (not merged, not queued).
func (s *Stack) ActiveBranches() []BranchRef {
var active []BranchRef
for _, b := range s.Branches {
if !b.IsSkipped() {
active = append(active, b)
}
}
return active
}
// MergedBranches returns only merged branches, preserving order.
func (s *Stack) MergedBranches() []BranchRef {
var merged []BranchRef
for _, b := range s.Branches {
if b.IsMerged() {
merged = append(merged, b)
}
}
return merged
}
// QueuedBranches returns only queued branches, preserving order.
func (s *Stack) QueuedBranches() []BranchRef {
var queued []BranchRef
for _, b := range s.Branches {
if b.IsQueued() {
queued = append(queued, b)
}
}
return queued
}
// FirstActiveBranchIndex returns the index of the first active (not merged, not queued) branch, or -1.
func (s *Stack) FirstActiveBranchIndex() int {
for i, b := range s.Branches {
if !b.IsSkipped() {
return i
}
}
return -1
}
// ActiveBranchIndices returns the indices of all active (not merged, not queued) branches.
func (s *Stack) ActiveBranchIndices() []int {
var indices []int
for i, b := range s.Branches {
if !b.IsSkipped() {
indices = append(indices, i)
}
}
return indices
}
// ActiveBaseBranch returns the effective parent for a branch, skipping merged
// and queued ancestors. For the first active branch (or any branch whose
// downstack is all merged/queued), this returns the trunk.
func (s *Stack) ActiveBaseBranch(branch string) string {
idx := s.IndexOf(branch)
if idx <= 0 {
return s.Trunk.Branch
}
for j := idx - 1; j >= 0; j-- {
if !s.Branches[j].IsSkipped() {
return s.Branches[j].Branch
}
}
return s.Trunk.Branch
}
// IsFullyMerged returns true if all branches in the stack have been merged.
func (s *Stack) IsFullyMerged() bool {
for _, b := range s.Branches {
if !b.IsMerged() {
return false
}
}
return len(s.Branches) > 0
}
// StackFile represents the JSON file stored in .git/gh-stack.
type StackFile struct {
SchemaVersion int `json:"schemaVersion"`
Repository string `json:"repository"`
Stacks []Stack `json:"stacks"`
// loadChecksum is the SHA-256 of the raw file bytes at Load time.
// Save uses it to detect concurrent modifications (optimistic concurrency).
// nil means the file did not exist when loaded.
loadChecksum []byte
}
// FindAllStacksForBranch returns all stacks that contain the given branch.
func (sf *StackFile) FindAllStacksForBranch(branch string) []*Stack {
var stacks []*Stack
for i := range sf.Stacks {
if sf.Stacks[i].Contains(branch) {
stacks = append(stacks, &sf.Stacks[i])
}
}
return stacks
}
// FindStackByPRNumber returns the first stack and branch whose PR number matches.
// Returns nil, nil if no match is found.
func (sf *StackFile) FindStackByPRNumber(prNumber int) (*Stack, *BranchRef) {
for i := range sf.Stacks {
for j := range sf.Stacks[i].Branches {
b := &sf.Stacks[i].Branches[j]
if b.PullRequest != nil && b.PullRequest.Number == prNumber {
return &sf.Stacks[i], b
}
}
}
return nil, nil
}
// ValidateNoDuplicateBranch checks that the branch is not already in any stack.
func (sf *StackFile) ValidateNoDuplicateBranch(branch string) error {
for _, s := range sf.Stacks {
if s.Contains(branch) {
return fmt.Errorf("branch %q is already part of a stack", branch)
}
}
return nil
}
// AddStack adds a new stack to the file.
func (sf *StackFile) AddStack(s Stack) {
sf.Stacks = append(sf.Stacks, s)
}
// RemoveStack removes the stack at the given index.
func (sf *StackFile) RemoveStack(idx int) {
sf.Stacks = append(sf.Stacks[:idx], sf.Stacks[idx+1:]...)
}
// RemoveStackForBranch removes the stack containing the given branch.
func (sf *StackFile) RemoveStackForBranch(branch string) bool {
for i := range sf.Stacks {
if sf.Stacks[i].Contains(branch) {
sf.RemoveStack(i)
return true
}
}
return false
}
// stackFilePath returns the path to the gh-stack file.
func stackFilePath(gitDir string) string {
return filepath.Join(gitDir, stackFileName)
}
// Load reads the stack file from the given git directory.
// Returns an empty StackFile if the file does not exist.
// The returned StackFile records a checksum of the on-disk content so that
// Save can detect concurrent modifications.
func Load(gitDir string) (*StackFile, error) {
path := stackFilePath(gitDir)
data, err := os.ReadFile(path)
if err != nil {
if errors.Is(err, os.ErrNotExist) {
// loadChecksum stays nil — sentinel for "file absent at load time".
return &StackFile{
SchemaVersion: schemaVersion,
Stacks: []Stack{},
}, nil
}
return nil, fmt.Errorf("reading stack file: %w", err)
}
var sf StackFile
if err := json.Unmarshal(data, &sf); err != nil {
return nil, fmt.Errorf("parsing stack file: %w", err)
}
if sf.SchemaVersion > schemaVersion {
return nil, fmt.Errorf("stack file has schema version %d, but this version of gh-stack only supports up to version %d — please upgrade gh-stack", sf.SchemaVersion, schemaVersion)
}
sum := sha256.Sum256(data)
sf.loadChecksum = sum[:]
return &sf, nil
}
// Save acquires an exclusive lock on the stack file, verifies the file hasn't
// been modified since Load (optimistic concurrency), writes sf as JSON, and
// releases the lock. The lock is held only for the read-compare-write window.
// Returns *LockError if the lock times out, or *StaleError if another process
// modified the file since it was loaded.
func Save(gitDir string, sf *StackFile) error {
lock, err := Lock(gitDir)
if err != nil {
return err // *LockError for contention, plain error for I/O failures
}
defer lock.Unlock()
if err := checkStale(gitDir, sf); err != nil {
return err
}
return writeStackFile(gitDir, sf)
}
// SaveNonBlocking attempts to save without blocking. If another process holds
// the lock or the file was modified since Load, the save is silently skipped.
// Use this for best-effort metadata persistence (e.g. syncing PR state in view).
func SaveNonBlocking(gitDir string, sf *StackFile) {
path := filepath.Join(gitDir, lockFileName)
f, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR, 0644)
if err != nil {
return
}
if tryLockFile(f) != nil {
f.Close()
return
}
lock := &FileLock{f: f}
defer lock.Unlock()
if checkStale(gitDir, sf) != nil {
return
}
_ = writeStackFile(gitDir, sf)
}
// checkStale compares the current on-disk content against the checksum
// captured at Load time. Returns *StaleError if the file was modified
// by another process. The caller must hold the lock.
func checkStale(gitDir string, sf *StackFile) error {
path := stackFilePath(gitDir)
data, err := os.ReadFile(path)
if errors.Is(err, os.ErrNotExist) {
// File absent on disk.
if sf.loadChecksum == nil {
return nil // was absent at Load time too — no conflict
}
// File existed at Load but is now gone. Allow the write to
// recreate it rather than erroring; this is not a lost-update.
return nil
}
if err != nil {
return fmt.Errorf("reading stack file for staleness check: %w", err)
}
// File exists on disk.
if sf.loadChecksum == nil {
// File was absent at Load but another process created it.
return &StaleError{Err: fmt.Errorf(
"stack file was created by another process since it was loaded")}
}
sum := sha256.Sum256(data)
if !bytes.Equal(sf.loadChecksum, sum[:]) {
return &StaleError{Err: fmt.Errorf(
"stack file was modified by another process since it was loaded")}
}
return nil
}
func writeStackFile(gitDir string, sf *StackFile) error {
sf.SchemaVersion = schemaVersion
if sf.Stacks == nil {
sf.Stacks = []Stack{}
}
data, err := json.MarshalIndent(sf, "", " ")
if err != nil {
return fmt.Errorf("marshaling stack file: %w", err)
}
path := stackFilePath(gitDir)
if err := os.WriteFile(path, data, 0644); err != nil {
return fmt.Errorf("writing stack file: %w", err)
}
// Refresh checksum so a second Save on the same StackFile doesn't
// spuriously fail the staleness check.
sum := sha256.Sum256(data)
sf.loadChecksum = sum[:]
return nil
}