package git

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"strings"
	"time"
)

var ErrUnsupportedService = errors.New("unsupported git service")

func subcommandForService(service string) (string, error) {
	switch service {
	case "git-upload-pack":
		return "upload-pack", nil
	case "git-receive-pack":
		return "receive-pack", nil
	default:
		return "", ErrUnsupportedService
	}
}

func pktLine(payload string) string {
	return fmt.Sprintf("%04x%s", len(payload)+4, payload)
}

func AdvertiseRefs(ctx context.Context, repoPath, service string, out io.Writer) error {
	subcmd, err := subcommandForService(service)
	if err != nil {
		return err
	}

	cctx, cancel := context.WithTimeout(ctx, 30*time.Second)
	defer cancel()

	var stdout, stderr bytes.Buffer
	cmd := exec.CommandContext(cctx, "git", subcmd, "--stateless-rpc", "--advertise-refs", repoPath)
	cmd.Env = append(os.Environ(), "GIT_TERMINAL_PROMPT=0", "LC_ALL=C")
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		return fmt.Errorf("git %s advertise-refs: %w (%s)", subcmd, err, strings.TrimSpace(stderr.String()))
	}

	header := pktLine(fmt.Sprintf("# service=%s\n", service)) + "0000"
	if _, err := io.WriteString(out, header); err != nil {
		return err
	}
	_, err = out.Write(stdout.Bytes())
	return err
}

func ServiceRPC(ctx context.Context, repoPath, service string, in io.Reader, out io.Writer) error {
	subcmd, err := subcommandForService(service)
	if err != nil {
		return err
	}

	cctx, cancel := context.WithTimeout(ctx, 2*time.Minute)
	defer cancel()

	var stderr bytes.Buffer
	cmd := exec.CommandContext(cctx, "git", subcmd, "--stateless-rpc", repoPath)
	cmd.Env = append(os.Environ(), "GIT_TERMINAL_PROMPT=0", "LC_ALL=C")
	cmd.Stdin = in
	cmd.Stdout = out
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		return fmt.Errorf("git %s stateless-rpc: %w (%s)", subcmd, err, strings.TrimSpace(stderr.String()))
	}

	if service == "git-receive-pack" {
		_, _ = EnsureDefaultBranch(ctx, repoPath, "main")
		_, _ = runGit(ctx, repoPath, 5*time.Second, "update-server-info")
	}

	return nil
}