#include "../drivers/vga.h"
#include "../syscall.h"

#include "sprites.h"
#include <stdbool.h>
#include <stdint.h>
#include "misc_utils.h"
#include "keymapping.h"
#include "pause_effect.h"
#include "random.h"
#include "sprites.h"
#include "sprite_data.h"
#include "maps.h"
#include "map_data.h"

#define FRAME_SIZE (VGA_GRAPHICS_WIDTH * VGA_GRAPHICS_HEIGHT)

#define HUD_OFFSET 3
#define GLYPH_SPACING 3

#define FONT_SPACE_INDEX 0
#define FONT_DIGIT_BASE 1
#define FONT_LETTER_BASE (FONT_DIGIT_BASE + 10)

uint8_t frame[FRAME_SIZE] = { 1 };

#define SNAKE_GAMEMODE_MAX_APPLES 10
#define SNAKE_GAMEMODE_DEFAULT_APPLES 5

typedef enum {
    game_screen_gaming,
    game_screen_pause,
    game_screen_select_map,
    game_screen_select_apple_count,
} game_screen_t;


#define SNAKE_START_Y  2
#define SNAKE_START_HEAD_X 4
#define SNAKE_START_PUPA_X 6

typedef enum {
    snake_direction_left = 0,
    snake_direction_right = 1,
    snake_direction_top = 2,
    snake_direction_bottom = 3,
} snake_direction_t;

#define WALKING_ANIM_TIME_SLOW 500
#define HATCHING_ANIM_TIME_SLOW 200
#define WALKING_ANIM_TIME_FAST 200
#define HATCHING_ANIM_TIME_FAST 80

typedef enum {
    waiting_reason_step,

    waiting_reason_p1,
    waiting_reason_p2,
    waiting_reason_cross,

    /* we go from cross pupa state to m1 pupa state through 'step',
     * not through a separate animation target */
    waiting_reason_m1,
    waiting_reason_zero_pupa,

    waiting_reason_postmortum,
} waiting_reason_t;

struct Snake {
    bool is_space_pressed;
    game_screen_t game_screen;
    bool have_game;
    /* from 0 to PLAYABLE_MAPS_COUNT - 1 */
    int selected_map_index;
    /* from 1 to SNAKE_GAMEMODE_MAX_APPLES, default is SNAKE_GAMEMODE_DEFAULT_APPLES */
    int gamemode_apples_count;
    RandomEngine r_eng;

    tile_t world[WORLD_WIDTH][WORLD_HEIGHT];
    uint8_t ghost_apples[WORLD_WIDTH][WORLD_HEIGHT];
    ivec2 snake_head;
    ivec2 snake_tail;
    snake_direction_t cur_snake_direction;
    snake_direction_t new_snake_direction;
    /* If we are about to make a step into a wall, we start dying,
     * we enter into dying mode, where we keep making steps, but the head
     * just disappears after walking, moving back.
     * When the pupa disappears this way, we enter 'awaiting postmortum' state, where
     * nothing moves.
     * If we are about to hit ourselves, we don't even move,
     * we immediately draw one small splash and enter 'awaiting postmortum' state.
     * There is no winning state, you just raise your score until you are dead.
     */
    bool is_dying;
    int score;
    /* from -1 to PUDDLE_SPRITES - 1 (where -1 means there is no puddle) */
    int puddle_sprite;
    ivec2 puddle_center;


    /* This stuff regulates game flow and animation progress */
    waiting_reason_t waiting_reason;
    uint32_t waiting_time;  // Measures how much time we already accumulated
    bool is_time_sped_up;
} snake = {1};

void init_snake() {
    snake.is_space_pressed = false;
    snake.game_screen = game_screen_pause;
    snake.have_game = false;
    snake.selected_map_index = 0;
    snake.gamemode_apples_count = SNAKE_GAMEMODE_DEFAULT_APPLES;
    snake.r_eng = (RandomEngine){.state = time_ms()};
    /* snake_head and snake_pupa and snake.world
     * and other gameplay-related variables will be initialized during
     * map loading */
}

bool place_random_apple() {
    for (int t = 0; t < 50; t++) {
        uint32_t i = RandomEngine_rnd_interval(&snake.r_eng, 0, WORLD_WIDTH * WORLD_HEIGHT);
        if ((&snake.world[0][0])[i] == tile_empty) {
            (&snake.world[0][0])[i] = tile_apple;
            return true;
        }
    }
    /* I had enough */
    for (uint32_t i = 0; i < WORLD_WIDTH * WORLD_HEIGHT; i++) {
        if ((&snake.world[0][0])[i] == tile_empty) {
            (&snake.world[0][0])[i] = tile_apple;
            return true;
        }
    }
    return false;
}

void start_snake_game() {
    snake.have_game = true;
    snake.game_screen = game_screen_gaming;
    const MapConfig* map_config = &map_list.maps[snake.selected_map_index];
    memcpy(&snake.world[0][0], &map_config->map[0][0], sizeof(tile_t) * WORLD_WIDTH * WORLD_HEIGHT);
    memset(&snake.ghost_apples, 0, sizeof(snake.ghost_apples));
    for (int tx = SNAKE_START_HEAD_X; tx < SNAKE_START_PUPA_X; tx++) {
        snake.world[tx][SNAKE_START_Y] = tile_snake_l;
    }
    snake.world[SNAKE_START_PUPA_X][SNAKE_START_Y] = tile_pupa_0_l;
    for (int app = 0; app < snake.gamemode_apples_count; app++) {

    }
    snake.new_snake_direction = snake.cur_snake_direction = snake_direction_left;
    snake.is_dying = false;
    snake.score = 0;

    snake.waiting_reason = waiting_reason_step;
    snake.waiting_time = 0;
    snake.is_time_sped_up = false;
    snake.puddle_sprite = -1;
}

void set_tile(ivec2 pos, tile_t val) {
    check(0 <= pos.x && pos.x < WORLD_WIDTH && 0 <= pos.y && pos.y < WORLD_HEIGHT);
    snake.world[pos.x][pos.y] = val;
}

tile_t get_tile(ivec2 pos) {
    check(0 <= pos.x && pos.x < WORLD_WIDTH && 0 <= pos.y && pos.y < WORLD_HEIGHT);
    return snake.world[pos.x][pos.y];
}

snake_direction_t get_opposite_direction(snake_direction_t x) {
    if (x == snake_direction_left) {
        return snake_direction_right;
    } else if (x == snake_direction_right) {
        return snake_direction_left;
    } else if (x == snake_direction_top) {
        return snake_direction_bottom;
    } else {
        return snake_direction_top;
    }
}

ivec2 world_walk_direction(ivec2 v, snake_direction_t dir) {
    if (dir == snake_direction_left) {
        return (ivec2){v.x == 0 ? WORLD_WIDTH - 1 : v.x - 1, v.y};
    } else if (dir == snake_direction_right) {
        return (ivec2){v.x + 1 == WORLD_WIDTH ? 0 : v.x + 1, v.y};
    } else if (dir == snake_direction_top) {
        return (ivec2){v.x, v.y == 0 ? WORLD_HEIGHT - 1 : v.y - 1};
    } else {
        return (ivec2){v.x, v.y + 1 == WORLD_HEIGHT ? 0 : v.y + 1};
    }
}

ivec2 get_puddle_center_for_contact(ivec2 head, snake_direction_t dir) {
    ivec2 tile_pos = (ivec2){TILE_WIDTH * head.x, TILE_HEIGHT * head.y};
    if (dir == snake_direction_left || dir == snake_direction_right) {
        tile_pos.y += TILE_WIDTH / 2;
    } else if (dir == snake_direction_bottom) {
        tile_pos.y += TILE_WIDTH;
    }
    if (dir == snake_direction_top || dir == snake_direction_bottom) {
        tile_pos.x += TILE_WIDTH / 2;
    } else if (dir == snake_direction_right) {
        tile_pos.x += TILE_WIDTH;
    }
    return tile_pos;
}

/* takes snake tile, returns cardinal direction of snake origin */
snake_direction_t get_snake_origin_dir(tile_t tile) {
    switch (tile) {
    case tile_snake_l:
        return snake_direction_right;
    case tile_snake_r:
        return snake_direction_left;
    case tile_snake_t:
        return snake_direction_bottom;
    case tile_snake_b:
        return snake_direction_top;
    case tile_snake_bl:
        return snake_direction_bottom;
    case tile_snake_br:
        return snake_direction_bottom;
    case tile_snake_lb:
        return snake_direction_left;
    case tile_snake_rb:
        return snake_direction_right;
    case tile_snake_tl:
        return snake_direction_top;
    case tile_snake_tr:
        return snake_direction_top;
    case tile_snake_lt:
        return snake_direction_left;
    case tile_snake_rt:
        return snake_direction_right;
    default:
        check(false);
    }
}

tile_t construct_snake_tile(snake_direction_t from, snake_direction_t to) {
    check(from != to);
    if (from == snake_direction_left) {
        if (to == snake_direction_right)
            return tile_snake_r;
        if (to == snake_direction_top)
            return tile_snake_lt;
        /* to bottom */
        return tile_snake_lb;
    }
    if (from == snake_direction_right) {
        if (to == snake_direction_left)
            return tile_snake_l;
        if (to == snake_direction_top)
            return tile_snake_rt;
        /* to bottom */
        return tile_snake_rb;
    }
    if (from == snake_direction_top) {
        if (to == snake_direction_left)
            return tile_snake_tl;
        if (to == snake_direction_right)
            return tile_snake_tr;
        /* to bottom */
        return tile_snake_b;
    }
    if (from == snake_direction_bottom) {
        if (to == snake_direction_left)
            return tile_snake_bl;
        if (to == snake_direction_right)
            return tile_snake_br;
        /* to top */
        return tile_snake_t;
    }
    check(false);
}

tile_t construct_head_snake_tile(snake_direction_t to) {
    return construct_snake_tile(get_opposite_direction(to), to);
}

tile_t construct_zero_pupa(snake_direction_t to) {
    if (to == snake_direction_left)
        return tile_pupa_0_l;
    if (to == snake_direction_right)
        return tile_pupa_0_r;
    if (to == snake_direction_top)
        return tile_pupa_0_t;
    if (to == snake_direction_bottom)
        return tile_pupa_0_b;
    check(false);
}

/* takes snake tile, returns it's target direction*/
snake_direction_t get_snake_destination(tile_t tile) {
    switch (tile) {
    case tile_snake_l:
        return snake_direction_left;
    case tile_snake_r:
        return snake_direction_right;
    case tile_snake_t:
        return snake_direction_top;
    case tile_snake_b:
        return snake_direction_bottom;
    case tile_snake_bl:
        return snake_direction_left;
    case tile_snake_br:
        return snake_direction_right;
    case tile_snake_lb:
        return snake_direction_bottom;
    case tile_snake_rb:
        return snake_direction_bottom;
    case tile_snake_tl:
        return snake_direction_left;
    case tile_snake_tr:
        return snake_direction_right;
    case tile_snake_lt:
        return snake_direction_top;
    case tile_snake_rt:
        return snake_direction_top;
    default:
        check(false);
    }
}

snake_direction_t get_zero_pupa_destination(tile_t tile) {
    if (tile == tile_pupa_0_r)
        return snake_direction_right;
    if (tile == tile_pupa_0_l)
        return snake_direction_left;
    if (tile == tile_pupa_0_t)
        return snake_direction_top;
    if (tile == tile_pupa_0_b)
        return snake_direction_bottom;
    check(false);
}

/* takes a tile that can possibly become a tail. Either straight snake or pupa */
bool is_tail_pupa(tile_t tile) {
    if (18 <= tile && tile <= 21)
        return false;
    if (tile == tile_pupa_0_r || tile == tile_pupa_0_l ||
        tile == tile_pupa_0_b || tile == tile_pupa_0_t) {
        return true;
    }
    check(false);
}

void clear_frame(uint8_t color) {
    for (uint32_t i = 0; i < FRAME_SIZE; i++) {
        frame[i] = color;
    }
}

void put_pixel(int x, int y, uint8_t color) {
    if (x < 0 || x >= VGA_GRAPHICS_WIDTH || y < 0 || y >= VGA_GRAPHICS_HEIGHT) {
        return;
    }
    frame[y * VGA_GRAPHICS_WIDTH + x] = color;
}

void draw_sprite(
    int dst_x, int dst_y, int sprite_width, int sprite_height,
    const uint8_t* sprite) {
    for (int x = 0; x < sprite_width; x++) {
        for (int y = 0; y < sprite_height; y++) {
            uint8_t color = sprite[x * sprite_height + y];
            if (color != TRANSPARENCY_COLOR) {
                put_pixel(dst_x + x, dst_y + y, color);
            }
        }
    }
}

bool font_index_for_char(char ch, int *out_index) {
    if (ch == ' ') {
        *out_index = FONT_SPACE_INDEX;
        return true;
    }
    if (ch >= '0' && ch <= '9') {
        *out_index = FONT_DIGIT_BASE + (ch - '0');
        return true;
    }
    if (ch >= 'A' && ch <= 'Z') {
        *out_index = FONT_LETTER_BASE + (ch - 'A');
        return true;
    }
    return false;
}

void draw_hud(const char *text) {
    // int lines_count = 1;
    int y0 = HUD_OFFSET;
    for (const char* line_start = text; *line_start;) {
        int glyph_count = 0;
        const char* p = line_start;
        for (; *p != '\n' && *p != 0; p++) {
            glyph_count++;
        }
        if (glyph_count > 0) {
            const int text_width = glyph_count * FONT_WIDTH + (glyph_count - 1) * GLYPH_SPACING;
            int x0 = VGA_GRAPHICS_WIDTH - HUD_OFFSET - text_width;
            for (const char* q = line_start; q != p; q++) {
                int glyph_index;
                check(font_index_for_char(*q, &glyph_index));
                draw_sprite(x0, y0, FONT_WIDTH, FONT_HEIGHT,
                    &sprite_data.font[glyph_index].tex[0][0]);
                x0 += FONT_WIDTH + GLYPH_SPACING;
            }
        }
        if (*p == 0) {
            break;
        }
        line_start = p + 1;
        y0 += FONT_HEIGHT + GLYPH_SPACING;
    }
}

/* You see, we never store pupa hatching stage in world array.
 * Instead, we store pupa 0 in world matrix and deduce the correct tile
 * in draw_game_world using snake.waiting_reason
 */
tile_t correct_game_tile(tile_t x) {
    /* waiting for p2 => we are in p1 */
    if (snake.waiting_reason == waiting_reason_p2) {
        if (x == tile_pupa_0_l)
            return tile_pupa_p1_l;
        if (x == tile_pupa_0_r)
            return tile_pupa_p1_r;
        if (x == tile_pupa_0_t)
            return tile_pupa_p1_t;
        if (x == tile_pupa_0_b)
            return tile_pupa_p1_b;
    }
    /* waiting for cross => we are in p2 */
    if (snake.waiting_reason == waiting_reason_cross) {
        if (x == tile_pupa_0_l)
            return tile_pupa_p2_l;
        if (x == tile_pupa_0_r)
            return tile_pupa_p2_r;
        if (x == tile_pupa_0_t)
            return tile_pupa_p2_t;
        if (x == tile_pupa_0_b)
            return tile_pupa_p2_b;
    }
    /* waiting for m1 => we are in m2 */
    if (snake.waiting_reason == waiting_reason_m1) {
        if (x == tile_pupa_0_l)
            return tile_pupa_m2_l;
        if (x == tile_pupa_0_r)
            return tile_pupa_m2_r;
        if (x == tile_pupa_0_t)
            return tile_pupa_m2_t;
        if (x == tile_pupa_0_b)
            return tile_pupa_m2_b;
    }
    /* waiting for zero_pupa => we are in m1 */
    if (snake.waiting_reason == waiting_reason_zero_pupa) {
        if (x == tile_pupa_0_l)
            return tile_pupa_m1_l;
        if (x == tile_pupa_0_r)
            return tile_pupa_m1_r;
        if (x == tile_pupa_0_t)
            return tile_pupa_m1_t;
        if (x == tile_pupa_0_b)
            return tile_pupa_m1_b;
    }
    /* When waiting postmortum, step or p1, pupa looks exactly the same
     * (default is zero pupa) */
    return x;
}

void draw_game_world() {
    if (!snake.have_game)
        return;

    for (int tx = 0; tx < WORLD_WIDTH; tx++) {
        for (int ty = 0; ty < WORLD_HEIGHT; ty++) {
            tile_t tt = correct_game_tile(snake.world[tx][ty]);
            if (tt == tile_empty)
                continue;
            check((uint8_t)tt < TILE_SPRITES);
            draw_sprite(TILE_WIDTH * tx, TILE_WIDTH * ty - TILE_HEIGHT_OFFSET,
                TILE_WIDTH, TILE_HEIGHT, &sprite_data.tile[tt].tex[0][0]);
        }
    }
    if (snake.game_screen != game_screen_gaming) {
        for (uint32_t pix = 0; pix < FRAME_SIZE; pix++) {
            frame[pix] = vga_to_gray(frame[pix]);
        }
    }
}

void draw_game_text() {
    StringBuilder hud = { 0 };
    if (snake.game_screen == game_screen_gaming) {
        StringBuilder_append_u32(&hud, snake.score);
    } else if (snake.game_screen == game_screen_pause) {
        if (snake.have_game) {
            StringBuilder_append_cstr(&hud, "PAUSED\n");
        }
        StringBuilder_append_cstr(&hud, "PRESS 1 FOR NEW GAME\n");
        if (snake.have_game) {
            StringBuilder_append_cstr(&hud, "PRESS ESC TO CONTINUE\n");
        }
        StringBuilder_append_cstr(&hud, "PRESS Q TO QUIT\n");
    } else if (snake.game_screen == game_screen_select_map) {
        StringBuilder_append_cstr(&hud, "SELECT LEVEL\nCURRENTLY SELECTED\n");
        check(snake.selected_map_index < PLAYABLE_MAPS_COUNT);
        StringBuilder_append_cstr(&hud, map_list.maps[snake.selected_map_index].name);
    } else if (snake.game_screen == game_screen_select_apple_count) {
        StringBuilder_append_cstr(&hud, "SELECT DIFFICULTY\n"
            "HOW MANY APPLES\nCURRENTLY SELECTED\n");
        StringBuilder_append_u32(&hud, snake.gamemode_apples_count);
    }
    draw_hud(StringBuilder_get_cstr(&hud));
}

void draw_game_puddles() {
    if (snake.puddle_sprite > 0) {
        const PuddleSprite* sprite = &sprite_data.puddle[snake.puddle_sprite];
        draw_sprite(
            snake.puddle_center.x - PUDDLE_WIDTH / 2,
            snake.puddle_center.y - PUDDLE_WIDTH / 2,
            PUDDLE_WIDTH, PUDDLE_WIDTH, (&sprite->tex[0][0]));
    }
}

void draw_frame() {
    clear_frame(226);
    draw_game_puddles();
    draw_game_world();
    draw_game_text();
}

/* Called when game_screen is game_screen_gaming */
void handle_gaming_keycode(uint8_t keycode) {
    if (keycode == KEYCODE_ESCAPE) {
        snake.game_screen = game_screen_pause;
    }
    if (!snake.is_dying) {
        if (is_keycode_for_press_left(keycode) &&
            snake.cur_snake_direction != snake_direction_right) {
            snake.new_snake_direction = snake_direction_left;
        } else if (is_keycode_for_press_right(keycode) &&
            snake.cur_snake_direction != snake_direction_left) {
            snake.new_snake_direction = snake_direction_right;
        } else if (is_keycode_for_press_up(keycode) &&
            snake.cur_snake_direction != snake_direction_bottom) {
            snake.new_snake_direction = snake_direction_top;
        } else if (is_keycode_for_press_down(keycode) &&
            snake.cur_snake_direction != snake_direction_top) {
            snake.new_snake_direction = snake_direction_bottom;
        }
    }
}

/* return 1 if we are quitting */
int handle_incoming_keycode_after_halt(uint8_t keycode) {
    if (keycode == KEYCODE_SPACE) {
        snake.is_space_pressed = true;
    } else if (keycode == (KEYCODE_SPACE | 0x80)) {
        snake.is_space_pressed = false;
    }
    if (keycode == KEYCODE_Q && snake.game_screen != game_screen_gaming) {
        return 1;
    }
    if (snake.game_screen == game_screen_gaming) {
        handle_gaming_keycode(keycode);
    } else if (snake.game_screen == game_screen_pause) {
        if (keycode == KEYCODE_1 || (keycode == KEYCODE_ENTER && !snake.have_game)) {
            snake.game_screen = game_screen_select_map;
        } else if (keycode == KEYCODE_ESCAPE && snake.have_game) {
            snake.game_screen = game_screen_gaming;
        }
    } else if (snake.game_screen == game_screen_select_map) {
        if (keycode == KEYCODE_ESCAPE) {
            snake.game_screen = game_screen_pause;
        } else if (is_keycode_for_press_left(keycode)) {
            snake.selected_map_index--;
            if (snake.selected_map_index < 0)
                snake.selected_map_index = PLAYABLE_MAPS_COUNT - 1;
        } else if (is_keycode_for_press_right(keycode)) {
            snake.selected_map_index++;
            if (snake.selected_map_index >= PLAYABLE_MAPS_COUNT)
                snake.selected_map_index = 0;
        } else if (keycode == KEYCODE_ENTER) {
            snake.game_screen = game_screen_select_apple_count;
        }
    } else if (snake.game_screen == game_screen_select_apple_count) {
        if (keycode == KEYCODE_ESCAPE) {
            snake.game_screen = game_screen_select_map;
        } else if (is_keycode_for_press_left(keycode)) {
            if (snake.gamemode_apples_count > 1)
                snake.gamemode_apples_count--;
        } else if (is_keycode_for_press_right(keycode)) {
            if (snake.gamemode_apples_count < SNAKE_GAMEMODE_MAX_APPLES)
                snake.gamemode_apples_count++;
        } else if (keycode == KEYCODE_ENTER) {
            start_snake_game();
        }
    }
    return 0;
}

/* Time flows only in gaming mode. This function can call frame drawing */
void handle_time_difference(uint32_t time_diff) {
    if (snake.game_screen != game_screen_gaming)
        return;
    if (snake.waiting_reason == waiting_reason_postmortum)
        return;
    snake.waiting_time += time_diff;
    uint32_t target_required_time;
    if (snake.is_time_sped_up) {
        if (snake.waiting_reason == waiting_reason_step) {
            target_required_time = WALKING_ANIM_TIME_SLOW;
        } else {
            target_required_time = HATCHING_ANIM_TIME_SLOW;
        }
    } else {
        if (snake.waiting_reason == waiting_reason_step) {
            target_required_time = WALKING_ANIM_TIME_FAST;
        } else {
            target_required_time = HATCHING_ANIM_TIME_FAST;
        }
    }
    if (snake.waiting_time > target_required_time) {
        snake.waiting_time -= target_required_time;
        if (snake.waiting_reason == waiting_reason_step) {
            ivec2 tile_pos_ahead = world_walk_direction(
                snake.snake_head, snake.new_snake_direction);
            tile_t tile_ahead = get_tile(tile_pos_ahead);
            /* Processing collisions */
            if (tile_ahead == tile_apple) {
                snake.ghost_apples[tile_pos_ahead.x][tile_pos_ahead.y] = 1;
            } else if (18 <= tile_ahead && tile_ahead <= 49) {
                snake.waiting_reason = waiting_reason_postmortum;
                snake.puddle_center = get_puddle_center_for_contact(
                    snake.snake_head, snake.new_snake_direction);
                snake.puddle_sprite = 0;
                return;
            } else if (2 <= tile_ahead && tile_ahead <= 17) {
                snake.is_dying = true;
                snake.puddle_center = get_puddle_center_for_contact(
                    snake.snake_head, snake.new_snake_direction);
                if (snake.puddle_sprite + 1 < PUDDLE_SPRITES) {
                    snake.puddle_sprite++;
                }
            }
            /* normal stuff */
            /* Step 1 */
            ivec2 old_head_pos = snake.snake_head;
            if (tile_ahead == tile_empty || tile_ahead == tile_apple) {
                set_tile(tile_pos_ahead,
                    construct_head_snake_tile(snake.new_snake_direction));
                snake.snake_head = tile_pos_ahead;
            }
            /* Step 2 */
            set_tile(old_head_pos, construct_snake_tile(
                get_opposite_direction(snake.cur_snake_direction), snake.new_snake_direction));
            snake.cur_snake_direction = snake.new_snake_direction;

            /* Steps 3... */
            if (is_tail_pupa(get_tile(snake.snake_tail))) {
                /* Step 3a */
                snake_direction_t pupa_dir = get_zero_pupa_destination(get_tile(snake.snake_tail));
                ivec2 penultimate_pos = world_walk_direction(snake.snake_tail, pupa_dir);
                set_tile(snake.snake_tail, tile_empty);
                /* Step 4a */
                snake_direction_t penultimate_part_dir = get_snake_destination(get_tile(penultimate_pos));
                set_tile(penultimate_pos, construct_zero_pupa(penultimate_part_dir));
                snake.snake_tail = penultimate_pos;
                /* WARNING: we updated snake_tail by moving pupa forward, we
                 * WARNING: should check if we moved onto a ghost apple */
                // check, this is important. This is the only place where we move pupa to a new pos
                // we check for ghost apples. Clear ghost apples and enter
                // p1-waiting state (instead of remaining in step awaiting state)
                if (snake.ghost_apples[penultimate_pos.x][penultimate_pos.y]) {
                    snake.ghost_apples[penultimate_pos.x][penultimate_pos.y] = 0;

                    syscall(SYS_set_beep, 5000);
                    snake.waiting_reason = waiting_reason_p1;
                    /* Nothing changed on screen because we need to wait even
                     * for the first stage of hatching.
                     * We could go to p1 immediately, though */
                }
            } else {
                snake_direction_t tail_dir = get_snake_destination(get_tile(snake.snake_tail));
                set_tile(snake.snake_tail, construct_zero_pupa(tail_dir));

                syscall(SYS_set_beep, 3000);
                snake.waiting_reason = waiting_reason_m1;
            }

            /* If we went with route 3a, pupa has moved and we definitely can
             * place an apple. But if it had not and we went through route 3b,
             * well, okay, we just won't have a free space for apple */
            if (tile_ahead == tile_apple) {
                place_random_apple();
            }
        } /* But there are more animation
        targets that can finish, other than 'step' */
        else if (snake.waiting_reason == waiting_reason_p1) {
            snake.waiting_reason = waiting_reason_p2;
        } else if (snake.waiting_reason == waiting_reason_p2) {
            snake.waiting_reason = waiting_reason_cross;
        } else if (snake.waiting_reason == waiting_reason_cross) {
            /* Finished pupa hatching */
            snake_direction_t tail_dir = get_zero_pupa_destination(get_tile(snake.snake_tail));
            set_tile(snake.snake_tail, construct_zero_pupa(tail_dir));
            syscall(SYS_set_beep, 0);
            snake.waiting_reason = waiting_reason_step;
        } else if (snake.waiting_reason == waiting_reason_m1) {
            snake.waiting_reason = waiting_reason_cross;
        } else if (snake.waiting_reason == waiting_reason_zero_pupa) {
            /* Finished pupa regrowing */
            syscall(SYS_set_beep, 0);
            snake.waiting_reason = waiting_reason_step;
        }
    }
}

void after_awake_action(uint32_t time_diff) {
    handle_time_difference(time_diff);
    snake.is_time_sped_up = false;
    draw_frame();
    syscall(SYS_swap_frame, (uintptr_t)frame);
}

int main(void) {
    init_snake();
    syscall(SYS_switch_to_graphics, 0);

    uint32_t prev_time = time_ms();
    while (1) {
        /* Returned from halt, we can enjoy keyboard input and animation progress*/
        for (int ch;(ch = syscall(SYS_getc, 0)) >= 0;) {
            int ret = handle_incoming_keycode_after_halt((uint8_t)ch);
            if (ret == 1)
                goto quit;
        }
        /* As an additional benefit, we can check if is_space_pressed here */
        if (snake.is_space_pressed) {
            snake.is_time_sped_up = true;
        }
        /* snake.is_time_sped_up will be relevant when checking animation end */

        uint32_t current_time = time_ms();
        after_awake_action(current_time - prev_time);

        prev_time = current_time;
        syscall(SYS_halt, 0);

    }
    quit:
    syscall(SYS_switch_to_text, 0);
    syscall(SYS_puts, (uintptr_t)"Quit from game\n");
    return 0;
}