// Copyright 2025-2026 肖其顿 (XIAO QI DUN)
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package ofdgo

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"image"
	"image/color"
	_ "image/gif"
	"math"

	_ "github.com/xiaoqidun/jbig2"
	_ "golang.org/x/image/bmp"
	"golang.org/x/image/draw"
	_ "golang.org/x/image/tiff"
)

// transparentEdgeImage 共享只读像素并按需计算透明边缘和采样边距
type transparentEdgeImage struct {
	source *image.NRGBA
	rect   image.Rectangle
}

// transparentEdgeImage64 按需补齐十六位像素边缘，保留原始只读图像
type transparentEdgeImage64 struct {
	source image.Image
	rect   image.Rectangle
}

// Bounds 返回含采样边距的图像边界
// 返回: image.Rectangle 图像边界
func (s *transparentEdgeImage) Bounds() image.Rectangle { return s.rect }

// ColorModel 返回非预乘颜色模型
// 返回: color.Model 颜色模型
func (s *transparentEdgeImage) ColorModel() color.Model { return color.NRGBAModel }

// NRGBAAt 读取原始像素或按邻域补齐透明边缘，边界外透明
// 入参: x 横向坐标, y 纵向坐标
// 返回: color.NRGBA 非预乘颜色
func (s *transparentEdgeImage) NRGBAAt(x, y int) color.NRGBA {
	if !image.Pt(x, y).In(s.rect) {
		return color.NRGBA{}
	}
	b := s.source.Bounds()
	sx, sy := b.Min.X+min(max(x-1, 0), b.Dx()-1), b.Min.Y+min(max(y-1, 0), b.Dy()-1)
	c := s.source.NRGBAAt(sx, sy)
	if c.A == 0 {
		if edge, ok := transparentEdgeColor(s.source, sx, sy); ok {
			c = edge
		}
	}
	if x == 0 || y == 0 || x == s.rect.Max.X-1 || y == s.rect.Max.Y-1 {
		c = transparentPaddingColor(c)
	}
	return c
}

// At 返回非预乘像素颜色
// 入参: x 横向坐标, y 纵向坐标
// 返回: color.Color 像素颜色
func (s *transparentEdgeImage) At(x, y int) color.Color { return s.NRGBAAt(x, y) }

// RGBA64At 返回预乘十六位像素，供采样器无装箱读取
// 入参: x 横向坐标, y 纵向坐标
// 返回: color.RGBA64 预乘颜色
func (s *transparentEdgeImage) RGBA64At(x, y int) color.RGBA64 {
	r, g, b, a := s.NRGBAAt(x, y).RGBA()
	return color.RGBA64{R: uint16(r), G: uint16(g), B: uint16(b), A: uint16(a)}
}

// Bounds 返回含采样边距的图像边界
// 返回: image.Rectangle 图像边界
func (s *transparentEdgeImage64) Bounds() image.Rectangle { return s.rect }

// ColorModel 返回十六位非预乘颜色模型
// 返回: color.Model 颜色模型
func (s *transparentEdgeImage64) ColorModel() color.Model { return color.NRGBA64Model }

// NRGBA64At 读取十六位原始颜色，透明邻域使用最小非零透明度保留边缘颜色
// 入参: x 横向坐标, y 纵向坐标
// 返回: color.NRGBA64 非预乘颜色
func (s *transparentEdgeImage64) NRGBA64At(x, y int) color.NRGBA64 {
	if !image.Pt(x, y).In(s.rect) {
		return color.NRGBA64{}
	}
	b := s.source.Bounds()
	sx, sy := b.Min.X+min(max(x-1, 0), b.Dx()-1), b.Min.Y+min(max(y-1, 0), b.Dy()-1)
	c := imageNRGBA64At(s.source, sx, sy)
	if c.A == 0 {
		var best color.NRGBA64
		for ny := max(sy-1, b.Min.Y); ny < min(sy+2, b.Max.Y); ny++ {
			for nx := max(sx-1, b.Min.X); nx < min(sx+2, b.Max.X); nx++ {
				v := imageNRGBA64At(s.source, nx, ny)
				if v.A > best.A {
					best = v
				}
			}
		}
		if best.A != 0 {
			best.A = 1
			c = best
		}
	}
	if x == 0 || y == 0 || x == s.rect.Max.X-1 || y == s.rect.Max.Y-1 {
		c.A = 1
	}
	return c
}

// At 返回非预乘十六位像素颜色
// 入参: x 横向坐标, y 纵向坐标
// 返回: color.Color 像素颜色
func (s *transparentEdgeImage64) At(x, y int) color.Color { return s.NRGBA64At(x, y) }

// RGBA64At 返回保留原采样精度的预乘颜色
// 入参: x 横向坐标, y 纵向坐标
// 返回: color.RGBA64 预乘颜色
func (s *transparentEdgeImage64) RGBA64At(x, y int) color.RGBA64 {
	r, g, b, a := s.NRGBA64At(x, y).RGBA()
	return color.RGBA64{R: uint16(r), G: uint16(g), B: uint16(b), A: uint16(a)}
}

// decodeImageData 解码图片数据
// 入参: data 图片数据
// 返回: image.Image 图片对象, string 图片格式, error 错误信息
func decodeImageData(data []byte) (image.Image, string, error) {
	if isJPEGData(data) || isPNGData(data) {
		img, err := newEncodedImage(data)
		if err != nil {
			return nil, "", err
		}
		return img, img.format, nil
	}
	img, format, err := image.Decode(bytes.NewReader(data))
	if err == nil {
		return img, normalizeSealType(format), nil
	}
	if img, err := decodeBMPImage(data); err == nil {
		return img, "bmp", nil
	}
	return nil, "", err
}

// isJPEGData 判断是否为JPEG图片数据
// 入参: data 图片数据
// 返回: bool 是否为JPEG图片数据
func isJPEGData(data []byte) bool {
	return len(data) >= 2 && data[0] == 0xFF && data[1] == 0xD8
}

// isPNGData 判断是否为PNG图片数据
// 入参: data 图片数据
// 返回: bool 是否为PNG图片数据
func isPNGData(data []byte) bool {
	return bytes.HasPrefix(data, []byte("\x89PNG\r\n\x1a\n"))
}

// decodeImageConfigData 解码图片尺寸
// 入参: data 图片数据
// 返回: image.Config 图片尺寸, string 图片格式, error 错误信息
func decodeImageConfigData(data []byte) (image.Config, string, error) {
	cfg, format, err := image.DecodeConfig(bytes.NewReader(data))
	if err == nil {
		return cfg, normalizeSealType(format), nil
	}
	if cfg, err := decodeBMPConfig(data); err == nil {
		return cfg, "bmp", nil
	}
	return image.Config{}, "", err
}

// decodeBMPConfig 解码BMP尺寸
// 入参: data 图片数据
// 返回: image.Config 图片尺寸, error 错误信息
func decodeBMPConfig(data []byte) (image.Config, error) {
	offset, width, height, bpp, compression, err := parseBMPHeader(data)
	if err != nil {
		return image.Config{}, err
	}
	if offset <= 0 || width <= 0 || height == 0 || compression != 0 {
		return image.Config{}, fmt.Errorf("unsupported bmp")
	}
	if bpp != 16 && bpp != 24 && bpp != 32 {
		return image.Config{}, fmt.Errorf("unsupported bmp")
	}
	if height < 0 {
		height = -height
	}
	return image.Config{ColorModel: color.NRGBAModel, Width: width, Height: height}, nil
}

// decodeBMPImage 解码BMP图片
// 入参: data 图片数据
// 返回: image.Image 图片对象, error 错误信息
func decodeBMPImage(data []byte) (image.Image, error) {
	offset, width, height, bpp, compression, err := parseBMPHeader(data)
	if err != nil {
		return nil, err
	}
	if compression != 0 {
		return nil, fmt.Errorf("unsupported bmp compression")
	}
	if bpp != 16 && bpp != 24 && bpp != 32 {
		return nil, fmt.Errorf("unsupported bmp depth")
	}
	topDown := height < 0
	if topDown {
		height = -height
	}
	if width <= 0 || height <= 0 {
		return nil, fmt.Errorf("invalid bmp size")
	}
	stride := ((int64(width)*int64(bpp) + 31) / 32) * 4
	if stride > int64(len(data)-offset)/int64(height) {
		return nil, fmt.Errorf("truncated bmp")
	}
	rowStride := int(stride)
	img := image.NewNRGBA(image.Rect(0, 0, width, height))
	for y := 0; y < height; y++ {
		srcY := y
		if !topDown {
			srcY = height - 1 - y
		}
		row := data[offset+srcY*rowStride:]
		for x := 0; x < width; x++ {
			switch bpp {
			case 16:
				v := binary.LittleEndian.Uint16(row[x*2:])
				img.SetNRGBA(x, y, color.NRGBA{
					R: uint8(((v >> 10) & 0x1F) * 255 / 31),
					G: uint8(((v >> 5) & 0x1F) * 255 / 31),
					B: uint8((v & 0x1F) * 255 / 31),
					A: 255,
				})
			case 24:
				p := x * 3
				img.SetNRGBA(x, y, color.NRGBA{R: row[p+2], G: row[p+1], B: row[p], A: 255})
			case 32:
				p := x * 4
				img.SetNRGBA(x, y, color.NRGBA{R: row[p+2], G: row[p+1], B: row[p], A: 255})
			}
		}
	}
	return img, nil
}

// parseBMPHeader 解析BMP文件头
// 入参: data 图片数据
// 返回: int 像素偏移, int 宽度, int 高度, uint16 位数, uint32 压缩方式, error 错误信息
func parseBMPHeader(data []byte) (int, int, int, uint16, uint32, error) {
	if len(data) < 54 || string(data[:2]) != "BM" {
		return 0, 0, 0, 0, 0, fmt.Errorf("not bmp")
	}
	offset := int(binary.LittleEndian.Uint32(data[10:14]))
	dibSize := binary.LittleEndian.Uint32(data[14:18])
	if dibSize < 40 {
		return 0, 0, 0, 0, 0, fmt.Errorf("unsupported bmp")
	}
	if uint64(dibSize)+14 > uint64(len(data)) || offset < 0 || uint64(offset) < uint64(dibSize)+14 || offset > len(data) {
		return 0, 0, 0, 0, 0, fmt.Errorf("invalid bmp pixel offset")
	}
	width := int(int32(binary.LittleEndian.Uint32(data[18:22])))
	height := int(int32(binary.LittleEndian.Uint32(data[22:26])))
	planes := binary.LittleEndian.Uint16(data[26:28])
	bpp := binary.LittleEndian.Uint16(data[28:30])
	compression := binary.LittleEndian.Uint32(data[30:34])
	if planes != 1 || width <= 0 || height == 0 || int64(height) == -int64(^uint(0)>>1)-1 {
		return 0, 0, 0, 0, 0, fmt.Errorf("invalid bmp")
	}
	return offset, width, height, bpp, compression, nil
}

// imageWithMask 应用图片蒙版
// 入参: img 图片对象, mask 蒙版图片
// 返回: image.Image 蒙版处理后的图片对象
func imageWithMask(img, mask image.Image) image.Image {
	if img == nil || mask == nil {
		return img
	}
	bounds := img.Bounds()
	if bounds.Empty() || mask.Bounds().Empty() {
		return img
	}
	source := imagePixelSource(img)
	maskSource := imagePixelSource(mask)
	maskBounds := maskSource.Bounds()
	var opacity image.Image = maskSource
	if bounds.Size() != maskBounds.Size() {
		resized := image.NewGray(bounds)
		draw.CatmullRom.Scale(resized, bounds, maskSource, maskBounds, draw.Src, nil)
		opacity = resized
		maskBounds = bounds
	}
	out := image.NewNRGBA(bounds)
	if src, ok := source.(*image.NRGBA); ok {
		for y := 0; y < bounds.Dy(); y++ {
			offset := src.PixOffset(bounds.Min.X, bounds.Min.Y+y)
			row := out.Pix[y*out.Stride : (y+1)*out.Stride]
			copy(row, src.Pix[offset:offset+len(row)])
			for x := 3; x < len(row); x += 4 {
				a := imageGrayAt(opacity, maskBounds.Min.X+x/4, maskBounds.Min.Y+y).Y
				row[x] = uint8(int(row[x]) * int(a) / 255)
			}
		}
		return out
	}
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			mx := maskBounds.Min.X + x - bounds.Min.X
			my := maskBounds.Min.Y + y - bounds.Min.Y
			a := imageGrayAt(opacity, mx, my).Y
			c := imageNRGBAAt(source, x, y)
			c.A = uint8(int(c.A) * int(a) / 255)
			out.SetNRGBA(x, y, c)
		}
	}
	return out
}

// imageWithAlpha 合并图片透明度
// 入参: img 图片对象, alpha 对象透明度
// 返回: image.Image 合并后的图片对象
func imageWithAlpha(img image.Image, alpha *int) image.Image {
	if img == nil || alpha == nil {
		return img
	}
	a := clampColor(*alpha)
	if a == 255 {
		return img
	}
	bounds := img.Bounds()
	out := image.NewNRGBA(bounds)
	source := imagePixelSource(img)
	if src, ok := source.(*image.NRGBA); ok {
		for y := 0; y < bounds.Dy(); y++ {
			offset := src.PixOffset(bounds.Min.X, bounds.Min.Y+y)
			row := out.Pix[y*out.Stride : (y+1)*out.Stride]
			copy(row, src.Pix[offset:offset+len(row)])
			for x := 3; x < len(row); x += 4 {
				row[x] = uint8(int(row[x]) * a / 255)
			}
		}
		return out
	}
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			c := imageNRGBAAt(source, x, y)
			c.A = uint8(int(c.A) * a / 255)
			out.SetNRGBA(x, y, c)
		}
	}
	return out
}

// imagePixelSource 获取图片像素源
// 入参: img 图片对象
// 返回: image.Image 图片像素源
func imagePixelSource(img image.Image) image.Image {
	if decoded, err := imagePixelData(img); err == nil {
		return decoded
	}
	return img
}

// imagePixelData 获取像素并保留惰性解码错误，供绘制和像素处理入口校验
// 入参: img 图片对象
// 返回: image.Image 解码像素, error 解码错误
func imagePixelData(img image.Image) (image.Image, error) {
	if src, ok := img.(interface{ Image() (image.Image, error) }); ok {
		return src.Image()
	}
	return img, nil
}

// imageGrayAt 获取图片灰度像素
// 入参: img 图片对象, x X坐标, y Y坐标
// 返回: color.Gray 灰度像素
func imageGrayAt(img image.Image, x, y int) color.Gray {
	if src, ok := img.(*image.Gray); ok {
		return src.GrayAt(x, y)
	}
	if src, ok := img.(*image.Paletted); ok {
		return color.GrayModel.Convert(src.At(x, y)).(color.Gray)
	}
	if src, ok := img.(image.RGBA64Image); ok {
		r, g, b, _ := src.RGBA64At(x, y).RGBA()
		return color.Gray{Y: uint8((19595*r + 38470*g + 7471*b + 1<<15) >> 24)}
	}
	return color.GrayModel.Convert(img.At(x, y)).(color.Gray)
}

// imageNRGBAAt 获取图片NRGBA像素
// 入参: img 图片对象, x X坐标, y Y坐标
// 返回: color.NRGBA NRGBA像素
func imageNRGBAAt(img image.Image, x, y int) color.NRGBA {
	if src, ok := img.(*image.NRGBA); ok {
		return src.NRGBAAt(x, y)
	}
	if src, ok := img.(*image.YCbCr); ok {
		r, g, b, _ := src.YCbCrAt(x, y).RGBA()
		return color.NRGBA{R: uint8(r >> 8), G: uint8(g >> 8), B: uint8(b >> 8), A: 255}
	}
	if src, ok := img.(*image.RGBA); ok {
		c := src.RGBA64At(x, y)
		if c.A == 0 {
			return color.NRGBA{}
		}
		r, g, b, a := uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A)
		if a != 0xffff {
			r = r * 0xffff / a
			g = g * 0xffff / a
			b = b * 0xffff / a
		}
		return color.NRGBA{R: uint8(r >> 8), G: uint8(g >> 8), B: uint8(b >> 8), A: uint8(a >> 8)}
	}
	return color.NRGBAModel.Convert(img.At(x, y)).(color.NRGBA)
}

// imageNRGBA64At 读取十六位非预乘像素，原生图像避免颜色装箱
// 入参: img 图片对象, x X坐标, y Y坐标
// 返回: color.NRGBA64 NRGBA64像素
func imageNRGBA64At(img image.Image, x, y int) color.NRGBA64 {
	switch src := img.(type) {
	case *image.NRGBA64:
		return src.NRGBA64At(x, y)
	case *image.Gray16:
		c := src.Gray16At(x, y)
		return color.NRGBA64{R: c.Y, G: c.Y, B: c.Y, A: 0xffff}
	case *image.Alpha16:
		c := src.Alpha16At(x, y)
		if c.A == 0 {
			return color.NRGBA64{}
		}
		return color.NRGBA64{R: 0xffff, G: 0xffff, B: 0xffff, A: c.A}
	case *image.RGBA, *image.RGBA64:
		c := src.(image.RGBA64Image).RGBA64At(x, y)
		if c.A == 0 {
			return color.NRGBA64{}
		}
		r, g, b, a := uint32(c.R), uint32(c.G), uint32(c.B), uint32(c.A)
		if a != 0xffff {
			r = r * 0xffff / a
			g = g * 0xffff / a
			b = b * 0xffff / a
		}
		return color.NRGBA64{R: uint16(r), G: uint16(g), B: uint16(b), A: c.A}
	}
	return color.NRGBA64Model.Convert(img.At(x, y)).(color.NRGBA64)
}

// transparentEdgeColor 获取透明像素相邻的可见颜色
// 入参: img 图片对象, x X坐标, y Y坐标
// 返回: color.NRGBA 颜色, bool 是否存在
func transparentEdgeColor(img *image.NRGBA, x, y int) (color.NRGBA, bool) {
	bounds := img.Bounds()
	best, alpha := 0, uint8(0)
	left, right := max(x-1, bounds.Min.X), min(x+2, bounds.Max.X)
scan:
	for ny := max(y-1, bounds.Min.Y); ny < min(y+2, bounds.Max.Y); ny++ {
		offset := img.PixOffset(left, ny)
		for nx := left; nx < right; nx++ {
			if (nx != x || ny != y) && img.Pix[offset+3] > alpha {
				best, alpha = offset, img.Pix[offset+3]
				if alpha == 255 {
					break scan
				}
			}
			offset += 4
		}
	}
	if alpha == 0 {
		return color.NRGBA{}, false
	}
	return color.NRGBA{R: img.Pix[best], G: img.Pix[best+1], B: img.Pix[best+2], A: 1}, true
}

// transparentPaddingColor 获取透明补齐颜色
// 入参: c 边缘颜色
// 返回: color.NRGBA 补齐颜色
func transparentPaddingColor(c color.NRGBA) color.NRGBA {
	c.A = 1
	return c
}

// clipStampImage 裁剪印章图像
// 入参: img 印章图像, box 印章区域, clip 裁剪区域
// 返回: image.Image 裁剪后的印章图像
func clipStampImage(img image.Image, box, clip Box) image.Image {
	bounds := img.Bounds()
	x0 := int(math.Floor(clip.X / box.W * float64(bounds.Dx())))
	y0 := int(math.Floor(clip.Y / box.H * float64(bounds.Dy())))
	x1 := int(math.Ceil((clip.X + clip.W) / box.W * float64(bounds.Dx())))
	y1 := int(math.Ceil((clip.Y + clip.H) / box.H * float64(bounds.Dy())))
	out := image.NewNRGBA(image.Rect(0, 0, x1-x0, y1-y0))
	draw.Draw(out, out.Bounds(), img, image.Pt(bounds.Min.X+x0, bounds.Min.Y+y0), draw.Src)
	return out
}

// stampImageWithTransparentWhite 处理印章图片白色底色
// 入参: img 印章图片对象
// 返回: image.Image 处理后的印章图片对象
func stampImageWithTransparentWhite(img image.Image) image.Image {
	if opaque, ok := img.(interface{ Opaque() bool }); ok && !opaque.Opaque() {
		return img
	}
	bounds := img.Bounds()
	out := image.NewNRGBA(bounds)
	hasAlpha := false
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			c := color.NRGBAModel.Convert(img.At(x, y)).(color.NRGBA)
			if c.A < 255 {
				hasAlpha = true
			}
			out.SetNRGBA(x, y, c)
		}
	}
	if hasAlpha {
		return img
	}
	for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			c := out.NRGBAAt(x, y)
			if c.R >= 250 && c.G >= 250 && c.B >= 250 {
				c.A = 0
				out.SetNRGBA(x, y, c)
			}
		}
	}
	return out
}

// imageWithTransparentEdge 补齐透明图片边缘颜色
// 入参: img 图片对象
// 返回: image.Image 补齐后的图片对象, int 补齐像素数
func imageWithTransparentEdge(img image.Image) (image.Image, int) {
	if img == nil {
		return img, 0
	}
	bounds := img.Bounds()
	w, h := bounds.Dx(), bounds.Dy()
	if w == 0 || h == 0 {
		return img, 0
	}
	if src, ok := img.(*EncodedImage); ok && src.MIME() == "image/jpeg" {
		return img, 0
	}
	source := imagePixelSource(img)
	if opaque, ok := source.(interface{ Opaque() bool }); ok && opaque.Opaque() {
		return img, 0
	}
	if model := source.ColorModel(); model == color.NRGBA64Model || model == color.RGBA64Model || model == color.Alpha16Model || model == color.Gray16Model {
		return imageWithTransparentEdge64(img, source)
	}
	hasZero, hasVisible := false, false
	src, ok := source.(*image.NRGBA)
	if ok {
		srcBounds := src.Bounds()
		hasZero = src.Pix[3] == 0
		hasVisible = !hasZero
	scan:
		for y := srcBounds.Min.Y; y < srcBounds.Max.Y; y++ {
			offset := src.PixOffset(srcBounds.Min.X, y) + 3
			for x := 0; x < w; x++ {
				if (src.Pix[offset] == 0) != hasZero {
					hasZero, hasVisible = true, true
					break scan
				}
				offset += 4
			}
		}
	} else {
		src = image.NewNRGBA(image.Rect(0, 0, w, h))
		for y := 0; y < h; y++ {
			for x := 0; x < w; x++ {
				c := imageNRGBAAt(source, bounds.Min.X+x, bounds.Min.Y+y)
				src.SetNRGBA(x, y, c)
				if c.A == 0 {
					hasZero = true
				} else {
					hasVisible = true
				}
			}
		}
	}
	if !hasZero || !hasVisible {
		return img, 0
	}
	return &transparentEdgeImage{source: src, rect: image.Rect(0, 0, w+2, h+2)}, 1
}

// imageWithTransparentEdge64 保留十六位颜色和透明度，不经八位图像中转
// 入参: original 原始图像, source 已解码的像素源
// 返回: image.Image 边缘处理结果, int 补齐像素数
func imageWithTransparentEdge64(original, source image.Image) (image.Image, int) {
	bounds := source.Bounds()
	hasZero, hasVisible := false, false
	for y := bounds.Min.Y; y < bounds.Max.Y && !(hasZero && hasVisible); y++ {
		for x := bounds.Min.X; x < bounds.Max.X; x++ {
			_, _, _, a := source.At(x, y).RGBA()
			if a == 0 {
				hasZero = true
			} else {
				hasVisible = true
			}
			if hasZero && hasVisible {
				break
			}
		}
	}
	if !hasZero || !hasVisible {
		return original, 0
	}
	return &transparentEdgeImage64{source: source, rect: image.Rect(0, 0, bounds.Dx()+2, bounds.Dy()+2)}, 1
}