"""Dependency-free config loading (ADR-0001).

One TOML-subset parser for the shapes this repo writes: dotted [section.name]

tables, string/boolean/string-list values. If a config outgrows this subset,

simplify the config, not the parser.

"""

from __future__ import annotations

from pathlib import Path

from typing import Any

try:

    import tomllib

except ModuleNotFoundError:  # Python 3.9/3.10 on stock macOS.

    tomllib = None  # type: ignore[assignment]

def load_toml(path: Path) -> dict[str, Any]:

    text = path.read_text()

    if tomllib is not None:

        return tomllib.loads(text)

    root: dict[str, Any] = {}

    current: dict[str, Any] | None = None

    for raw_line in text.splitlines():

        line = _strip_toml_comment(raw_line).strip()

        if not line:

            continue

        if line.startswith("[") and line.endswith("]"):

            parts = line[1:-1].split(".")

            current = root

            for part in parts:

                current = current.setdefault(part, {})

            continue

        if current is None or "=" not in line:

            continue

        key, value = [part.strip() for part in line.split("=", 1)]

        if value in {"true", "false"}:

            current[key] = value == "true"

        elif value.startswith('"') and value.endswith('"'):

            current[key] = value[1:-1]

        elif value.startswith("'") and value.endswith("'"):

            current[key] = value[1:-1]

        elif value.startswith("[") and value.endswith("]"):

            items = [item.strip().strip('"').strip("'") for item in value[1:-1].split(",") if item.strip()]

            current[key] = items

        else:

            current[key] = value

    return root

def _strip_toml_comment(raw_line: str) -> str:

    quote: str | None = None

    escaped = False

    for index, char in enumerate(raw_line):

        if escaped:

            escaped = False

            continue

        if char == "\\":

            escaped = quote == '"'

            continue

        if quote is not None:

            if char == quote:

                quote = None

            continue

        if char in {"'", '"'}:

            quote = char

            continue

        if char == "#":

            return raw_line[:index]

    return raw_line

def load_subject_config(path: Path) -> dict[str, Any]:

    data = load_toml(path)

    if "subjects" not in data:

        return {"subjects": {}}

    return {"subjects": data["subjects"]}