Add internal cache for styles generation code.

5 files changed, 465 insertions, 173 deletions

diff --git a/src/main/kotlin/pl/treksoft/kvision/core/Css.kt b/src/main/kotlin/pl/treksoft/kvision/core/Css.kt
index 9fc50097..8a468fe5 100644
--- a/src/main/kotlin/pl/treksoft/kvision/core/Css.kt
+++ b/src/main/kotlin/pl/treksoft/kvision/core/Css.kt
@@ -552,6 +552,8 @@ class Border private constructor(
         val w = width?.asString()
         return w.orEmpty() + " " + (style?.borderStyle).orEmpty() + " " + color.orEmpty()
     }
+
+    override fun toString() = asString()
 }
 
 /**
@@ -573,6 +575,8 @@ class Color private constructor(private val color: String? = null) {
     fun asString(): String {
         return color.orEmpty()
     }
+
+    override fun toString() = asString()
 }
 
 /**
@@ -676,6 +680,8 @@ class Background private constructor(
                 } + " " + (repeat?.repeat).orEmpty() + " " + (origin?.origin).orEmpty() + " " +
                 (clip?.clip).orEmpty() + " " + (attachment?.attachment).orEmpty()
     }
+
+    override fun toString() = asString()
 }
 
 /**
@@ -717,6 +723,8 @@ class TextDecoration private constructor(
                 (style?.textDecorationStyle).orEmpty() + " " +
                 color.orEmpty()
     }
+
+    override fun toString() = asString()
 }
 
 /**
@@ -764,4 +772,6 @@ class TextShadow private constructor(
                 (blurRadius?.asString()).orEmpty() + " " +
                 color.orEmpty()
     }
+
+    override fun toString() = asString()
 }
diff --git a/src/main/kotlin/pl/treksoft/kvision/core/Style.kt b/src/main/kotlin/pl/treksoft/kvision/core/Style.kt
index 549aa44c..282d2e7e 100644
--- a/src/main/kotlin/pl/treksoft/kvision/core/Style.kt
+++ b/src/main/kotlin/pl/treksoft/kvision/core/Style.kt
@@ -26,6 +26,7 @@ import com.github.snabbdom.h
 import org.w3c.dom.Node
 import pl.treksoft.jquery.JQuery
 import pl.treksoft.kvision.panel.Root
+import kotlin.reflect.KProperty
 
 /**
  * CSS style object.
@@ -38,6 +39,7 @@ import pl.treksoft.kvision.panel.Root
 @Suppress("TooManyFunctions")
 open class Style(className: String? = null, parentStyle: Style? = null, init: (Style.() -> Unit)? = null) :
     StyledComponent() {
+    private val propertyValues: MutableMap<String, Any?> = mutableMapOf()
 
     override var parent: Container? = Root.getFirstRoot()
 
@@ -133,6 +135,38 @@ open class Style(className: String? = null, parentStyle: Style? = null, init: (S
         styles.remove(this)
     }
 
+    protected fun <T> refreshOnUpdate(refreshFunction: ((T) -> Unit) = { this.refresh() }) =
+        RefreshDelegateProvider<T>(null, refreshFunction)
+
+    protected fun <T> refreshOnUpdate(initialValue: T, refreshFunction: ((T) -> Unit) = { this.refresh() }) =
+        RefreshDelegateProvider(initialValue, refreshFunction)
+
+    protected inner class RefreshDelegateProvider<T>(
+        private val initialValue: T?, private val refreshFunction: (T) -> Unit
+    ) {
+        operator fun provideDelegate(thisRef: Any?, prop: KProperty<*>): RefreshDelegate<T> {
+            if (initialValue != null) propertyValues[prop.name] = initialValue
+            return RefreshDelegate(refreshFunction)
+        }
+    }
+
+    protected inner class RefreshDelegate<T>(private val refreshFunction: ((T) -> Unit)) {
+        @Suppress("UNCHECKED_CAST")
+        operator fun getValue(thisRef: StyledComponent, property: KProperty<*>): T {
+            val value = propertyValues[property.name]
+            return if (value != null) {
+                value as T
+            } else {
+                null as T
+            }
+        }
+
+        operator fun setValue(thisRef: StyledComponent, property: KProperty<*>, value: T) {
+            propertyValues[property.name] = value
+            refreshFunction(value)
+        }
+    }
+
     companion object {
         internal var counter = 0
         internal var styles = mutableListOf<Style>()
diff --git a/src/main/kotlin/pl/treksoft/kvision/core/StyledComponent.kt b/src/main/kotlin/pl/treksoft/kvision/core/StyledComponent.kt
index 428728b7..1207ba5e 100644
--- a/src/main/kotlin/pl/treksoft/kvision/core/StyledComponent.kt
+++ b/src/main/kotlin/pl/treksoft/kvision/core/StyledComponent.kt
@@ -21,6 +21,7 @@
  */
 package pl.treksoft.kvision.core
 
+import pl.treksoft.kvision.utils.Cache
 import pl.treksoft.kvision.utils.asString
 import kotlin.reflect.KProperty
 
@@ -311,185 +312,196 @@ abstract class StyledComponent : Component {
      */
     @Suppress("ComplexMethod", "LongMethod")
     protected open fun getSnStyle(): List<StringPair> {
-        val snstyle = mutableListOf<StringPair>()
-        width?.let {
-            snstyle.add("width" to it.asString())
-        }
-        minWidth?.let {
-            snstyle.add("min-width" to it.asString())
-        }
-        maxWidth?.let {
-            snstyle.add("max-width" to it.asString())
-        }
-        height?.let {
-            snstyle.add("height" to it.asString())
-        }
-        minHeight?.let {
-            snstyle.add("min-height" to it.asString())
-        }
-        maxHeight?.let {
-            snstyle.add("max-height" to it.asString())
-        }
-        display?.let {
-            snstyle.add("display" to it.display)
-        }
-        position?.let {
-            snstyle.add("position" to it.position)
-        }
-        top?.let {
-            snstyle.add("top" to it.asString())
-        }
-        left?.let {
-            snstyle.add("left" to it.asString())
-        }
-        right?.let {
-            snstyle.add("right" to it.asString())
-        }
-        bottom?.let {
-            snstyle.add("bottom" to it.asString())
-        }
-        zIndex?.let {
-            snstyle.add("z-index" to it.toString())
-        }
-        overflow?.let {
-            snstyle.add("overflow" to it.overflow)
-        }
-        overflowWrap?.let {
-            snstyle.add("overflow-wrap" to it.overflowWrap)
-        }
-        resize?.let {
-            snstyle.add("resize" to it.resize)
-        }
-        border?.let {
-            snstyle.add("border" to it.asString())
-        }
-        borderTop?.let {
-            snstyle.add("border-top" to it.asString())
-        }
-        borderRight?.let {
-            snstyle.add("border-right" to it.asString())
-        }
-        borderBottom?.let {
-            snstyle.add("border-bottom" to it.asString())
-        }
-        borderLeft?.let {
-            snstyle.add("border-left" to it.asString())
-        }
-        margin?.let {
-            snstyle.add("margin" to it.asString())
-        }
-        marginTop?.let {
-            snstyle.add("margin-top" to it.asString())
-        }
-        marginRight?.let {
-            snstyle.add("margin-right" to it.asString())
-        }
-        marginBottom?.let {
-            snstyle.add("margin-bottom" to it.asString())
-        }
-        marginLeft?.let {
-            snstyle.add("margin-left" to it.asString())
-        }
-        padding?.let {
-            snstyle.add("padding" to it.asString())
-        }
-        paddingTop?.let {
-            snstyle.add("padding-top" to it.asString())
-        }
-        paddingRight?.let {
-            snstyle.add("padding-right" to it.asString())
-        }
-        paddingBottom?.let {
-            snstyle.add("padding-bottom" to it.asString())
-        }
-        paddingLeft?.let {
-            snstyle.add("padding-left" to it.asString())
-        }
-        color?.let {
-            snstyle.add("color" to it.asString())
-        }
-        opacity?.let {
-            snstyle.add("opacity" to it.toString())
-        }
-        background?.let {
-            snstyle.add("background" to it.asString())
-        }
-        textDirection?.let {
-            snstyle.add("direction" to it.direction)
-        }
-        letterSpacing?.let {
-            snstyle.add("letter-spacing" to it.asString())
-        }
-        lineHeight?.let {
-            snstyle.add("line-height" to it.asString())
-        }
-        textAlign?.let {
-            snstyle.add("text-align" to it.textAlign)
-        }
-        textDecoration?.let {
-            snstyle.add("text-decoration" to it.asString())
-        }
-        textIndent?.let {
-            snstyle.add("text-indent" to it.asString())
-        }
-        textShadow?.let {
-            snstyle.add("text-shadow" to it.asString())
-        }
-        textTransform?.let {
-            snstyle.add("text-transform" to it.textTransform)
-        }
-        textOverflow?.let {
-            snstyle.add("text-overflow" to it.textOverflow)
-        }
-        unicodeBidi?.let {
-            snstyle.add("unicode-bidi" to it.unicodeBidi)
-        }
-        verticalAlign?.let {
-            snstyle.add("vartical-align" to it.verticalAlign)
-        }
-        whiteSpace?.let {
-            snstyle.add("white-space" to it.whiteSpace)
-        }
-        wordSpacing?.let {
-            snstyle.add("word-spacing" to it.asString())
-        }
-        fontFamily?.let {
-            snstyle.add("font-family" to it)
-        }
-        fontSize?.let {
-            snstyle.add("font-size" to it.asString())
-        }
-        fontStyle?.let {
-            snstyle.add("font-style" to it.fontStyle)
-        }
-        fontWeight?.let {
-            snstyle.add("font-weight" to it.fontWeight)
-        }
-        fontVariant?.let {
-            snstyle.add("font-variant" to it.fontVariant)
-        }
-        float?.let {
-            snstyle.add("float" to it.posFloat)
-        }
-        clear?.let {
-            snstyle.add("clear" to it.clear)
-        }
-        wordBreak?.let {
-            snstyle.add("word-break" to it.wordBreak)
-        }
-        lineBreak?.let {
-            snstyle.add("line-break" to it.lineBreak)
+        val cacheKey = getCacheKey()
+        return globalStyleCache[cacheKey] ?: run {
+            val snstyle = mutableListOf<StringPair>()
+            width?.let {
+                snstyle.add("width" to it.asString())
+            }
+            minWidth?.let {
+                snstyle.add("min-width" to it.asString())
+            }
+            maxWidth?.let {
+                snstyle.add("max-width" to it.asString())
+            }
+            height?.let {
+                snstyle.add("height" to it.asString())
+            }
+            minHeight?.let {
+                snstyle.add("min-height" to it.asString())
+            }
+            maxHeight?.let {
+                snstyle.add("max-height" to it.asString())
+            }
+            display?.let {
+                snstyle.add("display" to it.display)
+            }
+            position?.let {
+                snstyle.add("position" to it.position)
+            }
+            top?.let {
+                snstyle.add("top" to it.asString())
+            }
+            left?.let {
+                snstyle.add("left" to it.asString())
+            }
+            right?.let {
+                snstyle.add("right" to it.asString())
+            }
+            bottom?.let {
+                snstyle.add("bottom" to it.asString())
+            }
+            zIndex?.let {
+                snstyle.add("z-index" to it.toString())
+            }
+            overflow?.let {
+                snstyle.add("overflow" to it.overflow)
+            }
+            overflowWrap?.let {
+                snstyle.add("overflow-wrap" to it.overflowWrap)
+            }
+            resize?.let {
+                snstyle.add("resize" to it.resize)
+            }
+            border?.let {
+                snstyle.add("border" to it.asString())
+            }
+            borderTop?.let {
+                snstyle.add("border-top" to it.asString())
+            }
+            borderRight?.let {
+                snstyle.add("border-right" to it.asString())
+            }
+            borderBottom?.let {
+                snstyle.add("border-bottom" to it.asString())
+            }
+            borderLeft?.let {
+                snstyle.add("border-left" to it.asString())
+            }
+            margin?.let {
+                snstyle.add("margin" to it.asString())
+            }
+            marginTop?.let {
+                snstyle.add("margin-top" to it.asString())
+            }
+            marginRight?.let {
+                snstyle.add("margin-right" to it.asString())
+            }
+            marginBottom?.let {
+                snstyle.add("margin-bottom" to it.asString())
+            }
+            marginLeft?.let {
+                snstyle.add("margin-left" to it.asString())
+            }
+            padding?.let {
+                snstyle.add("padding" to it.asString())
+            }
+            paddingTop?.let {
+                snstyle.add("padding-top" to it.asString())
+            }
+            paddingRight?.let {
+                snstyle.add("padding-right" to it.asString())
+            }
+            paddingBottom?.let {
+                snstyle.add("padding-bottom" to it.asString())
+            }
+            paddingLeft?.let {
+                snstyle.add("padding-left" to it.asString())
+            }
+            color?.let {
+                snstyle.add("color" to it.asString())
+            }
+            opacity?.let {
+                snstyle.add("opacity" to it.toString())
+            }
+            background?.let {
+                snstyle.add("background" to it.asString())
+            }
+            textDirection?.let {
+                snstyle.add("direction" to it.direction)
+            }
+            letterSpacing?.let {
+                snstyle.add("letter-spacing" to it.asString())
+            }
+            lineHeight?.let {
+                snstyle.add("line-height" to it.asString())
+            }
+            textAlign?.let {
+                snstyle.add("text-align" to it.textAlign)
+            }
+            textDecoration?.let {
+                snstyle.add("text-decoration" to it.asString())
+            }
+            textIndent?.let {
+                snstyle.add("text-indent" to it.asString())
+            }
+            textShadow?.let {
+                snstyle.add("text-shadow" to it.asString())
+            }
+            textTransform?.let {
+                snstyle.add("text-transform" to it.textTransform)
+            }
+            textOverflow?.let {
+                snstyle.add("text-overflow" to it.textOverflow)
+            }
+            unicodeBidi?.let {
+                snstyle.add("unicode-bidi" to it.unicodeBidi)
+            }
+            verticalAlign?.let {
+                snstyle.add("vartical-align" to it.verticalAlign)
+            }
+            whiteSpace?.let {
+                snstyle.add("white-space" to it.whiteSpace)
+            }
+            wordSpacing?.let {
+                snstyle.add("word-spacing" to it.asString())
+            }
+            fontFamily?.let {
+                snstyle.add("font-family" to it)
+            }
+            fontSize?.let {
+                snstyle.add("font-size" to it.asString())
+            }
+            fontStyle?.let {
+                snstyle.add("font-style" to it.fontStyle)
+            }
+            fontWeight?.let {
+                snstyle.add("font-weight" to it.fontWeight)
+            }
+            fontVariant?.let {
+                snstyle.add("font-variant" to it.fontVariant)
+            }
+            float?.let {
+                snstyle.add("float" to it.posFloat)
+            }
+            clear?.let {
+                snstyle.add("clear" to it.clear)
+            }
+            wordBreak?.let {
+                snstyle.add("word-break" to it.wordBreak)
+            }
+            lineBreak?.let {
+                snstyle.add("line-break" to it.lineBreak)
+            }
+            globalStyleCache[cacheKey] = snstyle
+            return snstyle
         }
-        return snstyle
     }
 
-    protected fun <T> refreshOnUpdate(refreshFunction: ((T) -> Unit) = { this.refresh() }) =
+    protected open fun getCacheKey(): String {
+        val SEP = "###KvSep###"
+        return propertyValues.map {
+            it.toString()
+        }.joinToString(SEP)
+    }
+
+    private fun <T> refreshOnUpdate(refreshFunction: ((T) -> Unit) = { this.refresh() }) =
         RefreshDelegateProvider<T>(null, refreshFunction)
 
-    protected fun <T> refreshOnUpdate(initialValue: T, refreshFunction: ((T) -> Unit) = { this.refresh() }) =
+    private fun <T> refreshOnUpdate(initialValue: T, refreshFunction: ((T) -> Unit) = { this.refresh() }) =
         RefreshDelegateProvider(initialValue, refreshFunction)
 
-    protected inner class RefreshDelegateProvider<T>(
+    private inner class RefreshDelegateProvider<T>(
         private val initialValue: T?, private val refreshFunction: (T) -> Unit
     ) {
         operator fun provideDelegate(thisRef: Any?, prop: KProperty<*>): RefreshDelegate<T> {
@@ -498,7 +510,7 @@ abstract class StyledComponent : Component {
         }
     }
 
-    protected inner class RefreshDelegate<T>(private val refreshFunction: ((T) -> Unit)) {
+    private inner class RefreshDelegate<T>(private val refreshFunction: ((T) -> Unit)) {
         @Suppress("UNCHECKED_CAST")
         operator fun getValue(thisRef: StyledComponent, property: KProperty<*>): T {
             val value = propertyValues[property.name]
@@ -514,4 +526,8 @@ abstract class StyledComponent : Component {
             refreshFunction(value)
         }
     }
+
+    companion object {
+        internal val globalStyleCache = Cache<String, List<StringPair>>()
+    }
 }
diff --git a/src/main/kotlin/pl/treksoft/kvision/core/Widget.kt b/src/main/kotlin/pl/treksoft/kvision/core/Widget.kt
index 9bf84209..f0be38cb 100644
--- a/src/main/kotlin/pl/treksoft/kvision/core/Widget.kt
+++ b/src/main/kotlin/pl/treksoft/kvision/core/Widget.kt
@@ -42,6 +42,7 @@ import pl.treksoft.kvision.utils.snAttrs
 import pl.treksoft.kvision.utils.snClasses
 import pl.treksoft.kvision.utils.snOpt
 import pl.treksoft.kvision.utils.snStyle
+import kotlin.reflect.KProperty
 
 /**
  * Base widget class. The parent of all component classes.
@@ -53,6 +54,7 @@ import pl.treksoft.kvision.utils.snStyle
  */
 @Suppress("TooManyFunctions", "LargeClass")
 open class Widget(classes: Set<String> = setOf()) : StyledComponent() {
+    private val propertyValues: MutableMap<String, Any?> = mutableMapOf()
 
     internal val classes = classes.toMutableSet()
     internal val surroundingClasses: MutableSet<String> = mutableSetOf()
@@ -765,6 +767,38 @@ open class Widget(classes: Set<String> = setOf()) : StyledComponent() {
     override fun dispose() {
     }
 
+    protected fun <T> refreshOnUpdate(refreshFunction: ((T) -> Unit) = { this.refresh() }) =
+        RefreshDelegateProvider<T>(null, refreshFunction)
+
+    protected fun <T> refreshOnUpdate(initialValue: T, refreshFunction: ((T) -> Unit) = { this.refresh() }) =
+        RefreshDelegateProvider(initialValue, refreshFunction)
+
+    protected inner class RefreshDelegateProvider<T>(
+        private val initialValue: T?, private val refreshFunction: (T) -> Unit
+    ) {
+        operator fun provideDelegate(thisRef: Any?, prop: KProperty<*>): RefreshDelegate<T> {
+            if (initialValue != null) propertyValues[prop.name] = initialValue
+            return RefreshDelegate(refreshFunction)
+        }
+    }
+
+    protected inner class RefreshDelegate<T>(private val refreshFunction: ((T) -> Unit)) {
+        @Suppress("UNCHECKED_CAST")
+        operator fun getValue(thisRef: StyledComponent, property: KProperty<*>): T {
+            val value = propertyValues[property.name]
+            return if (value != null) {
+                value as T
+            } else {
+                null as T
+            }
+        }
+
+        operator fun setValue(thisRef: StyledComponent, property: KProperty<*>, value: T) {
+            propertyValues[property.name] = value
+            refreshFunction(value)
+        }
+    }
+
     companion object {
         /**
          * DSL builder extension function.
diff --git a/src/main/kotlin/pl/treksoft/kvision/utils/Cache.kt b/src/main/kotlin/pl/treksoft/kvision/utils/Cache.kt
new file mode 100644
index 00000000..6a473661
--- /dev/null
+++ b/src/main/kotlin/pl/treksoft/kvision/utils/Cache.kt
@@ -0,0 +1,198 @@
+/*
+ * Copyright (c) 2017-present Robert Jaros
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package pl.treksoft.kvision.utils
+
+/*
+ * Copyright 2018 Nazmul Idris All rights reserved.
+ *
+ * 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.
+ */
+
+/**
+ * This is a LRU cache that has no performance impact for cache insertions
+ * once the capacity of the cache has been reached. For cache hit,
+ * performance is O(1) and for cache eviction, it is O(1).
+ */
+class Cache<K, V>(private val capacity: Int = 50) {
+    private val cache = HashMap<K, V>()
+    private val insertionOrder = LinkedList<K>()
+
+    /**
+     * [HashMap] put and remove is O(1).
+     * More info: https://stackoverflow.com/a/4578039/2085356
+     */
+    operator fun set(key: K, value: V): K? {
+        var evictedKey: K? = null
+        if (cache.size >= capacity) {
+            evictedKey = getKeyToEvict()
+            cache.remove(evictedKey)
+        }
+        cache[key] = value
+        insertionOrder.append(key)
+        return evictedKey
+    }
+
+    /**
+     * [HashMap] get is O(1).
+     * More info: https://stackoverflow.com/a/4578039/2085356
+     */
+    operator fun get(key: K): V? = cache[key]
+
+    /**
+     * The head of the [insertionOrder] is removed, which is O(1), since this
+     * is a linked list, and it's inexpensive to remove an item from head.
+     * More info: https://stackoverflow.com/a/42849573/2085356
+     */
+    private fun getKeyToEvict(): K? = insertionOrder.removeAtIndex(0)
+
+    override fun toString() = cache.toString()
+}
+
+/**
+ * Created by gazollajunior on 07/04/16.
+ */
+class Node<T>(var value: T) {
+    var next: Node<T>? = null
+    var previous: Node<T>? = null
+}
+
+class LinkedList<T> {
+
+    private var head: Node<T>? = null
+
+    var isEmpty: Boolean = head == null
+
+    fun first(): Node<T>? = head
+
+    fun last(): Node<T>? {
+        var node = head
+        if (node != null) {
+            while (node?.next != null) {
+                node = node.next
+            }
+            return node
+        } else {
+            return null
+        }
+    }
+
+    fun count(): Int {
+        var node = head
+        if (node != null) {
+            var counter = 1
+            while (node?.next != null) {
+                node = node.next
+                counter += 1
+            }
+            return counter
+        } else {
+            return 0
+        }
+    }
+
+    fun nodeAtIndex(index: Int): Node<T>? {
+        if (index >= 0) {
+            var node = head
+            var i = index
+            while (node != null) {
+                if (i == 0) return node
+                i -= 1
+                node = node.next
+            }
+        }
+        return null
+    }
+
+    fun append(value: T) {
+        val newNode = Node(value)
+
+        val lastNode = this.last()
+        if (lastNode != null) {
+            newNode.previous = lastNode
+            lastNode.next = newNode
+        } else {
+            head = newNode
+        }
+    }
+
+    fun removeAll() {
+        head = null
+    }
+
+    fun removeNode(node: Node<T>): T {
+        val prev = node.previous
+        val next = node.next
+
+        if (prev != null) {
+            prev.next = next
+        } else {
+            head = next
+        }
+        next?.previous = prev
+
+        node.previous = null
+        node.next = null
+
+        return node.value
+    }
+
+    fun removeLast(): T? {
+        val last = this.last()
+        if (last != null) {
+            return removeNode(last)
+        } else {
+            return null
+        }
+    }
+
+    fun removeAtIndex(index: Int): T? {
+        val node = nodeAtIndex(index)
+        if (node != null) {
+            return removeNode(node)
+        } else {
+            return null
+        }
+    }
+
+    override fun toString(): String {
+        var s = "["
+        var node = head
+        while (node != null) {
+            s += "${node.value}"
+            node = node.next
+            if (node != null) {
+                s += ", "
+            }
+        }
+        return s + "]"
+    }
+}