KT-50452 Make flexible html for customization (#2374)

12 files changed, 487 insertions, 133 deletions

diff --git a/plugins/base/api/base.api b/plugins/base/api/base.api
index a38c2cfd..101a00e9 100644
--- a/plugins/base/api/base.api
+++ b/plugins/base/api/base.api
@@ -71,27 +71,30 @@ public final class org/jetbrains/dokka/base/DokkaBaseConfiguration : org/jetbrai
 	public static final field mergeImplicitExpectActualDeclarationsDefault Z
 	public static final field separateInheritedMembersDefault Z
 	public fun <init> ()V
-	public fun <init> (Ljava/util/List;Ljava/util/List;ZLjava/lang/String;Z)V
-	public synthetic fun <init> (Ljava/util/List;Ljava/util/List;ZLjava/lang/String;ZILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public fun <init> (Ljava/util/List;Ljava/util/List;ZLjava/lang/String;ZLjava/io/File;)V
+	public synthetic fun <init> (Ljava/util/List;Ljava/util/List;ZLjava/lang/String;ZLjava/io/File;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun component1 ()Ljava/util/List;
 	public final fun component2 ()Ljava/util/List;
 	public final fun component3 ()Z
 	public final fun component4 ()Ljava/lang/String;
 	public final fun component5 ()Z
-	public final fun copy (Ljava/util/List;Ljava/util/List;ZLjava/lang/String;Z)Lorg/jetbrains/dokka/base/DokkaBaseConfiguration;
-	public static synthetic fun copy$default (Lorg/jetbrains/dokka/base/DokkaBaseConfiguration;Ljava/util/List;Ljava/util/List;ZLjava/lang/String;ZILjava/lang/Object;)Lorg/jetbrains/dokka/base/DokkaBaseConfiguration;
+	public final fun component6 ()Ljava/io/File;
+	public final fun copy (Ljava/util/List;Ljava/util/List;ZLjava/lang/String;ZLjava/io/File;)Lorg/jetbrains/dokka/base/DokkaBaseConfiguration;
+	public static synthetic fun copy$default (Lorg/jetbrains/dokka/base/DokkaBaseConfiguration;Ljava/util/List;Ljava/util/List;ZLjava/lang/String;ZLjava/io/File;ILjava/lang/Object;)Lorg/jetbrains/dokka/base/DokkaBaseConfiguration;
 	public fun equals (Ljava/lang/Object;)Z
 	public final fun getCustomAssets ()Ljava/util/List;
 	public final fun getCustomStyleSheets ()Ljava/util/List;
 	public final fun getFooterMessage ()Ljava/lang/String;
 	public final fun getMergeImplicitExpectActualDeclarations ()Z
 	public final fun getSeparateInheritedMembers ()Z
+	public final fun getTemplatesDir ()Ljava/io/File;
 	public fun hashCode ()I
 	public final fun setCustomAssets (Ljava/util/List;)V
 	public final fun setCustomStyleSheets (Ljava/util/List;)V
 	public final fun setFooterMessage (Ljava/lang/String;)V
 	public final fun setMergeImplicitExpectActualDeclarations (Z)V
 	public final fun setSeparateInheritedMembers (Z)V
+	public final fun setTemplatesDir (Ljava/io/File;)V
 	public fun toString ()Ljava/lang/String;
 }
 
@@ -99,6 +102,7 @@ public final class org/jetbrains/dokka/base/DokkaBaseConfiguration$Companion {
 	public final fun getDefaultCustomAssets ()Ljava/util/List;
 	public final fun getDefaultCustomStyleSheets ()Ljava/util/List;
 	public final fun getDefaultFooterMessage ()Ljava/lang/String;
+	public final fun getDefaultTemplatesDir ()Ljava/io/File;
 }
 
 public final class org/jetbrains/dokka/base/generation/SingleModuleGeneration : org/jetbrains/dokka/generation/Generation {
@@ -216,6 +220,7 @@ public final class org/jetbrains/dokka/base/parsers/moduleAndPackage/ParseModule
 }
 
 public final class org/jetbrains/dokka/base/renderers/ContentTypeCheckingKt {
+	public static final fun getURIExtension (Ljava/lang/String;)Ljava/lang/String;
 	public static final fun isImage (Ljava/lang/String;)Z
 	public static final fun isImage (Lorg/jetbrains/dokka/pages/ContentEmbeddedResource;)Z
 }
@@ -526,6 +531,7 @@ public final class org/jetbrains/dokka/base/renderers/html/TagsKt {
 	public static final fun templateCommand (Lkotlinx/html/TagConsumer;Lorg/jetbrains/dokka/base/templating/Command;Lkotlin/jvm/functions/Function1;)Ljava/lang/Object;
 	public static synthetic fun templateCommand$default (Lkotlinx/html/FlowOrMetaDataContent;Lorg/jetbrains/dokka/base/templating/Command;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)V
 	public static synthetic fun templateCommand$default (Lkotlinx/html/TagConsumer;Lorg/jetbrains/dokka/base/templating/Command;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)Ljava/lang/Object;
+	public static final fun templateCommandAsHtmlComment (Ljava/lang/Appendable;Lorg/jetbrains/dokka/base/templating/Command;Lkotlin/jvm/functions/Function1;)V
 	public static final fun templateCommandAsHtmlComment (Lkotlinx/html/FlowOrMetaDataContent;Lorg/jetbrains/dokka/base/templating/Command;Lkotlin/jvm/functions/Function1;)V
 	public static synthetic fun templateCommandAsHtmlComment$default (Lkotlinx/html/FlowOrMetaDataContent;Lorg/jetbrains/dokka/base/templating/Command;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)V
 	public static final fun templateCommandFor (Lorg/jetbrains/dokka/base/templating/Command;Lkotlinx/html/TagConsumer;)Lorg/jetbrains/dokka/base/renderers/html/TemplateCommand;
@@ -578,6 +584,55 @@ public final class org/jetbrains/dokka/base/renderers/html/command/consumers/Res
 	public fun processCommandAndFinalize (Lorg/jetbrains/dokka/base/templating/Command;Lkotlin/jvm/functions/Function1;Lorg/jetbrains/dokka/base/renderers/html/command/consumers/ImmediateResolutionTagConsumer;)Ljava/lang/Object;
 }
 
+public final class org/jetbrains/dokka/base/renderers/html/innerTemplating/DefaultTemplateModelFactory : org/jetbrains/dokka/base/renderers/html/innerTemplating/TemplateModelFactory {
+	public fun <init> (Lorg/jetbrains/dokka/plugability/DokkaContext;)V
+	public fun buildModel (Lorg/jetbrains/dokka/pages/PageNode;Ljava/util/List;Lorg/jetbrains/dokka/base/resolvers/local/LocationProvider;ZLjava/lang/String;)Ljava/util/Map;
+	public fun buildSharedModel ()Ljava/util/Map;
+	public final fun getContext ()Lorg/jetbrains/dokka/plugability/DokkaContext;
+}
+
+public final class org/jetbrains/dokka/base/renderers/html/innerTemplating/DefaultTemplateModelFactory$SourceSetModel {
+	public fun <init> (Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)V
+	public final fun component1 ()Ljava/lang/String;
+	public final fun component2 ()Ljava/lang/String;
+	public final fun component3 ()Ljava/lang/String;
+	public final fun copy (Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Lorg/jetbrains/dokka/base/renderers/html/innerTemplating/DefaultTemplateModelFactory$SourceSetModel;
+	public static synthetic fun copy$default (Lorg/jetbrains/dokka/base/renderers/html/innerTemplating/DefaultTemplateModelFactory$SourceSetModel;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;ILjava/lang/Object;)Lorg/jetbrains/dokka/base/renderers/html/innerTemplating/DefaultTemplateModelFactory$SourceSetModel;
+	public fun equals (Ljava/lang/Object;)Z
+	public final fun getFilter ()Ljava/lang/String;
+	public final fun getName ()Ljava/lang/String;
+	public final fun getPlatform ()Ljava/lang/String;
+	public fun hashCode ()I
+	public fun toString ()Ljava/lang/String;
+}
+
+public final class org/jetbrains/dokka/base/renderers/html/innerTemplating/DefaultTemplateModelMerger : org/jetbrains/dokka/base/renderers/html/innerTemplating/TemplateModelMerger {
+	public fun <init> ()V
+	public fun invoke (Ljava/util/List;Lkotlin/jvm/functions/Function1;)Ljava/util/Map;
+}
+
+public final class org/jetbrains/dokka/base/renderers/html/innerTemplating/DokkaTemplateTypes : java/lang/Enum {
+	public static final field BASE Lorg/jetbrains/dokka/base/renderers/html/innerTemplating/DokkaTemplateTypes;
+	public final fun getPath ()Ljava/lang/String;
+	public static fun valueOf (Ljava/lang/String;)Lorg/jetbrains/dokka/base/renderers/html/innerTemplating/DokkaTemplateTypes;
+	public static fun values ()[Lorg/jetbrains/dokka/base/renderers/html/innerTemplating/DokkaTemplateTypes;
+}
+
+public final class org/jetbrains/dokka/base/renderers/html/innerTemplating/HtmlTemplater {
+	public fun <init> (Lorg/jetbrains/dokka/plugability/DokkaContext;)V
+	public final fun renderFromTemplate (Lorg/jetbrains/dokka/base/renderers/html/innerTemplating/DokkaTemplateTypes;Lkotlin/jvm/functions/Function0;)Ljava/lang/String;
+	public final fun setupSharedModel (Ljava/util/Map;)V
+}
+
+public abstract interface class org/jetbrains/dokka/base/renderers/html/innerTemplating/TemplateModelFactory {
+	public abstract fun buildModel (Lorg/jetbrains/dokka/pages/PageNode;Ljava/util/List;Lorg/jetbrains/dokka/base/resolvers/local/LocationProvider;ZLjava/lang/String;)Ljava/util/Map;
+	public abstract fun buildSharedModel ()Ljava/util/Map;
+}
+
+public abstract interface class org/jetbrains/dokka/base/renderers/html/innerTemplating/TemplateModelMerger {
+	public abstract fun invoke (Ljava/util/List;Lkotlin/jvm/functions/Function1;)Ljava/util/Map;
+}
+
 public final class org/jetbrains/dokka/base/resolvers/anchors/SymbolAnchorHint : org/jetbrains/dokka/model/properties/ExtraProperty {
 	public static final field Companion Lorg/jetbrains/dokka/base/resolvers/anchors/SymbolAnchorHint$Companion;
 	public fun <init> (Ljava/lang/String;Lorg/jetbrains/dokka/pages/Kind;)V
diff --git a/plugins/base/build.gradle.kts b/plugins/base/build.gradle.kts
index c9f57df8..e77d271e 100644
--- a/plugins/base/build.gradle.kts
+++ b/plugins/base/build.gradle.kts
@@ -11,6 +11,10 @@ dependencies {
 
     val jackson_version: String by project
     implementation("com.fasterxml.jackson.module:jackson-module-kotlin:$jackson_version")
+
+    val freemarker_version: String by project
+    implementation("org.freemarker:freemarker:$freemarker_version")
+
     testImplementation(project(":plugins:base:base-test-utils"))
     testImplementation(project(":core:content-matcher-test-utils"))
 
diff --git a/plugins/base/src/main/kotlin/DokkaBaseConfiguration.kt b/plugins/base/src/main/kotlin/DokkaBaseConfiguration.kt
index 8ea8818d..a9ccf600 100644
--- a/plugins/base/src/main/kotlin/DokkaBaseConfiguration.kt
+++ b/plugins/base/src/main/kotlin/DokkaBaseConfiguration.kt
@@ -9,7 +9,8 @@ data class DokkaBaseConfiguration(
     var customAssets: List<File> = defaultCustomAssets,
     var separateInheritedMembers: Boolean = separateInheritedMembersDefault,
     var footerMessage: String = defaultFooterMessage,
-    var mergeImplicitExpectActualDeclarations: Boolean = mergeImplicitExpectActualDeclarationsDefault
+    var mergeImplicitExpectActualDeclarations: Boolean = mergeImplicitExpectActualDeclarationsDefault,
+    var templatesDir: File? = defaultTemplatesDir
 ) : ConfigurableBlock {
     companion object {
         val defaultFooterMessage = "© ${Year.now().value} Copyright"
@@ -17,5 +18,6 @@ data class DokkaBaseConfiguration(
         val defaultCustomAssets: List<File> = emptyList()
         const val separateInheritedMembersDefault: Boolean = false
         const val mergeImplicitExpectActualDeclarationsDefault: Boolean = false
+        val defaultTemplatesDir: File? = null
     }
 }
\ No newline at end of file
diff --git a/plugins/base/src/main/kotlin/renderers/contentTypeChecking.kt b/plugins/base/src/main/kotlin/renderers/contentTypeChecking.kt
index 4619bc53..1cec4769 100644
--- a/plugins/base/src/main/kotlin/renderers/contentTypeChecking.kt
+++ b/plugins/base/src/main/kotlin/renderers/contentTypeChecking.kt
@@ -8,8 +8,11 @@ fun ContentEmbeddedResource.isImage(): Boolean {
     return File(address).extension.toLowerCase() in imageExtensions
 }
 
+val String.URIExtension: String
+    get() = substringBefore('?').substringAfterLast('.')
+
 fun String.isImage(): Boolean =
-    substringBefore('?').substringAfterLast('.') in imageExtensions
+    URIExtension in imageExtensions
 
 object HtmlFileExtensions {
     val imageExtensions = setOf("png", "jpg", "jpeg", "gif", "bmp", "tif", "webp", "svg")
diff --git a/plugins/base/src/main/kotlin/renderers/html/HtmlRenderer.kt b/plugins/base/src/main/kotlin/renderers/html/HtmlRenderer.kt
index 0ba085cd..05559469 100644
--- a/plugins/base/src/main/kotlin/renderers/html/HtmlRenderer.kt
+++ b/plugins/base/src/main/kotlin/renderers/html/HtmlRenderer.kt
@@ -4,10 +4,12 @@ import kotlinx.html.*
 import kotlinx.html.stream.createHTML
 import org.jetbrains.dokka.DokkaSourceSetID
 import org.jetbrains.dokka.base.DokkaBase
-import org.jetbrains.dokka.base.DokkaBaseConfiguration
-import org.jetbrains.dokka.base.DokkaBaseConfiguration.Companion.defaultFooterMessage
 import org.jetbrains.dokka.base.renderers.*
 import org.jetbrains.dokka.base.renderers.html.command.consumers.ImmediateResolutionTagConsumer
+import org.jetbrains.dokka.base.renderers.html.innerTemplating.DefaultTemplateModelFactory
+import org.jetbrains.dokka.base.renderers.html.innerTemplating.DefaultTemplateModelMerger
+import org.jetbrains.dokka.base.renderers.html.innerTemplating.DokkaTemplateTypes
+import org.jetbrains.dokka.base.renderers.html.innerTemplating.HtmlTemplater
 import org.jetbrains.dokka.base.resolvers.anchors.SymbolAnchorHint
 import org.jetbrains.dokka.base.resolvers.local.DokkaBaseLocationProvider
 import org.jetbrains.dokka.base.templating.*
@@ -28,8 +30,6 @@ internal const val TEMPLATE_REPLACEMENT: String = "###"
 open class HtmlRenderer(
     context: DokkaContext
 ) : DefaultRenderer<FlowContent>(context) {
-    private val configuration = configuration<DokkaBase, DokkaBaseConfiguration>(context)
-
     private val sourceSetDependencyMap: Map<DokkaSourceSetID, List<DokkaSourceSetID>> =
         context.configuration.sourceSets.associate { sourceSet ->
             sourceSet.sourceSetID to context.configuration.sourceSets
@@ -37,6 +37,12 @@ open class HtmlRenderer(
                 .filter { it in sourceSet.dependentSourceSets }
         }
 
+    private val templateModelFactories = listOf(DefaultTemplateModelFactory(context)) // TODO: Make extension point
+    private val templateModelMerger = DefaultTemplateModelMerger()
+    private val templater = HtmlTemplater(context).apply {
+        setupSharedModel(templateModelMerger.invoke(templateModelFactories) { buildSharedModel() })
+    }
+
     private var shouldRenderSourceSetBubbles: Boolean = false
 
     override val preprocessors = context.plugin<DokkaBase>().query { htmlPreprocessors }
@@ -764,138 +770,34 @@ open class HtmlRenderer(
 
     override fun buildPage(page: ContentPage, content: (FlowContent, ContentPage) -> Unit): String =
         buildHtml(page, page.embeddedResources) {
-            div("main-content") {
-                id = "content"
-                attributes["pageIds"] = "${context.configuration.moduleName}::${page.pageId}"
-                content(this, page)
-            }
+            content(this, page)
         }
 
     private val String.isAbsolute: Boolean
         get() = URI(this).isAbsolute
 
-    open fun buildHtml(page: PageNode, resources: List<String>, content: FlowContent.() -> Unit): String {
-        val path = locationProvider.resolve(page)
-        val pathToRoot = locationProvider.pathToRoot(page)
-        return createHTML().prepareForTemplates().html {
-            head {
-                meta(name = "viewport", content = "width=device-width, initial-scale=1", charset = "UTF-8")
-                title(page.name)
-                templateCommandAsHtmlComment(PathToRootSubstitutionCommand(TEMPLATE_REPLACEMENT, default = pathToRoot)) {
-                    link(href = "${TEMPLATE_REPLACEMENT}images/logo-icon.svg", rel = "icon", type = "image/svg")
-                }
-                templateCommandAsHtmlComment(PathToRootSubstitutionCommand(TEMPLATE_REPLACEMENT, default = pathToRoot)) {
-                    script { unsafe { +"""var pathToRoot = "$TEMPLATE_REPLACEMENT";""" } }
-                }
-                // This script doesn't need to be there but it is nice to have since app in dark mode doesn't 'blink' (class is added before it is rendered)
-                script {
-                    unsafe {
-                        +"""
-                    const storage = localStorage.getItem("dokka-dark-mode")
-                    const savedDarkMode = storage ? JSON.parse(storage) : false
-                    if(savedDarkMode === true){
-                        document.getElementsByTagName("html")[0].classList.add("theme-dark")
-                    }
-                """.trimIndent()
-                    }
-                }
-                resources.forEach {
-                    when {
-                        it.substringBefore('?').substringAfterLast('.') == "css" ->
-                            if (it.isAbsolute) link(
-                                rel = LinkRel.stylesheet,
-                                href = it
-                            )
-                            else templateCommandAsHtmlComment(PathToRootSubstitutionCommand(TEMPLATE_REPLACEMENT, default = pathToRoot)) {
-                                link(
-                                    rel = LinkRel.stylesheet,
-                                    href = TEMPLATE_REPLACEMENT + it
-                                )
-                            }
-                        it.substringBefore('?').substringAfterLast('.') == "js" ->
-                            if (it.isAbsolute) script(
-                                type = ScriptType.textJavaScript,
-                                src = it
-                            ) {
-                                async = true
-                            } else templateCommandAsHtmlComment(PathToRootSubstitutionCommand(TEMPLATE_REPLACEMENT, default = pathToRoot)) {
-                                script(
-                                    type = ScriptType.textJavaScript,
-                                    src = TEMPLATE_REPLACEMENT + it
-                                ) {
-                                    if (it == "scripts/main.js")
-                                        defer = true
-                                    else
-                                        async = true
-                                }
-                            }
-                        it.isImage() -> if (it.isAbsolute) link(href = it)
-                        else templateCommandAsHtmlComment(PathToRootSubstitutionCommand(TEMPLATE_REPLACEMENT, default = pathToRoot)) {
-                            link(href = TEMPLATE_REPLACEMENT + it)
-                        }
-                        else -> unsafe { +it }
-                    }
-                }
-            }
-            body {
-                div("navigation-wrapper") {
-                    id = "navigation-wrapper"
-                    div {
-                        id = "leftToggler"
-                        span("icon-toggler")
-                    }
-                    div("library-name") {
-                        clickableLogo(page, pathToRoot)
-                    }
-                    div { templateCommand(ReplaceVersionsCommand(path.orEmpty())) }
-                    div("pull-right d-flex") {
-                        filterButtons(page)
-                        button {
-                            id = "theme-toggle-button"
-                            span {
-                                id = "theme-toggle"
-                            }
-                        }
-                        div {
-                            id = "searchBar"
-                        }
-                    }
-                }
-                div {
-                    id = "container"
-                    div {
-                        id = "leftColumn"
-                        div {
-                            id = "sideMenu"
-                        }
-                    }
-                    div {
-                        id = "main"
-                        content()
-                        div(classes = "footer") {
-                            span("go-to-top-icon") {
-                                a(href = "#content") {
-                                    id = "go-to-top-link"
-                                }
-                            }
-                            span {
-                                configuration?.footerMessage?.takeIf { it.isNotEmpty() }
-                                    ?.let { unsafe { raw(it) } }
-                                    ?: text(defaultFooterMessage)
-                            }
-                            span("pull-right") {
-                                span { text("Generated by ") }
-                                a(href = "https://github.com/Kotlin/dokka") {
-                                    span { text("dokka") }
-                                    span(classes = "padded-icon")
-                                }
-                            }
-                        }
+
+    open fun buildHtml(page: PageNode, resources: List<String>, content: FlowContent.() -> Unit): String =
+        templater.renderFromTemplate(DokkaTemplateTypes.BASE) {
+            val generatedContent =
+                createHTML().div("main-content") {
+                    id = "content"
+                    (page as? ContentPage)?.let {
+                        attributes["pageIds"] = "${context.configuration.moduleName}::${page.pageId}"
                     }
+                    content()
                 }
+
+            templateModelMerger.invoke(templateModelFactories) {
+                buildModel(
+                    page,
+                    resources,
+                    locationProvider,
+                    shouldRenderSourceSetBubbles,
+                    generatedContent
+                )
             }
         }
-    }
 
     /**
      * This is deliberately left open for plugins that have some other pages above ours and would like to link to them
diff --git a/plugins/base/src/main/kotlin/renderers/html/Tags.kt b/plugins/base/src/main/kotlin/renderers/html/Tags.kt
index 94a53c27..ef27b934 100644
--- a/plugins/base/src/main/kotlin/renderers/html/Tags.kt
+++ b/plugins/base/src/main/kotlin/renderers/html/Tags.kt
@@ -38,6 +38,12 @@ fun FlowOrMetaDataContent.templateCommandAsHtmlComment(data: Command, block: Flo
             comment(TEMPLATE_COMMAND_END_BORDER)
         }
 
+fun <T: Appendable> T.templateCommandAsHtmlComment(command: Command, action: T.() -> Unit ) {
+    append("<!--$TEMPLATE_COMMAND_BEGIN_BORDER$TEMPLATE_COMMAND_SEPARATOR${toJsonString(command)}-->")
+    action()
+    append("<!--$TEMPLATE_COMMAND_END_BORDER-->")
+}
+
 fun FlowOrMetaDataContent.templateCommand(data: Command, block: TemplateBlock = {}): Unit =
     (consumer as? ImmediateResolutionTagConsumer)?.processCommand(data, block)
         ?: TemplateCommand(attributesMapOf("data", toJsonString(data)), consumer).visit(block)
diff --git a/plugins/base/src/main/kotlin/renderers/html/innerTemplating/DefaultTemplateModelFactory.kt b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/DefaultTemplateModelFactory.kt
new file mode 100644
index 00000000..9f1ca57e
--- /dev/null
+++ b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/DefaultTemplateModelFactory.kt
@@ -0,0 +1,207 @@
+package org.jetbrains.dokka.base.renderers.html.innerTemplating
+
+import freemarker.core.Environment
+import freemarker.template.*
+import kotlinx.html.*
+import kotlinx.html.stream.createHTML
+import org.jetbrains.dokka.DokkaConfiguration
+import org.jetbrains.dokka.base.DokkaBase
+import org.jetbrains.dokka.base.DokkaBaseConfiguration
+import org.jetbrains.dokka.base.renderers.URIExtension
+import org.jetbrains.dokka.base.renderers.html.TEMPLATE_REPLACEMENT
+import org.jetbrains.dokka.base.renderers.html.command.consumers.ImmediateResolutionTagConsumer
+import org.jetbrains.dokka.base.renderers.html.templateCommand
+import org.jetbrains.dokka.base.renderers.html.templateCommandAsHtmlComment
+import org.jetbrains.dokka.base.renderers.isImage
+import org.jetbrains.dokka.base.resolvers.local.LocationProvider
+import org.jetbrains.dokka.base.templating.PathToRootSubstitutionCommand
+import org.jetbrains.dokka.base.templating.ProjectNameSubstitutionCommand
+import org.jetbrains.dokka.base.templating.ReplaceVersionsCommand
+import org.jetbrains.dokka.base.templating.SubstitutionCommand
+import org.jetbrains.dokka.model.DisplaySourceSet
+import org.jetbrains.dokka.model.withDescendants
+import org.jetbrains.dokka.pages.ContentPage
+import org.jetbrains.dokka.pages.PageNode
+import org.jetbrains.dokka.plugability.DokkaContext
+import org.jetbrains.dokka.plugability.configuration
+import java.net.URI
+
+class DefaultTemplateModelFactory(val context: DokkaContext) : TemplateModelFactory {
+    private val configuration = configuration<DokkaBase, DokkaBaseConfiguration>(context)
+    private val isPartial = context.configuration.delayTemplateSubstitution
+
+    private fun <R> TagConsumer<R>.prepareForTemplates() =
+        if (context.configuration.delayTemplateSubstitution || this is ImmediateResolutionTagConsumer) this
+        else ImmediateResolutionTagConsumer(this, context)
+
+    data class SourceSetModel(val name: String, val platform: String, val filter: String)
+
+    override fun buildModel(
+        page: PageNode,
+        resources: List<String>,
+        locationProvider: LocationProvider,
+        shouldRenderSourceSetBubbles: Boolean,
+        content: String
+    ): TemplateMap {
+        val path = locationProvider.resolve(page)
+        val pathToRoot = locationProvider.pathToRoot(page)
+        val mapper = mutableMapOf<String, Any>()
+        mapper["pageName"] = page.name
+        mapper["resources"] = PrintDirective {
+            val sb = StringBuilder()
+            if (isPartial)
+                sb.templateCommandAsHtmlComment(
+                    PathToRootSubstitutionCommand(
+                        TEMPLATE_REPLACEMENT,
+                        default = pathToRoot
+                    )
+                ) { resourcesForPage(TEMPLATE_REPLACEMENT, resources) }
+            else
+                sb.resourcesForPage(pathToRoot, resources)
+            sb.toString()
+        }
+        mapper["content"] = PrintDirective { content }
+        mapper["version"] = PrintDirective {
+            createHTML().prepareForTemplates().templateCommand(ReplaceVersionsCommand(path.orEmpty()))
+        }
+        mapper["template_cmd"] = TemplateDirective(context.configuration, pathToRoot)
+
+        if (shouldRenderSourceSetBubbles && page is ContentPage) {
+            val sourceSets = page.content.withDescendants()
+                .flatMap { it.sourceSets }
+                .distinct()
+                .sortedBy { it.comparableKey }
+                .map { SourceSetModel(it.name, it.platform.key, it.sourceSetIDs.merged.toString()) }
+                .toList()
+            mapper["sourceSets"] = sourceSets
+        }
+        return mapper
+    }
+
+    override fun buildSharedModel(): TemplateMap = mapOf<String, Any>(
+        "footerMessage" to (configuration?.footerMessage?.takeIf { it.isNotEmpty() }
+            ?: DokkaBaseConfiguration.defaultFooterMessage)
+    )
+
+    private val DisplaySourceSet.comparableKey
+        get() = sourceSetIDs.merged.let { it.scopeId + it.sourceSetName }
+    private val String.isAbsolute: Boolean
+        get() = URI(this).isAbsolute
+
+    private fun Appendable.resourcesForPage(pathToRoot: String, resources: List<String>): Unit =
+        resources.forEach {
+            append(with(createHTML()) {
+                when {
+                    it.URIExtension == "css" ->
+                        link(
+                            rel = LinkRel.stylesheet,
+                            href = if (it.isAbsolute) it else "$pathToRoot$it"
+                        )
+                    it.URIExtension == "js" ->
+                        script(
+                            type = ScriptType.textJavaScript,
+                            src = if (it.isAbsolute) it else "$pathToRoot$it"
+                        ) {
+                            if (it == "scripts/main.js")
+                                defer = true
+                            else
+                                async = true
+                        }
+                    it.isImage() -> link(href = if (it.isAbsolute) it else "$pathToRoot$it")
+                    else -> null
+                }
+            } ?: it)
+        }
+}
+
+private class PrintDirective(val generateData: () -> String) : TemplateDirectiveModel {
+    override fun execute(
+        env: Environment,
+        params: MutableMap<Any?, Any?>?,
+        loopVars: Array<TemplateModel>?,
+        body: TemplateDirectiveBody?
+    ) {
+        if (params?.isNotEmpty() == true) throw TemplateModelException(
+            "Parameters are not allowed"
+        )
+        if (loopVars?.isNotEmpty() == true) throw TemplateModelException(
+            "Loop variables are not allowed"
+        )
+        env.out.write(generateData())
+    }
+}
+
+private class TemplateDirective(val configuration: DokkaConfiguration, val pathToRoot: String) : TemplateDirectiveModel {
+    override fun execute(
+        env: Environment,
+        params: MutableMap<Any?, Any?>?,
+        loopVars: Array<TemplateModel>?,
+        body: TemplateDirectiveBody?
+    ) {
+        val commandName = params?.get(PARAM_NAME) ?: throw TemplateModelException(
+            "The required $PARAM_NAME parameter is missing."
+        )
+        val replacement = (params[PARAM_REPLACEMENT] as? SimpleScalar)?.asString ?: TEMPLATE_REPLACEMENT
+
+        when ((commandName as? SimpleScalar)?.asString) {
+            "pathToRoot" -> {
+                body ?: throw TemplateModelException(
+                    "No directive body for $commandName command."
+                )
+                executeSubstituteCommand(
+                    PathToRootSubstitutionCommand(
+                        replacement, pathToRoot
+                    ),
+                    "pathToRoot",
+                    pathToRoot,
+                    Context(env, body)
+                )
+            }
+            "projectName" -> {
+                body ?: throw TemplateModelException(
+                    "No directive body $commandName command."
+                )
+                executeSubstituteCommand(
+                    ProjectNameSubstitutionCommand(
+                        replacement, configuration.moduleName
+                    ),
+                    "projectName",
+                    configuration.moduleName,
+                    Context(env, body)
+                )
+            }
+            else -> throw TemplateModelException(
+                "The parameter $PARAM_NAME $commandName is unknown"
+            )
+        }
+    }
+
+    private data class Context(val env: Environment, val body: TemplateDirectiveBody)
+
+    private fun executeSubstituteCommand(
+        command: SubstitutionCommand,
+        name: String,
+        value: String,
+        ctx: Context
+    ) {
+        if (configuration.delayTemplateSubstitution)
+            ctx.env.out.templateCommandAsHtmlComment(command) {
+                renderWithLocalVar(name, command.pattern, ctx)
+            }
+        else {
+            renderWithLocalVar(name, value, ctx)
+        }
+    }
+
+    private fun renderWithLocalVar(name: String, value: String, ctx: Context) =
+        with(ctx) {
+            env.setVariable(name, SimpleScalar(value))
+            body.render(env.out)
+            env.setVariable(name, null)
+        }
+
+    companion object {
+        const val PARAM_NAME = "name"
+        const val PARAM_REPLACEMENT = "replacement"
+    }
+}
\ No newline at end of file
diff --git a/plugins/base/src/main/kotlin/renderers/html/innerTemplating/DefaultTemplateModelMerger.kt b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/DefaultTemplateModelMerger.kt
new file mode 100644
index 00000000..7d548721
--- /dev/null
+++ b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/DefaultTemplateModelMerger.kt
@@ -0,0 +1,16 @@
+package org.jetbrains.dokka.base.renderers.html.innerTemplating
+
+class DefaultTemplateModelMerger : TemplateModelMerger {
+    override fun invoke(
+        factories: List<TemplateModelFactory>,
+        buildModel: TemplateModelFactory.() -> TemplateMap
+    ): TemplateMap {
+        val mapper = mutableMapOf<String, Any?>()
+        factories.map(buildModel).forEach { partialModel ->
+            partialModel.forEach { (k, v) ->
+                mapper[k] = v
+            }
+        }
+        return mapper
+    }
+}
\ No newline at end of file
diff --git a/plugins/base/src/main/kotlin/renderers/html/innerTemplating/HtmlTemplater.kt b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/HtmlTemplater.kt
new file mode 100644
index 00000000..e3d16d98
--- /dev/null
+++ b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/HtmlTemplater.kt
@@ -0,0 +1,76 @@
+package org.jetbrains.dokka.base.renderers.html.innerTemplating
+
+import freemarker.cache.ClassTemplateLoader
+import freemarker.cache.FileTemplateLoader
+import freemarker.cache.MultiTemplateLoader
+import freemarker.log.Logger
+import freemarker.template.Configuration
+import freemarker.template.TemplateExceptionHandler
+import org.jetbrains.dokka.base.DokkaBase
+import org.jetbrains.dokka.base.DokkaBaseConfiguration
+import org.jetbrains.dokka.plugability.DokkaContext
+import org.jetbrains.dokka.plugability.configuration
+import java.io.StringWriter
+
+
+enum class DokkaTemplateTypes(val path: String) {
+    BASE("base.ftl")
+}
+
+typealias TemplateMap = Map<String, Any?>
+
+class HtmlTemplater(
+    context: DokkaContext
+) {
+
+    init {
+        // to disable logging, but it isn't reliable see [Logger.SYSTEM_PROPERTY_NAME_LOGGER_LIBRARY]
+        // (use SLF4j further)
+        System.setProperty(
+            Logger.SYSTEM_PROPERTY_NAME_LOGGER_LIBRARY,
+            System.getProperty(Logger.SYSTEM_PROPERTY_NAME_LOGGER_LIBRARY) ?: Logger.LIBRARY_NAME_NONE
+        )
+    }
+
+    private val configuration = configuration<DokkaBase, DokkaBaseConfiguration>(context)
+    private val templaterConfiguration =
+        Configuration(Configuration.VERSION_2_3_31).apply { configureTemplateEngine() }
+
+    private fun Configuration.configureTemplateEngine() {
+        val loaderFromResources = ClassTemplateLoader(javaClass, "/dokka/templates")
+        templateLoader = configuration?.templatesDir?.let {
+            MultiTemplateLoader(
+                arrayOf(
+                    FileTemplateLoader(it),
+                    loaderFromResources
+                )
+            )
+        } ?: loaderFromResources
+
+        unsetLocale()
+        defaultEncoding = "UTF-8"
+        templateExceptionHandler = TemplateExceptionHandler.RETHROW_HANDLER
+        logTemplateExceptions = false
+        wrapUncheckedExceptions = true
+        fallbackOnNullLoopVariable = false
+        templateUpdateDelayMilliseconds = Long.MAX_VALUE
+    }
+
+    fun setupSharedModel(model: TemplateMap) {
+        templaterConfiguration.setSharedVariables(model)
+    }
+
+    fun renderFromTemplate(
+        templateType: DokkaTemplateTypes,
+        generateModel: () -> TemplateMap
+    ): String {
+        val out = StringWriter()
+        // Freemarker has own thread-safe cache to keep templates
+        val template = templaterConfiguration.getTemplate(templateType.path)
+        val model = generateModel()
+        template.process(model, out)
+
+        return out.toString()
+    }
+}
+
diff --git a/plugins/base/src/main/kotlin/renderers/html/innerTemplating/TemplateModelFactory.kt b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/TemplateModelFactory.kt
new file mode 100644
index 00000000..ceecf201
--- /dev/null
+++ b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/TemplateModelFactory.kt
@@ -0,0 +1,16 @@
+package org.jetbrains.dokka.base.renderers.html.innerTemplating
+
+import org.jetbrains.dokka.base.resolvers.local.LocationProvider
+import org.jetbrains.dokka.pages.PageNode
+
+interface TemplateModelFactory {
+    fun buildModel(
+        page: PageNode,
+        resources: List<String>,
+        locationProvider: LocationProvider,
+        shouldRenderSourceSetBubbles: Boolean,
+        content: String
+    ): TemplateMap
+
+    fun buildSharedModel(): TemplateMap
+}
\ No newline at end of file
diff --git a/plugins/base/src/main/kotlin/renderers/html/innerTemplating/TemplateModelMerger.kt b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/TemplateModelMerger.kt
new file mode 100644
index 00000000..7ad96d8f
--- /dev/null
+++ b/plugins/base/src/main/kotlin/renderers/html/innerTemplating/TemplateModelMerger.kt
@@ -0,0 +1,5 @@
+package org.jetbrains.dokka.base.renderers.html.innerTemplating
+
+fun interface TemplateModelMerger {
+    fun invoke(factories: List<TemplateModelFactory>, buildModel: TemplateModelFactory.() -> TemplateMap): TemplateMap
+}
\ No newline at end of file
diff --git a/plugins/base/src/main/resources/dokka/templates/base.ftl b/plugins/base/src/main/resources/dokka/templates/base.ftl
new file mode 100644
index 00000000..853d1ca2
--- /dev/null
+++ b/plugins/base/src/main/resources/dokka/templates/base.ftl
@@ -0,0 +1,62 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <meta name="viewport" content="width=device-width, initial-scale=1" charset="UTF-8">
+    <title>${pageName}</title>
+    <@template_cmd name="pathToRoot">
+    <link href="${pathToRoot}images/logo-icon.svg" rel="icon" type="image/svg">
+    <script>var pathToRoot = "${pathToRoot}";</script>
+    </@template_cmd>
+    <#-- This script doesn't need to be there but it is nice to have
+    since app in dark mode doesn't 'blink' (class is added before it is rendered) -->
+    <script>const storage = localStorage.getItem("dokka-dark-mode")
+const savedDarkMode = storage ? JSON.parse(storage) : false
+if(savedDarkMode === true){
+    document.getElementsByTagName("html")[0].classList.add("theme-dark")
+}</script>
+    <#-- Resources (scripts, stylesheets) are handled by Dokka.
+    Use customStyleSheets and customAssets to change them. -->
+    <@resources/>
+</head>
+<body>
+<div class="navigation-wrapper" id="navigation-wrapper">
+    <div id="leftToggler"><span class="icon-toggler"></span></div>
+    <div class="library-name">
+        <@template_cmd name="pathToRoot">
+            <a href="${pathToRoot}index.html">
+                <@template_cmd name="projectName">
+                    <span>${projectName}</span>
+                </@template_cmd>
+            </a>
+        </@template_cmd>
+    </div>
+    <div>
+        <#-- This can be handled by a versioning plugin -->
+        <@version/>
+    </div>
+    <div class="pull-right d-flex">
+        <button id="theme-toggle-button"><span id="theme-toggle"></span></button>
+        <div id="searchBar"></div>
+        <#if sourceSets??>
+            <div class="filter-section" id="filter-section">
+                <#list sourceSets as ss>
+                    <button class="platform-tag platform-selector ${ss.platform}-like" data-active="" data-filter="${ss.filter}">${ss.name}</button>
+                </#list>
+            </div>
+        </#if>
+    </div>
+</div>
+<div id="container">
+    <div id="leftColumn">
+        <div id="sideMenu"></div>
+    </div>
+    <div id="main">
+        <@content/>
+        <div class="footer"><span class="go-to-top-icon"><a href="#content" id="go-to-top-link"></a></span><span>${footerMessage}</span><span
+                class="pull-right"><span>Generated by </span><a
+                href="https://github.com/Kotlin/dokka"><span>dokka</span><span class="padded-icon"></span></a></span>
+        </div>
+    </div>
+</div>
+</body>
+</html>
\ No newline at end of file