import type { MedicationRequest, MedicationStatement } from "fhir/r4";

// What a medication record says, from its own status, intent and negation only, for every list and summary. A prescription
// is a recorded order, not proof it is taken; a statement is reported use; anything else stays visible in its own words.
export type MedicationMeaning =
    | { group: "hidden" }
    | { group: "current"; kind: "prescription" | "reported-use" }
    | { group: "other"; label: string }
    | { group: "past"; label: string };

/** The intents that make an order a prescription. A proposal, a plan or an option is not one. */
const FORMAL_ORDER = new Set(["order", "original-order", "reflex-order", "filler-order", "instance-order"]);

const REQUEST_STATUS: Record<string, string> = {
    "on-hold": "On hold",
    unknown: "Status unknown",
    stopped: "Stopped",
    completed: "Completed",
    cancelled: "Cancelled",
};

const REQUEST_INTENT: Record<string, string> = { proposal: "Proposed", plan: "Planned", option: "An option" };

const STATEMENT_STATUS: Record<string, string> = {
    intended: "Intended",
    "on-hold": "On hold",
    unknown: "Status unknown",
    stopped: "Stopped",
    completed: "Completed",
    "not-taken": "Recorded as not taken",
};

const said = (table: Record<string, string>, value: string | undefined, absent: string): string =>
    value ? table[value] ?? `Recorded as ${value}` : absent;

export const requestMeaning = (request: Pick<MedicationRequest, "status" | "intent" | "doNotPerform">): MedicationMeaning => {
    const { status, intent } = request;
    if (status === "entered-in-error" || status === "draft") return { group: "hidden" };
    if (status === "stopped" || status === "completed" || status === "cancelled") return { group: "past", label: said(REQUEST_STATUS, status, "") };
    // An order not to give a medicine is never a claim that it is prescribed.
    if (request.doNotPerform === true) return { group: "other", label: "Recorded instruction not to take this" };
    const formal = Boolean(intent && FORMAL_ORDER.has(intent));
    if (status === "active" && formal) return { group: "current", kind: "prescription" };
    const label = [
        formal ? undefined : said(REQUEST_INTENT, intent, "Intent not recorded"),
        status === "active" ? undefined : said(REQUEST_STATUS, status, "Status not recorded"),
    ].filter(Boolean).join(" · ");
    return { group: "other", label };
};

export const statementMeaning = (statement: Pick<MedicationStatement, "status">): MedicationMeaning => {
    const status = statement.status as string | undefined;
    if (status === "entered-in-error" || status === "draft") return { group: "hidden" };
    if (status === "stopped" || status === "completed" || status === "not-taken") return { group: "past", label: said(STATEMENT_STATUS, status, "") };
    if (status === "active") return { group: "current", kind: "reported-use" };
    return { group: "other", label: said(STATEMENT_STATUS, status, "Status not recorded") };
};

/**
 * Who reported a statement, from its own `informationSource` only. The subject is themselves, a RelatedPerson is the
 * person caring for them, a clinician or practice is named as recorded; nothing else is guessed, so an absent or
 * unfamiliar source is said to be unrecorded rather than credited to the patient or the care team.
 */
export type StatementSource =
    | { who: "patient" }
    | { who: "helper"; name?: string }
    | { who: "clinician"; name?: string }
    | { who: "unknown" };

export const statementSource = (statement: Pick<MedicationStatement, "informationSource" | "subject">): StatementSource => {
    const reference = statement.informationSource?.reference ?? "";
    const name = statement.informationSource?.display?.trim() || undefined;
    if (reference.startsWith("Patient/") && reference === statement.subject?.reference) return { who: "patient" };
    if (reference.startsWith("RelatedPerson/")) return { who: "helper", name };
    if (/^(Practitioner|PractitionerRole|Organization)\//.test(reference)) return { who: "clinician", name };
    return { who: "unknown" };
};