// Copyright 2012 The go-gl Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package v45

import (
	"errors"
	"fmt"
	"github.com/go-gl/gl/v4.5-core/gl"
	"strings"
)

func NewProgram(vertexShaderSource, fragmentShaderSource string) (uint32, error) {
	vertexShader, err := compileShader(vertexShaderSource, gl.VERTEX_SHADER)
	if err != nil {
		return 0, err
	}
	fragmentShader, err := compileShader(fragmentShaderSource, gl.FRAGMENT_SHADER)
	if err != nil {
		return 0, err
	}
	program := gl.CreateProgram()
	gl.AttachShader(program, vertexShader)
	gl.AttachShader(program, fragmentShader)
	gl.LinkProgram(program)

	var status int32
	gl.GetProgramiv(program, gl.LINK_STATUS, &status)
	if status == gl.FALSE {
		var logLength int32
		gl.GetProgramiv(program, gl.INFO_LOG_LENGTH, &logLength)

		log := strings.Repeat("\x00", int(logLength+1))
		gl.GetProgramInfoLog(program, logLength, nil, gl.Str(log))

		gl.DeleteProgram(program)
		gl.DeleteShader(vertexShader)
		gl.DeleteShader(fragmentShader)

		return 0, errors.New(fmt.Sprintf("failed to link program: %v", log))
	}
	gl.DetachShader(program, vertexShader)
	gl.DetachShader(program, fragmentShader)

	gl.DeleteShader(vertexShader)
	gl.DeleteShader(fragmentShader)

	return program, nil
}

func compileShader(source string, shaderType uint32) (uint32, error) {
	shader := gl.CreateShader(shaderType)
	csource := gl.Str(source)
	gl.ShaderSource(shader, 1, &csource, nil)
	gl.CompileShader(shader)

	var status int32
	gl.GetShaderiv(shader, gl.COMPILE_STATUS, &status)
	if status == gl.FALSE {
		var logLength int32
		gl.GetShaderiv(shader, gl.INFO_LOG_LENGTH, &logLength)

		log := strings.Repeat("\x00", int(logLength+1))
		gl.GetShaderInfoLog(shader, logLength, nil, gl.Str(log))

		return 0, fmt.Errorf("failed to compile %v: %v", source, log)
	}
	return shader, nil
}