/**
 * Copyright since 2025 Mifos Initiative
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/**
 * Single source of truth for every age-derived client classification.
 *
 * These rules were previously re-implemented as bare literals in ten separate components (the client
 * stepper plus each product's account-details step), which is how a client could end up classified one
 * way on the client screen and another way on the account screen -- and, in the FD case, how a
 * 24-year-old ended up with a senior-citizen interest rate. Anything that needs to know whether a
 * client is a minor or a senior citizen must derive it from here rather than comparing ages inline.
 */

/** Below this age a client is a minor: guardian mapping required, restricted KYC/OVD document set. */
export const MINOR_AGE_THRESHOLD = 10;

/** At or above this age a client qualifies for senior-citizen benefits (higher deposit rates). */
export const SENIOR_CITIZEN_AGE_THRESHOLD = 60;

/**
 * Age at which a minor account must be converted to a regular one. Deliberately independent of
 * {@link MINOR_AGE_THRESHOLD}: legal majority in India is 18 regardless of the age at which this CBS
 * chooses to stop applying minor-specific onboarding rules.
 */
export const AGE_OF_MAJORITY = 18;

/** Parses the backend's date-of-birth representation -- either a `[yyyy, m, d]` array or a date string. */
export function parseClientDob(dob: any): Date | null {
  if (!dob) return null;
  if (Array.isArray(dob) && dob.length >= 3) {
    return new Date(dob[0], dob[1] - 1, dob[2]);
  }
  const parsed = new Date(dob);
  return isNaN(parsed.getTime()) ? null : parsed;
}

/**
 * Completed years between `dob` and `asOf`. Pass the tenant's business date as `asOf` wherever it is
 * available, so a back-dated or forward-dated business date classifies the client the same way the
 * rest of the system does.
 */
export function calculateAge(dob: Date, asOf?: Date | null): number {
  const today = asOf ?? new Date();
  let age = today.getFullYear() - dob.getFullYear();
  const monthDiff = today.getMonth() - dob.getMonth();
  if (monthDiff < 0 || (monthDiff === 0 && today.getDate() < dob.getDate())) {
    age--;
  }
  return age;
}

/** True when the age qualifies as a minor. `null` (unknown DOB) is never a minor. */
export function isMinorAge(age: number | null | undefined): boolean {
  return age !== null && age !== undefined && age < MINOR_AGE_THRESHOLD;
}

/** True when the age qualifies for senior-citizen benefits. `null` (unknown DOB) never qualifies. */
export function isSeniorCitizenAge(age: number | null | undefined): boolean {
  return age !== null && age !== undefined && age >= SENIOR_CITIZEN_AGE_THRESHOLD;
}

/**
 * Whether a client record represents a natural person. Only a natural person can be a minor or a
 * senior citizen -- an entity/company has no age, so age-derived benefits must never apply to one
 * even if some incorporation date happens to be stored against it.
 */
export function isIndividualClient(client: any): boolean {
  const legalForm = client?.legalForm;
  if (!legalForm) return true; // absent legal form: treat as individual, matching the backend default
  const code = String(legalForm.code ?? '').toLowerCase();
  if (code) return code.includes('individual') && !code.includes('nonindividual');
  const value = String(legalForm.value ?? legalForm.name ?? '').toLowerCase();
  return value === 'individual';
}

/**
 * The senior-citizen decision for a whole client record: individual, known DOB, and old enough.
 * Returns the derived age alongside the verdict so callers can show "why" without recomputing it.
 */
export function deriveSeniorCitizenStatus(
  client: any,
  asOf?: Date | null
): { isSeniorCitizen: boolean; age: number | null; isIndividual: boolean } {
  const isIndividual = isIndividualClient(client);
  const dob = parseClientDob(client?.dateOfBirth);
  const age = dob ? calculateAge(dob, asOf) : null;
  return {
    isSeniorCitizen: isIndividual && isSeniorCitizenAge(age),
    age,
    isIndividual
  };
}