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+/*
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+ * Nextcloud Android Library is available under MIT license
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+ *
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+ * @author Álvaro Brey Vilas
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+ * Copyright (C) 2022 Álvaro Brey Vilas
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+ * Copyright (C) 2022 Nextcloud GmbH
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+ *
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+ * Permission is hereby granted, free of charge, to any person obtaining a copy
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+ * of this software and associated documentation files (the "Software"), to deal
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+ * in the Software without restriction, including without limitation the rights
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+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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+ * copies of the Software, and to permit persons to whom the Software is
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+ * furnished to do so, subject to the following conditions:
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+ *
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+ * The above copyright notice and this permission notice shall be included in
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+ * all copies or substantial portions of the Software.
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+ *
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+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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+ * THE SOFTWARE.
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+ */
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+
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+package com.owncloud.android.ui.fragment.util
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+
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+import android.graphics.Canvas
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+import android.graphics.Rect
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+import android.view.MotionEvent
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+import androidx.recyclerview.widget.GridLayoutManager
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+import androidx.recyclerview.widget.RecyclerView
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+import androidx.recyclerview.widget.RecyclerView.ItemDecoration
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+import androidx.recyclerview.widget.RecyclerView.SimpleOnItemTouchListener
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+import com.afollestad.sectionedrecyclerview.ItemCoord
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+import com.owncloud.android.datamodel.GalleryItems
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+import com.owncloud.android.ui.adapter.GalleryAdapter
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+import me.zhanghai.android.fastscroll.FastScroller
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+import me.zhanghai.android.fastscroll.PopupTextProvider
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+import me.zhanghai.android.fastscroll.Predicate
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+import kotlin.math.ceil
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+
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+/**
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+ * Custom ViewHelper to get fast scroll working on gallery, which has a gridview and variable height (due to headers)
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+ *
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+ * Copied from me.zhanghai.android.fastscroll.RecyclerViewHelper and heavily modified for gallery structure
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+ */
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+class GalleryFastScrollViewHelper(
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+ private val mView: RecyclerView,
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+ private val mPopupTextProvider: PopupTextProvider?
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+) : FastScroller.ViewHelper {
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+ // used to calculate paddings
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+ private val mTempRect = Rect()
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+
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+ private val layoutManager by lazy { mView.layoutManager as GridLayoutManager }
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+
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+ // header is always 1st in the adapter
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+ private val headerHeight by lazy { getItemHeight(0) }
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+ // the 2nd element is always an item
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+ private val rowHeight by lazy { getItemHeight(1) }
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+
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+ private val columnCount by lazy { layoutManager.spanCount }
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+
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+ private fun getItemHeight(position: Int): Int {
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+ if (mView.childCount <= position) {
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+ return 0
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+ }
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+ val itemView = mView.getChildAt(position)
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+ mView.getDecoratedBoundsWithMargins(itemView, mTempRect)
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+ return mTempRect.height()
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+ }
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+
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+ override fun addOnPreDrawListener(onPreDraw: Runnable) {
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+ mView.addItemDecoration(object : ItemDecoration() {
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+ override fun onDraw(canvas: Canvas, parent: RecyclerView, state: RecyclerView.State) {
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+ onPreDraw.run()
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+ }
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+ })
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+ }
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+
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+ override fun addOnScrollChangedListener(onScrollChanged: Runnable) {
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+ mView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
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+ override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
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+ onScrollChanged.run()
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+ }
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+ })
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+ }
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+
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+ override fun addOnTouchEventListener(onTouchEvent: Predicate<MotionEvent?>) {
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+ mView.addOnItemTouchListener(object : SimpleOnItemTouchListener() {
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+ override fun onInterceptTouchEvent(recyclerView: RecyclerView, event: MotionEvent): Boolean {
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+ return onTouchEvent.test(event)
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+ }
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+
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+ override fun onTouchEvent(recyclerView: RecyclerView, event: MotionEvent) {
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+ onTouchEvent.test(event)
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+ }
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+ })
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+ }
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+
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+ override fun getScrollRange(): Int {
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+ val headerCount = getHeaderCount()
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+ val rowCount = getRowCount()
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+
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+ if (headerCount == 0 || rowCount == 0) {
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+ return 0
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+ }
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+ val totalHeaderHeight = headerCount * headerHeight
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+ val totalRowHeight = rowCount * rowHeight
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+ return mView.paddingTop + totalHeaderHeight + totalRowHeight + mView.paddingBottom
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+ }
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+
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+ private fun getHeaderCount(): Int {
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+ val adapter = mView.adapter as GalleryAdapter
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+ return adapter.sectionCount
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+ }
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+
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+ private fun getRowCount(): Int {
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+ val adapter = mView.adapter as GalleryAdapter
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+ if (adapter.sectionCount == 0) return 0
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+ // in each section, the final row may contain less than the max of items
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+ return adapter.files.sumOf { itemCountToRowCount(it.files.size) }
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+ }
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+
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+ /**
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+ * Calculates current absolute offset depending on view state (first visible element)
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+ */
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+ override fun getScrollOffset(): Int {
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+ val firstItemPosition = getFirstItemAdapterPosition()
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+ if (firstItemPosition == RecyclerView.NO_POSITION) {
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+ return 0
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+ }
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+
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+ val adapter = mView.adapter as GalleryAdapter
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+ val itemCoord: ItemCoord = adapter.getRelativePosition(firstItemPosition)
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+ val isHeader = itemCoord.relativePos() == -1
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+
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+ val seenRowsInPreviousSections = adapter.files
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+ .subList(0, itemCoord.section())
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+ .sumOf { itemCountToRowCount(it.files.size) }
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+ val seenRowsInThisSection = if (isHeader) 0 else itemCountToRowCount(itemCoord.relativePos())
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+ val totalSeenRows = seenRowsInPreviousSections + seenRowsInThisSection
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+
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+ val seenHeaders = when {
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+ isHeader -> itemCoord.section() // don't count the current section header
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+ else -> itemCoord.section() + 1
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+ }
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+
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+ val firstItemTop = getFirstItemOffset()
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+
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+ val totalRowOffset = totalSeenRows * rowHeight
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+ val totalHeaderOffset = seenHeaders * headerHeight
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+ return mView.paddingTop + totalHeaderOffset + totalRowOffset - firstItemTop
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+ }
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+
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+ /**
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+ * Scrolls to an absolute offset
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+ */
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+ override fun scrollTo(offset: Int) {
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+ mView.stopScroll()
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+ val offsetTmp = offset - mView.paddingTop
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+ val (position, remainingOffset) = findPositionForOffset(offsetTmp)
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+ scrollToPositionWithOffset(position, -remainingOffset)
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+ }
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+
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+ /**
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+ * Given an absolute offset, returns the closest position to that offset (without going over it),
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+ * and the remaining offset
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+ */
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+ private fun findPositionForOffset(offset: Int): Pair<Int, Int> {
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+ val adapter = mView.adapter as GalleryAdapter
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+
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+ // find section
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+ val sectionStartOffsets = getSectionStartOffsets(adapter.files)
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+ val previousSections = sectionStartOffsets.filter { it <= offset }
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+
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+ val section = previousSections.size - 1
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+ val sectionStartOffset = previousSections.last()
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+
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+ // now calculate where to scroll within the section
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+ var remainingOffset = offset - sectionStartOffset
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+ val positionWithinSection: Int
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+ if (remainingOffset <= headerHeight) {
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+ // header position
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+ positionWithinSection = -1
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+ } else {
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+ // row position
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+ remainingOffset -= headerHeight
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+ val rowCount = remainingOffset / rowHeight
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+ if (rowCount > 0) {
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+ val rowStartIndex = rowCount * columnCount
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+ positionWithinSection = rowStartIndex
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+
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+ remainingOffset -= rowCount * rowHeight
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+ } else {
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+ positionWithinSection = 0 // first item
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+ }
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+ }
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+ val absolutePosition = adapter.getAbsolutePosition(section, positionWithinSection)
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+ return Pair(absolutePosition, remainingOffset)
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+ }
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+
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+ /**
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+ * Returns a list of the offset heights at which the section corresponding to that index starts
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+ */
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+ private fun getSectionStartOffsets(files: List<GalleryItems>): List<Int> {
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+ val sectionHeights =
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+ files.map { headerHeight + itemCountToRowCount(it.files.size) * rowHeight }
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+ val sectionStartOffsets = sectionHeights.indices.map { i ->
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+ when (i) {
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+ 0 -> 0
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+ else -> sectionHeights.subList(0, i).sum()
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+ }
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+ }
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+ return sectionStartOffsets
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+ }
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+
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+ private fun itemCountToRowCount(itemsCount: Int): Int {
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+ return ceil(itemsCount.toDouble() / columnCount).toInt()
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+ }
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+
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+ override fun getPopupText(): String? {
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+ var popupTextProvider: PopupTextProvider? = mPopupTextProvider
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+ if (popupTextProvider == null) {
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+ val adapter = mView.adapter
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+ if (adapter is PopupTextProvider) {
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+ popupTextProvider = adapter
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+ }
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+ }
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+ if (popupTextProvider == null) {
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+ return null
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+ }
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+ val position = getFirstItemAdapterPosition()
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+ return if (position == RecyclerView.NO_POSITION) {
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+ null
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+ } else popupTextProvider.getPopupText(position)
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+ }
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+
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+ private fun getFirstItemAdapterPosition(): Int {
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+ if (mView.childCount == 0) {
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+ return RecyclerView.NO_POSITION
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+ }
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+ val itemView = mView.getChildAt(0)
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+ return layoutManager.getPosition(itemView)
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+ }
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+
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+ private fun getFirstItemOffset(): Int {
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+ if (mView.childCount == 0) {
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+ return RecyclerView.NO_POSITION
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+ }
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+ val itemView = mView.getChildAt(0)
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+ mView.getDecoratedBoundsWithMargins(itemView, mTempRect)
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+ return mTempRect.top
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+ }
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+
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+ private fun scrollToPositionWithOffset(position: Int, offset: Int) {
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+ var offsetTmp = offset
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+ // LinearLayoutManager actually takes offset from paddingTop instead of top of RecyclerView.
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+ offsetTmp -= mView.paddingTop
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+ layoutManager.scrollToPositionWithOffset(position, offsetTmp)
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+ }
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+}
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Álvaro Brey