/*
 * Created by snapshot112 on 15/10/2025
 */

#define _POSIX_C_SOURCE 199309

#include "snake.h"

#include <ncurses.h>
#include <stdlib.h>
#include <time.h>
#include <pthread.h>
#include <unistd.h>

#include "../../engine/grid_game_engine.h"

#define CELL_EMPTY ' '
#define CELL_FOOD '$'
#define CELL_WALL '#'
#define DIRECTION_COUNT 4
#define OFFSET_X 6
#define OFFSET_Y 3

typedef enum {
    SNAKE_MOVE = 0,
    SNAKE_EAT = 1,
    SNAKE_DIE = 2
} snake_action;

typedef enum {
    DIRECTION_UP = 0,
    DIRECTION_RIGHT = 1,
    DIRECTION_DOWN = 2,
    DIRECTION_LEFT = 3
} direction;

// Snake globals
static direction PREVIOUS_DIRECTION;
static direction CURRENT_DIRECTION;
static coordinate SNAKE_HEAD;
static coordinate SNAKE_TAIL;

// Map globals
static coordinate RENDER_AT;
static coordinate MESSAGE_LOCATION = {0,0};
static int MAP_HEIGHT = 20;
static int MAP_WIDTH = 20;
static grid *GRID;
static pthread_mutex_t SNAKE_MUTEX;

/*
 * Create a snake body part.
 *
 * Input:
 * dir: the direction the body part should point to.
 *
 * Output:
 * a character representing that body part.
 */
static char get_body_part(const direction dir) {
    return (char)(dir + '0');
}

/*
 * Gets the direction of a body part.
 *
 * Input:
 * body_part: A part of the snake's body.
 *
 * Output:
 * The direction the next body part is pointing to.
 */
static direction get_body_part_direction(const char body_part) {
    return (direction)(body_part - '0');
}

/*
 * Create a grid for snake with a given height and width.
 *
 * Input:
 * height: The height of the map.
 * width:  The width of the map.
 *
 * Returns:
 * A pointer to the grid.
 */
static void create_grid(void) {
    const int grid_size = (MAP_WIDTH + 1) * MAP_HEIGHT + 1;
    char *map = malloc(grid_size * sizeof(char));
    if (map == NULL) {
        return;
    }

    for (int i = 1; i <= (MAP_WIDTH + 1) * MAP_HEIGHT; i++) {
        // Also subtract the null terminator
        const int bottom_line = i > grid_size - (MAP_WIDTH + 2);
        const int top_line = i < MAP_WIDTH + 1;

        const int line_position = modulo(i, MAP_WIDTH + 1);

        const int line_start = line_position == 1;
        const int line_end = line_position == MAP_WIDTH;

        const int newline = line_position == 0;

        if (newline) {
            map[i - 1] = '\n';
        } else if (top_line || bottom_line || line_start || line_end) {
            map[i - 1] = CELL_WALL;
        } else {
            map[i - 1] = CELL_EMPTY;
        }
    }

    map[grid_size - 1] = '\0';

    GRID = grid_create_from_string(map);

    free(map);
}

/*
 * Spawn a piece of food at an empty grid location.
 *
 * Side Effect:
 * One of the empty grid spaces gets replaced with a piece of food.
 */
static void generate_food(void) {
    coordinate empty_spots[MAP_HEIGHT * MAP_WIDTH];

    int available_spots = 0;

    for (int x = 0; x < MAP_WIDTH; x++) {
        for (int y = 0; y < MAP_HEIGHT; y++) {
            if (grid_fetch(GRID, x, y) == CELL_EMPTY) {
                const coordinate new_spot = {x, y};
                empty_spots[available_spots] = new_spot;
                available_spots++;
            }
        }
    }

    const coordinate food_location = empty_spots[modulo(rand(), available_spots)];

    grid_put(GRID, food_location.x, food_location.y, CELL_FOOD);
}

/*
 * Setup the game(map)
 *
 * Output:
 * A pointer to the game grid.
 *
 * Side Effects:
 * Seed random with the current time.
 * (Re)set the global variables.
 * initialize the mutex
 *
 */
static void initialize(void) {
    // Seed random.
    srand(time(NULL));

    // Create the grid.
    create_grid();
    if (GRID == NULL) {
        return;
    }

    // Set globals.
    CURRENT_DIRECTION = DIRECTION_DOWN;
    PREVIOUS_DIRECTION = DIRECTION_DOWN;
    SNAKE_HEAD = (coordinate){.x = grid_width(GRID) / 2, .y = grid_height(GRID) / 2};
    SNAKE_TAIL = SNAKE_HEAD;
    RENDER_AT = (coordinate){.x = OFFSET_X, .y = OFFSET_Y};
    MESSAGE_LOCATION = (coordinate){.x = RENDER_AT.x, .y = RENDER_AT.y + grid_height(GRID) + 2};

    // Create the first body part and spawn the first piece of food.
    grid_put(GRID, SNAKE_HEAD.x, SNAKE_HEAD.y, get_body_part(CURRENT_DIRECTION));
    generate_food();

    pthread_mutex_init(&SNAKE_MUTEX, NULL);
}

/*
 * Checks what happens when the snake moves over a given char.
 *
 * Input:
 * c: The char to check.
 *
 * Returns:
 * The snake will move forward: SNAKE_MOVE
 * The snake will eat an apple: SNAKE_EAT
 * The snake will die:          SNAKE_DIE
 */
static snake_action collision_check(const char c) {
    if (c == CELL_EMPTY) {
        return SNAKE_MOVE;
    }

    if (c == CELL_FOOD) {
        return SNAKE_EAT;
    }

    return SNAKE_DIE;
}

/*
 * Move the snake to a given location
 *
 * Input:
 * new_location: The location the snake should move to.
 *
 * Side effects:
 * In case nothing is encountered: The snake moves to the new location.
 * In case an obstacle is encountered (wall or part of the snake): The snake dies.
 * In case a piece of food is encountered: The snake eats the food and grows by 1.
 *
 * Note:
 * Moving to a location the snake can't reach is undefined behaviour.
 */
static void update_snake(const coordinate new_location) {
    const snake_action action = collision_check(grid_fetch(GRID, new_location.x, new_location.y));

    if (action == SNAKE_DIE) {
        grid_put_state(GRID, STATE_VERLOREN);
        return;
    }

    if (action == SNAKE_MOVE) {
        coordinate new_tail = SNAKE_TAIL;

        switch (get_body_part_direction(grid_fetch(GRID, SNAKE_TAIL.x, SNAKE_TAIL.y))) {
            case DIRECTION_UP:
                new_tail.y--;
                break;
            case DIRECTION_RIGHT:
                new_tail.x++;
                break;
            case DIRECTION_DOWN:
                new_tail.y++;
                break;
            case DIRECTION_LEFT:
                new_tail.x--;
                break;
        }

        grid_put(GRID, SNAKE_TAIL.x, SNAKE_TAIL.y, CELL_EMPTY);
        SNAKE_TAIL = new_tail;
    }

    // New head placed after tail moves. It can occupy the empty space created by the tail moving.
    grid_put(GRID, new_location.x, new_location.y, get_body_part(CURRENT_DIRECTION));
    SNAKE_HEAD = new_location;
    PREVIOUS_DIRECTION = CURRENT_DIRECTION;

    if (action == SNAKE_EAT) {
        generate_food();
    }
}

/*
 * Handle snake movement.
 *
 * Input:
 * NULL, this signature is so it can be run as a thread.
 *
 * Returns:
 * NULL when finished
 *
 * Side Effects:
 * While the game is running, it moves the snake forward every 0.25 seconds and updates the game
 * state accordingly.
 *
 * In case an obstacle is encountered (wall or part of the snake): It dies.
 * In case a piece of food is encountered: It eats the apple and grows by 1.
 */
static void *snake_move(void *arg) {
    struct timespec timer;
    timer.tv_sec = 0;
    timer.tv_nsec = 250000000L; // Snake moves every 0.25 seconds.

    while (grid_fetch_state(GRID) == STATE_AAN_HET_SPELEN) {
        nanosleep(&timer, NULL);
        pthread_mutex_lock(&SNAKE_MUTEX);
        coordinate new_location = SNAKE_HEAD;
        switch (CURRENT_DIRECTION) {
            case DIRECTION_UP:
                new_location.y--;
                break;
            case DIRECTION_RIGHT:
                new_location.x++;
                break;
            case DIRECTION_DOWN:
                new_location.y++;
                break;
            case DIRECTION_LEFT:
                new_location.x--;
                break;
        }

        update_snake(new_location);
        show_grid_on_offset(GRID, OFFSET_X, OFFSET_Y);
        pthread_mutex_unlock(&SNAKE_MUTEX);
    }
    return NULL;
}

/*
 * Turn the snake in the given direction.
 *
 * Input:
 * direction: The direction the snake should turn to.
 *
 * Side effects:
 * If the snake is able to turn in the given direction:
 *          The snake's direction gets updated with the new value.
 * If the snake is unable to turn in the given direction:
 *          The snake's direction remains unchanged.
 */
static void turn_snake(const direction dir) {
    // If the snake has a length of 1, it is able to turn around on the spot.
    if ((direction)modulo((int)dir + 2, DIRECTION_COUNT) == PREVIOUS_DIRECTION
        && !same_coordinate(SNAKE_HEAD, SNAKE_TAIL)) {
        return;
    }
    grid_put(GRID, SNAKE_HEAD.x, SNAKE_HEAD.y, get_body_part(dir));
    CURRENT_DIRECTION = dir;
    show_grid_on_offset(GRID, OFFSET_X, OFFSET_Y);
}

/*
 * Handle user input.
 *
 * Input:
 * NULL, this signature is so it can be run as a thread.
 *
 * Returns:
 * NULL when finished
 *
 * Side Effects:
 * While the game is running, it constantly updates the direction the snake is pointing to
 * based on user input.
 *
 * In case ESCAPE or BACKSPACE is pressed it quits the game.
 */
static void *user_input(void *arg) {
    while (grid_fetch_state(GRID) == STATE_AAN_HET_SPELEN) {
        timeout(1);
        const int c = getch();
        pthread_mutex_lock(&SNAKE_MUTEX);
        switch (c) {
            case KEY_UP: // fallthrough
            case 'w':
            case 'W':
                turn_snake(DIRECTION_UP);
                break;
            case KEY_DOWN: // fallthrough
            case 's':
            case 'S':
                turn_snake(DIRECTION_DOWN);
                break;
            case KEY_LEFT: // fallthrough
            case 'a':
            case 'A':
                turn_snake(DIRECTION_LEFT);
                break;
            case KEY_RIGHT: // fallthrough
            case 'd':
            case 'D':
                turn_snake(DIRECTION_RIGHT);
                break;
            case KEY_BACKSPACE:
            case KEY_ESCAPE:
                grid_put_state(GRID, STATE_QUIT);
                break;
        }
        pthread_mutex_unlock(&SNAKE_MUTEX);
    }
    return NULL;
}

/*
 * Waits for the user to press their SPACEBAR before starting the game.
 *
 * Side Effects:
 * If the user presses backspace or escape, the whole game quits.
 */
static void wait_for_start(void) {
    const char start_message[] = "Press SPACEBAR to start playing.";
    const char empty_message[] = "                                ";
    mvaddstr(MESSAGE_LOCATION.y, MESSAGE_LOCATION.x, start_message);

    grid_put_state(GRID, STATE_AAN_HET_SPELEN);

    for (int c = getch(); c != ' '; c = getch()) {
        switch (c) {
            case KEY_BACKSPACE:
            case KEY_ESCAPE:
                grid_put_state(GRID, STATE_QUIT);
                mvaddstr(MESSAGE_LOCATION.y, MESSAGE_LOCATION.x, empty_message);
                return;
        }
    }

    // Cleanup the start playing message.
    mvaddstr(MESSAGE_LOCATION.y, MESSAGE_LOCATION.x, empty_message);
}

/*
 * Cleanup the snake memory
 *
 * Side effects:
 * Frees all the memory used by the snake
 */
static void snake_cleanup(void) {
    pthread_mutex_destroy(&SNAKE_MUTEX);
    grid_cleanup(GRID);
}

void snake(void) {
    initialize();
    if (GRID == NULL) {
        return;
    }

    // Show game.
    erase();
    show_grid_on_offset(GRID, OFFSET_X, OFFSET_Y);

    wait_for_start();

    if (grid_fetch_state(GRID) == STATE_AAN_HET_SPELEN) {
        // Create and start necessary threads.
        pthread_t input_thread;
        pthread_t game_tick_thread;

        pthread_create(&input_thread, NULL, user_input, NULL);
        pthread_create(&game_tick_thread, NULL, snake_move, NULL);

        // Wait until the gamestate is no longer STATE_AAN_HET_SPELEN
        pthread_join(game_tick_thread, NULL);
        pthread_join(input_thread, NULL);
    }

    game_exit_message(GRID, MESSAGE_LOCATION);

    snake_cleanup();
}