Estimates how much time a project has taken according to the commit timeline.

git-estimate.sh

#!/usr/bin/env sh
# shellcheck disable=SC2214
#
# A POSIX-compliant shell script that estimates the number of hours taken to
# create the contents of a Git repository. The heuristic is based on grouping
# bundles of commits according to a certain period limit, accumulating time
# differences between pairs of commits in each bundle, and compensating for its
# first commit with another parametrized quantity. Timestamps are taken from
# the author of the commit.
#
# It accepts three options to customize its behavior, described as follows. The
# last argument must be a valid Git folder, with the current folder as default.
#
#   -f,  --first-delay=<amount>
#           Consider that the first commit of each bundle took <amount> seconds
#           to create. The default value is 1800, i.e. half an hour. Note that
#           this must be smaller or equal than the amount set by -g, such that
#           the bundles do not overlap.
#
#   -g,  --group-period=<amount>
#           Create a new bundle of commits when the difference between two
#           timestamps is greater than <amount> seconds. The default value is
#           7200, or two hours.
#
#   -p,  --pass-options=<options>
#           Pass options to git-log(1). Suggested options are
#           --author/--committer, --since/--until, --no-merges etc.
#
# Parsing of long options is adapted from https://stackoverflow.com/a/28466267.

FIRST_DELAY=1800
GROUP_TIME=7200
OTHER_OPT="--"

while getopts f:g:p:-: OPT ; do
  if [ "$OPT" = "-" ] ; then
    OPT="${OPTARG%%=*}"
    OPTARG="${OPTARG#$OPT}"
    OPTARG="${OPTARG#=}"
  fi
  case "$OPT" in
    f | first-delay ) FIRST_DELAY="${OPTARG:-$FIRST_DELAY}" ;;
    g | group-period ) GROUP_TIME="${OPTARG:-$GROUP_TIME}" ;;
    p | pass-options ) OTHER_OPT="${OPTARG:-$OTHER_OPT}" ;;
    ??* ) exit 1 ;;
    \? ) exit 2 ;;
  esac
done

shift $((OPTIND - 1))
FOLDER="${1:-.}"

: $((DIFF=GROUP_TIME - FIRST_DELAY))
if [ ! -d "${FOLDER}/.git" ] || [ $((DIFF)) -lt 0 ] ; then
  cat <<-EOF
Usage: sh ${0##*/} [options] [folder]
  -f,  --first-delay=<seconds>
  -g,  --group-period=<seconds>
  -p,  --pass-options=<options>
EOF
exit 1
fi

git -C "$FOLDER" log --format="%at" "$OTHER_OPT" | sort \
  | awk -v first="$FIRST_DELAY" -v threshold="$GROUP_TIME" '
  {
    diff = $0 - prev;
    spent += (diff > threshold) ? first : diff;
    prev = $0;
  }
  END { print spent / 3600 }'