package levels

import (
	"github.com/inkyblackness/hacked/editor/render"
	"github.com/inkyblackness/hacked/ss1/content/archive/level"
	"github.com/inkyblackness/hacked/ui/opengl"
)

var gridVertexShaderSource = `
#version 150
precision mediump float;

in vec3 vertexPosition;

uniform mat4 viewMatrix;
uniform mat4 projectionMatrix;

out vec4 gridColor;
out vec3 originalPosition;

void main(void) {
   gl_Position = projectionMatrix * viewMatrix * vec4(vertexPosition, 1.0);

   gridColor = vec4(0.0, 0.1, 0.0, 0.6);
   originalPosition = vertexPosition;
}
`

var gridFragmentShaderSource = `
#version 150
precision mediump float;

uniform vec4 gridSize;

in vec4 gridColor;
in vec3 originalPosition;

out vec4 fragColor;

float modulo(float x, float y) {
   return x - y * floor(x/y);
}

float nearGrid(float stepSize, float value) {
   float remainder = modulo(value - (stepSize / 2.0), stepSize) * 2.0;

   if (remainder >= stepSize) {
      remainder = (stepSize * 2.0) - remainder;
   }

   return remainder / stepSize;
}

void main(void) {
   float alphaX = nearGrid(256.0, originalPosition.x);
   float alphaY = nearGrid(256.0, originalPosition.y);
   bool beyondX = (originalPosition.x / 256.0) >= gridSize.x || (originalPosition.x < 0.0);
   bool beyondY = (originalPosition.y / 256.0) >= gridSize.y || (originalPosition.y < 0.0);
   float alpha = 0.0;

   if (!beyondX && !beyondY) {
      alpha = max(alphaX, alphaY);
   } else if (beyondX && !beyondY) {
      alpha = alphaX;
   } else if (beyondY && !beyondX) {
      alpha = alphaY;
   } else {
      alpha = min(alphaX, alphaY);
   }

   alpha = pow(2.0, 10.0 * (alpha - 1.0));

   fragColor = vec4(gridColor.rgb, gridColor.a * alpha);
}
`

// BackgroundGrid renders a grid with transparent holes.
type BackgroundGrid struct {
	context *render.Context

	program                 uint32
	vao                     *opengl.VertexArrayObject
	vertexPositionBuffer    uint32
	vertexPositionAttrib    int32
	gridSizeUniform         opengl.Vector4Uniform
	viewMatrixUniform       opengl.Matrix4Uniform
	projectionMatrixUniform opengl.Matrix4Uniform

	lastReportedColumns int
	lastReportedRows    int
}

// NewBackgroundGrid returns a new instance of BackgroundGrid.
func NewBackgroundGrid(context *render.Context) *BackgroundGrid {
	gl := context.OpenGL
	program, programErr := opengl.LinkNewStandardProgram(gl, gridVertexShaderSource, gridFragmentShaderSource)
	if programErr != nil {
		panic(opengl.NamedShaderError{Name: "BackgroundGridShader", Nested: programErr})
	}
	grid := &BackgroundGrid{
		context:                 context,
		program:                 program,
		vao:                     opengl.NewVertexArrayObject(gl, program),
		vertexPositionBuffer:    gl.GenBuffers(1)[0],
		vertexPositionAttrib:    gl.GetAttribLocation(program, "vertexPosition"),
		viewMatrixUniform:       opengl.Matrix4Uniform(gl.GetUniformLocation(program, "viewMatrix")),
		projectionMatrixUniform: opengl.Matrix4Uniform(gl.GetUniformLocation(program, "projectionMatrix")),
		gridSizeUniform:         opengl.Vector4Uniform(gl.GetUniformLocation(program, "gridSize")),
	}

	return grid
}

// Render renders the grid.
func (grid *BackgroundGrid) Render(columns, rows int) {
	gl := grid.context.OpenGL

	grid.setGridSize(columns, rows)

	grid.vao.OnShader(func() {
		grid.viewMatrixUniform.Set(gl, grid.context.ViewMatrix)
		grid.projectionMatrixUniform.Set(gl, &grid.context.ProjectionMatrix)
		grid.gridSizeUniform.Set(gl, &[4]float32{float32(columns), float32(rows), 0, 0})

		gl.DrawArrays(opengl.TRIANGLES, 0, 6)
	})
}

func (grid *BackgroundGrid) setGridSize(columns, rows int) {
	if (grid.lastReportedColumns == columns) && (grid.lastReportedRows == rows) {
		return
	}
	grid.lastReportedColumns = columns
	grid.lastReportedRows = rows

	gl := grid.context.OpenGL
	{
		hTiles := float32(columns)
		vTiles := float32(rows)

		gl.BindBuffer(opengl.ARRAY_BUFFER, grid.vertexPositionBuffer)
		fineHalf := level.FineCoordinatesPerTileSide / float32(2.0)
		hLimit := level.FineCoordinatesPerTileSide*hTiles + fineHalf
		vLimit := level.FineCoordinatesPerTileSide*vTiles + fineHalf
		var vertices = []float32{
			-fineHalf, -fineHalf, 0.0,
			hLimit, -fineHalf, 0.0,
			hLimit, vLimit, 0.0,

			hLimit, vLimit, 0.0,
			-fineHalf, vLimit, 0.0,
			-fineHalf, -fineHalf, 0.0}
		gl.BufferData(opengl.ARRAY_BUFFER, len(vertices)*4, vertices, opengl.STATIC_DRAW)
		gl.BindBuffer(opengl.ARRAY_BUFFER, 0)
	}
	grid.vao.WithSetter(func(gl opengl.OpenGL) {
		gl.EnableVertexAttribArray(uint32(grid.vertexPositionAttrib))
		gl.BindBuffer(opengl.ARRAY_BUFFER, grid.vertexPositionBuffer)
		gl.VertexAttribOffset(uint32(grid.vertexPositionAttrib), 3, opengl.FLOAT, false, 0, 0)
		gl.BindBuffer(opengl.ARRAY_BUFFER, 0)
	})
}