// Copyright 2019-2020 David Robillard <d@drobilla.net>
// SPDX-License-Identifier: ISC

#ifndef EXAMPLES_SHADER_UTILS_H
#define EXAMPLES_SHADER_UTILS_H

#include "glad/glad.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
  GLuint vertexShader;
  GLuint fragmentShader;
  GLuint program;
} Program;

static GLuint
compileShader(const char* header, const char* source, const GLenum type)
{
  const GLchar* sources[] = {header, source};
  const GLint   lengths[] = {(GLint)strlen(header), (GLint)strlen(source)};
  GLuint        shader    = glCreateShader(type);
  glShaderSource(shader, 2, sources, lengths);
  glCompileShader(shader);

  int status = 0;
  glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
  if (status == GL_FALSE) {
    GLint length = 0;
    glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &length);

    char* log = (char*)calloc(1, (size_t)length);
    glGetShaderInfoLog(shader, length, &length, log);
    fprintf(stderr, "error: Failed to compile shader (%s)\n", log);
    free(log);

    return 0;
  }

  return shader;
}

static void
deleteProgram(Program program)
{
  glDeleteShader(program.vertexShader);
  glDeleteShader(program.fragmentShader);
  glDeleteProgram(program.program);
}

static Program
compileProgram(const char* headerSource,
               const char* vertexSource,
               const char* fragmentSource)
{
  static const Program nullProgram = {0, 0, 0};

  Program program = {
    compileShader(headerSource, vertexSource, GL_VERTEX_SHADER),
    compileShader(headerSource, fragmentSource, GL_FRAGMENT_SHADER),
    glCreateProgram(),
  };

  if (!program.vertexShader || !program.fragmentShader || !program.program) {
    deleteProgram(program);
    return nullProgram;
  }

  glAttachShader(program.program, program.vertexShader);
  glAttachShader(program.program, program.fragmentShader);
  glLinkProgram(program.program);

  GLint status = 0;
  glGetProgramiv(program.program, GL_LINK_STATUS, &status);
  if (status == GL_FALSE) {
    GLint length = 0;
    glGetProgramiv(program.program, GL_INFO_LOG_LENGTH, &length);

    char* log = (char*)calloc(1, (size_t)length);
    glGetProgramInfoLog(program.program, length, &length, &log[0]);
    fprintf(stderr, "error: Failed to link program (%s)\n", log);
    free(log);

    deleteProgram(program);
    return nullProgram;
  }

  return program;
}

#endif // EXAMPLES_SHADER_UTILS_H