#!/bin/bash

function unique_list_of_committers() {
	git log --format="%aN <%aE>" | sort -u
}

function change_author() {
	FROM_EMAIL=$1
	FROM_NAME=$2
	TO_EMAIL=$3
	TO_NAME=$4

	if [ -z "$FROM_EMAIL" ] || [ -z "$FROM_NAME" ] || [ -z "$TO_EMAIL" ] || [ -z "$TO_NAME" ]; then
		echo "usage: $0 <from-email> <from-name> <to-email> <to-name>"
		exit 1
	fi

	if [ "$FROM_EMAIL" == "$TO_EMAIL" ] && [ "$FROM_NAME" == "$TO_NAME" ]; then
		echo "usage: $0 <from-email> <from-name> <to-email> <to-name>"
		echo "from and to emails and names are the same"
		exit 1
	fi

	if [[ ! "$FROM_EMAIL" =~ ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ ]]; then
		echo "usage: $0 <from-email> <from-name> <to-email> <to-name>"
		echo "from email is not valid"
		exit 1
	fi

	if [[ ! "$TO_EMAIL" =~ ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ ]]; then
		echo "usage: $0 <from-email> <from-name> <to-email> <to-name>"
		echo "to email is not valid"
		exit 1
	fi

	git filter-branch -f --env-filter "GIT_COMMITTER_NAME='$FROM_NAME'; GIT_COMMITTER_EMAIL='$FROM_EMAIL'; GIT_AUTHOR_NAME='$TO_NAME'; GIT_AUTHOR_EMAIL='$TO_EMAIL';" HEAD;
}

printf 'listing unique committers before change:\n\n'
unique_list_of_committers

printf '\nchanging author..\n\n'
change_author "$@"

printf '\nlisting unique committers after change:\n\n';
unique_list_of_committers

# example usage:
# change-author.sh "from@mail.com" "to be changed" "to@mail.com" "change to"