package gateway

import (
	"encoding/binary"
	"unicode/utf8"
)

const (
	apolloChannelGeneric  = 0
	apolloChannelUrgent   = 1
	apolloChannelKeyboard = 2
	apolloChannelMouse    = 3
	apolloChannelUTF8     = 6
	apolloChannelGamepad  = 16
)

type apolloInputPacket struct {
	channel uint8
	payload []byte
}

func encodeApolloInputEvent(event InputEvent) ([]apolloInputPacket, error) {
	switch event.Device {
	case "keyboard":
		if event.Code < 0 || event.Code > 0xffff || len(event.Payload) > 1 {
			return nil, ErrInputMalformed
		}
		packet := make([]byte, 14)
		binary.BigEndian.PutUint32(packet[:4], 10)
		if event.Pressed {
			binary.LittleEndian.PutUint32(packet[4:8], 3)
		} else {
			binary.LittleEndian.PutUint32(packet[4:8], 4)
		}
		binary.LittleEndian.PutUint16(packet[9:11], uint16(event.Code))
		if len(event.Payload) == 1 {
			packet[11] = event.Payload[0]
		}
		return []apolloInputPacket{{channel: apolloChannelKeyboard, payload: packet}}, nil
	case "mouse-button":
		if event.Code < 1 || event.Code > 8 || len(event.Payload) != 0 {
			return nil, ErrInputMalformed
		}
		packet := make([]byte, 9)
		binary.BigEndian.PutUint32(packet[:4], 5)
		magic := uint32(8)
		if !event.Pressed {
			magic = 9
		}
		binary.LittleEndian.PutUint32(packet[4:8], magic)
		packet[8] = byte(event.Code)
		return []apolloInputPacket{{channel: apolloChannelMouse, payload: packet}}, nil
	case "mouse-relative":
		if event.Pressed || len(event.Payload) != 4 {
			return nil, ErrInputMalformed
		}
		packet := make([]byte, 12)
		binary.BigEndian.PutUint32(packet[:4], 8)
		binary.LittleEndian.PutUint32(packet[4:8], 7)
		copy(packet[8:], event.Payload)
		return []apolloInputPacket{{channel: apolloChannelMouse, payload: packet}}, nil
	case "utf8":
		if event.Pressed || len(event.Payload) == 0 || len(event.Payload) > utf8.UTFMax || !utf8.Valid(event.Payload) || utf8.RuneCount(event.Payload) != 1 {
			return nil, ErrInputMalformed
		}
		packet := make([]byte, 8+len(event.Payload))
		binary.BigEndian.PutUint32(packet[:4], uint32(4+len(event.Payload)))
		binary.LittleEndian.PutUint32(packet[4:8], 0x17)
		copy(packet[8:], event.Payload)
		return []apolloInputPacket{{channel: apolloChannelUTF8, payload: packet}}, nil
	case "controller":
		if event.Code < 0 || event.Code > 15 || len(event.Payload) != 16 {
			return nil, ErrInputMalformed
		}
		packet := make([]byte, 34)
		binary.BigEndian.PutUint32(packet[:4], 30)
		binary.LittleEndian.PutUint32(packet[4:8], 0x0c)
		binary.LittleEndian.PutUint16(packet[8:10], 0x1a)
		binary.LittleEndian.PutUint16(packet[10:12], uint16(event.Code))
		copy(packet[12:14], event.Payload[:2])
		binary.LittleEndian.PutUint16(packet[14:16], 0x14)
		copy(packet[16:28], event.Payload[2:14])
		binary.LittleEndian.PutUint16(packet[28:30], 0x9c)
		copy(packet[30:32], event.Payload[14:16])
		binary.LittleEndian.PutUint16(packet[32:34], 0x55)
		return []apolloInputPacket{{channel: apolloChannelGamepad + uint8(event.Code), payload: packet}}, nil
	case "mouse-absolute":
		if event.Pressed || event.Code != 0 || !validAbsolutePayload(event.Payload) {
			return nil, ErrInputMalformed
		}
		width, height := binary.BigEndian.Uint16(event.Payload[4:6]), binary.BigEndian.Uint16(event.Payload[6:8])
		if width < 2 || height < 2 || width > 0x7fff || height > 0x7fff {
			return nil, ErrInputMalformed
		}
		packet := make([]byte, 18)
		binary.BigEndian.PutUint32(packet[:4], 14)
		binary.LittleEndian.PutUint32(packet[4:8], 5)
		copy(packet[8:12], event.Payload[:4])
		binary.BigEndian.PutUint16(packet[14:16], width-1)
		binary.BigEndian.PutUint16(packet[16:18], height-1)
		return []apolloInputPacket{{channel: apolloChannelMouse, payload: packet}}, nil
	case "mouse-scroll":
		if event.Pressed || event.Code != 0 || len(event.Payload) != 4 {
			return nil, ErrInputMalformed
		}
		packets := make([]apolloInputPacket, 0, 2)
		if event.Payload[0] != 0 || event.Payload[1] != 0 {
			packet := make([]byte, 14)
			binary.BigEndian.PutUint32(packet[:4], 10)
			binary.LittleEndian.PutUint32(packet[4:8], 10)
			copy(packet[8:10], event.Payload[:2])
			copy(packet[10:12], event.Payload[:2])
			packets = append(packets, apolloInputPacket{channel: apolloChannelMouse, payload: packet})
		}
		if event.Payload[2] != 0 || event.Payload[3] != 0 {
			packet := make([]byte, 10)
			binary.BigEndian.PutUint32(packet[:4], 6)
			binary.LittleEndian.PutUint32(packet[4:8], 0x55000001)
			copy(packet[8:10], event.Payload[2:4])
			packets = append(packets, apolloInputPacket{channel: apolloChannelMouse, payload: packet})
		}
		return packets, nil
	default:
		return nil, ErrInputMalformed
	}
}