//
//  dolmetschctl
//
//
//  Copyright (C) 2019 Christian Pointner <equinox@spreadspace.org>
//
//  This file is part of dolmetschctl.
//
//  dolmetschctl is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  any later version.
//
//  dolmetschctl is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with dolmetschctl. If not, see <http://www.gnu.org/licenses/>.
//

package main

import (
	"fmt"
	"log"

	"spreadspace.org/dolmetschctl/pkg/mixer"
)

type State int

const (
	StateNew = iota
	StateSettling
	StateSettled
)

func (s State) String() string {
	switch s {
	case StateNew:
		return "new"
	case StateSettling:
		return "settling"
	case StateSettled:
		return "settled"
	default:
		return "unknown"
	}
}

type Language string

func (l Language) String() string {
	if l == "" {
		return "none"
	}
	return string(l)
}

type MixerChannelState struct {
	level mixer.FaderLevel
	mute  mixer.Mute
}

type MixerChannel struct {
	num     mixer.Channel
	target  MixerChannelState
	current MixerChannelState
}

type MixerChannels struct {
	main  MixerChannel
	voice MixerChannel
}

type selectLangRequest struct {
	l        Language
	resultCh chan error
}

type StateMachine struct {
	mixer        *mixer.Mixer
	selectLangCh chan selectLangRequest
	quitCh       chan bool
	exitedCh     chan struct{}
	mixerEventCh chan mixer.Event

	languages    map[Language]*MixerChannels
	channel2lang map[mixer.Channel]Language

	currentState State
	currentLang  Language
	targetLang   Language
}

func (sm *StateMachine) handleMixerEvent(ev mixer.Event) {
	lang, exists := sm.channel2lang[ev.Channel]
	if !exists {
		// TODO: make this panic?
		log.Printf("got mixer-event for unknown channel: %s", ev)
		return
	}

	mcs, exists := sm.languages[lang]
	if !exists {
		panic(fmt.Sprintf("channel2lang map contains unknown language entries!"))
		return
	}

	var mc *MixerChannel
	switch ev.Channel {
	case mcs.main.num:
		mc = &mcs.main
	case mcs.voice.num:
		mc = &mcs.voice
	default:
		panic(fmt.Sprintf("channel2lang points to language that does not use the channel!"))
		return
	}

	switch ev.Type {
	case mixer.EventFaderChange:
		mc.current.level = ev.Level
	case mixer.EventMute:
		mc.current.mute = ev.Mute
	}
}

// make sure that our state and the mixer are in sync
func (sm *StateMachine) initMixer() {
	for _, mcs := range sm.languages {
		sm.mixer.SetLevel(mcs.main.num, mixer.FaderLevel0db-1)
		sm.mixer.SetLevel(mcs.main.num, mixer.FaderLevel0db)
		mcs.main.target.level = mixer.FaderLevel0db

		sm.mixer.SetLevel(mcs.voice.num, mixer.FaderLevelOff+1)
		sm.mixer.SetLevel(mcs.voice.num, mixer.FaderLevelOff)
		mcs.voice.target.level = mixer.FaderLevelOff
	}
	sm.currentLang = ""
	sm.targetLang = ""
	sm.currentState = StateSettled
}

// the "current language" is what is currently spoken on stage
func (sm *StateMachine) selectLang(l Language) error {
	if l != "" {
		if _, exists := sm.languages[l]; !exists {
			return fmt.Errorf("language '%s' does not exist", l)
		}
	}
	sm.targetLang = l
	log.Printf("new target language: '%s'", sm.targetLang)
	return nil
}

func (sm *StateMachine) reconcile() {
	for lang, mcs := range sm.languages {
		if sm.targetLang == "" || lang == sm.targetLang || mcs.voice.current.mute == mixer.MuteMuted {
			mcs.main.target.level = mixer.FaderLevel0db
			mcs.voice.target.level = mixer.FaderLevelOff
		} else {
			mcs.main.target.level = 30 // TODO: hardcoded Value!!
			mcs.voice.target.level = mixer.FaderLevel0db
		}
	}

	sm.currentState = StateSettled
	for _, mcs := range sm.languages {
		if mcs.main.target.level != mcs.main.current.level {
			sm.mixer.SetLevel(mcs.main.num, mcs.main.target.level) // TODO: implement smooth fading!!
			sm.currentState = StateSettling
		}
		if mcs.voice.target.level != mcs.voice.current.level {
			sm.mixer.SetLevel(mcs.voice.num, mcs.voice.target.level) // TODO: implement smooth fading!!
			sm.currentState = StateSettling
		}
	}
}

func (sm *StateMachine) run() {
	defer close(sm.exitedCh)

	sm.initMixer()
	for {
		select {
		case req := <-sm.selectLangCh:
			req.resultCh <- sm.selectLang(req.l)
			sm.reconcile()
		case ev := <-sm.mixerEventCh:
			sm.handleMixerEvent(ev)
			sm.reconcile()
		case <-sm.quitCh:
			return
		}
	}
}

func NewStateMachine(m *mixer.Mixer) (*StateMachine, error) {
	sm := &StateMachine{mixer: m}
	sm.selectLangCh = make(chan selectLangRequest, 10)
	sm.quitCh = make(chan bool, 1)
	sm.exitedCh = make(chan struct{})
	sm.mixerEventCh = make(chan mixer.Event, 1000)

	sm.languages = make(map[Language]*MixerChannels)
	sm.channel2lang = make(map[mixer.Channel]Language)

	sm.currentState = StateNew
	sm.currentLang = ""
	sm.targetLang = ""
	return sm, nil
}

// TODO: currently we can only deal with 2 languages...
func (sm *StateMachine) AddLanguage(name Language, main, voice mixer.Channel) error {
	if sm.currentState != StateNew {
		return fmt.Errorf("adding languages is only allowed during startup")
	}
	if name == "none" {
		return fmt.Errorf("language 'none' is reserved")
	}
	if _, exists := sm.languages[name]; exists {
		return fmt.Errorf("language '%s' already exists", name)
	}
	for ch := range []mixer.Channel{main, voice} {
		if _, exists := sm.languages[name]; exists {
			return fmt.Errorf("mixer channel %v is already in use by language '%s'", ch, name)
		}
	}

	unknown := MixerChannelState{level: mixer.FaderLevelUnknown, mute: mixer.MuteUnknown}
	chMain := MixerChannel{num: main, current: unknown, target: unknown}
	chVoice := MixerChannel{num: voice, current: unknown, target: unknown}

	sm.languages[name] = &MixerChannels{chMain, chVoice}
	sm.channel2lang[main] = name
	sm.channel2lang[voice] = name

	sm.mixer.Subscribe(main, sm.mixerEventCh)
	sm.mixer.Subscribe(voice, sm.mixerEventCh)
	return nil
}

func (sm *StateMachine) Start() {
	go sm.run()
}

func (sm *StateMachine) SelectLanguage(l Language) error {
	resultCh := make(chan error)
	sm.selectLangCh <- selectLangRequest{l, resultCh}
	return <-resultCh
}

func (sm *StateMachine) Shutdown() {
	select {
	case sm.quitCh <- true:
	default:
	}
	<-sm.exitedCh
}