/**
 * Rank strength-bearing products above substances in the drug pickers.
 *
 * The drug fields bind the US Core medication set, which by definition includes ingredient-level
 * codes (`metformin`) alongside products (`metformin hydrochloride 500 MG Oral Tablet`). Snowstorm
 * orders matches shortest-first, so the vaguest term types always win the top of the list and a
 * clinician typing "metfor" sees substances first - the exact thing a prescription cannot use.
 *
 * THIS IS NOT A SUBSTITUTION AND DOES NOT BELONG IN compositeValueSetExpansion.ts. That table works
 * around value sets the server REFUSES and records each refusal verbatim; the medication set now
 * expands fine. The reason here is rank. The prescribable set is a strict subset of the parent, so
 * asking it first and the parent second, then deduping, yields the identical set of concepts -
 * reordered, with the products in front.
 *
 * THE SLOTS ARE RESERVED, NOT FIRST-COME. Prescribable alone answers "metfor" with 135 rows; left to
 * fill the whole page it would push the ingredient-level `metformin` off the screen entirely, which
 * is the opposite bug. A few rows are held back for the parent's own matches, so the dose-unknown
 * case stays one glance away.
 */

import { mergeExpansionContains } from './compositeValueSetExpansion.ts';

export const US_CORE_MEDICATION_CODES = 'http://cts.nlm.nih.gov/fhir/ValueSet/2.16.840.1.113762.1.4.1010.4';
export const PRESCRIBABLE_MEDICATIONS = 'http://akashichealthrecords.com/fhir/ValueSet/prescribable-medications';

export type SearchTiers = {
    /** Expanded first; its matches lead the list. */
    readonly first: string;
    /** Rows the picker shows, and the `count` each tier is asked for. */
    readonly limit: number;
    /** Rows held back for the parent's own matches when the lead tier could fill them all. */
    readonly reserved: number;
};

export const MEDICATION_SEARCH_TIERS: Readonly<Record<string, SearchTiers>> = {
    [US_CORE_MEDICATION_CODES]: { first: PRESCRIBABLE_MEDICATIONS, limit: 20, reserved: 5 },
};

export const searchTiersFor = (valueSetUrl: string): SearchTiers | undefined =>
    MEDICATION_SEARCH_TIERS[valueSetUrl];

type Concept = { system?: string; code?: string; display?: string };

const key = (c: Concept): string => `${c.system ?? ''}|${c.code ?? ''}`;

/**
 * Merge the lead tier and the rest into one page.
 *
 * A tier that failed (`undefined`) or answered with nothing is a fallback trigger: the other tier
 * fills the page alone. When both answer, the lead takes up to `limit - reserved` rows and the
 * rest - minus anything the lead already holds - takes what is left; either side absorbs the
 * other's slack, so a rare drug with two products still fills the page.
 */
export const mergeSearchTiers = (
    first: readonly Concept[] | undefined,
    rest: readonly Concept[] | undefined,
    { limit, reserved }: Pick<SearchTiers, 'limit' | 'reserved'>,
): Concept[] => {
    const lead = mergeExpansionContains([first]);
    if (lead.length === 0) return mergeExpansionContains([rest]).slice(0, limit);

    const held = new Set(lead.map(key));
    const remainder = mergeExpansionContains([rest]).filter((c) => !held.has(key(c)));

    const keep = Math.min(reserved, remainder.length);
    const leadTake = Math.min(lead.length, limit - keep);
    return [...lead.slice(0, leadTake), ...remainder.slice(0, limit - leadTake)];
};