#include <c64.h>
#include <stdint.h>
#include <string.h>

// Video RAM address for bitmap mode
#define SCREEN_MEM 0x0400
#define BITMAP_MEM 0x2000
#define CHARSET_MEM 0x3800

// Screen size
#define WIDTH 320
#define HEIGHT 200

// Project 3D point into 2D using simple perspective
void project(int x, int y, int z, int *sx, int *sy) {
    int distance = 4;
    int scale = 60;
    int px = x * scale / (z + distance);
    int py = y * scale / (z + distance);

    *sx = px + WIDTH / 2;
    *sy = py + HEIGHT / 2;
}

// Simple line drawing (Bresenham-style)
void draw_line(uint8_t *bitmap, int x0, int y0, int x1, int y1) {
    int dx = abs(x1 - x0), sx = x0 < x1 ? 1 : -1;
    int dy = -abs(y1 - y0), sy = y0 < y1 ? 1 : -1;
    int err = dx + dy, e2;

    while (1) {
        int byte_index = (y0 * 320 + x0) / 8;
        int bit_index = 7 - (x0 % 8);
        bitmap[byte_index] |= (1 << bit_index);

        if (x0 == x1 && y0 == y1) break;
        e2 = 2 * err;
        if (e2 >= dy) { err += dy; x0 += sx; }
        if (e2 <= dx) { err += dx; y0 += sy; }
    }
}

// Entry point
void main(void) {
    uint8_t *bitmap = (uint8_t*) BITMAP_MEM;

    // Enable bitmap mode
    VIC.ctrl1 = (VIC.ctrl1 & 0x7F) | 0x20;  // Enable bitmap mode
    VIC.addr  = (VIC.addr & 0xF1) | 0x08;   // Bitmap at $2000, screen at $0400

    // Clear bitmap
    memset(bitmap, 0x00, 8000);

    // Cube vertices
    int cube[8][3] = {
        {-1, -1, -1},
        { 1, -1, -1},
        { 1,  1, -1},
        {-1,  1, -1},
        {-1, -1,  1},
        { 1, -1,  1},
        { 1,  1,  1},
        {-1,  1,  1}
    };

    int projected[8][2];

    // Project cube vertices
    for (int i = 0; i < 8; i++) {
        project(cube[i][0], cube[i][1], cube[i][2], &projected[i][0], &projected[i][1]);
    }

    // Draw cube edges
    int edges[12][2] = {
        {0,1}, {1,2}, {2,3}, {3,0},
        {4,5}, {5,6}, {6,7}, {7,4},
        {0,4}, {1,5}, {2,6}, {3,7}
    };

    for (int i = 0; i < 12; i++) {
        draw_line(bitmap,
                  projected[edges[i][0]][0], projected[edges[i][0]][1],
                  projected[edges[i][1]][0], projected[edges[i][1]][1]);
    }

    while (1);  // Stay alive
}