"""Validation utilities for user profile fields."""

import json
from pathlib import Path

from bech32 import bech32_decode
from email_validator import EmailNotValidError, validate_email

# Load validation rules from shared constants
_constants_path = Path(__file__).parent.parent / "shared" / "constants.json"
with open(_constants_path) as f:
    _constants = json.load(f)

TELEGRAM_RULES = _constants["validation"]["telegram"]
SIGNAL_RULES = _constants["validation"]["signal"]
NPUB_RULES = _constants["validation"]["nostrNpub"]


def validate_contact_email(value: str | None) -> str | None:
    """
    Validate contact email format.

    Returns None if valid, error message if invalid.
    Empty/None values are valid (field is optional).
    """
    if not value:
        return None

    try:
        validate_email(value, check_deliverability=False)
        return None
    except EmailNotValidError as e:
        return str(e)


def validate_telegram(value: str | None) -> str | None:
    """
    Validate Telegram handle.

    Must start with @ if provided, with characters after @ within max length.
    Returns None if valid, error message if invalid.
    Empty/None values are valid (field is optional).
    """
    if not value:
        return None

    prefix = TELEGRAM_RULES["mustStartWith"]
    max_len = TELEGRAM_RULES["maxLengthAfterAt"]

    if not value.startswith(prefix):
        return f"Telegram handle must start with {prefix}"

    handle = value[1:]
    if not handle:
        return f"Telegram handle must have at least one character after {prefix}"

    if len(handle) > max_len:
        return f"Telegram handle must be at most {max_len} characters (after {prefix})"

    return None


def validate_signal(value: str | None) -> str | None:
    """
    Validate Signal username.

    Any non-empty string within max length is valid.
    Returns None if valid, error message if invalid.
    Empty/None values are valid (field is optional).
    """
    if not value:
        return None

    max_len = SIGNAL_RULES["maxLength"]

    # Signal usernames are fairly permissive, just check it's not empty
    if len(value.strip()) == 0:
        return "Signal username cannot be empty"

    if len(value) > max_len:
        return f"Signal username must be at most {max_len} characters"

    return None


def validate_nostr_npub(value: str | None) -> str | None:
    """
    Validate Nostr npub (public key in bech32 format).

    Must be valid bech32 with 'npub' prefix.
    Returns None if valid, error message if invalid.
    Empty/None values are valid (field is optional).
    """
    if not value:
        return None

    prefix = NPUB_RULES["prefix"]
    expected_words = NPUB_RULES["bech32Words"]

    if not value.startswith(prefix):
        return f"Nostr npub must start with '{prefix}'"

    # Decode bech32 to validate checksum
    hrp, data = bech32_decode(value)

    if hrp is None or data is None:
        return "Invalid Nostr npub: bech32 checksum failed"

    if hrp != "npub":
        return "Nostr npub must have 'npub' prefix"

    # npub should decode to 32 bytes (256 bits) for a public key
    # In bech32, each character encodes 5 bits, so 32 bytes = 52 characters of data
    if len(data) != expected_words:
        return "Invalid Nostr npub: incorrect length"

    return None


def validate_profile_fields(
    contact_email: str | None = None,
    telegram: str | None = None,
    signal: str | None = None,
    nostr_npub: str | None = None,
) -> dict[str, str]:
    """
    Validate all profile fields at once.

    Returns a dict of field_name -> error_message for any invalid fields.
    Empty dict means all fields are valid.
    """
    errors: dict[str, str] = {}

    if err := validate_contact_email(contact_email):
        errors["contact_email"] = err

    if err := validate_telegram(telegram):
        errors["telegram"] = err

    if err := validate_signal(signal):
        errors["signal"] = err

    if err := validate_nostr_npub(nostr_npub):
        errors["nostr_npub"] = err

    return errors