// main.c
#include <stdio.h>
#include <stdlib.h>

#include "gl_utils.h"
#include "sand_sim.h"
#define GRID_W 2048
#define GRID_H 2048
static int g_fbWidth = 800;
static int g_fbHeight = 800;
static double g_cursorX = 0.0;
static double g_cursorY = 0.0;
SandSim sim;

static void cursor_pos_callback(GLFWwindow* window, double xpos, double ypos) {
    (void)window;
    g_cursorX = xpos;
    g_cursorY = ypos;
}

static void render_sand(SandSim* sim,
                        GLuint program,
                        GLuint vao,
                        int fbW,
                        int fbH,
                        float brushX,
                        float brushY,
                        float brushRadius) {
    glUseProgram(program);

    GLint uResLoc = glGetUniformLocation(program, "u_resolution");
    GLint uGridLoc = glGetUniformLocation(program, "u_gridSize");
    GLint uStateLoc = glGetUniformLocation(program, "u_state");
    GLint uBrushPosLoc = glGetUniformLocation(program, "u_brushPos");
    GLint uBrushRadLoc = glGetUniformLocation(program, "u_brushRadius");
    GLint uShowBrushLoc = glGetUniformLocation(program, "u_showBrush");

    if (uResLoc >= 0) {
        glUniform2f(uResLoc, (float)fbW, (float)fbH);
    }
    if (uGridLoc >= 0) {
        glUniform2i(uGridLoc, sim->gridW, sim->gridH);
    }
    if (uStateLoc >= 0) {
        glActiveTexture(GL_TEXTURE0);
        glBindTexture(GL_TEXTURE_2D, sim->tex_curr);
        glUniform1i(uStateLoc, 0);
    }

    if (uBrushPosLoc >= 0) {
        glUniform2f(uBrushPosLoc, brushX, brushY);
    }
    if (uBrushRadLoc >= 0) {
        glUniform1f(uBrushRadLoc, brushRadius);
    }
    if (uShowBrushLoc >= 0) {
        glUniform1i(uShowBrushLoc, 1);  // always show for now
    }

    glBindVertexArray(vao);
    glDrawArrays(GL_TRIANGLES, 0, 3);
}

int main(void) {
    GLFWwindow* window = init_glfw_glad("Falling Sand - Fullscreen Quad", g_fbWidth, g_fbHeight);
    if (!window) {
        return EXIT_FAILURE;
    }
    glfwSetCursorPosCallback(window, cursor_pos_callback);
    glfwGetFramebufferSize(window, &g_fbWidth, &g_fbHeight);
    glViewport(0, 0, g_fbWidth, g_fbHeight);
    printf("Renderer: %s\n", (const char*)glGetString(GL_RENDERER));
    printf("OpenGL:   %s\n", (const char*)glGetString(GL_VERSION));
    printf("GLSL:     %s\n", (const char*)glGetString(GL_SHADING_LANGUAGE_VERSION));

    // --- Create fullscreen triangle geometry (VAO + VBO) ---
    float vertices[] = {
        // x, y
        -1.0f, -1.0f,
        3.0f, -1.0f,
        -1.0f, 3.0f};

    GLuint vao = 0, vbo = 0;
    glGenVertexArrays(1, &vao);
    glGenBuffers(1, &vbo);

    glBindVertexArray(vao);

    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

    // layout(location = 0) in vec2 aPos;
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(
        0,
        2,
        GL_FLOAT,
        GL_FALSE,
        2 * sizeof(float),
        (void*)0);

    glBindVertexArray(0);
    if (!sand_init(&sim, GRID_W, GRID_H, "shaders/sand_step.comp")) {
        fprintf(stderr, "Failed to initialize sand sim\n");
        return EXIT_FAILURE;
    }
    // --- Create shader program ---
    GLuint program = create_program_from_files(
        "shaders/fullscreen.vert",
        "shaders/sand_display.frag");

    glUseProgram(program);

    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    double sim_dt = 1.0 / 360.0;
    double currentTime = glfwGetTime();
    double accumulator = 0.0;
    float brushX = 0.0f;
    float brushY = 0.0f;
    
    // --- Main loop ---
    while (!glfwWindowShouldClose(window)) {
        double newTime = glfwGetTime();
        double frameTime = newTime - currentTime;
        currentTime = newTime;
        if (frameTime > 0.25) frameTime = 0.25;
        accumulator += frameTime;

        while (accumulator >= sim_dt) {
            sand_step_gpu(&sim);  // one discrete CA step on the GPU 
            sand_relax_gpu(&sim);
            accumulator -= sim_dt;
        }
        int paintMode = 0;
        glfwPollEvents();
        if (glfwGetMouseButton(window, GLFW_MOUSE_BUTTON_LEFT) == GLFW_PRESS) {
            paintMode = 1;
        } else if (glfwGetMouseButton(window, GLFW_MOUSE_BUTTON_RIGHT) == GLFW_PRESS) {
            paintMode = -1;
        }
        // Re-query framebuffer size each frame (cheap and simple)
        int fbw, fbh;
        glfwGetFramebufferSize(window, &fbw, &fbh);
        if (fbw != g_fbWidth || fbh != g_fbHeight) {
            g_fbWidth = fbw;
            g_fbHeight = fbh;
            glViewport(0, 0, g_fbWidth, g_fbHeight);
        }
        if (g_fbWidth > 0 && g_fbHeight > 0) {
            float uvx = (float)g_cursorX / (float)g_fbWidth;
            float uvy = (float)g_cursorY / (float)g_fbHeight;
            brushX = uvx * (float)sim.gridW;
            brushY = uvy * (float)sim.gridH;
        }
        float brushRadius = 60.0f;
        sand_paint_gpu(&sim, brushX, brushY, brushRadius, paintMode);
        glClear(GL_COLOR_BUFFER_BIT);

        render_sand(&sim, program, vao, g_fbWidth, g_fbHeight, brushX, brushY, brushRadius);

        glfwSwapBuffers(window);
    }

    // --- Cleanup ---
    glDeleteProgram(program);
    glDeleteBuffers(1, &vbo);
    glDeleteVertexArrays(1, &vao);

    glfwDestroyWindow(window);
    glfwTerminate();
    return EXIT_SUCCESS;
}