package main

import (
	"bufio"
	"flag"
	"fmt"
	"image"
	_ "image/gif"
	_ "image/jpeg"
	_ "image/png"
	"io"
	"os"
	"path/filepath"
	"slices"

	runewidth "github.com/mattn/go-runewidth"
	_ "golang.org/x/image/bmp"
	"golang.org/x/image/draw"
	_ "golang.org/x/image/tiff"
	_ "golang.org/x/image/webp"
	"golang.org/x/sys/unix"
	"roseh.moe/pkg/sixel"
)

var (
	x = flag.Int("x", 15, "set image width in columns")
	m = flagPrintMode(flag.CommandLine, "m", modeSixel, "one of 'block', 'block24', or 'sixel'")
)

type printMode int

const (
	modeInvalid printMode = iota
	modeBlock
	modeBlock24
	modeSixel
)

type printModeValue printMode

func (m *printModeValue) String() string {
	switch printMode(*m) {
	case modeBlock:
		return "block"
	case modeBlock24:
		return "block24"
	case modeSixel:
		return "sixel"
	default:
		return "invalid"
	}
}

func (m *printModeValue) Set(s string) error {
	var mode printMode
	switch s {
	case "block":
		mode = modeBlock
	case "block24":
		mode = modeBlock24
	case "sixel":
		mode = modeSixel
	default:
		return fmt.Errorf("bad mode type %q, should be one of 'block', 'block24', or 'sixel'", s)
	}
	*m = printModeValue(mode)
	return nil
}

func flagPrintMode(fs *flag.FlagSet, name string, value printMode, usage string) *printMode {
	fs.Var((*printModeValue)(&value), name, usage)
	return &value
}

func isDir(filename string) bool {
	stat, err := os.Stat(filename)
	return err == nil && stat.IsDir()
}

func isImage(filename string) bool {
	f, err := os.Open(filename)
	if err != nil {
		return false
	}
	defer f.Close()
	_, _, err = image.DecodeConfig(f)
	return err == nil
}

func imageDimensions(filename string) (width, height int, err error) {
	f, err := os.Open(filename)
	if err != nil {
		return 0, 0, err
	}
	defer f.Close()
	config, _, err := image.DecodeConfig(f)
	return config.Width, config.Height, err
}

func load(filename string) (image.Image, error) {
	f, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	img, _, err := image.Decode(f)
	if err != nil {
		return nil, fmt.Errorf("decode %q: %s", filename, err)
	}

	return img, nil
}

func printImg(w io.Writer, img image.Image) {
	switch *m {
	case modeBlock:
		sixel.PrintXTerm16(w, img)
	case modeBlock24:
		sixel.PrintBlock(w, img)
	case modeSixel:
		sixel.Print(w, img, nil)
	default:
		panic("invalid mode")
	}
}

type pixelAspectRatio struct {
	x, y int
}

func compositeImageRow(imagePaths []string, width, rowWidth, cellX int, aspectRatio pixelAspectRatio) (image.Image, error) {
	var logicalWidth, maxHeight int
	for i, filename := range imagePaths {
		if i > 0 {
			logicalWidth += 2 * cellX
		}
		fileNameWidth := cellX * runewidth.StringWidth(filepath.Base(filename))
		logicalWidth += max(width, fileNameWidth)

		imageWidth, imageHeight, err := imageDimensions(filename)
		if err != nil {
			return nil, err
		}
		maxHeight = max(maxHeight, imageHeight*width/(imageWidth*aspectRatio.y/aspectRatio.x))
	}
	bounds := image.Rect(0, 0, rowWidth, maxHeight)
	result := image.NewRGBA(bounds)
	offset := 0
	for _, filename := range imagePaths {
		img, err := load(filename)
		if err != nil {
			return nil, err
		}
		height := img.Bounds().Dy() * width / (img.Bounds().Dx() * aspectRatio.y / aspectRatio.x)
		imageWidth := max(width, cellX*runewidth.StringWidth(filepath.Base(filename)))
		start := (offset*rowWidth + logicalWidth - 1) / logicalWidth
		end := ((offset+imageWidth)*rowWidth + logicalWidth - 1) / logicalWidth
		offsetStart := start + (end-start-width)/2
		dstBounds := image.Rect(offsetStart, (maxHeight-height)/2, offsetStart+width, (maxHeight-height)/2+height)
		draw.BiLinear.Scale(result, dstBounds, img, img.Bounds(), draw.Src, nil)
		offset += imageWidth + 2*cellX
	}
	return result, nil
}

func splitRows(imagePaths []string, width, rowWidth int) [][]string {
	var rows [][]string
	for len(imagePaths) > 0 {
		row := imagePaths[:0]
		thisRowWidth := 0
		for ; len(row) < len(imagePaths); row = row[:len(row)+1] {
			nextW := max(width, runewidth.StringWidth(filepath.Base(imagePaths[len(row)])))
			if len(row) > 0 {
				nextW += 2
			}
			if thisRowWidth > 0 && thisRowWidth+nextW > rowWidth {
				break
			}
			thisRowWidth += nextW
		}
		imagePaths = imagePaths[len(row):]
		rows = append(rows, row)
	}
	return rows
}

func thumbnailFiles(w io.Writer, imagePaths []string, width, rowWidth, cellX, cellY int) error {
	padding := 2
	aspectRatio := pixelAspectRatio{1, 1}
	switch *m {
	case modeBlock:
		aspectRatio = pixelAspectRatio{cellX, cellY}
		cellX = 1
	case modeBlock24:
		aspectRatio = pixelAspectRatio{2 * cellX, cellY}
		cellX = 1
	case modeSixel:
		padding *= cellX
	}
	rows := splitRows(imagePaths, width, rowWidth)
	rowImages := make([]chan image.Image, len(rows))
	for i := range rowImages {
		rowImages[i] = make(chan image.Image, 1)
	}
	errCh := make(chan error, 1)
	go func() {
		sem := make(chan struct{}, 20)
		for i, row := range rows {
			sem <- struct{}{}
			go func() {
				defer func() { <-sem }()
				img, err := compositeImageRow(row, width*cellX, rowWidth*cellX, cellX, aspectRatio)
				if err != nil {
					select {
					case errCh <- err:
					default:
					}
					return
				}
				rowImages[i] <- img
			}()
		}
	}()
	for i, row := range rows {
		thisRowWidth := 0
		for j, filename := range row {
			if j > 0 {
				thisRowWidth += 2
			}
			thisRowWidth += max(width, runewidth.StringWidth(filepath.Base(filename)))
		}
		var rowImage image.Image
		select {
		case err := <-errCh:
			return err
		case rowImage = <-rowImages[i]:
		}
		printImg(w, rowImage)
		fmt.Fprintln(w)
		offset := 0
		realOffset := 0
		for i, filename := range row {
			if i > 0 {
				offset += 2
			}
			start := (offset*rowWidth + thisRowWidth - 1) / thisRowWidth
			fmt.Fprintf(w, "%*s", start-realOffset, "")
			realOffset = start
			fileNameWidth := runewidth.StringWidth(filepath.Base(filename))
			offset += max(width, fileNameWidth)
			end := (offset*rowWidth + thisRowWidth - 1) / thisRowWidth
			padding := (end - start - fileNameWidth) / 2
			fmt.Fprintf(w, "%*s%s", padding, "", filepath.Base(filename))
			realOffset += padding + fileNameWidth
		}
		fmt.Fprintln(w)
	}
	return nil
}

func readDir(d string) ([]string, error) {
	files, err := os.ReadDir(d)
	if err != nil {
		return nil, err
	}
	filenames := make([]string, len(files))
	for i, f := range files {
		filenames[i] = filepath.Join(d, f.Name())
	}
	return filenames, nil
}

func thumbnailDir(w io.Writer, dir string, width, rowWidth, cellX, cellY int) error {
	files, err := readDir(dir)
	if err != nil {
		return err
	}
	files = slices.DeleteFunc(files, func(filename string) bool { return !isImage(filename) })
	return thumbnailFiles(w, files, width, rowWidth, cellX, cellY)
}

func thumbnailer(args []string) error {
	cols := *x
	if *x <= 0 {
		return fmt.Errorf("-x must be greater than 0")
	}
	ws, err := unix.IoctlGetWinsize(int(os.Stdout.Fd()), unix.TIOCGWINSZ)
	if err != nil {
		return fmt.Errorf("terminal size: %s", err)
	}
	termCols := int(ws.Col)
	cellX, cellY := int(ws.Xpixel)/int(ws.Col), int(ws.Ypixel)/int(ws.Row)

	cols = min(cols, termCols)

	var files, dirs []string
	if len(args) == 0 {
		dirs = []string{"."}
	} else {
		for _, arg := range args {
			if isDir(arg) {
				dirs = append(dirs, arg)
			} else {
				files = append(files, arg)
			}
		}
	}
	w := bufio.NewWriter(os.Stdout)
	defer w.Flush()
	if err := thumbnailFiles(w, files, cols, termCols, cellX, cellY); err != nil {
		return err
	}
	if len(files) > 0 && len(dirs) > 0 {
		fmt.Fprintln(w)
	}
	for i, d := range dirs {
		if i > 0 {
			fmt.Fprintln(w)
		}
		if len(dirs) > 1 {
			fmt.Fprintf(w, "%s:\n", d)
		}
		if err := thumbnailDir(w, d, cols, termCols, cellX, cellY); err != nil {
			return err
		}
	}

	return nil
}

func main() {
	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "Usage: thumbnailer [OPTION]... [FILE]...\n")
		flag.PrintDefaults()
	}
	flag.Parse()

	if err := thumbnailer(flag.Args()); err != nil {
		fmt.Fprintf(os.Stderr, "Failed: %s\n", err)
		os.Exit(1)
	}
}