// Copyright 2014 Hajime Hoshi
//
// 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 graphics

import (
	"errors"
	"fmt"
	"github.com/hajimehoshi/ebiten/internal/graphics/opengl"
)

func glMatrix(m *[4][4]float64) []float32 {
	return []float32{
		float32(m[0][0]), float32(m[1][0]), float32(m[2][0]), float32(m[3][0]),
		float32(m[0][1]), float32(m[1][1]), float32(m[2][1]), float32(m[3][1]),
		float32(m[0][2]), float32(m[1][2]), float32(m[2][2]), float32(m[3][2]),
		float32(m[0][3]), float32(m[1][3]), float32(m[2][3]), float32(m[3][3]),
	}
}

type Matrix interface {
	Element(i, j int) float64
}

var vertices = make([]int16, 16*quadsMaxNum)

var shadersInitialized = false

func drawTexture(c *opengl.Context, texture opengl.Texture, projectionMatrix *[4][4]float64, quads TextureQuads, geo Matrix, color Matrix) error {
	// NOTE: WebGL doesn't seem to have Check gl.MAX_ELEMENTS_VERTICES or gl.MAX_ELEMENTS_INDICES so far.
	// Let's use them to compare to len(quads) in the future.

	if !shadersInitialized {
		if err := initialize(c); err != nil {
			return err
		}
		shadersInitialized = true
	}

	if quads.Len() == 0 {
		return nil
	}
	if quadsMaxNum < quads.Len() {
		return errors.New(fmt.Sprintf("len(quads) must be equal to or less than %d", quadsMaxNum))
	}

	p := programContext{
		program:          programTexture,
		context:          c,
		projectionMatrix: glMatrix(projectionMatrix),
		texture:          texture,
		geoM:             geo,
		colorM:           color,
	}
	p.begin()
	defer p.end()

	for i := 0; i < quads.Len(); i++ {
		x0, y0, x1, y1 := quads.Vertex(i)
		u0, v0, u1, v1 := quads.Texture(i)
		vertices[16*i] = int16(x0)
		vertices[16*i+1] = int16(y0)
		vertices[16*i+2] = int16(u0)
		vertices[16*i+3] = int16(v0)
		vertices[16*i+4] = int16(x1)
		vertices[16*i+5] = int16(y0)
		vertices[16*i+6] = int16(u1)
		vertices[16*i+7] = int16(v0)
		vertices[16*i+8] = int16(x0)
		vertices[16*i+9] = int16(y1)
		vertices[16*i+10] = int16(u0)
		vertices[16*i+11] = int16(v1)
		vertices[16*i+12] = int16(x1)
		vertices[16*i+13] = int16(y1)
		vertices[16*i+14] = int16(u1)
		vertices[16*i+15] = int16(v1)
	}
	if len(vertices) == 0 {
		return nil
	}
	c.BufferSubData(c.ArrayBuffer, vertices[:16*quads.Len()])
	c.DrawElements(c.Triangles, 6*quads.Len())
	return nil
}