import { chapterText, type TxtChapter } from "./chapters";

export interface SearchHit {
  ch: number;
  /** 命中在章内文本的起点 */
  pos: number;
  snippet: string;
  matchStart: number; // snippet 内
  matchLen: number;
}

const CTX = 20; // snippet 前后文

/** 全书线性扫描（文本已分章在内存,量级足够;大小写不敏感,不折叠全半角）。 */
export function searchChapters(text: string, chapters: TxtChapter[], q: string, limit = 500): SearchHit[] {
  const needle = q.trim().toLowerCase();
  if (!needle) return [];
  const bodies = chapters.map((_, ci) => chapterText(text, chapters, ci).toLowerCase());
  const hits: SearchHit[] = [];
  for (let ci = 0; ci < chapters.length && hits.length < limit; ci++) {
    const body = bodies[ci];
    let from = 0;
    for (;;) {
      const at = body.indexOf(needle, from);
      if (at < 0 || hits.length >= limit) break;
      const raw = chapterText(text, chapters, ci);
      const s = Math.max(0, at - CTX);
      const e = Math.min(raw.length, at + needle.length + CTX);
      hits.push({
        ch: ci,
        pos: at,
        snippet: (s > 0 ? "…" : "") + raw.slice(s, e) + (e < raw.length ? "…" : ""),
        matchStart: at - s + (s > 0 ? 1 : 0),
        matchLen: needle.length,
      });
      from = at + needle.length;
    }
  }
  return hits;
}

export function splitHighlight(snippet: string, matchStart: number, matchLen: number) {
  return {
    before: snippet.slice(0, matchStart),
    match: snippet.slice(matchStart, matchStart + matchLen),
    after: snippet.slice(matchStart + matchLen),
  };
}