#!/bin/sh

# hstow -- POSIX sh minimal reimplementation of GNU Stow for dotfiles
#
# Copyright (C) 2022  Sean Whitton <spwhitton@spwhitton.name>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or (at
# your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# The point of this script is to obtain minimally functional dotfiles
# handling in one's home directory on even machines that lack a Perl
# interpreter.  As such, many of GNU Stow's more advanced features are
# not reimplemented.  Git depends on Perl, for now, but my two methods
# for deploying my dotfiles to remote machines -- my INSINUATE-DOTFILES
# Consfigurator property and 'insinuate-dotfiles' shell script -- do not
# depend on having Git on the remote side.  See also 'bstraph' script.
#
# We completely skip filenames containing control characters, including
# newline and tab, as POSIX find(1) lacks -print0, and it's unlikely
# you'd need to stow any such files.
# Technique from <https://dwheeler.com/essays/filenames-in-shell.html>.

set -efu
IFS="$(printf '\n\t')"
export LC_ALL=C
tab="$(printf '\t')"
cchars="$(printf '*[\001-\037\177]*')"

if ! command -v readlink >/dev/null; then
    readlink () {
	# Safe parse of ls(1) output given its POSIX specification.
	ls -ld "$1" | tr -s ' ' \
	    | cut -d' ' -f9- | cut -c$((4 + $(echo "$1" | wc -m)))-
    }
fi

read_globs_file () {
    if [ -e "$DIR/$1" ]; then
	while read -r line; do
	    printf "|./%s" "$line"
	done <"$DIR/$1" | cut -c2-
    fi
}

dir_contents () {
    ( cd "$1"; find . ! -name . ! -name "$cchars" 2>/dev/null )
}

fail () {
    echo >&2 "hstow: $*"
    exit 127
}

usage () {
    fail "usage: hstow stow|unstow|restow|adopt DIRECTORY"
}

stow () {
    cd "$DIR"
    [ -d "$HOME/.STOW" ] || mkdir "$HOME/.STOW"
    [ -f "$HOME/.STOW/.stow" ] || touch "$HOME/.STOW/.stow"
    [ -h "$HOME/.STOW/$NAME" ] \
	|| ( cd "$HOME/.STOW"; ln -s "$DIR" "$NAME" )
    conflicts=
    ignores="$(read_globs_file .hstow-local-ignore)"

    # Files that (i) always/often have their symlinks replaced with
    # regular files when applications access them; and (ii) we don't
    # ever want to edit the copy under $DIR directly, but only via the
    # link/copy under $HOME.
    $always_adopt || adoptions="$(read_globs_file .hstow-always-adopt)"

    for file in $(find . ! -name . ! -type d ! -name "$cchars" \
		       ! -name .gitignore \
		       ! -name .hstow-local-ignore \
		       ! -name .hstow-always-adopt \
		      | grep -v '^\./\.git/'); do
	file_dir="$(dirname $file)"
	if [ -n "$ignores" ]; then
	    eval case "'$file'"     in "${ignores})" continue ";;" esac
	    eval case "'$file_dir'" in "${ignores})" continue ";;" esac
	fi

	rel="$(echo $file|sed -E 's#/dot[-.]([^/]+)#/.\1#g; s#^\./##')"
	dotdotslashes="$(echo $rel|sed -E 's#[^/]*$##; s#[^/]+#..#g')"
	target="${dotdotslashes}.STOW/$NAME/$rel"
	link="$HOME/$rel"
	link_target=
	[ -h "$link" ] && link_target="$(readlink $link)"

	[ "$target" = "$link_target" ] && continue

	if [ ! -h "$link" -a ! -h "$file" -a -f "$link" ]; then
	    if $always_adopt \
		    || ( [ -n "$adoptions" ] \
			     && eval case "'$file'" in \
				     "${adoptions})" exit 0 ";;" \
				     "*)"            exit 1 ";;" \
				     esac ); then
		mv -f "$link" "$file"
		ln -s "$target" "$link"
	    else
		conflicts="$conflicts${tab}$file"
	    fi
	elif [ -h "$link" ]; then
	    # With at least GNU ln(1), passing -f, but not also -T, does
	    # not replace an existing link in some cases.
	    # -T is not POSIX, so we remove any existing link first.
	    rm "$link"
	    ln -s "$target" "$link"
	else
	    mkdir -p "$HOME/$file_dir"
	    ln -s "$target" "$link"
	fi
    done
    [ -z "$conflicts" ] && return
    echo >&2 "hstow: encountered conflicts:"
    for conflict in $conflicts; do echo >&2 "  $conflict"; done
    exit 127
}

unstow () {
    cd "$HOME"

    # For speed, skip directories into which we'll never stow anything.
    ignores="$([ -e "$DIR/.hstow-unstow-ignore" ] || exit 0
    	       while read -r line; do
	           printf "|./%s/" "$line"
	       done <"$DIR/.hstow-unstow-ignore")"

    dir_pat=".$(echo $DIR | cut -c$(echo $HOME | wc -m | tr -d ' ')-)/"
    dirs_pat="$(echo "^($dir_pat$ignores)" | sed -e 's#\.#\\.#g')"
    for file in $(find . -type l ! -name . ! -name "$cchars" 2>/dev/null \
		      | grep -Ev "$dirs_pat"); do
	if readlink "$file" | grep -Eq '^(\.\./)*\.STOW/'"$NAME/"; then
	    rm "$file"
	    while true; do
		file="$(dirname $file)"
		[ "$file" = . ] && break
		if [ -z "$(dir_contents $file)" ]; then
		    rmdir "$file"
		else
		    break
		fi
	    done
	fi
    done
    [ -e "$HOME/.STOW/$NAME" ] && rm "$HOME/.STOW/$NAME"
    if [ -d "$HOME/.STOW" ] \
	   && [ "$(dir_contents $HOME/.STOW)" = "./.stow" ]; then
	rm "$HOME/.STOW/.stow"
	rmdir "$HOME/.STOW"
    fi
}

[ $# = 2 ] || usage
[ -d "$2" ] || fail "$2 is not an existing directory"
DIR="$(cd $2; pwd)"
[ "$(echo $DIR | cut -c-$(($(echo $HOME | wc -m) - 1)))" = "$HOME" ] \
    || fail "$DIR is not below $HOME"

NAME="$(echo $DIR | tr / _)"
always_adopt=false
case "$1" in
    'stow')   stow			;;
    'unstow') unstow			;;
    'restow') unstow; stow		;;
    'adopt')  always_adopt=true; stow	;;
    *)        usage                     ;;
esac