'use client'

import posthog from 'posthog-js'

/**
 * Product analytics events, and the only way the app sends them.
 *
 * PostHog runs in cloud mode and on the demo instance; a self-hosted install
 * never starts it, and then nothing here sends anything.
 *
 * Calls made before PostHog has started are held and sent once it has. The
 * provider starts it in an effect in the root layout, and React runs a page's
 * effects before its layout's, so an event fired when a page mounts would
 * otherwise be dropped on every full page load.
 *
 * Names follow PostHog's guide: lowercase snake case, fixed strings,
 * `category:object_action` with a present-tense verb. Anything that varies
 * goes in a property, never in the name.
 */

export type AnalyticsEvent =
  /** A work order opened, with the layout it was drawn in. */
  | 'work_order:page_view'
  /** A browser moved between the classic and the overhauled work order page. */
  | 'work_order:layout_switch'
  /** The invitation to try the overhauled page closed without trying it. */
  | 'work_order:layout_invite_dismiss'

type Properties = Record<string, string | number | boolean | null>

type Pending =
  | { kind: 'capture'; event: AnalyticsEvent; properties?: Properties }
  | { kind: 'register'; properties: Properties }

/** A page opened and closed many times before PostHog starts, or on an install that never does. */
const MAX_PENDING = 20

let ready = false
const pending: Pending[] = []

function hold(item: Pending) {
  if (pending.length < MAX_PENDING) pending.push(item)
}

/** Sends one event, or holds it until PostHog has started. */
export function track(event: AnalyticsEvent, properties?: Properties): void {
  if (ready) posthog.capture(event, properties)
  else hold({ kind: 'capture', event, properties })
}

/**
 * Attaches properties to every later event from this browser, autocaptured
 * clicks and page views included (PostHog's super properties). For facts
 * about the browser rather than about one action: the layout it shows, say.
 */
export function registerAnalyticsProperties(properties: Properties): void {
  if (ready) posthog.register(properties)
  else hold({ kind: 'register', properties })
}

/** Called by the provider once PostHog has started: sends what was held, in order. */
export function analyticsStarted(): void {
  ready = true
  for (const item of pending.splice(0)) {
    if (item.kind === 'register') posthog.register(item.properties)
    else posthog.capture(item.event, item.properties)
  }
}