laika.render.epub.HtmlNavRenderer.scala Maven / Gradle / Ivy

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/*
 * Copyright 2012-2020 the original author or authors.
 *
 * 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 laika.render.epub

import laika.ast.{NavigationItem, NavigationLink}
import laika.io.model.RenderedTreeRoot
import laika.render.TagFormatter
import laika.render.epub.StyleSupport.collectStylePaths

/** Renders the entire content of an EPUB HTML navigation file.
  *
  * @author Jens Halm
  */
class HtmlNavRenderer {


  /** Inserts the specified (pre-rendered) navPoints into the NCX document template
    * and returns the content of the entire NCX file.
    */
  def fileContent (title: String, styles: String, navItems: String, coverDoc: Option[String] = None, titleDoc: Option[String] = None): String =
    s"""
       |
       |
       |  
       |    
       |    
       |    $title
       |    $styles
       |  
       |  
       |    
       |      $title
       |$navItems
       |    
       |  
       |
       |
    """.stripMargin.replaceAll("[\n]+", "\n")

  /** Renders a single navigation link.
    */
  private def navLink (title: String, link: String, pos: Int, children: String): String =
    s"""        
       |          ${TagFormatter.escape(title)}
       |$children
       |        """.stripMargin

  /** Always use the link to the first child of a navigation header.
    * Despite the fact that the EPUB spec supports "unlinked headers", 
    * which are just a `` element instead of an `` element,
    * many e-book readers such as iBooks choke on them to the point of rendering navigation menus useless.
    * 
    * Unlinked navigation headers are described in the EPUB spec here:
    * https://www.w3.org/publishing/epub32/epub-packages.html#sec-package-nav-def-model
    */
  private def linkOfFirstChild (children: Seq[NavigationItem]): NavigationLink = 
    children.head.link.getOrElse(linkOfFirstChild(children.head.content))

  /** Generates navigation entries for the structure of the DocumentTree. Individual
    * entries can stem from tree or subtree titles, document titles or
    * document sections, depending on which recursion depth is configured.
    * The configuration key for setting the recursion depth is `epub.toc.depth`.
    *
    * @param bookNav the navigation items to generate navPoints for
    * @return the navPoint XML nodes for the specified document tree as a String
    */
  private def navItems (bookNav: Seq[NavigationItem], pos: Iterator[Int] = Iterator.from(0)): String =
    if (bookNav.isEmpty) ""
    else bookNav.map { item =>
      navLink(
        item.title.extractText, 
        item.link.getOrElse(linkOfFirstChild(item.content)).target.render(),
        pos.next(), 
        navItems(item.content, pos)
      )
    }.mkString("      \n", "\n", "\n      ")

  /** Renders the entire content of an EPUB HTML navigation file for
    * the specified document tree. The recursion depth will be applied
    * to the tree structure obtained by recursively processing titles of document
    * trees, documents and sections.
    * The configuration key for setting the recursion depth is `epub.toc.depth`.
    */
  def render[F[_]] (result: RenderedTreeRoot[F], title: String, depth: Option[Int]): String = {
    val bookNav = NavigationBuilder.forTree(result.tree, depth)
    val styles = collectStylePaths(result).map { path =>
      s""""""
    }.mkString("\n    ")
    val renderedNavPoints = navItems(bookNav)
    val coverDoc = result.coverDocument.map(doc => NavigationBuilder.fullPath(doc.path, forceXhtml = true))
    val titleDoc = result.titleDocument.map(doc => NavigationBuilder.fullPath(doc.path, forceXhtml = true))

    fileContent(title, styles, renderedNavPoints, coverDoc, titleDoc)
  }


}