"use client";

/**
 * MentionTextarea — a textarea with inline "@" mention autocomplete.
 *
 * As the user types an `@token` at the caret, a suggestion list opens above
 * the field (prioritised following → followers → others). Picking a user (tap
 * or ↑/↓ + Enter/Tab) replaces the token with `@handle `. The list is portaled
 * with `pointer-events-auto` so it works inside a modal vaul drawer, and
 * dismisses on blur — no document listener that could fight the drawer.
 *
 * Enter (without Shift) submits via `onSubmit` ONLY when no suggestion list is
 * open; while the list is open, Enter/Tab pick the highlighted user. The
 * underlying <textarea> ref is forwarded so callers can focus it / splice text
 * (e.g. the emoji picker).
 */

import {
  forwardRef,
  useEffect,
  useImperativeHandle,
  useRef,
  useState,
} from "react";
import { createPortal } from "react-dom";
import { Loader2 } from "lucide-react";
import { posts, type UserSummary } from "@/lib/social";
import { UserAvatar } from "@/components/ui/user-avatar";

const SUGGEST_LIMIT = 8;
// "@" at line start or after whitespace, then up to 30 handle chars, at the
// end of the text before the caret. Avoids matching emails (foo@bar).
const MENTION_RE = /(^|\s)@([A-Za-z0-9_]{0,30})$/;

type Mention = { start: number; query: string };
type PanelPos = { left: number; bottom: number; width: number };

export const MentionTextarea = forwardRef<
  HTMLTextAreaElement,
  {
    value: string;
    onChange: (v: string) => void;
    /** Called on Enter (no Shift) when the suggestion list is closed. */
    onSubmit?: () => void;
    placeholder?: string;
    className?: string;
    maxLength?: number;
    rows?: number;
  }
>(function MentionTextarea(
  { value, onChange, onSubmit, placeholder, className, maxLength, rows = 1 },
  ref,
) {
  const innerRef = useRef<HTMLTextAreaElement>(null);
  useImperativeHandle(ref, () => innerRef.current as HTMLTextAreaElement, []);

  const [mention, setMention] = useState<Mention | null>(null);
  const [items, setItems] = useState<UserSummary[]>([]);
  const [loading, setLoading] = useState(false);
  const [active, setActive] = useState(0);
  const [pos, setPos] = useState<PanelPos | null>(null);
  const reqRef = useRef(0);
  const blurTimer = useRef<number | null>(null);

  // Detect the active @token from the text up to the caret.
  function detect(el: HTMLTextAreaElement) {
    const caret = el.selectionStart ?? 0;
    const m = MENTION_RE.exec(el.value.slice(0, caret));
    if (!m) {
      setMention(null);
      return;
    }
    setMention({ start: caret - m[2].length - 1, query: m[2] });
    setActive(0);
    const r = el.getBoundingClientRect();
    setPos({
      left: r.left,
      bottom: window.innerHeight - r.top + 6,
      width: r.width,
    });
  }

  // Fetch suggestions (debounced) whenever the active token changes.
  useEffect(() => {
    if (!mention) return;
    const token = ++reqRef.current;
    const t = window.setTimeout(() => {
      setLoading(true);
      posts
        .mentionSuggest(mention.query, { limit: SUGGEST_LIMIT, offset: 0 })
        .then((res) => {
          if (reqRef.current === token) setItems(res);
        })
        .catch(() => {
          if (reqRef.current === token) setItems([]);
        })
        .finally(() => {
          if (reqRef.current === token) setLoading(false);
        });
    }, 150);
    return () => window.clearTimeout(t);
  }, [mention]);

  function select(u: UserSummary) {
    const el = innerRef.current;
    if (!el || !mention) return;
    const caret = el.selectionStart ?? value.length;
    const insert = `@${u.handle} `;
    const next = value.slice(0, mention.start) + insert + value.slice(caret);
    onChange(next);
    setMention(null);
    const newCaret = mention.start + insert.length;
    requestAnimationFrame(() => {
      const node = innerRef.current;
      if (!node) return;
      node.focus();
      node.setSelectionRange(newCaret, newCaret);
    });
  }

  const listOpen = !!mention && (loading || items.length > 0);

  function onKeyDown(e: React.KeyboardEvent<HTMLTextAreaElement>) {
    if (listOpen && items.length > 0) {
      if (e.key === "ArrowDown") {
        e.preventDefault();
        setActive((a) => Math.min(a + 1, items.length - 1));
        return;
      }
      if (e.key === "ArrowUp") {
        e.preventDefault();
        setActive((a) => Math.max(a - 1, 0));
        return;
      }
      if (e.key === "Enter" || e.key === "Tab") {
        e.preventDefault();
        select(items[active] ?? items[0]);
        return;
      }
      if (e.key === "Escape") {
        e.preventDefault();
        setMention(null);
        return;
      }
    }
    if (e.key === "Enter" && !e.shiftKey) {
      e.preventDefault();
      onSubmit?.();
    }
  }

  return (
    <div className="relative flex-1">
      <textarea
        ref={innerRef}
        value={value}
        rows={rows}
        maxLength={maxLength}
        placeholder={placeholder}
        className={className}
        autoComplete="off"
        onChange={(e) => {
          onChange(e.target.value);
          detect(e.target);
        }}
        onKeyUp={(e) => detect(e.currentTarget)}
        onClick={(e) => detect(e.currentTarget)}
        onKeyDown={onKeyDown}
        onBlur={() => {
          // Defer so a result tap (mousedown→click) lands before close.
          blurTimer.current = window.setTimeout(() => setMention(null), 120);
        }}
      />

      {listOpen && pos && typeof document !== "undefined"
        ? createPortal(
            <div
              role="listbox"
              aria-label="Mention suggestions"
              style={{
                position: "fixed",
                left: pos.left,
                bottom: pos.bottom,
                width: pos.width,
              }}
              // pointer-events-auto: the comments drawer is a modal vaul sheet
              // (body gets pointer-events:none); without this the list would be
              // click-through.
              className="pointer-events-auto z-[101] max-h-56 overflow-y-auto overscroll-contain rounded-lg border border-border bg-card shadow-xl"
              onTouchMove={(e) => e.stopPropagation()}
            >
              {items.map((u, i) => (
                <button
                  key={u.id ?? u.handle}
                  type="button"
                  role="option"
                  aria-selected={i === active}
                  // Keep textarea focus + cancel the pending blur-close so the
                  // click registers before the list would otherwise close.
                  onMouseDown={(e) => {
                    e.preventDefault();
                    if (blurTimer.current)
                      window.clearTimeout(blurTimer.current);
                  }}
                  onMouseEnter={() => setActive(i)}
                  onClick={() => select(u)}
                  className={`flex w-full items-center gap-2.5 px-3 py-2 text-left transition-colors ${
                    i === active ? "bg-muted/70" : "hover:bg-muted/60"
                  }`}
                >
                  <UserAvatar
                    src={u.avatar_url}
                    name={u.name}
                    className="size-8"
                    textClassName="text-xs"
                  />
                  <span className="min-w-0">
                    <span className="block truncate text-sm font-medium text-foreground">
                      {u.name}
                    </span>
                    <span className="block truncate text-xs text-muted-foreground">
                      @{u.handle}
                    </span>
                  </span>
                </button>
              ))}
              {loading ? (
                <div className="flex justify-center py-2">
                  <Loader2 className="size-4 animate-spin text-muted-foreground" />
                </div>
              ) : null}
            </div>,
            document.body,
          )
        : null}
    </div>
  );
});