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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.svl;

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

import java.io.*;
import java.lang.reflect.*;
import java.util.*;

import org.apache.juneau.internal.*;

/**
 * A var resolver session that combines a {@link VarResolver} with one or more session objects.
 *
 * <p>
 * Instances of this class are considered light-weight and fast to construct, use, and discard.
 *
 * <p>
 * This class contains the workhorse code for var resolution.
 *
 * <p>
 * Instances of this class are created through the {@link VarResolver#createSession()} and
 * {@link VarResolver#createSession(Map)} methods.
 *
 * <p>
 * Instances of this class are NOT guaranteed to be thread safe.
 *
 * <h5 class='section'>See Also:</h5>
 * <ul>
 *    <li class='link'>{@doc juneau-svl.VarResolvers}
 * </ul>
 */
public class VarResolverSession {

   private final VarResolverContext context;
   private final Map<String,Object> sessionObjects;

   /**
    * Constructor.
    *
    * @param context
    *    The {@link VarResolver} context object that contains the {@link Var Vars} and context objects associated with
    *    that resolver.
    * @param sessionObjects The session objects.
    *
    */
   public VarResolverSession(VarResolverContext context, Map<String,Object> sessionObjects) {
      this.context = context;
      if (sessionObjects != null)
         this.sessionObjects = sessionObjects;
      else
         this.sessionObjects = new HashMap<>();
   }

   /**
    * Adds a session object to this session.
    *
    * @param name The name of the session object.
    * @param o The session object.
    * @return This method (for method chaining).
    */
   public VarResolverSession sessionObject(String name, Object o) {
      sessionObjects.put(name, o);
      return this;
   }

   /**
    * Resolve all variables in the specified string.
    *
    * @param s
    *    The string to resolve variables in.
    * @return
    *    The new string with all variables resolved, or the same string if no variables were found.
    *    <br>Returns <jk>null</jk> if the input was <jk>null</jk>.
    */
   public String resolve(String s) {

      if (s == null || s.isEmpty())
         return s;

      if (s.indexOf('$') == -1 && s.indexOf('\\') == -1)
         return s;

      // Special case where value consists of a single variable with no embedded variables (e.g. "$X{...}").
      // This is a common case, so we want an optimized solution that doesn't involve string builders.
      if (isSimpleVar(s)) {
         String var = s.substring(1, s.indexOf('{'));
         String val = s.substring(s.indexOf('{')+1, s.length()-1);
         Var v = getVar(var);
         if (v != null) {
            try {
               if (v.streamed) {
                  StringWriter sw = new StringWriter();
                  v.resolveTo(this, sw, val);
                  return sw.toString();
               }
               s = v.doResolve(this, val);
               if (s == null)
                  s = "";
               return (v.allowRecurse() ? resolve(s) : s);
            } catch (VarResolverException e) {
               throw e;
            } catch (Exception e) {
               throw new VarResolverException(e, "Problem occurred resolving variable ''{0}'' in string ''{1}''", var, s);
            }
         }
         return s;
      }

      try {
         return resolveTo(s, new StringWriter()).toString();
      } catch (IOException e) {
         throw new RuntimeException(e); // Never happens.
      }
   }

   /**
    * Convenience method for resolving variables in arbitrary objects.
    *
    * <p>
    * Supports resolving variables in the following object types:
    * <ul>
    *    <li>{@link CharSequence}
    *    <li>Arrays containing values of type {@link CharSequence}.
    *    <li>Collections containing values of type {@link CharSequence}.
    *       <br>Collection class must have a no-arg constructor.
    *    <li>Maps containing values of type {@link CharSequence}.
    *       <br>Map class must have a no-arg constructor.
    * </ul>
    *
    * @param o The object.
    * @return The same object if no resolution was needed, otherwise a new object or data structure if resolution was
    * needed.
    */
   @SuppressWarnings({ "rawtypes", "unchecked" })
   public <T> T resolve(T o) {
      if (o == null)
         return null;
      if (o instanceof CharSequence)
         return (T)resolve(o.toString());
      if (o.getClass().isArray()) {
         if (! containsVars(o))
            return o;
         Object o2 = Array.newInstance(o.getClass().getComponentType(), Array.getLength(o));
         for (int i = 0; i < Array.getLength(o); i++)
            Array.set(o2, i, resolve(Array.get(o, i)));
         return (T)o2;
      }
      if (o instanceof Collection) {
         try {
            Collection c = (Collection)o;
            if (! containsVars(c))
               return o;
            Collection c2 = c.getClass().newInstance();
            for (Object o2 : c)
               c2.add(resolve(o2));
            return (T)c2;
         } catch (VarResolverException e) {
            throw e;
         } catch (Exception e) {
            throw new VarResolverException(e, "Problem occurred resolving collection.");
         }
      }
      if (o instanceof Map) {
         try {
            Map m = (Map)o;
            if (! containsVars(m))
               return o;
            Map m2 = m.getClass().newInstance();
            for (Map.Entry e : (Set<Map.Entry>)m.entrySet())
               m2.put(e.getKey(), resolve(e.getValue()));
            return (T)m2;
         } catch (VarResolverException e) {
            throw e;
         } catch (Exception e) {
            throw new VarResolverException(e, "Problem occurred resolving map.");
         }
      }
      return o;
   }

   private static boolean containsVars(Object array) {
      for (int i = 0; i < Array.getLength(array); i++) {
         Object o = Array.get(array, i);
         if (o instanceof CharSequence && o.toString().contains("$"))
            return true;
      }
      return false;
   }

   @SuppressWarnings("rawtypes")
   private static boolean containsVars(Collection c) {
      for (Object o : c)
         if (o instanceof CharSequence && o.toString().contains("$"))
            return true;
      return false;
   }

   @SuppressWarnings("rawtypes")
   private static boolean containsVars(Map m) {
      for (Object o : m.values())
         if (o instanceof CharSequence && o.toString().contains("$"))
            return true;
      return false;
   }

   /*
    * Checks to see if string is of the simple form "$X{...}" with no embedded variables.
    * This is a common case, and we can avoid using StringWriters.
    */
   private static boolean isSimpleVar(String s) {
      int S1 = 1;    // Not in variable, looking for $
      int S2 = 2;    // Found $, Looking for {
      int S3 = 3;    // Found {, Looking for }
      int S4 = 4;    // Found }

      int length = s.length();
      int state = S1;
      for (int i = 0; i < length; i++) {
         char c = s.charAt(i);
         if (state == S1) {
            if (c == '$') {
               state = S2;
            } else {
               return false;
            }
         } else if (state == S2) {
            if (c == '{') {
               state = S3;
            } else if (c < 'A' || c > 'z' || (c > 'Z' && c < 'a')) {   // False trigger "$X "
               return false;
            }
         } else if (state == S3) {
            if (c == '}')
               state = S4;
            else if (c == '{' || c == '$')
               return false;
         } else if (state == S4) {
            return false;
         }
      }
      return state == S4;
   }

   /**
    * Resolves variables in the specified string and sends the output to the specified writer.
    *
    * <p>
    * More efficient than first parsing to a string and then serializing to the writer since this method doesn't need
    * to construct a large string.
    *
    * @param s The string to resolve variables in.
    * @param out The writer to write to.
    * @return The same writer.
    * @throws IOException
    */
   public Writer resolveTo(String s, Writer out) throws IOException {

      int S1 = 1;    // Not in variable, looking for $
      int S2 = 2;    // Found $, Looking for {
      int S3 = 3;    // Found {, Looking for }

      int state = S1;
      boolean isInEscape = false;
      boolean hasInternalVar = false;
      boolean hasInnerEscapes = false;
      String varType = null;
      String varVal = null;
      int x = 0, x2 = 0;
      int depth = 0;
      int length = s.length();
      for (int i = 0; i < length; i++) {
         char c = s.charAt(i);
         if (state == S1) {
            if (isInEscape) {
               if (c == '\\' || c == '$') {
                  out.append(c);
               } else {
                  out.append('\\').append(c);
               }
               isInEscape = false;
            } else if (c == '\\') {
               isInEscape = true;
            } else if (c == '$') {
               x = i;
               x2 = i;
               state = S2;
            } else {
               out.append(c);
            }
         } else if (state == S2) {
            if (isInEscape) {
               isInEscape = false;
            } else if (c == '\\') {
               hasInnerEscapes = true;
               isInEscape = true;
            } else if (c == '{') {
               varType = s.substring(x+1, i);
               x = i;
               state = S3;
            } else if (c < 'A' || c > 'z' || (c > 'Z' && c < 'a')) {  // False trigger "$X "
               if (hasInnerEscapes)
                  out.append(unEscapeChars(s.substring(x, i+1), AS1));
               else
                  out.append(s, x, i+1);
               x = i + 1;
               state = S1;
               hasInnerEscapes = false;
            }
         } else if (state == S3) {
            if (isInEscape) {
               isInEscape = false;
            } else if (c == '\\') {
               isInEscape = true;
               hasInnerEscapes = true;
            } else if (c == '{') {
               depth++;
               hasInternalVar = true;
            } else if (c == '}') {
               if (depth > 0) {
                  depth--;
               } else {
                  varVal = s.substring(x+1, i);
                  Var r = getVar(varType);
                  if (r == null) {
                     if (hasInnerEscapes)
                        out.append(unEscapeChars(s.substring(x2, i+1), AS2));
                     else
                        out.append(s, x2, i+1);
                     x = i+1;
                  } else {
                     varVal = (hasInternalVar && r.allowNested() ? resolve(varVal) : varVal);
                     try {
                        if (r.streamed)
                           r.resolveTo(this, out, varVal);
                        else {
                           String replacement = r.doResolve(this, varVal);
                           if (replacement == null)
                              replacement = "";
                           // If the replacement also contains variables, replace them now.
                           if (replacement.indexOf('$') != -1 && r.allowRecurse())
                              replacement = resolve(replacement);
                           out.append(replacement);
                        }
                     } catch (VarResolverException e) {
                        throw e;
                     } catch (Exception e) {
                        throw new VarResolverException(e, "Problem occurred resolving variable ''{0}'' in string ''{1}''", varType, s);
                     }
                     x = i+1;
                  }
                  state = 1;
                  hasInnerEscapes = false;
               }
            }
         }
      }
      if (isInEscape)
         out.append('\\');
      else if (state == S2)
         out.append('$').append(unEscapeChars(s.substring(x+1), AS1));
      else if (state == S3)
         out.append('$').append(varType).append('{').append(unEscapeChars(s.substring(x+1), AS2));
      return out;
   }

   private static final AsciiSet
      AS1 = AsciiSet.create("\\{"),
      AS2 = AsciiSet.create("\\${}")
   ;

   /**
    * Returns the session object with the specified name.
    *
    * <p>
    * Casts it to the specified class type for you.
    *
    * @param c The class type to cast to.
    * @param name The name of the session object.
    * @param throwNotSetException Throw a {@link VarResolverException} if the session object is not set.
    * @return
    *    The session object.
    *    <br>Never <jk>null</jk>.
    * @throws VarResolverException If session object with specified name does not exist.
    */
   @SuppressWarnings("unchecked")
   public <T> T getSessionObject(Class<T> c, String name, boolean throwNotSetException) {
      T t = null;
      try {
         t = (T)sessionObjects.get(name);
         if (t == null) {
            sessionObjects.put(name, this.context.getContextObject(name));
            t = (T)sessionObjects.get(name);
         }
      } catch (Exception e) {
         throw new VarResolverException(e,
            "Session object ''{0}'' or context object ''SvlContext.{0}'' could not be converted to type ''{1}''.", name, c);
      }
      if (t == null && throwNotSetException)
         throw new VarResolverException(
            "Session object ''{0}'' or context object ''SvlContext.{0}'' not found.", name);
      return t;
   }

   /**
    * Returns the {@link Var} with the specified name.
    *
    * @param name The var name (e.g. <js>"S"</js>).
    * @return The {@link Var} instance, or <jk>null</jk> if no <code>Var</code> is associated with the specified name.
    */
   protected Var getVar(String name) {
      return this.context.getVarMap().get(name);
   }
}