/**
 * External dependencies
 */
import type { ConversionEvent, Maybe, TrackEvent } from '@nab/types';

/**
 * Internal dependencies
 */
import type { Session, Settings } from '../types';
import { getSettings } from '../utils/helpers/internal/get-settings';

function sendToGA4( eventData: TrackEvent ) {
	const settings = getSettings();
	if (
		( ! settings?.ga4TrackingMethod ||
			settings.ga4TrackingMethod === 'gtm' ) &&
		hasDataLayer( window )
	) {
		window.dataLayer.push( {
			event:
				eventData.kind === 'visit'
					? 'experiment_impression'
					: 'conversion',
			experiment_id: eventData.experiment,
			variant_id: eventData.alternative,
			variant_name: getVariantName( settings, eventData ),
			...( eventData.kind === 'conversion' && {
				goal_id: eventData.goal,
				goal_name: getGoalName( settings, eventData ),
			} ),
		} );
	} else if (
		( ! settings?.ga4TrackingMethod ||
			settings.ga4TrackingMethod === 'gtag' ) &&
		hasGTag( window )
	) {
		window.gtag(
			'event',
			eventData.kind === 'visit' ? 'experiment_impression' : 'conversion',
			{
				experiment_id: eventData.experiment,
				variant_id: eventData.alternative,
				variant_name: getVariantName( settings, eventData ),
				...( eventData.kind === 'conversion' && {
					goal_id: eventData.goal,
					goal_name: getGoalName( settings, eventData ),
				} ),
			}
		);
	}
}

const hasGTag = (
	win: unknown
): win is {
	gtag: (
		command: string,
		eventName: string,
		params?: Record< string, unknown >
	) => void;
} => !! win && 'object' === typeof win && 'gtag' in win;

const hasDataLayer = (
	win: unknown
): win is {
	dataLayer: Array< Record< string, unknown > >;
} => !! win && 'object' === typeof win && 'dataLayer' in win;

export function initGA4Tracking( session: Session ): void {
	if ( ! session.isGA4Integrated ) {
		return;
	}

	window.addEventListener(
		'nelio-ab-testing/track',
		( e: CustomEventInit< { event: TrackEvent } > ) => {
			if (
				e.detail &&
				e.detail.event &&
				[ 'visit', 'conversion' ].includes( e.detail.event.kind )
			) {
				sendToGA4( e.detail.event );
			}
		}
	);
}

export function getGA4ClientId(): string | undefined {
	const match = document.cookie.match( /_ga=GA\d\.\d\.(\d+\.\d+)/ );
	return match ? match[ 1 ] : undefined;
}

function getVariantName(
	settings: Maybe< Required< Settings > >,
	eventData: TrackEvent
): Maybe< string > {
	if ( ! settings ) {
		return undefined;
	}

	const exp = settings.experiments.find(
		( e ) => e.id === eventData.experiment
	);
	if ( ! exp ) {
		return undefined;
	}

	if ( ! exp.alternatives ) {
		return undefined;
	}

	if ( ! exp.alternatives[ eventData.alternative ] ) {
		return undefined;
	}

	const alt = exp.alternatives[ eventData.alternative ];
	if (
		!! alt &&
		typeof alt === 'object' &&
		'name' in alt &&
		typeof alt.name === 'string'
	) {
		return alt.name;
	}

	return eventData.alternative === 0
		? 'Control'
		: `Variant ${ eventData.alternative }`;
}

function getGoalName(
	settings: Maybe< Required< Settings > >,
	eventData: ConversionEvent
): Maybe< string > {
	if ( ! settings ) {
		return undefined;
	}

	const exp = settings.experiments.find(
		( e ) => e.id === eventData.experiment
	);
	if ( ! exp ) {
		return undefined;
	}

	if ( ! exp.goals ) {
		return undefined;
	}

	if ( ! exp.goals[ eventData.goal ] ) {
		return undefined;
	}

	const goal = exp.goals[ eventData.goal ];
	if ( ! goal ) {
		return undefined;
	}

	return goal.name;
}