// Command epdctl is a small CLI for the epd7in3e panel. Every
// command runs Init, draws, then Sleep. With -dry-run out.png a
// command instead writes the quantised 800x480 frame to out.png, so
// the pipeline can be checked without hardware.
package main

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"image"
	"image/png"
	"math"
	"os"

	_ "image/jpeg" // register JPEG with image.Decode
	_ "image/png"  // register PNG with image.Decode

	"go-epd7in3e"
	"golang.org/x/image/draw"
)

// panelColours lists the six panel colours with their Palette index.
var panelColours = []struct {
	name  string
	col   epd7in3e.Color
	index uint8
}{
	{"black", epd7in3e.Black, 0},
	{"white", epd7in3e.White, 1},
	{"yellow", epd7in3e.Yellow, 2},
	{"red", epd7in3e.Red, 3},
	{"blue", epd7in3e.Blue, 4},
	{"green", epd7in3e.Green, 5},
}

func main() {
	if err := run(os.Args[1:]); err != nil {
		fmt.Fprintf(os.Stderr, "epdctl: %v\n", err)
		os.Exit(1)
	}
}

func run(args []string) error {
	if len(args) == 0 {
		usage()
		return errors.New("no command given")
	}
	cmd, rest := args[0], args[1:]
	switch cmd {
	case "clear":
		return doClear(rest)
	case "bars":
		return doBars(rest)
	case "show":
		return doShow(rest)
	case "help", "-h", "--help":
		usage()
		return nil
	}
	return fmt.Errorf("unknown command %q (want clear, bars, show or help)", cmd)
}

func usage() {
	fmt.Fprint(os.Stderr, `epdctl drives the Waveshare epd7in3e e-paper panel.

Usage:
  epdctl clear [black|white|yellow|red|blue|green]  fill the panel (default white)
  epdctl bars                                       six vertical colour bars
  epdctl show <file.png|file.jpg>                   letterbox, dither and display

Each command initialises the panel, draws, then puts it to sleep.
Add -dry-run out.png to write the quantised 800x480 frame to out.png
instead of touching the hardware. Add -v to log every command and
busy-wait duration to stderr (bring-up diagnostics, HARDWARE_CHECK.md).
`)
}

// dryRunFlag registers the -dry-run flag: when it names a file, the
// quantised frame is written there and the panel is never opened.
func dryRunFlag(fs *flag.FlagSet) *string {
	return fs.String("dry-run", "", "write the quantised frame to this PNG file instead of touching the panel")
}

func verboseFlag(fs *flag.FlagSet) *bool {
	return fs.Bool("v", false, "log every command and busy-wait duration to stderr")
}

// onPanel opens the HAT and runs the fixed lifecycle: Init, op,
// Sleep, then power off. Dither: true is set explicitly so the
// zero-value Opts field cannot turn it off.
func onPanel(v bool, op func(d *epd7in3e.Dev, ctx context.Context) error) error {
	d, err := epd7in3e.NewHAT(&epd7in3e.Opts{Dither: true, Verbose: v})
	if err != nil {
		return err
	}
	ctx := context.Background()
	if err := d.Init(ctx); err != nil {
		return err
	}
	if err := op(d, ctx); err != nil {
		return err
	}
	if err := d.Sleep(ctx); err != nil {
		return err
	}
	return d.Halt()
}

// writeFrame saves the quantised frame as a PNG.
func writeFrame(path string, frame *image.Paletted) error {
	f, err := os.Create(path)
	if err != nil {
		return fmt.Errorf("create %s: %w", path, err)
	}
	if err := png.Encode(f, frame); err != nil {
		f.Close()
		return fmt.Errorf("encode %s: %w", path, err)
	}
	if err := f.Close(); err != nil {
		return fmt.Errorf("close %s: %w", path, err)
	}
	b := frame.Bounds()
	fmt.Printf("wrote %dx%d preview to %s\n", b.Dx(), b.Dy(), path)
	return nil
}

func doClear(args []string) error {
	fs := flag.NewFlagSet("clear", flag.ExitOnError)
	out := dryRunFlag(fs)
	v := verboseFlag(fs)
	fs.Parse(args)

	name := "white"
	if fs.NArg() == 1 {
		name = fs.Arg(0)
	}
	var c epd7in3e.Color
	found := false
	for _, pc := range panelColours {
		if pc.name == name {
			c, found = pc.col, true
			break
		}
	}
	if !found {
		return fmt.Errorf("unknown colour %q (want black, white, yellow, red, blue or green)", name)
	}
	if *out != "" {
		return writeFrame(*out, solidFrame(c))
	}
	return onPanel(*v, func(d *epd7in3e.Dev, ctx context.Context) error {
		return d.Clear(ctx, c)
	})
}

func doBars(args []string) error {
	fs := flag.NewFlagSet("bars", flag.ExitOnError)
	out := dryRunFlag(fs)
	v := verboseFlag(fs)
	fs.Parse(args)
	if fs.NArg() != 0 {
		return errors.New("bars takes no arguments")
	}
	frame := barsFrame()
	if *out != "" {
		return writeFrame(*out, frame)
	}
	return onPanel(*v, func(d *epd7in3e.Dev, ctx context.Context) error {
		return d.Display(ctx, frame)
	})
}

// barsFrame builds six vertical bars, one per panel colour.
func barsFrame() *image.Paletted {
	img := image.NewPaletted(image.Rect(0, 0, epd7in3e.Width, epd7in3e.Height), epd7in3e.Palette)
	for i, pc := range panelColours {
		x0, x1 := i*epd7in3e.Width/6, (i+1)*epd7in3e.Width/6
		for x := x0; x < x1; x++ {
			for y := 0; y < epd7in3e.Height; y++ {
				img.Pix[y*img.Stride+x] = pc.index
			}
		}
	}
	return img
}

func doShow(args []string) error {
	fs := flag.NewFlagSet("show", flag.ExitOnError)
	out := dryRunFlag(fs)
	v := verboseFlag(fs)
	fs.Parse(args)
	if fs.NArg() != 1 {
		return errors.New("show needs one image file (png or jpg)")
	}
	f, err := os.Open(fs.Arg(0))
	if err != nil {
		return fmt.Errorf("open image: %w", err)
	}
	defer f.Close()
	src, format, err := image.Decode(f)
	if err != nil {
		return fmt.Errorf("decode %s: %w", fs.Arg(0), err)
	}
	if format != "png" && format != "jpeg" {
		return fmt.Errorf("%s: %s image, want png or jpg", fs.Arg(0), format)
	}
	frame := letterboxDithered(src)
	if *out != "" {
		return writeFrame(*out, frame)
	}
	return onPanel(*v, func(d *epd7in3e.Dev, ctx context.Context) error {
		return d.Display(ctx, frame)
	})
}

// letterboxDithered scales src to fit within 800x480 preserving its
// aspect ratio, centers it on a white field, then dithers the result
// to the panel's palette.
func letterboxDithered(src image.Image) *image.Paletted {
	b := src.Bounds()
	w, h := b.Dx(), b.Dy()
	if w <= 0 || h <= 0 {
		w, h = 1, 1
	}
	scale := math.Min(float64(epd7in3e.Width)/float64(w), float64(epd7in3e.Height)/float64(h))
	sw := int(math.Round(float64(w) * scale))
	sh := int(math.Round(float64(h) * scale))
	if sw < 1 {
		sw = 1
	}
	if sh < 1 {
		sh = 1
	}
	scaled := scaleTo(src, sw, sh)

	canvas := image.NewNRGBA(image.Rect(0, 0, epd7in3e.Width, epd7in3e.Height))
	for i := range canvas.Pix {
		canvas.Pix[i] = 255 // white letterbox
	}
	// Center the scaled image. The offset goes on the destination
	// rectangle: draw.Draw's source point is a point in the source's
	// coordinate system that is translated to the destination's
	// top-left, so passing the offset there would crop the source
	// instead of shifting it.
	ox := (epd7in3e.Width - sw) / 2
	oy := (epd7in3e.Height - sh) / 2
	draw.Draw(canvas, image.Rect(ox, oy, ox+sw, oy+sh), scaled, scaled.Bounds().Min, draw.Over)
	return epd7in3e.Quantise(canvas, true)
}

// scaleTo resizes src to exactly sw x sh with Catmull-Rom filtering.
func scaleTo(src image.Image, sw, sh int) *image.NRGBA {
	b := src.Bounds()
	if n, ok := src.(*image.NRGBA); ok && n.Rect.Dx() == b.Dx() && n.Rect.Dy() == b.Dy() {
		return scaleToNRGBA(n, b, sw, sh)
	}
	n := image.NewNRGBA(b)
	draw.Draw(n, b, src, b.Min, draw.Src)
	return scaleToNRGBA(n, b, sw, sh)
}

func scaleToNRGBA(src *image.NRGBA, sr image.Rectangle, sw, sh int) *image.NRGBA {
	dst := image.NewNRGBA(image.Rect(0, 0, sw, sh))
	draw.CatmullRom.Scale(dst, dst.Bounds(), src, sr, draw.Src, nil)
	return dst
}

// solidFrame builds an 800x480 frame in one colour, for the
// dry-run preview.
func solidFrame(c epd7in3e.Color) *image.Paletted {
	img := image.NewPaletted(image.Rect(0, 0, epd7in3e.Width, epd7in3e.Height), epd7in3e.Palette)
	var idx uint8
	for _, pc := range panelColours {
		if pc.col == c {
			idx = pc.index
			break
		}
	}
	for i := range img.Pix {
		img.Pix[i] = idx
	}
	return img
}