laika.bundle.RewriteRules.scala Maven / Gradle / Ivy

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/*
 * Copyright 2013-2016 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.bundle

import laika.ast.{DocumentCursor, Element, RewriteRule}
import laika.rewrite.link.LinkResolver
import laika.rewrite.nav.SectionBuilder

/** Utilities for dealing with rewrite rules.
 * 
 *  @author Jens Halm
 */
object RewriteRules {

  
  /** Chains the specified rules into one PartialFunction composition.
   *  The resulting function is always defined, but is returned
   *  as a PartialFunction as required by the `ElementTraversal` API.
   */
  def chain (rules: Seq[RewriteRule]): RewriteRule = {
    
    def extractRules (rule: RewriteRule): Seq[RewriteRule] = rule match {
      case ChainedRewriteRules(rules) => rules
      case other => Seq(other)
    }
    
    ChainedRewriteRules(rules.flatMap(extractRules))
  }
  
  private case class ChainedRewriteRules (rules: Seq[RewriteRule]) extends RewriteRule {
    
    def apply (element: Element): Option[Element] = {
      
      val fallback: RewriteRule = { case e => Some(e) }
    
      val f = 
        if (rules.isEmpty) fallback  
        else (rules map { _ orElse fallback }) reduceRight { (ruleA,ruleB) => ruleA andThen (_ flatMap ruleB) }
      
      f(element)
    }
      
    def isDefinedAt (element: Element): Boolean = true
    
  }
  
  /** Chains the specified rule factory functions into a single factory function.
    */
  def chainFactories (rules: Seq[DocumentCursor => RewriteRule]): DocumentCursor => RewriteRule =
    cursor => chain(rules map (_(cursor)))

  /** The default built-in rewrite rules, dealing with section building and link resolution.
    * These are not installed as part of any default extension bundle as they have specific
    * ordering requirements not compatible with the standard bundle ordering in `OperationConfig`.
    */
  val defaults = Seq(LinkResolver, SectionBuilder)

}