import { useCallback, useEffect, useLayoutEffect, useMemo, useRef, useState } from 'react';
import { useAtom } from 'jotai';
import { curtainPinnedByTabAtom } from '../../state/mobilePagerHeader';
import {
  CHIP_GAP_PX,
  CHIP_ROW_PX,
  CURTAIN_BREATHER_PX,
  CURTAIN_SNAP_MS,
  SEARCH_FORM_BASE_PX,
  TABS_ROW_PX,
} from './geometry';

// Discrete snap stops for the curtain. The curtain's resting `top`
// is derived from this value plus the live finger drag delta. There
// is no separate «active vs peek» mode flag — the snap encodes both.
export type CurtainSnap =
  | 'closed' // curtain flush under tabs row; nothing peeking
  | 'peek' // both action chips (search + new chat) revealed
  | 'form-search' // full search form revealed
  | 'form-chat'; // full new-chat form revealed

export const isFormSnap = (snap: CurtainSnap): snap is 'form-search' | 'form-chat' =>
  snap === 'form-search' || snap === 'form-chat';

export const isPeekSnap = (snap: CurtainSnap): snap is 'peek' => snap === 'peek';

// Form kind currently rendered in the header. Stays set during the
// curtain's close transition so the form has content to slide behind;
// cleared by `acknowledgeClosed` after the snap settles at `closed`.
export type ActiveForm = 'search' | 'chat' | null;

export type CurtainState = {
  snap: CurtainSnap;
  // Per-tab pin overlay. Stored in `curtainPinnedByTabAtom` keyed by
  // the consumer-supplied `pinKey` so the lock survives the route-
  // driven listing-pane unmount when the user taps into a Room and
  // back. Each tab keeps its own pin (Direct/Channels/Bots are
  // independent).
  pinned: boolean;
  // Setter for the pinned overlay. Called by the gesture hook on
  // commit (drag-up-from-closed past threshold sets true; drag-down-
  // while-pinned past threshold sets false).
  setPinned: (next: boolean) => void;
  activeForm: ActiveForm;
  // Live finger delta in px. Added to the snap-derived resting top to
  // compute the curtain's visible top. Stays at 0 when no gesture is
  // in flight. Positive = finger pulled down (peek reveal); negative =
  // finger pulled up (close gesture).
  liveDragPx: number;
  // True while a touch gesture is in flight. Controls the curtain's
  // `top` transition: disabled while dragging (curtain tracks finger
  // 1:1), restored on release so the snap commit animates smoothly.
  isDragging: boolean;
  // Live measured height of the active form's outer; used to compute
  // the curtain's resting `top` when `snap === 'form-*'`. `null` while
  // no form is mounted.
  formHeightPx: number | null;
  // Ref pointing at the rendered form's outer — a ResizeObserver
  // watches this to feed `formHeightPx`. Consumer attaches it to the
  // form's wrapping element.
  formMeasureRef: React.RefObject<HTMLDivElement>;
  // Open a form. Sets `snap` and `activeForm` synchronously.
  open: (form: 'search' | 'chat') => void;
  // Close the curtain (raise it back to `closed`). Keeps `activeForm`
  // set until the snap transition lands so the form stays mounted
  // during the slide-up.
  close: () => void;
  // Commit a snap stop directly. Used by the touch gesture on release.
  // Also resets `liveDragPx` and `isDragging` in one batched update.
  // Narrowed to the two non-form destinations the gesture hooks ever
  // reach — peek-reveal and close. Form snaps are entered through
  // `open()` which sets `activeForm` synchronously alongside the snap.
  commit: (next: 'peek' | 'closed') => void;
  // Setter for the live drag delta — called from the touch gesture on
  // every touchmove. Updates are batched by React inside event handlers.
  setLiveDrag: (px: number, dragging: boolean) => void;
  // Notify the hook that the curtain reached `closed` so any lingering
  // form can be unmounted (called from the curtain element's
  // `onTransitionEnd`).
  acknowledgeClosed: () => void;
};

// Resting `top` (px) of the curtain for a given snap stop and the
// currently measured form height (null falls back to the base).
// Snap-top math mirrors the DOM layout of the chip stack so the
// curtain's resting edge always lands on the boundary of the next
// row (no «next chip pill peeking through» bug). Chip rows are 56px
// each; between them is `CHIP_GAP_PX` (chip-to-chip, tighter); after
// the last revealed chip is `CURTAIN_BREATHER_PX` (chip-to-curtain,
// wider). Forms use just the breather.
export function snapTopPx(snap: CurtainSnap, formH: number | null): number {
  switch (snap) {
    case 'closed':
      return TABS_ROW_PX;
    case 'peek':
      return TABS_ROW_PX + CHIP_ROW_PX + CHIP_GAP_PX + CHIP_ROW_PX + CURTAIN_BREATHER_PX;
    case 'form-search':
    case 'form-chat':
      return TABS_ROW_PX + (formH ?? SEARCH_FORM_BASE_PX) + CURTAIN_BREATHER_PX;
    default:
      return TABS_ROW_PX;
  }
}

export function useCurtainState(pinKey: string): CurtainState {
  const [snap, setSnap] = useState<CurtainSnap>('closed');
  const [activeForm, setActiveForm] = useState<ActiveForm>(null);
  const [formHeightPx, setFormHeightPx] = useState<number | null>(null);
  const [liveDragPx, setLiveDragPx] = useState(0);
  const [isDragging, setIsDragging] = useState(false);
  // Per-tab pin lives in `curtainPinnedByTabAtom` so the lock survives
  // the route-driven listing-pane unmount that happens when the user
  // taps into a Room and back. The atom outlives any individual
  // StreamHeader instance.
  const [pinnedMap, setPinnedMap] = useAtom(curtainPinnedByTabAtom);
  const pinned = !!pinnedMap[pinKey];

  const formMeasureRef = useRef<HTMLDivElement>(null);

  const setPinned = useCallback(
    (next: boolean) => {
      setPinnedMap((prev) => {
        // Compare-and-skip so we don't allocate a fresh object (and
        // re-render every other subscriber of the atom) when nothing
        // actually changes.
        if (!!prev[pinKey] === next) return prev;
        return { ...prev, [pinKey]: next };
      });
      // Drop any in-flight live drag on commit so the curtain renders
      // at the new pinned-derived top without a residual finger offset.
      setLiveDragPx(0);
      setIsDragging(false);
    },
    [pinKey, setPinnedMap]
  );

  const open = useCallback(
    (form: 'search' | 'chat') => {
      setActiveForm(form);
      setSnap(form === 'search' ? 'form-search' : 'form-chat');
      setLiveDragPx(0);
      setIsDragging(false);
      // Safety net: clear pin so the form is visible. In practice the
      // visible openers (static pager header icons, in-pane chips on
      // non-pager surfaces) are all covered by the curtain when pinned,
      // so the user can't trigger this directly — but a future
      // programmatic open() would otherwise mount the form behind the
      // still-pinned curtain at curtainTop=0 and present an invisible
      // form.
      setPinned(false);
    },
    [setPinned]
  );

  const close = useCallback(() => {
    setSnap('closed');
    setLiveDragPx(0);
    setIsDragging(false);
  }, []);

  const commit = useCallback((next: 'peek' | 'closed') => {
    setSnap(next);
    setLiveDragPx(0);
    setIsDragging(false);
    // `activeForm` is intentionally NOT cleared here — it stays set
    // so the closing transition has form content beneath the curtain
    // as it slides up. `acknowledgeClosed` clears it once the snap
    // settles at `closed`.
  }, []);

  const setLiveDrag = useCallback((px: number, dragging: boolean) => {
    setLiveDragPx(px);
    setIsDragging(dragging);
  }, []);

  const acknowledgeClosed = useCallback(() => {
    if (snap === 'closed') setActiveForm(null);
  }, [snap]);

  // Measure the form's outer height while it's mounted. We do NOT
  // overwrite the measured height to null on unmount — keeping the
  // last-known height stable lets the close transition target the
  // same `top` value as the open transition (no jump at SNAP_MS-end).
  useLayoutEffect(() => {
    if (!activeForm) return undefined;
    const el = formMeasureRef.current;
    if (!el) return undefined;
    const measure = () => setFormHeightPx(el.offsetHeight);
    measure();
    const ro = new ResizeObserver(measure);
    ro.observe(el);
    return () => ro.disconnect();
  }, [activeForm]);

  // Safety-net for missed `transitionend` (route unmount mid-anim,
  // browser quirks). Once snap settles at `closed`, force-drop the
  // form after a generous window past the snap duration.
  const timerRef = useRef<number | null>(null);
  useEffect(() => {
    if (snap !== 'closed') {
      if (timerRef.current !== null) {
        window.clearTimeout(timerRef.current);
        timerRef.current = null;
      }
      return undefined;
    }
    timerRef.current = window.setTimeout(() => {
      setActiveForm(null);
    }, CURTAIN_SNAP_MS + 200);
    return () => {
      if (timerRef.current !== null) {
        window.clearTimeout(timerRef.current);
        timerRef.current = null;
      }
    };
  }, [snap]);

  return useMemo(
    () => ({
      snap,
      pinned,
      setPinned,
      activeForm,
      liveDragPx,
      isDragging,
      formHeightPx,
      formMeasureRef,
      open,
      close,
      commit,
      setLiveDrag,
      acknowledgeClosed,
    }),
    [
      snap,
      pinned,
      setPinned,
      activeForm,
      liveDragPx,
      isDragging,
      formHeightPx,
      open,
      close,
      commit,
      setLiveDrag,
      acknowledgeClosed,
    ]
  );
}