package pixel

import (
	"fmt"
	"image/color"

	"github.com/go-gl/mathgl/mgl64"
)

// Batch is a Target that allows for efficient drawing of many objects with the same Picture (but
// different slices of the same Picture are allowed).
//
// To put an object into a Batch, just draw it onto it:
//   object.Draw(batch)
type Batch struct {
	cont Drawer

	mat Matrix
	col NRGBA
}

var _ BasicTarget = (*Batch)(nil)

// NewBatch creates an empty Batch with the specified Picture and container.
//
// The container is where objects get accumulated. Batch will support precisely those vertex
// properties, that the supplied container supports.
//
// Note, that if the container does not support TrianglesColor, color masking will not work.
func NewBatch(container Triangles, pic Picture) *Batch {
	return &Batch{
		cont: Drawer{Triangles: container, Picture: pic},
		mat:  IM,
		col:  NRGBA{1, 1, 1, 1},
	}
}

// Clear removes all objects from the Batch.
func (b *Batch) Clear() {
	b.cont.Triangles.SetLen(0)
	b.cont.Dirty()
}

// Draw draws all objects that are currently in the Batch onto another Target.
func (b *Batch) Draw(t Target) {
	b.cont.Draw(t)
}

// SetMatrix sets a Matrix that every point will be projected by.
func (b *Batch) SetMatrix(m Matrix) {
	b.mat = m
}

// SetColorMask sets a mask color used in the following draws onto the Batch.
func (b *Batch) SetColorMask(c color.Color) {
	if c == nil {
		b.col = NRGBA{1, 1, 1, 1}
		return
	}
	b.col = NRGBAModel.Convert(c).(NRGBA)
}

// MakeTriangles returns a specialized copy of the provided Triangles that draws onto this Batch.
func (b *Batch) MakeTriangles(t Triangles) TargetTriangles {
	bt := &batchTriangles{
		Triangles: t.Copy(),
		orig:      MakeTrianglesData(t.Len()),
		trans:     MakeTrianglesData(t.Len()),
		dst:       b,
	}
	bt.orig.Update(t)
	bt.trans.Update(bt.orig)
	return bt
}

// MakePicture returns a specialized copy of the provided Picture that draws onto this Batch.
func (b *Batch) MakePicture(p Picture) TargetPicture {
	if p.Original() != b.cont.Picture.Original() {
		panic(fmt.Errorf("(%T).MakePicture: Picture is not a slice of Batch's Picture", b))
	}
	bp := &batchPicture{
		Picture: p,
		dst:     b,
	}
	bp.orig = bp
	return bp
}

type batchTriangles struct {
	Triangles
	orig, trans *TrianglesData

	dst *Batch
}

func (bt *batchTriangles) draw(bp *batchPicture) {
	for i := range *bt.trans {
		transPos := mgl64.Mat3(bt.dst.mat).Mul3x1(mgl64.Vec3{
			(*bt.orig)[i].Position.X(),
			(*bt.orig)[i].Position.Y(),
			1,
		})
		(*bt.trans)[i].Position = V(float64(transPos.X()), float64(transPos.Y()))
		(*bt.trans)[i].Color = (*bt.orig)[i].Color.Mul(bt.dst.col)
		(*bt.trans)[i].Picture = (*bt.orig)[i].Picture
		(*bt.trans)[i].Intensity = (*bt.orig)[i].Intensity
	}

	bt.Triangles.Update(bt.trans)

	cont := bt.dst.cont.Triangles
	cont.SetLen(cont.Len() + bt.Triangles.Len())
	cont.Slice(cont.Len()-bt.Triangles.Len(), cont.Len()).Update(bt.Triangles)
	bt.dst.cont.Dirty()
}

func (bt *batchTriangles) Draw() {
	bt.draw(nil)
}

type batchPicture struct {
	Picture

	orig *batchPicture
	dst  *Batch
}

func (bp *batchPicture) Slice(r Rect) Picture {
	return &batchPicture{
		Picture: bp.Picture.Slice(r),
		orig:    bp.orig,
		dst:     bp.dst,
	}
}

func (bp *batchPicture) Original() Picture {
	return bp.orig
}

func (bp *batchPicture) Draw(t TargetTriangles) {
	bt := t.(*batchTriangles)
	if bp.dst != bt.dst {
		panic(fmt.Errorf("(%T).Draw: TargetTriangles generated by different Batch", bp))
	}
	bt.draw(bp)
}