package main

import (
	"encoding/gob"
	"errors"
	"io/fs"
	"log"
	"os"
	"sync"

	"github.com/probakowski/go-satel"
)

var EXPECTED_PERSISTENCE_FILE_MAGIC = [...]byte{'H', 'S', 'W', 'R', 'O', 'A', 'L', 'A', 'R', 'M', 'B', 'O', 'T'}

const EXPECTED_PERSISTENCE_FILE_VERSION = 0

type EventKey struct {
	ChangeType satel.ChangeType
	Index      int
}

type EventValue struct{ Value bool }

type LastSeenRecord struct {
	Key   EventKey
	Value EventValue
}

type PersistenceData struct {
	Magic       [len(EXPECTED_PERSISTENCE_FILE_MAGIC)]byte
	FileVersion uint32
	LastSeen    []LastSeenRecord
}

type DataStore struct {
	mtx                 sync.Mutex
	logger              *log.Logger
	persistenceFilePath string

	lastSeen map[EventKey]EventValue
}

func loadSystemState(logger *log.Logger, persistenceFilePath string) map[EventKey]EventValue {
	lastSeen := make(map[EventKey]EventValue)
	f, err := os.OpenFile(persistenceFilePath, os.O_RDONLY|os.O_CREATE, 0600)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			// File not existing is fine, we'll create one later
			return lastSeen
		}
		panic(err)
	}
	defer f.Close()

	dec := gob.NewDecoder(f)
	data := PersistenceData{}
	err = dec.Decode(&data)
	if err != nil {
		logger.Println("Error reading persistence file", persistenceFilePath, "from disk:", err, ". Discarding and starting over.")
		return lastSeen
	}
	if data.Magic != EXPECTED_PERSISTENCE_FILE_MAGIC {
		logger.Println("Error reading persistence file", persistenceFilePath, "from disk: Wrong magic string. Discarding and starting over.")
		return lastSeen
	}
	if data.FileVersion != EXPECTED_PERSISTENCE_FILE_VERSION {
		logger.Println("Error reading persistence file", persistenceFilePath, "from disk: Wrong version: expected ",
			EXPECTED_PERSISTENCE_FILE_VERSION, ", got ", data.FileVersion, ". Discarding and starting over.")
		return lastSeen
	}
	for _, readData := range data.LastSeen {
		lastSeen[readData.Key] = readData.Value
	}

	return lastSeen
}

func (self *DataStore) saveSystemState() {
	f, err := os.OpenFile(self.persistenceFilePath, os.O_WRONLY|os.O_CREATE, 0600)
	if err != nil {
		panic(err)
	}
	defer f.Close()
	enc := gob.NewEncoder(f)
	data := PersistenceData{
		Magic:       EXPECTED_PERSISTENCE_FILE_MAGIC,
		FileVersion: EXPECTED_PERSISTENCE_FILE_VERSION,
		LastSeen:    make([]LastSeenRecord, len(self.lastSeen)),
	}
	i := 0
	for k, v := range self.lastSeen {
		data.LastSeen[i] = LastSeenRecord{Key: k, Value: v}
		i += 1
	}
	err = enc.Encode(data)
	if err != nil {
		panic(err)
	}
}

func MakeDataStore(logger *log.Logger, persistenceFilePath string) DataStore {
	return DataStore{
		logger:              logger,
		persistenceFilePath: persistenceFilePath,
		lastSeen:            loadSystemState(logger, persistenceFilePath),
	}
}

func (self *DataStore) GetSystemState() map[EventKey]EventValue {
	self.mtx.Lock()
	defer self.mtx.Unlock()

	copiedMap := make(map[EventKey]EventValue)
	for key, value := range self.lastSeen {
		copiedMap[key] = value
	}
	return copiedMap
}

func (self *DataStore) SetSystemState(key EventKey, value EventValue) {
	self.mtx.Lock()
	self.lastSeen[key] = value
	self.saveSystemState()
	self.mtx.Unlock()
}