import re
import aiosqlite

from services.fts import build_match_query

MAX_EXAMPLES = 3
MAX_EXAMPLE_CHARS = 1800
MAX_CONTEXT_CHARS = 5200


def _compact(text: str, limit: int = MAX_EXAMPLE_CHARS) -> str:
    text = re.sub(r"\n{3,}", "\n\n", (text or "").strip())
    if len(text) <= limit:
        return text
    return text[:limit].rstrip() + "\n..."


def _format_examples(rows: list[aiosqlite.Row], purpose: str) -> str:
    if not rows:
        return ""
    heading = {
        "topic": "历史人工修订报告参考（用于学习话题命名和分类口径）",
        "summary": "历史人工修订报告参考（只学习结构、措辞和关注点，不得照抄历史事实）",
    }.get(purpose, "历史人工修订报告参考")
    parts = [heading]
    total = len(parts[0])
    for idx, row in enumerate(rows, 1):
        block = (
            f"\n\n--- 示例 {idx} ---\n"
            f"群聊：{row['group_name'] or row['talker'] or row['group_id']}\n"
            f"话题标题：{row['title']}\n"
            f"报告内容：\n{_compact(row['content'])}"
        )
        if total + len(block) > MAX_CONTEXT_CHARS:
            break
        parts.append(block)
        total += len(block)
    return "".join(parts).strip()


async def build_report_learning_context(
    db: aiosqlite.Connection,
    *,
    group_id: int | None,
    query: str = "",
    exclude_topic_id: int | None = None,
    purpose: str = "summary",
    limit: int = MAX_EXAMPLES,
) -> str:
    params: list[object] = []
    exclude_sql = ""
    if exclude_topic_id is not None:
        exclude_sql = " AND t.id<>?"
        params.append(exclude_topic_id)

    selected: list[aiosqlite.Row] = []
    seen_doc_ids: set[int] = set()

    if group_id is not None:
        async with db.execute(
            f"""
            SELECT k.id, k.content, k.updated_at, t.id AS topic_id, t.title, t.group_id,
                   g.name AS group_name, g.talker
            FROM knowledge_docs k
            JOIN topics t ON t.id = k.topic_id
            LEFT JOIN groups g ON g.id = t.group_id
            WHERE k.curated_at IS NOT NULL
              AND t.group_id=?
              {exclude_sql}
            ORDER BY k.curated_at DESC, k.updated_at DESC
            LIMIT ?
            """,
            [group_id, *params, limit],
        ) as cur:
            rows = await cur.fetchall()
        for row in rows:
            selected.append(row)
            seen_doc_ids.add(int(row["id"]))

    if len(selected) < limit:
        remaining = limit - len(selected)
        fts_query = build_match_query(query or "")
        if fts_query:
            async with db.execute(
                f"""
                SELECT k.id, k.content, k.updated_at, t.id AS topic_id, t.title, t.group_id,
                       g.name AS group_name, g.talker
                FROM knowledge_docs k
                JOIN topics t ON t.id = k.topic_id
                LEFT JOIN groups g ON g.id = t.group_id
                WHERE k.curated_at IS NOT NULL
                  AND k.id IN (SELECT doc_id FROM knowledge_fts WHERE knowledge_fts MATCH ?)
                  {exclude_sql}
                ORDER BY CASE WHEN t.group_id=? THEN 0 ELSE 1 END,
                         k.curated_at DESC,
                         k.updated_at DESC
                LIMIT ?
                """,
                [fts_query, *params, group_id or -1, remaining * 3],
            ) as cur:
                rows = await cur.fetchall()
            for row in rows:
                doc_id = int(row["id"])
                if doc_id in seen_doc_ids:
                    continue
                selected.append(row)
                seen_doc_ids.add(doc_id)
                if len(selected) >= limit:
                    break

    if len(selected) < limit:
        remaining = limit - len(selected)
        async with db.execute(
            f"""
            SELECT k.id, k.content, k.updated_at, t.id AS topic_id, t.title, t.group_id,
                   g.name AS group_name, g.talker
            FROM knowledge_docs k
            JOIN topics t ON t.id = k.topic_id
            LEFT JOIN groups g ON g.id = t.group_id
            WHERE k.curated_at IS NOT NULL
              {exclude_sql}
            ORDER BY CASE WHEN t.group_id=? THEN 0 ELSE 1 END,
                     k.curated_at DESC,
                     k.updated_at DESC
            LIMIT ?
            """,
            [*params, group_id or -1, remaining * 3],
        ) as cur:
            rows = await cur.fetchall()
        for row in rows:
            doc_id = int(row["id"])
            if doc_id in seen_doc_ids:
                continue
            selected.append(row)
            seen_doc_ids.add(doc_id)
            if len(selected) >= limit:
                break

    return _format_examples(selected[:limit], purpose)