package epd

import (
	"fmt"
	"image"
	"log/slog"
	"os"
	"periph.io/x/conn/v3/gpio"
	"periph.io/x/conn/v3/physic"
	"periph.io/x/conn/v3/spi"
	"periph.io/x/conn/v3/spi/spireg"
	"periph.io/x/host/v3/bcm283x"
	"time"
)

const (
	Width  = 800
	Height = 480
)

type EPD struct {
	width  int
	height int

	resetPin gpio.PinOut
	dcPin    gpio.PinOut
	busyPin  gpio.PinIn
	csPin    gpio.PinOut
	pwrPin   gpio.PinOut

	partFlag byte

	spi    spi.Conn
	spiReg spi.PortCloser
}

func New() (*EPD, error) {
	epd := &EPD{
		width:    Width,
		height:   Height,
		resetPin: bcm283x.GPIO17,
		dcPin:    bcm283x.GPIO25,
		busyPin:  bcm283x.GPIO24,
		csPin:    bcm283x.GPIO8,
		pwrPin:   bcm283x.GPIO18,
		partFlag: 1,
	}

	return epd, nil
}

func (e *EPD) reset() {
	e.resetPin.Out(gpio.High)
	time.Sleep(20 * time.Millisecond)
	e.resetPin.Out(gpio.Low)
	time.Sleep(2 * time.Millisecond)
	e.resetPin.Out(gpio.High)
	time.Sleep(20 * time.Millisecond)
}

func (e *EPD) sendCommand(cmd byte) {
	e.dcPin.Out(gpio.Low)
	e.csPin.Out(gpio.Low)
	if _, err := e.spiWrite([]byte{cmd}); err != nil {
		slog.Error("writing to spi", "err", err)
		os.Exit(1)
	}
	e.csPin.Out(gpio.High)
}

func (e *EPD) sendData(data byte) {
	e.dcPin.Out(gpio.High)
	e.csPin.Out(gpio.Low)
	if _, err := e.spiWrite([]byte{data}); err != nil {
		slog.Error("writing to spi", "err", err)
		os.Exit(1)
	}
	e.csPin.Out(gpio.High)
}

func (e *EPD) sendDataSlice(data []byte) {
	e.dcPin.Out(gpio.High)
	toSend := len(data)
	const maxSize = 4096
	if toSend <= maxSize {
		e.csPin.Out(gpio.Low)
		if _, err := e.spiWrite(data); err != nil {
			slog.Error("writing to spi", "err", err)
			os.Exit(1)
		}
		e.csPin.Out(gpio.High)
		return
	}

	cursor := 0
	for cursor < toSend {
		chunk := data[cursor:min(cursor+maxSize, toSend)]
		e.csPin.Out(gpio.Low)
		if _, err := e.spiWrite(chunk); err != nil {
			slog.Error("writing to spi", "err", err)
			os.Exit(1)
		}
		e.csPin.Out(gpio.High)
		cursor = min(cursor+maxSize, toSend)
	}
}

func (e *EPD) spiWrite(write []byte) ([]byte, error) {
	read := make([]byte, len(write))

	if err := e.spi.Tx(write, read); err != nil {
		return nil, fmt.Errorf("tx: %w", err)
	}

	return read, nil
}

func (e *EPD) readBusy() {
	e.sendCommand(0x71)
	for e.busyPin.Read() == gpio.Low {
		time.Sleep(20 * time.Millisecond)
		e.sendCommand(0x71)
	}
	time.Sleep(20 * time.Millisecond)
}

func (e *EPD) turnOn() error {
	slog.Info("turning on")
	if err := e.resetPin.Out(gpio.Low); err != nil {
		return fmt.Errorf("setting reset pin to low: %w", err)
	}
	if err := e.dcPin.Out(gpio.Low); err != nil {
		return fmt.Errorf("setting dc pin to low: %w", err)
	}
	if err := e.csPin.Out(gpio.Low); err != nil {
		return fmt.Errorf("setting cs pin to low: %w", err)
	}
	if err := e.pwrPin.Out(gpio.High); err != nil {
		return fmt.Errorf("setting pwr pin to low: %w", err)
	}

	var err error

	if e.spiReg, err = spireg.Open("0"); err != nil {
		return fmt.Errorf("opening SPI: %w", err)
	}

	c, err := e.spiReg.Connect(4*physic.MegaHertz, spi.Mode0, 8)
	if err != nil {
		return fmt.Errorf("connecting to SPI: %w", err)
	}

	e.spi = c

	return nil
}

func (e *EPD) Init() error {
	slog.Info("initializing EPD")

	if err := e.turnOn(); err != nil {
		return fmt.Errorf("turning on: %w", err)
	}

	e.reset()

	e.sendCommand(0x06)
	e.sendDataSlice([]byte{0x17, 0x17, 0x28, 0x17})

	e.sendCommand(0x01)
	e.sendDataSlice([]byte{0x07, 0x07, 0x28, 0x17})

	e.sendCommand(0x04)
	time.Sleep(100 * time.Millisecond)
	e.readBusy()

	e.sendCommand(0x00)
	e.sendData(0x1f)

	e.sendCommand(0x61)
	e.sendDataSlice([]byte{0x03, 0x20, 0x01, 0xe0})

	e.sendCommand(0x15)
	e.sendData(0x00)

	e.sendCommand(0x50)
	e.sendDataSlice([]byte{0x10, 0x07})

	e.sendCommand(0x60)
	e.sendData(0x22)

	return nil
}

func (e *EPD) InitFast() error {
	slog.Info("initializing Fast EPD")

	if err := e.turnOn(); err != nil {
		return fmt.Errorf("turning on: %w", err)
	}

	e.reset()

	e.sendCommand(0x00)
	e.sendData(0x1f)

	e.sendCommand(0x50)
	e.sendDataSlice([]byte{0x10, 0x07})

	e.sendCommand(0x04)
	time.Sleep(100 * time.Millisecond)
	e.readBusy()

	e.sendCommand(0x06)
	e.sendDataSlice([]byte{0x27, 0x27, 0x18, 0x17})

	e.sendCommand(0xe0)
	e.sendData(0x02)

	e.sendCommand(0xe5)
	e.sendData(0x5a)

	return nil
}

func (e *EPD) Clear() {
	slog.Info("clearing epd")
	e.Send(image.White)
}

func (e *EPD) Refresh() {
	slog.Info("refreshing...")
	e.sendCommand(0x12)
	time.Sleep(100 * time.Millisecond)
	e.readBusy()
}

func (e *EPD) Sleep() error {
	slog.Info("sleeping display...")
	e.sendCommand(0x02)
	e.readBusy()

	e.sendCommand(0x07)
	e.sendData(0xa5)

	time.Sleep(2 * time.Second)
	if err := e.turnOff(); err != nil {
		return fmt.Errorf("turning off: %w", err)
	}

	return nil
}

func (e *EPD) turnOff() error {
	slog.Info("turning off...")
	if err := e.spiReg.Close(); err != nil {
		return fmt.Errorf("closing SPI: %w", err)
	}

	e.resetPin.Out(gpio.Low)
	e.dcPin.Out(gpio.Low)
	e.pwrPin.Out(gpio.Low)

	return nil
}

func (e *EPD) Send(img image.Image) {
	if img == nil {
		slog.Info("empty img")
		return
	}

	slog.Info("sending img...")
	toSend := make([]byte, 0, e.height*e.width/8)
	toSend2 := make([]byte, 0, e.height*e.width/8)
	for row := 0; row < e.height; row++ {
		for col := 0; col < e.width; col += 8 {
			// this loop converts individual pixels into a single byte
			// 8-pixels at a time and then sends that byte to render
			var b byte = 0xFF
			for px := 0; px < 8; px++ {
				var pixel = img.At(col+px, row)
				if isdark(pixel.RGBA()) {
					b &= ^(0x80 >> (px % 8))
				}
			}
			toSend = append(toSend, ^b)
			toSend2 = append(toSend2, b)
		}
	}

	e.sendCommand(0x10)
	e.sendDataSlice(toSend2)

	e.sendCommand(0x13)
	e.sendDataSlice(toSend)
}

func isdark(r, g, b, _ uint32) bool {
	return r < 65535 || g < 65535 || b < 65535
}