#!/bin/sh
# Bootstrap file for XDG_CONFIG_HOME
# by Case Duckworth <acdw@acdw.net>

### License:

# Everyone is permitted to do whatever with this software, without
# limitation.  This software comes without any warranty whatsoever,
# but with two pieces of advice:
# - Don't hurt yourself.
# - Make good choices.

### Commentary:

# For some time now, there has been a standard place to put configuration files
# for various programs: $XDG_CONFIG_HOME.  Slowly but surely, programs have
# been adapting to that standard for their configuration files, but there have
# been some stubborn holdouts.  Examples include shells such as sh, bash, and
# zsh.

# Luckily, the filesystem can help us.  This script takes input from a file in
# its $PWD, bootstrap.manifest, and reads linking directions from tab-delimited
# lines in that file.  Then, it creates links from within the cozy confines of
# $XDG_CONFIG_HOME to the wild west of ~, so that everyone is happy: you have
# your zen garden of configuration, and misbehaving programs have their bazaar.

### Code:

### Main entry point

main() {
	## Sanity checking
	# Since bootstrap.sh does some naive path-mangling, let's show an error
	# if it's not run correctly.  Yes, there are other ways to run a
	# script.  But this script should ideally be run, like, one time.  Also
	# you can obviously comment this out or change it if you know what
	# you're doing!

	case "$0" in
	./*) ;; # this is the way bootstrap.sh /should/ be run.
	*)
		printf >&2 'Weird invocation! %s\n' "$*"
		printf >&2 'Try: cd <bootstrap-dir>; ./bootstrap.sh\n'
		exit 127
		;;
	esac

	## Variables

	# option: -d/--dry-run
	: "${BOOTSTRAP_ACTION:=link}"
	# option: -v/--verbose
	: "${BOOTSTRAP_DEBUG:=false}"
	# option: -k/--keep-going
	: "${BOOTSTRAP_QUIT_ON_ERROR:=true}"
	# option: -m/--manifest FILE
	: "${BOOTSTRAP_MANIFEST_FILE:=bootstrap.manifest}"
	# option: -- (rest are passed to ln)
	: "${BOOTSTRAP_LN_ARGS:=-s}"

	## Handle command-line flags
	# Basically an easier way of setting the above variables.
	while [ -n "$1" ]; do
		case "$1" in
		-h | --help)
			cat >&2 <<END_HELP
Usage: ./bootstrap.sh [-d] [-v] [-k] [-m FILE] [-f] [-- LN_OPTS]
OPTIONS:
    -d, --dry-run
        Only print what would happen.
    -v, --verbose
        Be more verbose about things.
    -k, --keep-going
        Keep going after an error.
    -f, --force
        Force linking.  Passes -f to ln.
    -m FILE, --manifest FILE
        Use FILE as manifest.
        Default: bootstrap.manifest.
    --	Signify end of options.  The rest are passed to ln.
END_HELP
			exit
			;;
		-d | --dry-run)
			BOOTSTRAP_ACTION=print
			shift 1
			;;
		-v | --verbose)
			BOOTSTRAP_DEBUG=true
			shift 1
			;;
		-k | --keep-going)
			BOOTSTRAP_QUIT_ON_ERROR=false
			shift 1
			;;
		-m | --manifest)
			case "$2" in
			'' | -*)
				printf >&2 "Bad argument: '$2'"
				exit 129
				;;
			esac
			BOOTSTRAP_MANIFEST_FILE="$2"
			shift 2
			;;
		-f | --force)
			BOOTSTRAP_LN_ARGS="$BOOTSTRAP_LN_ARGS -f"
			shift 1
			;;
		--)
			shift 1
			BOOTSTRAP_LN_ARGS="$@"
			break
			;;
		esac
	done

	## Main loop
	while read -r source destination; do
		# Ignore lines beginning with '#'
		case "$source" in
		'#'*)
			if "$BOOTSTRAP_DEBUG"; then
				printf >&2 '%s %s\n' \
					"$source" "$destination"
			fi
			continue
			;;
		esac

		# Ignore empty lines, or lines with only SOURCE or DESTINATION
		if [ -z "$source" ] || [ -z "$destination" ]; then
			if "$BOOTSTRAP_DEBUG"; then
				printf >&2 'Skipping line: %s\t%s\n' \
					"$source" "$destination"
			fi
			continue
		fi

		# Do the thing
		if ! dispatch "$source" "$destination"; then
			printf >&2 'ERROR: %s -> %s\n' \
				"$source" "$destination"
			if "$BOOTSTRAP_QUIT_ON_ERROR"; then
				exit "$dispatch_error"
			fi
		fi
	done <"$BOOTSTRAP_MANIFEST_FILE"
}

### Functions

dispatch() { # dispatch SOURCE DESTINATION
	# Depending on environment variables, do the linking or displaying or
	# whatever of a source and a destination.

	## Variables

	src="$1"
	dest="$2"
	dispatch_error=0 # success

	## Sanitize pathnames

	# If the SOURCE starts with ~, /, or $, keep it as-is; otherwise,
	# prepend "$PWD/".
	case "$src" in
	'/'* | '~'* | '$'*) ;;
	*) src="$PWD/$src" ;;
	esac

	# Convert ~ to $HOME in SOURCE and DESTINATION, to get around shell
	# quoting rules.
	src="$(printf '%s\n' "$src" | sed "s#^~#$HOME#")"
	dest="$(printf '%s\n' "$dest" | sed "s#^~#$HOME#")"

	## Do the thing

	# /Always/ tell the user what we're doing.
	if [ -f "$dest" ]; then
		printf >&2 'mv %s %s.old\n' "$dest" "$dest"
	fi
	printf >&2 "ln %s %s %s\n" "$BOOTSTRAP_LN_ARGS" "$src" "$dest"

	case "$BOOTSTRAP_ACTION" in
	link) # actually ... do the links
		# if DESTINATION exists, move it to DESTINATION.old
		if [ -f "$dest" ]; then
			mv "$dest" "$dest.old"
		fi

		ln $BOOTSTRAP_LN_ARGS "$src" "$dest" ||
			dispatch_error="$?"
		;;
	print) ;; # already printed.
	esac

	return "$dispatch_error"
}

### Do the thing

main "$@"