export function cleanseAssertionOperators<T extends number | string | symbol = string>(
  parsedName: string
): T {
  return <T>parsedName.replace(/[?!]/g, "");
}

export interface NameofOptions {
  /**
   * Take only the last property of nested properties.
   */
  lastProp?: boolean;
}

export function nameof<T extends Object>(
  nameFunction: ((obj: T) => any) | { new (...params: any[]): T },
  options?: NameofOptions
): string {
  const fnStr = nameFunction.toString();

  // ES6 class name:
  // "class ClassName { ..."
  if (
    fnStr.startsWith("class ") &&
    // Theoretically could, for some ill-advised reason, be "class => class.prop".
    !fnStr.startsWith("class =>")
  ) {
    return cleanseAssertionOperators(
      fnStr.substring("class ".length, fnStr.indexOf(" {"))
    );
  }

  // ES6 prop selector:
  // "x => x.prop"
  if (fnStr.includes("=>")) {
    return cleanseAssertionOperators(fnStr.substring(fnStr.indexOf(".") + 1));
  }

  // ES5 prop selector:
  // "function (x) { return x.prop; }"
  // webpack production build excludes the spaces and optional trailing semicolon:
  //   "function(x){return x.prop}"
  // FYI - during local dev testing i observed carriage returns after the curly brackets as well
  // Note by maintainer: See https://github.com/IRCraziestTaxi/ts-simple-nameof/pull/13#issuecomment-567171802 for explanation of this regex.
  const matchRegex = /function\s*\(\w+\)\s*\{[\r\n\s]*return\s+\w+\.((\w+\.)*(\w+))/i;

  const es5Match = fnStr.match(matchRegex);

  if (es5Match) {
    return options && options.lastProp ? es5Match[3] : es5Match[1];
  }

  // ES5 class name:
  // "function ClassName() { ..."
  if (fnStr.startsWith("function ")) {
    return cleanseAssertionOperators(
      fnStr.substring("function ".length, fnStr.indexOf("("))
    );
  }

  // Invalid function.
  throw new Error("nameof: Invalid function.");
}

export function nameOf<T extends Object>(
  nameFunction: (obj: T) => unknown
): keyof T {
  const fnStr = nameFunction.toString();

  // ES6 class name:
  // "class ClassName { ..."
  if (
    fnStr.startsWith("class ") &&
    // Theoretically could, for some ill-advised reason, be "class => class.prop".
    !fnStr.startsWith("class =>")
  ) {
    return cleanseAssertionOperators<keyof T>(
      fnStr.substring("class ".length, fnStr.indexOf(" {"))
    );
  }

  // ES6 prop selector:
  // "x => x.prop"
  if (fnStr.includes("=>")) {
    return cleanseAssertionOperators<keyof T>(
      fnStr.substring(fnStr.indexOf(".") + 1)
    );
  }

  // ES5 prop selector:
  // "function (x) { return x.prop; }"
  // webpack production build excludes the spaces and optional trailing semicolon:
  //   "function(x){return x.prop}"
  // FYI - during local dev testing i observed carriage returns after the curly brackets as well
  // Note by maintainer: See https://github.com/IRCraziestTaxi/ts-simple-nameof/pull/13#issuecomment-567171802 for explanation of this regex.
  const matchRegex = /function\s*\(\w+\)\s*\{[\r\n\s]*return\s+\w+\.((\w+\.)*(\w+))/i;

  const es5Match = fnStr.match(matchRegex);

  if (es5Match) {
    return <keyof T>es5Match[1];
  }

  // ES5 class name:
  // "function ClassName() { ..."
  if (fnStr.startsWith("function ")) {
    return cleanseAssertionOperators(
      fnStr.substring("function ".length, fnStr.indexOf("("))
    );
  }

  // Invalid function.
  throw new Error("nameof: Invalid function.");
}

export default nameof;