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

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

	"golang.org/x/sys/unix"

	"proxyctl/internal/securefs"
)

type Locker interface {
	Lock(context.Context) (func(), error)
}

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

type Group struct{ locks []Locker }

func NewGroup(locks ...Locker) *Group { return &Group{locks: append([]Locker(nil), locks...)} }

func (g *Group) Lock(ctx context.Context) (func(), error) {
	var unlocks []func()
	for _, lock := range g.locks {
		unlock, err := lock.Lock(ctx)
		if err != nil {
			for i := len(unlocks) - 1; i >= 0; i-- {
				unlocks[i]()
			}
			return nil, err
		}
		unlocks = append(unlocks, unlock)
	}
	return func() {
		for i := len(unlocks) - 1; i >= 0; i-- {
			unlocks[i]()
		}
	}, nil
}

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")
	}
	store := securefs.Store{TrustedRoot: securefs.ExistingTrustedRoot(l.path)}
	if l.owned {
		store.Owner = &securefs.Owner{UID: l.uid, GID: l.gid}
	}
	file, err := store.OpenRegular(l.path, unix.O_CREAT|unix.O_RDWR|unix.O_NONBLOCK, 0o600)
	if err != nil {
		return nil, fmt.Errorf("open operation lock securely: %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
}