package git

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"slices"
	"strconv"
	"strings"
	"syscall"
	"time"
)

type RepoInfo struct {
	Root          string
	DefaultBranch string
	Remote        string
}

func Inspect(path string) (RepoInfo, error) {
	abs, err := filepath.Abs(path)
	if err != nil {
		return RepoInfo{}, err
	}

	root, err := run(abs, "rev-parse", "--show-toplevel")
	if err != nil {
		return RepoInfo{}, err
	}

	root, err = filepath.EvalSymlinks(root)
	if err != nil {
		return RepoInfo{}, err
	}

	abs, err = filepath.EvalSymlinks(abs)
	if err != nil {
		return RepoInfo{}, err
	}

	if root != abs {
		return RepoInfo{}, fmt.Errorf("%s is inside the repo at %s; register the repo root", abs, root)
	}

	branch, err := run(root, "symbolic-ref", "--short", "HEAD")
	if err != nil {
		return RepoInfo{}, err
	}

	remote, err := run(root, "remote", "get-url", "origin")
	if err != nil {
		return RepoInfo{}, err
	}

	return RepoInfo{Root: root, DefaultBranch: branch, Remote: remote}, nil
}

func AddWorktree(repo, path, branch, base string) (string, error) {
	sha, err := run(repo, "rev-parse", "--verify", base+"^{commit}")
	if err != nil {
		return "", err
	}

	_, err = run(repo, "worktree", "add", "-b", branch, path, sha)
	if err != nil {
		return "", err
	}

	return sha, nil
}

func AddDetachedWorktree(repo, path, commit string) error {
	_, err := run(repo, "worktree", "add", "--detach", path, commit)
	return err
}

func RemoveDetachedWorktree(repo, path string) error {
	_, err := os.Stat(path)
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	_, err = run(repo, "worktree", "remove", "--force", path)
	return err
}

func RemoveWorktree(repo, path, branch string) error {
	list, err := run(repo, "worktree", "list", "--porcelain")
	if err != nil {
		return err
	}
	_, statErr := os.Stat(path)
	if statErr == nil || slices.Contains(strings.Split(list, "\n"), "worktree "+path) {
		_, err = run(repo, "worktree", "remove", "--force", path)
		if err != nil {
			return err
		}
	}

	_, _, code, err := runCode(repo, nil, "rev-parse", "--verify", "--quiet", "refs/heads/"+branch)
	if err != nil || code != 0 {
		return err
	}
	_, err = run(repo, "branch", "-D", branch)
	return err
}

type Unmerged struct {
	Commits     int
	Files       int
	Insertions  int
	Deletions   int
	Uncommitted int
}

type ConflictError struct {
	Files []string
}

func (e *ConflictError) Error() string {
	return "merge conflicts in " + strings.Join(e.Files, ", ")
}

func UnmergedChanges(worktree, target string) (Unmerged, error) {
	u := Unmerged{}

	count, err := run(worktree, "rev-list", "--count", target+"..HEAD")
	if err != nil {
		return u, err
	}
	u.Commits, err = strconv.Atoi(count)
	if err != nil {
		return u, err
	}

	status, err := run(worktree, "status", "--porcelain", "--untracked-files=all")
	if err != nil {
		return u, err
	}
	if status != "" {
		u.Uncommitted = len(strings.Split(status, "\n"))
	}

	tree, err := Snapshot(worktree)
	if err != nil {
		return u, err
	}
	base, err := run(worktree, "merge-base", target, "HEAD")
	if err != nil {
		return u, err
	}
	numstat, err := run(worktree, "diff", "--numstat", base, tree)
	if err != nil {
		return u, err
	}
	for _, line := range strings.Split(numstat, "\n") {
		if line == "" {
			continue
		}
		fields := strings.SplitN(line, "\t", 3)
		u.Files++
		adds, err := strconv.Atoi(fields[0])
		if err != nil {
			continue
		}
		dels, err := strconv.Atoi(fields[1])
		if err != nil {
			continue
		}
		u.Insertions += adds
		u.Deletions += dels
	}

	return u, nil
}

func SquashCommit(repo, worktree, target, message string, env []string) (string, error) {
	checkedOut, err := run(repo, "symbolic-ref", "--short", "HEAD")
	if err != nil {
		return "", err
	}
	if checkedOut != target {
		return "", fmt.Errorf("%s has %s checked out, not %s", repo, checkedOut, target)
	}

	tree, err := Snapshot(worktree)
	if err != nil {
		return "", err
	}
	base, err := run(worktree, "merge-base", target, "HEAD")
	if err != nil {
		return "", err
	}
	head, err := run(repo, "rev-parse", target)
	if err != nil {
		return "", err
	}

	out, stderr, code, err := runCode(repo, nil, "merge-tree", "--write-tree", "--name-only", "--merge-base="+base, head, tree)
	if err != nil {
		return "", err
	}
	lines := strings.Split(out, "\n")
	if code == 1 {
		conflict := &ConflictError{}
		for _, l := range lines[1:] {
			if l == "" {
				break
			}
			conflict.Files = append(conflict.Files, l)
		}
		return "", conflict
	}
	if code != 0 {
		return "", fmt.Errorf("git merge-tree exited %d: %s", code, stderr)
	}

	headTree, err := run(repo, "rev-parse", head+"^{tree}")
	if err != nil {
		return "", err
	}
	if lines[0] == headTree {
		return "", nil
	}

	return runEnv(repo, env, "commit-tree", lines[0], "-p", head, "-m", message)
}

const Remote = "origin"

const networkTimeout = 2 * time.Minute

var networkEnv = []string{
	"GIT_TERMINAL_PROMPT=0",
	"GIT_SSH_COMMAND=ssh -o BatchMode=yes -o ConnectTimeout=30",
}

var ErrRemoteMoved = errors.New("the remote's branch has moved")

func Push(ctx context.Context, repo, commit, branch, notes string) error {
	out, stderr, code, err := runNetwork(ctx, repo, "push", "--atomic", "--porcelain", Remote, commit+":refs/heads/"+branch, notes+":"+NotesRef)
	if err != nil {
		return err
	}
	if code == 0 {
		return nil
	}
	for _, line := range strings.Split(out, "\n") {
		if strings.HasPrefix(line, "!") && strings.Contains(line, "[rejected]") && (strings.Contains(line, "(fetch first)") || strings.Contains(line, "(non-fast-forward)")) {
			return fmt.Errorf("pushing %s to %s: %w", branch, Remote, ErrRemoteMoved)
		}
	}
	return fmt.Errorf("pushing %s to %s: exit status %d: %s", branch, Remote, code, strings.TrimSpace(out+"\n"+stderr))
}

func FastForward(repo, rev string) error {
	_, err := run(repo, "merge", "--ff-only", rev)
	return err
}

func Fetch(ctx context.Context, repo string) error {
	_, stderr, code, err := runNetwork(ctx, repo, "fetch", Remote)
	if err != nil {
		return err
	}
	if code != 0 {
		return fmt.Errorf("git fetch %s: exit status %d: %s", Remote, code, stderr)
	}
	return nil
}

func FetchFastForward(ctx context.Context, repo, branch string) error {
	err := Fetch(ctx, repo)
	if err != nil {
		return err
	}
	return FastForward(repo, Remote+"/"+branch)
}

func Head(dir string) (string, error) {
	return run(dir, "rev-parse", "HEAD")
}

func IsAncestor(dir, ancestor, descendant string) (bool, error) {
	_, stderr, code, err := runCode(dir, nil, "merge-base", "--is-ancestor", ancestor, descendant)
	if err != nil {
		return false, err
	}
	switch code {
	case 0:
		return true, nil
	case 1:
		return false, nil
	}
	return false, fmt.Errorf("git merge-base --is-ancestor %s %s: exit status %d: %s", ancestor, descendant, code, stderr)
}

func MergeInProgress(dir string) (bool, error) {
	_, _, code, err := runCode(dir, nil, "rev-parse", "--quiet", "--verify", "MERGE_HEAD")
	return err == nil && code == 0, err
}

func AbortMerge(dir string) error {
	merging, err := MergeInProgress(dir)
	if err != nil || !merging {
		return err
	}
	_, err = run(dir, "merge", "--abort")
	return err
}

func ReadFile(repo, rev, path string) (string, bool, error) {
	_, _, code, err := runCode(repo, nil, "cat-file", "-e", rev+":"+path)
	if err != nil {
		return "", false, err
	}
	if code != 0 {
		return "", false, nil
	}
	out, err := run(repo, "cat-file", "blob", rev+":"+path)
	return out, true, err
}

func CommitAll(dir, message, name, email string) (string, error) {
	status, err := run(dir, "status", "--porcelain", "--untracked-files=all")
	if err != nil {
		return "", err
	}
	merging, err := MergeInProgress(dir)
	if err != nil {
		return "", err
	}
	if status == "" && !merging {
		return "", nil
	}

	env := []string{
		"GIT_AUTHOR_NAME=" + name,
		"GIT_AUTHOR_EMAIL=" + email,
		"GIT_COMMITTER_NAME=" + name,
		"GIT_COMMITTER_EMAIL=" + email,
	}
	_, err = runEnv(dir, env, "add", "--all")
	if err != nil {
		return "", err
	}
	_, err = runEnv(dir, env, "commit", "--quiet", "--message", message)
	if err != nil {
		return "", err
	}
	return Head(dir)
}

func Merge(dir, rev, message, name, email string) error {
	env := []string{
		"GIT_AUTHOR_NAME=" + name,
		"GIT_AUTHOR_EMAIL=" + email,
		"GIT_COMMITTER_NAME=" + name,
		"GIT_COMMITTER_EMAIL=" + email,
	}
	_, err := runEnv(dir, env, "merge", "--no-ff", "--quiet", "--message", message, rev)
	return err
}

func run(dir string, args ...string) (string, error) {
	return runEnv(dir, nil, args...)
}

func runEnv(dir string, env []string, args ...string) (string, error) {
	out, stderr, code, err := runCode(dir, env, 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
}

func runInput(dir string, env []string, input string, args ...string) (string, error) {
	out, stderr, code, err := runCodeInput(context.Background(), dir, env, 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
}

func runCode(dir string, env []string, args ...string) (string, string, int, error) {
	return runCodeInput(context.Background(), dir, env, nil, args...)
}

func runNetwork(ctx context.Context, dir string, args ...string) (string, string, int, error) {
	ctx, cancel := context.WithTimeout(ctx, networkTimeout)
	defer cancel()
	return runCodeInput(ctx, dir, networkEnv, nil, args...)
}

func runCodeInput(ctx context.Context, dir string, env []string, stdin io.Reader, args ...string) (string, string, int, error) {
	cmd := exec.CommandContext(ctx, "git", args...)
	cmd.Dir = dir
	cmd.Env = append(os.Environ(), env...)
	cmd.Stdin = stdin
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
	cmd.Cancel = func() error {
		return syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL)
	}
	cmd.WaitDelay = 5 * time.Second
	stderr := &strings.Builder{}
	cmd.Stderr = stderr
	out, err := cmd.Output()
	if ctx.Err() != nil {
		return "", "", 0, fmt.Errorf("git %s: %w: %s", strings.Join(args, " "), context.Cause(ctx), strings.TrimSpace(stderr.String()))
	}
	exit := &exec.ExitError{}
	if errors.As(err, &exit) {
		return strings.TrimSpace(string(out)), strings.TrimSpace(stderr.String()), exit.ExitCode(), nil
	}
	if err != nil {
		return "", "", 0, fmt.Errorf("git %s: %w", strings.Join(args, " "), err)
	}
	return strings.TrimSpace(string(out)), strings.TrimSpace(stderr.String()), 0, nil
}