/**
 * Validation utilities for user profile fields.
 *
 * These validation functions mirror the backend validation logic in
 * backend/validation.py. Both use shared rules from shared/constants.json
 * to ensure consistent validation across frontend and backend.
 */

import { bech32 } from "bech32";

import constants from "../../../shared/constants.json";

const { telegram: telegramRules, signal: signalRules, nostrNpub: npubRules } = constants.validation;

/**
 * Validate contact email format.
 * Returns undefined if valid, error message if invalid.
 * Empty values are valid (field is optional).
 */
export function validateEmail(value: string): string | undefined {
  if (!value) return undefined;
  // Comprehensive email regex that matches email-validator behavior
  // Checks for: local part, @, domain with at least one dot, valid TLD
  const emailRegex =
    /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)+$/;
  if (!emailRegex.test(value)) {
    return "Please enter a valid email address";
  }
  return undefined;
}

/**
 * Validate Telegram handle.
 * Must start with @ if provided, with characters after @ within max length.
 * Returns undefined if valid, error message if invalid.
 * Empty values are valid (field is optional).
 */
export function validateTelegram(value: string): string | undefined {
  if (!value) return undefined;
  if (!value.startsWith(telegramRules.mustStartWith)) {
    return `Telegram handle must start with ${telegramRules.mustStartWith}`;
  }
  const handle = value.slice(1);
  if (handle.length < 1) {
    return `Telegram handle must have at least one character after ${telegramRules.mustStartWith}`;
  }
  if (handle.length > telegramRules.maxLengthAfterAt) {
    return `Telegram handle must be at most ${telegramRules.maxLengthAfterAt} characters (after ${telegramRules.mustStartWith})`;
  }
  return undefined;
}

/**
 * Validate Signal username.
 * Any non-empty string within max length is valid.
 * Returns undefined if valid, error message if invalid.
 * Empty values are valid (field is optional).
 */
export function validateSignal(value: string): string | undefined {
  if (!value) return undefined;
  if (value.trim().length === 0) {
    return "Signal username cannot be empty";
  }
  if (value.length > signalRules.maxLength) {
    return `Signal username must be at most ${signalRules.maxLength} characters`;
  }
  return undefined;
}

/**
 * Validate Nostr npub (public key in bech32 format).
 * Must be valid bech32 with 'npub' prefix.
 * Returns undefined if valid, error message if invalid.
 * Empty values are valid (field is optional).
 */
export function validateNostrNpub(value: string): string | undefined {
  if (!value) return undefined;
  if (!value.startsWith(npubRules.prefix)) {
    return `Nostr npub must start with '${npubRules.prefix}'`;
  }

  try {
    const decoded = bech32.decode(value);
    if (decoded.prefix !== "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 (decoded.words.length !== npubRules.bech32Words) {
      return "Invalid Nostr npub: incorrect length";
    }
    return undefined;
  } catch {
    return "Invalid Nostr npub: bech32 checksum failed";
  }
}

/**
 * Field errors object type.
 */
export interface FieldErrors {
  contact_email?: string;
  telegram?: string;
  signal?: string;
  nostr_npub?: string;
}

/**
 * Validate all profile fields at once.
 * Returns an object with field_name -> error_message for any invalid fields.
 * Empty object means all fields are valid.
 */
export function validateProfileFields(data: {
  contact_email?: string;
  telegram?: string;
  signal?: string;
  nostr_npub?: string;
}): FieldErrors {
  const errors: FieldErrors = {};

  const emailError = validateEmail(data.contact_email || "");
  if (emailError) errors.contact_email = emailError;

  const telegramError = validateTelegram(data.telegram || "");
  if (telegramError) errors.telegram = telegramError;

  const signalError = validateSignal(data.signal || "");
  if (signalError) errors.signal = signalError;

  const npubError = validateNostrNpub(data.nostr_npub || "");
  if (npubError) errors.nostr_npub = npubError;

  return errors;
}