from __future__ import annotations
from dataclasses import dataclass
from pathlib import Path
from typing import Iterable

SCALE_NATIVE = {
    "Z": 20_000_000,
    "A": 3_000_000,
    "B": 1_000_000,
    "C": 200_000,
    "D": 100_000,
    "E": 50_000,
    "F": 20_000,
    "G": 7_500,
}

@dataclass(frozen=True)
class CellFile:
    path: Path
    relative_path: Path
    scale_code: str
    native_scale: int

@dataclass(frozen=True)
class ScanResult:
    root: Path
    cells: tuple[CellFile, ...]
    object_dictionary: Path | None
    attribute_dictionary: Path | None

def _find_case_insensitive(root: Path, names: set[str]) -> Path | None:
    lowers = {n.lower() for n in names}
    for p in root.rglob("*"):
        if p.is_file() and p.name.lower() in lowers:
            return p
    return None

def scan_cm93(root: Path) -> ScanResult:
    root = root.resolve()
    if not root.exists():
        raise FileNotFoundError(root)
    cells = []
    for p in root.rglob("*"):
        if not p.is_file():
            continue
        ext = p.suffix.upper().lstrip(".")
        if ext in SCALE_NATIVE:
            cells.append(
                CellFile(
                    path=p,
                    relative_path=p.relative_to(root),
                    scale_code=ext,
                    native_scale=SCALE_NATIVE[ext],
                )
            )
    cells.sort(key=lambda c: (c.scale_code, str(c.relative_path).lower()))
    obj = _find_case_insensitive(root, {"CM93OBJ.DIC"})
    attr = _find_case_insensitive(root, {"ATTRLUT.DIC", "CM93ATTR.DIC"})
    return ScanResult(root, tuple(cells), obj, attr)