package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"syscall"
)

type store struct {
	path    string
	lock    *os.File
	Watches map[string]*watch `json:"watches"`
}

func openStore(path string) (*store, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0700); err != nil {
		return nil, err
	}
	lock, err := os.OpenFile(path+".lock", os.O_CREATE|os.O_RDWR, 0600)
	if err != nil {
		return nil, err
	}
	if err := syscall.Flock(int(lock.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
		return nil, fmt.Errorf("checkpoint is already in use: %w", errors.Join(err, lock.Close()))
	}
	s := &store{path: path, lock: lock, Watches: make(map[string]*watch)}
	data, err := os.ReadFile(path)
	if errors.Is(err, os.ErrNotExist) {
		return s, nil
	}
	if err == nil {
		err = json.Unmarshal(data, s)
	}
	if err == nil && s.Watches == nil {
		err = errors.New("checkpoint has no watches")
	}
	if err != nil {
		return nil, errors.Join(err, s.close())
	}
	for _, w := range s.Watches {
		if w.Known && w.Goal != nil && w.Goal.Status.waiting() && w.Turn.Status == "failed" {
			if w.Hold != nil && w.Goal.Status == "usageLimited" && w.Hold.Status == "usageLimited" {
				w.Hold = nil
			}
			if w.Hold == nil {
				w.Armed = true
			}
		}
	}
	return s, nil
}

func (s *store) close() error { return s.lock.Close() }

func (s *store) save() error {
	data, err := json.Marshal(s)
	if err != nil {
		return err
	}
	f, err := os.CreateTemp(filepath.Dir(s.path), ".state-*")
	if err != nil {
		return err
	}
	defer func() { _ = os.Remove(f.Name()) }()
	if _, err = f.Write(data); err == nil {
		err = f.Sync()
	}
	closeErr := f.Close()
	if err != nil {
		return err
	}
	if closeErr != nil {
		return closeErr
	}
	return os.Rename(f.Name(), s.path)
}

func (s *store) watch(id string) *watch {
	w := s.Watches[id]
	if w == nil {
		w = &watch{}
		s.Watches[id] = w
	}
	return w
}