package gzev

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/hex"
	"encoding/json"
	"errors"
	"os"
	"path/filepath"
	"syscall"
	"time"
)

type recoveryTicket struct {
	Code    string    `json:"code"`
	Expires time.Time `json:"expires"`
}

func recoveryLock(path string, fn func() error) error {
	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
		return err
	}
	f, err := os.OpenFile(path+".lock", os.O_CREATE|os.O_RDWR, 0600)
	if err != nil {
		return err
	}
	defer f.Close()
	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX); err != nil {
		return err
	}
	defer syscall.Flock(int(f.Fd()), syscall.LOCK_UN)
	return fn()
}
func EnsureRecoveryCode(path string) (string, error) {
	var code string
	err := recoveryLock(path, func() error {
		b, err := os.ReadFile(path)
		var ticket recoveryTicket
		if err == nil && json.Unmarshal(b, &ticket) == nil && ticket.Expires.After(time.Now()) && len(ticket.Code) == 48 {
			code = ticket.Code
			return nil
		}
		nonce := make([]byte, 24)
		if _, err := rand.Read(nonce); err != nil {
			return err
		}
		code = hex.EncodeToString(nonce)
		ticket = recoveryTicket{Code: code, Expires: time.Now().Add(48 * time.Hour)}
		f, err := os.CreateTemp(filepath.Dir(path), ".recovery-*")
		if err != nil {
			return err
		}
		defer os.Remove(f.Name())
		if err := json.NewEncoder(f).Encode(ticket); err != nil {
			f.Close()
			return err
		}
		if err := f.Close(); err != nil {
			return err
		}
		return os.Rename(f.Name(), path)
	})
	return code, err
}

// ConsumeRecovery serializes all writers and only consumes a ticket after a successful update.
func ConsumeRecovery(path, code string, action func() error) error {
	return recoveryLock(path, func() error {
		b, err := os.ReadFile(path)
		var ticket recoveryTicket
		if err != nil || json.Unmarshal(b, &ticket) != nil || !ticket.Expires.After(time.Now()) || len(code) != 48 || subtle.ConstantTimeCompare([]byte(code), []byte(ticket.Code)) != 1 {
			return errors.New("invalid recovery code")
		}
		if err := action(); err != nil {
			return err
		}
		return os.Remove(path)
	})
}