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// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
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// *                                                                                                                         *
// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
// *                                                                                                                         *
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// * specific language governing permissions and limitations under the License.                                              *
// ***************************************************************************************************************************
package org.apache.juneau.svl;

import static org.apache.juneau.internal.CollectionUtils.*;

import java.io.*;
import java.util.*;
import java.util.concurrent.*;

import org.apache.juneau.*;
import org.apache.juneau.cp.*;
import org.apache.juneau.internal.*;
import org.apache.juneau.svl.vars.*;

/**
 * Utility class for resolving variables of the form <js>"$X{key}"</js> in strings.
 *
 * <p>
 * Variables are of the form <c>$X{key}</c>, where <c>X</c> can consist of zero or more ASCII characters.
 * <br>The variable key can contain anything, even nested variables that get recursively resolved.
 *
 * <p>
 * Variables are defined through the {@link Builder#vars(Class[])} method.
 *
 * <p>
 * The {@link Var} interface defines how variables are converted to values.
 *
 * <h5 class='section'>Example:</h5>
 * <p class='bjava'>
 *    <jk>public class</jk> SystemPropertiesVar <jk>extends</jk> SimpleVar {
 *
 *       <jc>// Must have a no-arg constructor!</jc>
 *       <jk>public</jk> SystemPropertiesVar() {
 *          <jk>super</jk>(<js>"S"</js>);
 *       }
 *
 *       <ja>@Override</ja>
 *       <jk>public</jk> String resolve(VarResolverSession <jv>session</jv>, String <jv>value</jv>) {
 *          <jk>return</jk> System.<jsm>getProperty</jsm>(<jv>value</jv>);
 *       }
 *    }
 *
 *    <jc>// Create a variable resolver that resolves system properties (e.g. "$S{java.home}")</jc>
 *    VarResolver <jv>varResolver</jv> = VarResolver.<jsm>create</jsm>().vars(SystemPropertiesVar.<jk>class</jk>).build();
 *
 *    <jc>// Use it!</jc>
 *    System.<jsf>out</jsf>.println(<jv>varResolver</jv>.resolve(<js>"java.home is set to $S{java.home}"</js>));
 * </p>
 *
 * <h5 class='section'>See Also:</h5><ul>
 *    <li class='link'><a class="doclink" href="../../../../index.html#jm.SimpleVariableLanguage">Simple Variable Language</a>

 * </ul>
 */
public class VarResolver {

   //-----------------------------------------------------------------------------------------------------------------
   // Static
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Default string variable resolver with support for system properties and environment variables:
    *
    * <ul>
    *    <li><c>$S{key[,default]}</c> - {@link SystemPropertiesVar}
    *    <li><c>$E{key[,default]}</c> - {@link EnvVariablesVar}
    *    <li><c>$A{key[,default]}</c> - {@link ArgsVar}
    *    <li><c>$MF{key[,default]}</c> - {@link ManifestFileVar}
    *    <li><c>$SW{stringArg,pattern:thenValue[,pattern:thenValue...]}</c> - {@link SwitchVar}
    *    <li><c>$IF{arg,then[,else]}</c> - {@link IfVar}
    *    <li><c>$CO{arg[,arg2...]}</c> - {@link CoalesceVar}
    *    <li><c>$PM{arg,pattern}</c> - {@link PatternMatchVar}
    *    <li><c>$PR{stringArg,pattern,replace}</c>- {@link PatternReplaceVar}
    *    <li><c>$PE{arg,pattern,groupIndex}</c> - {@link PatternExtractVar}
    *    <li><c>$UC{arg}</c> - {@link UpperCaseVar}
    *    <li><c>$LC{arg}</c> - {@link LowerCaseVar}
    *    <li><c>$NE{arg}</c> - {@link NotEmptyVar}
    *    <li><c>$LN{arg[,delimiter]}</c> - {@link LenVar}
    *    <li><c>$ST{arg,start[,end]}</c> - {@link SubstringVar}
    * </ul>
    */
   public static final VarResolver DEFAULT = create().defaultVars().build();

   /**
    * Instantiates a new clean-slate {@link Builder} object.
    *
    * @return A new {@link Builder} object.
    */
   public static Builder create() {
      return new Builder();
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Builder
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Builder class.
    */
   @FluentSetters
   public static class Builder extends BeanBuilder<VarResolver> {

      final VarList vars;

      /**
       * Constructor.
       */
      protected Builder() {
         super(VarResolver.class, BeanStore.create().build());
         vars = VarList.create();
      }

      /**
       * Copy constructor.
       *
       * @param copyFrom The bean to copy from.
       */
      protected Builder(VarResolver copyFrom) {
         super(copyFrom.getClass(), copyFrom.beanStore);
         vars = VarList.of(copyFrom.vars);
      }

      @Override /* BeanBuilder */
      protected VarResolver buildDefault() {
         return new VarResolver(this);
      }

      //-------------------------------------------------------------------------------------------------------------
      // Properties
      //-------------------------------------------------------------------------------------------------------------

      /**
       * Register new variables with this resolver.
       *
       * @param values
       *    The variable resolver classes.
       *    These classes must subclass from {@link Var} and have no-arg constructors.
       * @return This object .
       */
      @SafeVarargs
      public final Builder vars(Class<? extends Var>...values) {
         vars.append(values);
         return this;
      }

      /**
       * Register new variables with this resolver.
       *
       * @param values
       *    The variable resolver classes.
       *    These classes must subclass from {@link Var} and have no-arg constructors.
       * @return This object .
       */
      public Builder vars(Var...values) {
         vars.append(values);
         return this;
      }

      /**
       * Register new variables with this resolver.
       *
       * @param values
       *    The variable resolver classes.
       *    These classes must subclass from {@link Var} and have no-arg constructors.
       * @return This object .
       */
      public Builder vars(VarList values) {
         vars.append(values);
         return this;
      }

      /**
       * Adds the default variables to this builder.
       *
       * <p>
       * The default variables are:
       * <ul>
       *    <li>{@link SystemPropertiesVar}
       *    <li>{@link EnvVariablesVar}
       *    <li>{@link ArgsVar}
       *    <li>{@link ManifestFileVar}
       *    <li>{@link SwitchVar}
       *    <li>{@link IfVar}
       *    <li>{@link CoalesceVar}
       *    <li>{@link PatternMatchVar}
       *    <li>{@link PatternReplaceVar}
       *    <li>{@link PatternExtractVar}
       *    <li>{@link UpperCaseVar}
       *    <li>{@link LowerCaseVar}
       *    <li>{@link NotEmptyVar}
       *    <li>{@link LenVar}
       *    <li>{@link SubstringVar}
       * </ul>
       *
       * @return This object .
       */
      public Builder defaultVars() {
         vars.addDefault();
         return this;
      }

      /**
       * Adds a bean to the bean store in this session.
       *
       * @param <T> The bean type.
       * @param c The bean type.
       * @param value The bean.
       * @return This object .
       */
      public <T> Builder bean(Class<T> c, T value) {
         beanStore().addBean(c, value);
         return this;
      }

      // <FluentSetters>

      @Override /* GENERATED - org.apache.juneau.BeanBuilder */
      public Builder impl(Object value) {
         super.impl(value);
         return this;
      }

      @Override /* GENERATED - org.apache.juneau.BeanBuilder */
      public Builder type(Class<?> value) {
         super.type(value);
         return this;
      }

      // </FluentSetters>
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Instance
   //-----------------------------------------------------------------------------------------------------------------

   final Var[] vars;
   private final Map<String,Var> varMap;
   final BeanStore beanStore;

   /**
    * Constructor.
    *
    * @param builder The builder for this object.
    */
   protected VarResolver(Builder builder) {
      this.vars = builder.vars.stream().map(x -> toVar(builder.beanStore(),x)).toArray(Var[]::new);

      Map<String,Var> m = new ConcurrentSkipListMap<>();
      for (Var v : vars)
         m.put(v.getName(), v);

      this.varMap = unmodifiable(m);
      this.beanStore = BeanStore.of(builder.beanStore());
   }

   private static Var toVar(BeanStore bs, Object o) {
      if (o instanceof Class)
         return bs.createBean(Var.class).type((Class<?>)o).run();
      return (Var)o;
   }

   /**
    * Returns a new builder object using the settings in this resolver as a base.
    *
    * @return A new var resolver builder.
    */
   public Builder copy() {
      return new Builder(this);
   }

   /**
    * Returns an unmodifiable map of {@link Var Vars} associated with this context.
    *
    * @return A map whose keys are var names (e.g. <js>"S"</js>) and values are {@link Var} instances.
    */
   protected Map<String,Var> getVarMap() {
      return varMap;
   }

   /**
    * Returns an array of variables define in this variable resolver context.
    *
    * @return A new array containing the variables in this context.
    */
   protected Var[] getVars() {
      return Arrays.copyOf(vars, vars.length);
   }

   /**
    * Adds a bean to this session.
    *
    * @param <T> The bean type.
    * @param c The bean type.
    * @param value The bean.
    * @return This object .
    */
   public <T> VarResolver addBean(Class<T> c, T value) {
      beanStore.addBean(c, value);
      return this;
   }

   /**
    * Creates a new resolver session with no session objects.
    *
    * @return A new resolver session.
    */
   public VarResolverSession createSession() {
      return new VarResolverSession(this, null);
   }

   /**
    * Same as {@link #createSession()} except allows you to specify a bean store for resolving beans.
    *
    * @param beanStore The bean store to associate with this session.
    * @return A new resolver session.
    */
   public VarResolverSession createSession(BeanStore beanStore) {
      return new VarResolverSession(this, beanStore);
   }

   /**
    * Resolve variables in the specified string.
    *
    * <p>
    * This is a shortcut for calling <code>createSession(<jk>null</jk>).resolve(s);</code>.
    * <br>This method can only be used if the string doesn't contain variables that rely on the existence of session
    * variables.
    *
    * @param s The input string.
    * @return The string with variables resolved, or the same string if it doesn't contain any variables to resolve.
    */
   public String resolve(String s) {
      return createSession(null).resolve(s);
   }

   /**
    * Resolve variables in the specified string and sends the results to the specified writer.
    *
    * <p>
    * This is a shortcut for calling <code>createSession(<jk>null</jk>).resolveTo(s, w);</code>.
    * <br>This method can only be used if the string doesn't contain variables that rely on the existence of session
    * variables.
    *
    * @param s The input string.
    * @param w The writer to send the result to.
    * @throws IOException Thrown by underlying stream.
    */
   public void resolveTo(String s, Writer w) throws IOException {
      createSession(null).resolveTo(s, w);
   }
}