import { Extension } from "fhir/r4";

// Patient availability preference for a time-window appointment request (request-only +
// `time-window`): preferred days of week + times of day, with no practitioner or slot. The server
// passes this through untouched - only the plugin reads/writes it - so it is NOT mirrored server-side.
export const APPOINTMENT_PREFERRED_AVAILABILITY_EXTENSION_URL =
    "https://akashichealthrecords.com/fhir/StructureDefinition/appointment-preferred-availability";

const DAY_SUB_URL = "day";
const TIME_OF_DAY_SUB_URL = "timeOfDay";

export const PREFERRED_DAY_OPTIONS: { code: string; label: string }[] = [
    { code: "mon", label: "Mon" },
    { code: "tue", label: "Tue" },
    { code: "wed", label: "Wed" },
    { code: "thu", label: "Thu" },
    { code: "fri", label: "Fri" },
    { code: "sat", label: "Sat" },
    { code: "sun", label: "Sun" },
];

export const PREFERRED_TIME_OF_DAY_OPTIONS: { code: string; label: string }[] = [
    { code: "morning", label: "Morning" },
    { code: "afternoon", label: "Afternoon" },
    { code: "evening", label: "Evening" },
];

// Builds the complex extension from the patient's selected day + time-of-day codes.
export const buildPreferredAvailabilityExtension = (
    dayCodes: string[],
    timeOfDayCodes: string[],
): Extension => ({
    url: APPOINTMENT_PREFERRED_AVAILABILITY_EXTENSION_URL,
    extension: [
        ...dayCodes.map((code) => ({ url: DAY_SUB_URL, valueCode: code })),
        ...timeOfDayCodes.map((code) => ({ url: TIME_OF_DAY_SUB_URL, valueCode: code })),
    ],
});

const labelFor = (
    options: { code: string; label: string }[],
    code?: string,
): string => options.find((o) => o.code === code)?.label ?? code ?? "";

const DAY_PLURALS: Record<string, string> = {
    mon: "Mondays", tue: "Tuesdays", wed: "Wednesdays", thu: "Thursdays",
    fri: "Fridays", sat: "Saturdays", sun: "Sundays",
};

const TIME_OF_DAY_PLURALS: Record<string, string> = {
    morning: "mornings", afternoon: "afternoons", evening: "evenings",
};

const sayList = (items: string[]): string =>
    items.length < 2 ? items.join("") : `${items.slice(0, -1).join(", ")} and ${items[items.length - 1]}`;

// The patient's own choice as a sentence, e.g. "Mondays, Wednesdays and Fridays, mornings."
export const describePreferredAvailability = (dayCodes: string[], timeOfDayCodes: string[]): string => {
    const inOrder = (codes: string[], options: { code: string }[]) =>
        [...codes].sort((a, b) => options.findIndex((o) => o.code === a) - options.findIndex((o) => o.code === b));
    const days = sayList(inOrder(dayCodes, PREFERRED_DAY_OPTIONS).map((code) => DAY_PLURALS[code] ?? code));
    const times = sayList(inOrder(timeOfDayCodes, PREFERRED_TIME_OF_DAY_OPTIONS).map((code) => TIME_OF_DAY_PLURALS[code] ?? code));
    return `${[days, times].filter(Boolean).join(", ")}.`;
};

// Returns a readable summary like "Mon, Wed - Morning, Afternoon", or "" when the preference is absent.
export const formatPreferredAvailability = (appointment?: {
    extension?: Extension[];
}): string => {
    const root = appointment?.extension?.find(
        (e) => e.url === APPOINTMENT_PREFERRED_AVAILABILITY_EXTENSION_URL,
    );
    if (!root?.extension?.length) return "";

    const days = root.extension
        .filter((e) => e.url === DAY_SUB_URL)
        .map((e) => labelFor(PREFERRED_DAY_OPTIONS, e.valueCode));
    const times = root.extension
        .filter((e) => e.url === TIME_OF_DAY_SUB_URL)
        .map((e) => labelFor(PREFERRED_TIME_OF_DAY_OPTIONS, e.valueCode));

    const parts: string[] = [];
    if (days.length) parts.push(days.join(", "));
    if (times.length) parts.push(times.join(", "));
    return parts.join(" · ");
};