//
//  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 mixer

import (
	"container/list"
	"errors"
	"fmt"
	"log"
	"strings"
	"sync"

	"github.com/scgolang/midi"
)

// TODO: make this configurable
const (
	CC_MUTE  = byte(0xB1)
	CC_FADER = byte(0xB0)
)

type Channel uint8
type EventType int

const (
	EventFaderChange EventType = iota
	EventMute
)

func (et EventType) String() string {
	switch et {
	case EventFaderChange:
		return "fader-change"
	case EventMute:
		return "mute"
	default:
		return "unknown"
	}
}

type FaderLevel uint8

// TODO: make the values configurable
const (
	FaderLevelUnknown = FaderLevel(0xFF)
	FaderLevelMax     = FaderLevel(0x7F)
	FaderLevel0db     = FaderLevel(0x60)
	FaderLevelOff     = FaderLevel(0x00)
)

func (fl FaderLevel) String() string {
	if fl > FaderLevelMax {
		return "unknown"
	}
	val := fmt.Sprintf("%3d", fl)
	switch fl {
	case FaderLevelMax:
		return val + " (max)"
	case FaderLevel0db:
		return val + " (0db)"
	case FaderLevelOff:
		return val + " (off)"
	default:
		return val
	}
}

type Mute int8

const (
	MuteUnknown = Mute(-1)
	MuteUnmuted = Mute(0)
	MuteMuted   = Mute(1)
)

func (m Mute) String() string {
	switch m {
	case MuteUnmuted:
		return "unmuted"
	case MuteMuted:
		return "muted"
	default:
		return "unknown"
	}
}

type Event struct {
	Channel Channel
	Type    EventType
	Level   FaderLevel
	Mute    Mute
}

func (e Event) String() string {
	return fmt.Sprintf("Event(%s) for channel %d: level=%s, muted=%s", e.Type, e.Channel, e.Level, e.Mute)
}

type subscriber struct {
	publish     chan<- Event
	unsubscribe <-chan struct{}
}

type Mixer struct {
	DevIn           *midi.Device
	DevOut          *midi.Device
	subscribersLock sync.Mutex
	subscribers     map[Channel]*list.List
}

func openDevice(devices []*midi.Device, prefix string) (d *midi.Device, err error) {
	for _, device := range devices {
		if strings.HasPrefix(device.Name, prefix) {
			d = device
		}
	}
	if d == nil {
		return nil, errors.New("could not find device with prefix: " + prefix)
	}
	return d, d.Open()
}

func NewMixer(c Config) (*Mixer, error) {
	devices, err := midi.Devices()
	if err != nil {
		return nil, err
	}

	// TODO: add support for DevIn == DevOut
	m := &Mixer{}
	if m.DevIn, err = openDevice(devices, c.DevIn); err != nil {
		return nil, err
	}
	m.DevIn.QueueSize = 100
	if m.DevOut, err = openDevice(devices, c.DevOut); err != nil {
		return nil, err
	}

	m.subscribers = make(map[Channel]*list.List)
	return m, nil
}

func (m *Mixer) publishEvent(ev Event) {
	m.subscribersLock.Lock()
	defer m.subscribersLock.Unlock()

	subs, exists := m.subscribers[ev.Channel]
	if exists && subs != nil {
		var next *list.Element
		for entry := subs.Front(); entry != nil; entry = next {
			next = entry.Next()

			sub, ok := (entry.Value).(subscriber)
			if !ok {
				panic(fmt.Sprintf("mixer: subscriber list element value has wrong type: %T", entry.Value))
			}

			select {
			case <-sub.unsubscribe:
				log.Printf("mixer: removing subscriber '%v', because it has unsubscribed", sub.publish)
				close(sub.publish)
				subs.Remove(entry)
			default:
				select {
				case sub.publish <- ev:
				default:
					// subscriber is not responding...
					log.Printf("mixer: removing subscriber '%v', because it is not responding", sub.publish)
					close(sub.publish)
					subs.Remove(entry)
				}
			}
		}
	}
}

func (m *Mixer) handleMidiPacket(p midi.Packet) {
	ev := Event{Level: FaderLevelUnknown, Mute: MuteUnknown}
	ev.Channel = Channel(p.Data[1])
	switch p.Data[0] {
	case CC_FADER:
		ev.Type = EventFaderChange
		ev.Level = FaderLevel(p.Data[2])
	case CC_MUTE:
		ev.Type = EventMute
		ev.Mute = MuteUnmuted
		if p.Data[2] > 0 {
			ev.Mute = MuteMuted
		}
	default:
		return
	}
	m.publishEvent(ev)
}

func (m *Mixer) Init() error {
	ch, err := m.DevIn.Packets()
	if err != nil {
		return err
	}

	go func() {
		for {
			// TODO: handle Errors (reopen the device!)
			m.handleMidiPacket(<-ch)
		}
	}()
	return nil
}

func (m *Mixer) Shutdown() error {
	if m.DevIn != nil {
		m.DevIn.Close()
	}
	if m.DevOut != nil {
		m.DevOut.Close()
	}
	// TODO: also close all subscribed channels
	//       terminate go-routine started by Init()
	return nil
}

func (m *Mixer) sendMute(channel byte, value byte) error {
	n, err := m.DevOut.Write([]byte{CC_MUTE, channel, value})
	if err != nil {
		// reopen device?
		return err
	}
	if n != 3 {
		return errors.New("sending mute command failed.")
	}
	return nil
}

func (m *Mixer) Mute(ch Channel) error {
	return m.sendMute(byte(ch), 0x7F)
}

func (m *Mixer) Unmute(ch Channel) error {
	return m.sendMute(byte(ch), 0x00)
}

func (m *Mixer) SetLevel(ch Channel, level FaderLevel) error {
	if level > FaderLevelMax {
		level = FaderLevelMax
	}
	n, err := m.DevOut.Write([]byte{CC_FADER, byte(ch), byte(level)})
	if err != nil {
		// reopen device?
		return err
	}
	if n != 3 {
		return errors.New("setting fader level failed.")
	}
	return nil
}

func (m *Mixer) Subscribe(ch Channel, out chan<- Event) chan<- struct{} {
	m.subscribersLock.Lock()
	defer m.subscribersLock.Unlock()

	subs, exists := m.subscribers[ch]
	if !exists {
		subs = list.New()
		m.subscribers[ch] = subs
	}

	log.Printf("mixer: subscribing '%v' to events for channel: %v", out, ch)
	unsubscribe := make(chan struct{})
	subs.PushBack(subscriber{publish: out, unsubscribe: unsubscribe})
	return unsubscribe
}