type ValidationFunction = (x: any) => string | undefined;

export const validateArgs = function (
  args: {value: any, name: string, func: ValidationFunction}[],
): string | undefined {
  for (const arg of args) {
    const errmsg = arg.func(arg.value);
    if (errmsg) return `${arg.name}`+errmsg;
  }
}

export const validateString = function(s: any): string | undefined {
  if (s === null || s === undefined || s.constructor !== String) {
    return `' should be a String`;
  }
  if (s.length === 0) return `' cannot be an empty String.`;
}

export const validateStringArray = function(a: any): string | undefined {
  if (a === null || a === undefined || a.constructor !== Array) {
    return `' should be a String[].`;
  }
  if (a.length === 0) return `' cannot be an empty Array.`;
  for (let i = 0; i < a.length; i++) {
    let v = a[i];
    if (v === null || v === undefined || v.constructor !== String) {
      return `[${i}]' should be a String.`;
    }
  }
}

export const validateObject = function(o: any): string | undefined {
  if (o === null || o === undefined || o.constructor !== Object) {
    return `' should be an Object.`;
  }
}

const saneCheckDate = new Date('2022');
// Sane check for date value but also a check for numeric value producing a valid date. 
export const validateDate = function(date: any): string | undefined {
  if (!(new Date(date) > saneCheckDate)) return `date' is invalid or too small. Received: '${date}'.`;
}