// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * @template T
 * @interface
 */
UI.ListDelegate = function() {};

UI.ListDelegate.prototype = {
  /**
   * @param {T} item
   * @return {!Element}
   */
  createElementForItem(item) {},

  /**
   * This method is not called in NonViewport mode.
   * Return zero to make list measure the item (only works in SameHeight mode).
   * @param {T} item
   * @return {number}
   */
  heightForItem(item) {},

  /**
   * @param {T} item
   * @return {boolean}
   */
  isItemSelectable(item) {},

  /**
   * @param {?T} from
   * @param {?T} to
   * @param {?Element} fromElement
   * @param {?Element} toElement
   */
  selectedItemChanged(from, to, fromElement, toElement) {},
};

/** @enum {symbol} */
UI.ListMode = {
  NonViewport: Symbol('UI.ListMode.NonViewport'),
  EqualHeightItems: Symbol('UI.ListMode.EqualHeightItems'),
  VariousHeightItems: Symbol('UI.ListMode.VariousHeightItems')
};

/**
 * @template T
 */
UI.ListControl = class {
  /**
   * @param {!UI.ListModel<T>} model
   * @param {!UI.ListDelegate<T>} delegate
   * @param {!UI.ListMode=} mode
   */
  constructor(model, delegate, mode) {
    this.element = createElement('div');
    this.element.style.overflowY = 'auto';
    this._topElement = this.element.createChild('div');
    this._bottomElement = this.element.createChild('div');
    this._firstIndex = 0;
    this._lastIndex = 0;
    this._renderedHeight = 0;
    this._topHeight = 0;
    this._bottomHeight = 0;

    this._model = model;
    this._model.addEventListener(UI.ListModel.Events.ItemsReplaced, this._replacedItemsInRange, this);
    /** @type {!Map<T, !Element>} */
    this._itemToElement = new Map();
    this._selectedIndex = -1;
    /** @type {?T} */
    this._selectedItem = null;

    this.element.tabIndex = -1;
    this.element.addEventListener('click', this._onClick.bind(this), false);
    this.element.addEventListener('keydown', this._onKeyDown.bind(this), false);

    this._delegate = delegate;
    this._mode = mode || UI.ListMode.EqualHeightItems;
    this._fixedHeight = 0;
    this._variableOffsets = new Int32Array(0);
    this._clearContents();

    if (this._mode !== UI.ListMode.NonViewport) {
      this.element.addEventListener('scroll', () => {
        this._updateViewport(this.element.scrollTop, this.element.offsetHeight);
      }, false);
    }
  }

  /**
   * @param {!UI.ListModel<T>} model
   */
  setModel(model) {
    this._itemToElement.clear();
    const length = this._model.length;
    this._model.removeEventListener(UI.ListModel.Events.ItemsReplaced, this._replacedItemsInRange, this);
    this._model = model;
    this._model.addEventListener(UI.ListModel.Events.ItemsReplaced, this._replacedItemsInRange, this);
    this.invalidateRange(0, length);
  }

  /**
   * @param {!Common.Event} event
   */
  _replacedItemsInRange(event) {
    const data = /** @type {{index: number, removed: !Array<T>, inserted: number}} */ (event.data);
    const from = data.index;
    const to = from + data.removed.length;

    const oldSelectedItem = this._selectedItem;
    const oldSelectedElement = oldSelectedItem ? (this._itemToElement.get(oldSelectedItem) || null) : null;
    for (let i = 0; i < data.removed.length; i++)
      this._itemToElement.delete(data.removed[i]);
    this._invalidate(from, to, data.inserted);

    if (this._selectedIndex >= to) {
      this._selectedIndex += data.inserted - (to - from);
      this._selectedItem = this._model.at(this._selectedIndex);
    } else if (this._selectedIndex >= from) {
      let index = this._findFirstSelectable(from + data.inserted, +1, false);
      if (index === -1)
        index = this._findFirstSelectable(from - 1, -1, false);
      this._select(index, oldSelectedItem, oldSelectedElement);
    }
  }

  /**
   * @param {T} item
   */
  refreshItem(item) {
    const index = this._model.indexOf(item);
    if (index === -1) {
      console.error('Item to refresh is not present');
      return;
    }
    this._itemToElement.delete(item);
    this.invalidateRange(index, index + 1);
    if (this._selectedIndex !== -1)
      this._select(this._selectedIndex, null, null);
  }

  /**
   * @param {number} from
   * @param {number} to
   */
  invalidateRange(from, to) {
    this._invalidate(from, to, to - from);
  }

  viewportResized() {
    if (this._mode === UI.ListMode.NonViewport)
      return;
    // TODO(dgozman): try to keep visible scrollTop the same.
    const scrollTop = this.element.scrollTop;
    const viewportHeight = this.element.offsetHeight;
    this._clearViewport();
    this._updateViewport(Number.constrain(scrollTop, 0, this._totalHeight() - viewportHeight), viewportHeight);
  }

  invalidateItemHeight() {
    if (this._mode !== UI.ListMode.EqualHeightItems) {
      console.error('Only supported in equal height items mode');
      return;
    }
    this._fixedHeight = 0;
    if (this._model.length) {
      this._itemToElement.clear();
      this._invalidate(0, this._model.length, this._model.length);
    }
  }

  /**
   * @param {?Node} node
   * @return {?T}
   */
  itemForNode(node) {
    while (node && node.parentNodeOrShadowHost() !== this.element)
      node = node.parentNodeOrShadowHost();
    if (!node)
      return null;
    const element = /** @type {!Element} */ (node);
    const index = this._model.findIndex(item => this._itemToElement.get(item) === element);
    return index !== -1 ? this._model.at(index) : null;
  }

  /**
   * @param {T} item
   * @param {boolean=} center
   */
  scrollItemIntoView(item, center) {
    const index = this._model.indexOf(item);
    if (index === -1) {
      console.error('Attempt to scroll onto missing item');
      return;
    }
    this._scrollIntoView(index, center);
  }

  /**
   * @return {?T}
   */
  selectedItem() {
    return this._selectedItem;
  }

  /**
   * @return {number}
   */
  selectedIndex() {
    return this._selectedIndex;
  }

  /**
   * @param {?T} item
   * @param {boolean=} center
   * @param {boolean=} dontScroll
   */
  selectItem(item, center, dontScroll) {
    let index = -1;
    if (item !== null) {
      index = this._model.indexOf(item);
      if (index === -1) {
        console.error('Attempt to select missing item');
        return;
      }
      if (!this._delegate.isItemSelectable(item)) {
        console.error('Attempt to select non-selectable item');
        return;
      }
    }
    if (this._selectedIndex !== index)
      this._select(index);
    if (index !== -1 && !dontScroll)
      this._scrollIntoView(index, center);
  }

  /**
   * @param {boolean=} canWrap
   * @param {boolean=} center
   * @return {boolean}
   */
  selectPreviousItem(canWrap, center) {
    if (this._selectedIndex === -1 && !canWrap)
      return false;
    let index = this._selectedIndex === -1 ? this._model.length - 1 : this._selectedIndex - 1;
    index = this._findFirstSelectable(index, -1, !!canWrap);
    if (index !== -1) {
      this._scrollIntoView(index, center);
      this._select(index);
      return true;
    }
    return false;
  }

  /**
   * @param {boolean=} canWrap
   * @param {boolean=} center
   * @return {boolean}
   */
  selectNextItem(canWrap, center) {
    if (this._selectedIndex === -1 && !canWrap)
      return false;
    let index = this._selectedIndex === -1 ? 0 : this._selectedIndex + 1;
    index = this._findFirstSelectable(index, +1, !!canWrap);
    if (index !== -1) {
      this._scrollIntoView(index, center);
      this._select(index);
      return true;
    }
    return false;
  }

  /**
   * @param {boolean=} center
   * @return {boolean}
   */
  selectItemPreviousPage(center) {
    if (this._mode === UI.ListMode.NonViewport)
      return false;
    let index = this._selectedIndex === -1 ? this._model.length - 1 : this._selectedIndex;
    index = this._findPageSelectable(index, -1);
    if (index !== -1) {
      this._scrollIntoView(index, center);
      this._select(index);
      return true;
    }
    return false;
  }

  /**
   * @param {boolean=} center
   * @return {boolean}
   */
  selectItemNextPage(center) {
    if (this._mode === UI.ListMode.NonViewport)
      return false;
    let index = this._selectedIndex === -1 ? 0 : this._selectedIndex;
    index = this._findPageSelectable(index, +1);
    if (index !== -1) {
      this._scrollIntoView(index, center);
      this._select(index);
      return true;
    }
    return false;
  }

  /**
   * @param {number} index
   * @param {boolean=} center
   */
  _scrollIntoView(index, center) {
    if (this._mode === UI.ListMode.NonViewport) {
      this._elementAtIndex(index).scrollIntoViewIfNeeded(!!center);
      return;
    }

    const top = this._offsetAtIndex(index);
    const bottom = this._offsetAtIndex(index + 1);
    const viewportHeight = this.element.offsetHeight;
    if (center) {
      const scrollTo = (top + bottom) / 2 - viewportHeight / 2;
      this._updateViewport(Number.constrain(scrollTo, 0, this._totalHeight() - viewportHeight), viewportHeight);
      return;
    }

    const scrollTop = this.element.scrollTop;
    if (top < scrollTop)
      this._updateViewport(top, viewportHeight);
    else if (bottom > scrollTop + viewportHeight)
      this._updateViewport(bottom - viewportHeight, viewportHeight);
  }

  /**
   * @param {!Event} event
   */
  _onClick(event) {
    const item = this.itemForNode(/** @type {?Node} */ (event.target));
    if (item && this._delegate.isItemSelectable(item))
      this.selectItem(item);
  }

  /**
   * @param {!Event} event
   */
  _onKeyDown(event) {
    let selected = false;
    switch (event.key) {
      case 'ArrowUp':
        selected = this.selectPreviousItem(true, false);
        break;
      case 'ArrowDown':
        selected = this.selectNextItem(true, false);
        break;
      case 'PageUp':
        selected = this.selectItemPreviousPage(false);
        break;
      case 'PageDown':
        selected = this.selectItemNextPage(false);
        break;
    }
    if (selected)
      event.consume();
  }

  /**
   * @return {number}
   */
  _totalHeight() {
    return this._offsetAtIndex(this._model.length);
  }

  /**
   * @param {number} offset
   * @return {number}
   */
  _indexAtOffset(offset) {
    if (this._mode === UI.ListMode.NonViewport)
      throw 'There should be no offset conversions in non-viewport mode';
    if (!this._model.length || offset < 0)
      return 0;
    if (this._mode === UI.ListMode.VariousHeightItems) {
      return Math.min(
          this._model.length - 1, this._variableOffsets.lowerBound(offset, undefined, 0, this._model.length));
    }
    if (!this._fixedHeight)
      this._measureHeight();
    return Math.min(this._model.length - 1, Math.floor(offset / this._fixedHeight));
  }

  /**
   * @param {number} index
   * @return {!Element}
   */
  _elementAtIndex(index) {
    const item = this._model.at(index);
    let element = this._itemToElement.get(item);
    if (!element) {
      element = this._delegate.createElementForItem(item);
      this._itemToElement.set(item, element);
    }
    return element;
  }

  /**
   * @param {number} index
   * @return {number}
   */
  _offsetAtIndex(index) {
    if (this._mode === UI.ListMode.NonViewport)
      throw 'There should be no offset conversions in non-viewport mode';
    if (!this._model.length)
      return 0;
    if (this._mode === UI.ListMode.VariousHeightItems)
      return this._variableOffsets[index];
    if (!this._fixedHeight)
      this._measureHeight();
    return index * this._fixedHeight;
  }

  _measureHeight() {
    this._fixedHeight = this._delegate.heightForItem(this._model.at(0));
    if (!this._fixedHeight)
      this._fixedHeight = UI.measurePreferredSize(this._elementAtIndex(0), this.element).height;
  }

  /**
   * @param {number} index
   * @param {?T=} oldItem
   * @param {?Element=} oldElement
   */
  _select(index, oldItem, oldElement) {
    if (oldItem === undefined)
      oldItem = this._selectedItem;
    if (oldElement === undefined)
      oldElement = this._itemToElement.get(oldItem) || null;
    this._selectedIndex = index;
    this._selectedItem = index === -1 ? null : this._model.at(index);
    const newItem = this._selectedItem;
    const newElement = this._selectedIndex !== -1 ? this._elementAtIndex(index) : null;
    this._delegate.selectedItemChanged(oldItem, newItem, /** @type {?Element} */ (oldElement), newElement);
  }

  /**
   * @param {number} index
   * @param {number} direction
   * @param {boolean} canWrap
   * @return {number}
   */
  _findFirstSelectable(index, direction, canWrap) {
    const length = this._model.length;
    if (!length)
      return -1;
    for (let step = 0; step <= length; step++) {
      if (index < 0 || index >= length) {
        if (!canWrap)
          return -1;
        index = (index + length) % length;
      }
      if (this._delegate.isItemSelectable(this._model.at(index)))
        return index;
      index += direction;
    }
    return -1;
  }

  /**
   * @param {number} index
   * @param {number} direction
   * @return {number}
   */
  _findPageSelectable(index, direction) {
    let lastSelectable = -1;
    const startOffset = this._offsetAtIndex(index);
    // Compensate for zoom rounding errors with -1.
    const viewportHeight = this.element.offsetHeight - 1;
    while (index >= 0 && index < this._model.length) {
      if (this._delegate.isItemSelectable(this._model.at(index))) {
        if (Math.abs(this._offsetAtIndex(index) - startOffset) >= viewportHeight)
          return index;
        lastSelectable = index;
      }
      index += direction;
    }
    return lastSelectable;
  }

  /**
   * @param {number} length
   * @param {number} copyTo
   */
  _reallocateVariableOffsets(length, copyTo) {
    if (this._variableOffsets.length < length) {
      const variableOffsets = new Int32Array(Math.max(length, this._variableOffsets.length * 2));
      variableOffsets.set(this._variableOffsets.slice(0, copyTo), 0);
      this._variableOffsets = variableOffsets;
    } else if (this._variableOffsets.length >= 2 * length) {
      const variableOffsets = new Int32Array(length);
      variableOffsets.set(this._variableOffsets.slice(0, copyTo), 0);
      this._variableOffsets = variableOffsets;
    }
  }

  /**
   * @param {number} from
   * @param {number} to
   * @param {number} inserted
   */
  _invalidate(from, to, inserted) {
    if (this._mode === UI.ListMode.NonViewport) {
      this._invalidateNonViewportMode(from, to - from, inserted);
      return;
    }

    if (this._mode === UI.ListMode.VariousHeightItems) {
      this._reallocateVariableOffsets(this._model.length + 1, from + 1);
      for (let i = from + 1; i <= this._model.length; i++)
        this._variableOffsets[i] = this._variableOffsets[i - 1] + this._delegate.heightForItem(this._model.at(i - 1));
    }

    const viewportHeight = this.element.offsetHeight;
    const totalHeight = this._totalHeight();
    const scrollTop = this.element.scrollTop;

    if (this._renderedHeight < viewportHeight || totalHeight < viewportHeight) {
      this._clearViewport();
      this._updateViewport(Number.constrain(scrollTop, 0, totalHeight - viewportHeight), viewportHeight);
      return;
    }

    const heightDelta = totalHeight - this._renderedHeight;
    if (to <= this._firstIndex) {
      const topHeight = this._topHeight + heightDelta;
      this._topElement.style.height = topHeight + 'px';
      this.element.scrollTop = scrollTop + heightDelta;
      this._topHeight = topHeight;
      this._renderedHeight = totalHeight;
      const indexDelta = inserted - (to - from);
      this._firstIndex += indexDelta;
      this._lastIndex += indexDelta;
      return;
    }

    if (from >= this._lastIndex) {
      const bottomHeight = this._bottomHeight + heightDelta;
      this._bottomElement.style.height = bottomHeight + 'px';
      this._bottomHeight = bottomHeight;
      this._renderedHeight = totalHeight;
      return;
    }

    // TODO(dgozman): try to keep visible scrollTop the same
    // when invalidating after firstIndex but before first visible element.
    this._clearViewport();
    this._updateViewport(Number.constrain(scrollTop, 0, totalHeight - viewportHeight), viewportHeight);
  }

  /**
   * @param {number} start
   * @param {number} remove
   * @param {number} add
   */
  _invalidateNonViewportMode(start, remove, add) {
    let startElement = this._topElement;
    for (let index = 0; index < start; index++)
      startElement = startElement.nextElementSibling;
    while (remove--)
      startElement.nextElementSibling.remove();
    while (add--)
      this.element.insertBefore(this._elementAtIndex(start + add), startElement.nextElementSibling);
  }

  _clearViewport() {
    if (this._mode === UI.ListMode.NonViewport) {
      console.error('There should be no viewport updates in non-viewport mode');
      return;
    }
    this._firstIndex = 0;
    this._lastIndex = 0;
    this._renderedHeight = 0;
    this._topHeight = 0;
    this._bottomHeight = 0;
    this._clearContents();
  }

  _clearContents() {
    // Note: this method should not force layout. Be careful.
    this._topElement.style.height = '0';
    this._bottomElement.style.height = '0';
    this.element.removeChildren();
    this.element.appendChild(this._topElement);
    this.element.appendChild(this._bottomElement);
  }

  /**
   * @param {number} scrollTop
   * @param {number} viewportHeight
   */
  _updateViewport(scrollTop, viewportHeight) {
    // Note: this method should not force layout. Be careful.
    if (this._mode === UI.ListMode.NonViewport) {
      console.error('There should be no viewport updates in non-viewport mode');
      return;
    }
    const totalHeight = this._totalHeight();
    if (!totalHeight) {
      this._firstIndex = 0;
      this._lastIndex = 0;
      this._topHeight = 0;
      this._bottomHeight = 0;
      this._renderedHeight = 0;
      this._topElement.style.height = '0';
      this._bottomElement.style.height = '0';
      return;
    }

    const firstIndex = this._indexAtOffset(scrollTop - viewportHeight);
    const lastIndex = this._indexAtOffset(scrollTop + 2 * viewportHeight) + 1;

    while (this._firstIndex < Math.min(firstIndex, this._lastIndex)) {
      this._elementAtIndex(this._firstIndex).remove();
      this._firstIndex++;
    }
    while (this._lastIndex > Math.max(lastIndex, this._firstIndex)) {
      this._elementAtIndex(this._lastIndex - 1).remove();
      this._lastIndex--;
    }

    this._firstIndex = Math.min(this._firstIndex, lastIndex);
    this._lastIndex = Math.max(this._lastIndex, firstIndex);
    for (let index = this._firstIndex - 1; index >= firstIndex; index--) {
      const element = this._elementAtIndex(index);
      this.element.insertBefore(element, this._topElement.nextSibling);
    }
    for (let index = this._lastIndex; index < lastIndex; index++) {
      const element = this._elementAtIndex(index);
      this.element.insertBefore(element, this._bottomElement);
    }

    this._firstIndex = firstIndex;
    this._lastIndex = lastIndex;
    this._topHeight = this._offsetAtIndex(firstIndex);
    this._topElement.style.height = this._topHeight + 'px';
    this._bottomHeight = totalHeight - this._offsetAtIndex(lastIndex);
    this._bottomElement.style.height = this._bottomHeight + 'px';
    this._renderedHeight = totalHeight;
    this.element.scrollTop = scrollTop;
  }
};