"""Readable concept keys — `TYPE_SUBJECT`, the label a person or an agent searches by.

Asked for in the 2026-09-08 discussion (m1). The shape is the one agreed there:
the type first, then what the entry is *about*, in capitals — `GLOSSARY_PA`,
never the entry's full text. Two properties it exists to provide:

- **One concept, one key.** `PA` drawn from five documents still reads
  `GLOSSARY_PA`, so an agent that needs a term's definition writes the key and
  looks it up directly — no scan, no embedding, no model call.
- **Readable at a glance.** Capitals were a deliberate call (lowercase reads
  worse in a list), and lookups are capitals too.

**A key is a label, never an identity — this is m2.** `entity_id` in `ids.py`
stays the thing an expert's approval hangs on, because it is a hash of content
and survives a re-run untouched. A key is built from a *surface*, so it moves
the moment clustering canonicalises that surface differently. Both travel
together and neither substitutes for the other: the hash identifies, the key
reads. Collapsing the two is exactly how approvals get orphaned, which is the
failure `ids.py` was written to prevent.

Prefixes use the `kind` column's own vocabulary (English, singular) so the
system holds one spelling of each branch rather than two to keep in sync
(decided 2026-09-14).
"""

from __future__ import annotations

import hashlib
import re
import unicodedata
from collections.abc import Iterable, Mapping
from typing import Any

# Keyed by the `kind` column's values, so a new kind that forgets to register
# here returns None rather than silently inventing a prefix.
_PREFIX: dict[str, str] = {
    "glossary": "GLOSSARY",
    "rule": "RULE",
    "formula": "FORMULA",
    "document": "DOCUMENT",
    "domain": "DOMAIN",
}

# Past this a subject stops being a label and becomes the content it was meant
# to stand in for. A rule's `statement` can be a whole paragraph.
MAX_SUBJECT = 40

# Short, and deliberately NOT the full `entity_id`: this digest separates two
# rules that govern the same term. It does not identify the row — `entity_id`
# does, and shortening a hash for readability is only safe because of that.
DIGEST_LEN = 6


def slugify(surface: str) -> str:
    """`Physical of Availability (PA)` -> `PHYSICAL_OF_AVAILABILITY_PA`.

    Accents are folded rather than dropped so an Indonesian or a borrowed term
    keeps its letters. Everything that is not a letter or a digit becomes a
    single underscore, because a key that carries brackets or slashes cannot be
    typed from memory — which is the whole point of having one.
    """
    folded = unicodedata.normalize("NFKD", surface or "")
    folded = "".join(c for c in folded if not unicodedata.combining(c))
    slug = re.sub(r"[^A-Za-z0-9]+", "_", folded).upper()
    slug = re.sub(r"_+", "_", slug).strip("_")
    if len(slug) <= MAX_SUBJECT:
        return slug
    # Cut on a word boundary so the tail is not half a word — but a single long
    # token has no boundary to cut on, and an empty subject is worse than a
    # blunt one.
    cut = slug[:MAX_SUBJECT]
    head, _, _tail = cut.rpartition("_")
    return (head or cut).strip("_")


def _digest(value: str) -> str:
    return hashlib.sha256(value.encode("utf-8")).hexdigest()[:DIGEST_LEN].upper()


def term_surfaces(glossary_payloads: Iterable[Mapping[str, Any]] | None) -> dict[str, str]:
    """`term_id` -> the term's surface, for keying the rules that govern it.

    Built by the caller from the same run's glossary payloads, because a rule
    payload carries `term_ids` and no surfaces — the words live on the glossary
    entry, not on the rule.
    """
    out: dict[str, str] = {}
    for payload in glossary_payloads or []:
        term_id = payload.get("term_id")
        term = payload.get("term")
        if term_id and isinstance(term, str) and term.strip():
            out[str(term_id)] = term.strip()
    return out


def _rule_subject(
    payload: Mapping[str, Any], entity_id: str, surfaces: Mapping[str, str]
) -> str:
    """A rule has no canonical surface of its own — it is a sentence.

    So it borrows the term it governs and adds a short digest, because one term
    usually governs several rules: `RULE_PA_C07BE4`. Asking the model to name
    the rule was the obvious alternative and is the one `ids.py` already rules
    out — a model cannot produce a stable identifier, and a model-written
    `rule_id` was a real defect here, returning a different slug for the same
    rule on consecutive runs at temperature 0. A rule that governs no term
    keeps the digest alone; that it is not searchable by word was accepted when
    this was agreed.
    """
    for term_id in payload.get("term_ids") or []:
        surface = slugify(surfaces.get(str(term_id), ""))
        if surface:
            return f"{surface}_{_digest(entity_id)}"
    return _digest(entity_id)


def _subject(
    kind: str,
    payload: Mapping[str, Any],
    entity_id: str,
    doc_id: str,
    surfaces: Mapping[str, str],
) -> str:
    if kind == "glossary":
        return slugify(payload.get("term") or "")
    if kind == "formula":
        # A formula may legitimately have no name; `entity_id` already falls
        # back name -> latex -> chunk_id, so the digest inherits that work.
        return slugify(payload.get("name") or "") or _digest(entity_id)
    if kind == "document":
        # The document's own id reads better than its title. A title is a
        # verbatim transcription and routinely carries the PDF's broken
        # spacing — correct to store, useless to type.
        return slugify(doc_id) or _digest(entity_id)
    if kind == "domain":
        return slugify(payload.get("domain_name") or "")
    if kind == "rule":
        return _rule_subject(payload, entity_id, surfaces)
    return ""


def concept_key(
    kind: str,
    payload: Mapping[str, Any],
    *,
    entity_id: str,
    doc_id: str = "",
    surfaces: Mapping[str, str] | None = None,
) -> str | None:
    """The `TYPE_SUBJECT` key for one entry; None when the kind is unregistered.

    Never raises: the caller writes this into a row alongside content it has
    already validated, and a key that cannot be built is a degraded label, not
    a reason to lose the entry.
    """
    prefix = _PREFIX.get(kind)
    if prefix is None:
        return None
    subject = _subject(kind, payload, entity_id, doc_id, surfaces or {})
    return f"{prefix}_{subject}" if subject else prefix