// gl_utils.c
#include "gl_utils.h"

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

void glfw_error_callback(int error, const char* description) {
    fprintf(stderr, "GLFW error %d: %s\n", error, description);
}

char* load_text_file(const char* path) {
    FILE* f = fopen(path, "rb");
    if (!f) {
        fprintf(stderr, "Failed to open '%s': %s\n", path, strerror(errno));
        return NULL;
    }

    if (fseek(f, 0, SEEK_END) != 0) {
        fprintf(stderr, "fseek failed on '%s'\n", path);
        fclose(f);
        return NULL;
    }

    long size = ftell(f);
    if (size < 0) {
        fprintf(stderr, "ftell failed on '%s'\n", path);
        fclose(f);
        return NULL;
    }

    rewind(f);

    char* buffer = malloc((size_t)size + 1);
    if (!buffer) {
        fprintf(stderr, "Out of memory reading '%s'\n", path);
        fclose(f);
        return NULL;
    }

    size_t read = fread(buffer, 1, (size_t)size, f);
    fclose(f);

    if (read != (size_t)size) {
        fprintf(stderr, "Short read on '%s'\n", path);
        free(buffer);
        return NULL;
    }

    buffer[size] = '\0';
    return buffer;
}

GLuint compile_shader(GLenum type, const char* source, const char* debugName) {
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &source, NULL);
    glCompileShader(shader);

    GLint success = 0;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &success);
    if (!success) {
        char log[1024];
        glGetShaderInfoLog(shader, sizeof(log), NULL, log);
        fprintf(stderr, "Shader compile failed (%s):\n%s\n", debugName ? debugName : "unknown", log);
        glDeleteShader(shader);
        exit(EXIT_FAILURE);
    }

    return shader;
}

GLuint create_program_from_files(const char* vsPath, const char* fsPath) {
    char* vsSource = load_text_file(vsPath);
    if (!vsSource) {
        fprintf(stderr, "Could not load vertex shader from '%s'\n", vsPath);
        exit(EXIT_FAILURE);
    }

    char* fsSource = load_text_file(fsPath);
    if (!fsSource) {
        fprintf(stderr, "Could not load fragment shader from '%s'\n", fsPath);
        free(vsSource);
        exit(EXIT_FAILURE);
    }

    GLuint vs = compile_shader(GL_VERTEX_SHADER,   vsSource, vsPath);
    GLuint fs = compile_shader(GL_FRAGMENT_SHADER, fsSource, fsPath);

    free(vsSource);
    free(fsSource);

    GLuint prog = glCreateProgram();
    glAttachShader(prog, vs);
    glAttachShader(prog, fs);
    glLinkProgram(prog);

    glDeleteShader(vs);
    glDeleteShader(fs);

    GLint linked = 0;
    glGetProgramiv(prog, GL_LINK_STATUS, &linked);
    if (!linked) {
        char log[1024];
        glGetProgramInfoLog(prog, sizeof(log), NULL, log);
        fprintf(stderr, "Program link failed:\n%s\n", log);
        glDeleteProgram(prog);
        exit(EXIT_FAILURE);
    }

    return prog;
}

GLFWwindow* init_glfw_glad(const char* title, int width, int height) {
    glfwSetErrorCallback(glfw_error_callback);

    // Prefer Wayland if this GLFW build supports it
    if (glfwPlatformSupported(GLFW_PLATFORM_WAYLAND)) {
        glfwInitHint(GLFW_PLATFORM, GLFW_PLATFORM_WAYLAND);
        fprintf(stderr, "[info] Requesting Wayland platform via glfwInitHint\n");
    } else {
        fprintf(stderr, "[warn] Wayland platform not supported by this GLFW build, using default\n");
    }

    if (!glfwInit()) {
        fprintf(stderr, "[fatal] glfwInit failed\n");
        return NULL;
    }

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GLFW_TRUE);

    GLFWwindow* window = glfwCreateWindow(width, height, title, NULL, NULL);
    if (!window) {
        fprintf(stderr, "[fatal] glfwCreateWindow failed\n");
        glfwTerminate();
        return NULL;
    }

    glfwMakeContextCurrent(window);

    if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)) {
        fprintf(stderr, "[fatal] Failed to initialize GLAD\n");
        glfwDestroyWindow(window);
        glfwTerminate();
        return NULL;
    }

    return window;
}