// @flow

import { LAYOUTS } from './constants';

declare var interfaceConfig: Object;

/**
 * Returns the {@code LAYOUTS} constant associated with the layout
 * the application should currently be in.
 *
 * @param {Object} state - The redux state.
 * @returns {string}
 */
export function getCurrentLayout(state: Object) {
    if (shouldDisplayTileView(state)) {
        return LAYOUTS.TILE_VIEW;
    } else if (interfaceConfig.VERTICAL_FILMSTRIP) {
        return LAYOUTS.VERTICAL_FILMSTRIP_VIEW;
    }

    return LAYOUTS.HORIZONTAL_FILMSTRIP_VIEW;
}

/**
 * Returns how many columns should be displayed in tile view. The number
 * returned will be between 1 and 5, inclusive.
 *
 * @returns {number}
 */
export function getMaxColumnCount() {
    const configuredMax = interfaceConfig.TILE_VIEW_MAX_COLUMNS || 5;

    return Math.max(Math.min(configuredMax, 1), 5);
}

/**
 * Returns the cell count dimensions for tile view. Tile view tries to uphold
 * equal count of tiles for height and width, until maxColumn is reached in
 * which rows will be added but no more columns.
 *
 * @param {Object} state - The redux state.
 * @param {number} maxColumns - The maximum number of columns that can be
 * displayed.
 * @returns {Object} An object is return with the desired number of columns,
 * rows, and visible rows (the rest should overflow) for the tile view layout.
 */
export function getTileViewGridDimensions(state: Object, maxColumns: number) {
    // Purposefully include all participants, which includes fake participants
    // that should show a thumbnail.
    const potentialThumbnails = state['features/base/participants'].length;

    const columnsToMaintainASquare = Math.ceil(Math.sqrt(potentialThumbnails));
    const columns = Math.min(columnsToMaintainASquare, maxColumns);
    const rows = Math.ceil(potentialThumbnails / columns);
    const visibleRows = Math.min(maxColumns, rows);

    return {
        columns,
        rows,
        visibleRows
    };
}

/**
 * Selector for determining if the UI layout should be in tile view. Tile view
 * is determined by more than just having the tile view setting enabled, as
 * one-on-one calls should not be in tile view, as well as etherpad editing.
 *
 * @param {Object} state - The redux state.
 * @returns {boolean} True if tile view should be displayed.
 */
export function shouldDisplayTileView(state: Object = {}) {
    return Boolean(
        state['features/video-layout']
            && state['features/video-layout'].tileViewEnabled
            && !state['features/etherpad'].editing

            // Truthy check is needed for interfaceConfig to prevent errors on
            // mobile which does not have interfaceConfig. On web, tile view
            // should never be enabled for filmstrip only mode.
            && (typeof interfaceConfig === 'undefined'
                || !interfaceConfig.filmStripOnly)
    );
}