wp-calypso/client/dashboard/app/queries/me-preferences.ts

import { fetchPreferences, updatePreferences } from '../../data/me-preferences';
import { queryClient } from '../query-client';
import type { UserPreferences } from '../../data/me-preferences';

const defaultValues: Required< UserPreferences > = {
	'sites-view': {},
	'some-string': '',
};

// Returns all user preferences, without applying any defaults.
export const rawUserPreferencesQuery = () => ( {
	queryKey: [ 'me', 'preferences' ],
	queryFn: fetchPreferences,
} );

export const userPreferenceQuery = < P extends keyof UserPreferences >( preferenceName: P ) => ( {
	queryKey: rawUserPreferencesQuery().queryKey,
	queryFn: fetchPreferences,
	select: ( data: UserPreferences ): Required< UserPreferences >[ P ] => {
		const fetchedValue = data[ preferenceName ];
		return fetchedValue === undefined
			? defaultValues[ preferenceName ]
			: // `fetchedValue` is a `NonNullable< UserPreferences[ P ] >`, which we know is the same
			  // as `Required< UserPreferences >[ P ]`, but the later gives better type hints when
			  // the query is used in the component.
			  ( fetchedValue as Required< UserPreferences >[ P ] );
	},
} );

export const userPreferenceMutation = < P extends keyof UserPreferences >(
	preferenceName: P
) => ( {
	mutationFn: ( data: Required< UserPreferences >[ P ] ) =>
		updatePreferences( {
			[ preferenceName ]: data,
		} ),
	onSuccess: ( newData: UserPreferences ) => {
		queryClient.setQueryData(
			rawUserPreferencesQuery().queryKey,
			( oldData: UserPreferences | undefined ) => ( oldData ? { ...oldData, ...newData } : newData )
		);
	},
} );