#include "MantidKernel/ChecksumHelper.h"

#include <boost/regex.hpp>
#include <boost/scoped_ptr.hpp>
#include <boost/shared_array.hpp>

#include <Poco/SHA1Engine.h>
#include <Poco/DigestStream.h>

#include <fstream>
#include <sstream>
#include <string>

namespace Mantid
{
namespace Kernel
{

namespace ChecksumHelper
{
  namespace //anonymous
  {
    /**
     * Load contents of file into a string. The line endings are preserved
     * @param filepath Full path to the file to be opened
     * @param unixEOL If true convert all lineendings to Unix-style \n
     */
    std::string loadFile(const std::string & filepath, const bool unixEOL = false)
    {
      std::ifstream filein(filepath.c_str(), std::ios::in | std::ios::binary);
      if(!filein) return "";

      std::string contents;
      filein.seekg(0, std::ios::end);
      contents.resize(filein.tellg());
      filein.seekg(0, std::ios::beg);
      filein.read(&contents[0], contents.size());
      filein.close();

      if(unixEOL)
      {
        static boost::regex eol("\\R"); // \R is Perl syntax for matching any EOL sequence
        contents = boost::regex_replace(contents, eol, "\n"); // converts all to LF
      }
      return contents;
    }

    /**
     * Create sha1 out of data and an optional header
     * @param data Contents as a string
     * @param header An optional string to prepend to the data
     */
    std::string createSHA1(const std::string & data, const std::string & header = "")
    {
      using Poco::DigestEngine;
      using Poco::SHA1Engine;
      using Poco::DigestOutputStream;

      SHA1Engine sha1;
      DigestOutputStream outstr(sha1);
      outstr << header << data;
      outstr.flush(); //to pass everything to the digest engine
      return DigestEngine::digestToHex(sha1.digest());
    }
  }


  /** Creates a SHA-1 checksum from a string
  * @param input The string to checksum
  * @returns a checksum string
  **/
  std::string sha1FromString(const std::string& input)
  {
    return ChecksumHelper::createSHA1(input);
  }

  /** Creates a SHA-1 checksum from a file
  * @param filepath The path to the file
  * @returns a checksum string
  **/
  std::string sha1FromFile(const std::string& filepath)
  {
    if(filepath.empty()) return "";
    return ChecksumHelper::createSHA1(loadFile(filepath));
  }

  /** Creates a git checksum from a file (these match the git hash-object command).
  * This works by reading in the file, converting all line endings into linux style endings,
  * then the following is prepended to the file contents "blob <content_length>\0",  
  * the result is then ran through a SHA-1 checksum.
  * @param filepath The path to the file
  * @returns a checksum string
  **/
  std::string gitSha1FromFile(const std::string& filepath)
  {
    if(filepath.empty()) return "";
    const bool unixEOL(true);
    std::string contents = loadFile(filepath, unixEOL);
    std::stringstream header;
    header << "blob " << contents.size() << '\0';
    return ChecksumHelper::createSHA1(contents, header.str());
  }
  
} // namespace ChecksumHelper
} // namespace Kernel
} // namespace Mantid