import type { Money } from 'fhir/r4';

/**
 * Money is handled as integer minor units (cents) EVERYWHERE in this codebase.
 * FHIR `Money.value` is a decimal and Stripe wants integer minor units, so decimal is a
 * serialization detail - this module is the ONLY place conversion is allowed to happen.
 *
 * Why this exists: AddOnsPage.tsx:84 does float arithmetic on whole dollars. That bug class
 * must never reach money a patient actually pays.
 */

export const DEFAULT_CURRENCY = 'USD';

/** Formats integer cents for display. 28500 -> "$285.00" */
export const formatMoney = (cents: number, currency: string = DEFAULT_CURRENCY): string =>
    new Intl.NumberFormat('en-US', { style: 'currency', currency }).format(cents / 100);

/** Converts integer cents to a FHIR Money. */
export const toFhirMoney = (cents: number, currency: string = DEFAULT_CURRENCY): Money => ({
    value: cents / 100,
    currency,
});

/**
 * Reads a FHIR Money back to integer cents.
 * Rounds, because `value * 100` carries float representation error (19.99 * 100 === 1998.9999999999998).
 * Returns 0 for absent/invalid input rather than propagating NaN into an amount.
 */
export const fromFhirMoney = (money?: Money): number => {
    if (typeof money?.value !== 'number' || !Number.isFinite(money.value)) {
        return 0;
    }

    return Math.round(money.value * 100);
};

/** Sums integer cents. Exact by construction - this is the point of cents. */
export const sumCents = (values: number[]): number =>
    values.reduce((total, value) => total + value, 0);

/**
 * Computes sales tax in integer cents from a taxable subtotal (also integer cents) and a percent rate
 * (e.g. 8.25 for 8.25%). Rounded to the nearest cent - same convention as fromFhirMoney/parseDollarsToCents.
 * A 0 rate (or a 0 taxable subtotal) always returns exactly 0.
 */
export const computeTax = (taxableSubtotalCents: number, ratePercent: number): number =>
    Math.round((taxableSubtotalCents * ratePercent) / 100);

/** Parses user-entered dollar text ("$1,285.50") to integer cents. Undefined if not a number. */
export const parseDollarsToCents = (input: string): number | undefined => {
    const cleaned = input.replace(/[$,\s]/g, '');

    if (cleaned === '' || !/^-?\d*\.?\d*$/.test(cleaned)) {
        return undefined;
    }

    const parsed = Number(cleaned);

    if (!Number.isFinite(parsed)) {
        return undefined;
    }

    return Math.round(parsed * 100);
};