import Hashids from 'hashids';

const env = (typeof import.meta !== 'undefined' && import.meta.env
  ? import.meta.env
  : {}) as Record<string, string | undefined>;

export const HASHER_SETTINGS = {
  minHashLength: Number(env.VITE_HASHER_MIN_LENGTH) || 11,
  salt: (env.VITE_HASHER_SALT as string) || '',
};

let hasher = new Hashids(HASHER_SETTINGS.salt, HASHER_SETTINGS.minHashLength);

export function updateHasherSettings(salt?: string, minLength?: number | string): void {
  let updated = false;
  if (salt && typeof salt === 'string' && salt.trim() !== '') {
    HASHER_SETTINGS.salt = salt.trim();
    updated = true;
  }
  if (minLength !== undefined && minLength !== null && minLength !== '') {
    const parsed = Number(minLength);
    if (!isNaN(parsed) && parsed > 0) {
      HASHER_SETTINGS.minHashLength = parsed;
      updated = true;
    }
  }
  if (updated) {
    hasher = new Hashids(HASHER_SETTINGS.salt, HASHER_SETTINGS.minHashLength);
  }
}

/**
 * Validates if candidate is already a HashID generated by this hasher.
 */
export function isHashId(candidate: string | null | undefined): boolean {
  if (!candidate || typeof candidate !== 'string' || candidate.length < HASHER_SETTINGS.minHashLength) {
    return false;
  }
  try {
    const decodedNumbers = hasher.decode(candidate);
    if (Array.isArray(decodedNumbers) && decodedNumbers.length > 0) return true;
    const decodedHex = hasher.decodeHex(candidate);
    if (decodedHex && decodedHex.length > 0) return true;
  } catch {
    return false;
  }
  return false;
}

/**
 * Encodes a user idNumber using Hashids Hex encoding.
 * Supports South African national IDs (13 digits), passports, and alphanumeric keys.
 */
export function encodeIdNumberHex(idNumber: string | number | null | undefined): string {
  if (idNumber === undefined || idNumber === null) return '';
  const str = String(idNumber).trim();
  if (!str) return '';

  // Prevent double-encoding if already a Hashid
  if (isHashId(str)) {
    return str;
  }

  // If already pure hex digits (e.g. standard decimal SA ID 9501015800085 or hex hash)
  if (/^[0-9a-fA-F]+$/.test(str)) {
    try {
      const encoded = hasher.encodeHex(str.toLowerCase());
      if (encoded) return encoded;
    } catch {
      // Fallback below
    }
  }

  // For arbitrary alphanumeric ID strings, encode character bytes to hex
  try {
    const hex = Array.from(str)
      .map((c) => c.charCodeAt(0).toString(16).padStart(2, '0'))
      .join('');
    const encoded = hasher.encodeHex(hex);
    return encoded || str;
  } catch {
    return str;
  }
}

/**
 * Decodes a Hashids Hex encoded string back to original idNumber.
 */
export function decodeIdNumberHex(hash: string | null | undefined): string {
  if (!hash || typeof hash !== 'string') return '';
  const trimmed = hash.trim();
  if (!trimmed) return '';

  try {
    const decodedHex = hasher.decodeHex(trimmed);
    if (!decodedHex) return trimmed;

    // Check if decoded hex represents ASCII text with 2-char hex pairs
    if (/^[0-9a-fA-F]{4,}$/.test(decodedHex) && decodedHex.length % 2 === 0) {
      let isText = true;
      let text = '';
      for (let i = 0; i < decodedHex.length; i += 2) {
        const code = parseInt(decodedHex.slice(i, i + 2), 16);
        if (code < 32 || code > 126) {
          isText = false;
          break;
        }
        text += String.fromCharCode(code);
      }
      if (isText && text.length > 0) return text;
    }

    return decodedHex;
  } catch {
    return trimmed;
  }
}

/**
 * Converts any numeric or string ID to a safe 64-bit integer string.
 * Preserves precision beyond 2^53 - 1 by avoiding standard float coercion.
 */
export function toSafeInt64String(val: string | number | bigint | null | undefined): string {
  if (val === undefined || val === null || val === '') return '';
  if (typeof val === 'bigint') return val.toString();
  if (typeof val === 'number') {
    if (isNaN(val) || !isFinite(val)) return '';
    return Math.trunc(val).toString();
  }
  const str = String(val).trim();
  if (/^-?\d+$/.test(str)) {
    return str;
  }
  return str;
}

/**
 * Deterministically encodes a numeric ID or 64-bit integer into a standard HashID string.
 */
export function encodeEntityId(id: string | number | bigint | null | undefined): string {
  if (id === undefined || id === null || id === '') return '';

  const str = typeof id === 'bigint' ? id.toString() : String(id).trim();
  if (!str) return '';

  if (isHashId(str)) return str;

  // If safe integer range
  if (/^\d+$/.test(str)) {
    try {
      const num = Number(str);
      if (num <= Number.MAX_SAFE_INTEGER && num >= 0) {
        return hasher.encode(num);
      }
      // For integers above 2^53 - 1, encode as hex
      const bigHex = BigInt(str).toString(16);
      return hasher.encodeHex(bigHex);
    } catch {
      // Fall through
    }
  }

  return str;
}

/**
 * Deterministically decodes a standard HashID string to its canonical ID representation as string.
 */
export function decodeEntityId(hashId: string | number | null | undefined): string {
  if (hashId === undefined || hashId === null || hashId === '') return '';
  const str = String(hashId).trim();
  if (!str) return '';

  if (/^-?\d+$/.test(str)) return str;

  try {
    const decoded = hasher.decode(str);
    if (Array.isArray(decoded) && decoded.length > 0) {
      return decoded[0].toString();
    }
    const decodedHex = hasher.decodeHex(str);
    if (decodedHex) {
      try {
        return BigInt('0x' + decodedHex).toString();
      } catch {
        return decodedHex;
      }
    }
  } catch {
    // Return raw
  }

  return str;
}