#! /bin/bash

max_abbrev=12

scale=10

total=`git rev-list --all | wc -l`

echo "Conflicts:"

echo "Format:   [abbrev length]: number of conflicts / total number of refs (percentage conflicts)"

for ((x = 1 ; x <= ${max_abbrev} ; x++)) ; do

    conflicts=`git rev-list --all --abbrev=$x --abbrev-commit | sort | uniq -D -w$x | wc -l`

    percent=`echo "scale=$scale ; 100 * $conflicts / $total" | bc | awk '{ printf("%1.2f\n", $0); }'`

    echo "    [$x]: $conflicts / $total ($percent %)"

    if test "$conflicts" = "0" ; then break ; fi

done

##

## probability calculation is based on this random link, that I found

## online:

## http://blog.cuviper.com/2013/11/10/how-short-can-git-abbreviate/

##

## I have not verified the accuracy of the calculation at that link,

## but if it is online, it must be true, of course. ;-)

##

min_abbrev=$x

echo

echo "Probability of collision on your next commit:"

echo "Format:   [abbrev length]: probability of collision"

for ((x = ${min_abbrev}; x <= ${max_abbrev} ; x++)) ; do

    percent=`echo "scale=$scale ; 100 * ($total) / (16 ^ $x)" | bc | awk '{ printf("%1.4f\n", $0); }'`

    echo "    [$x]: $percent %"

done

commits_last_year=`git rev-list --all --since="1 year ago" | wc -l`

echo

echo "Probability of collision in the next year (based on commits last year):"

echo "Format:   [abbrev length]: probability of collision"

for ((x = ${min_abbrev}; x <= ${max_abbrev} ; x++)) ; do

    percent=`echo "scale=$scale ; 100 * (1 - ((1 - ($total / (16 ^ $x))) ^ ${commits_last_year}))" | bc | awk '{ printf("%1.4f\n", $0); }'`

    echo "    [$x]: $percent %"

done