#define GL_GLEXT_PROTOTYPES
#include <stdio.h>
#include <string.h>
#include <GL/gl.h>
#include <stdlib.h>
#include "renderer.h"

void checkGlError() {
    //const char *err = SDL_GetError();
    //if (*err != 0) {
    //    printf("OpenGL error: %s", err);
    //}
}

/// returns 0 if failed.
GLuint compile_shader(GLuint type, const char *src) {
    GLuint id = glCreateShader(type);
    glShaderSource(id, 1, &src, 0);
    glCompileShader(id);

    int result;
    glGetShaderiv(id, GL_COMPILE_STATUS, &result);
    if (result == GL_FALSE) {
        int length;
        glGetShaderiv(id, GL_INFO_LOG_LENGTH, &result);
        char *message = alloca(length * sizeof(char));
        glGetShaderInfoLog(id, length, &length, message);
        printf("failed to compile %s shader\n", type == GL_VERTEX_SHADER ? "vertex" : "fragment");
        printf("%s\n", message);
        glDeleteShader(id);
        return 0;
    }

    return id;
}

const char *vertex_shader_src =
//"attribute vec4 vPosition; \n"
//"void main() \n"
//"{ \n"
//" gl_Position = vPosition; \n"
//"} \n";
"#version 320 es\n"
"\n"
"layout(location = 0) in vec2 aPos;\n"
"\n"
"void main() {\n"
"    gl_Position = vec4(aPos, 0.0, 1.0);\n"
"}\n";

/// returns 0 if failed.
GLuint create_shader(const char *fragment_src) {
    GLuint program = glCreateProgram();
    GLuint vertex_shader = compile_shader(GL_VERTEX_SHADER, vertex_shader_src);
    GLuint fragment_shader = compile_shader(GL_FRAGMENT_SHADER, fragment_src);
    if (!((fragment_shader == 0) || (vertex_shader == 0))) {
        glAttachShader(program, vertex_shader);
        glAttachShader(program, fragment_shader);
        glLinkProgram(program);
        glValidateProgram(program);
        glDeleteShader(vertex_shader);
        glDeleteShader(fragment_shader);
        return program;
    } else {
        return 0;
    }
}

GLuint load_shader(const char *path) {
    FILE *handle = fopen(path, "r");
    if (handle == NULL) {
        printf("failed to open shader file\n");
        exit(1);
    }
    fseek(handle, 0L, SEEK_END);
    long length = ftell(handle);
    fseek(handle, 0L, SEEK_SET);
    char *string = malloc(length * sizeof(char));
    if (!fread(string, sizeof(char), length, handle)) {
        printf("failed to read shader file\n");
        exit(1);
    }
    fclose(handle);

    GLuint shader = create_shader(string);

    //if (shader == 0) {
    //    // print file
    //    int line_count = 1;
    //    printf("%i\t", line_count);
    //    line_count++;
    //    for (int i = 0; i < length; i++) {
    //        printf("%c", string[i]);
    //        if (string[i] == '\n') {
    //            printf("%i\t", line_count);
    //            line_count++;
    //        }
    //    }
    //    printf("\n");
    //}

    free(string);
    return shader;
}

Renderer new_renderer() {
    const char *version_str = (const char *)glGetString(GL_VERSION);
    const char *renderer_str = (const char *)glGetString(GL_RENDERER);
    printf("GL_VERSION: %s\n", version_str);
    printf("GL_RENDERER: %s\n", renderer_str);

    glEnable(GL_DEPTH_TEST);

    // buffers
    // Load the vertex data
    GLfloat vertices[] = {
        -1.0, 1.0,
        -1.0, -1.0,
        1.0, -1.0,

        1.0, -1.0,
        1.0, 1.0,
        -1.0, 1.0,
    };
    GLuint vao, vbo;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER,
                 sizeof(vertices),
                 vertices,
                 GL_STATIC_DRAW);
    
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(
        0,              // location
        2,              // vec2
        GL_FLOAT,
        GL_FALSE,
        0,
        (void *)0
    );

    Renderer renderer = { "", 0, vao };
    return renderer;
}

/// shader_path cannot be NULL.
void render(Renderer *state, int w, int h, double time, char *shader_path, int reload_shader) {
    if (reload_shader || strcmp(state->shader_path, shader_path)) {
        state->shader = load_shader(shader_path);
        state->shader_path = shader_path;
    }

    checkGlError();

    // Rendorrrr
    glViewport(0, 0, w, h);

    glClearColor(0.3f, 0.3f, 0.3f, 1.0f);  // Dark gray background
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // Shader parameters.
    glUseProgram(state->shader);

    int uniform_WindowSize = glGetUniformLocation(state->shader, "WindowSize");
    glUniform2f(uniform_WindowSize, w, h);

    int uniform_time = glGetUniformLocation(state->shader, "time");
    glUniform1f(uniform_time, (float)time);

    //glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vVertices);
    //glEnableVertexAttribArray(0);
    //glDrawArrays(GL_TRIANGLES, 0, 6);

    glBindVertexArray(state->vao);
    glDrawArrays(GL_TRIANGLES, 0, 6);
}