"""Unit: KB overview generator (phase 31, task 02).

The prompt tests are pure (no DB): ``KB_OVERVIEW_MODE`` system prompt,
per-document user lines (source/path/title/first summary line), and the
input cap with the shared ``[…truncated…]`` marker. The loader and
regenerator tests run against the local compose Postgres (preferred —
real single-row upsert), skipping with clear instructions when the stack
is not up — same pattern as ``test_importer.py``.
"""
from __future__ import annotations

import asyncio
import logging
import uuid
from datetime import UTC, datetime

import pytest
from sqlalchemy import text
from sqlalchemy.orm import Session

from app.config import Settings, get_settings
from app.models import Document, KbOverview
from app.rag.llm import LLMError
from app.rag.overview import (
    KB_OVERVIEW_MODE,
    OVERVIEW_INSTRUCTION,
    SYSTEM_PROMPT,
    build_overview_prompt,
    load_kb_overview,
    regenerate_overview,
)
from app.rag.retriever import TRUNCATION_MARKER

REPLY = "- Homelab\n  - Kubernetes (k3s)\n- Deployments\n  - Borg backups"


class _FakeLLM:
    """Duck-typed stand-in for ``LLMClient`` (``chat`` + ``settings``).

    Records the messages and the ``model`` kwarg it was called with;
    returns a canned reply or raises (e.g. :class:`LLMError`).
    """

    def __init__(self, reply: str = REPLY, fail: Exception | None = None) -> None:
        self._reply = reply
        self._fail = fail
        self.settings = Settings(_env_file=None)  # pyright: ignore[reportCallIssue]
        self.messages: list[dict[str, str]] = []
        self.model: str | None = None
        self.calls = 0

    async def chat(
        self, messages: list[dict[str, str]], model: str | None = None
    ) -> str:
        self.calls += 1
        self.messages = list(messages)
        self.model = model
        if self._fail is not None:
            raise self._fail
        return self._reply


# ---------- build_overview_prompt: system ----------


def test_system_prompt_has_marker_and_locked_instruction() -> None:
    assert SYSTEM_PROMPT.startswith(KB_OVERVIEW_MODE)
    assert OVERVIEW_INSTRUCTION in SYSTEM_PROMPT
    for fragment in (
        "compact plain-text outline",
        "basic categories and topics",
        "Group by source",
        "use `-` bullet lines",
        "~1500 characters",
        "no markdown headings",
        "no topics not present in the list",
    ):
        assert fragment in SYSTEM_PROMPT
    system, _ = build_overview_prompt([])
    assert system == SYSTEM_PROMPT
    assert KB_OVERVIEW_MODE in system  # the marker the E2E mock keys on


# ---------- build_overview_prompt: user lines ----------


def test_user_lines_carry_source_path_title_and_first_summary_line() -> None:
    rows = [
        ("Homelab", "kubernetes/k3s.md", "K3s Cluster", None),
        (
            "Deployments",
            "backups/borg.yaml",
            "Borg Backups",
            "Backups run nightly via the borg schedule.\nSource: Deployments/backups/borg.yaml",
        ),
    ]
    system, user = build_overview_prompt(rows)
    assert system == SYSTEM_PROMPT
    assert user == (
        "Homelab — kubernetes/k3s.md — K3s Cluster\n"
        "Deployments — backups/borg.yaml — Borg Backups — "
        "Backups run nightly via the borg schedule."
    )


def test_user_line_omits_summary_field_when_absent() -> None:
    _, user = build_overview_prompt([("Homelab", "a.md", "Title A", None)])
    assert user == "Homelab — a.md — Title A"
    assert not user.endswith(" — ")  # no dangling dash


def test_user_line_omits_summary_field_when_blank() -> None:
    _, user = build_overview_prompt([("Homelab", "a.md", "Title A", "  \n\t ")])
    assert user == "Homelab — a.md — Title A"


def test_user_line_uses_only_first_summary_line() -> None:
    """Multi-line summaries contribute their first line only (the
    model-written lead sentence; the ``Source: …`` pointer is last)."""
    _, user = build_overview_prompt(
        [
            (
                "Homelab",
                "a.yaml",
                "Title A",
                "First line.\nSecond line.\nSource: Homelab/a.yaml",
            )
        ]
    )
    assert user == "Homelab — a.yaml — Title A — First line."
    assert "Second line" not in user
    assert "Source:" not in user


def test_zero_rows_yield_empty_user() -> None:
    _, user = build_overview_prompt([])
    assert user == ""


# ---------- build_overview_prompt: input cap ----------


def test_user_prompt_truncated_with_marker_when_over_custom_cap() -> None:
    rows = [("S", f"p{i}.md", f"T{i}", None) for i in range(10)]
    _, full = build_overview_prompt(rows, max_chars=10_000)
    cap = 25
    _, user = build_overview_prompt(rows, max_chars=cap)
    assert user == full[:cap] + "\n" + TRUNCATION_MARKER
    assert user.endswith(TRUNCATION_MARKER)
    assert len(user) > cap  # the marker makes the cut visible past the cap


def test_user_prompt_at_exact_cap_not_truncated() -> None:
    rows = [("S", "p.md", "T", None)]  # "S — p.md — T" = 12 chars
    _, user = build_overview_prompt(rows, max_chars=12)
    assert user == "S — p.md — T"
    assert TRUNCATION_MARKER not in user


def test_user_prompt_truncated_at_default_cap() -> None:
    """No explicit cap → ``BOR_OVERVIEW_INPUT_MAX_CHARS`` (read from the
    live settings, so the test holds for any configured value)."""
    cap = get_settings().overview_input_max_chars
    rows = [("S", f"p{i}.md", "T", None) for i in range(3_000)]
    _, user = build_overview_prompt(rows)
    assert user.endswith(TRUNCATION_MARKER)
    body = user.removesuffix("\n" + TRUNCATION_MARKER)
    assert len(body) == cap  # cut exactly at the cap, marker on its own line
    assert "p2999.md" not in body  # the overflow never reaches the model


# ---------- load_kb_overview ----------


def test_load_kb_overview_no_row_empty(db: Session) -> None:
    db.execute(text("DELETE FROM kb_overview"))
    db.commit()
    assert load_kb_overview(db) == ""


def test_load_kb_overview_returns_trimmed_content(db: Session) -> None:
    db.execute(text("DELETE FROM kb_overview"))
    db.add(KbOverview(id=1, content=f"  {REPLY}  \n"))
    db.commit()
    assert load_kb_overview(db) == REPLY


def test_load_kb_overview_whitespace_only_row_empty(db: Session) -> None:
    db.execute(text("DELETE FROM kb_overview"))
    db.add(KbOverview(id=1, content="  \n\t "))
    db.commit()
    assert load_kb_overview(db) == ""


# ---------- regenerate_overview ----------


def _add_doc(
    db: Session, source: str, path: str, title: str, summary: str | None = None
) -> Document:
    doc = Document(
        id=uuid.uuid4(),
        source=source,
        path=path,
        full_path=f"/tmp/{path}",
        title=title,
        content="body",
        content_hash="0" * 64,
        summary=summary,
    )
    db.add(doc)
    db.commit()
    return doc


def _truncate_documents(db: Session) -> None:
    db.execute(text("TRUNCATE chunks, documents"))
    db.commit()


def _overview_row(db: Session) -> KbOverview | None:
    return db.get(KbOverview, 1)


@pytest.fixture()
def clean_overview(db: Session):
    db.execute(text("DELETE FROM kb_overview"))
    db.commit()
    yield
    db.execute(text("DELETE FROM kb_overview"))
    db.commit()


def test_regenerate_happy_path_creates_single_row_id_1(
    db: Session, clean_overview, caplog: pytest.LogCaptureFixture
) -> None:
    _truncate_documents(db)
    try:
        _add_doc(db, "Homelab", "b.md", "B")
        _add_doc(db, "Homelab", "a.md", "A", "A summary.\nSource: Homelab/a.md")
        llm = _FakeLLM()
        with caplog.at_level(logging.INFO, logger="app.rag.overview"):
            ok = asyncio.run(regenerate_overview(llm, db))
            assert ok is True
            assert llm.calls == 1
            row = db.get(KbOverview, 1)
            assert row is not None, "the single row must be upserted"
            assert row.id == 1
            assert row.content == REPLY
            assert row.updated_at is not None
            age = datetime.now(UTC) - row.updated_at
            assert age.total_seconds() < 300, "updated_at must be a fresh UTC timestamp"
            assert f"overview: regenerated docs=2 chars={len(REPLY)}" in caplog.text
    finally:
        _truncate_documents(db)


def test_regenerate_updates_existing_row_in_place(db: Session, clean_overview) -> None:
    _truncate_documents(db)
    past = datetime(2020, 1, 1, 12, 0, 0, tzinfo=UTC)
    db.add(KbOverview(id=1, content="old outline", updated_at=past))
    db.commit()
    try:
        _add_doc(db, "Homelab", "a.md", "A")
        ok = asyncio.run(regenerate_overview(_FakeLLM(), db))
        assert ok is True
        count = db.scalar(text("SELECT count(*) FROM kb_overview"))
        assert count == 1, "still exactly one row after the re-generation"
        row = db.get(KbOverview, 1)
        assert row is not None
        assert row.content == REPLY  # replaced, not appended
        assert row.updated_at is not None and row.updated_at > past
    finally:
        _truncate_documents(db)


def test_regenerate_orders_documents_by_source_path(db: Session, clean_overview) -> None:
    _truncate_documents(db)
    try:
        # Inserted out of order — the model must see a deterministic order.
        _add_doc(db, "Deployments", "z.md", "Z")
        _add_doc(db, "Homelab", "b.md", "B")
        _add_doc(db, "Homelab", "a.md", "A")
        llm = _FakeLLM()
        assert asyncio.run(regenerate_overview(llm, db)) is True
    finally:
        _truncate_documents(db)

    user = next(m["content"] for m in llm.messages if m["role"] == "user")
    assert user == (
        "Deployments — z.md — Z\nHomelab — a.md — A\nHomelab — b.md — B"
    )


def test_regenerate_calls_the_configured_summary_model(
    db: Session, clean_overview
) -> None:
    _truncate_documents(db)
    try:
        _add_doc(db, "Homelab", "a.md", "A")
        llm = _FakeLLM()
        assert asyncio.run(regenerate_overview(llm, db)) is True
    finally:
        _truncate_documents(db)

    assert llm.model == llm.settings.llm_summary_model  # the ``lite`` default
    assert llm.model == "lite"
    assert [m["role"] for m in llm.messages] == ["system", "user"]
    assert KB_OVERVIEW_MODE in llm.messages[0]["content"]
    assert "A" in llm.messages[1]["content"]


def test_regenerate_zero_docs_leaves_existing_row_untouched(
    db: Session, clean_overview
) -> None:
    db.execute(text("DELETE FROM kb_overview"))
    db.add(KbOverview(id=1, content="old outline"))
    db.commit()
    _truncate_documents(db)
    llm = _FakeLLM()
    ok = asyncio.run(regenerate_overview(llm, db))
    assert ok is False
    assert llm.calls == 0, "no KB → no wasted lite-model call"
    row = db.get(KbOverview, 1)
    assert row is not None and row.content == "old outline"  # untouched


def test_regenerate_zero_docs_without_row_creates_nothing(db: Session, clean_overview) -> None:
    _truncate_documents(db)
    llm = _FakeLLM()
    ok = asyncio.run(regenerate_overview(llm, db))
    assert ok is False
    assert llm.calls == 0
    assert _overview_row(db) is None, "no row must be invented for an empty KB"


def test_regenerate_llm_error_leaves_previous_row_intact(
    db: Session, clean_overview, caplog: pytest.LogCaptureFixture
) -> None:
    db.execute(text("DELETE FROM kb_overview"))
    db.add(KbOverview(id=1, content="old outline"))
    db.commit()
    _truncate_documents(db)
    try:
        _add_doc(db, "Homelab", "a.md", "A")
        llm = _FakeLLM(fail=LLMError("simulated lite-model failure"))
        with caplog.at_level(logging.ERROR, logger="app.rag.overview"):
            ok = asyncio.run(regenerate_overview(llm, db))
            assert ok is False, "fail-soft: the import must not be dragged down"
            row = db.get(KbOverview, 1)
            assert row is not None and row.content == "old outline", (
                "the previous outline stays — an old outline is better than none"
            )
            assert "overview: regeneration failed —" in caplog.text
            assert "simulated lite-model failure" in caplog.text
    finally:
        _truncate_documents(db)


def test_regenerate_llm_error_without_row_creates_nothing(
    db: Session, clean_overview
) -> None:
    _truncate_documents(db)
    try:
        _add_doc(db, "Homelab", "a.md", "A")
        llm = _FakeLLM(fail=LLMError("simulated lite-model failure"))
        ok = asyncio.run(regenerate_overview(llm, db))
    finally:
        _truncate_documents(db)

    assert ok is False
    assert _overview_row(db) is None


def test_regenerate_opens_own_session_when_none(db: Session, clean_overview) -> None:
    """``session=None`` → a private ``SessionLocal`` session is opened,
    committed, and closed (the import-script call path)."""
    _truncate_documents(db)
    try:
        _add_doc(db, "Homelab", "a.md", "A")
        ok = asyncio.run(regenerate_overview(_FakeLLM()))
    finally:
        _truncate_documents(db)

    assert ok is True
    row = db.get(KbOverview, 1)  # fresh lookup via the test session
    assert row is not None and row.content == REPLY