/**
 * ------------------------------------------------------------
 * StringUtils
 * ------------------------------------------------------------
 * Centralized string manipulation utility.
 *
 * Features:
 * - 🛡️ Null-safe (handles null/undefined gracefully)
 * - ⛓️ Fluent and immutable API (chainable methods)
 * - 🛠️ Common formatting utilities (Capitalization, Truncation)
 * - 🎲 Generator utilities (Random string, Slugs)
 *
 * @example
 * // Basic Chaining
 * StringUtils.of("  hello world  ")
 * .trim()
 * .capitalizeEachWord()
 * .value(); // "Hello World"
 * ------------------------------------------------------------
 */

/* ------------------------------------------------------------------
 * Types
 * ------------------------------------------------------------------ */

export type StringInput = string | number | null | undefined;

/* ------------------------------------------------------------------
 * Interfaces
 * ------------------------------------------------------------------ */

interface IStringUtils {
  // --- Output & Conversion ---
  value(): string;
  toString(): string;
  toJSON(): string;

  // --- Manipulations (Chainable) ---
  upperCase(): IStringUtils;
  lowerCase(): IStringUtils;
  capitalizeFirst(): IStringUtils;
  capitalizeEachWord(): IStringUtils;
  limit(maxLength: number, suffix?: string): IStringUtils;
  trim(): IStringUtils;
  slugify(): IStringUtils;
  mask(visibleStart: number, visibleEnd: number, maskChar?: string): IStringUtils;

  // --- Inspection & Fallback ---
  isEmpty(): boolean;
  orElse(defaultValue: string): string;
}

/* ------------------------------------------------------------------
 * StringUtils
 * ------------------------------------------------------------------ */

export class StringUtils implements IStringUtils {
  private readonly _value: string;

  /* ----------------------------------------------------------------
   * Constructor & Static Initializers
   * ---------------------------------------------------------------- */

  constructor(value?: StringInput) {
    // Defensive coding: Convert null/undefined/number to string immediately
    if (value === null || value === undefined) {
      this._value = '';
    } else {
      this._value = String(value);
    }
  }

  /**
   * Static factory method for cleaner chaining.
   *
   * @param value - The input string, number, or null/undefined.
   * @example
   * StringUtils.of("hello").upperCase().value()
   */
  static of(value?: StringInput): StringUtils {
    return new StringUtils(value);
  }

  /**
   * Generates a random alphanumeric string.
   * Useful for IDs, tokens, or temporary passwords.
   *
   * @param length - Length of the generated string (default: 10).
   * @example
   * StringUtils.random(8).value() // "aB9x2Z1m"
   */
  static random(length: number = 10): StringUtils {
    const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
    let result = '';
    for (let i = 0; i < length; i++) {
      result += chars.charAt(Math.floor(Math.random() * chars.length));
    }
    return new StringUtils(result);
  }

  /* ----------------------------------------------------------------
   * Core Manipulations
   * ---------------------------------------------------------------- */

  /**
   * Converts string to UPPERCASE.
   *
   * @example
   * StringUtils.of("hello").upperCase().value() // "HELLO"
   */
  upperCase(): StringUtils {
    return new StringUtils(this._value.toUpperCase());
  }

  /**
   * Converts string to lowercase.
   *
   * @example
   * StringUtils.of("HELLO").lowerCase().value() // "hello"
   */
  lowerCase(): StringUtils {
    return new StringUtils(this._value.toLowerCase());
  }

  /**
   * Capitalizes only the first letter of the entire string.
   * Remainder is forced to lowercase (Sentence case).
   *
   * @example
   * StringUtils.of("HELLO world").capitalizeFirst().value() // "Hello world"
   */
  capitalizeFirst(): StringUtils {
    if (!this._value) return this;
    const lower = this._value.toLowerCase();
    return new StringUtils(lower.charAt(0).toUpperCase() + lower.slice(1));
  }

  /**
   * Capitalizes the first letter of every word (Title Case).
   * Automatically handles multiple spaces.
   *
   * @example
   * StringUtils.of("hello world").capitalizeEachWord().value() // "Hello World"
   * StringUtils.of("hello   world").capitalizeEachWord().value() // "Hello World"
   */
  capitalizeEachWord(): StringUtils {
    if (!this._value) return this;
    const transformed = this._value
      .toLowerCase()
      .split(/\s+/) // Split by any whitespace regex to handle double spaces
      .map((word) => word.charAt(0).toUpperCase() + word.slice(1))
      .join(' ');
    return new StringUtils(transformed);
  }

  /**
   * Truncates string to a specific length and adds a suffix.
   *
   * @param maxLength - The character limit.
   * @param suffix - The string to append if truncated (default: "...").
   * @example
   * StringUtils.of("Lorem Ipsum").limit(5).value() // "Lorem..."
   * StringUtils.of("Lorem Ipsum").limit(5, "").value() // "Lorem"
   */
  limit(maxLength: number, suffix: string = '...'): StringUtils {
    if (this._value.length <= maxLength) return this;
    return new StringUtils(this._value.substring(0, maxLength) + suffix);
  }

  /* ----------------------------------------------------------------
   * Utility Extensions
   * ---------------------------------------------------------------- */

  /**
   * Removes whitespace from both ends of the string.
   *
   * @example
   * StringUtils.of("  data  ").trim().value() // "data"
   */
  trim(): StringUtils {
    return new StringUtils(this._value.trim());
  }

  /**
   * Converts string to URL-friendly slug.
   * Removes special characters and replaces spaces with dashes.
   *
   * @example
   * StringUtils.of("Hello World!").slugify().value() // "hello-world"
   * StringUtils.of("C# & .NET").slugify().value() // "c-net"
   */
  slugify(): StringUtils {
    const slug = this._value
      .toLowerCase()
      .trim()
      .replace(/[^\w\s-]/g, '') // Remove non-word chars
      .replace(/[\s_-]+/g, '-') // Replace spaces and underscores with -
      .replace(/^-+|-+$/g, ''); // Remove leading/trailing -
    return new StringUtils(slug);
  }

  /**
   * Masks part of the string. Useful for PII (emails/phones).
   *
   * @param visibleStart - Number of characters to show at the start.
   * @param visibleEnd - Number of characters to show at the end.
   * @param maskChar - The character to use for masking (default: "*").
   * @example
   * StringUtils.of("08123456789").mask(4, 3).value() // "0812****789"
   */
  mask(visibleStart: number = 0, visibleEnd: number = 0, maskChar: string = '*'): StringUtils {
    if (this._value.length <= visibleStart + visibleEnd) return this;

    const start = this._value.slice(0, visibleStart);
    const end = this._value.slice(-visibleEnd);
    const middle = maskChar.repeat(this._value.length - visibleStart - visibleEnd);

    return new StringUtils(start + middle + end);
  }

  /* ----------------------------------------------------------------
   * Inspection & Output
   * ---------------------------------------------------------------- */

  /**
   * Checks if the string is empty or contains only whitespace.
   *
   * @returns true if string is empty or whitespace-only.
   * @example
   * StringUtils.of("").isEmpty() // true
   * StringUtils.of("   ").isEmpty() // true
   */
  isEmpty(): boolean {
    return this._value.trim().length === 0;
  }

  /**
   * Returns the raw string value.
   */
  value(): string {
    return this._value;
  }

  /**
   * Returns default value if current string is empty.
   *
   * @param defaultValue - The fallback string.
   * @example
   * StringUtils.of(null).orElse("N/A") // "N/A"
   */
  orElse(defaultValue: string): string {
    return this.isEmpty() ? defaultValue : this._value;
  }

  /**
   * Allows default JS string interpolation to work.
   *
   * @example
   * const name = StringUtils.of("John");
   * console.log(`Hello ${name}`); // "Hello John"
   */
  toString(): string {
    return this._value;
  }

  /**
   * Allows JSON.stringify to serialize just the string, not the object wrapper.
   *
   * @example
   * JSON.stringify({ name: StringUtils.of("John") }) // '{"name":"John"}'
   */
  toJSON(): string {
    return this._value;
  }
}