#!/bin/sh

# Copyright 2010, The Regents of The University of Michigan, All Rights Reserved
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Diffs two text files code blocks.
#
# Bryan Smith - bryanesmith@gmail.com
# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

usage() {
  cat <<MYUSAGE

USAGE 
  bdiff.sh [file] [line start] [line end] [file] [line start] [line end]

DESCRIPTION
  Compares two text file regions specified by line numbers.

EXAMPLES

  bdiff.sh file1 3 23 file2 7 27
    This will diff lines 3-23 in file1 with lines 7-27 in file2

  bdiff.sh file1 file2 7 27
    This will fail with exit code of 1 since all parameters are
    required!

EXIT CODES
  0: Exitted normally
  1: Wrong number of arguments
  2: File not found
  3: Temporary file already exists

MYUSAGE

}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
error() {
    if [ "$#" -eq "2" ]; then
        echo
        echo "ERROR: $2"
    fi

    usage

    exit $1
}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
assertexists() {
  if [ ! -e $1 ]; then
    error 2 "Error: $1 not found"
  fi 
}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
checktempfileexists() {
  if [ -e $1 ]; then
    error 3 "Temporary file ($1) already exists. I'm being super safe, so please move this file so I can do my job. (I don't want to clobber your files.)"
  fi
}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
printportion() {
  awk "NR>=${2}&&NR<=${3}" "$1" > $4
}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# Main execution

if [ "$#" -ne 6 ]; then
  error 1 "Error: Wrong number of arguments. Expected 6, but found: $#"
fi

# ~ Grab parameters ~
file1=$1
start1=$2
end1=$3

file2=$4
start2=$5
end2=$6

# ~ Check parameters ~
assertexists $file1
assertexists $file2

# ~ Copy text regions to temp files and diff ~
Temp1=".bdiff1"
Temp2=".bdiff2"

checktempfileexists $Temp1
checktempfileexists $Temp2

printportion "$file1" $start1 $end1 $Temp1
printportion "$file2" $start2 $end2 $Temp2

diff --ignore-all-space --ignore-blank-lines $Temp1 $Temp2

# ~ Clean up ~
rm $Temp1
rm $Temp2