package main

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"net"
	"os"
	"path/filepath"
	"strings"
	"syscall"

	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/plumbing"

)

var (
	err_get_fd    = errors.New("unable to get file descriptor")
	err_get_ucred = errors.New("failed getsockopt")
)

// hooks_handle_connection handles a connection from git_hooks_client via the
// unix socket.
func hooks_handle_connection(conn net.Conn) {
	defer conn.Close()

	// There aren't reasonable cases where someone would run this as
	// another user.
	ucred, err := get_ucred(conn)
	if err != nil {
		if _, err := conn.Write([]byte{1}); err != nil {
			return
		}
		fmt.Fprintln(conn, "Unable to get peer credentials:", err.Error())
		return
	}
	if ucred.Uid != uint32(os.Getuid()) {
		if _, err := conn.Write([]byte{1}); err != nil {
			return
		}
		fmt.Fprintln(conn, "UID mismatch")
		return
	}

	cookie := make([]byte, 64)
	_, err = conn.Read(cookie)
	if err != nil {
		if _, err := conn.Write([]byte{1}); err != nil {
			return
		}
		fmt.Fprintln(conn, "Failed to read cookie:", err.Error())
		return
	}

	pack_to_hook, ok := pack_to_hook_by_cookie.Load(string(cookie))
	if !ok {
		if _, err := conn.Write([]byte{1}); err != nil {
			return
		}
		fmt.Fprintln(conn, "Invalid handler cookie")
		return
	}

	var argc64 uint64
	err = binary.Read(conn, binary.NativeEndian, &argc64)
	if err != nil {
		if _, err := conn.Write([]byte{1}); err != nil {
			return
		}
		fmt.Fprintln(conn, "Failed to read argc:", err.Error())
		return
	}
	var args []string
	for i := uint64(0); i < argc64; i++ {
		var arg bytes.Buffer
		for {
			b := make([]byte, 1)
			n, err := conn.Read(b)
			if err != nil || n != 1 {
				if _, err := conn.Write([]byte{1}); err != nil {
					return
				}
				fmt.Fprintln(conn, "Failed to read arg:", err.Error())
				return
			}
			if b[0] == 0 {
				break
			}
			arg.WriteByte(b[0])
		}
		args = append(args, arg.String())
	}

	var stdin bytes.Buffer
	_, err = io.Copy(&stdin, conn)
	if err != nil {
		fmt.Fprintln(conn, "Failed to read to the stdin buffer:", err.Error())
	}

	switch filepath.Base(args[0]) {
	case "pre-receive":
		if pack_to_hook.direct_access {
			if _, err := conn.Write([]byte{0}); err != nil {
				return
			}
		} else {

			ref_ok := make(map[string]uint8)
			// 0 for ok
			// 1 for rejection due to not a contrib branch
			// 2 for rejection due to not being a new branch

			all_ok := true
			messages := make([]string, 0)

			for {
				line, err := stdin.ReadString('\n')
				if errors.Is(err, io.EOF) {
					break
				}
				line = line[:len(line)-1]

				old_oid, rest, found := strings.Cut(line, " ")
				if !found {
					if _, err := conn.Write([]byte{1}); err != nil {
						return
					}
					fmt.Fprintln(conn, "Invalid pre-receive line:", line)
					break
				}

				new_oid, ref_name, found := strings.Cut(rest, " ")
				if !found {
					if _, err := conn.Write([]byte{1}); err != nil {
						return
					}
					fmt.Fprintln(conn, "Invalid pre-receive line:", line)
					break
				}

				_ = new_oid

				if strings.HasPrefix(ref_name, "refs/heads/contrib/") {

					if all_zero_num_string(old_oid) {
						ref_ok[ref_name] = 0

					if all_zero_num_string(old_oid) { // New branch
						messages = append(messages, "Acceptable push to new contrib branch: "+ref_name)

						// TODO: Create a merge request. If that fails,
						// we should just reject this entire push
						// immediately.

					} else {
						ref_ok[ref_name] = 2

					} else { // Existing contrib branch

						// TODO: Check if the current user is authorized
						// to push to this contrib branch.

						// Then, check if this push is a fast-forward.
						// If not, we create a MR history archive ref
						// that points to the old object name.

						repo, err := git.PlainOpen(pack_to_hook.repo_path)
						if err != nil {
							if _, err := conn.Write([]byte{1}); err != nil {
								return
							}
							fmt.Fprintln(conn, "Daemon failed to open repo:", err.Error())
							return
						}

						old_hash := plumbing.NewHash(old_oid)
						fmt.Println(old_hash)

						old_commit, err := repo.CommitObject(old_hash)
						if err != nil {
							if _, err := conn.Write([]byte{1}); err != nil {
								return
							}
							fmt.Fprintln(conn, "Daemon failed to get old commit:", err.Error())
							return
						}

						// Potential BUG: I'm not sure if new_commit is guaranteed to be
						// detectable as they haven't been merged into the main repo's
						// objects yet. But it seems to work, and I don't think there's
						// any reason for this to only work intermitently.
						new_hash := plumbing.NewHash(new_oid)
						new_commit, err := repo.CommitObject(new_hash)
						if err != nil {
							if _, err := conn.Write([]byte{1}); err != nil {
								return
							}
							fmt.Fprintln(conn, "Daemon failed to get new commit:", err.Error())
							return
						}

						is_ancestor, err := old_commit.IsAncestor(new_commit)
						if err != nil {
							if _, err := conn.Write([]byte{1}); err != nil {
								return
							}
							fmt.Fprintln(conn, "Daemon failed to check if old commit is ancestor:", err.Error())
							return
						}

						if !is_ancestor {
							// TODO: Create MR snapshot ref instead
							all_ok = false
							messages = append(messages, "Rejecting force push to contrib branch: "+ref_name)
							continue
						}

						messages = append(messages, "Acceptable push to existing contrib branch: "+ref_name)

					}

				} else {
					ref_ok[ref_name] = 1

				} else { // Non-contrib branch
					all_ok = false
					messages = append(messages, "Rejecting push to non-contrib branch: "+ref_name)

				}
			}

			if or_all_in_map(ref_ok) == 0 {

			if all_ok {

				if _, err := conn.Write([]byte{0}); err != nil {
					return
				}

				fmt.Fprintln(conn, "Stuff")

			} else {
				if _, err := conn.Write([]byte{1}); err != nil {
					return
				}

				for ref, status := range ref_ok {
					switch status {
					case 0:
						fmt.Fprintln(conn, "Acceptable", ref)
					case 1:
						fmt.Fprintln(conn, "Not in the contrib/ namespace", ref)
					case 2:
						fmt.Fprintln(conn, "Branch already exists", ref)
					default:
						panic("Invalid branch status")
					}
				}

			}

			for _, message := range messages {
				fmt.Fprintln(conn, message)

			}
		}
	default:
		if _, err := conn.Write([]byte{1}); err != nil {
			return
		}
		fmt.Fprintln(conn, "Invalid hook:", args[0])
	}
}

func serve_git_hooks(listener net.Listener) error {
	for {
		conn, err := listener.Accept()
		if err != nil {
			return err
		}
		go hooks_handle_connection(conn)
	}
}

func get_ucred(conn net.Conn) (*syscall.Ucred, error) {
	unix_conn := conn.(*net.UnixConn)
	fd, err := unix_conn.File()
	if err != nil {
		return nil, err_get_fd
	}
	defer fd.Close()

	ucred, err := syscall.GetsockoptUcred(int(fd.Fd()), syscall.SOL_SOCKET, syscall.SO_PEERCRED)
	if err != nil {
		return nil, err_get_ucred
	}
	return ucred, nil
}

func all_zero_num_string(s string) bool {
	for _, r := range s {
		if r != '0' {
			return false
		}
	}
	return true
}

func or_all_in_map[K comparable, V uint8 | uint16 | uint32 | uint64](m map[K]V) (result V) {
	for _, value := range m {
		result |= value
	}
	return
}