common

#!/bin/sh

# compares the contents of two files, returning 1 if they're different and nothing if identical
# $1: first file
# $2: second file
are_files_different() {
	if [ "$(file_hash "$1")" != "$(file_hash "$2")" ]; then
		echo 1
	fi
}

# checks whether git(1) is functional and offers to install it if missing
# $1: path to repository (optional)
# $2: name of Git client package to offer to install (optional)
check_git_client() {
	if [ ! "$(which git)" ]; then
		message=
		if [ -n "$1" ]; then
			message="$1 looks like a Git repository, but "
		fi
		echo -e "\n${message}git(1) is not installed."
		if [ -z "$2" ]; then
			return 1
		else
			if [ ! "$(which pkg)" ]; then
				return 1
			fi
			prompt_Yn "Install package \`$GIT_CLIENT_PACKAGE\`?"
			if [ $(confirm) ]; then
				pkg install "$GIT_CLIENT_PACKAGE" || return 1
			else
				return 1
			fi
		fi
	fi
}

# checks whether svnlite(1) is functional
# $1: path to repository (optional)
check_subversion_client() {
	if [ ! "$(which svnlite)" ]; then
		message=
		if [ -n "$1" ]; then
			message="$1 looks like a Subversion repository, but "
		fi
		echo -e "\n${message}svnlite(1) is not installed."
		return 1
	fi
}

# reads yes/no confirmation input, returning 1 for yes and nothing for no
# $1: default response: 'Y' or 'y' for yes, 'N' or 'n' for no (optional; defaults to yes)
confirm() {
	selection="$(input '[nNyY]|$')"
	case "$selection" in
		N|n)	;;
		Y|y)	echo 1;;
		*)		case "$1" in
					N|n)	;;
					*)		echo 1;
				esac
	esac
}

# returns the console's current number of columns
console_width() {
	tput cols
}

# escapes any special characters in the given string for safe use in a regular expression
# $1: string to be escaped
escape_for_regexp() {
	echo "$1" | sed -e 's/([/.])/\\\1/g' -r
}

# returns the hash of the given file, or nothing if the file doesn't exist
# $1: path of file to hash
file_hash() {
	if [ -f "$1" ]; then
		sha256 -q "$1"
	fi
}

# returns the file name (if any) from the end of the given path
# $1: path from which to extract the file name
file_name_from_path() {
	echo "$1" | sed -e 's/([^/]*\/)*(.*)/\2/' -r
}

# prints the given string inside a terminal-wide header
# $1: string
header() {
	columns=$(console_width)
	repeat '=' "$((columns - 1))"
	echo -e "\n$1"
	repeat '=' "$((columns - 1))"
}

# reads console input until it matches the given regular expression (whole-line match)
# $1: regular expression against which to match input
input() {
	until [ ]; do
		read input
		is_match "$input" "$1" && break
	done
}

# interactively merges two given files, saving the result to the latter
# $1: origin file path
# $2: destination file path
interactively_merge_files() {
	destination_file_path="$2"
	merged_file_path="${2}.merged"
	origin_file_path="$1"

	echo
	sdiff -dsw "$(console_width)" -o "$merged_file_path" \
			"$origin_file_path" "$destination_file_path"
	if [ -s "$merged_file_path" -a $(are_files_different "$destination_file_path" \
			"$merged_file_path") ]; then
		header 'Beginning of resulting merged file'
		echo -e '\n'
		less --QUIT-AT-EOF "$merged_file_path"
		echo
		header 'End of resulting merged file'
		echo
		prompt_Yn "Write to ${destination_file_path}?"
		if [ $(confirm) ]; then
			mv -v "$merged_file_path" "$destination_file_path"
		else
			echo '    Changes discarded.'
		fi
	else
		echo '    No changes made.'
	fi
	rm "$merged_file_path" 2> /dev/null
}

# determines whether the given string matches the given regular expression (whole-line match)
# $1: string to test
# $2: regular expression against which to match
is_match() {
	echo "$1" | egrep --line-regexp "$2"
}

# prompts for input
# $1: prompt text
prompt() {
	if [ -n "$1" ]; then
		echo
		echo -n ">>> $(echo -e "$1") "
	fi
}

# prompts for yes/no confirmation, with yes as the default
# $1: prompt text
prompt_Yn() {
	if [ -n "$1" ]; then
		prompt "$1"
		echo -n '[Y/n] '
	fi
}

# prompts for yes/no confirmation, with no as the default
# $1: prompt text
prompt_yN() {
	if [ -n "$1" ]; then
		prompt "$1"
		echo -n '[y/N] '
	fi
}

# repeats the given string a certain number of times
# $1: string to repeat
# $2: number of repetitions
repeat() {
	i=0
	until [ $i -eq "$2" ]; do
		echo -n "$1"
		i="$(($i + 1))"
	done
}

# strips the given path or file name of its rightmost file name extension, if any
# $1: file name or path
strip_extension() {
	echo "${1%[.-]?*}"
}

# strips the last component (file name or directory) from the given path
# $1: path whose last component is to be stripped
strip_last_path_component() {
	echo "${1%/}" | sed -e 's/(.+\/)([^/]*)/\1/' -r
}

# strips the given path or file name of its file name prefix, if any
# $1: file name or path
# $2: a regular expression of one or more prefixes to strip out
strip_prefixes() {
	echo "$1" | sed -e "s/(^|.*\/)$2/\1/" -r
}

# merges differences between two files (e.g. old and new versions of a sample configuration file)
# into a third file (e.g. a locally modified copy), first attempting an automatic merge and falling
# back to interactive if that fails
# $1: path to origin file to be compared to $2
# $2: path to origin file to be compared to $1
# $3: path to destination file into which to merge differences between $1 and $2
# returns 0 if no differences were encountered, or 1 if any were
three_way_merge_files() {
	differences_found=
	need_interaction=1
	# if both origin files exist and differ, automatically merge differences into destination file
	if [ -f "$1" -a -f "$2" ]; then
		if [ ! $(are_files_different "$1" "$2") ]; then
			need_interaction=
		else
			differences_found=1
			prompt_Yn "$2 differs from $1. Attempt to automatically merge the differences into $3?"
			if [ $(confirm) ]; then
				diff --minimal --unified "$1" "$2" | patch -N -r /dev/null -s "$3" > /dev/null
				if [ $? -eq 0 ]; then
					echo '    [√] Differences successfully merged.'
					rm "$3.orig"
					need_interaction=
				else
					if [ $(are_files_different "$3.orig" "$3") ]; then
						echo -e '    [-] Only some changes applied cleanly:\n'
						diff --minimal --unified "$3.orig" "$3" | less --QUIT-AT-EOF
					else
						echo '    [X] All changes failed to apply.'
					fi
				fi
			fi
		fi
	fi
	# if automatic merging failed or only partially succeeded, offer to interactively merge any
	# remaining changes
	if [ $need_interaction ]; then
		differences_found=1
		prompt_Yn "Interactively merge $2 and $3?"
		if [ $(confirm) ]; then
			interactively_merge_files "$2" "$3"
		fi
	fi
	return $differences_found
}