/**
 * WordPress dependencies
 */
import { useSelect } from '@safe-wordpress/data';

/**
 * External dependencies
 */
import { sum } from 'lodash';
import { store as NAB_DATA } from '@nab/data';
import type { AlternativeId, ExperimentId, Maybe } from '@nab/types';

export type Results =
	| { readonly status: 'loading' }
	| { readonly status: 'error' }
	| {
			readonly status: 'ready';
			readonly isUnique: boolean;
			readonly views: number;
			readonly conversions: number;
			readonly currentLeader: Maybe< number >;
			readonly improvement: number;
	  };

export const useResults = ( experimentId: ExperimentId ): Results =>
	useSelect(
		( select ): Results => {
			const isLoading =
				select( NAB_DATA ).isResolving( 'getExperiment', [
					experimentId,
				] ) ||
				select( NAB_DATA ).isResolving( 'getExperimentResults', [
					experimentId,
				] );

			if ( isLoading ) {
				return { status: 'loading' };
			}

			const experiment = select( NAB_DATA ).getExperiment( experimentId );
			const rawResults =
				select( NAB_DATA ).getExperimentResults( experimentId );
			const isError =
				select( NAB_DATA ).hasResolutionFailed( 'getExperiment', [
					experimentId,
				] ) ||
				select( NAB_DATA ).hasResolutionFailed(
					'getExperimentResults',
					[ experimentId ]
				);

			if ( ! experiment || isError || ! rawResults ) {
				return { status: 'error' };
			}

			const isUnique =
				select( NAB_DATA ).areUniqueResultsVisible( experimentId );

			const goalId = experiment.goals[ 0 ]?.id ?? '';
			const alternatives = Object.values( rawResults.alternatives ?? {} );
			const conversions = sum(
				alternatives.map( ( a ) =>
					isUnique
						? a.uniqueConversions[ goalId ] ?? 0
						: a.conversions[ goalId ] ?? 0
				)
			);

			type AlternativeSummary = {
				readonly id: AlternativeId;
				readonly index: number;
				readonly improvement: number;
			};
			// eslint-disable-next-line @wordpress/no-unused-vars-before-return
			const [ _, ...alternativeIds ] = experiment.alternatives.map(
				( a ) => a.id
			);
			const bestAlternative = alternativeIds
				.map(
					( id, index ): AlternativeSummary => ( {
						id,
						index: index + 1,
						improvement: isUnique
							? rawResults.alternatives[ id ]
									?.uniqueImprovementFactors[ goalId ] ?? 0
							: rawResults.alternatives[ id ]?.improvementFactors[
									goalId
							  ] ?? 0,
					} )
				)
				.reduce(
					( r, c ): AlternativeSummary => {
						if ( ! r ) {
							return c;
						}
						return c.improvement > r.improvement ? c : r;
					},
					{ id: 'control' as const, index: 0, improvement: 0 }
				);

			const currentLeader =
				// eslint-disable-next-line no-nested-ternary
				bestAlternative.improvement > 0
					? bestAlternative.index
					: bestAlternative.improvement < 0
					? 0
					: undefined;

			return {
				status: 'ready',
				isUnique,
				views: isUnique
					? select( NAB_DATA ).getUniquePageViews( experimentId )
					: select( NAB_DATA ).getPageViews( experimentId ),
				conversions,
				currentLeader,
				improvement: bestAlternative?.improvement ?? 0,
			};
		},
		[ experimentId ]
	);