#!/bin/sh

# hstow -- POSIX sh minimal reimplementation of GNU Stow for dotfiles
#
# Copyright (C) 2022-2023  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]*')"

. ~/src/dotfiles/lib-src/posix-defuns.sh

# readlink(1) is not POSIX, so we require an alternative.
# For simplicity, always use this even if readlink(1) is installed.
readlinks () {
    local restc=$1 assume="${2:-false}" first= rest=
    local fields_temp="$(mkstemp)" targets_temp="$(mkstemp)"
    # This first pipeline involves a safe parse of ls(1) output given
    # its POSIX specification.
    # We want the ninth field onwards in the output of ls(1) in awk's
    # sense -- i.e. collapsing runs of multiple blanks between the first
    # nine fields -- but we mustn't collapse blanks from there onwards.
    exec 3>&1
    while read -r first rest; do
	[ -n "$rest" ] && rest="$tab$rest"
	if $assume || [ -h "$first" ]; then
	    echo "$first"
	    echo "$first$rest" >>"$fields_temp"
	else
	    echo "$first$rest" >&3
	fi
    done \
	| awk '{ gsub(/"/, "\"'"'"'\"'"'"'\"")
		 printf "\"%s\"\n", $0 }' | xargs -E '' -- ls -ld \
	| sed -E 's/^([^[:blank:]]+[[:blank:]]+){8}//; /^\.$/d' \
	| sort -o "$targets_temp" # undo how ls(1) sorts non-dirs first
    sort -t"$tab" -k1 -o "$fields_temp" "$fields_temp"

    if [ "$(wc -l <"$fields_temp")" \
	     -ne "$(wc -l <"$targets_temp")" ]; then
	rm "$fields_temp" "$targets_temp"
	fail "line counts unequal; are there newlines in link targets?"
    fi

    # Only BREs have backreferences in POSIX.
    paste "$fields_temp" "$targets_temp" \
	| sed 's/^\([^\t]\{1,\}\)\t\('\
"$(printf "%${restc}s" | sed 's/ /[^\\t]\\{1,\\}\\t/g')"\
'\)\1 -> /\1\t\2/' \
	| awk -F'\t' 'NF == '$((2+$restc))' && $NF !~ /[\001-\037\177]/'

    rm "$fields_temp" "$targets_temp"
}

disjoin_file () {
    if [ -e "$DIR/$1" ]; then
	while read -r line; do
	    [ -n "$line" ] && printf "|$2" "$line"
	done <"$DIR/$1" | sed 's#^.##; s#/#\\/#g'
    fi
}

dir_contents () {
    ( cd "$1"; find . ! -name . ! -name "$cchars" -print -prune )
}

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="$(stow1)"
    [ -z "$conflicts" ] && return
    echo >&2 "hstow: encountered conflicts:"
    for conflict in $conflicts; do echo >&2 "  $conflict"; done
    exit 127
}

stow1 () {
    ignores="$(disjoin_file .hstow-local-ignore "./%s")"

    # 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.
    $always_adopt \
	&& adoptp=1 \
	|| adoptp="rel ~ /^($(disjoin_file .hstow-always-adopt "%s"))/"

    find . ! -name . ! -type d ! -name "$cchars" \
	 ! -name .gitignore \
	 ! -name .hstow-local-ignore \
	 ! -name .hstow-always-adopt \
	 ! -name .hstow-unstow-ignore \
	| awk -F'\n' -vOFS='\t' '! /^(\.\/\.git\/|'"$ignores"')/ \
{ rel = $1; gsub(/\/dot[-.]/, "/.", rel); gsub(/^\.\//, "", rel)
  dotdotslashes = rel
  sub(/[^\/]*$/, "", dotdotslashes)
  gsub(/[^\/]+/, "..", dotdotslashes)
  $2 = $1
  $3 = $1; sub(/\/[^/]+$/, "", $3)
  $1 = ENVIRON["HOME"] "/" rel
  $4 = '"$adoptp"' ? "true" : "false"
  $5 = dotdotslashes ".STOW/'"$NAME"'/" rel
  print
}' | readlinks 4 \
	| while read -r link file file_dir adopt target link_target; do
	if [ "$target" = "$link_target" ]; then
	    continue
	elif [ -z "$link_target" -a ! -h "$file" -a -f "$link" ]; then
	    if $adopt; then
		mv -f "$link" "$file"
		ln -s "$target" "$link"
	    else
		echo "$file"	# into $conflicts
	    fi
	elif [ -n "$link_target" ]; 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
}

unstow () {
    cd "$HOME"

    # For speed, skip directories into which we'll never stow anything.
    ignores="$(disjoin_file .hstow-unstow-ignore "./%s")"

    dir_pat=".$(echo $DIR | cut -c$(echo $HOME | wc -m | tr -d ' ')-)/"
    dirs_pat="$(echo "^($dir_pat|$ignores)" | sed -e 's#\.#\\.#g')"
    # awk's close() calls pclose(3), completing all the link deletions.
    # POSIX.1 "Utility Description Defaults", "Consequences of Errors"
    # implies that should rmdir(1) encounter a non-empty directory, it
    # should proceed to attempt to remove the next operand.
    # Thus, here, -p means that we do not need to sort the operands.
    # We don't know the code with which rmdir(1) will exit, and if it is
    # 255 then xargs will give up.  So we wrap in a call to sh -c.
    find . ! \( -user "$(id -un)" -o -group "$(id -gn)" \) \
	 -prune -o -type l ! -name . ! -name "$cchars" -print \
	| grep -Ev "$dirs_pat" | readlinks 0 true \
	| awk -F'\t' -vOFS='\t' '$2 ~ /^(\.\.\/)*\.STOW\/'"$NAME"'\// \
{ gsub(/"/, "\"'"'"'\"'"'"'\"", $1)
  printf "\"%s\"\n", $1 | "xargs -E '' -- rm -f"
  sub(/^.\//, "", $1)
  sub(/\/?[^/]+$/, "", $1)
  if ($1) dirs[++i] = $1
} END { close("xargs -E '' -- rm -f")
	for (d in dirs) printf "\"%s\"\n", dirs[d]
}' | xargs -E '' -- sh -c 'rmdir -p -- "$@" 2>/dev/null ||:' --

    [ -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