package gitutil

import (
	"bytes"
	"fmt"
	"os"
	"os/exec"
	"strings"

	"gitbay.org/gitbay/internal/toolpath"
)

// FetchInto copies srcRef from srcDir into dstDir as dstRef, forcing the
// update. Objects are copied, not shared — the destination owns everything
// afterward, which is what keeps MRs alive when their fork is deleted.
func FetchInto(dstDir, srcDir, srcRef, dstRef string) error {
	cmd := exec.Command(toolpath.Look("git"), "-C", dstDir, "fetch", "--quiet", "--no-write-fetch-head",
		srcDir, "+"+srcRef+":"+dstRef)
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("fetch %s from %s: %v\n%s", srcRef, srcDir, err, out)
	}
	return nil
}

// UpdateRefCAS points ref at newSHA only if it currently points at oldSHA
// (empty oldSHA = must not exist). This is the compare-and-swap that makes
// merges safe against concurrent pushes.
func UpdateRefCAS(dir, ref, newSHA, oldSHA string) error {
	args := []string{"-C", dir, "update-ref", ref, newSHA}
	if oldSHA != "" {
		args = append(args, oldSHA)
	}
	cmd := exec.Command(toolpath.Look("git"), args...)
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("update-ref %s: %v\n%s", ref, err, out)
	}
	return nil
}

func DeleteRef(dir, ref string) error {
	cmd := exec.Command(toolpath.Look("git"), "-C", dir, "update-ref", "-d", ref)
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("delete-ref %s: %v\n%s", ref, err, out)
	}
	return nil
}

// RefExists reports whether ref is present, whatever it points at. Unlike
// ResolveRef it does not need the object to exist, so a ref left dangling
// by an interrupted prune still reads as present and gets deleted.
func RefExists(dir, ref string) bool {
	return exec.Command(toolpath.Look("git"), "-C", dir, "show-ref", "--verify", "--quiet", ref).Run() == nil
}

// PruneNow repacks the repository and drops every unreachable object at
// once, instead of after git's two-week grace. For when a ref was deleted
// so that what it pointed at stops being fetchable by sha. Without the
// grace, a push whose objects have left quarantine but whose ref is not
// yet written can lose them; the window is milliseconds, and the one
// caller is an explicit admin command, not a timer.
func PruneNow(dir string) error {
	cmd := exec.Command(toolpath.Look("git"), "-C", dir, "gc", "--quiet", "--prune=now")
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("gc --prune=now: %v\n%s", err, out)
	}
	return nil
}

// FsckConnectivity checks that every object reachable from the
// repository's refs is present, without reading blob contents. A backup
// verify runs it on each archived repository (#259). dir is the git
// directory itself; it is passed as --git-dir so that a directory that is
// not a repository fails instead of git checking one enclosing it.
func FsckConnectivity(dir string) error {
	cmd := exec.Command(toolpath.Look("git"), "--git-dir="+dir, "fsck", "--connectivity-only", "--no-progress", "--no-dangling")
	if out, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("fsck --connectivity-only: %v\n%s", err, out)
	}
	return nil
}

// RevListRange returns commits in old..new, newest first.
func RevListRange(dir, old, new string) ([]string, error) {
	cmd := exec.Command(toolpath.Look("git"), "-C", dir, "rev-list", "--end-of-options", new, "^"+old)
	out, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("rev-list %s..%s: %w", old, new, err)
	}
	var shas []string
	for _, l := range strings.Split(strings.TrimSpace(string(out)), "\n") {
		if l != "" {
			shas = append(shas, l)
		}
	}
	return shas, nil
}

// MergeTree performs a real merge of ours and theirs, returning the merged
// tree id. conflict=true means the merge cannot be done automatically.
func MergeTree(dir, ours, theirs string) (tree string, conflict bool, err error) {
	cmd := exec.Command(toolpath.Look("git"), "-C", dir, "merge-tree", "--write-tree", "--end-of-options", ours, theirs)
	out, runErr := cmd.Output()
	tree = strings.TrimSpace(strings.SplitN(string(out), "\n", 2)[0])
	if runErr != nil {
		if ee, ok := runErr.(*exec.ExitError); ok && ee.ExitCode() == 1 {
			return "", true, nil // conflicted merge
		}
		return "", false, fmt.Errorf("merge-tree: %w", runErr)
	}
	return tree, false, nil
}

// CommitTree creates a merge commit with the given parents, authored and
// committed by the merging user. There is no server signing key by design.
func CommitTree(dir, tree string, parents []string, name, email, message string) (string, error) {
	args := []string{"-C", dir, "commit-tree", tree, "-m", message}
	for _, p := range parents {
		args = append(args, "-p", p)
	}
	cmd := exec.Command(toolpath.Look("git"), args...)
	cmd.Env = append(os.Environ(),
		"GIT_AUTHOR_NAME="+name, "GIT_AUTHOR_EMAIL="+email,
		"GIT_COMMITTER_NAME="+name, "GIT_COMMITTER_EMAIL="+email,
	)
	out, err := cmd.Output()
	if err != nil {
		return "", fmt.Errorf("commit-tree: %w", err)
	}
	return strings.TrimSpace(string(out)), nil
}

// Diff returns the patch for old..new (three-dot semantics are the caller's
// job: pass the merge base as old), cut at limit bytes on a line boundary;
// truncated says whether it was cut, so the caller can say so instead of
// rendering a hunk that ends mid-line (#117).
func Diff(dir, old, new string, limit int64) (patch string, truncated bool, err error) {
	cmd := exec.Command(toolpath.Look("git"), "-C", dir, "diff", "--stat", "--patch", "--end-of-options", old, new)
	out, err := cmd.Output()
	if err != nil {
		return "", false, fmt.Errorf("diff: %w", err)
	}
	out, truncated = cutAtLine(out, limit)
	return string(out), truncated, nil
}

// cutAtLine keeps at most limit bytes, ending on the last newline before
// the limit.
func cutAtLine(out []byte, limit int64) ([]byte, bool) {
	if int64(len(out)) <= limit {
		return out, false
	}
	cut := out[:limit]
	if i := bytes.LastIndexByte(cut, '\n'); i >= 0 {
		cut = cut[:i+1]
	}
	return cut, true
}

// PatchID identifies the change between old and new independently of the
// commits carrying it: git patch-id --stable over the whole-range diff.
// Two revisions with the same PatchID propose the same change, whatever
// was rebased underneath. "" when the range has no diff.
func PatchID(dir, old, new string) (string, error) {
	diff := exec.Command(toolpath.Look("git"), "-C", dir, "diff", "--end-of-options", old, new)
	pid := exec.Command(toolpath.Look("git"), "-C", dir, "patch-id", "--stable")
	pipe, err := diff.StdoutPipe()
	if err != nil {
		return "", err
	}
	pid.Stdin = pipe
	if err := diff.Start(); err != nil {
		return "", fmt.Errorf("diff: %w", err)
	}
	out, err := pid.Output()
	if werr := diff.Wait(); werr != nil {
		return "", fmt.Errorf("diff: %w", werr)
	}
	if err != nil {
		return "", fmt.Errorf("patch-id: %w", err)
	}
	fields := strings.Fields(string(out))
	if len(fields) == 0 {
		return "", nil
	}
	return fields[0], nil
}

// MergeBase returns the best common ancestor, or an error if none exists.
func MergeBase(dir, a, b string) (string, error) {
	cmd := exec.Command(toolpath.Look("git"), "-C", dir, "merge-base", "--end-of-options", a, b)
	out, err := cmd.Output()
	if err != nil {
		return "", fmt.Errorf("no common history between %s and %s", a, b)
	}
	return strings.TrimSpace(string(out)), nil
}

// CommitFileChange writes content at path on branch as a new commit and
// advances the branch with compare-and-swap. Used by web edits; hooks do not
// run, so callers enforce policy themselves.
func CommitFileChange(dir, branch, path string, content []byte, name, email, message string) (string, error) {
	branchRef := "refs/heads/" + branch
	parent, err := ResolveRef(dir, branchRef)
	if err != nil {
		// An unborn branch is a root commit only in a repository with no
		// refs at all. Anywhere else an unresolvable branch is a typo, and
		// starting an orphan branch for it would be worse than refusing.
		if !isEmptyRepo(dir) {
			return "", fmt.Errorf("branch %s: %w", branch, err)
		}
		parent = ""
	}

	sha, err := CommitWithFile(dir, parent, path, "100644", content, name, email, message)
	if err != nil {
		return "", err
	}
	if err := UpdateRefCAS(dir, branchRef, sha, parent); err != nil {
		return "", fmt.Errorf("branch moved during edit; reload and retry: %w", err)
	}
	return sha, nil
}

// CommitWithFile writes a commit on parent ("" for a root commit) whose
// tree is parent's with content at path, as a file of mode (100644 or
// 100755), authored and committed as name <email>. No ref moves: the
// caller updates one, and enforces policy, since no hook runs.
func CommitWithFile(dir, parent, path, mode string, content []byte, name, email, message string) (string, error) {
	// Hash the new blob.
	hb := exec.Command(toolpath.Look("git"), "-C", dir, "hash-object", "-w", "--stdin")
	hb.Stdin = strings.NewReader(string(content))
	out, err := hb.Output()
	if err != nil {
		return "", fmt.Errorf("hash-object: %w", err)
	}
	blob := strings.TrimSpace(string(out))

	// Stage the parent tree in a temporary index, splice the blob in, and
	// write the new tree.
	idx, err := os.CreateTemp("", "gitbay-index-*")
	if err != nil {
		return "", err
	}
	idx.Close()
	defer os.Remove(idx.Name())
	env := append(os.Environ(), "GIT_INDEX_FILE="+idx.Name())

	tree0 := parent + "^{tree}"
	if parent == "" {
		tree0 = "--empty"
	}
	rt := exec.Command(toolpath.Look("git"), "-C", dir, "read-tree", tree0)
	rt.Env = env
	if out, err := rt.CombinedOutput(); err != nil {
		return "", fmt.Errorf("read-tree: %v\n%s", err, out)
	}
	ui := exec.Command(toolpath.Look("git"), "-C", dir, "update-index", "--add", "--cacheinfo", mode+","+blob+","+path)
	ui.Env = env
	if out, err := ui.CombinedOutput(); err != nil {
		return "", fmt.Errorf("update-index: %v\n%s", err, out)
	}
	wt := exec.Command(toolpath.Look("git"), "-C", dir, "write-tree")
	wt.Env = env
	out, err = wt.Output()
	if err != nil {
		return "", fmt.Errorf("write-tree: %w", err)
	}
	tree := strings.TrimSpace(string(out))

	var parents []string
	if parent != "" {
		parents = []string{parent}
	}
	return CommitTree(dir, tree, parents, name, email, message)
}

// isEmptyRepo reports whether dir has no refs at all — a repository
// created but never pushed to.
func isEmptyRepo(dir string) bool {
	out, err := exec.Command(toolpath.Look("git"), "-C", dir, "rev-list", "-n1", "--all").Output()
	return err == nil && strings.TrimSpace(string(out)) == ""
}

// CommitParents returns the parent SHAs of a commit.
func CommitParents(dir, sha string) ([]string, error) {
	out, err := exec.Command(toolpath.Look("git"), "-C", dir, "rev-list", "--parents", "-n1", "--end-of-options", sha).Output()
	if err != nil {
		return nil, fmt.Errorf("rev-list --parents %s: %w", sha, err)
	}
	fields := strings.Fields(string(out))
	if len(fields) < 1 {
		return nil, fmt.Errorf("no output for %s", sha)
	}
	return fields[1:], nil
}

// AuthorIdent returns a commit's author name, email, and ISO date.
func AuthorIdent(dir, sha string) (name, email, date string, err error) {
	out, err := exec.Command(toolpath.Look("git"), "-C", dir, "log", "-1", "--format=%an%x1f%ae%x1f%aI", "--end-of-options", sha).Output()
	if err != nil {
		return "", "", "", fmt.Errorf("log %s: %w", sha, err)
	}
	parts := strings.SplitN(strings.TrimSpace(string(out)), "\x1f", 3)
	if len(parts) != 3 {
		return "", "", "", fmt.Errorf("bad ident for %s", sha)
	}
	return parts[0], parts[1], parts[2], nil
}

// CommitMessage returns a commit's full message.
func CommitMessage(dir, sha string) (string, error) {
	out, err := exec.Command(toolpath.Look("git"), "-C", dir, "log", "-1", "--format=%B", "--end-of-options", sha).Output()
	if err != nil {
		return "", fmt.Errorf("log %s: %w", sha, err)
	}
	return strings.TrimRight(string(out), "\n"), nil
}

// MergeTreeOnto replays commit's changes (relative to base) onto onto,
// returning the resulting tree. conflict=true when it cannot apply cleanly.
func MergeTreeOnto(dir, base, onto, commit string) (tree string, conflict bool, err error) {
	cmd := exec.Command(toolpath.Look("git"), "-C", dir, "merge-tree", "--write-tree", "--merge-base="+base, "--end-of-options", onto, commit)
	out, runErr := cmd.Output()
	tree = strings.TrimSpace(strings.SplitN(string(out), "\n", 2)[0])
	if runErr != nil {
		if ee, ok := runErr.(*exec.ExitError); ok && ee.ExitCode() == 1 {
			return "", true, nil
		}
		return "", false, fmt.Errorf("merge-tree: %w", runErr)
	}
	return tree, false, nil
}

// CommitTreeIdent creates a commit with distinct author and committer
// identities. Empty authorDate means now.
func CommitTreeIdent(dir, tree string, parents []string,
	authorName, authorEmail, authorDate, committerName, committerEmail, message string) (string, error) {
	args := []string{"-C", dir, "commit-tree", tree, "-m", message}
	for _, p := range parents {
		args = append(args, "-p", p)
	}
	cmd := exec.Command(toolpath.Look("git"), args...)
	env := append(os.Environ(),
		"GIT_AUTHOR_NAME="+authorName, "GIT_AUTHOR_EMAIL="+authorEmail,
		"GIT_COMMITTER_NAME="+committerName, "GIT_COMMITTER_EMAIL="+committerEmail,
	)
	if authorDate != "" {
		env = append(env, "GIT_AUTHOR_DATE="+authorDate)
	}
	cmd.Env = env
	out, err := cmd.Output()
	if err != nil {
		return "", fmt.Errorf("commit-tree: %w", err)
	}
	return strings.TrimSpace(string(out)), nil
}

// ResolveTree returns the tree id of a commit.
func ResolveTree(dir, sha string) (string, error) {
	out, err := exec.Command(toolpath.Look("git"), "-C", dir, "rev-parse", "--verify", "--end-of-options", sha+"^{tree}").Output()
	if err != nil {
		return "", fmt.Errorf("rev-parse %s^{tree}: %w", sha, err)
	}
	return strings.TrimSpace(string(out)), nil
}

// DiffFiles lists the paths changed between old and new.
func DiffFiles(dir, old, new string) ([]string, error) {
	out, err := exec.Command(toolpath.Look("git"), "-C", dir, "diff", "--name-only", "--end-of-options", old, new).Output()
	if err != nil {
		return nil, fmt.Errorf("diff --name-only: %w", err)
	}
	var files []string
	for _, l := range strings.Split(strings.TrimSpace(string(out)), "\n") {
		if l != "" {
			files = append(files, l)
		}
	}
	return files, nil
}

// RangeDiff compares two revisions of the same work: what the commits
// between oldBase and oldHead became between newBase and newHead. This is
// what answers "what changed since I reviewed this", which a plain diff
// of the two heads cannot — that shows the whole branch again, rebases
// and all.
//
// Each side carries its own base, because the target moves: comparing
// both revisions against today's base would attribute every commit that
// landed on the target in between to the author of this merge request.
//
// --creation-factor is raised from git's default of 60. That default is
// tuned for comparing two independently developed patch series, where
// refusing to pair is the safe answer. Here the two sides are known to be
// revisions of one branch, and the commonest revision of all — a commit
// that adds a file, with one line inside it changed — is not paired at
// 60: git reports the commit as deleted and a different one added, which
// tells a reviewer nothing. It pairs at 80, and two genuinely unrelated
// commits are still left unpaired there; both measured.
func RangeDiff(dir, oldBase, oldHead, newBase, newHead string, limit int64) (patch string, truncated bool, err error) {
	cmd := exec.Command(toolpath.Look("git"), "-C", dir, "range-diff", "--creation-factor=80", "--end-of-options",
		oldBase+".."+oldHead, newBase+".."+newHead)
	out, err := cmd.Output()
	if err != nil {
		return "", false, fmt.Errorf("range-diff: %w", err)
	}
	out, truncated = cutAtLine(out, limit)
	return string(out), truncated, nil
}