from __future__ import annotations

import fcntl
import json
import os
from pathlib import Path
import tempfile
from typing import Callable, TypeVar


ALIAS_REGISTRY_VERSION = 1
MAX_ALIAS_LENGTH = 48
UpdateResult = TypeVar("UpdateResult")


class AliasRegistryError(RuntimeError):
    """A display-name registry error which is safe to show to the user."""


def normalize_alias(label: str) -> str:
    normalized = label.strip()
    if len(normalized) > MAX_ALIAS_LENGTH:
        raise ValueError(f"display name must be at most {MAX_ALIAS_LENGTH} characters")
    if any(ord(character) < 32 or ord(character) == 127 for character in normalized):
        raise ValueError("display name must not contain control characters")
    return normalized


def default_alias_registry_path() -> Path:
    if override := os.environ.get("HERDR_HUB_ALIASES_FILE"):
        return Path(override).expanduser()
    config_home = os.environ.get("XDG_CONFIG_HOME")
    root = Path(config_home).expanduser() if config_home else Path.home() / ".config"
    return root / "herdr-hub" / "aliases.json"


class AliasRegistry:
    def __init__(self, path: Path | None = None) -> None:
        self.path = path or default_alias_registry_path()

    @property
    def lock_path(self) -> Path:
        return self.path.with_name(f".{self.path.name}.lock")

    def load(self) -> dict[str, str]:
        if not self.path.exists():
            return {}
        try:
            payload = json.loads(self.path.read_text(encoding="utf-8"))
        except (OSError, json.JSONDecodeError) as error:
            raise AliasRegistryError(f"cannot read {self.path}: {error}") from error
        return _parse_aliases(payload, self.path)

    def set(self, endpoint_key: str, label: str) -> bool:
        _validate_endpoint_key(endpoint_key)
        normalized = normalize_alias(label)

        def update(aliases: dict[str, str]) -> tuple[dict[str, str], bool]:
            updated = dict(aliases)
            if normalized:
                changed = updated.get(endpoint_key) != normalized
                updated[endpoint_key] = normalized
            else:
                changed = endpoint_key in updated
                updated.pop(endpoint_key, None)
            return updated, changed

        return self._update(update)

    def _update(
        self,
        callback: Callable[[dict[str, str]], tuple[dict[str, str], UpdateResult]],
    ) -> UpdateResult:
        try:
            self.path.parent.mkdir(mode=0o700, parents=True, exist_ok=True)
            with self.lock_path.open("a+", encoding="utf-8") as lock:
                fcntl.flock(lock.fileno(), fcntl.LOCK_EX)
                aliases = self.load()
                updated, outcome = callback(aliases)
                if updated != aliases:
                    self._write(updated)
                return outcome
        except AliasRegistryError:
            raise
        except OSError as error:
            raise AliasRegistryError(f"cannot update {self.path}: {error}") from error

    def _write(self, aliases: dict[str, str]) -> None:
        payload = {
            "version": ALIAS_REGISTRY_VERSION,
            "aliases": dict(sorted(aliases.items())),
        }
        temporary_name: str | None = None
        try:
            with tempfile.NamedTemporaryFile(
                mode="w",
                encoding="utf-8",
                dir=self.path.parent,
                prefix=f".{self.path.name}.",
                delete=False,
            ) as temporary:
                temporary_name = temporary.name
                json.dump(payload, temporary, ensure_ascii=False, indent=2)
                temporary.write("\n")
                temporary.flush()
                os.fsync(temporary.fileno())
            os.chmod(temporary_name, 0o600)
            os.replace(temporary_name, self.path)
            directory_fd = os.open(self.path.parent, os.O_RDONLY | os.O_DIRECTORY)
            try:
                os.fsync(directory_fd)
            finally:
                os.close(directory_fd)
        finally:
            if temporary_name is not None:
                try:
                    Path(temporary_name).unlink(missing_ok=True)
                except OSError:
                    pass


def _parse_aliases(payload: object, path: Path) -> dict[str, str]:
    if (
        not isinstance(payload, dict)
        or payload.get("version") != ALIAS_REGISTRY_VERSION
    ):
        raise AliasRegistryError(f"{path} has an unsupported or missing version")
    raw_aliases = payload.get("aliases")
    if not isinstance(raw_aliases, dict):
        raise AliasRegistryError(f"{path} does not contain an aliases object")

    aliases: dict[str, str] = {}
    for key, raw_label in raw_aliases.items():
        if not isinstance(key, str) or not isinstance(raw_label, str):
            raise AliasRegistryError(f"{path} contains an invalid alias entry")
        try:
            _validate_endpoint_key(key)
            label = normalize_alias(raw_label)
        except ValueError as error:
            raise AliasRegistryError(f"{path}: {error}") from error
        if not label:
            raise AliasRegistryError(f"{path}: display names must not be empty")
        aliases[key] = label
    return dict(sorted(aliases.items()))


def _validate_endpoint_key(key: str) -> None:
    if not key or len(key) > 1024:
        raise ValueError("endpoint key has an invalid length")
    if any(ord(character) < 32 or ord(character) == 127 for character in key):
        raise ValueError("endpoint key must not contain control characters")