/*
The software in this package is distributed under the GNU General
Public License version 2 (with a special exception described below).

A copy of GNU General Public License (GPL) is included in this distribution,
in the file COPYING.GPL.

As a special exception, if other files instantiate templates or use macros
or inline functions from this file, or you compile this file and link it
with other works to produce a work based on this file, this file
does not by itself cause the resulting work to be covered
by the GNU General Public License.

However the source code for this file must still be made available
in accordance with section (3) of the GNU General Public License.

This exception does not invalidate any other reasons why a work based
on this file might be covered by the GNU General Public License.
*/
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>

#include <fstream>
#include <stdexcept>

#include <boost/scoped_array.hpp>

#include "logread.hxx"

using namespace std;

/// Constructor
logread::logread(string filename, bool _goto_end)
{
    this->filename = filename;
    reset();

    if (_goto_end)
        goto_end();
}

/// Reset line state engine
void logread::reset()
{
    logsize = 0;
    logsize_old = 0;

    line.clear();
    line_complete = false;
}

/// Skip initial content. Useful when parsing /var/log/messages
void logread::goto_end()
{
    struct stat my_stat;
    if (stat(filename.c_str(), &my_stat) == 0) {
        logsize = my_stat.st_size;
        logsize_old = logsize;
    }
}

/// Main read loop
void logread::read()
{
    // check if size changed
    if (check_changed()) {
        if (logsize > logsize_old) {
            string logChanges = getLogChanges();

            do {
                extractSingeLine (logChanges);
                line_complete == true ? processLine() : processUnfinishedLine();
            } while (!logChanges.empty());
        } else
            reset();    // file got truncated

        logsize_old = logsize;
    }
}

/// Check if file is modified
bool logread::check_changed()
{
    bool changed = false;

    struct stat my_stat;
    if (stat(filename.c_str(), &my_stat) == 0
        && my_stat.st_size != logsize)
    {
        logsize = my_stat.st_size;
        changed = true;
    }

    return changed;
}

/// Get changed content since last read
string logread::getLogChanges()
{
    // open logfile
    ifstream log( filename.c_str(), ifstream::in );
    if ( !log.is_open() )
        return "";

    // read logfile
    int size = logsize-logsize_old;

    boost::scoped_array<char> read_buffer( new char[ size + 1 ] );
    log.seekg( logsize_old, fstream::beg );
    if ( log.rdstate() != fstream::goodbit )
        throw runtime_error("can't seek in file " + filename);
    log.read( read_buffer.get(), size );
    if ( log.rdstate() != fstream::goodbit )
        throw runtime_error("error reading from file " + filename);
    log.close();

    read_buffer[size] = 0;
    string changes( read_buffer.get() );

    return changes;
}

/// Extract a single line from input buffer
void logread::extractSingeLine(string &input)
{
    string::size_type rtn_pos, copysize;

    // go to next line
    if (line_complete) {
        line_complete = false;
        line.clear();
    }

    rtn_pos = input.find("\n", 0);

    // complete line or even multi-line
    if (rtn_pos != string::npos)
        copysize = rtn_pos;
    else
        copysize = input.length();

    line.append (input.c_str(), copysize);

    // Erase data from the input buffer
    if (rtn_pos == string::npos)    // no return found
        input.erase (0, copysize);
    else {
        // also erase the return
        input.erase (0, copysize+1);
        line_complete = true;
    }
}

/** Short example

#include <iostream>
class logread_syslog : public logread
{
public:
    logread_syslog() : logread("messages", false) {};

    void processLine()
    {
        cout << "finished: " << line << endl;
    }

    void processUnfinishedLine()
    {
        cout << "unfinished: " << line << endl;
    }
};

int main(void)
{
    logread_syslog messages;

    while (1) {
        messages.read();
        sleep(1);
    }

    return 0;
}
*/