package git

import (
	"bufio"
	"context"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strconv"
	"strings"
)

func RenameRefs(repo string, rename func(string) string) error {
	branches, err := run(repo, "for-each-ref", "--format=%(refname:short)", "refs/heads/byre/")
	if err != nil {
		return err
	}
	for _, b := range splitLines(branches) {
		if rename(b) == b {
			continue
		}
		_, err = run(repo, "branch", "-m", b, rename(b))
		if err != nil {
			return err
		}
	}

	snaps, err := run(repo, "for-each-ref", "--format=%(objectname) %(refname)", "refs/byre/tasks/")
	if err != nil {
		return err
	}
	b := &strings.Builder{}
	for _, l := range splitLines(snaps) {
		sha, ref, _ := strings.Cut(l, " ")
		if rename(ref) == ref {
			continue
		}
		fmt.Fprintf(b, "create %s %s\ndelete %s %s\n", rename(ref), sha, ref, sha)
	}
	if b.Len() == 0 {
		return nil
	}
	_, err = runInput(repo, nil, b.String(), "update-ref", "--stdin")
	return err
}

func RepairWorktrees(repo string, paths []string) error {
	if len(paths) == 0 {
		return nil
	}
	_, err := run(repo, append([]string{"worktree", "repair"}, paths...)...)
	return err
}

func RewriteNotes(repo string, rewrite func(string) string) error {
	parent, stderr, code, err := runCode(repo, nil, "rev-parse", "--verify", "--quiet", NotesRef)
	if err != nil {
		return err
	}
	if code == 1 {
		return nil
	}
	if code != 0 {
		return fmt.Errorf("git rev-parse %s: exit status %d: %s", NotesRef, code, stderr)
	}

	listing, err := run(repo, "ls-tree", "-r", parent)
	if err != nil {
		return err
	}
	paths := map[string]string{}
	shas := []string{}
	for _, l := range splitLines(listing) {
		meta, path, _ := strings.Cut(l, "\t")
		fields := strings.Fields(meta)
		paths[fields[2]] = path
		shas = append(shas, fields[2])
	}
	if len(shas) == 0 {
		return nil
	}

	contents, err := catBlobs(repo, shas)
	if err != nil {
		return err
	}

	dir, err := os.MkdirTemp("", "byre-notes-*")
	if err != nil {
		return err
	}
	defer os.RemoveAll(dir)

	changed := []string{}
	files := []string{}
	for _, sha := range shas {
		text := rewrite(contents[sha])
		if text == contents[sha] {
			continue
		}
		file := filepath.Join(dir, sha)
		err = os.WriteFile(file, []byte(text), 0o644)
		if err != nil {
			return err
		}
		changed = append(changed, sha)
		files = append(files, file)
	}
	if len(changed) == 0 {
		return nil
	}

	blobs, err := runInput(repo, nil, strings.Join(files, "\n")+"\n", "hash-object", "-w", "--stdin-paths")
	if err != nil {
		return err
	}
	index := []string{"GIT_INDEX_FILE=" + filepath.Join(dir, "index")}
	_, err = runEnv(repo, index, "read-tree", parent)
	if err != nil {
		return err
	}
	b := &strings.Builder{}
	for i, blob := range splitLines(blobs) {
		fmt.Fprintf(b, "100644 %s\t%s\n", blob, paths[changed[i]])
	}
	_, err = runInput(repo, index, b.String(), "update-index", "--index-info")
	if err != nil {
		return err
	}
	tree, err := runEnv(repo, index, "write-tree")
	if err != nil {
		return err
	}
	who, err := run(repo, "log", "-1", "--format=%cn%n%ce", parent)
	if err != nil {
		return err
	}
	name, email, _ := strings.Cut(who, "\n")
	env := []string{"GIT_AUTHOR_NAME=" + name, "GIT_AUTHOR_EMAIL=" + email, "GIT_COMMITTER_NAME=" + name, "GIT_COMMITTER_EMAIL=" + email}
	commit, err := runEnv(repo, env, "commit-tree", "-p", parent, "-m", "Rewrite byre ids in notes", tree)
	if err != nil {
		return err
	}
	_, err = run(repo, "update-ref", NotesRef, commit, parent)
	return err
}

func catBlobs(repo string, shas []string) (map[string]string, error) {
	out, err := runRaw(repo, strings.Join(shas, "\n")+"\n", "cat-file", "--batch")
	if err != nil {
		return nil, err
	}
	r := bufio.NewReader(strings.NewReader(out))
	contents := map[string]string{}
	for range shas {
		header, err := r.ReadString('\n')
		if err != nil {
			return nil, err
		}
		fields := strings.Fields(header)
		if len(fields) != 3 {
			return nil, fmt.Errorf("git cat-file --batch: unexpected header %q", header)
		}
		size, err := strconv.Atoi(fields[2])
		if err != nil {
			return nil, err
		}
		body := make([]byte, size+1)
		_, err = io.ReadFull(r, body)
		if err != nil {
			return nil, err
		}
		contents[fields[0]] = string(body[:size])
	}
	return contents, nil
}

func splitLines(out string) []string {
	if out == "" {
		return []string{}
	}
	return strings.Split(out, "\n")
}

func runRaw(dir, input string, args ...string) (string, error) {
	out, stderr, code, err := runCodeInput(context.Background(), dir, nil, strings.NewReader(input), args...)
	if err != nil {
		return "", err
	}
	if code != 0 {
		return "", fmt.Errorf("git %s: exit status %d: %s", strings.Join(args, " "), code, stderr)
	}
	return out, nil
}