#!/usr/bin/env python3
#
# Copyright 2015 Ville Rantanen
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published
# by the Free Software Foundation, either version 3 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 Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#

'''simple tail for tsv/csv files.'''
from __future__ import print_function

__author__ = "Ville Rantanen <ville.q.rantanen@gmail.com>"

__version__ = "0.1"

import sys,os,argparse
from argparse import ArgumentParser

def setup_options():
    ''' Create command line options '''
    usage='''
simple implementation of tail, keeping the header row

'''

    parser=ArgumentParser(description=usage,
                          formatter_class=argparse.RawDescriptionHelpFormatter,
                          epilog="\n".join(["Version: "+__version__,__author__]))
    common_group=parser.add_argument_group('common', 'Common options')
    common_group.add_argument("-v","--version",action="version",version=__version__)
    common_group.add_argument("-n",type=str,dest="lines",default=False,
                     help="Lines to show from end of file. +K to start output from the Kth. Default: 10")
    parser.add_argument("file",type=str, nargs='*',
                     help="File(s) to be headed")
    opts=parser.parse_args()
    if not opts.lines:
        try:
            int(opts.file[0])
            opts.lines=opts.file.pop(0)
        except:
            pass
    if not opts.lines:
        opts.lines="10"
    if opts.lines.startswith("+"):
        opts.lines=-int(opts.lines)
    else:
        opts.lines=int(opts.lines)
    return opts

def tail(fileob,opts):

    header=fileob.readline()
    sys.stdout.write(header)
    if opts.lines>=0:
        tail_ordinary(fileob, opts.lines)
    else:
        tail_allbutfirst(fileob, -opts.lines)

def tail_allbutfirst(fileob, lines):
    for i,row in enumerate(fileob):
        if i<lines-1:
            continue
        sys.stdout.write(row)

def tail_ordinary(fileob, lines):
    buf=[]
    for row in fileob:
        buf.append(row)
        if len(buf)>lines:
            buf.pop(0)
    [sys.stdout.write(l) for l in buf]

def main():
    opts=setup_options()
    try:
        if (not sys.stdin.isatty()):
            tail(sys.stdin, opts)
        for fi in opts.file:
            tail(open(fi,'r'), opts)
    except IOError as xxx_todo_changeme:
        (n,e) = xxx_todo_changeme.args
        if  n==32:
            pass
        else:
            import traceback
            print(traceback.format_exc())
    except KeyboardInterrupt:
        pass

if __name__ == "__main__":
    main()