#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <time.h>

enum {
  BOARD_SIZE = 10,
};

struct state {
    char board[BOARD_SIZE][BOARD_SIZE];
    int game_over;
};

struct position {
    int x;
    int y;
};

enum orientation {
  O_VERTICAL,
  O_HORIZONTAL
};

struct boat {
    enum orientation orientation;

    /** left upper corner */
    struct position position;

    int length;
};

struct position read_position(void);

struct boat generate_boat(int length);

struct state generate_state(void);

void display_state(struct state state);

int valid_position(struct position p);

/**
 * Simulates one step of battleship.
 *
 * Performs the following steps:
 *
 * - apply hit to board
 * - check sunken ships
 * - check game over
 */
void update_state(struct state * state, struct position hit);

enum target {
   T_WATER,
   T_BOAT,
   T_COMPLETE_BOAT,
};

enum target check_hit(struct state state, struct position hit);

int main(void) {
    srand(time(NULL));

    struct state state = generate_state();

    while (!state.game_over) {
        display_state(state);

        struct position hit = read_position();

        /* game logic */
        update_state(&state, hit);
    }
}

struct position read_position(void) {
    printf("enter coordinate: ");
    while (1) {
        char* line = NULL;
        size_t size = 0;
        getline(&line, &size, stdin);
        fflush(stdout);

        struct position position;
        char col;
        sscanf(line, "%c%d", &col, &position.y);
        free(line);

        position.x = tolower(col) - 'a';
        if (valid_position(position)) {
            return position;
        }

        puts("invalid input!");
    }
}

struct position random_position(void) {
    struct position p;
    p.x = rand() % BOARD_SIZE;
    p.y = rand() % BOARD_SIZE;
    return p;
}

enum orientation random_orientation(void) {
    return (rand() % 2);
}

struct boat generate_boat(int length) {
    struct boat b;
    b.length = length;
    b.position = random_position();
    b.orientation = random_orientation();
    return b;
}

int valid_position(struct position p) {
    return (p.x >= 0) && (p.x < BOARD_SIZE) && (p.y >= 0) && (p.y < BOARD_SIZE);
}

int place_boat(struct state * state, struct boat boat, char c) {
    int dx = (boat.orientation == O_VERTICAL) ? 1 : 0;
    int dy = (boat.orientation == O_HORIZONTAL) ? 1 : 0;

    struct position curpos = boat.position;
    for (int i = 0; i < boat.length; ++i) {
        if (!valid_position(curpos)) return 0;
        if (state->board[curpos.y][curpos.x] != 0) return 0;

        if (c) {
            state->board[curpos.y][curpos.x] = c;
        }

        curpos.x += dx;
        curpos.y += dy;
    }

    return 1;
}

/* const int BOAT_LENGTHS[] = { 5, 4, 4, 3, 3, 3, 2, 2, 2, 2 }; */
const int BOAT_LENGTHS[] = {1};

struct state
generate_state(void) {
  struct state state;

  memset(state.board, 0, BOARD_SIZE*BOARD_SIZE);
  state.game_over = 0;

  // generate some boats
  char boat_char = 'A';
  for (size_t i = 0; i < sizeof(BOAT_LENGTHS) / sizeof(BOAT_LENGTHS[0]); ++i) {
      int length = BOAT_LENGTHS[i];
      struct boat boat;
      do {
          boat = generate_boat(length);
      } while(!place_boat(&state, boat, '\0'));
      place_boat(&state, boat, boat_char);
      boat_char++;
  }

  return state;
}

void display_state(struct state state) {
    for (int y = 0; y < BOARD_SIZE; ++y) {
        for (int x = 0; x < BOARD_SIZE; ++x) {
            if (state.board[y][x]) {
                printf("%c", state.board[y][x]);
            } else {
                printf("~");
            }
        }
        printf("\n");
    }
    puts("---");
}


enum target check_hit(struct state state, struct position pos) {
  char ship = state.board[pos.y][pos.x];

  // check if we hit anything
  if (ship == 0) return T_WATER;
  ship = toupper(ship);

  int count = 0;
  for (int y = 0; y < BOARD_SIZE; ++y) {
    for (int x = 0; x < BOARD_SIZE; ++x) {
      if (state.board[y][x] == ship) {
        count += 1;
      }
    }
  }

  return (count > 1) ? T_BOAT : T_COMPLETE_BOAT;
}

void sink_ship(struct state * state, struct position pos) {
  char ship = state->board[pos.y][pos.x];
  for (int x = 0; x < BOARD_SIZE; ++x) {
    for (int y = 0; y < BOARD_SIZE; ++y) {
      if (ship == toupper(state->board[y][x])) {
        state->board[y][x] = '#';
      }
    }
  }
}

void update_state(struct state * state, struct position pos) {
  enum target target = check_hit(*state, pos);

  // update board
  switch (target) {
    case T_BOAT:
      state->board[pos.y][pos.x] = tolower(state->board[pos.y][pos.x]);
      break;
    case T_COMPLETE_BOAT: {
      sink_ship(state, pos);
      break;
    }
    default:
      state->board[pos.y][pos.x] = '*';
      break;
  }

  // check for game over
  int letter_count = 0;
  for (int x = 0; x < BOARD_SIZE; ++x) {
    for (int y = 0; y < BOARD_SIZE; ++y) {
      if (isalpha(state->board[y][x])) {
        letter_count += 1;
      }
    }
  }
  state->game_over = (letter_count == 0);
}