/*
 * 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
 *
 *      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 org.apache.juneau.commons.svl;

import static org.apache.juneau.commons.utils.CollectionUtils.*;
import static org.apache.juneau.commons.utils.Shorts.*;

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

import org.apache.juneau.commons.inject.*;
import org.apache.juneau.commons.svl.functions.*;
import org.apache.juneau.commons.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="https://juneau.apache.org/docs/topics/MarshallSimpleVariableLanguage">Marshall Simple Variable Language</a>
 * </ul>
 */
@SuppressWarnings({
   "java:S3740", // Raw Var/Class types used intentionally for dynamic variable resolver registration where type parameters are not available
   "resource", // VarResolver manages Closeable resources
   "unchecked" // Var class/instance registration casts (Class<? extends Var>) and the raw Class passed to addBean come from Builder-validated entries
})
public class VarResolver {

   /**
    * Builder class.
    */
   public static class Builder {

      private final WritableBeanStore beanStore;
      final VarList vars;
      final LinkedHashMap<Class<?>,Object> userBeans;
      final List<VarFunction> functions;

      /**
       * Constructor.
       */
      protected Builder() {
         this.beanStore = new BasicBeanStore();
         vars = VarList.create();
         userBeans = new LinkedHashMap<>();
         functions = l();
      }

      /**
       * Copy constructor.
       *
       * @param copyFrom The bean to copy from.  Must not be {@code null}.
       */
      protected Builder(VarResolver copyFrom) {
         this.beanStore = copyFrom.beanStore;
         vars = VarList.of(copyFrom.vars);
         userBeans = new LinkedHashMap<>();
         functions = list(copyFrom.functions);
      }

      /**
       * Returns the bean store used by this builder.
       *
       * @return The bean store used by this builder.
       */
      public WritableBeanStore beanStore() {
         return beanStore;
      }

      /**
       * Adds a bean to the resolved {@link VarResolver}'s local bean store.
       *
       * <p>
       * The bean is stored on this builder and merged into the resolver's local bean store at
       * {@link #build()} time.  The parent bean store passed at construction is not mutated, so beans
       * added here are isolated to {@link VarResolver}s built from this builder.
       *
       * @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) {
         userBeans.put(c, value);
         return this;
      }

      /**
       * Adds the default variables to this builder.
       *
       * <p>
       * The default variables are:
       * <ul>
       *    <li>{@link SystemPropertiesVar}
       *    <li>{@link EnvVariablesVar}
       *    <li>{@link EnvFileVar}
       *    <li>{@link DotenvVar}
       *    <li>{@link ArgsVar}
       *    <li>{@link ManifestFileVar}
       * </ul>
       *
       * <p>
       * The 11 transformation {@code Var}s previously listed here ({@code SwitchVar},
       * {@code IfVar}, {@code CoalesceVar}, {@code PatternMatchVar}, {@code PatternReplaceVar},
       * {@code PatternExtractVar}, {@code UpperCaseVar}, {@code LowerCaseVar},
       * {@code NotEmptyVar}, {@code LenVar}, {@code SubstringVar}) were deleted in 10.0.0 and
       * replaced by the {@code #{...}} script syntax. Use {@link #defaultFunctions()} to
       * register the built-in catalog.
       *
       * @return This object .
       */
      public Builder defaultVars() {
         vars.addDefault();
         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 .
       */
      @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;
      }

      /**
       * Register one or more {@link VarFunction} instances on this builder.
       *
       * <p>
       * Functions registered here win over {@code BeanStore} / {@code ServiceLoader} / built-in
       * catalog entries with the same {@link VarFunction#name() name} (later-wins-on-collision).
       * Discovery channels merge these registrations with the auto-discovered set at
       * {@link #build()} time.
       *
       * @param values The functions to register.
       * @return This builder.
       */
      public Builder functions(VarFunction... values) {
         Collections.addAll(functions, values);
         return this;
      }

      /**
       * Register one or more {@link VarFunction} <i>classes</i> on this builder. Each class
       * must have a public no-arg constructor; instances are created via the bean store at
       * {@link #build()} time so dependency injection works the same way it does for
       * {@link Var}s.
       *
       * @param values The function classes to register.
       * @return This builder.
       */
      @SafeVarargs
      public final Builder functions(Class<? extends VarFunction>... values) {
         for (var c : values)
            functions.add(BeanInstantiator.of(VarFunction.class, beanStore).type(c).run());
         return this;
      }

      /**
       * Registers the built-in {@link VarFunction} catalog plus any third-party functions
       * discovered via {@link ServiceLoader#load(Class)} on {@link VarFunction}.
       *
       * <p>
       * Registration order is:
       * <ol>
       *    <li>Built-in catalog — string, type-conversion, arithmetic, boolean, conditional,
       *       regex, encoding, date, random/UUID, and JSON-navigation functions.
       *    <li>Third-party functions from {@code META-INF/services/org.apache.juneau.commons.svl.VarFunction}.
       * </ol>
       *
       * <p>
       * Later registrations win on name collision — third-party {@code ServiceLoader} entries
       * override built-ins, and explicit {@link #functions(VarFunction...)} /
       * {@link #functions(Class...)} calls override both.
       *
       * @return This builder.
       */
      public Builder defaultFunctions() {
         for (var c : BUILTIN_FUNCTION_CLASSES)
            functions.add(BeanInstantiator.of(VarFunction.class, beanStore).type(c).run());
         for (var f : ServiceLoader.load(VarFunction.class, VarResolver.class.getClassLoader()))
            functions.add(f);
         return this;
      }

      /**
       * Builds the var resolver.
       *
       * @return A new {@link VarResolver}.
       */
      public VarResolver build() {
         return new VarResolver(this);
      }
   }

   /**
    * Built-in {@link VarFunction} classes registered by {@link Builder#defaultFunctions()}.
    *
    * <p>
    * Order matters only for collisions inside the built-in catalog itself (and there should be
    * none). Third-party functions discovered via {@link ServiceLoader} register <i>after</i>
    * this list, so they override built-ins on name collision.
    */
   private static final Class<? extends VarFunction>[] BUILTIN_FUNCTION_CLASSES = (Class<? extends VarFunction>[]) concat(
      StringFunctions.ALL,
      TypeConversionFunctions.ALL,
      ArithmeticFunctions.ALL,
      BooleanFunctions.ALL,
      ConditionalFunctions.ALL,
      RegexFunctions.ALL,
      EncodingFunctions.ALL,
      DateFunctions.ALL,
      RandomFunctions.ALL,
      JsonFunctions.ALL
   );

   @SafeVarargs
   private static <T> Class<? extends T>[] concat(Class<? extends T>[]... arrays) {
      var total = 0;
      for (var a : arrays) total += a.length;
      var out = new Class[total];
      var idx = 0;
      for (var a : arrays) {
         System.arraycopy(a, 0, out, idx, a.length);
         idx += a.length;
      }
      return out;
   }

   /**
    * Default string variable resolver with support for system properties, environment
    * variables, and the built-in {@link VarFunction} catalog.
    *
    * <h5 class='section'>Built-in {@link Var} bindings:</h5>
    * <ul>
    *    <li><c>$S{key[,default]}</c> - {@link SystemPropertiesVar}
    *    <li><c>$E{key[,default]}</c> - {@link EnvVariablesVar}
    *    <li><c>$EF{key[,default]}</c> - {@link EnvFileVar}
    *    <li><c>$DE{key[,default]}</c> - {@link DotenvVar}
    *    <li><c>$A{key[,default]}</c> - {@link ArgsVar}
    *    <li><c>$MF{key[,default]}</c> - {@link ManifestFileVar}
    * </ul>
    *
    * <h5 class='section'>Built-in {@link VarFunction} catalog:</h5>
    * <p>
    * Ships ~68 built-in functions across 10 categories — string, type-conversion, arithmetic,
    * boolean, conditional, regex, encoding, date/time, random/UUID, and JSON-navigation.
    * Functions are invoked via the {@code #{name(args...)}} syntax. See
    * {@link Builder#defaultFunctions()} for the registration mechanism.
    *
    * <p>
    * The 11 transformation/conditional {@code Var}s previously bundled here
    * ({@code SwitchVar}, {@code IfVar}, {@code CoalesceVar}, {@code PatternMatchVar},
    * {@code PatternReplaceVar}, {@code PatternExtractVar}, {@code UpperCaseVar},
    * {@code LowerCaseVar}, {@code NotEmptyVar}, {@code LenVar}, {@code SubstringVar}) were
    * deleted in 10.0.0; their behavior is now covered by the {@code #{...}} script syntax.
    */
   public static final VarResolver DEFAULT = create().defaultVars().defaultFunctions().build();

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

   private static Var toVar(BeanStore bs, Object o) {
      if (o instanceof Class<?> o2) {
         var subType = (Class<? extends Var>) o2;
         return BeanInstantiator.of(Var.class, bs).type(subType).run();
      }
      return (Var)o;
   }

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

   final VarFunction[] functions;
   private final Map<String,VarFunction> functionMap;

   final WritableBeanStore beanStore;

   /**
    * Constructor.
    *
    * @param builder The builder for this object.
    */
   @SuppressWarnings({
      "rawtypes" // Same reason — Builder.bean(Class<T>, T) ensures Class/value pairing
   })
   protected VarResolver(Builder builder) {
      this.vars = builder.vars.stream().map(x -> toVar(builder.beanStore(), x)).toArray(Var[]::new);

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

      this.varMap = u(m);
      this.functions = builder.functions.toArray(new VarFunction[0]);

      var fm = new ConcurrentSkipListMap<String,VarFunction>();
      for (var f : functions)
         fm.put(f.name(), f);
      this.functionMap = u(fm);

      var bs = new BasicBeanStore(builder.beanStore());
      builder.userBeans.forEach((c, v) -> bs.addBean((Class) c, v));
      this.beanStore = bs;
   }

   /**
    * 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;
   }

   /**
    * 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);
   }

   /**
    * 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.  May be {@code null}.
    * @return A new resolver session.
    */
   public VarResolverSession createSession(WritableBeanStore 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.  May be {@code null}.
    * @return The string with variables resolved, or the same string if it doesn't contain any variables to resolve.  Returns {@code null} if the input was {@code null}.
    */
   public String resolve(String s) {
      return createSession(null).resolve(s);
   }

   /**
    * Compiles a template string into a reusable {@link VarTemplate}.
    *
    * <p>
    * Compilation is the dual of {@link #resolve(String)} — instead of tokenizing and resolving
    * in one pass, the input is parsed once and the result returned as an immutable
    * {@link VarTemplate} that callers can reuse across many resolutions:
    *
    * <p class='bjava'>
    *    <jc>// Compile once...</jc>
    *    <jk>var</jk> <jv>tpl</jv> = <jv>vr</jv>.compile(<js>"hello, ${name:world}"</js>);
    *
    *    <jc>// ...resolve many times.</jc>
    *    <jk>for</jk> (<jk>var</jk> <jv>req</jv> : <jv>requests</jv>) {
    *       <jk>var</jk> <jv>session</jv> = <jv>vr</jv>.createSession().bean(<jv>req</jv>);
    *       <jv>writer</jv>.write(<jv>tpl</jv>.resolve(<jv>session</jv>));
    *    }
    * </p>
    *
    * <p>
    * The returned {@link VarTemplate} is immutable and threadsafe; the {@link VarResolverSession}
    * passed to {@link VarTemplate#resolve(VarResolverSession)} inherits its own threadsafety
    * contract (sessions are <b>not</b> threadsafe). Use {@link #resolveSupplier(String)} or
    * {@link VarTemplate#asSupplierWithFreshSessions(VarResolver)} for a threadsafe re-evaluating
    * Supplier.
    *
    * <h5 class='section'>Compile-binding contract:</h5>
    * <p>
    * The compiled template is bound to <i>this</i> resolver. Cached {@link Var} (and, in the
    * future, function) references are resolved at compile time. Passing the compiled template
    * to a session belonging to a different {@link VarResolver} is undefined behavior.
    * Rebuilding the resolver invalidates compiled templates from the previous instance.
    *
    * <p>
    * Templates are <b>not</b> cached on the resolver. Callers that compile the same input
    * repeatedly (e.g. framework consumers compiling per {@code @Value} field) should cache
    * the returned {@link VarTemplate} on their own per-site metadata.
    *
    * @param input The template string to compile. May be {@code null}.
    * @return A new {@link VarTemplate} bound to this resolver.
    */
   public VarTemplate compile(String input) {
      return VarTemplateCompiler.compile(this, input);
   }

   /**
    * Returns a threadsafe {@link Supplier} that resolves the given template against this
    * resolver each time {@link Supplier#get()} is called.
    *
    * <p>
    * Each call to {@link Supplier#get()} opens a fresh {@link VarResolverSession}, so the
    * returned {@code Supplier} is safe to share across threads — making it the recommended
    * default for user-facing code (e.g. {@code @Value Supplier<String>} field types,
    * hot-reload config patterns).
    *
    * <p>
    * Equivalent to {@code compile(input).asSupplierWithFreshSessions(this)}.
    *
    * <p>
    * For a session-bound (and therefore <i>not</i> threadsafe) variant, see
    * {@link VarResolverSession#resolveSupplier(String)}.
    *
    * @param input The template string. May be {@code null}.
    * @return A threadsafe {@code Supplier<String>}.
    */
   public Supplier<String> resolveSupplier(String input) {
      return compile(input).asSupplierWithFreshSessions(this);
   }

   /**
    * 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.  May be {@code null}, in which case the writer is left unchanged.
    * @param w The writer to send the result to.  Must not be {@code null}.
    * @throws IOException Thrown by underlying stream.
    */
   public void resolveTo(String s, Writer w) throws IOException {
      createSession(null).resolveTo(s, w);
   }

   /**
    * 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); }

   /**
    * Returns an unmodifiable map of {@link VarFunction VarFunctions} associated with this context.
    *
    * @return A map whose keys are function names (e.g. <js>"upper"</js>) and values are
    *  {@link VarFunction} instances.
    */
   protected Map<String,VarFunction> getFunctionMap() { return functionMap; }
}