//go:build windows

package clipmon

import (
	"bytes"
	"encoding/binary"
	"image"
	"image/color"
	"image/png"
	"strings"
	"syscall"
	"time"
	"unsafe"
)

const (
	cfBitmap      = 2
	cfDIB         = 8
	cfUnicodeText = 13
)

var (
	user32                           = syscall.NewLazyDLL("user32.dll")
	kernel32                         = syscall.NewLazyDLL("kernel32.dll")
	procOpenClipboard                = user32.NewProc("OpenClipboard")
	procCloseClipboard               = user32.NewProc("CloseClipboard")
	procGetClipboardData             = user32.NewProc("GetClipboardData")
	procIsClipboardFormatAvailable   = user32.NewProc("IsClipboardFormatAvailable")
	procGetClipboardSequenceNumber   = user32.NewProc("GetClipboardSequenceNumber")
	procGlobalLock                   = kernel32.NewProc("GlobalLock")
	procGlobalUnlock                 = kernel32.NewProc("GlobalUnlock")
	procGlobalSize                   = kernel32.NewProc("GlobalSize")
)

type bitmapInfoHeader struct {
	Size          uint32
	Width         int32
	Height        int32
	Planes        uint16
	BitCount      uint16
	Compression   uint32
	SizeImage     uint32
	XPelsPerMeter int32
	YPelsPerMeter int32
	ClrUsed       uint32
	ClrImportant  uint32
}

func startPlatform(w *Writer, events chan Event, stop <-chan struct{}, done chan struct{}) error {
	go func() {
		defer close(done)
		pollClipboard(w, stop)
	}()
	return nil
}

func pollClipboard(w *Writer, stop <-chan struct{}) {
	lastSeq := sequenceNumber()
	ticker := time.NewTicker(300 * time.Millisecond)
	defer ticker.Stop()

	for {
		select {
		case <-stop:
			return
		case <-ticker.C:
			seq := sequenceNumber()
			if seq == lastSeq {
				continue
			}
			lastSeq = seq
			captureClipboard(w)
		}
	}
}

func sequenceNumber() uint32 {
	n, _, _ := procGetClipboardSequenceNumber.Call()
	return uint32(n)
}

func captureClipboard(w *Writer) {
	ok, _, _ := procOpenClipboard.Call(0)
	if ok == 0 {
		return
	}
	defer procCloseClipboard.Call()

	if text, ok := readClipboardText(); ok && strings.TrimSpace(text) != "" {
		emit(Event{Kind: "text", Text: TrimText(text)})
	}
	if pngData, ok := readClipboardImage(); ok {
		rel, err := w.SavePNG(pngData)
		if err != nil {
			return
		}
		emit(Event{Kind: "image", ImagePath: rel})
	}
}

func readClipboardText() (string, bool) {
	ok, _, _ := procIsClipboardFormatAvailable.Call(cfUnicodeText)
	if ok == 0 {
		return "", false
	}
	handle, _, _ := procGetClipboardData.Call(cfUnicodeText)
	if handle == 0 {
		return "", false
	}
	ptr, _, _ := procGlobalLock.Call(handle)
	if ptr == 0 {
		return "", false
	}
	defer procGlobalUnlock.Call(handle)
	size, _, _ := procGlobalSize.Call(handle)
	if size == 0 {
		return "", false
	}
	data := unsafe.Slice((*uint16)(unsafe.Pointer(ptr)), size/2)
	for i, unit := range data {
		if unit == 0 {
			return syscall.UTF16ToString(data[:i]), true
		}
	}
	return syscall.UTF16ToString(data), true
}

func readClipboardImage() ([]byte, bool) {
	if dib, ok := readClipboardDIB(); ok {
		return dib, true
	}
	return readClipboardBitmap()
}

func readClipboardDIB() ([]byte, bool) {
	ok, _, _ := procIsClipboardFormatAvailable.Call(cfDIB)
	if ok == 0 {
		return nil, false
	}
	handle, _, _ := procGetClipboardData.Call(cfDIB)
	if handle == 0 {
		return nil, false
	}
	ptr, _, _ := procGlobalLock.Call(handle)
	if ptr == 0 {
		return nil, false
	}
	defer procGlobalUnlock.Call(handle)
	size, _, _ := procGlobalSize.Call(handle)
	if size == 0 {
		return nil, false
	}
	raw := unsafe.Slice((*byte)(unsafe.Pointer(ptr)), size)
	return dibToPNG(append([]byte(nil), raw...))
}

func readClipboardBitmap() ([]byte, bool) {
	ok, _, _ := procIsClipboardFormatAvailable.Call(cfBitmap)
	if ok == 0 {
		return nil, false
	}
	// ponytail: CF_BITMAP needs a DC to read pixels; most apps also publish CF_DIB
	return nil, false
}

func dibToPNG(raw []byte) ([]byte, bool) {
	if len(raw) < int(unsafe.Sizeof(bitmapInfoHeader{})) {
		return nil, false
	}
	var header bitmapInfoHeader
	if err := binary.Read(bytes.NewReader(raw), binary.LittleEndian, &header); err != nil {
		return nil, false
	}
	if header.Size < uint32(unsafe.Sizeof(bitmapInfoHeader{})) || header.BitCount != 24 && header.BitCount != 32 {
		return nil, false
	}
	width := int(header.Width)
	height := int(header.Height)
	if width <= 0 || height <= 0 || width > 8192 || height > 8192 {
		return nil, false
	}
	topDown := false
	if height < 0 {
		topDown = true
		height = -height
	}

	headerSize := int(header.Size)
	colorTable := int(header.ClrUsed) * 4
	if header.BitCount <= 8 && header.ClrUsed == 0 {
		colorTable = (1 << header.BitCount) * 4
	}
	offset := headerSize + colorTable
	if offset > len(raw) {
		return nil, false
	}
	pixels := raw[offset:]
	stride := ((width*int(header.BitCount) + 31) / 32) * 4
	if len(pixels) < stride*height {
		return nil, false
	}

	img := image.NewRGBA(image.Rect(0, 0, width, height))
	bytesPerPixel := int(header.BitCount) / 8
	for y := 0; y < height; y++ {
		srcY := y
		if !topDown {
			srcY = height - 1 - y
		}
		row := pixels[srcY*stride:]
		for x := 0; x < width; x++ {
			i := x * bytesPerPixel
			if i+2 >= len(row) {
				continue
			}
			b, g, r := row[i], row[i+1], row[i+2]
			a := uint8(255)
			if bytesPerPixel == 4 && i+3 < len(row) {
				a = row[i+3]
			}
			img.SetRGBA(x, y, color.RGBA{R: r, G: g, B: b, A: a})
		}
	}

	var out bytes.Buffer
	if err := png.Encode(&out, img); err != nil {
		return nil, false
	}
	return out.Bytes(), true
}