Implement a basic LazyList for DOM

CHANGELOG.md

@@ -4,7 +4,7 @@
 [Unreleased]: https://github.com/cashapp/redwood/compare/0.11.0...HEAD
 
 New:
-- Nothing yet!
+- Added a basic DOM-based LazyList implementation.
 
 Changed:
 - Nothing yet!

redwood-lazylayout-dom/build.gradle

@@ -1,6 +1,7 @@
 apply plugin: 'org.jetbrains.kotlin.multiplatform'
 
 redwoodBuild {
+  publishing()
 }
 
 kotlin {

redwood-lazylayout-dom/src/commonMain/kotlin/app/cash/redwood/lazylayout/dom/HTMLLazyList.kt

@@ -22,53 +22,141 @@ import app.cash.redwood.layout.api.Constraint
 import app.cash.redwood.layout.api.CrossAxisAlignment
 import app.cash.redwood.lazylayout.api.ScrollItemIndex
 import app.cash.redwood.lazylayout.widget.LazyList
+import app.cash.redwood.lazylayout.widget.LazyListScrollProcessor
+import app.cash.redwood.lazylayout.widget.LazyListUpdateProcessor
 import app.cash.redwood.lazylayout.widget.RefreshableLazyList
 import app.cash.redwood.ui.Margin
-import app.cash.redwood.widget.HTMLElementChildren
-import app.cash.redwood.widget.MutableListChildren
+import app.cash.redwood.widget.Widget
 import org.w3c.dom.Document
+import org.w3c.dom.Element
 import org.w3c.dom.HTMLDivElement
 import org.w3c.dom.HTMLElement
+import org.w3c.dom.get
 
 internal open class HTMLLazyList(document: Document) : LazyList<HTMLElement> {
   override var modifier: Modifier = Modifier
 
-  final override val placeholder = MutableListChildren<HTMLElement>()
-
   final override val value = document.createElement("div") as HTMLDivElement
 
+  private val processor = object : LazyListUpdateProcessor<HTMLElement, HTMLElement>() {
+    override fun insertRows(index: Int, count: Int) {
+    }
+
+    override fun deleteRows(index: Int, count: Int) {
+    }
+
+    override fun setContent(view: HTMLElement, content: Widget<HTMLElement>?) {
+      if (content != null) {
+        view.appendChild(content.value)
+      }
+    }
+  }
+
+  private val scrollProcessor = object : LazyListScrollProcessor() {
+    override fun contentSize(): Int = processor.size
+
+    override fun programmaticScroll(firstIndex: Int, animated: Boolean) {
+      TODO("Not yet implemented")
+    }
+  }
+
+  private val visibleSet = mutableSetOf<Element>()
+  private var highestEverVisibleIndex = 0
+
+  private val intersectionObserver = IntersectionObserver(
+    { entries, _ ->
+      entries.forEach { entry ->
+        if (entry.isIntersecting) {
+          visibleSet.add(entry.target)
+        } else {
+          visibleSet.remove(entry.target)
+        }
+      }
+
+      val highestVisibleIndex = items.widgets.indexOfLast { it.value in visibleSet }
+      if (highestVisibleIndex > highestEverVisibleIndex) {
+        highestEverVisibleIndex = highestVisibleIndex
+        // We currently won't unload any items that have been scrolled out of view
+        scrollProcessor.onUserScroll(firstIndex = 0, lastIndex = highestEverVisibleIndex)
+      }
+    },
+  )
+
   init {
     value.style.display = "flex"
   }
 
-  final override val items = HTMLElementChildren(value)
+  final override val items: Widget.Children<HTMLElement> = object : Widget.Children<HTMLElement> by processor.items {
+    override fun insert(index: Int, widget: Widget<HTMLElement>) {
+      processor.items.insert(index, widget)
+      intersectionObserver.observe(widget.value)
+
+      // Null element returned when index == childCount causes insertion at end.
+      val current = value.children[index]
+      value.insertBefore(widget.value, current)
+    }
+
+    override fun remove(index: Int, count: Int) {
+      for (i in index..<index + count) {
+        intersectionObserver.unobserve(value.children[i]!!)
+      }
+      processor.items.remove(index, count)
+
+      repeat(count) {
+        value.removeChild(value.children[index]!!)
+      }
+    }
+  }
+
+  final override val placeholder = processor.placeholder
 
   override fun width(width: Constraint) {
+    value.style.width = width.toCss()
   }
 
   override fun height(height: Constraint) {
+    value.style.height = height.toCss()
   }
 
   override fun margin(margin: Margin) {
+    value.style.apply {
+      marginInlineStart = margin.start.toPxString()
+      marginInlineEnd = margin.end.toPxString()
+      marginTop = margin.top.toPxString()
+      marginBottom = margin.bottom.toPxString()
+    }
   }
 
   override fun crossAxisAlignment(crossAxisAlignment: CrossAxisAlignment) {
   }
 
   override fun scrollItemIndex(scrollItemIndex: ScrollItemIndex) {
+    scrollProcessor.scrollItemIndex(scrollItemIndex)
   }
 
   override fun isVertical(isVertical: Boolean) {
-    value.style.flexDirection = if (isVertical) "column" else "row"
+    value.style.apply {
+      flexDirection = if (isVertical) "column" else "row"
+      if (isVertical) {
+        overflowY = "scroll"
+        removeProperty("overflowX")
+      } else {
+        overflowX = "scroll"
+        removeProperty("overflowY")
+      }
+    }
   }
 
   override fun onViewportChanged(onViewportChanged: (firstVisibleItemIndex: Int, lastVisibleItemIndex: Int) -> Unit) {
+    scrollProcessor.onViewportChanged(onViewportChanged)
   }
 
   override fun itemsBefore(itemsBefore: Int) {
+    processor.itemsBefore(itemsBefore)
   }
 
   override fun itemsAfter(itemsAfter: Int) {
+    processor.itemsAfter(itemsAfter)
   }
 }
 

redwood-lazylayout-dom/src/commonMain/kotlin/app/cash/redwood/lazylayout/dom/IntersectionObserver.kt

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * 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.
+ */
+package app.cash.redwood.lazylayout.dom
+
+import org.w3c.dom.DOMRect
+import org.w3c.dom.Element
+import org.w3c.dom.ParentNode
+
+/**
+ * https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API
+ */
+internal external class IntersectionObserver(
+  callback: (entries: Array<IntersectionObserverEntry>, observer: IntersectionObserver) -> Unit,
+  options: IntersectionObserverOptions = definedExternally,
+) {
+  val root: ParentNode
+
+  val rootMargin: String
+  val thresholds: Array<Double>
+
+  fun disconnect()
+
+  fun observe(target: Element)
+
+  fun unobserve(target: Element)
+}
+
+internal sealed external interface IntersectionObserverOptions {
+  var root: ParentNode?
+  var rootMargin: String?
+  var threshold: Array<Double>?
+}
+
+internal external class IntersectionObserverEntry {
+  val boundingClientRect: DOMRect
+
+  val intersectionRatio: Double
+
+  val intersectionRect: DOMRect
+
+  val isIntersecting: Boolean
+
+  val rootBounds: DOMRect?
+
+  val target: Element
+
+  val time: Double
+}

redwood-lazylayout-dom/src/commonMain/kotlin/app/cash/redwood/lazylayout/dom/utils.kt

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * 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.
+ */
+package app.cash.redwood.lazylayout.dom
+
+import app.cash.redwood.layout.api.Constraint
+import app.cash.redwood.ui.Density
+import app.cash.redwood.ui.Dp
+import kotlin.math.roundToInt
+import org.w3c.dom.css.CSSStyleDeclaration
+
+internal fun Dp.toPxString(): String = with(Density(1.0)) {
+  "${toPx().roundToInt()}px"
+}
+
+internal fun Constraint.toCss() = when (this) {
+  Constraint.Wrap -> "auto"
+  Constraint.Fill -> "100%"
+  else -> throw AssertionError()
+}
+
+internal var CSSStyleDeclaration.marginInlineStart: String
+  get() = this.getPropertyValue("margin-inline-start")
+  set(value) {
+    this.setProperty("margin-inline-start", value)
+  }
+
+internal var CSSStyleDeclaration.marginInlineEnd: String
+  get() = this.getPropertyValue("margin-inline-end")
+  set(value) {
+    this.setProperty("margin-inline-end", value)
+  }