update.ts

import {
  Scope,
  EventStream,
  EventStreamSeed,
  isEventStreamSeed,
  isPropertySeed,
  Property,
  PropertySeed,
  isScope,
} from "./abstractions"
import { merge } from "./merge"
import { scan } from "./scan"
import { map } from "./map"
import { applyScopeMaybe } from "./applyscope"
import { toString } from "./tostring"
import { rename } from "./util"

export type UpdateTrigger<T> = EventStream<T> | EventStreamSeed<T>
type UpdateParam<T> = UpdateTrigger<T> | Property<T>

/**
 *  [Update](#update) pattern consisting of a single EventStream and a accumulator function.
 */
export type UpdatePattern1<I1, O> = [
  UpdateTrigger<I1>,
  O | ((acc: O, a: I1) => O)
]
/**
 *  [Update](#update) pattern consisting of 2 Observables and an accumulrator function.
 */
export type UpdatePattern2<I1, I2, O> = [
  UpdateTrigger<I1>,
  Property<I1>,
  O | ((acc: O, a: I1, b: I2) => O)
]
/**
 *  [Update](#update) pattern consisting of 3 Observables and an accumulrator function.
 */
export type UpdatePattern3<I1, I2, I3, O> = [
  UpdateTrigger<I1>,
  Property<I1>,
  Property<I3>,
  O | ((acc: O, a: I1, b: I2, c: I3) => O)
]
/**
 *  [Update](#update) pattern consisting of 4 Observables and an accumulrator function.
 */
export type UpdatePattern4<I1, I2, I3, I4, O> = [
  UpdateTrigger<I1>,
  Property<I1>,
  Property<I3>,
  Property<I4>,
  O | ((acc: O, a: I1, b: I2, c: I3, d: I4) => O)
]
/**
 *  [Update](#update) pattern consisting of 5 Observables and an accumulrator function.
 */
export type UpdatePattern5<I1, I2, I3, I4, I5, O> = [
  UpdateTrigger<I1>,
  Property<I1>,
  Property<I3>,
  Property<I4>,
  Property<I5>,
  O | ((acc: O, a: I1, b: I2, c: I3, d: I4, e: I5) => O)
]
/**
 *  [Update](#update) pattern consisting of 6 Observables and an accumulrator function.
 */
export type UpdatePattern6<I1, I2, I3, I4, I5, I6, O> = [
  UpdateTrigger<I1>,
  Property<I1>,
  Property<I3>,
  Property<I4>,
  Property<I5>,
  Property<I6>,
  O | ((acc: O, a: I1, b: I2, c: I3, d: I4, e: I5, f: I6) => O)
]

/**
 *  [Update](#update) pattern type, allowing up to 6 sources per pattern.
 */
export type UpdatePattern<O> =
  | UpdatePattern1<any, O>
  | UpdatePattern2<any, any, O>
  | UpdatePattern3<any, any, any, O>
  | UpdatePattern4<any, any, any, any, O>
  | UpdatePattern5<any, any, any, any, any, O>
  | UpdatePattern6<any, any, any, any, any, any, O>

/**
 Creates a Property from an initial value and updates the value based on multiple inputs.
 The inputs are defined similarly to [`Bacon.when`](#bacon-when), like this:

 ```js
 var result = Bacon.update(
 initial,
 [x,y,z, (previous,x,y,z) => { ... }],
 [x,y,   (previous,x,y) => { ... }])
 ```

 As input, each function above will get the previous value of the `result` Property, along with values from the listed Observables.
 The value returned by the function will be used as the next value of `result`.

 Just like in [`Bacon.when`](#when), only EventStreams will trigger an update, while Properties will be just sampled.
 So, if you list a single EventStream and several Properties, the value will be updated only when an event occurs in the EventStream.

 Here's a simple gaming example:

 ```js
 let scoreMultiplier = Bacon.constant(1)
 let hitUfo = Bacon.interval(1000)
 let hitMotherShip = Bacon.later(10000)
 let score = Bacon.update(
 0,
 [hitUfo, scoreMultiplier, (score, _, multiplier) => score + 100 * multiplier ],
 [hitMotherShip, (score, _) => score + 2000 ]
 )
 ```

 In the example, the `score` property is updated when either `hitUfo` or `hitMotherShip` occur. The `scoreMultiplier` Property is sampled to take multiplier into account when `hitUfo` occurs.

 * @param initial
 * @param {UpdatePattern<Out>} patterns
 * @returns {Property<Out>}
 */
export function update<Out>(
  initial: Out,
  ...patterns: UpdatePattern<Out>[]
): PropertySeed<Out>
export function update<Out>(
  scope: Scope,
  initial: Out,
  ...patterns: UpdatePattern<Out>[]
): Property<Out>

export function update<Out>(...args: any[]): any {
  let scope: Scope | undefined
  let initial: Out
  let patterns: UpdatePattern<Out>[]
  if (isScope(args[0])) {
    scope = args[0]
    initial = args[1]
    patterns = args.slice(2)
  } else {
    scope = undefined
    initial = args[0]
    patterns = args.slice(1)
  }

  let mutators: EventStreamSeed<Mutation<Out>>[] = patterns.map((pattern) => {
    if (pattern.length < 2)
      throw Error(`Illegal pattern ${pattern}, length must be >= 2`)
    let sources: UpdateParam<Out>[] = pattern.slice(
      0,
      pattern.length - 1
    ) as any
    const trigger = sources[0]
    if (!isEventStreamSeed(trigger))
      throw Error(`Illegal pattern ${pattern}, must contain one EventStream`)
    const properties = sources.slice(1) as Property<any>[]
    for (let prop of properties) {
      if (!isPropertySeed(prop))
        throw Error(
          `Illegal pattern ${pattern}. After one EventStream the rest on the observables must be Properties`
        )
    }
    let combinator = pattern[pattern.length - 1] as (...args: any) => Out
    if (!(combinator instanceof Function)) {
      const constantValue = combinator
      combinator = () => constantValue
    }
    return map((v1) => {
      return (state: Out) => {
        const propValues = properties.map((p) => p.get())
        return combinator(state, v1, ...propValues)
      }
    })(trigger as EventStreamSeed<any>)
  })

  return rename(
    ["update", [initial, patterns]],
    applyScopeMaybe(
      scan<Mutation<Out>, Out>(initial, (state, mutation) => mutation(state))(
        merge(mutators)
      ),
      scope
    )
  )
}

type Mutation<V> = (prev: V) => V