/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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
    *
    *      https://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 org.apache.commons.jexl3.internal;
  
  import java.util.Collections;
  import java.util.LinkedHashSet;
  import java.util.Map;
  import java.util.Objects;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  
  import org.apache.commons.jexl3.JexlEngine;
  import org.apache.commons.jexl3.JexlException;
  import org.apache.commons.jexl3.introspection.JexlPropertyGet;
  import org.apache.commons.jexl3.introspection.JexlUberspect;
  
  /**
   * Helper resolving a simple class name into a Fully Qualified Class Name (hence FqcnResolver) using
   * package names and classes as roots of import.
   * <p>This only keeps the names of the classes to avoid any class loading/reloading/permissions issue.</p>
   */
  public class FqcnResolver implements JexlUberspect.ClassConstantResolver {
      /**
       * The uberspect.
       */
      private final JexlUberspect uberspect;
      /**
       * The set of packages to be used as import roots.
       */
      private final Set<String> imports = Collections.synchronizedSet(new LinkedHashSet<>());
      /**
       * The map of solved fqcns based on imports keyed on (simple) name,
       * valued as fully qualified class name.
       */
      private final Map<String, String> fqcns = new ConcurrentHashMap<>();
      /**
       * Optional parent solver.
       */
      private final FqcnResolver parent;
  
      /**
       * Creates a class name solver.
       *
       * @param solver the parent solver
       * @throws NullPointerException if parent solver is null
       */
      FqcnResolver(final FqcnResolver solver) {
          this.parent = Objects.requireNonNull(solver, "solver");
          this.uberspect = solver.uberspect;
      }
  
      /**
       * Creates a class name solver.
       *
       * @param uber     the optional class loader
       * @param packages the optional package names
       */
      FqcnResolver(final JexlUberspect uber, final Iterable<String> packages) {
          this.uberspect = Objects.requireNonNull(uber, "uberspect");
          this.parent = null;
          importCheck(packages);
      }
  
      /**
       * Gets a fully qualified class name from a simple class name and imports.
       *
       * @param name the simple name
       * @return the fqcn
       */
      String getQualifiedName(final String name) {
          String fqcn;
          if (parent != null && (fqcn = parent.getQualifiedName(name)) != null) {
              return fqcn;
          }
          return fqcns.computeIfAbsent(name, this::solveClassName);
      }
  
      /**
       * Attempts to solve a fully qualified class name from a simple class name.
       * <p>It tries to solve the class name as package.classname or package$classname (inner class).</p>
       *
       * @param name the simple class name
       * @return the fully qualified class name or null if not found
       */
      private String solveClassName(final String name) {
         for (final String pkg : imports) {
             // try package.classname or fqcn$classname (inner class)
             for (final char dot : new char[]{'.', '$'}) {
                 final Class<?> clazz = uberspect.getClassByName(pkg + dot + name);
                 // solved it
                 if (clazz != null) {
                     return clazz.getName();
                 }
             }
         }
         return null;
     }
 
     /**
      * Adds a collection of packages/classes as import root, check each name point to one or the other.
      *
      * @param names the package names
      */
     private void importCheck(final Iterable<String> names) {
         if (names != null) {
             names.forEach(this::importCheck);
         }
     }
 
     /**
      * Adds a package as import root, checks the name points to a package or a class.
      *
      * @param name the package name
      */
     private void importCheck(final String name) {
         if (name == null || name.isEmpty()) {
             return;
         }
         // check the package name actually points to a package to avoid clutter
         final Package pkg = Package.getPackage(name);
         if (pkg == null) {
             // if it is a class, solve it now
             final Class<?> clazz = uberspect.getClassByName(name);
             if (clazz == null) {
                 throw new JexlException(null, "Cannot import '" + name + "' as it is neither a package nor a class");
             }
             fqcns.put(name, clazz.getName());
         }
         imports.add(name);
     }
 
     /**
      * Imports a list of packages as solving roots.
      *
      * @param packages the packages
      * @return this solver
      */
     FqcnResolver importPackages(final Iterable<String> packages) {
         if (packages != null) {
             if (parent == null) {
                 importCheck(packages);
             } else {
                 packages.forEach(pkg -> {
                     if (!parent.isImporting(pkg)) {
                         importCheck(pkg);
                     }
                 });
             }
         }
         return this;
     }
 
     /**
      * Checks is a package is imported by this solver of one of its ascendants.
      *
      * @param pkg the package name
      * @return true if an import exists for this package, false otherwise
      */
     boolean isImporting(final String pkg) {
         if (parent != null && parent.isImporting(pkg)) {
             return true;
         }
         return imports.contains(pkg);
     }
 
     @Override
     public String resolveClassName(final String name) {
         return getQualifiedName(name);
     }
 
     @Override
     public Object resolveConstant(final String cname) {
         return getConstant(cname.split("\\."));
     }
 
     private Object getConstant(final String... ids) {
         if (ids.length == 1) {
             final String pname = ids[0];
             for (final String cname : fqcns.keySet()) {
                 final Object constant = getConstant(cname, pname);
                 if (constant != JexlEngine.TRY_FAILED) {
                     return constant;
                 }
             }
         } else if (ids.length == 2) {
             final String cname = ids[0];
             final String id = ids[1];
             final String fqcn = resolveClassName(cname);
             if (fqcn != null) {
                 final Class<?> clazz = uberspect.getClassByName(fqcn);
                 if (clazz != null) {
                     final JexlPropertyGet getter = uberspect.getPropertyGet(clazz, id);
                     if (getter != null && getter.isConstant()) {
                         try {
                             return getter.invoke(clazz);
                         } catch (final Exception xany) {
                             // ignore
                         }
                     }
                 }
             }
         }
         return JexlEngine.TRY_FAILED;
     }
 }