import { useCallback, useState } from "react";

export function useFieldVisibility() {
  const [touched, setTouched] = useState<Record<string, boolean>>({});
  const [submitted, setSubmitted] = useState(false);

  const touch = useCallback((field: string) => {
    setTouched((prev) => (prev[field] ? prev : { ...prev, [field]: true }));
  }, []);

  const visible = useCallback(
    (field: string) => submitted || Boolean(touched[field]),
    [submitted, touched],
  );

  const markSubmitted = useCallback(() => setSubmitted(true), []);

  return { touch, visible, markSubmitted };
}

export function isRequiredString(value: string): boolean {
  return value.trim().length > 0;
}

export function isValidEmail(value: string): boolean {
  const trimmed = value.trim();
  if (!trimmed) return false;
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(trimmed);
}

export function isValidPassword(value: string): boolean {
  return value.length >= 8;
}

/** Parses a non-negative decimal, or null if empty/invalid. */
export function parseNonNegativeNumber(value: string): number | null {
  const trimmed = value.trim();
  if (!trimmed) return null;
  const n = Number(trimmed);
  if (Number.isNaN(n) || n < 0) return null;
  return n;
}

export function isValidTaxRate(value: string): boolean {
  const n = parseNonNegativeNumber(value);
  if (n === null) return false;
  return n <= 100;
}

export type LineItemInput = {
  description: string;
  hours: string;
  rate: string;
};

export function validateLineItems(items: LineItemInput[]): string | null {
  if (items.length === 0) return "Add at least one line item";

  for (const item of items) {
    if (!isRequiredString(item.description)) return "Each line needs a description";
    if (parseNonNegativeNumber(item.hours) === null) return "Hours must be a valid number";
    if (parseNonNegativeNumber(item.rate) === null) return "Rate must be a valid number";
  }

  return null;
}