package main

import (
	"fmt"

	"github.com/go-gl/gl/v4.1-core/gl"
	"github.com/go-gl/mathgl/mgl32"
)

type Shader struct {
	ProgramID uint32
}

func NewShader(vSource, fSource string) (*Shader, error) {
	vertexShader := compileShader(gl.VERTEX_SHADER, vSource)
	fragmentShader := compileShader(gl.FRAGMENT_SHADER, fSource)

	program := gl.CreateProgram()
	gl.AttachShader(program, vertexShader)
	gl.AttachShader(program, fragmentShader)
	gl.LinkProgram(program)

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

		log := make([]byte, logLength+1)
		gl.GetProgramInfoLog(program, logLength, nil, &log[0])
		fmt.Printf("Failed to link program: %s\n", log)
		return nil, fmt.Errorf("failed to link shader program")
	}

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

	return &Shader{ProgramID: program}, nil
}

func (s *Shader) Use() {
	gl.UseProgram(s.ProgramID)
}

func (s *Shader) SetUniform(name string, value float32) {
	location := s.getUniformLocation(name)
	gl.Uniform1f(location, value)
}

func (s *Shader) SetUniformM(name string, matrix mgl32.Mat4) {
	location := s.getUniformLocation(name)
	gl.UniformMatrix4fv(location, 1, false, &matrix[0])
}

func (s *Shader) SetUniform4f(name string, v0, v1, v2, v3 float32) {
	location := gl.GetUniformLocation(s.ProgramID, gl.Str(name+"\x00"))
	gl.Uniform4f(location, v0, v1, v2, v3)
}

func (s *Shader) getUniformLocation(name string) int32 {
	cName := gl.Str(name + "\x00")
	return gl.GetUniformLocation(s.ProgramID, cName)
}

func compileShader(shaderType uint32, source string) uint32 {
	shader := gl.CreateShader(shaderType)
	cSource, free := gl.Strs(source + "\x00")
	gl.ShaderSource(shader, 1, cSource, nil)
	free()
	gl.CompileShader(shader)

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

		log := make([]byte, logLength+1)
		gl.GetShaderInfoLog(shader, logLength, nil, &log[0])
		fmt.Printf("Failed to compile shader: %s\n", log)
	}
	return shader
}