hswro-alarm-bot/filters.go

package main

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

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

func FilterByType(ev <-chan satel.Event, allowedTypes []satel.ChangeType) <-chan satel.Event {
	returnChan := make(chan satel.Event)

	if len(allowedTypes) == 0 {
		// no allowed types == all types are allowed
		go func() {
			for e := range ev {
				returnChan <- e
			}
			close(returnChan)
		}()
	} else {
		go func() {
			for e := range ev {
				for _, allowedType := range allowedTypes {
					if allowedType == e.Type {
						returnChan <- e
						continue
					}
				}
			}
			close(returnChan)
		}()
	}

	return returnChan
}

type EventKey struct {
	ChangeType satel.ChangeType
	Index      int
}

type EventValue struct{ Value bool }

type PersistenceRecord struct {
	Key   EventKey
	Value EventValue
}

func persistMapOnDisk(lastSeen *map[EventKey]bool, persistenceFilePath string) {
	f, err := os.OpenFile(persistenceFilePath, os.O_WRONLY|os.O_CREATE, 0600)
	if err != nil {
		panic(err)
	}
	defer f.Close()
	enc := gob.NewEncoder(f)
	data := make([]PersistenceRecord, len(*lastSeen))
	i := 0
	for k, v := range *lastSeen {
		data[i] = PersistenceRecord{Key: k, Value: EventValue{v}}
		i += 1
	}
	err = enc.Encode(data)
	if err != nil {
		panic(err)
	}
}

func readMapFromDisk(persistenceFilePath string, logger *log.Logger) map[EventKey]bool {
	lastSeen := make(map[EventKey]bool)
	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 := make([]PersistenceRecord, 0)
	err = dec.Decode(&data)
	if err != nil {
		logger.Println("Error reading persistence file", persistenceFilePath, "from disk:", err, ". Discarding and starting over.")
		return lastSeen
	}
	for _, readData := range data {
		lastSeen[readData.Key] = readData.Value.Value
	}

	return lastSeen
}

func FilterByLastSeen(ev <-chan satel.Event, persistenceFilePath string, logger *log.Logger) <-chan satel.Event {
	returnChan := make(chan satel.Event)

	go func() {
		lastSeen := readMapFromDisk(persistenceFilePath, logger)
		for e := range ev {
			val, ok := lastSeen[EventKey{e.Type, e.Index}]
			if !ok || val != e.Value {
				lastSeen[EventKey{e.Type, e.Index}] = e.Value
				returnChan <- e

				persistMapOnDisk(&lastSeen, persistenceFilePath)
			}
		}
		close(returnChan)
	}()

	return returnChan
}