// Package operationlock serializes proxyctl state mutations across processes.
package operationlock

import (
	"context"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"time"

	"golang.org/x/sys/unix"

	"proxyctl/internal/securefs"
)

type Lock struct {
	path  string
	uid   int
	gid   int
	owned bool
}

func New(path string) *Lock { return &Lock{path: path} }
func NewOwned(path string, uid, gid int) *Lock {
	return &Lock{path: path, uid: uid, gid: gid, owned: true}
}

func (l *Lock) Lock(ctx context.Context) (func(), error) {
	if !filepath.IsAbs(l.path) {
		return nil, errors.New("operation lock path must be absolute")
	}
	directory := filepath.Dir(l.path)
	if err := os.MkdirAll(directory, 0o700); err != nil {
		return nil, fmt.Errorf("create operation lock directory: %w", err)
	}
	if err := os.Chmod(directory, 0o700); err != nil {
		return nil, fmt.Errorf("secure operation lock directory: %w", err)
	}
	if l.owned && (os.Geteuid() != l.uid || os.Getegid() != l.gid) {
		if err := os.Chown(directory, l.uid, l.gid); err != nil {
			return nil, fmt.Errorf("set operation lock directory owner: %w", err)
		}
	}
	file, err := securefs.OpenNoFollow(l.path, unix.O_CREAT|unix.O_RDWR|unix.O_NONBLOCK, 0o600)
	if err != nil {
		return nil, fmt.Errorf("open operation lock: %w", err)
	}
	info, err := file.Stat()
	if err != nil || !info.Mode().IsRegular() {
		file.Close()
		if err != nil {
			return nil, fmt.Errorf("inspect operation lock: %w", err)
		}
		return nil, errors.New("operation lock is not a regular file")
	}
	if err := file.Chmod(0o600); err != nil {
		file.Close()
		return nil, fmt.Errorf("secure operation lock: %w", err)
	}
	if l.owned && (os.Geteuid() != l.uid || os.Getegid() != l.gid) {
		if err := file.Chown(l.uid, l.gid); err != nil {
			file.Close()
			return nil, fmt.Errorf("set operation lock owner: %w", err)
		}
	}
	for {
		err = unix.Flock(int(file.Fd()), unix.LOCK_EX|unix.LOCK_NB)
		if err == nil {
			break
		}
		if !errors.Is(err, unix.EWOULDBLOCK) && !errors.Is(err, unix.EAGAIN) {
			file.Close()
			return nil, fmt.Errorf("acquire operation lock: %w", err)
		}
		select {
		case <-ctx.Done():
			file.Close()
			return nil, ctx.Err()
		case <-time.After(10 * time.Millisecond):
		}
	}
	return func() { _ = unix.Flock(int(file.Fd()), unix.LOCK_UN); _ = file.Close() }, nil
}