Observing and interfering with player-world interaction

maybe-observer.js

'use strict';

/**
 * Represents a single player
 */
let Player = function(x, y, health) {
  this.events = {
    encroach: [],
    enter: [],
    exit: []
  };

  this.position = {
    x: x,
    y: y
  };

  this.health = health;
};

/**
 * Executes a callback when a certain type of event fires
 */
Player.prototype.addObserver = function(event, callback) {
  this.events[event].push(callback);
};

/**
 * Removes the specified observer
 */
Player.prototype.removeObserver = function(event, callback) {
  let observers = this.events[event];

  for (let i = 0; i < observers.length; i++) {
    if (observers[i] === callback) {
      observers.splice(i, 1);
      break;
    }
  }
};

Player.prototype.modifyHealth = function(health_mod) {
  this.health += health_mod;

  if (this.health <= 0) {
    console.log('PLAYER HAS DIED.');
    return true;
  }

  return false;
};

/**
 * Returns displayable information about our player
 */
Player.prototype.toString = function() {
  return "X: " + this.position.x + ", Y: " + this.position.y + ", HP: " + this.health;
};

/**
 * Attempts to move a player
 */
Player.prototype.move = function(x_offset, y_offset) {
  if (this.health <= 0) {
    return console.log('CANNOT MOVE, PLAYER IS DEAD');
  }

  let block = false;

  for (let handler of this.events.exit) {
    let gonnaBlock = handler(this.position);

    if (gonnaBlock) {
      block = true;
    }
  }

  if (this.health <= 0) { return; }

  if (block) { console.log('NO EXIT'); return console.log(this.toString()); }

  let target = {
    x: this.position.x + x_offset,
    y: this.position.y + y_offset
  };

  console.log('ATTEMPT MOVE TO X: ' + target.x + ', Y: ' + target.y)

  for (let handler of this.events.encroach) {
    let gonnaBlock = handler(target);

    if (gonnaBlock) {
      block = true;
    }
  }

  if (this.health <= 0) { return; }

  if (block) { console.log('NO ENCROACH'); return console.log(this.toString()); }

  for (let handler of this.events.enter) {
    handler(target);
  }

  if (this.health <= 0) { return; }

  this.position = target;

  console.log(this.toString());
};


/**
 * Keeps track of a collection of enemies
 */
let Enemies = function() {
  this.enemies = [];
};

/**
 * Adds an enemy to the collection
 */
Enemies.prototype.add = function(x, y, attack) {
  this.enemies.push({
    x: x,
    y: y,
    attack: attack
  });
};

/**
 * Observes the player for encroach events (the player attempts to collide with enemy)
 */
Enemies.prototype.observe = function(player) {
  const self = this;

  player.addObserver('encroach', function(coord) {
    let block = false;

    for (let enemy of self.enemies) {
      if (enemy.x === coord.x && enemy.y === coord.y) {
        block = true;
        //enemy.health -= player.attack;
        player.modifyHealth(-1 * enemy.attack);
      }
    }

    return block;
  });
};


/**
 * A collection of items
 */
let Items = function() {
  this.items = [];
};

/**
 * Adds a new item
 */
Items.prototype.add = function(x, y, health_mod) {
  this.items.push({
    x: x,
    y: y,
    health_mod: health_mod
  });
};

/**
 * Tracks if a player enters a tile with an item, applies item health mod and destroys item
 */
Items.prototype.observe = function(player) {
  const self = this;

  player.addObserver('enter', function(coord) {
    for (let i = 0; i < self.items.length; i++) {
      let item = self.items[i];

      if (item.x === coord.x && item.y === coord.y) {
        console.log('ITEM AFFECT HEALTH', item.health_mod);
        player.modifyHealth(item.health_mod);
        self.items.splice(i, 1);
      }
    }

    return false;
  });
};


/**
 * A collection of traps
 */
let Traps = function() {
  this.traps = [];
};

/**
 * Adds a new trap
 *
 * @param damage The amount of damage caused to the player
 * @param stuck Ratio of difficulty of player leaving trap
 */
Traps.prototype.add = function(x, y, damage, stuck) {
  this.traps.push({
    x: x,
    y: y,
    damage: damage,
    stuck: stuck
  });
};

/**
 * If a player enters a trap, they will receive damage for the trap
 * If a player exits a trap, we check to see if stuck, preventing them from leaving and damaging
 */
Traps.prototype.observe = function(player) {
  const self = this;

  player.addObserver('enter', function(coord) {
    for (let trap of self.traps) {
      if (trap.x === coord.x && trap.y === coord.y) {
        player.modifyHealth(-1 * trap.damage);
        console.log('TRAP DAMAGE', trap.damage);
      }
    }

    return false;
  });

  player.addObserver('exit', function(coord) {
    let block = false;

    for (let trap of self.traps) {
      if (trap.x === coord.x && trap.y === coord.y && trap.stuck >= Math.random()) {
        console.log('TRAP STUCK', trap.stuck, trap.damage);
        player.modifyHealth(-1 * trap.damage);
        block = true;
      }
    }

    return block;
  });
};


// Initialize game

let enemies = new Enemies();
let items = new Items();
let traps = new Traps();

let player = new Player(10, 10, 100);

enemies.observe(player);
items.observe(player);
traps.observe(player);

enemies.add(9, 10, 5); // Gnoll
enemies.add(11, 10, 25); // Dragon

items.add(10, 9, 10); // Potion
items.add(10, 8, -50); // Poison

traps.add(10, 6, 10, 0.0); // Explosion
traps.add(10, 5, 2, 0.9); // Tar Pit

// Player moves around a bit

player.move(-1, 0); // West, into Gnoll
player.move(-1, 0); // West, into Gnoll
player.move(-1, 0); // West, into Gnoll

player.move(1, 0); // East, into Dragon

player.move(0, -1); // North, into Potion
player.move(0, -1); // North, into Poison
player.move(0, -1); // North
player.move(0, -1); // North, into Explosion
player.move(0, -1); // North, into Tar Pit

player.move(1, 0); // East
player.move(1, 0); // East
player.move(1, 0); // East
player.move(1, 0); // East
player.move(1, 0); // East

console.log("FINISHED.", player.toString());

ATTEMPT MOVE TO X: 9, Y: 10
NO ENCROACH
X: 10, Y: 10, HP: 95
ATTEMPT MOVE TO X: 9, Y: 10
NO ENCROACH
X: 10, Y: 10, HP: 90
ATTEMPT MOVE TO X: 9, Y: 10
NO ENCROACH
X: 10, Y: 10, HP: 85
ATTEMPT MOVE TO X: 11, Y: 10
NO ENCROACH
X: 10, Y: 10, HP: 60
ATTEMPT MOVE TO X: 10, Y: 9
ITEM AFFECT HEALTH 10
X: 10, Y: 9, HP: 70
ATTEMPT MOVE TO X: 10, Y: 8
ITEM AFFECT HEALTH -50
X: 10, Y: 8, HP: 20
ATTEMPT MOVE TO X: 10, Y: 7
X: 10, Y: 7, HP: 20
ATTEMPT MOVE TO X: 10, Y: 6
TRAP DAMAGE 10
X: 10, Y: 6, HP: 10
ATTEMPT MOVE TO X: 10, Y: 5
TRAP DAMAGE 2
X: 10, Y: 5, HP: 8
TRAP STUCK 0.9 2
NO EXIT
X: 10, Y: 5, HP: 6
TRAP STUCK 0.9 2
NO EXIT
X: 10, Y: 5, HP: 4
TRAP STUCK 0.9 2
NO EXIT
X: 10, Y: 5, HP: 2
TRAP STUCK 0.9 2
PLAYER HAS DIED.
CANNOT MOVE, PLAYER IS DEAD
FINISHED. X: 10, Y: 5, HP: 0