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

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

function sendToGA4( eventData: TrackEvent ) {
	const settings = getSettings();

	const goal =
		eventData.kind === 'conversion'
			? getGoal( settings, eventData )
			: undefined;
	if ( false === goal ) {
		return;
	}

	const eventName =
		// eslint-disable-next-line no-nested-ternary
		eventData.kind === 'visit'
			? 'experiment_impression'
			: goal
			? goal.eventName?.trim() || 'conversion'
			: 'conversion';

	const eventDetails = {
		experiment_id: eventData.experiment,
		experiment_name: getExperimentName( settings, eventData ),
		variant_id: eventData.alternative,
		variant_name: getAlternativeName( eventData ),
		...( goal &&
			eventData.kind === 'conversion' && {
				goal_id: eventData.goal,
				...( goal.goalName && { goal_name: goal.goalName } ),
			} ),
	};

	if (
		( ! settings?.ga4TrackingMethod ||
			settings.ga4TrackingMethod === 'gtm' ) &&
		hasDataLayer( window )
	) {
		window.dataLayer.push( { event: eventName, ...eventDetails } );
	} else if (
		( ! settings?.ga4TrackingMethod ||
			settings.ga4TrackingMethod === 'gtag' ) &&
		hasGTag( window )
	) {
		window.gtag( 'event', eventName, eventDetails );
	}
}

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

	return settings.experiments.find( ( e ) => e.id === eventData.experiment )
		?.extensions?.ga4?.experimentName;
}

function getAlternativeName( eventData: TrackEvent ): Maybe< string > {
	return eventData.alternative === 0
		? 'Control'
		: `Variant ${ getLetter( eventData.alternative ) }`;
}

type GA4Goal = Required<
	Required< ExperimentSummary >[ 'extensions' ]
>[ 'ga4' ][ 'goals' ][ number ];
function getGoal(
	settings: Maybe< Required< Settings > >,
	eventData: ConversionEvent
): Exclude< GA4Goal | false, undefined > {
	if ( ! settings ) {
		return false;
	}

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

	const goals = exp.extensions?.ga4?.goals ?? [];
	if ( ! goals.length ) {
		return false;
	}

	return goals[ eventData.goal ] || false;
}

function getLetter( index: number ): string {
	const letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
	if ( index >= letters.length ) {
		return `${ index }`;
	}
	return letters.charAt( index );
}