Btreee

The extra e is for... error

Install

yarn add btreee

How to use

Start off by creating the root of your tree with a node. The root node must be one of leafNode, sequenceNode, selectorNode, inverterNode, or parallelNode.

Each "branch" of the tree must terminate with a leaf node that returns a STATUS.

Tree

• The main constructor/entry point for btreee
• Takes in a funciton that returns a single node.

sequenceNode

• Takes in a function that returns an array of nodes.
• Will keep running nodes until an explicit STATUS.FAILURE.
• Will return STATUS.SUCCESS is all nodes succeeded.
• Will return STATUS.FAILURE if any node failed.

selectorNode

• Takes in a function that returns an array of nodes.
• Will keep running nodes until an explicit STATUS.SUCCESS.
• Will return STATUS.SUCCESS is any node succeeded.
• Will return STATUS.FAILURE if all nodes failed.

leafNode

• Takes in a function that returns a STATUS.

inverterNode

• Takes in a node and inverts that nodes STATUS.

parallelNode

• Takes in a function that returns an array of nodes.
• Param 2 is the minimum amount of successes required to return STATUS.SUCCESS
• Param 3 is the minimum amount of failures required to return STATUS.FAILURE
• This will run all of the nodes given to it and evaluate once those are done

Basic Example

import { Tree, sequenceNode, selectorNode, leafNode, STATUS } from 'btreee'

const tree = new Tree()

// Set the root of the tree
tree.setRoot(
  // Run everything in array until fail
  () =>
    sequenceNode(() => [
      // If not hungry, fail and stop sequence
      leafNode(() => (amIHungry() ? STATUS.SUCCESS : STATUS.FAILURE)),

      // Run everything in array until fail
      sequenceNode(() => [
        // Run until a success
        selectorNode(() => [
          leafNode(() =>
            isThereSomethingIReallyWant() ? STATUS.SUCCESS : STATUS.FAILURE,
          ),
          leafNode(() => (isThereAnyFood() ? STATUS.SUCCESS : STATUS.FAILURE)),
          leafNode(() => (areThereDrinks() ? STATUS.SUCCESS : STATUS.FAILURE)),
        ]),

        // Only executes is previous node returned a success
        leafNode(() => eatOrDrink() && STATUS.SUCCESS),
      ]),
    ]),
)

// Executes the tree
tree.tick()

Complex Example

Let's assume we have an EvilNPC we want to give some behivors to. Here is the interface:

type Direction = 'forward' | 'backward'

interface EvilNPC {
  // Senses
  getHealth: () => number // 0-100
  feel: (
    direction: Direction,
  ) => {
    isEmpty: () => boolean
    isWall: () => boolean
    isUnit: () => boolean
    getUnit: () => {
      isEnemy: () => boolean
    }
  }

  // Actions
  walk: (direction: Direction) => void
  attack: (direction: Direction) => void
  pivot: () => void
  heal: () => void
}

Our goal is to have this npc seek out and kill the player. The game world is very rudimentary, there's only forward and backward.

Here's what our basic tree would look like. Start reading from the bottom up to get a better understanding. Below is flowchart.

import { Tree, sequenceNode, selectorNode, leafNode, STATUS } from 'btreee'

const evilNpc: EvilNPC = new EvilNPC()

// NPC State
const state: {
  health: number
  direction: Direction
} = {
  health: 100,
  direction: 'forward',
}

// Simple Helper Functions
const isSomethingThere = (direction: Direction) =>
  evilNpc.feel(direction).isEmpty() ? STATUS.FAILURE : STATUS.SUCCESS

const isSomethingInFrontOfMe = () => leafNode(() => isSomethingThere('forward'))
const isSomethingBehindMe = () => leafNode(() => isSomethingThere('backward'))

const isWallInFrontOfMe = () =>
  sequenceNode(() => [
    isSomethingInFrontOfMe(),
    leafNode(() =>
      evilNpc.feel('forward').isWall() ? STATUS.SUCCESS : STATUS.FAILURE,
    ),
  ])

const isUnitInFrontOfMe = () =>
  sequenceNode(() => [
    isSomethingInFrontOfMe(),
    leafNode(() =>
      evilNpc.feel('forward').isUnit() ? STATUS.SUCCESS : STATUS.FAILURE,
    ),
  ])

const isEnemyInFrontOfMe = () =>
  sequenceNode(() => [
    isUnitInFrontOfMe(),
    leafNode(() =>
      evilNpc.feel('forward').getUnit().isEnemy()
        ? STATUS.SUCCESS
        : STATUS.FAILURE,
    ),
  ])

const isWallBehindMe = () =>
  sequenceNode(() => [
    isSomethingBehindMe(),
    leafNode(() =>
      evilNpc.feel('backward').isWall() ? STATUS.SUCCESS : STATUS.FAILURE,
    ),
  ])

const isUnitBehindMe = () =>
  sequenceNode(() => [
    isSomethingBehindMe(),
    leafNode(() =>
      evilNpc.feel('backward').isUnit() ? STATUS.SUCCESS : STATUS.FAILURE,
    ),
  ])

const isEnemyBehindMe = () =>
  sequenceNode(() => [
    isUnitBehindMe(),
    leafNode(() =>
      evilNpc.feel('backward').getUnit().isEnemy()
        ? STATUS.SUCCESS
        : STATUS.FAILURE,
    ),
  ])

const shouldIHeal = () =>
  leafNode(() => (state.health <= 25 ? STATUS.SUCCESS : STATUS.FAILURE))

// Leaf Nodes / Actions
const walk = (direction: Direction) =>
  leafNode(() => (evilNpc.walk(direction), STATUS.SUCCESS))
const attack = (direction: Direction) =>
  leafNode(() => (evilNpc.attack(direction), STATUS.SUCCESS))
const pivot = () => {
  state.direction = state.direction === 'forward' ? 'backward' : 'forward'
  return leafNode(() => (evilNpc.pivot(), STATUS.SUCCESS))
}
const heal = () => leafNode(() => (evilNpc.heal(), STATUS.SUCCESS))

// Sequences
const hunter = () =>
  selectorNode(() => [
    selectorNode(() => [isEnemyBehindMe(), attack('backward')]),
    selectorNode(() => [isEnemyInFrontOfMe(), attack('forward')]),
  ])

const pivoter = () =>
  selectorNode(() => [
    sequenceNode(() => [isWallInFrontOfMe(), pivot()]),
    sequenceNode(() => [isWallBehindMe(), pivot()]),
  ])

const walker = () => sequenceNode(() => [pivoter(), walk(state.direction)])
const healer = () => sequenceNode(() => [shouldIHeal(), heal()])

const actions = () => selectorNode(() => [hunter(), walker(), healer()])
const preActions = () =>
  leafNode(() => ((state.health = evilNpc.getHealth()), STATUS.SUCCESS))

const root = () => sequenceNode(() => [preActions(), actions()])

const tree = new Tree()
tree.setRoot(root)

const tick = () =>
  process.nextTick(() => {
    tree.tick()
    tick()
  })