"use client";

/**
 * MentionAutocomplete — a search field for tagging users. Results render
 * INLINE (in normal flow) directly below the input, not as a floating
 * popover. This is deliberate: a floating popover inside a drawer/modal
 * overflows the sheet and its outside-click listener fights the drawer's own
 * dismiss. Inline results:
 *   • never resize/overflow the drawer (the container scrolls them),
 *   • close on blur (no document listener → outside clicks don't close the
 *     drawer),
 *   • only appear once the user types (no suggestions on bare focus).
 *
 * Suggestions come from the backend prioritised (following → followers →
 * others), 20 per page, infinite-scrolling. Already-selected users are
 * filtered out. Selecting a user adds it (via onSelect) and closes the list.
 */

import { useEffect, useRef, useState } from "react";
import Image from "next/image";
import { Loader2 } from "lucide-react";
import { posts, type UserSummary } from "@/lib/social";

const PAGE = 20;

export function MentionAutocomplete({
  excludeIds = [],
  onSelect,
  placeholder = "Search people to mention…",
  autoFocus = false,
}: {
  excludeIds?: string[];
  onSelect: (user: UserSummary) => void;
  placeholder?: string;
  autoFocus?: boolean;
}) {
  const [q, setQ] = useState("");
  const [open, setOpen] = useState(false);
  const [items, setItems] = useState<UserSummary[]>([]);
  const [loading, setLoading] = useState(false);
  const [hasMore, setHasMore] = useState(false);

  const reqRef = useRef(0);
  const busyRef = useRef(false);
  const blurTimer = useRef<number | null>(null);

  const query = q.trim();
  const showResults = open && query !== "";

  // (Re)load page 0 when the query changes — debounced, only when non-empty.
  // No fetch on bare focus, so suggestions appear "while typing" only.
  useEffect(() => {
    if (query === "") return;
    const t = window.setTimeout(() => {
      const token = ++reqRef.current;
      busyRef.current = true;
      setLoading(true);
      posts
        .mentionSuggest(query, { limit: PAGE, offset: 0 })
        .then((res) => {
          if (reqRef.current !== token) return;
          setItems(res);
          setHasMore(res.length === PAGE);
        })
        .catch(() => {
          if (reqRef.current === token) {
            setItems([]);
            setHasMore(false);
          }
        })
        .finally(() => {
          if (reqRef.current === token) {
            setLoading(false);
            busyRef.current = false;
          }
        });
    }, 200);
    return () => window.clearTimeout(t);
  }, [query]);

  function loadMore() {
    if (busyRef.current || !hasMore) return;
    const token = reqRef.current;
    busyRef.current = true;
    setLoading(true);
    posts
      .mentionSuggest(query, { limit: PAGE, offset: items.length })
      .then((res) => {
        if (reqRef.current !== token) return;
        setItems((prev) => [...prev, ...res]);
        setHasMore(res.length === PAGE);
      })
      .catch(() => {})
      .finally(() => {
        if (reqRef.current === token) {
          setLoading(false);
          busyRef.current = false;
        }
      });
  }

  const excluded = new Set(excludeIds);
  const visible = items.filter((u) => !u.id || !excluded.has(u.id));

  return (
    <div>
      <input
        type="text"
        value={q}
        autoFocus={autoFocus}
        onFocus={() => setOpen(true)}
        onChange={(e) => {
          setQ(e.target.value);
          setOpen(true);
        }}
        onBlur={() => {
          // Defer so a result tap (which fires onMouseDown→onClick) isn't
          // pre-empted by the list closing. Plain blur (tapping elsewhere)
          // just closes the inline list — the drawer is unaffected.
          blurTimer.current = window.setTimeout(() => setOpen(false), 120);
        }}
        placeholder={placeholder}
        autoComplete="off"
        // 16px on mobile so iOS Safari doesn't auto-zoom on focus.
        className="w-full rounded-lg border border-border bg-background px-3 py-2 text-base sm:text-sm text-foreground outline-none placeholder:text-muted-foreground focus-visible:ring-2 focus-visible:ring-ring"
      />

      {showResults ? (
        <div
          onScroll={(e) => {
            const el = e.currentTarget;
            if (el.scrollHeight - el.scrollTop - el.clientHeight < 80) {
              loadMore();
            }
          }}
          className="mt-2 max-h-56 overflow-y-auto overscroll-contain rounded-lg border border-border bg-card"
        >
          {visible.length === 0 && !loading ? (
            <p className="px-3 py-3 text-sm text-muted-foreground">
              No people found.
            </p>
          ) : (
            visible.map((u) => (
              <button
                key={u.id ?? u.handle}
                type="button"
                // Keep 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);
                }}
                onClick={() => {
                  onSelect(u);
                  setQ("");
                  setOpen(false);
                }}
                className="flex w-full items-center gap-2.5 px-3 py-2 text-left transition-colors hover:bg-muted/60"
              >
                <RowAvatar src={u.avatar_url} name={u.name} />
                <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>
      ) : null}
    </div>
  );
}

function RowAvatar({ src, name }: { src: string | null; name: string }) {
  if (src) {
    return (
      <Image
        src={src}
        alt={name}
        width={32}
        height={32}
        className="size-8 shrink-0 rounded-full object-cover ring-1 ring-foreground/10"
        unoptimized
      />
    );
  }
  const initials =
    name
      .split(/\s+/)
      .map((p) => p[0])
      .slice(0, 2)
      .join("")
      .toUpperCase() || "?";
  return (
    <span className="flex size-8 shrink-0 items-center justify-center rounded-full bg-primary/15 text-xs font-semibold text-primary ring-1 ring-foreground/10">
      {initials}
    </span>
  );
}