/**
 * The plugin row's client-facing knobs, fetched once per page.
 *
 * The client bundle ships statically and never sees the row config, so the
 * host republishes the client-relevant subset at {@link CLIENT_CONFIG_ROUTE}
 * (src/index.ts). Two effects read it — turn-fold's desktop switch and
 * keyboard-avoid's fallback tuning — so the request is memoized here rather
 * than fired once per reader.
 *
 * Defaults live in THIS file, not in the host: the route omits a knob the
 * row never set, so there is exactly one place each default is written and
 * no way for the two halves to drift apart on the value. The host's job is
 * only to validate and clamp what a user actually typed.
 *
 * Every read is total — a failed request, a non-JSON body, or a garbage
 * value all fall back to the defaults rather than throwing into an effect.
 */

/** Mirror of src/index.ts CLIENT_CONFIG_ROUTE (client tsconfig cannot reach it). */
export const CLIENT_CONFIG_ROUTE = '/_dsh/mobile-nav/client-config'

/**
 * Tuning for the estimated-lift path in effects/keyboard-avoid.ts — the
 * fallback for a keyboard the browser cannot see at all. There is nothing to
 * measure on those devices, so these are estimates, and estimates about
 * hardware need a knob: IME toolbars, foldables, and PWA shells all sit at
 * different heights, and the person holding the phone is the only one who
 * can see whether the composer cleared the keys.
 */
export interface KeyboardTuning {
  /** Share of the layout viewport the estimated lift starts from. */
  liftRatio: number
  /** Ceiling on that estimate, so a tall viewport cannot strand the composer mid-screen. */
  liftMaxPx: number
  /** Extra clearance above a keyboard the browser DID react to (Android only). */
  safetyPadPx: number
}

/** Shipped tuning: the values measured on the one reported device (issue #1,
 * WeType ~315 CSS px on an 858px viewport) plus the Android IME under-report
 * pad. Changing these changes the default for every install — a per-device
 * fix belongs in that install's plugin row instead. */
export const KEYBOARD_DEFAULTS: KeyboardTuning = {
  liftRatio: 0.42,
  liftMaxPx: 400,
  safetyPadPx: 15,
}

/** Everything the client half reads off the plugin row. */
export interface ClientConfig {
  /** Fold each turn's process at every width, not just below the phone breakpoint. */
  turnFoldDesktop: boolean
  keyboard: KeyboardTuning
}

/** One published number, or the shipped default when the row left it unset
 * (the route omits the key) or the body is not what it claims to be. */
function num(value: unknown, fallback: number): number {
  return typeof value === 'number' && Number.isFinite(value) ? value : fallback
}

/** Parse one route body. Exported for scripts/check-client-config.mjs. */
export function parseClientConfig(body: unknown): ClientConfig {
  const row: Record<string, unknown> = typeof body === 'object' && body !== null
    ? body as Record<string, unknown>
    : {}
  return {
    turnFoldDesktop: row['turnFoldDesktop'] === true,
    keyboard: {
      liftRatio: num(row['keyboardLiftRatio'], KEYBOARD_DEFAULTS.liftRatio),
      liftMaxPx: num(row['keyboardLiftMaxPx'], KEYBOARD_DEFAULTS.liftMaxPx),
      safetyPadPx: num(row['keyboardSafetyPadPx'], KEYBOARD_DEFAULTS.safetyPadPx),
    },
  }
}

let cached: Promise<ClientConfig> | undefined

/** The row config, fetched at most once per page load. Never rejects. */
export function clientConfig(): Promise<ClientConfig> {
  cached ??= fetch(CLIENT_CONFIG_ROUTE, { cache: 'no-store' })
    .then((res) => (res.ok ? res.json() as Promise<unknown> : undefined))
    .catch(() => undefined)
    .then(parseClientConfig)
  return cached
}