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

Builds the ``KB_OVERVIEW_MODE`` prompt from the document catalogue
(one line per document: source, path, title, first summary line —
ordered RECENT-FIRST by the document's date, phase 142 task 02),
calls the aipi ``lite`` model through the one-shot ``LLMClient.chat``
(phase 30, same model as document summaries — no new model management),
and stores the plain-text outline in the single ``kb_overview`` row
(migration 0005).

The recency-first order is what makes the input cap honest: when
``BOR_OVERVIEW_INPUT_MAX_CHARS`` cuts the list, the documents that fall
off are the OLDEST, so the outline always represents the recent state
of the KB. The sort reads ``Document.created_at`` — phase 106's
git-history/mtime-derived, owner-correctable document date (the same
date the ``read`` tool's ``date:`` line shows); ``created_at_manual``
rows are included exactly as stored, the ordering never re-derives
dates. Same-date documents tie-break by ``(source, path)``, keeping
the pre-phase-142 lexicographic order within a date (deterministic for
the mock's digest; byte-identical for single-date KBs).

Chat turns never generate an overview — they read the stored row
(:func:`load_kb_overview`, one indexed PK lookup) and inject it into the
system prompt of every turn as the ``<knowledge_base>`` section
(phase 31, task 03). Generation happens at import time (phase 31, task
04) and is **best-effort and change-gated**: callers invoke it only when
an import added/updated at least one document (or no row exists yet),
and a ``lite`` failure logs and leaves the previous outline intact — an
old outline is better than none (phase locked decisions).

After the model's outline, :func:`regenerate_overview` appends ONE
deterministic, non-LLM line — ``Sources: <name> (<k> doc|docs), …``
(phase 162, LOCKED A2). The 2026-10-07 live finding: the ``lite``
outline is lossy — it listed 3 groups of a 14-source index, so the
1-doc sources (``ikea_instructions``, ``players_handbook``) were
invisible to ``<knowledge_base>``. Small sources must be visible
without a model call, so the line is computed mechanically from the
catalogue rows (:func:`_source_inventory`) — the mock/real model
outputs never affect it, and ``build_overview_prompt`` never sees the
tail (the model input stays byte-identical). The longest-prefix cap in
``build_kb_section`` applies to the WHOLE stored text: at the default
``BOR_KB_OVERVIEW_MAX_CHARS`` (4000) the ~1500-char outline plus the
one-line tail (~15 chars/source) always fit; a smaller owner-set cap
cuts the tail first — accepted, the cap is owner-tunable.

The ``KB_OVERVIEW_MODE`` marker follows the ``SUMMARY_MODE`` /
``DEFLECT_MODE`` convention: the deterministic E2E mock LLM keys on it
in the system prompt (wired in phase 31, task 05).
"""
from __future__ import annotations

import logging
from collections.abc import Sequence
from datetime import UTC, datetime
from typing import Protocol

from sqlalchemy import select
from sqlalchemy.orm import Session

from app.config import Settings, get_settings
from app.db import SessionLocal
from app.models import Document, KbOverview
from app.rag.llm import LLMError
from app.rag.retriever import TRUNCATION_MARKER

logger = logging.getLogger("app.rag.overview")

#: System-prompt marker for KB overview generation — the E2E mock LLM keys
#: on it (same convention as ``SUMMARY_MODE`` / ``DEFLECT_MODE``).
KB_OVERVIEW_MODE = "KB_OVERVIEW_MODE"

#: Locked instruction for the ``lite`` model (phase 31): the overview is
#: the agent's *a priori* picture of the knowledge base, so it must be a
#: compact plain-text outline of basic categories and topics — strictly
#: grounded in the document list, nothing invented.
OVERVIEW_INSTRUCTION = (
    "From the document list below, write a compact plain-text outline of "
    "the basic categories and topics this knowledge base covers. Group by "
    "source where useful, use `-` bullet lines, at most ~1500 characters, "
    "no markdown headings, and no topics not present in the list."
)

#: Full system prompt: marker first (the mock's key), then the instruction.
SYSTEM_PROMPT = f"{KB_OVERVIEW_MODE}: {OVERVIEW_INSTRUCTION}"


class OverviewLLM(Protocol):
    """The one-shot chat surface the overview generator needs.

    :class:`app.rag.llm.LLMClient` satisfies it; unit tests pass a
    duck-typed fake (``chat`` + ``settings``) instead — same pattern as
    the summarizer's ``SummaryLLM`` protocol.
    """

    settings: Settings

    async def chat(
        self, messages: list[dict[str, str]], model: str | None = None
    ) -> str: ...


def _first_summary_line(summary: str | None) -> str:
    """First line of a stored summary, stripped; ``''`` when absent.

    The stored summary (phase 30) ends in the code-appended
    ``Source: …`` pointer line, so its first line is the model-written
    lead sentence — the best one-line picture of the document for the
    outline. Blank/whitespace-only summaries yield ``''`` as well.
    """
    if not summary:
        return ""
    for line in summary.splitlines():
        stripped = line.strip()
        if stripped:
            return stripped
    return ""


def _source_inventory(rows: Sequence[tuple[str, str, str, str | None]]) -> str:
    """The phase-162 deterministic source inventory (LOCKED A2).

    Mechanical, non-LLM: one entry per **distinct** source in catalog
    order (``source, path`` — first occurrence in the ``source,
    path``-ordered rows), each ``<name> (<k> doc|docs)`` — singular
    ``doc`` at k=1, ``docs`` otherwise — joined with ``, `` behind the
    ``Sources: `` prefix. The ``lite`` outline stays the model's job;
    this line guarantees no source — not even a 1-doc one like the
    2026-10-07 ``ikea_instructions`` case — can be invisible to
    ``<knowledge_base>``, whatever the model outputs. The mock/real
    model outputs never affect it.

    *rows* is the existing ``(source, path, title, summary)``
    projection :func:`regenerate_overview` already reads — no new
    query. At the default ``BOR_KB_OVERVIEW_MAX_CHARS`` (4000) the
    outline plus this one line always fit; a smaller owner-set cap
    cuts the tail first (accepted — the cap is owner-tunable).
    """
    counts: dict[str, int] = {}
    for source, _path, _title, _summary in rows:
        counts[source] = counts.get(source, 0) + 1
    entries = ", ".join(
        f"{name} ({count} {'doc' if count == 1 else 'docs'})"
        for name, count in sorted(counts.items())
    )
    return f"Sources: {entries}"


def build_overview_prompt(
    rows: Sequence[tuple[str, str, str, str | None]], max_chars: int | None = None
) -> tuple[str, str]:
    """The ``(system, user)`` message pair for one overview call.

    Each row is ``(source, path, title, summary)``.

    * ``system`` — :data:`SYSTEM_PROMPT`: the ``KB_OVERVIEW_MODE`` marker
      + the locked instruction.
    * ``user`` — one line per document,
      ``source — path — title — {first line of summary}``, joined with
      newlines, in the EXACT order the caller passes *rows* (order-
      preserving; the caller — :func:`regenerate_overview` — passes the
      catalogue recent-first, phase 142 task 02). The summary field is
      omitted when the document has no summary (pre-phase-30 rows, the
      fail-soft path, and pre-backfill NULL rows — no dangling dash).
      The list is capped at *max_chars* (default
      ``BOR_OVERVIEW_INPUT_MAX_CHARS``): overflow is cut exactly at the
      cap and the shared ``[…truncated…]`` marker is appended on its own
      line, so the model never sees more than the cap and the cut is
      visible (summarizer convention, phase 30).
    """
    limit = max_chars if max_chars is not None else get_settings().overview_input_max_chars
    lines: list[str] = []
    for source, path, title, summary in rows:
        line = f"{source} — {path} — {title}"
        first = _first_summary_line(summary)
        if first:
            line += f" — {first}"
        lines.append(line)
    user = "\n".join(lines)
    if len(user) > limit:
        user = user[:limit] + "\n" + TRUNCATION_MARKER
    return SYSTEM_PROMPT, user


def load_kb_overview(db: Session) -> str:
    """The stored KB outline for prompt injection (phase 31, task 03).

    One indexed PK lookup (the single row, ``id = 1``) returning
    ``content`` trimmed. Returns ``""`` when the row is missing or
    empty — the chat path then omits the ``<knowledge_base>`` section
    entirely, keeping the prompt byte-identical to the pre-phase text
    (phase 15 convention).
    """
    row = db.get(KbOverview, 1)
    if row is None:
        return ""
    return (row.content or "").strip()


async def regenerate_overview(
    llm: OverviewLLM, session: Session | None = None
) -> bool:
    """Generate a fresh KB outline with the ``lite`` model and upsert it.

    Best-effort and change-gated by the caller (phase locked decisions):
    the import script (phase 31, task 04) and the admin sync (phase 32)
    invoke this only when an import added/updated at least one document
    (or no row exists yet). *session* may be supplied (the import
    script's own session, tests); a private one is opened and closed
    otherwise — same convention as ``import_sources``.

    * Zero documents → the existing row (if any) is left untouched and
      ``False`` is returned — no KB, no outline, no wasted model call.
    * Happy path → the model's text (trailing newlines rstripped) plus
      the deterministic ``Sources: …`` inventory line (phase 162,
      LOCKED A2 — :func:`_source_inventory`) is upserted into the
      single row (``id = 1``, fresh UTC ``updated_at``), committed, and
      ``overview: regenerated docs=… chars=…`` is logged (chars = the
      FULL stored content, tail included); returns ``True``. Idempotent
      by construction: one row, always ``id = 1``. The model input
      never sees the tail; the zero-doc and ``LLMError`` paths below
      leave a previous row byte-identical — an existing tail is part of
      the stored content and is preserved on failure.
    * :class:`LLMError` → ``overview: regeneration failed — …`` is
      logged and ``False`` is returned with the previous row intact —
      an old outline is better than none.
    """
    owns_session = session is None
    if session is None:
        session = SessionLocal()
    try:
        # RECENT-FIRST (phase 142, task 02): the document's date
        # (``created_at``, phase 106) descending, so when the input cap
        # bites the OLDEST documents fall off — the outline always
        # represents the recent KB. The (source, path) tie-break keeps
        # same-date documents in the pre-phase-142 lexicographic order
        # (deterministic digest; byte-identical for single-date KBs).
        result = session.execute(
            select(Document.source, Document.path, Document.title, Document.summary)
            .order_by(Document.created_at.desc(), Document.source, Document.path)
        ).all()
        rows: list[tuple[str, str, str, str | None]] = [
            (source, path, title, summary)
            for source, path, title, summary in result
        ]
        if not rows:
            logger.info(
                "overview: no documents in the knowledge base — "
                "leaving any existing outline untouched"
            )
            return False

        system, user = build_overview_prompt(rows)
        try:
            text = await llm.chat(
                [{"role": "system", "content": system}, {"role": "user", "content": user}],
                model=llm.settings.llm_summary_model,
            )
        except LLMError as e:
            logger.error("overview: regeneration failed — %s", e)
            return False

        # Phase 162 (LOCKED A2): the deterministic source inventory is
        # appended to the STORED content after the model's outline —
        # mechanical, non-LLM, so no source can be invisible to
        # `<knowledge_base>`. The model input above never sees the tail.
        content = text.rstrip("\n") + "\n" + _source_inventory(rows)

        now = datetime.now(UTC)
        row = session.get(KbOverview, 1)
        if row is None:
            session.add(KbOverview(id=1, content=content, updated_at=now))
        else:
            row.content = content
            row.updated_at = now
        session.commit()
        logger.info("overview: regenerated docs=%d chars=%d", len(rows), len(content))
        return True
    finally:
        if owns_session:
            session.close()