import { todo } from './todo.js'
/** @import { Point, Input, Stream } from './types' */

/**
 * An event stream as a pure automaton (a Mealy machine).
 * `Stream<A> = { step: input => [outputs, nextStream] }`: feed one input, get the (possibly empty) array
 * of outputs it produced and the stream to use for the next input. Nothing is mutated, so a stream value
 * can be run any number of times with the same results.
 * Inputs: `{tag:'Time', t}`, `{tag:'KeyDown', key}`, `{tag:'KeyUp', key}`, and from Module 13 `{tag:'Click', x, y}`
 * (a mouse click, in canvas pixels). Every stream ignores the kinds of input it does not use.
 */

/** Emits the `key` of every KeyDown input; ignores everything else.
 * @type {Stream<string>} */
export const keyDowns = { step: () => todo('m08') }

/** Emits the `key` of every KeyUp input; ignores everything else.
 * @type {Stream<string>} */
export const keyUps = { step: () => todo('m08') }

/**
 * (m13) Emits `{x, y}` for every Click input; ignores everything else.
 * Given: nothing to write here. It is the third source, built exactly like your `keyDowns`.
 * @type {Stream<Point>}
 */
export const clicks = { step: (i) => [i.tag === 'Click' ? [{ x: i.x, y: i.y }] : [], clicks] }

/**
 * On `Time t`, emits every multiple `k*ms` with `last < k*ms <= t`, ascending, where `last` starts at 0
 * and becomes `t` afterwards. A big time jump can emit several values. Ignores key inputs.
 * Hint: write a private helper that carries `last`.
 * @type {(ms: number) => Stream<number>}
 */
export const interval = (ms) => todo('m08')

/** Apply `f` to every output of `s`.
 * @type {<A, B>(s: Stream<A>, f: (a: A) => B) => Stream<B>} */
export const map = (s, f) => todo('m08')

/** Keep only the outputs of `s` for which `p` is true.
 * @type {<A>(s: Stream<A>, p: (a: A) => boolean) => Stream<A>} */
export const filter = (s, p) => todo('m08')

/** Apply `f` to every output of `s`; `f` returns a value or `null`, and nulls are dropped.
 * @type {<A, B>(s: Stream<A>, f: (a: A) => B | null) => Stream<B>} */
export const filterMap = (s, f) => todo('m08')

/** Both streams step on every input; the outputs of `a` come before the outputs of `b`.
 * @type {<A>(a: Stream<A>, b: Stream<A>) => Stream<A>} */
export const merge = (a, b) => todo('m08')

/** Fold the outputs of `s` into an accumulator, starting from `z`; emits each new accumulator (not `z` itself).
 * @type {<A, B>(s: Stream<A>, f: (acc: B, a: A) => B, z: B) => Stream<B>} */
export const scan = (s, f, z) => todo('m08')

/**
 * Emit `v` once, before the outputs of the first step; later steps are unaffected.
 * Note: streams only act when an input arrives, so if no input ever arrives, `v` is never emitted.
 * @type {<A>(s: Stream<A>, v: A) => Stream<A>}
 */
export const startWith = (s, v) => todo('m08')

/**
 * (m10) Limit how far one Time input can move the clock that `s` sees, so a long silence (a background tab)
 * does not turn into hundreds of beats at once.
 * `s` gets a clock of its own, starting at 0. On `Time t` that clock advances by `t - last`, but by at most `maxGap`
 * and never by less than 0 (time does not run backwards), where `last` is the `t` of the previous Time input
 * (0 at the start). `s` is then stepped with `{tag:'Time', t: clock}`. Key inputs are passed to `s` unchanged.
 * Hint: a private helper that carries `last` and `clock`, like the one for `interval`.
 * @type {<A>(s: Stream<A>, maxGap: number) => Stream<A>}
 */
export const clampTime = (s, maxGap) => todo('m10')

/** Feed all inputs through the stream and collect every output, in order. A pure fold (reduce).
 * @type {<A>(s: Stream<A>, inputs: Input[]) => A[]} */
export const run = (s, inputs) => todo('m08')