/*
  IterTreeExplorer(Test)  -  verify tree expanding and backtracking iterator

  Copyright (C)         Lumiera.org
    2017,               Hermann Vosseler <Ichthyostega@web.de>

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License as
  published by the Free Software Foundation; either version 2 of
  the License, or (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

* *****************************************************/

/** @file iter-tree-explorer-test.cpp
 ** The \ref IterTreeExplorer_test covers and demonstrates a generic mechanism
 ** to expand and evaluate tree like structures. In its current shape (as of 2017),
 ** it can be seen as an preliminary step towards retrofitting IterExplorer into
 ** a framework of building blocks for tree expanding and backtracking evaluations.
 ** Due to the nature of Lumiera's design, we repeatedly encounter this kind of
 ** algorithms, when it comes to matching configuration and parametrisation against
 ** a likewise hierarchical and rules based model. To keep the code base maintainable,
 ** we deem it crucial to reduce the inherent complexity in such algorithms by clearly
 ** separate the _mechanics of evaluation_ from the actual logic of the target domain.
 ** 
 ** Similar to IterExplorer_test, the his test relies on a demonstration setup featuring
 ** a custom encapsulated state type: we rely on a counter with start and end value,
 ** embedded into an iterator. Basically, this running counter, when iterated, generates
 ** a sequence of numbers start ... end.
 ** So -- conceptually -- this counting iterator can be thought to represent this
 ** sequence of numbers. Note that this is a kind of abstract or conceptual
 ** representation, not a factual representation of the sequence in memory.
 ** The whole point is _not to represent_ this sequence in runtime state at once,
 ** rather to pull and expand it on demand.
 ** 
 ** All these tests work by first defining these _functional structures_, which just
 ** yields an iterator entity. We get the whole structure it conceptually defines
 ** only if we "pull" this iterator until exhaustion -- which is precisely what
 ** the test does to verify proper operation. Real world code of course would
 ** just not proceed in this way, like pulling everything from such an iterator.
 ** Often, the very reason we're using such a setup is the ability to represent
 ** infinite structures. Like e.g. the evaluation graph of video passed through
 ** a complex processing pipeline.
 */



#include "lib/test/run.hpp"
#include "lib/test/test-helper.hpp"
#include "lib/iter-adapter-stl.hpp"
#include "lib/format-cout.hpp"
#include "lib/format-util.hpp"
#include "lib/util.hpp"

#include "lib/iter-tree-explorer.hpp"
#include "lib/meta/trait.hpp"

#include <utility>
#include <vector>
#include <string>


namespace lib {
namespace test{
  
  using ::Test;
  using util::isnil;
  using util::isSameObject;
  using lib::iter_stl::eachElm;
  using lumiera::error::LUMIERA_ERROR_ITER_EXHAUST;
  using std::vector;
  using std::string;
  
  
  namespace { // test substrate: simple number sequence iterator
    
    /**
     * This iteration _"state core" type_ describes
     * a sequence of numbers yet to be delivered.
     */
    class State
      {
        uint p,e;
        
      public:
        State(uint start =0, uint end =0)
          : p(start)
          , e(end)
          { }
        
        friend bool
        checkPoint (State const& st)
        {
          return st.p > st.e;
        }
        
        friend uint&
        yield (State const& st)
        {
          return util::unConst(checkPoint(st)? st.p : st.e);
        }
        
        friend void
        iterNext (State & st)
        {
          if (not checkPoint(st)) return;
          --st.p;
        }
      };
    
    
    
    /**
     * A straight ascending number sequence as basic test iterator.
     * The tests will dress up this source sequence in various ways.
     */
    class NumberSequence
      : public IterStateWrapper<uint, State>
      {
          
        public:
          explicit
          NumberSequence(uint end = 0)
            : IterStateWrapper<uint,State> (State(0,end))
            { }
          NumberSequence(uint start, uint end)
            : IterStateWrapper<uint,State> (State(start,end))
            { }
      };
    
    inline NumberSequence
    seq (uint end)
    {
      return NumberSequence(end);
    }
    
    inline NumberSequence
    seq (uint start, uint end)
    {
      return NumberSequence(start, end);
    }
    
    NumberSequence NIL_Sequence;
    
    
    
    /** Diagnostic helper: "squeeze out" the given iterator
     * and join all the elements yielded into a string
     */
    template<class II>
    inline string
    materialise (II&& ii)
    {
      return util::join (std::forward<II> (ii), "-");
    }
    
    template<class II>
    inline void
    pullOut (II & ii)
    {
      while (ii)
        {
          cout << *ii;
          if (++ii) cout << "-";
        }
      cout << endl;
    }
    
  } // (END) test helpers
  
  
  
  
  
  
  
  /*******************************************************************//**
   * @test use a simple source iterator yielding numbers
   *       to build various functional evaluation structures,
   *       based on the \ref IterExplorer template.
   *       - the [state adapter](\ref verifyStateAdapter() )
   *          iterator construction pattern
   *       - helper to [chain iterators](\ref verifyChainedIterators() )
   *       - building [tree exploring structures](\ref verifyDepthFirstExploration())
   *       - the [monadic nature](\ref verifyMonadOperator()) of IterExplorer
   *       - a [recursively self-integrating](\ref verifyRecrusiveSelfIntegration())
   *         evaluation pattern
   * 
   * ## Explanation
   * 
   * Both this test and the IterExplorer template might be bewildering
   * and cryptic, unless you know the *Monad design pattern*. Monads are
   * heavily used in functional programming, actually they originate
   * from Category Theory. Basically, Monad is a pattern where we
   * combine several computation steps in a specific way; but instead
   * of intermingling the individual computation steps and their
   * combination, the goal is to isolate and separate the _mechanics
   * of combination_, so we can focus on the actual _computation steps:_
   * The mechanics of combination are embedded into the Monad type,
   * which acts as a kind of container, holding some entities
   * to be processed. The actual processing steps are then
   * fed to the monad as "function object" parameters.
   * 
   * Using the monad pattern is well suited when both the mechanics of
   * combination and the individual computation steps tend to be complex.
   * In such a situation, it is beneficial to develop and test both
   * in isolation. The IterExplorer template applies this pattern
   * to the task of processing a source sequence. Typically we use
   * this in situations where we can't afford building elaborate
   * data structures in (global) memory, but rather strive at
   * doing everything on-the-fly. A typical example is the
   * processing of a variably sized data set without
   * using heap memory for intermediary results.
   * 
   * @see TreeExplorer
   * @see IterAdapter
   */
  class IterTreeExplorer_test : public Test
    {
      
      virtual void
      run (Arg)
        {
          verify_wrappedState();
          verify_wrappedIterator();
          
          verify_mapOperation();
          verify_expandOperation();
          verify_expandMapCombination();
          
          verify_depthFirstExploration();
          demonstrate_LayeredEvaluation();
        }
      
      
      
      /** @test without using any extra functionality,
       *        TreeExplorer just wraps an iterable state.
       */
      void
      verify_wrappedState()
        {
          auto ii = treeExplore (State{5,0});
          CHECK (!isnil (ii));
          CHECK (5 == *ii);
          ++ii;
          CHECK (4 == *ii);
          pullOut(ii);
          CHECK ( isnil (ii));
          CHECK (!ii);
          
          VERIFY_ERROR (ITER_EXHAUST, *ii );
          VERIFY_ERROR (ITER_EXHAUST, ++ii );
          
          ii = treeExplore (State{5});
          CHECK (materialise(ii) == "5-4-3-2-1");
          ii = treeExplore (State{7,4});
          CHECK (materialise(ii) == "7-6-5");
          ii = treeExplore (State{});
          CHECK ( isnil (ii));
          CHECK (!ii);
        }
      
      
      /** @test TreeExplorer is able to wrap any _Lumiera Forward Iterator_ */
      void
      verify_wrappedIterator()
        {
          vector<int> numz{1,-2,3,-5,8,-13};
          auto ii = eachElm(numz);
          CHECK (!isnil (ii));
          CHECK (1 == *ii);
          ++ii;
          CHECK (-2 == *ii);
          
          auto jj = treeExplore(ii);
          CHECK (!isnil (jj));
          CHECK (-2 == *jj);
          ++jj;
          CHECK (3 == *jj);
          
          // we passed a LValue-Ref, thus a copy was made
          CHECK (-2 == *ii);

          CHECK (materialise(ii) == "-2-3--5-8--13");
          CHECK (materialise(jj) ==    "3--5-8--13");
          
          // can adapt STL container automatically
          auto kk = treeExplore(numz);
          CHECK (!isnil (kk));
          CHECK (1 == *kk);
          CHECK (materialise(kk) == "1--2-3--5-8--13");
        }
      
      
      
      /** @test pipe each result through a transformation function
       */
      void
      verify_mapOperation()
        {
          UNIMPLEMENTED("map function onto the results");
        }
      
      
      /** @test use a preconfigured "expand" functor to recurse into children
       */
      void
      verify_expandOperation()
        {
          UNIMPLEMENTED("expand children");
        }
      
      
      /** @test combie the recursion into children with a tail mapping operation
       */
      void
      verify_expandMapCombination()
        {
          UNIMPLEMENTED("combine child expansion and result mapping");
        }
      
      
      /** @test use a preconfigured exploration scheme to expand depth-first until exhaustion
       */
      void
      verify_depthFirstExploration()
        {
          UNIMPLEMENTED("preconfigured repeated depth-first expansion");
        }
      
      
      /** @test Demonstration how to build complex algorithms by layered tree expanding iteration
       * @remarks this is the actual use case which inspired the design of TreeExplorer
       */
      void
      demonstrate_LayeredEvaluation()
        {
          UNIMPLEMENTED("build algorithm by layering iterator evaluation");
        }
    };
  
  
  
  LAUNCHER (IterTreeExplorer_test, "unit common");
  
  
}} // namespace lib::test