package canvas

import (
	"image/color"
	"math"
	"sort"
)

// Gradient 渐变接口
type Gradient interface {
	At(x, y int) color.Color
}

// GradientStop 渐变色标
type GradientStop struct {
	Offset float64
	Color  color.Color
}

// LinearGradient 线性渐变
type LinearGradient struct {
	X0, Y0, X1, Y1 float64
	Stops          []GradientStop
}

// NewLinearGradient 创建线性渐变
func NewLinearGradient(x0, y0, x1, y1 float64) *LinearGradient {
	return &LinearGradient{
		X0: x0, Y0: y0, X1: x1, Y1: y1,
		Stops: []GradientStop{},
	}
}

// AddColorStop 添加色标
func (g *LinearGradient) AddColorStop(offset float64, color color.Color) {
	g.Stops = append(g.Stops, GradientStop{Offset: offset, Color: color})
	sort.Slice(g.Stops, func(i, j int) bool {
		return g.Stops[i].Offset < g.Stops[j].Offset
	})
}

// At 获取指定位置的颜色
func (g *LinearGradient) At(x, y int) color.Color {
	if len(g.Stops) == 0 {
		return color.Transparent
	}

	// 计算投影位置 (0-1)
	dx := g.X1 - g.X0
	dy := g.Y1 - g.Y0
	lenSq := dx*dx + dy*dy
	t := 0.0

	if lenSq > 0 {
		t = ((float64(x)-g.X0)*dx + (float64(y)-g.Y0)*dy) / lenSq
		if t < 0 {
			t = 0
		} else if t > 1 {
			t = 1
		}
	}

	// 查找色标区间
	var start, end GradientStop
	for i, stop := range g.Stops {
		if stop.Offset >= t {
			if i == 0 {
				return stop.Color
			}
			start = g.Stops[i-1]
			end = stop
			break
		}
	}
	if start.Color == nil {
		return g.Stops[len(g.Stops)-1].Color
	}

	// 区间插值
	localT := (t - start.Offset) / (end.Offset - start.Offset)
	return interpolateColor(start.Color, end.Color, localT)
}

// RadialGradient 径向渐变
type RadialGradient struct {
	X0, Y0, R0, X1, Y1, R1 float64
	Stops                  []GradientStop
}

// NewRadialGradient 创建径向渐变
func NewRadialGradient(x0, y0, r0, x1, y1, r1 float64) *RadialGradient {
	return &RadialGradient{
		X0: x0, Y0: y0, R0: r0, X1: x1, Y1: y1, R1: r1,
		Stops: []GradientStop{},
	}
}

// AddColorStop 添加色标
func (g *RadialGradient) AddColorStop(offset float64, color color.Color) {
	g.Stops = append(g.Stops, GradientStop{Offset: offset, Color: color})
	sort.Slice(g.Stops, func(i, j int) bool {
		return g.Stops[i].Offset < g.Stops[j].Offset
	})
}

// At 获取指定位置的颜色
func (g *RadialGradient) At(x, y int) color.Color {
	if len(g.Stops) == 0 {
		return color.Transparent
	}

	// 计算到焦点的距离
	dx1, dy1 := float64(x)-g.X1, float64(y)-g.Y1
	d1 := math.Sqrt(dx1*dx1 + dy1*dy1)

	// 计算梯度值 (0-1)
	t := (d1 - g.R0) / (g.R1 - g.R0)
	if t < 0 {
		t = 0
	} else if t > 1 {
		t = 1
	}

	// 查找色标区间
	var start, end GradientStop
	for i, stop := range g.Stops {
		if stop.Offset >= t {
			if i == 0 {
				return stop.Color
			}
			start = g.Stops[i-1]
			end = stop
			break
		}
	}
	if start.Color == nil {
		return g.Stops[len(g.Stops)-1].Color
	}

	// 区间插值
	localT := (t - start.Offset) / (end.Offset - start.Offset)
	return interpolateColor(start.Color, end.Color, localT)
}