/*
    * 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.Arrays;
  import java.util.concurrent.atomic.AtomicReference;
  
  /**
   * A call frame, created from a scope, stores the arguments and local variables in a "stack frame" (sic).
   * @since 3.0
   */
  public class Frame {
      /** The scope. */
      private final Scope scope;
      /** The actual stack frame. */
      protected final Object[] stack;
      /** Number of curried parameters. */
      private final int curried;
  
      /**
       * Creates a new frame.
       * @param s the scope
       * @param r the stack frame
       * @param c the number of curried parameters
       */
      protected Frame(final Scope s, final Object[] r, final int c) {
          scope = s;
          stack = r;
          curried = c;
          final String[] symbols = scope.getSymbols();
          if (symbols.length != r.length) {
              throw new IllegalArgumentException("Scope and stack frame size mismatch: "
                      + symbols.length + " != " + r.length);
          }
      }
  
      /**
       * Assign values to this frame.
       * @param values the values
       * @return this frame
       */
      Frame assign(final Object... values) {
          if (stack != null) {
              final int nparm = scope.getArgCount();
              final Object[] copy = stack.clone();
              int ncopy = 0;
              if (values != null && values.length > 0) {
                  ncopy = Math.min(nparm - curried, Math.min(nparm, values.length));
                  System.arraycopy(values, 0, copy, curried, ncopy);
              }
              // unbound parameters are defined as null
              Arrays.fill(copy, curried + ncopy, nparm, null);
              return newFrame(scope, copy, curried + ncopy);
          }
          return this;
      }
  
      /**
       * Creates a new from of this frame"s class.
       * @param s the scope
       * @param r the arguments
       * @param c the number of curried parameters
       * @return a new instance of frame
       */
      Frame newFrame(final Scope s, final Object[] r, final int c) {
          return new Frame(s, r, c);
      }
  
      /**
       * Captures a value.
       * @param s the offset in this frame
       * @param lexical true if this captured symbol is redefined locally
       * @return the stacked value
       */
      Object capture(final int s, final boolean lexical) {
          return stack[s];
      }
  
      /**
       * Gets a value.
       * @param s the offset in this frame
       * @return the stacked value
       */
      Object get(final int s) {
          return stack[s];
     }
 
     /**
      * Sets a value.
      * @param r the offset in this frame
      * @param value the value to set in this frame
      */
     void set(final int r, final Object value) {
         stack[r] = value;
     }
 
     /**
      * Gets the scope.
      * @return this frame scope
      */
     public Scope getScope() {
         return scope;
     }
 
     /**
      * Gets this script unbound parameters, i.e. parameters not bound through curry().
      * @return the parameter names
      */
     public String[] getUnboundParameters() {
         return scope.getParameters(curried);
     }
 
     /**
      * Tests whether this frame defines a symbol, ie declared it and assigned it a value.
      * @param s the offset in this frame
      * @return true if this symbol has been assigned a value, false otherwise
      */
     boolean has(final int s) {
         return s >= 0 && s < stack.length && stack[s] != Scope.UNDECLARED;
     }
 
     /**
      * Replace any instance of a closure in this stack by its (fuzzy encoded) offset in it.
      * <p>This is to avoid the cyclic dependency between the closure and its frame stack that
      * may point back to it that occur with recursive function definitions.</p>
      * @param closure the owning closure
      * @return the cleaned-up stack or the stack itself (most of the time)
      */
     Object[] nocycleStack(final Closure closure) {
         Object[] ns = stack;
         for(int i = 0; i < stack.length; ++i) {
             if (stack[i] == closure) {
                 if (ns == stack) {
                     ns = stack.clone();
                 }
                 // fuzz it a little
                 ns[i] = Closure.class.hashCode() + i;
             }
         }
         return ns;
     }
 }
 
 /**
  * Pass-by-reference frame.
  */
 class ReferenceFrame extends Frame {
     ReferenceFrame(final Scope s, final Object[] r, final int c) {
         super(s, r, c);
     }
 
     @Override
     Frame newFrame(final Scope s, final Object[] r, final int c) {
         return new ReferenceFrame(s, r, c);
     }
 
     @Override
     Object capture(final int s, final boolean lexical) {
         final Object o = stack[s];
         if (o instanceof CaptureReference) {
             final CaptureReference ref = (CaptureReference) o;
             // if the captured symbol is lexical, it is redefined locally; a new reference is needed to share it with callees
             // otherwise share the reference
             return lexical ? (stack[s] = new CaptureReference(ref.get())) : ref;
         }
         // capture the register, wrap the value in a reference to share it with callees
         return stack[s] = new CaptureReference(o);
     }
 
     @Override
     Object get(final int s) {
         final Object o = stack[s];
         return o instanceof CaptureReference ? ((CaptureReference) o).get() : o;
     }
 
     @Override
     void set(final int r, final Object value) {
         final Object o = stack[r];
         if (o instanceof CaptureReference) {
             if (value != Scope.UNDEFINED && value != Scope.UNDECLARED) {
                 ((CaptureReference) o).set(value);
             }
         } else {
             stack[r] = value;
         }
     }
 }
 
 /**
  * Captured variable reference.
  */
 class CaptureReference extends AtomicReference<Object> {
     CaptureReference(final Object o) {
         super(o);
     }
 }