"""Shared utilities for Companion (e.g. validation for config sync)."""

from __future__ import annotations

import logging
from typing import Any, Dict, Optional

from openhop_core.companion.constants import DEFAULT_MAX_CONTACTS

logger = logging.getLogger(__name__)

_INVALID_NODE_NAME_CHARS = "\n\r\x00"

# Optional per-companion RepeaterCompanionBridge constructor settings (power-user).
COMPANION_BRIDGE_SETTING_KEYS = frozenset({"max_contacts", "offline_queue_size"})

# Settings that must not be applied from config (fixed at openhop_core defaults).
_COMPANION_IGNORED_BRIDGE_KEYS = frozenset({"max_channels", "adv_type"})

# Contact flag bit 0 marks a favourite (protected from forced-trim eviction).
_CONTACT_FLAG_FAVOURITE = 0x01


class CompanionContactCapacityError(Exception):
    """Persisted companion contacts exceed configured max_contacts."""

    def __init__(
        self,
        companion_hash: str,
        stored_count: int,
        max_contacts: int,
        companion_name: Optional[str] = None,
    ) -> None:
        self.companion_hash = companion_hash
        self.stored_count = stored_count
        self.max_contacts = max_contacts
        self.companion_name = companion_name
        label = f"'{companion_name}'" if companion_name else companion_hash
        super().__init__(
            f"Companion {label}: {stored_count} contacts in storage exceeds "
            f"max_contacts={max_contacts}. Increase max_contacts or remove contacts before starting."
        )


def normalize_companion_identity_key(identity_key: str) -> str:
    """Strip whitespace and remove optional 0x prefix so fromhex() is consistent across installs."""
    s = identity_key.strip()
    if s.lower().startswith("0x"):
        s = s[2:].strip()
    return s


def validate_companion_node_name(value: str) -> str:
    """Validate node_name for config sync: non-empty, max 31 bytes UTF-8, no control chars."""
    if not isinstance(value, str):
        raise ValueError("node_name must be a string")
    s = value.strip()
    if not s:
        raise ValueError("node_name cannot be empty")
    if len(s.encode("utf-8")) > 31:
        raise ValueError("node_name too long (max 31 bytes UTF-8)")
    if any(c in s for c in _INVALID_NODE_NAME_CHARS):
        raise ValueError("node_name contains invalid characters")
    return s


def parse_positive_int(value: Any, field_name: str, *, minimum: int = 1) -> int:
    """Parse a positive integer from config or API input."""
    try:
        n = int(value)
    except (TypeError, ValueError) as e:
        raise ValueError(f"{field_name} must be a positive integer") from e
    if n < minimum:
        raise ValueError(f"{field_name} must be >= {minimum}")
    return n


def parse_companion_bridge_kwargs(settings: dict) -> Dict[str, int]:
    """Extract optional RepeaterCompanionBridge kwargs from companion settings.

    Only ``max_contacts`` and ``offline_queue_size`` are honored. ``max_channels`` and
    ``adv_type`` are ignored with a warning if present.
    """
    if not settings:
        return {}
    for key in _COMPANION_IGNORED_BRIDGE_KEYS:
        if key in settings:
            logger.warning(
                "Companion setting %r is not supported and will be ignored (fixed default)",
                key,
            )
    kwargs: Dict[str, int] = {}
    if "max_contacts" in settings:
        max_contacts = parse_positive_int(settings["max_contacts"], "max_contacts")
        kwargs["max_contacts"] = max_contacts
    if "offline_queue_size" in settings:
        # 0 is valid and means "off" (no offline message storage).
        kwargs["offline_queue_size"] = parse_positive_int(
            settings["offline_queue_size"], "offline_queue_size", minimum=0
        )
    return kwargs


def effective_max_contacts(bridge_kwargs: Dict[str, int]) -> int:
    """Return max_contacts from parsed kwargs or openhop_core default."""
    return bridge_kwargs.get("max_contacts", DEFAULT_MAX_CONTACTS)


def merge_companion_settings_update(current_settings: dict, patch: dict) -> Dict[str, Any]:
    """Merge a companion settings PATCH into current settings.

    Raises:
        ValueError: Unknown setting or invalid bridge setting value.
    """
    merged = dict(current_settings or {})
    for key, value in patch.items():
        if key not in COMPANION_SETTINGS_ALLOWLIST:
            raise ValueError(f"Unknown companion setting: {key}")
        if key in COMPANION_BRIDGE_SETTING_KEYS:
            parsed = parse_companion_bridge_kwargs({key: value})
            merged[key] = parsed[key]
        else:
            merged[key] = value
    return merged


def validate_companion_config_capacity(
    identity: dict,
    sqlite_handler: Any,
    *,
    companion_name: Optional[str] = None,
    settings: Optional[dict] = None,
) -> None:
    """Raise CompanionContactCapacityError if persisted contacts exceed configured max_contacts."""
    if sqlite_handler is None:
        return
    identity_key = identity.get("identity_key")
    if not identity_key:
        return
    merged_settings = settings if settings is not None else (identity.get("settings") or {})
    max_contacts = effective_max_contacts(parse_companion_bridge_kwargs(merged_settings))
    companion_hash = companion_hash_str_from_identity_key(identity_key)
    check_companion_contact_capacity(
        companion_hash,
        max_contacts,
        sqlite_handler,
        companion_name=companion_name,
    )


def check_companion_contact_capacity(
    companion_hash: str,
    max_contacts: int,
    sqlite_handler: Any,
    *,
    companion_name: Optional[str] = None,
) -> None:
    """Raise CompanionContactCapacityError if persisted contacts exceed max_contacts."""
    if sqlite_handler is None:
        return
    stored_count = sqlite_handler.companion_count_contacts(companion_hash)
    if stored_count > max_contacts:
        raise CompanionContactCapacityError(
            companion_hash, stored_count, max_contacts, companion_name=companion_name
        )


def select_companion_contacts_to_trim(contacts, max_contacts: int):
    """Select which persisted contacts to keep/remove to fit ``max_contacts``.

    Mirrors ``ContactStore.add_or_overwrite`` eviction: the oldest non-favourite
    contacts (by ``lastmod``) are removed first; favourites (flags bit 0) are
    never evicted.

    Returns:
        (keep, removed): lists of contact dicts.

    Raises:
        ValueError: favourites alone exceed ``max_contacts`` (cannot trim).
    """
    contacts = list(contacts)
    if len(contacts) <= max_contacts:
        return contacts, []
    favourites = [c for c in contacts if int(c.get("flags", 0)) & _CONTACT_FLAG_FAVOURITE]
    if len(favourites) > max_contacts:
        raise ValueError(
            f"Cannot trim to max_contacts={max_contacts}: "
            f"{len(favourites)} favourite contacts cannot be evicted"
        )
    non_favourites = [c for c in contacts if not int(c.get("flags", 0)) & _CONTACT_FLAG_FAVOURITE]
    # Keep the newest non-favourites by lastmod; evict the oldest.
    non_favourites.sort(key=lambda c: int(c.get("lastmod", 0)))
    keep_count = max_contacts - len(favourites)
    removed = non_favourites[: len(non_favourites) - keep_count]
    kept_non_favourites = non_favourites[len(non_favourites) - keep_count :]
    return favourites + kept_non_favourites, removed


def trim_companion_contacts_to_fit(
    sqlite_handler: Any, companion_hash: str, max_contacts: int
) -> int:
    """Trim persisted contacts (favourite-aware) down to ``max_contacts``.

    Loads the companion's contacts, evicts the oldest non-favourites per
    :func:`select_companion_contacts_to_trim`, persists the kept set, and returns
    the number removed (0 if already within the limit).

    Raises:
        ValueError: favourites alone exceed ``max_contacts`` (cannot trim).
        RuntimeError: persisting the trimmed contact list failed.
    """
    if sqlite_handler is None:
        return 0
    contacts = sqlite_handler.companion_load_contacts(companion_hash)
    keep, removed = select_companion_contacts_to_trim(contacts, max_contacts)
    if not removed:
        return 0
    if not sqlite_handler.companion_save_contacts(companion_hash, keep):
        raise RuntimeError(f"Failed to persist trimmed contacts for {companion_hash}")
    return len(removed)


def enforce_companion_contact_capacity(
    companion_hash: str,
    max_contacts: int,
    sqlite_handler: Any,
    *,
    trim: bool = False,
    companion_name: Optional[str] = None,
) -> int:
    """Ensure persisted contacts fit ``max_contacts`` at load time.

    With ``trim=False`` (default) this is a guard: it raises
    :class:`CompanionContactCapacityError` when over capacity. With ``trim=True``
    (the ``trim_contacts_on_overflow`` policy) it trims favourite-aware to fit,
    persists, and returns the number of contacts removed.
    """
    if not trim:
        check_companion_contact_capacity(
            companion_hash, max_contacts, sqlite_handler, companion_name=companion_name
        )
        return 0
    return trim_companion_contacts_to_fit(sqlite_handler, companion_hash, max_contacts)


def format_companion_bridge_limits(bridge_kwargs: Dict[str, int]) -> str:
    """Format non-default bridge limits for log lines."""
    if not bridge_kwargs:
        return ""
    parts = [f"{k}={v}" for k, v in sorted(bridge_kwargs.items())]
    return ", " + ", ".join(parts)


def companion_hash_str_from_identity_key(identity_key: Any) -> str:
    """Derive companion_hash storage key (0xHH) from an identity_key config value."""
    from openhop_core import LocalIdentity

    if isinstance(identity_key, str):
        key_bytes = bytes.fromhex(normalize_companion_identity_key(identity_key))
    elif isinstance(identity_key, bytes):
        key_bytes = identity_key
    else:
        raise ValueError("identity_key has unknown type")
    pubkey_byte = LocalIdentity(seed=key_bytes).get_public_key()[0]
    return f"0x{pubkey_byte:02x}"


# All companion settings writable via identity API (tcp + bridge power-user keys).
COMPANION_SETTINGS_ALLOWLIST = frozenset(
    {
        "node_name",
        "tcp_port",
        "bind_address",
        "tcp_timeout",
        # Persistent opt-in: trim oldest non-favourite contacts to fit max_contacts
        # at load instead of refusing to start when over capacity.
        "trim_contacts_on_overflow",
        *COMPANION_BRIDGE_SETTING_KEYS,
    }
)