#include <assert.h>
#include "sys.h"
#include "device/device.h"

sys_i32 sys_cam_dx, sys_cam_dy;
sys_i32 sys_clip_x0, sys_clip_y0, sys_clip_x1, sys_clip_y1;
sys_color sys_dpal[256];

// primitives (forward declare)
void sys_pixel_internal_set(sys_i32 x, sys_i32 y, sys_color c);
void sys_scanline_internal_set(
    sys_i32 x0, sys_i32 x1, sys_i32 y, sys_color c, bool fill
);

// == public ==
void sys_clip_set(sys_i32 x0, sys_i32 y0, sys_i32 x1, sys_i32 y1) {
    assert(sys_get_initialized());

    sys_clip_set_ext(x0, y0, x1, y1, false);
}

void sys_clip_reset() {
    assert(sys_get_initialized());

    sys_clip_set(0, 0, DEVICE_W, DEVICE_H);
}

void sys_clip_set_ext(sys_i32 x0, sys_i32 y0, sys_i32 x1, sys_i32 y1, bool clip_previous) {
    assert(sys_get_initialized());
    sys_clip_x0 = sys_max_i32(x0, clip_previous ? sys_clip_x0 : 0);
    sys_clip_y0 = sys_max_i32(y0, clip_previous ? sys_clip_y0 : 0);
    sys_clip_x1 = sys_min_i32(x1, clip_previous ? sys_clip_x1 : DEVICE_W);
    sys_clip_y1 = sys_min_i32(y1, clip_previous ? sys_clip_y1 : DEVICE_H);
}

void sys_pixel_set(sys_i32 x, sys_i32 y, sys_color c) {
    assert(sys_get_initialized());

    x += sys_cam_dx;
    y += sys_cam_dy;

    sys_pixel_internal_set(x, y, c);
}

sys_color sys_pixel_get(sys_i32 x, sys_i32 y) {
    assert(sys_get_initialized());

    x += sys_cam_dx;
    y += sys_cam_dy;

    if (x < 0 || y < 0 || x >= DEVICE_W || y >= DEVICE_H) {
        return SYS_COLOR_TRANSPARENT;
    }

    return device_pixels[y][x];
}

void sys_cls(sys_color c) {
    assert(sys_get_initialized());

    for (int x = 0; x < DEVICE_W; x++) {
        for (int y = 0; y < DEVICE_W; y++) {
            sys_pixel_internal_set(x, y, c);
        }
    }
}

void sys_camera_set(sys_i32 x, sys_i32 y) {
    assert(sys_get_initialized());

    sys_cam_dx = -x;
    sys_cam_dy = -y;
}

void sys_camera_reset() {
    assert(sys_get_initialized());

    sys_camera_set(0, 0);
}

// Based on bresenham implementations by alois zingl
// https://zingl.github.io/bresenham.html
void sys_circ_draw(sys_i32 x, sys_i32 y, sys_i32 r, sys_color c) {
    assert(sys_get_initialized());

    sys_circ_draw_ext(x, y, r, c, false);
}

void sys_circ_fill(sys_i32 x, sys_i32 y, sys_i32 r, sys_color c) {
    assert(sys_get_initialized());

    sys_circ_draw_ext(x, y, r, c, true);
}

void sys_circ_draw_ext(
    sys_i32 x, sys_i32 y, sys_i32 r, sys_color c, bool fill
) {
    assert(sys_get_initialized());

    if (r < 0) { return; }

    sys_oval_draw_ext(x - r, y - r, x + r + 1, y + r + 1, c, fill);
}

void sys_oval_draw(
    sys_i32 x0, sys_i32 y0, sys_i32 x1, sys_i32 y1, sys_color c
) {
    assert(sys_get_initialized());

    sys_oval_draw_ext(x0, y0, x1, y1, c, false);
}

void sys_oval_fill(
    sys_i32 x0, sys_i32 y0, sys_i32 x1, sys_i32 y1, sys_color c
) {
    assert(sys_get_initialized());

    sys_oval_draw_ext(x0, y0, x1, y1, c, true);
}

void sys_oval_draw_ext(
    sys_i32 x0, sys_i32 y0, sys_i32 x1, sys_i32 y1, sys_color c, bool fill
) {
    if (x0 == x1 || y0 == y1) { return; }
    if (x0 > x1) { sys_i32 tmp = x0; x0 = x1; x1 = tmp; }
    if (y0 > y1) { sys_i32 tmp = y0; y0 = y1; y1 = tmp; }
    // alois' algorithm for this implies the bounds are inclusive 
    x1 -= 1; y1 -= 1;

    int64_t a = x1 - x0;
    int64_t b = y1 - y0;
    int64_t b1 = b & 1;

    int64_t dx = 4 * (1 - a) * b * b;
    int64_t dy = 4 * (b1 + 1) * a * a;
    int64_t err = dx + dy + b1 * a * a;

    y0 += (b + 1) / 2;
    y1 = y0 - b1;
    a *= 8 * a;
    b1 = 8 * b * b;

    do {
        // draw the points at the edge of the line
        sys_scanline_internal_set(x0, x1, y0, c, false);
        sys_scanline_internal_set(x0, x1, y1, c, false);
        int64_t e2 = 2 * err;
        if (e2 <= dy) { 
            if (fill) {
                // draw the whole line
                sys_scanline_internal_set(x0, x1, y0, c, true);
                sys_scanline_internal_set(x0, x1, y1, c, true);
            }
            y0++; y1--; dy += a; err += dy; 
        }
        if (e2 >= dx || 2 * err > dy) { x0++; x1--; dx += b1; err += dx; }
    } while (x0 <= x1);

    while (y0 - y1 < b) {
        sys_scanline_internal_set(x0 - 1, x1 + 1, y0, c, fill); y0++;
        sys_scanline_internal_set(x0 - 1, x1 + 1, y1, c, fill); y1--;
    }
}

void sys_spal_set(sys_color c0, sys_screen_color rc1) {
    assert(sys_get_initialized());

    device_palette[c0] = rc1;
}

void sys_spal_reset() {
    assert(sys_get_initialized());

    for (int i = 0; i < SYS_COLOR_N; i++) {
        sys_spal_set(i, 0x000000ff);
    }
}

void sys_dpal_set(sys_color c0, sys_color c1) {
    assert(sys_get_initialized());

    sys_dpal[c0] = c1;
}

void sys_dpal_reset() {
    assert(sys_get_initialized());

    for (int i = 0; i < SYS_COLOR_N; i++) {
        sys_dpal_set(i, i);
    }
}

// == internal primitives ==
void sys_pixel_internal_set(sys_i32 x, sys_i32 y, sys_color c) {
    sys_color realc = sys_dpal[c];
    if (realc == SYS_COLOR_TRANSPARENT) { return; }

    if (
        x < sys_clip_x0 || y < sys_clip_y0 || 
        x >= sys_clip_x1 || y >= sys_clip_y1
    ) { 
        return; 
    }

    assert(x >= 0);
    assert(y >= 0);
    assert(x < DEVICE_W);
    assert(y < DEVICE_H);

    device_pixels[y][x] = realc;
}
void sys_scanline_internal_set(
    sys_i32 x0, sys_i32 x1, sys_i32 y, sys_color c, 
    bool fill
) {
    if (fill) {
        for (sys_i32 x = x0; x <= x1; x++) {
            sys_pixel_internal_set(x, y, c);
        }
    } else {
        sys_pixel_internal_set(x0, y, c);
        sys_pixel_internal_set(x1, y, c);
    }
}