"""What this instance decided, read from `kb/CONVENTIONS.md`.

`kb/CONTRACT.md` and this file answer two different questions. The contract
holds what the code enforces - what a collection is, which files are generated,
how `provenance:` works - and is identical in every instance, so `dist export`
ships it verbatim. `kb/CONVENTIONS.md` holds what each instance decides for
itself: the language its pages are written in, the relationship-label
vocabulary, the tone examples, the hedging rule, the ADR prefix. The
distribution ships only `kb/CONVENTIONS.md.template`, exactly the split
`USER.md`/`SOUL.md` already use one directory up.

Only one part of it is machine-read, and it is the part that used to be Python:
the three section headings `xref add` and `cite add` write. While
`RELATIONSHIPS = "Beziehungen"` sat in `sections.py`, an instance writing its
pages in any other language had to edit the compiler to say so - which made the
KB language a stack property in code while every document called it an instance
decision.

**A missing conventions file is not an error here.** It is the state an
instance is in between installing this machinery and running the migration that
writes the file, and every command has to keep working through it. The fallback
is `PRE_CONVENTIONS_NAMES` - not "the stack's language", but *what this stack
hardcoded before the file existed*, which is by construction what any corpus
reaching that state was written with. `wikitool doctor` is what says the file is
missing; degrading loudly here would take out `doctor` itself.
"""
from __future__ import annotations

from pathlib import Path
from typing import Any, Optional

from chemenu import config
from chemenu.frontmatter_io import read_page

CONVENTIONS_FILENAME = "CONVENTIONS.md"
CONVENTIONS_TEMPLATE = f"{CONVENTIONS_FILENAME}.template"

# The two tool-owned regions, keyed by the block name in `chemenu.blocks`. The
# block name is the identifier - it is what the marker pair carries and what the
# tool locates the region by - while the heading text below it is prose the
# instance chooses.
#
# `see_also` is gone as a section: it was the reciprocal half of the old
# bidirectional `xref add`, and under authored directional edges it is a *label*
# inside the links block rather than a region of its own.
SECTIONS_KEY = "sections"
LANGUAGE_KEY = "language"

# What a heading renders as when the instance has not said. Purely cosmetic, and
# that is a genuine change from before: while the tool located a region by
# matching this text, a wrong default silently split a page into two sections and
# `xref add` appended to the wrong one. Now the marker pair carries the identity,
# so a region rendered under the wrong words is a *display* fault that the next
# write repairs by itself once `kb/CONVENTIONS.md` says otherwise.
#
# So this is a fallback for the window between installing the machinery and
# writing the conventions file - `doctor` is what makes that window loud - and
# not a language the compiler has an opinion about.
DEFAULT_HEADINGS: dict[str, str] = {
    "links": "Relationships",
    "footnotes": "Footnotes",
}


def conventions_file() -> Path:
    return config.KB_DIR / CONVENTIONS_FILENAME


# (path, mtime_ns, size) -> frontmatter. `heading_re()` is called once per page
# per lint run, so re-reading the file each time would put a stat+parse on a
# per-page path for a document that changes about once per instance. Keyed on
# the stat rather than on the path alone, so a test that rewrites the file
# inside one process is not answered out of the cache.
_CACHE: dict[tuple[str, int, int], dict[str, Any]] = {}


def read_conventions() -> dict[str, Any]:
    """`kb/CONVENTIONS.md`'s frontmatter, or `{}` if the file is absent.

    Permissive on purpose, like `read_page` itself: a conventions file with
    broken YAML degrades to the pre-conventions defaults rather than taking
    every command down with it. `doctor` and `docs verify` are where that
    surfaces as a finding.
    """
    path = conventions_file()
    if not path.is_file():
        return {}
    stat = path.stat()
    key = (str(path), stat.st_mtime_ns, stat.st_size)
    if key not in _CACHE:
        frontmatter, _ = read_page(path)
        _CACHE.clear()
        _CACHE[key] = frontmatter
    return _CACHE[key]


def reset_cache() -> None:
    """Drop the parsed conventions. For a caller that rewrote the file and has
    to see the new value within the same stat resolution."""
    _CACHE.clear()


def _mapping(key: str) -> dict[str, Any]:
    value = read_conventions().get(key)
    return value if isinstance(value, dict) else {}


def language() -> Optional[str]:
    """The declared KB language tag (e.g. `de`), or None if undeclared.

    Nothing in the compiler branches on it - the language is carried by the
    prose the instance writes, not by a switch. It is here because the
    conventions file is where a human and an agent look the answer up, and
    because `doctor` reports it.
    """
    value = read_conventions().get(LANGUAGE_KEY)
    if value is None:
        return None
    return str(value).strip() or None


def heading(block: str) -> str:
    """The heading this instance renders above `block`'s generated region."""
    declared = _mapping(SECTIONS_KEY).get(block)
    if isinstance(declared, str) and declared.strip():
        return declared.strip()
    return DEFAULT_HEADINGS.get(block, block.title())


def declaration_issues() -> list[str]:
    """What is wrong with this instance's conventions file, if anything.

    Shared by `doctor` (which FAILs on it) and `docs verify` (which refuses a
    tree with it), so the two cannot disagree about what a valid declaration
    looks like. An absent file is *not* reported here - that is a separate
    finding with a separate fix, and only `doctor` makes it one.
    """
    from chemenu import blocks

    path = conventions_file()
    if not path.is_file():
        return []

    issues: list[str] = []
    frontmatter, _ = read_page(path)
    if not frontmatter:
        return [
            f"kb/{CONVENTIONS_FILENAME} has no readable frontmatter - it must declare "
            f"`{SECTIONS_KEY}:` with the headings this instance renders"
        ]

    declared = frontmatter.get(SECTIONS_KEY)
    if not isinstance(declared, dict):
        return [
            f"kb/{CONVENTIONS_FILENAME}: `{SECTIONS_KEY}:` must be a mapping of "
            f"{'/'.join(blocks.BLOCKS)} to the heading this instance renders above it"
        ]
    for block in blocks.BLOCKS:
        value = declared.get(block)
        if not isinstance(value, str) or not value.strip():
            issues.append(
                f"kb/{CONVENTIONS_FILENAME}: `{SECTIONS_KEY}.{block}` is missing or empty - "
                f"the generated `{block}` region would render under a default heading rather "
                "than this instance's own"
            )
    for block in sorted(set(declared) - set(blocks.BLOCKS)):
        issues.append(
            f"kb/{CONVENTIONS_FILENAME}: `{SECTIONS_KEY}.{block}` is not a region the tool "
            f"generates; the regions are {', '.join(blocks.BLOCKS)}"
        )

    if config.TEMPLATE_SENTINEL in path.read_text(encoding="utf-8"):
        issues.append(
            f"kb/{CONVENTIONS_FILENAME} still carries the `{config.TEMPLATE_SENTINEL}` line - "
            "a renamed template is not a filled one"
        )
    return issues