blob: c0ea5a8d675e1e85278917262f7309450162b9ba [file] [log] [blame]
// Copyright (C) 2016 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
(function() {
'use strict';
const ScrollBehavior = {
NEVER: 'never',
KEEP_VISIBLE: 'keep-visible',
};
Polymer({
is: 'gr-cursor-manager',
properties: {
stops: {
type: Array,
value() {
return [];
},
observer: '_updateIndex',
},
/**
* @type (?Object)
*/
target: {
type: Object,
notify: true,
observer: '_scrollToTarget',
},
/**
* The height of content intended to be included with the target.
* @type (?number)
*/
_targetHeight: Number,
/**
* The index of the current target (if any). -1 otherwise.
*/
index: {
type: Number,
value: -1,
notify: true,
},
/**
* The class to apply to the current target. Use null for no class.
*/
cursorTargetClass: {
type: String,
value: null,
},
/**
* The scroll behavior for the cursor. Values are 'never' and
* 'keep-visible'. 'keep-visible' will only scroll if the cursor is beyond
* the viewport.
* TODO (beckysiegel) figure out why it can be undefined
* @type (string|undefined)
*/
scrollBehavior: {
type: String,
value: ScrollBehavior.NEVER,
},
/**
* When true, will call element.focus() during scrolling.
*/
focusOnMove: {
type: Boolean,
value: false,
},
},
detached() {
this.unsetCursor();
},
next(opt_condition, opt_getTargetHeight) {
this._moveCursor(1, opt_condition, opt_getTargetHeight);
},
previous(opt_condition) {
this._moveCursor(-1, opt_condition);
},
/**
* Set the cursor to an arbitrary element.
* @param {!HTMLElement} element
* @param {boolean=} opt_noScroll prevent any potential scrolling in response
* setting the cursor.
*/
setCursor(element, opt_noScroll) {
let behavior;
if (opt_noScroll) {
behavior = this.scrollBehavior;
this.scrollBehavior = ScrollBehavior.NEVER;
}
this.unsetCursor();
this.target = element;
this._updateIndex();
this._decorateTarget();
if (opt_noScroll) { this.scrollBehavior = behavior; }
},
unsetCursor() {
this._unDecorateTarget();
this.index = -1;
this.target = null;
this._targetHeight = null;
},
isAtStart() {
return this.index === 0;
},
isAtEnd() {
return this.index === this.stops.length - 1;
},
moveToStart() {
if (this.stops.length) {
this.setCursor(this.stops[0]);
}
},
setCursorAtIndex(index, opt_noScroll) {
this.setCursor(this.stops[index], opt_noScroll);
},
/**
* Move the cursor forward or backward by delta. Noop if moving past either
* end of the stop list.
* @param {number} delta either -1 or 1.
* @param {!Function=} opt_condition Optional stop condition. If a condition
* is passed the cursor will continue to move in the specified direction
* until the condition is met.
* @param {!Function=} opt_getTargetHeight Optional function to calculate the
* height of the target's 'section'. The height of the target itself is
* sometimes different, used by the diff cursor.
* @private
*/
_moveCursor(delta, opt_condition, opt_getTargetHeight) {
if (!this.stops.length) {
this.unsetCursor();
return;
}
this._unDecorateTarget();
const newIndex = this._getNextindex(delta, opt_condition);
let newTarget = null;
if (newIndex !== -1) {
newTarget = this.stops[newIndex];
}
this.index = newIndex;
this.target = newTarget;
if (!this.target) { return; }
if (opt_getTargetHeight) {
this._targetHeight = opt_getTargetHeight(newTarget);
} else {
this._targetHeight = newTarget.scrollHeight;
}
if (this.focusOnMove) { this.target.focus(); }
this._decorateTarget();
},
_decorateTarget() {
if (this.target && this.cursorTargetClass) {
this.target.classList.add(this.cursorTargetClass);
}
},
_unDecorateTarget() {
if (this.target && this.cursorTargetClass) {
this.target.classList.remove(this.cursorTargetClass);
}
},
/**
* Get the next stop index indicated by the delta direction.
* @param {number} delta either -1 or 1.
* @param {!Function=} opt_condition Optional stop condition.
* @return {number} the new index.
* @private
*/
_getNextindex(delta, opt_condition) {
if (!this.stops.length || this.index === -1) {
return -1;
}
let newIndex = this.index;
do {
newIndex = newIndex + delta;
} while (newIndex > 0 &&
newIndex < this.stops.length - 1 &&
opt_condition && !opt_condition(this.stops[newIndex]));
newIndex = Math.max(0, Math.min(this.stops.length - 1, newIndex));
// If we failed to satisfy the condition:
if (opt_condition && !opt_condition(this.stops[newIndex])) {
if (delta > 0) {
return this.stops.length - 1;
} else if (delta < 0) {
return 0;
}
return this.index;
}
return newIndex;
},
_updateIndex() {
if (!this.target) {
this.index = -1;
return;
}
const newIndex = Array.prototype.indexOf.call(this.stops, this.target);
if (newIndex === -1) {
this.unsetCursor();
} else {
this.index = newIndex;
}
},
/**
* Calculate where the element is relative to the window.
* @param {!Object} target Target to scroll to.
* @return {number} Distance to top of the target.
*/
_getTop(target) {
let top = target.offsetTop;
for (let offsetParent = target.offsetParent;
offsetParent;
offsetParent = offsetParent.offsetParent) {
top += offsetParent.offsetTop;
}
return top;
},
/**
* @return {boolean}
*/
_targetIsVisible(top) {
return this.scrollBehavior === ScrollBehavior.KEEP_VISIBLE &&
top > window.pageYOffset &&
top < window.pageYOffset + window.innerHeight;
},
_calculateScrollToValue(top, target) {
return top - (window.innerHeight / 3) + (target.offsetHeight / 2);
},
_scrollToTarget() {
if (!this.target || this.scrollBehavior === ScrollBehavior.NEVER) {
return;
}
const top = this._getTop(this.target);
const bottomIsVisible = this._targetHeight ?
this._targetIsVisible(top + this._targetHeight) : true;
const scrollToValue = this._calculateScrollToValue(top, this.target);
if (this._targetIsVisible(top)) {
// Don't scroll if either the bottom is visible or if the position that
// would get scrolled to is higher up than the current position. this
// woulld cause less of the target content to be displayed than is
// already.
if (bottomIsVisible || scrollToValue < window.scrollY) {
return;
}
}
// Scroll the element to the middle of the window. Dividing by a third
// instead of half the inner height feels a bit better otherwise the
// element appears to be below the center of the window even when it
// isn't.
window.scrollTo(0, scrollToValue);
},
});
})();