"""Locked system-prompt builder (PLAN §6).

The persona + HONESTY GATE text is **locked verbatim** — change it through
the plan, not here. (PLAN §6 revision, 2026-08-22: the owner's working-tree
persona edits are preserved — no mandated ``"you've got this"`` tagline and
no mandated deflection opening; the honesty gate itself is unchanged.)

Two modes:

* ``HIGH`` — grounded turn: full top-document texts under ``<documents>``.
* ``LOW``  — deflection turn: weak-hit *titles only* plus the
  ``DEFLECT_MODE`` marker (the E2E mock LLM keys on that marker).

Steering (phase 15): when the owner has stored tuning notes, both modes
carry a ``<tuning>`` section between ``<relevance>…</relevance>`` and the
mode body. With zero notes the prompt is byte-identical to the
pre-steering text.

KB overview (phase 31): when the single ``kb_overview`` row holds a
lite-generated outline of the knowledge base, both modes carry a
``<knowledge_base>`` section between ``<relevance>…</relevance>`` and
the ``<tuning>`` section (order: ``<relevance>`` →
``<knowledge_base>`` → ``<tuning>`` → mode body) — the agent knows
roughly what the KB contains before retrieval. With an empty row the
prompt is byte-identical to the pre-phase text.

Agent tools (phase 37): the **HIGH** prompt only carries a ``<tools>``
section after the ``<documents>`` body — the grounded turn may call the
server-side ``list_documents`` / ``read_document`` tools (round-capped,
see :mod:`app.rag.agent`). The LOW/deflection prompt never carries it
and stays byte-identical to the pre-phase text.
"""
from __future__ import annotations

from collections.abc import Sequence

from app.config import get_settings
from app.models import Document
from app.rag.retriever import TRUNCATION_MARKER

#: PLAN §6 verbatim (line wrapping included); ``{relevance}`` is filled by
#: :func:`_base`.
PERSONA: str = (
    'You are "Brain of Reese" — the digital brain of Reese, a self-hoster and\n'
    "homelab tinkerer. Personality: chippy, upbeat, warm, and genuinely\n"
    "optimistic about the user's ability to do things.\n"
    "\n"
    "Rules:\n"
    "1. Answer ONLY from the provided document context. Cite which document(s)\n"
    "   you used, by path.\n"
    "2. Be concrete: names, versions, ports, hosts, schedules — the specifics in\n"
    "   the docs are the value.\n"
    '3. HONESTY GATE: if <relevance> is "LOW", you must NOT pretend to know.\n'
    "   Offer 2-3 alternative questions about things you DO have notes on.\n"
    "4. Never invent facts, hosts, or steps that are not in the context.\n"
    "5. Keep answers tight: short paragraphs, bullets where helpful.\n"
    "\n"
    "<relevance>{relevance}</relevance>"
)

#: One-line intro of the ``<tuning>`` section (phase 15): the owner's notes
#: steer the answer and win over the defaults when they conflict.
_STEERING_INTRO = (
    "The owner of this brain asked you to steer your answers as follows. "
    "Where these instructions conflict with the defaults above, follow the owner:\n"
)

#: One-line intro of the ``<knowledge_base>`` section (phase 31): the
#: lite-generated outline is the agent's a-priori picture of the KB.
_KB_INTRO = (
    "The basic categories of everything in this knowledge base "
    "(generated at import time):\n"
)

#: The ``<tools>`` instructions section — **HIGH prompt only** (phase 37,
#: task 03): a grounded turn may extend its context through the two
#: server-side tools (round cap: ``BOR_AGENT_MAX_ROUNDS``, see
#: :mod:`app.rag.agent`). Appended after
#: the mode body (``<documents>``), so the instructions are the last
#: thing the model reads. The LOW/deflection prompt never carries it —
#: a deflection has no grounded context to extend — and stays
#: byte-identical to the pre-phase text. The E2E mock keys off the
#: ``<tools>`` marker's *presence*, not this wording.
TOOLS_SECTION: str = (
    "<tools>\n"
    "If the documents in your context reference other files, or you need "
    "content that is not included above, call `list_documents` to see what "
    "is indexed, then `read_document` to pull in exactly one more document. "
    "Answer as soon as you have what you need — do not read more than one "
    "extra document.\n"
    "</tools>"
)


def _base(relevance: str) -> str:
    if relevance not in ("HIGH", "LOW"):
        raise ValueError(f"relevance must be HIGH or LOW, got {relevance!r}")
    return PERSONA.replace("{relevance}", relevance)


def build_steering_section(notes: Sequence[str], max_chars: int | None = None) -> str:
    """The ``<tuning>`` section of the system prompt (phase 15).

    * No notes (or only blank ones) → ``""`` — callers then build the
      prompt exactly as before, so a zero-note prompt is byte-identical to
      the pre-steering text.
    * Otherwise: numbered notes (in the given order — the chat turn passes
      them oldest-first, so #1 is the oldest note) capped at *max_chars*
      (default ``BOR_STEERING_MAX_CHARS``). When the budget cannot hold
      every note, the oldest-fitting prefix is kept and the overflow is
      replaced by the shared ``[…truncated…]`` marker.
    """
    cleaned = [str(n).strip() for n in notes]
    cleaned = [n for n in cleaned if n]
    if not cleaned:
        return ""
    limit = max_chars if max_chars is not None else get_settings().steering_max_chars
    if limit <= 0:
        return ""

    def render(count: int) -> str:
        lines = [f"{i}. {note}" for i, note in enumerate(cleaned[:count], start=1)]
        if count < len(cleaned):
            lines.append(TRUNCATION_MARKER)
        return f"<tuning>\n{_STEERING_INTRO}" + "\n".join(lines) + "\n</tuning>"

    for count in range(len(cleaned), 0, -1):
        rendered = render(count)
        if len(rendered) <= limit:
            return rendered
    # Pathological budget: not even the empty note list fits. The section
    # must still respect the cap — the bare marker when it fits, else none.
    if len(TRUNCATION_MARKER) <= limit:
        return TRUNCATION_MARKER
    return ""


def build_kb_section(overview: str, max_chars: int | None = None) -> str:
    """The ``<knowledge_base>`` section of the system prompt (phase 31).

    * No outline (or only whitespace) → ``""`` — callers then build the
      prompt exactly as before, so a no-overview prompt is byte-identical
      to the pre-phase text (phase 15 convention).
    * Otherwise: the intro line + the stored outline, capped at
      *max_chars* (default ``BOR_KB_OVERVIEW_MAX_CHARS``). When the budget
      cannot hold the whole outline, the longest-fitting prefix is kept
      and the overflow is replaced by the shared ``[…truncated…]`` marker
      on its own line — the exact :func:`build_steering_section` pattern,
      including its pathological-budget handling (never exceed the cap;
      bare marker when even one outline character does not fit).
    """
    text = str(overview or "").strip()
    if not text:
        return ""
    limit = max_chars if max_chars is not None else get_settings().kb_overview_max_chars
    if limit <= 0:
        return ""

    def render(cut: int) -> str:
        lines = [text[:cut]]
        if cut < len(text):
            lines.append(TRUNCATION_MARKER)
        return f"<knowledge_base>\n{_KB_INTRO}" + "\n".join(lines) + "\n</knowledge_base>"

    for cut in range(len(text), 0, -1):
        rendered = render(cut)
        if len(rendered) <= limit:
            return rendered
    # Pathological budget: not even one outline character fits. The
    # section must still respect the cap — the bare marker when it fits,
    # else none (steering precedent, phase 15).
    if len(TRUNCATION_MARKER) <= limit:
        return TRUNCATION_MARKER
    return ""


def build_high_prompt(
    documents: Sequence[Document],
    notes: Sequence[str] | None = None,
    kb_overview: str | None = None,
) -> str:
    """Grounded turn: locked persona (+ steering, + KB overview) + full
texts of the top documents + the ``<tools>`` instructions (phase 37).

    Section order: ``<relevance>`` → ``<knowledge_base>`` → ``<tuning>``
    → ``<documents>`` → ``<tools>``; empty steering/overview omit their
    section. ``<tools>`` is always present in the HIGH prompt (the round
    cap — not the prompt — decides whether the tools are actually
    offered to the model, see :mod:`app.rag.agent`).
    """
    blocks = [
        f'<document source="{doc.source}" path="{doc.path}" title="{doc.title}">\n'
        f"{doc.content}\n"
        "</document>"
        for doc in documents
    ]
    body = "\n\n".join(blocks) if blocks else (
        "(no documents matched — do not invent specifics)"
    )
    prompt = _base("HIGH")
    for part in (build_kb_section(kb_overview or ""), build_steering_section(notes or [])):
        if part:
            prompt += "\n" + part
    return prompt + "\n<documents>\n" + body + "\n</documents>\n" + TOOLS_SECTION


def build_deflect_prompt(
    titles: Sequence[str],
    notes: Sequence[str] | None = None,
    kb_overview: str | None = None,
) -> str:
    """Deflection turn: weak-hit titles only (no document content).

    Section order (phase 31): ``<relevance>`` → ``<knowledge_base>`` →
    ``<tuning>`` → ``DEFLECT_MODE`` body; empty steering/overview omit
    their section, keeping the prompt byte-identical to the pre-phase text.
    """
    weak = "\n".join(f"- {t}" for t in titles) if titles else "(nothing close at all)"
    mid = "\n".join(
        part
        for part in (build_kb_section(kb_overview or ""), build_steering_section(notes or []))
        if part
    )
    gap = f"\n{mid}\n" if mid else "\n"
    return (
        _base("LOW")
        + gap
        + "DEFLECT_MODE: retrieval was weak — the titles below are the closest "
        "your notes come to the question. They are titles only; do not pretend "
        "they answer it. Use them to propose 2-3 alternative questions.\n"
        + weak
    )