"""Unique result-directory creation and JSON output."""

from __future__ import annotations

from dataclasses import dataclass
from datetime import datetime
import json
import os
from pathlib import Path
import re
from typing import Any, Mapping


@dataclass(frozen=True)
class ResultDirectory:
	path: Path
	metadata_path: Path
	commands_path: Path


def create_result_directory(
	root: Path,
	test_name: str,
	started_at: datetime | None = None,
) -> ResultDirectory:
	name = _slug(test_name)
	started = started_at or datetime.now().astimezone()
	base_name = f"{started:%Y%m%d-%H%M%S}-{name}"
	root.mkdir(parents=True, exist_ok=True)
	path = _mkdir_unique(root, base_name)
	metadata_path = path / "metadata.json"
	commands_path = path / "commands.log"
	commands_path.touch(exist_ok=False)
	write_json(
		metadata_path,
		{
			"test": name,
			"started_at": started.isoformat(),
			"result_directory": str(path),
		},
	)
	return ResultDirectory(path, metadata_path, commands_path)


def write_json(path: Path, value: Mapping[str, Any]) -> None:
	path.parent.mkdir(parents=True, exist_ok=True)
	temporary = path.with_name(f".{path.name}.{os.getpid()}.tmp")
	with temporary.open("w", encoding="utf-8") as handle:
		json.dump(value, handle, indent=2, sort_keys=True)
		handle.write("\n")
	temporary.replace(path)


def _slug(value: str) -> str:
	result = re.sub(r"[^a-z0-9]+", "-", value.casefold()).strip("-")
	if not result:
		raise ValueError("test_name must contain a letter or digit")
	return result


def _mkdir_unique(root: Path, base_name: str) -> Path:
	for index in range(1000):
		suffix = "" if index == 0 else f"-{index:02d}"
		candidate = root / f"{base_name}{suffix}"
		try:
			candidate.mkdir()
		except FileExistsError:
			continue
		return candidate
	raise FileExistsError(f"Could not allocate a unique result directory for {base_name}")