#!/usr/bin/env python3
"""Compute nDCG@10 over the RAG retrieval feedback table (TaskMaster #50).

Outputs aggregated metrics as JSON:

    {
        "generated_at": "2026-05-26T12:34:56+00:00",
        "k": 10,
        "summary": {
            "total_searches_with_feedback": int,
            "total_searches_logged": int,
            "feedback_coverage_pct": float,
            "avg_ndcg_at_10": float | null
        },
        "by_search_type": [
            {"search_type": "precedent_library",
             "searches_with_feedback": int,
             "avg_ndcg_at_10": float | null},
            ...
        ],
        "by_week": [
            {"week_start": "2026-05-19",
             "search_type": "precedent_library",
             "searches_with_feedback": int,
             "avg_ndcg_at_10": float | null},
            ...
        ],
        "top_cited_case_law": [
            {"case_law_id": "...", "case_number": "...",
             "case_name": "...", "cite_count": int},
            ...
        ]
    }

Run:
    python ~/legal-ai/scripts/compute_ndcg.py
    python ~/legal-ai/scripts/compute_ndcg.py --weeks 12 --k 10
    python ~/legal-ai/scripts/compute_ndcg.py --pretty
"""
from __future__ import annotations

import argparse
import asyncio
import json
import math
import os
import sys
from datetime import datetime, timezone
from pathlib import Path

import asyncpg

# Allow running as a standalone script — no package install required.
REPO_ROOT = Path(__file__).resolve().parent.parent
sys.path.insert(0, str(REPO_ROOT / "mcp-server" / "src"))


def _postgres_url() -> str:
    """Resolve POSTGRES_URL the same way the MCP server does."""
    url = os.environ.get("POSTGRES_URL")
    if url:
        return url
    user = os.environ.get("POSTGRES_USER", "legal_ai")
    pw = os.environ.get("POSTGRES_PASSWORD", "")
    host = os.environ.get("POSTGRES_HOST", "127.0.0.1")
    port = os.environ.get("POSTGRES_PORT", "5433")
    db = os.environ.get("POSTGRES_DB", "legal_ai")
    return f"postgres://{user}:{pw}@{host}:{port}/{db}"


def dcg(relevances: list[int]) -> float:
    """Discounted Cumulative Gain at the length of ``relevances``.

    Uses the "gain = 2^rel - 1" form so high-relevance hits get
    significantly more weight than marginal ones — matches the
    convention used by most IR papers and TREC-EVAL.
    """
    total = 0.0
    for i, rel in enumerate(relevances, start=1):
        gain = (2 ** rel) - 1
        total += gain / math.log2(i + 1)
    return total


def ndcg_at_k(rel_at_rank: dict[int, int], k: int) -> float | None:
    """Compute nDCG@k.

    Args:
        rel_at_rank: ``{rank (1-based): relevance_score (0..3)}``.
            Ranks above ``k`` are ignored. Missing ranks count as 0.
        k: cutoff.

    Returns:
        nDCG in [0,1], or ``None`` if there's nothing to score
        (no relevant hits in the top-k -> IDCG = 0).
    """
    actual = [rel_at_rank.get(r, 0) for r in range(1, k + 1)]
    if not any(actual):
        return None
    ideal = sorted(actual, reverse=True)
    idcg = dcg(ideal)
    if idcg == 0:
        return None
    return dcg(actual) / idcg


async def _fetch_feedback_rows(conn: asyncpg.Connection, weeks: int | None) -> list[dict]:
    """Pull all (search_log_id, rank, relevance_score, search_type, created_at)
    rows where there's at least one feedback row.

    Restricting to recent weeks keeps the scan cheap on a growing log.
    """
    where = ""
    params: list = []
    if weeks is not None and weeks > 0:
        where = "WHERE sl.created_at >= NOW() - ($1::int * INTERVAL '1 week')"
        params.append(weeks)
    sql = f"""
        SELECT sl.id::text          AS search_log_id,
               sl.search_type       AS search_type,
               sl.created_at        AS created_at,
               srf.rank             AS rank,
               srf.relevance_score  AS relevance_score
          FROM search_relevance_feedback srf
          JOIN search_logs sl ON sl.id = srf.search_log_id
         {where}
    """
    rows = await conn.fetch(sql, *params)
    return [dict(r) for r in rows]


async def _fetch_corpus_totals(conn: asyncpg.Connection, weeks: int | None) -> dict[str, int]:
    """Total search_logs count (overall and by type) — used for coverage %."""
    where = ""
    params: list = []
    if weeks is not None and weeks > 0:
        where = "WHERE created_at >= NOW() - ($1::int * INTERVAL '1 week')"
        params.append(weeks)
    total_row = await conn.fetchrow(
        f"SELECT COUNT(*) AS n FROM search_logs {where}",
        *params,
    )
    by_type = await conn.fetch(
        f"SELECT search_type, COUNT(*) AS n FROM search_logs {where} GROUP BY search_type",
        *params,
    )
    return {
        "_total": int(total_row["n"]) if total_row else 0,
        **{r["search_type"]: int(r["n"]) for r in by_type},
    }


async def _fetch_top_cited(conn: asyncpg.Connection, limit: int = 20) -> list[dict]:
    """Most-cited case_law (from auto-inferred feedback)."""
    rows = await conn.fetch(
        """
        SELECT cl.id::text         AS case_law_id,
               cl.case_number      AS case_number,
               cl.case_name        AS case_name,
               COUNT(*)            AS cite_count
          FROM search_relevance_feedback srf
          JOIN case_law cl ON cl.id = srf.case_law_id
         WHERE srf.feedback_source = 'cited_in_decision'
         GROUP BY cl.id, cl.case_number, cl.case_name
         ORDER BY COUNT(*) DESC
         LIMIT $1
        """,
        limit,
    )
    return [dict(r) for r in rows]


def _aggregate(
    feedback_rows: list[dict],
    k: int,
) -> tuple[dict[str, float], dict[tuple[str, str], float], int]:
    """Group feedback by search_log, compute per-log nDCG, then aggregate
    by search_type and by (week, search_type)."""
    by_log: dict[str, dict] = {}
    for row in feedback_rows:
        slid = row["search_log_id"]
        if slid not in by_log:
            by_log[slid] = {
                "search_type": row["search_type"],
                "created_at": row["created_at"],
                "rels": {},
            }
        rank = int(row["rank"])
        if 1 <= rank <= k:
            by_log[slid]["rels"][rank] = int(row["relevance_score"])

    type_ndcg: dict[str, list[float]] = {}
    week_ndcg: dict[tuple[str, str], list[float]] = {}
    total_logs_with_feedback = 0
    for entry in by_log.values():
        score = ndcg_at_k(entry["rels"], k)
        if score is None:
            continue
        total_logs_with_feedback += 1
        type_ndcg.setdefault(entry["search_type"], []).append(score)
        week_start = entry["created_at"].date()
        # Round down to ISO week Monday.
        week_start = week_start.fromordinal(
            week_start.toordinal() - week_start.weekday()
        )
        wkey = (week_start.isoformat(), entry["search_type"])
        week_ndcg.setdefault(wkey, []).append(score)

    type_avg = {t: sum(v) / len(v) for t, v in type_ndcg.items() if v}
    week_avg = {k_: sum(v) / len(v) for k_, v in week_ndcg.items() if v}
    return type_avg, week_avg, total_logs_with_feedback


async def compute(weeks: int | None, k: int) -> dict:
    conn = await asyncpg.connect(_postgres_url())
    try:
        fb_rows = await _fetch_feedback_rows(conn, weeks)
        totals = await _fetch_corpus_totals(conn, weeks)
        top_cited = await _fetch_top_cited(conn)
    finally:
        await conn.close()

    type_avg, week_avg, logs_scored = _aggregate(fb_rows, k)

    total_logs = totals.get("_total", 0)
    overall_avg = (
        sum(v * len([s for s in type_avg]) for v in []) or None  # placeholder
    )
    # Recompute overall_avg cleanly: micro-average over all per-log scores.
    all_scores: list[float] = []
    for v in [type_avg[t] for t in type_avg]:
        # type_avg already collapsed per-type — instead, re-run aggregation
        # over fb_rows by reusing the per-log calc, micro-averaged.
        pass
    # Simpler: redo with per-log granularity for overall mean.
    by_log_overall: dict[str, dict[int, int]] = {}
    log_to_type: dict[str, str] = {}
    for row in fb_rows:
        slid = row["search_log_id"]
        by_log_overall.setdefault(slid, {})
        rank = int(row["rank"])
        if 1 <= rank <= k:
            by_log_overall[slid][rank] = int(row["relevance_score"])
        log_to_type[slid] = row["search_type"]
    per_log_scores: list[float] = []
    for slid, rels in by_log_overall.items():
        s = ndcg_at_k(rels, k)
        if s is not None:
            per_log_scores.append(s)
    overall_avg = (sum(per_log_scores) / len(per_log_scores)) if per_log_scores else None

    by_search_type = []
    for t, totals_n in sorted(totals.items()):
        if t == "_total":
            continue
        by_search_type.append({
            "search_type": t,
            "searches_logged": totals_n,
            "searches_with_feedback": sum(
                1 for slid, tp in log_to_type.items() if tp == t
            ),
            "avg_ndcg_at_k": round(type_avg[t], 4) if t in type_avg else None,
        })

    by_week = [
        {
            "week_start": week,
            "search_type": stype,
            "avg_ndcg_at_k": round(score, 4),
        }
        for (week, stype), score in sorted(week_avg.items())
    ]

    return {
        "generated_at": datetime.now(timezone.utc).isoformat(),
        "k": k,
        "window_weeks": weeks,
        "summary": {
            "total_searches_logged": total_logs,
            "total_searches_with_feedback": logs_scored,
            "feedback_coverage_pct": (
                round(100 * logs_scored / total_logs, 2) if total_logs else 0.0
            ),
            "avg_ndcg_at_k": round(overall_avg, 4) if overall_avg is not None else None,
        },
        "by_search_type": by_search_type,
        "by_week": by_week,
        "top_cited_case_law": [
            {**r, "cite_count": int(r["cite_count"])} for r in top_cited
        ],
    }


def main() -> int:
    p = argparse.ArgumentParser(description="Compute nDCG@k from search_relevance_feedback")
    p.add_argument("--k", type=int, default=10, help="cutoff (default: 10)")
    p.add_argument(
        "--weeks",
        type=int,
        default=None,
        help="restrict to the last N weeks (default: all time)",
    )
    p.add_argument("--pretty", action="store_true", help="indented JSON output")
    args = p.parse_args()

    result = asyncio.run(compute(weeks=args.weeks, k=args.k))
    indent = 2 if args.pretty else None
    print(json.dumps(result, ensure_ascii=False, indent=indent, default=str))
    return 0


if __name__ == "__main__":
    raise SystemExit(main())