JSingleFileScanner.hh

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#ifndef __JSUPPORT__JSINGLEFILESCANNER__
#define __JSUPPORT__JSINGLEFILESCANNER__
 
#include <string>
#include <limits>
#include <filesystem>
 
#include "JLang/JObjectIterator.hh"
#include "JLang/JTypeList.hh"
#include "JLang/JNullType.hh"
#include "JLang/JMultiEquals.hh"
#include "JLang/JException.hh"
 
#include "JSupport/JLimit.hh"
#include "JSupport/JFileScanner.hh"
 
 
/**
 * \file
 * Scanning of objects from a single file according a format that follows from the extension of each file name.
 * \author mdejong
 */
namespace JSUPPORT {}
namespace JPP { using namespace JSUPPORT; }
 
namespace JSUPPORT {
 
  using JLANG::JRewindableObjectIterator;
  using JLANG::JTypeList;
  using JLANG::JTYPELIST;
  using JLANG::JNullType;
  using JLANG::JMultiEquals;
  using JLANG::skip_type;
  using JLANG::JException;
 
 
  /**
   * Auxiliary base class for file name.
   */
  struct JSingleFileScanner_t :
    public std::string
  {
    /**
     * Default constructor.
     */
    JSingleFileScanner_t()
    {}
 
    
    /**
     * Constructor.
     *
     * \param  file_name        file name
     */
    JSingleFileScanner_t(const std::string& file_name) :
      std::string(file_name)
    {}
 
 
    /**
     * Get file name.
     * This method constitutes a light weight wrapper to resolve symbolic links on the fly.
     *
     * \return                  file name
     */
    const std::string getFilename() const
    {
      using namespace std::filesystem;
 
      path ps(static_cast<const std::string&>(*this));
 
      if (is_symlink(ps)) {
        ps = read_symlink(ps);
      }
 
      return ps.string();
    }
  };
 
 
  /**
   * Object reading from a list of files.
   */
  template<class T = JNullType>
  class JSingleFileScanner;
 
 
  /**
   * Template specialisation of JSingleFileScanner for undefined type.\n
   * This specialisation is used as a virtual base class for all implementations of JSingleFileScanner for defined type(s).
   *
   * This class is a simple container for a single file name and has an additional counter limit by extending from JSUPPORT::JLimit.\n
   * This counter limit will be used to limit the number of calls to the method <tt>next</tt> of the derived class.\n
   * Note that the counter limit can only be set via the member or friend methods of JSUPPORT::JLimit.
   */
  template<>
  class JSingleFileScanner<JNullType> :
    public JSingleFileScanner_t,
    public JLimit,
    public JMultiEquals<JSingleFileScanner<JNullType>,
                        JTYPELIST<JSingleFileScanner_t, JLimit>::typelist>
  {
  public:
 
    typedef JSingleFileScanner_t                input_type;
    
    /**
     * Default constructor.
     */
    JSingleFileScanner() 
    {}
 
    
    /**
     * Virtual destructor.
     */
    virtual ~JSingleFileScanner()
    {}
 
    
    /**
     * Configure.
     *
     * \param  input             file name
     * \param  limit             limit
     */
    void configure(const input_type& input, const JLimit& limit)
    {
      static_cast<JSingleFileScanner_t&>(*this) = input;
 
      this->setLimit(limit);
    }
 
    
    /**
     * Configure.
     *
     * \param  input             file name
     */
    void configure(const input_type& input)
    {
      this->configure(input, JLimit());
    }
    
 
    /**
     * Read single file scanner from input.
     *
     * \param  in               input stream
     * \param  file_name        single file scanner
     * \return                  input stream
     */
    friend inline std::istream& operator>>(std::istream& in, JSingleFileScanner& file_name)
    {
      return in >> static_cast<std::string&>(file_name);
    }
 
 
    /**
     * Write single file scanner to output.
     *
     * \param  out              output stream
     * \param  file_name        single file scanner
     * \return                  output stream
     */
    friend inline std::ostream& operator<<(std::ostream& out, const JSingleFileScanner& file_name)
    {
      return out << static_cast<const std::string&>(file_name);
    }
  }; 
 
 
  /**
   * Object reading from a single file name.
   *
   * This class implements the JLANG::JRewindableObjectIterator interface.
   */
  template<class T>
  class JSingleFileScanner :
    public virtual JSingleFileScanner<>,
    public JRewindableObjectIterator<T>
  {
  public:
 
    typedef JSingleFileScanner<>::input_type                     input_type;
    typedef typename JRewindableObjectIterator<T>::pointer_type  pointer_type;
    
    /**
     * Default constructor.
     */
    JSingleFileScanner() :
      counter(0)
    {}
 
 
    /**
     * Copy constructor.
     *
     * Note that the counter limit is not copied and the counter is set to zero.
     *
     * \param  input            input
     */
    template<class JTypelist_t>
    JSingleFileScanner(const JSingleFileScanner<JTypelist_t>& input) :
      counter(0)
    {
      this->configure(input.getFilename(), JLimit());
    }
 
 
    /**
     * Constructor.
     *
     * \param  file_name        file name
     */
    JSingleFileScanner(const input_type& file_name) :
      counter(0)
    {
      this->configure(file_name, JLimit());
    }
 
 
    /**
     * Constructor.
     *
     * \param  file_name        file name
     * \param  limit            limit
     */
    JSingleFileScanner(const input_type& file_name, const JLimit& limit) :
      counter(0)
    {
      this->configure(file_name, limit);
    }
 
 
    /**
     * Get counter.
     *
     * \return                  counter
     */
    counter_type getCounter() const
    {
      return counter;
    }
 
 
    /**
     * Rewind.
     */
    virtual void rewind() override 
    {
      if (scanner.is_open()) {
        scanner.close();
      }
 
      counter = 0;
 
      scanner.reset();
    }
 
 
    /**
     * Check availability of next element.
     *
     * \return                  true if the iteration has more elements; else false
     */
    virtual bool hasNext() override 
    {
      if (is_valid()) {
 
        if (counter < getUpperLimit()) {
 
          // first time around
 
          if (!scanner.is_open()) {
            scanner.open(this->getFilename().c_str());
          }
 
          if (counter < getLowerLimit()) {
            counter += scanner.skip(getLowerLimit() - counter);
          }
          
          if (!scanner.hasNext()) {
 
            scanner.close();
 
            return false;
          }
          
          return true;
            
        } else {
 
          // last time around
 
          if (scanner.is_open()) {
            scanner.close();
          }
 
          scanner.reset();
        }
      }
 
      return false;
    }
 
 
    /**
     * Get next element.
     *
     * \return                  pointer to element
     */
    virtual const pointer_type& next() override 
    {
      ++counter;
 
      return scanner.next();
    }
 
 
    /**
     * Skip items.
     *
     * \param  ns               number of items to skip
     * \return                  number of items skipped
     */
    virtual skip_type skip(const skip_type ns) override 
    {
      const skip_type previous = counter;
 
      counter += scanner.skip(ns);
 
      return counter - previous;
    }
 
 
  protected:
    JFileScanner<T> scanner;
    counter_type    counter;
  }; 
 
 
  /**
   * Template specialisation of JSingleFileScanner for single data types.
   *
   * This class implements the JLANG::JRewindableObjectIterator interface for
   * each data type.
   * The method rewind(), rewinds each object iterator.
   */
  template<class JHead_t, class JTail_t>
  class JSingleFileScanner< JTypeList<JHead_t, JTail_t> > :
    public virtual JSingleFileScanner<>,
    public JSingleFileScanner<JHead_t>,
    public JSingleFileScanner<JTail_t>,
    public JRewindableObjectIterator< JTypeList<JHead_t, JTail_t> >
  {
  public:
 
    typedef JSingleFileScanner<>::input_type                     input_type;
 
    using JSingleFileScanner<JHead_t>::hasNext;
    using JSingleFileScanner<JHead_t>::next;
 
 
    /**
     * Default constructor.
     */
    JSingleFileScanner() :
      JSingleFileScanner<>()
    {}
 
 
    /**
     * Copy constructor.
     *
     * Note that the counter limit is not copied and the counter is set to zero.
     *
     * \param  input            input
     */
    template<class JTypelist_t>
    JSingleFileScanner(const JSingleFileScanner<JTypelist_t>& input)
    {
      this->configure(input.getFilename(), JLimit());
    }
 
 
    /**
     * Constructor.
     *
     * \param  file_name        file name
     */
    JSingleFileScanner(const input_type& file_name)
    {
      this->configure(file_name, JLimit());
    }
 
 
    /**
     * Constructor.
     *
     * \param  file_name        file name
     * \param  limit            limit
     */
    JSingleFileScanner(const input_type& file_name, const JLimit& limit) 
    {
      this->configure(file_name, limit);
    }
 
 
    /**
     * Rewind.\n
     * This method rewinds the JSingleFileScanner for each data type.
     */
    virtual void rewind() override 
    {
      JSingleFileScanner<JHead_t>::rewind();
      JSingleFileScanner<JTail_t>::rewind();
    }
 
 
    /**
     * Skip items.
     *
     * \param  ns               number of items to skip
     * \return                  number of items skipped
     */
    virtual skip_type skip(const skip_type ns) override 
    {
      if (JSingleFileScanner<JHead_t>::skip(ns) == ns &&
          JSingleFileScanner<JTail_t>::skip(ns) == ns)
        return ns;
      else
        THROW(JException, "JSingleFileScanner::skip(): inconsistent number of items skipped.");
    }
  };
 
 
  /**
   * Terminator class of recursive JSingleFileScanner class.
   */
  template<class JHead_t>
  class JSingleFileScanner< JTypeList<JHead_t, JNullType> > :
    public JSingleFileScanner<JHead_t>
  {
  public:
 
    typedef JSingleFileScanner<>::input_type                     input_type;
    
    /**
     * Default constructor.
     */
    JSingleFileScanner() :
      JSingleFileScanner<JHead_t>()
    {}
 
 
    /**
     * Copy constructor.
     *
     * Note that the counter limit is not copied and the counter is set to zero.
     *
     * \param  input            input
     */
    template<class JTypelist_t>
    JSingleFileScanner(const JSingleFileScanner<JTypelist_t>& input)
    {
      this->configure(input.getFilename(), JLimit());
    }
 
 
    /**
     * Constructor.
     *
     * \param  file_name        file name
     */
    JSingleFileScanner(const input_type& file_name) :
      JSingleFileScanner<JHead_t>()
    {
      this->configure(file_name, JLimit());
    }
 
 
    /**
     * Constructor.
     *
     * \param  file_name        file name
     * \param  limit            limit
     */
    JSingleFileScanner(const input_type& file_name, const JLimit& limit) :
      JSingleFileScanner<JHead_t>()
    {
      this->configure(file_name, limit);
    }
  };
}
 
#endif