package pixel

import (
	"fmt"
	"image/color"
)

// TrianglesData specifies a list of Triangles vertices with three common properties: Position,
// Color and Texture.
type TrianglesData []struct {
	Position Vec
	Color    NRGBA
	Texture  Vec
}

// Len returns the number of vertices in TrianglesData.
func (td *TrianglesData) Len() int {
	return len(*td)
}

// Draw is unimplemented for TrianglesData and panics.
func (td *TrianglesData) Draw() {
	panic(fmt.Errorf("%T.Draw: invalid operation", td))
}

// Update copies vertex properties from the supplied Triangles into this TrianglesData.
//
// TrianglesPosition, TrianglesColor and TrianglesTexture are supported.
func (td *TrianglesData) Update(t Triangles) {
	if t.Len() > td.Len() {
		*td = append(*td, make(TrianglesData, t.Len()-td.Len())...)
	}
	if t.Len() < td.Len() {
		*td = (*td)[:t.Len()]
	}

	// fast path optimization
	if t, ok := t.(*TrianglesData); ok {
		copy(*td, *t)
		return
	}

	// slow path manual copy
	if t, ok := t.(TrianglesPosition); ok {
		for i := range *td {
			(*td)[i].Position = t.Position(i)
		}
	}
	if t, ok := t.(TrianglesColor); ok {
		for i := range *td {
			(*td)[i].Color = NRGBAModel.Convert(t.Color(i)).(NRGBA)
		}
	}
	if t, ok := t.(TrianglesTexture); ok {
		for i := range *td {
			(*td)[i].Texture = t.Texture(i)
		}
	}
}

// Append adds supplied Triangles to the end of the TrianglesData.
func (td *TrianglesData) Append(t Triangles) {
	newTd := make(TrianglesData, t.Len())
	newTd.Update(t)
	*td = append(*td, newTd...)
}

// Copy returns an exact independent copy of this TrianglesData.
func (td *TrianglesData) Copy() Triangles {
	copyTd := make(TrianglesData, td.Len())
	copyTd.Update(td)
	return &copyTd
}

// Position returns the position property of i-th vertex.
func (td *TrianglesData) Position(i int) Vec {
	return (*td)[i].Position
}

// Color returns the color property of i-th vertex.
func (td *TrianglesData) Color(i int) NRGBA {
	return (*td)[i].Color
}

// Texture returns the texture property of i-th vertex.
func (td *TrianglesData) Texture(i int) Vec {
	return (*td)[i].Texture
}

// TrianglesDrawer is a helper type that wraps Triangles and turns them into a Drawer.
//
// It does so by creating a separate Triangles instance for each Target. The instances are
// correctly updated alongside the wrapped Triangles.
type TrianglesDrawer struct {
	Triangles

	tris  map[Target]Triangles
	dirty bool
}

func (td *TrianglesDrawer) flush() {
	if !td.dirty {
		return
	}
	td.dirty = false

	for _, t := range td.tris {
		t.Update(td.Triangles)
	}
}

// Draw draws the wrapped Triangles onto the provided Target.
func (td *TrianglesDrawer) Draw(target Target) {
	if td.tris == nil {
		td.tris = make(map[Target]Triangles)
	}

	td.flush()

	tri := td.tris[target]
	if tri == nil {
		tri = target.MakeTriangles(td.Triangles)
		td.tris[target] = tri
	}
	tri.Draw()
}

// Update updates the wrapped Triangles with the supplied Triangles.
//
// Call only this method to update the wrapped Triangles, otherwise the TrianglesDrawer will not
// work correctly.
func (td *TrianglesDrawer) Update(t Triangles) {
	td.dirty = true
	td.Triangles.Update(t)
}

// Append appends the supplied Triangles to the wrapped Triangles.
//
// Call only this method to append to the wrapped Triangles, otherwise the TrianglesDrawer will not
// work correctly.
func (td *TrianglesDrawer) Append(t Triangles) {
	td.dirty = true
	td.Triangles.Append(t)
}

// Sprite is a picture, positioned somewhere, with an optional mask color.
type Sprite struct {
	td        TrianglesDrawer
	pic       *Picture
	transform []Transform
	maskColor color.Color
}

// NewSprite creates a Sprite with the supplied Picture. The dimensions of the returned Sprite match
// the dimensions of the Picture.
func NewSprite(pic *Picture) *Sprite {
	s := &Sprite{
		td: TrianglesDrawer{Triangles: &TrianglesData{}},
	}
	s.SetPicture(pic)
	return s
}

// SetPicture changes the Picture of the Sprite and resizes it accordingly.
func (s *Sprite) SetPicture(pic *Picture) {
	w, h := pic.Bounds().Size.XY()
	s.td.Update(&TrianglesData{
		{Position: V(0, 0), Color: NRGBA{1, 1, 1, 1}, Texture: V(0, 0)},
		{Position: V(w, 0), Color: NRGBA{1, 1, 1, 1}, Texture: V(1, 0)},
		{Position: V(w, h), Color: NRGBA{1, 1, 1, 1}, Texture: V(1, 1)},
		{Position: V(0, 0), Color: NRGBA{1, 1, 1, 1}, Texture: V(0, 0)},
		{Position: V(w, h), Color: NRGBA{1, 1, 1, 1}, Texture: V(1, 1)},
		{Position: V(0, h), Color: NRGBA{1, 1, 1, 1}, Texture: V(0, 1)},
	})
	s.pic = pic
}

// Picture returns the current Picture of the Sprite.
func (s *Sprite) Picture() *Picture {
	return s.pic
}

// SetTransform sets a chain of Transforms that will be applied to this Sprite in reverse order.
func (s *Sprite) SetTransform(t ...Transform) {
	s.transform = t
}

// Transform returns the current chain of Transforms that this Sprite is transformed by.
func (s *Sprite) Transform() []Transform {
	return s.transform
}

// SetMaskColor changes the mask color of the Sprite.
func (s *Sprite) SetMaskColor(c color.Color) {
	s.maskColor = c
}

// MaskColor returns the current mask color of the Sprite.
func (s *Sprite) MaskColor() color.Color {
	return s.maskColor
}

// Draw draws the Sprite onto the provided Target.
func (s *Sprite) Draw(target Target) {
	target.SetPicture(s.pic)
	target.SetTransform(s.transform...)
	target.SetMaskColor(s.maskColor)
	s.td.Draw(target)
}