// Emoji data + search.
//
// The data file is generated by `scripts/gen-emoji-data.mjs` from emojibase-data
// and ships as a static asset at /emoji-data.json.

import { useEffect, useState } from "react";

export interface Skin {
  n: string;
}

export interface Emoji {
  /** Canonical shortcode, e.g. "grinning-face". */
  id: string;
  /** Human-readable name, e.g. "Grinning Face". */
  m: string;
  /** Tags for keyword search. */
  k: string[];
  /** Skin variants. s[0] is always the default (no tone modifier);
   *  s[1..5] correspond to Fitzpatrick tones 1-5 when the emoji supports them. */
  s: Skin[];
}

export interface EmojiData {
  /** Map of canonical id → emoji. */
  emojis: { [id: string]: Emoji };
  /** Alternate shortcodes (e.g. "shrug" → "person-shrugging") pointing to the canonical id. */
  aliases: { [alias: string]: string };
}

/** Returns the native character for a given Fitzpatrick tone (0 = default). */
export function getSkinNative(emoji: Emoji, skinTone: number = 0): string {
  return (emoji.s[skinTone] ?? emoji.s[0]).n;
}

const DATA_URL = "/emoji-data.json";

// Module-level promise cache so concurrent callers (e.g. two chat inputs
// mounting at the same time) share a single fetch. The HTTP layer also caches,
// but we don't want to fire two parses for the same data.
let dataPromise: Promise<EmojiData> | null = null;

export function getEmojiData(): Promise<EmojiData> {
  if (dataPromise) return dataPromise;
  dataPromise = fetch(DATA_URL)
    .then((r) => {
      if (!r.ok) throw new Error(`emoji-data fetch failed: ${r.status}`);
      return r.json() as Promise<EmojiData>;
    })
    .catch((err) => {
      // If the fetch fails, drop the promise so a future call can retry.
      dataPromise = null;
      throw err;
    });
  return dataPromise;
}

/** React hook: returns the loaded emoji data, or null until it's ready. */
export function useEmojiData(): EmojiData | null {
  const [data, setData] = useState<EmojiData | null>(null);
  useEffect(() => {
    let cancelled = false;
    getEmojiData()
      .then((d) => {
        if (!cancelled) setData(d);
      })
      .catch((err) => {
        console.error("Failed to load emoji data", err);
      });
    return () => {
      cancelled = true;
    };
  }, []);
  return data;
}

const MIN_QUERY_LENGTH = 3;
const MAX_RESULTS = 10;

/**
 * Rank-matching emoji for a `:`-prefixed query.
 *
 * Ported from the React Native reference implementation in
 * `js/components/src/components/chat/chat-box.tsx`. Match order, all else equal:
 *   0. exact alias  → 1. alias startsWith  → 2. alias includes
 *   3. exact id     → 4. id startsWith     → 5. id includes
 *   6. name includes → 7. keyword includes
 *
 * Ties on matchType are broken by position of the substring within the
 * matched field.
 *
 * @param data the loaded emoji data, or null when not yet available
 * @param query the text after the last `:` (no colon), already lowercased
 * @param limit cap on the result list
 */
export function searchEmojis(
  data: EmojiData | null,
  query: string,
  limit: number = MAX_RESULTS,
): Emoji[] {
  if (!data) return [];
  if (query.length < MIN_QUERY_LENGTH) return [];
  if (query.includes(" ")) return [];

  // For each alias, compute a match type (0=exact, 1=prefix, 2=contains) and
  // the substring position. We then collapse aliases to "the best one per
  // emoji" so each emoji is only represented once.
  const aliasMatches = Object.entries(data.aliases)
    .map(([alias, emojiId]) => {
      const aliasLower = alias.toLowerCase();
      if (aliasLower === query) {
        return { emojiId, alias, matchType: 0, index: 0 };
      }
      if (aliasLower.startsWith(query)) {
        return { emojiId, alias, matchType: 1, index: 0 };
      }
      if (aliasLower.includes(query)) {
        return {
          emojiId,
          alias,
          matchType: 2,
          index: aliasLower.indexOf(query),
        };
      }
      return null;
    })
    .filter((m): m is NonNullable<typeof m> => m !== null);

  // Best alias match per emoji id.
  const bestAliasMatch: Record<
    string,
    { matchType: number; index: number; alias: string }
  > = {};
  for (const match of aliasMatches) {
    const prev = bestAliasMatch[match.emojiId];
    if (
      !prev ||
      match.matchType < prev.matchType ||
      (match.matchType === prev.matchType && match.index < prev.index)
    ) {
      bestAliasMatch[match.emojiId] = match;
    }
  }

  const allEmojis = Object.values(data.emojis);
  const seen = new Set<string>();
  const out: { emoji: Emoji; sort: number[] }[] = [];

  for (const emoji of allEmojis) {
    if (seen.has(emoji.id)) continue;
    const aliasMatch = bestAliasMatch[emoji.id];
    if (aliasMatch) {
      seen.add(emoji.id);
      out.push({
        emoji,
        sort: [aliasMatch.matchType, aliasMatch.index, 0],
      });
      continue;
    }
    const idLower = emoji.id.toLowerCase();
    if (idLower === query) {
      seen.add(emoji.id);
      out.push({ emoji, sort: [3, 0, 0] });
      continue;
    }
    if (idLower.startsWith(query)) {
      seen.add(emoji.id);
      out.push({ emoji, sort: [4, 0, 0] });
      continue;
    }
    if (idLower.includes(query)) {
      seen.add(emoji.id);
      out.push({ emoji, sort: [5, idLower.indexOf(query), 0] });
      continue;
    }
    const nameLower = emoji.m.toLowerCase();
    if (nameLower.includes(query)) {
      seen.add(emoji.id);
      out.push({ emoji, sort: [6, nameLower.indexOf(query), 0] });
      continue;
    }
    if (emoji.k.some((kw) => kw.toLowerCase().includes(query))) {
      seen.add(emoji.id);
      out.push({ emoji, sort: [7, 0, 0] });
      continue;
    }
  }

  out.sort((a, b) => {
    for (let i = 0; i < a.sort.length; i++) {
      if (a.sort[i] !== b.sort[i]) return a.sort[i] - b.sort[i];
    }
    return 0;
  });

  return out.slice(0, limit).map((e) => e.emoji);
}