package resize

import "image"

func floatToUint8(x float32) uint8 {
	// Nearest-neighbor values are always
	// positive no need to check lower-bound.
	if x > 0xfe {
		return 0xff
	}
	return uint8(x)
}

func floatToUint16(x float32) uint16 {
	if x > 0xfffe {
		return 0xffff
	}
	return uint16(x)
}

func nearestGeneric(in image.Image, out *image.RGBA64, scale float64, coeffs []bool, offset []int, filterLength int) {
	oldBounds := in.Bounds()
	newBounds := out.Bounds()

	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
			var rgba [4]float32
			var sum float32
			start := offset[y]
			ci := (y - newBounds.Min.Y) * filterLength
			for i := 0; i < filterLength; i++ {
				if coeffs[ci+i] {
					xi := start + i
					switch {
					case uint(xi) < uint(oldBounds.Max.X):
						break
					case xi >= oldBounds.Max.X:
						xi = oldBounds.Min.X
					default:
						xi = oldBounds.Max.X - 1
					}
					r, g, b, a := in.At(xi, x).RGBA()
					rgba[0] += float32(r)
					rgba[1] += float32(g)
					rgba[2] += float32(b)
					rgba[3] += float32(a)
					sum++
				}
			}

			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
			value := floatToUint16(rgba[0] / sum)
			out.Pix[offset+0] = uint8(value >> 8)
			out.Pix[offset+1] = uint8(value)
			value = floatToUint16(rgba[1] / sum)
			out.Pix[offset+2] = uint8(value >> 8)
			out.Pix[offset+3] = uint8(value)
			value = floatToUint16(rgba[2] / sum)
			out.Pix[offset+4] = uint8(value >> 8)
			out.Pix[offset+5] = uint8(value)
			value = floatToUint16(rgba[3] / sum)
			out.Pix[offset+6] = uint8(value >> 8)
			out.Pix[offset+7] = uint8(value)
		}
	}
}

func nearestRGBA(in *image.RGBA, out *image.RGBA, scale float64, coeffs []bool, offset []int, filterLength int) {
	oldBounds := in.Bounds()
	newBounds := out.Bounds()
	minX := oldBounds.Min.X * 4
	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 4

	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
			var rgba [4]float32
			var sum float32
			start := offset[y]
			ci := (y - newBounds.Min.Y) * filterLength
			for i := 0; i < filterLength; i++ {
				if coeffs[ci+i] {
					xi := start + i
					switch {
					case uint(xi) < uint(oldBounds.Max.X):
						xi *= 4
					case xi >= oldBounds.Max.X:
						xi = maxX
					default:
						xi = minX
					}
					rgba[0] += float32(row[xi+0])
					rgba[1] += float32(row[xi+1])
					rgba[2] += float32(row[xi+2])
					rgba[3] += float32(row[xi+3])
					sum++
				}
			}

			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*4
			out.Pix[xo+0] = floatToUint8(rgba[0] / sum)
			out.Pix[xo+1] = floatToUint8(rgba[1] / sum)
			out.Pix[xo+2] = floatToUint8(rgba[2] / sum)
			out.Pix[xo+3] = floatToUint8(rgba[3] / sum)
		}
	}
}

func nearestRGBA64(in *image.RGBA64, out *image.RGBA64, scale float64, coeffs []bool, offset []int, filterLength int) {
	oldBounds := in.Bounds()
	newBounds := out.Bounds()
	minX := oldBounds.Min.X * 8
	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 8

	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
			var rgba [4]float32
			var sum float32
			start := offset[y]
			ci := (y - newBounds.Min.Y) * filterLength
			for i := 0; i < filterLength; i++ {
				if coeffs[ci+i] {
					xi := start + i
					switch {
					case uint(xi) < uint(oldBounds.Max.X):
						xi *= 8
					case xi >= oldBounds.Max.X:
						xi = maxX
					default:
						xi = minX
					}
					rgba[0] += float32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
					rgba[1] += float32(uint16(row[xi+2])<<8 | uint16(row[xi+3]))
					rgba[2] += float32(uint16(row[xi+4])<<8 | uint16(row[xi+5]))
					rgba[3] += float32(uint16(row[xi+6])<<8 | uint16(row[xi+7]))
					sum++
				}
			}

			xo := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*8
			value := floatToUint16(rgba[0] / sum)
			out.Pix[xo+0] = uint8(value >> 8)
			out.Pix[xo+1] = uint8(value)
			value = floatToUint16(rgba[1] / sum)
			out.Pix[xo+2] = uint8(value >> 8)
			out.Pix[xo+3] = uint8(value)
			value = floatToUint16(rgba[2] / sum)
			out.Pix[xo+4] = uint8(value >> 8)
			out.Pix[xo+5] = uint8(value)
			value = floatToUint16(rgba[3] / sum)
			out.Pix[xo+6] = uint8(value >> 8)
			out.Pix[xo+7] = uint8(value)
		}
	}
}

func nearestGray(in *image.Gray, out *image.Gray, scale float64, coeffs []bool, offset []int, filterLength int) {
	oldBounds := in.Bounds()
	newBounds := out.Bounds()
	minX := oldBounds.Min.X
	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1)

	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
			var gray float32
			var sum float32
			start := offset[y]
			ci := (y - newBounds.Min.Y) * filterLength
			for i := 0; i < filterLength; i++ {
				if coeffs[ci+i] {
					xi := start + i
					switch {
					case uint(xi) < uint(oldBounds.Max.X):
						break
					case xi >= oldBounds.Max.X:
						xi = maxX
					default:
						xi = minX
					}
					gray += float32(row[xi])
					sum++
				}
			}

			offset := (y-newBounds.Min.Y)*out.Stride + (x - newBounds.Min.X)
			out.Pix[offset] = floatToUint8(gray / sum)
		}
	}
}

func nearestGray16(in *image.Gray16, out *image.Gray16, scale float64, coeffs []bool, offset []int, filterLength int) {
	oldBounds := in.Bounds()
	newBounds := out.Bounds()
	minX := oldBounds.Min.X * 2
	maxX := (oldBounds.Max.X - oldBounds.Min.X - 1) * 2

	for x := newBounds.Min.X; x < newBounds.Max.X; x++ {
		row := in.Pix[(x-oldBounds.Min.Y)*in.Stride:]
		for y := newBounds.Min.Y; y < newBounds.Max.Y; y++ {
			var gray float32
			var sum float32
			start := offset[y]
			ci := (y - newBounds.Min.Y) * filterLength
			for i := 0; i < filterLength; i++ {
				if coeffs[ci+i] {
					xi := start + i
					switch {
					case uint(xi) < uint(oldBounds.Max.X):
						xi *= 2
					case xi >= oldBounds.Max.X:
						xi = maxX
					default:
						xi = minX
					}
					gray += float32(uint16(row[xi+0])<<8 | uint16(row[xi+1]))
					sum++
				}
			}

			offset := (y-newBounds.Min.Y)*out.Stride + (x-newBounds.Min.X)*2
			value := floatToUint16(gray / sum)
			out.Pix[offset+0] = uint8(value >> 8)
			out.Pix[offset+1] = uint8(value)
		}
	}
}