// The packet editor's rules, kept pure so they can be tested without the page. The server re-checks every one.
import type { Questionnaire } from 'fhir/r4';
import {
    MAX_PACKET_MEMBERS, MAX_PACKET_TITLE,
    type PacketInput, type PacketTrigger, type QuestionnairePacket,
} from '../services/QuestionnairePacketService';

export const emptyPacketDraft = (): PacketInput => ({
    title: '', status: 'draft', members: [], trigger: 'off', priority: 'routine',
});

export const draftOfPacket = (packet: QuestionnairePacket): PacketInput => ({
    title: packet.title,
    status: packet.status,
    members: packet.members.map((member) => member.questionnaireId),
    trigger: packet.trigger,
    priority: packet.priority,
});

/** Moves one member by `delta` places; an index or target off either end leaves the order unchanged. */
export const moveMember = (members: string[], index: number, delta: number): string[] => {
    const target = index + delta;
    if (index < 0 || index >= members.length || target < 0 || target >= members.length) return members;
    const next = [...members];
    [next[index], next[target]] = [next[target], next[index]];
    return next;
};

/** Questionnaires that can still be added: in the clinical library, not retired, not already a member. */
export const addableQuestionnaires = (library: Questionnaire[], members: string[]): Questionnaire[] =>
    library.filter((questionnaire) => questionnaire.id
        && (questionnaire.status === 'active' || questionnaire.status === 'draft')
        && !members.includes(questionnaire.id));

export type MemberStanding = 'active' | 'draft' | 'retired' | 'missing';

/** A member absent from the clinical library is missing to this author, never assumed fine. */
export const memberStanding = (library: Questionnaire[], questionnaireId: string): MemberStanding => {
    const status = library.find((questionnaire) => questionnaire.id === questionnaireId)?.status;
    if (status === 'active' || status === 'draft') return status;
    return status ? 'retired' : 'missing';
};

/** The first thing stopping a save, in the author's words, or undefined when the draft can be sent. */
export const packetDraftProblem = (draft: PacketInput, library: Questionnaire[]): string | undefined => {
    const title = draft.title.trim();
    if (!title) return 'Name the packet.';
    if (title.length > MAX_PACKET_TITLE) return `Keep the name to ${MAX_PACKET_TITLE} characters.`;
    if (draft.members.length === 0) return 'Add at least one questionnaire.';
    if (draft.members.length > MAX_PACKET_MEMBERS) return `A packet holds up to ${MAX_PACKET_MEMBERS} questionnaires.`;
    const standings = draft.members.map((id) => memberStanding(library, id));
    if (standings.includes('missing')) return 'Remove the questionnaire that is no longer in your library.';
    if (standings.includes('retired')) return 'Remove the retired questionnaire.';
    if (draft.status === 'active' && standings.includes('draft')) {
        return 'An active packet can hold only active questionnaires. Activate the draft or keep the packet as a draft.';
    }
    return undefined;
};

/** Whether the draft differs from what was opened, by the fields the server stores. */
export const packetDraftChanged = (draft: PacketInput, opened: PacketInput): boolean =>
    draft.title.trim() !== opened.title.trim()
    || draft.status !== opened.status
    || draft.trigger !== opened.trigger
    || (draft.trigger !== 'off' && draft.priority !== opened.priority)
    || draft.members.join('\n') !== opened.members.join('\n');

export const triggerSummary = (trigger: PacketTrigger): string => {
    switch (trigger) {
        case 'all-appointments': return 'Assigned automatically for every appointment';
        case 'new-patient-appointments': return 'Assigned automatically for new patient appointments';
        default: return 'Not assigned automatically';
    }
};