package com.example.widgets;

import com.example.data.ChartDataService;
import com.example.data.DashboardFilter;
import com.vaadin.flow.shared.Registration;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.function.Consumer;

/**
 * The dashboard's current {@link DashboardFilter} plus the widgets listening to
 * it — the small event bus between the filter bar (which sets) and the widgets
 * (which subscribe and re-request their data from
 * {@link ChartDataService}). Neither side knows the other.
 * <p>
 * One context per dashboard instance, deliberately not a Spring bean: it is
 * view state, so nothing leaks between users, tabs or visits. For the same
 * reason the filter is <em>not persisted</em> — a reload starts from
 * {@link DashboardFilter#defaults()}, unlike the grid layout, which
 * {@code GridStackLayout} keeps in {@code localStorage}.
 */
public class DashboardContext {

    private final List<Consumer<DashboardFilter>> listeners = new ArrayList<>();
    private DashboardFilter filter = DashboardFilter.defaults();

    public DashboardFilter getFilter() {
        return filter;
    }

    /**
     * Applies a filter and hands it to every listener. A filter equal to the
     * current one changes nothing and notifies nobody, so re-picking the same
     * value in the filter bar does not make the widgets re-fetch.
     */
    public void setFilter(DashboardFilter filter) {
        Objects.requireNonNull(filter, "filter");
        if (this.filter.equals(filter)) {
            return;
        }
        this.filter = filter;
        // Over a copy: a listener may unsubscribe while being notified (a
        // widget closing in reaction to the update).
        List.copyOf(listeners).forEach(listener -> listener.accept(filter));
    }

    /**
     * Subscribes to later filter changes. The listener is not called with the
     * current filter — a widget is built from it already — so a subscriber
     * feeds itself once and then only reacts.
     */
    public Registration addFilterChangeListener(Consumer<DashboardFilter> listener) {
        listeners.add(listener);
        return () -> listeners.remove(listener);
    }

    /** How many widgets are currently listening; for tests and diagnostics. */
    public int getListenerCount() {
        return listeners.size();
    }
}