var $ = jQuery,
	mw = window.mediaWiki,
	actions = {},
	types = require( './actionTypes' ),
	wait = require( './wait' ),

	// See the following for context around this value.
	//
	// * https://phabricator.wikimedia.org/T161284
	// * https://phabricator.wikimedia.org/T70861#3129780
	FETCH_START_DELAY = 150, // ms.

	// The delay after which a FETCH_COMPLETE action should be dispatched.
	//
	// If the API endpoint responds faster than 500 ms (or, say, the API
	// response is served from the UA's cache), then we introduce a delay of
	// 500 - t to make the preview delay consistent to the user.
	FETCH_COMPLETE_TARGET_DELAY = 500, // ms.

	ABANDON_END_DELAY = 300; // ms.

/**
 * Mixes in timing information to an action.
 *
 * Warning: the `baseAction` parameter is modified and returned.
 *
 * @param {Object} baseAction
 * @return {Object}
 */
function timedAction( baseAction ) {
	baseAction.timestamp = mw.now();

	return baseAction;
}

/**
 * Represents Page Previews booting.
 *
 * When a Redux store is created, the `@@INIT` action is immediately
 * dispatched to it. To avoid overriding the term, we refer to booting rather
 * than initializing.
 *
 * Page Previews persists critical pieces of information to local storage.
 * Since reading from and writing to local storage are synchronous, Page
 * Previews is booted when the browser is idle (using
 * [`mw.requestIdleCallback`](https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback))
 * so as not to impact latency-critical events.
 *
 * @param {Boolean} isEnabled See `isEnabled.js`
 * @param {mw.user} user
 * @param {ext.popups.UserSettings} userSettings
 * @param {Function} generateToken
 * @param {mw.Map} config The config of the MediaWiki client-side application,
 *  i.e. `mw.config`
 * @returns {Object}
 */
actions.boot = function (
	isEnabled,
	user,
	userSettings,
	generateToken,
	config
) {
	var editCount = config.get( 'wgUserEditCount' ),
		previewCount = userSettings.getPreviewCount();

	return {
		type: types.BOOT,
		isEnabled: isEnabled,
		isNavPopupsEnabled: config.get( 'wgPopupsConflictsWithNavPopupGadget' ),
		sessionToken: user.sessionId(),
		pageToken: generateToken(),
		page: {
			title: config.get( 'wgTitle' ),
			namespaceID: config.get( 'wgNamespaceNumber' ),
			id: config.get( 'wgArticleId' )
		},
		user: {
			isAnon: user.isAnon(),
			editCount: editCount,
			previewCount: previewCount
		}
	};
};

/**
 * Represents Page Previews fetching data via the gateway.
 *
 * @param {ext.popups.Gateway} gateway
 * @param {Element} el
 * @param {String} token The unique token representing the link interaction that
 *  triggered the fetch
 * @return {Redux.Thunk}
 */
actions.fetch = function ( gateway, el, token ) {
	var title = $( el ).data( 'page-previews-title' ),
		titleText = title.getPrefixedText(),
		namespaceID = title.namespace;

	return function ( dispatch ) {
		var request;

		dispatch( timedAction( {
			type: types.FETCH_START,
			el: el,
			title: titleText,
			namespaceID: namespaceID
		} ) );

		request = gateway.getPageSummary( titleText )
			.then( function ( result ) {
				dispatch( timedAction( {
					type: types.FETCH_END,
					el: el
				} ) );

				return result;
			} )
			.fail( function () {
				dispatch( {
					type: types.FETCH_FAILED,
					el: el
				} );
			} );

		$.when( request, wait( FETCH_COMPLETE_TARGET_DELAY - FETCH_START_DELAY ) )
			.then( function ( result ) {
				dispatch( timedAction( {
					type: types.FETCH_COMPLETE,
					el: el,
					result: result,
					token: token
				} ) );
			} );
	};
};

/**
 * Represents the user dwelling on a link, either by hovering over it with
 * their mouse or by focussing it using their keyboard or an assistive device.
 *
 * @param {Element} el
 * @param {Event} event
 * @param {ext.popups.Gateway} gateway
 * @param {Function} generateToken
 * @return {Redux.Thunk}
 */
actions.linkDwell = function ( el, event, gateway, generateToken ) {
	var token = generateToken(),
		title = $( el ).data( 'page-previews-title' ),
		titleText = title.getPrefixedText(),
		namespaceID = title.namespace;

	return function ( dispatch, getState ) {
		var action = timedAction( {
			type: types.LINK_DWELL,
			el: el,
			event: event,
			token: token,
			title: titleText,
			namespaceID: namespaceID
		} );

		// Has the new generated token been accepted?
		function isNewInteraction() {
			return getState().preview.activeToken === token;
		}

		dispatch( action );

		if ( !isNewInteraction() ) {
			return;
		}

		wait( FETCH_START_DELAY )
			.then( function () {
				var previewState = getState().preview;

				if ( previewState.enabled && isNewInteraction() ) {
					dispatch( actions.fetch( gateway, el, token ) );
				}
			} );
	};
};

/**
 * Represents the user abandoning a link, either by moving their mouse away
 * from it or by shifting focus to another UI element using their keyboard or
 * an assistive device, or abandoning a preview by moving their mouse away
 * from it.
 *
 * @return {Redux.Thunk}
 */
actions.abandon = function () {
	return function ( dispatch, getState ) {
		var token = getState().preview.activeToken;

		if ( !token ) {
			return;
		}

		dispatch( timedAction( {
			type: types.ABANDON_START,
			token: token
		} ) );

		wait( ABANDON_END_DELAY )
			.then( function () {
				dispatch( {
					type: types.ABANDON_END,
					token: token
				} );
			} );
	};
};

/**
 * Represents the user clicking on a link with their mouse, keyboard, or an
 * assistive device.
 *
 * @param {Element} el
 * @return {Object}
 */
actions.linkClick = function ( el ) {
	return timedAction( {
		type: types.LINK_CLICK,
		el: el
	} );
};

/**
 * Represents the user dwelling on a preview with their mouse.
 *
 * @return {Object}
 */
actions.previewDwell = function () {
	return {
		type: types.PREVIEW_DWELL
	};
};

/**
 * Represents a preview being shown to the user.
 *
 * This action is dispatched by the `./changeListeners/render.js` change
 * listener.
 *
 * @param {String} token
 * @return {Object}
 */
actions.previewShow = function ( token ) {
	return timedAction( {
		type: types.PREVIEW_SHOW,
		token: token
	} );
};

/**
 * Represents the user clicking either the "Enable previews" footer menu link,
 * or the "cog" icon that's present on each preview.
 *
 * @return {Object}
 */
actions.showSettings = function () {
	return {
		type: types.SETTINGS_SHOW
	};
};

/**
 * Represents the user closing the settings dialog and saving their settings.
 *
 * @return {Object}
 */
actions.hideSettings = function () {
	return {
		type: types.SETTINGS_HIDE
	};
};

/**
 * Represents the user saving their settings.
 *
 * N.B. This action returns a Redux.Thunk not because it needs to perform
 * asynchronous work, but because it needs to query the global state for the
 * current enabled state. In order to keep the enabled state in a single
 * place (the preview reducer), we query it and dispatch it as `wasEnabled`
 * so that other reducers (like settings) can act on it without having to
 * duplicate the `enabled` state locally.
 * See doc/adr/0003-keep-enabled-state-only-in-preview-reducer.md for more
 * details.
 *
 * @param {Boolean} enabled if previews are enabled or not
 * @return {Redux.Thunk}
 */
actions.saveSettings = function ( enabled ) {
	return function ( dispatch, getState ) {
		dispatch( {
			type: types.SETTINGS_CHANGE,
			wasEnabled: getState().preview.enabled,
			enabled: enabled
		} );
	};
};

/**
 * Represents the queued event being logged `changeListeners/eventLogging.js`
 * change listener.
 *
 * @return {Object}
 */
actions.eventLogged = function () {
	return {
		type: types.EVENT_LOGGED
	};
};

/**
 * Represents the queued statsv event being logged.
 * See `mw.popups.changeListeners.statsv` change listener.
 *
 * @return {Object}
 */
actions.statsvLogged = function () {
	return {
		type: types.STATSV_LOGGED
	};
};
module.exports = actions;