feast/src/game/ai.ts

import { Creature } from './creature'
import { Encounter, Action } from './combat'
import { LogEntry } from './interface'
import { PassAction } from './combat/actions'
import { NoPassDecider, NoReleaseDecider, ChanceDecider, NoSurrenderDecider } from './ai/deciders'

/**
 * A Decider determines how favorable an action is to perform.
 */
export interface Decider {
  decide: (encounter: Encounter, user: Creature, target: Creature, action: Action) => number;
}

export class AI {
  constructor (private deciders: Decider[]) {

  }

  decide (actor: Creature, encounter: Encounter): LogEntry {
    const options = encounter.combatants.flatMap(enemy => actor.validActions(enemy).map(action => ({
      target: enemy,
      action: action,
      weight: 1
    })))

    this.deciders.forEach(
      decider => options.forEach(
        option => { option.weight *= decider.decide(encounter, actor, option.target, option.action) }
      )
    )

    let total = options.reduce(
      (sum: number, option) => sum + option.weight,
      0
    )

    total *= Math.random()

    const chosen = options.find(
      option => {
        if (total < option.weight) {
          return true
        } else {
          total -= option.weight
          return false
        }
      }
    )

    if (chosen !== undefined) {
      return chosen.action.try(actor, chosen.target)
    }

    // if we filtered out EVERY action, we should just give up and pass

    return new PassAction().try(actor, actor)
  }
}

/**
 * The VoreAI tries to eat opponents, but only if the odds are good enough
 */
export class VoreAI extends AI {
  constructor () {
    super(
      [
        new NoReleaseDecider(),
        new NoSurrenderDecider(),
        new NoPassDecider(),
        new ChanceDecider()
      ]
    )
  }
}