/*
    * Licensed to The Apereo Foundation under one or more contributor license
    * agreements. See the NOTICE file distributed with this work for additional
    * information regarding copyright ownership.
    *
    *
    * The Apereo Foundation licenses this file to you under the Educational
    * Community 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://opensource.org/licenses/ecl2.txt
   *
   * 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.opencastproject.util;
  
  import static org.opencastproject.util.data.Monadics.mlist;
  
  import org.opencastproject.util.data.Collections;
  import org.opencastproject.util.data.Function;
  import org.opencastproject.util.data.Function2;
  import org.opencastproject.util.data.Monadics;
  import org.opencastproject.util.data.Option;
  import org.opencastproject.util.data.Prelude;
  
  import org.json.simple.JSONArray;
  import org.json.simple.JSONObject;
  
  import java.util.ArrayList;
  import java.util.Date;
  import java.util.List;
  
  /** JSON builder based on json-simple. */
  public final class Jsons {
    private Jsons() {
    }
  
    /** Check if a value is not {@link #ZERO_VAL}. */
    public static final Function<Val, Boolean> notZero = new Function<Val, Boolean>() {
      @Override public Boolean apply(Val val) {
        return !ZERO_VAL.equals(val);
      }
    };
  
    /** Get the value from a property. */
    public static final Function<Prop, Val> getVal = new Function<Prop, Val>() {
      @Override public Val apply(Prop prop) {
        return prop.getVal();
      }
    };
  
    /** JSON null. */
    public static final Val NULL = new Val() {
    };
  
    /** Identity for {@link Val values}. */
    public static final Val ZERO_VAL = new Val() {
    };
  
    /** Identity for {@link Obj objects}. */
    public static final Obj ZERO_OBJ = obj();
  
    /** Identity for {@link Arr arrays}. */
    public static final Arr ZERO_ARR = arr();
  
    public static final class Prop {
      private final String name;
      private final Val val;
  
      private Prop(String name, Val val) {
        this.name = name;
        this.val = val;
      }
  
      public String getName() {
        return name;
      }
  
      public Val getVal() {
        return val;
      }
    }
  
    // sum type
    public abstract static class Val {
    }
  
    private static final class SVal extends Val {
      private final Object val;
  
      private SVal(Object val) {
        this.val = val;
     }
 
     public Object getVal() {
       return val;
     }
   }
 
   public static final class Obj extends Val {
     private final List<Prop> props;
 
     private Obj(List<Prop> props) {
       this.props = props;
     }
 
     public List<Prop> getProps() {
       return props;
     }
 
     public Obj append(Obj o) {
       if (!ZERO_OBJ.equals(o))
         return new Obj(Collections.<Prop, List>concat(props, o.getProps()));
       else
         return o;
     }
 
     public String toJson() {
       return Jsons.toJson(this);
     }
   }
 
   public static final class Arr extends Val {
     private final List<Val> vals;
 
     public Arr(List<Val> vals) {
       this.vals = vals;
     }
 
     public List<Val> getVals() {
       return vals;
     }
 
     public String toJson() {
       return Jsons.toJson(this);
     }
   }
 
   //
 
   public static String toJson(Obj obj) {
     return toJsonSimple(obj).toString();
   }
 
   public static String toJson(Arr arr) {
     return toJsonSimple(arr).toString();
   }
 
   private static JSONObject toJsonSimple(Obj obj) {
     return mlist(obj.getProps()).foldl(new JSONObject(), new Function2<JSONObject, Prop, JSONObject>() {
       @Override public JSONObject apply(JSONObject jo, Prop prop) {
         jo.put(prop.getName(), toJsonSimple(prop.getVal()));
         return jo;
       }
     });
   }
 
   private static JSONArray toJsonSimple(Arr arr) {
     return mlist(arr.getVals()).foldl(new JSONArray(), new Function2<JSONArray, Val, JSONArray>() {
       @Override public JSONArray apply(JSONArray ja, Val val) {
         ja.add(toJsonSimple(val));
         return ja;
       }
     });
   }
 
   private static Object toJsonSimple(Val val) {
     if (val instanceof SVal) {
       return ((SVal) val).getVal();
     }
     if (val instanceof Obj) {
       return toJsonSimple((Obj) val);
     }
     if (val instanceof Arr) {
       return toJsonSimple((Arr) val);
     }
     if (val.equals(NULL)) {
       return null;
     }
     return Prelude.unexhaustiveMatch();
   }
 
   /** Create an object. */
   public static Obj obj(Prop... ps) {
     return new Obj(mlist(ps).filter(notZero.o(getVal)).value());
   }
 
   /** Create an array. */
   public static Arr arr(Val... vs) {
     return new Arr(mlist(vs).filter(notZero).value());
   }
 
   /** Create an array. */
   public static Arr arr(List<Val> vs) {
     return new Arr(mlist(vs).filter(notZero).value());
   }
 
   /** Create an array. */
   public static Arr arr(Monadics.ListMonadic<Val> vs) {
     return new Arr(vs.filter(notZero).value());
   }
 
   public static Val v(Number v) {
     return new SVal(v);
   }
 
   public static Val v(String v) {
     return new SVal(v);
   }
 
   public static final Function<String, Val> stringVal = new Function<String, Val>() {
     @Override public Val apply(String s) {
       return v(s);
     }
   };
 
   public static Val v(Boolean v) {
     return new SVal(v);
   }
 
   public static Val v(Date v) {
     return new SVal(DateTimeSupport.toUTC(v.getTime()));
   }
 
   /** Create a property. */
   public static Prop p(String key, Val val) {
     return new Prop(key, val);
   }
 
   /** Create a property. Passing none is like setting {@link #ZERO_VAL} which erases the property. */
   public static Prop p(String key, Option<Val> val) {
     return new Prop(key, val.getOrElse(ZERO_VAL));
   }
 
   /** Create a property. Convenience. */
   public static Prop p(String key, Number value) {
     return new Prop(key, v(value));
   }
 
   /** Create a property. Convenience. */
   public static Prop p(String key, String value) {
     return new Prop(key, v(value));
   }
 
   /** Create a property. Convenience. */
   public static Prop p(String key, Boolean value) {
     return new Prop(key, v(value));
   }
 
   /** Merge a list of objects into one (last one wins). */
   public static Obj append(Obj... os) {
     final List<Prop> props = mlist(os).foldl(new ArrayList<Prop>(), new Function2<ArrayList<Prop>, Obj, ArrayList<Prop>>() {
       @Override public ArrayList<Prop> apply(ArrayList<Prop> props, Obj obj) {
         props.addAll(obj.getProps());
         return props;
       }
     });
     return new Obj(props);
   }
 
   /** Append a list of arrays into one. */
   public static Arr append(Arr... as) {
     final List<Val> vals = mlist(as).foldl(new ArrayList<Val>(), new Function2<ArrayList<Val>, Arr, ArrayList<Val>>() {
       @Override public ArrayList<Val> apply(ArrayList<Val> vals, Arr arr) {
         vals.addAll(arr.getVals());
         return vals;
       }
     });
     return new Arr(vals);
   }
 }