#!/bin/sh
# Default Terminal Execution Utility
# Reference implementation of proposed Default Terminal Execution Specification
# https://gitlab.freedesktop.org/terminal-wg/specifications/-/merge_requests/3
#
# by Vladimir Kudrya
# https://github.com/Vladimir-csp/
# https://gitlab.freedesktop.org/Vladimir-csp/
#
# This script 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. See <http://www.gnu.org/licenses/>.
#
# Contributors:
# Roman Chistokhodov    https://github.com/FreeSlave/
# fluvf                 https://github.com/fluvf

# Treat non-zero exit status from simple commands as an error
# Treat unset variables as errors when performing parameter expansion
# Disable pathname expansion
set -euf

# Store original IFS value, assumed to contain the default: <space><tab><newline>
OIFS="$IFS"
# Newline, utility variable used throughout the script
N='
'

# name of executable
SELF_NAME=${0##*/}

# ASCII Record Separator for cache saving
RSEP=$(printf '%b' '\036')

# ASCII Unit Separator for Exec parsing
USEP=$(printf '%b' '\037')

error() {
	# Print messages to stderr
	printf '%s\n' "$@" >&2
}

check_bool() {
	case "$1" in
	true | True | TRUE | yes | Yes | YES | 1) return 0 ;;
	false | False | FALSE | no | No | NO | 0) return 1 ;;
	*)
		error "Assuming '$1' means no"
		return 1
		;;
	esac
}

# Utility function to print debug messages to stderr (or not)
if check_bool "${DEBUG-0}"; then
	debug() { printf 'D: %s\n' "$@" >&2; }
else
	debug() { :; }
fi

# Populates global constants and lists for later use and iteration
make_paths() {
	IFS=':'

	# Populate list of config files to read, in descending order of preference
	for dir in ${XDG_CONFIG_HOME:-"${HOME}/.config"}${IFS}${XDG_CONFIG_DIRS:-/etc/xdg}; do
		# Normalise base path and append the data subdirectory with a trailing '/'
		for desktop in ${LOWERCASE_XDG_CURRENT_DESKTOP}; do
			CONFIGS=${CONFIGS:+${CONFIGS}${IFS}}${dir%/}/${desktop}-xdg-terminals.list
		done
		CONFIGS=${CONFIGS:+${CONFIGS}${IFS}}${dir%/}/xdg-terminals.list
	done

	# append xdg-terminal-exec dirs in XDG_DATA_DIRS to config hierarchy for distro/upstream level defaults
	for dir in ${XDG_DATA_DIRS:-/usr/local/share:/usr/share}; do
		# Normalise base path and append the data subdirectory with a trailing '/'
		for desktop in ${LOWERCASE_XDG_CURRENT_DESKTOP}; do
			CONFIGS=${CONFIGS:+${CONFIGS}${IFS}}${dir%/}/xdg-terminal-exec/${desktop}-xdg-terminals.list
		done
		CONFIGS=${CONFIGS:+${CONFIGS}${IFS}}${dir%/}/xdg-terminal-exec/xdg-terminals.list
	done

	# Populate list of directories to search for entries in, in ascending order of preference
	for dir in ${XDG_DATA_HOME:-${HOME}/.local/share}${IFS}${XDG_DATA_DIRS:-/usr/local/share:/usr/share}; do
		# Normalise base path and append the data subdirectory with a trailing '/'
		APPLICATIONS_DIRS=${dir%/}/applications/${APPLICATIONS_DIRS:+${IFS}${APPLICATIONS_DIRS}}
	done

	# cache
	XDG_CACHE_HOME=${XDG_CACHE_HOME:-"${HOME}/.cache"}
	CACHE_FILE="${XDG_CACHE_HOME}/xdg-terminal-exec"

	debug "paths:" "CONFIGS=${CONFIGS}" "APPLICATIONS_DIRS=${APPLICATIONS_DIRS}"
}
# Mask IFS withing function to allow temporary changes
alias make_paths='IFS= make_paths'

gen_hash() {
	# return md5 of custom string, XDG_CURRENT_DESKTOP and ls -LRl output for config and data paths
	# md5 is 4x faster than sha*, and there is no need for cryptography here
	# shellcheck disable=SC2034
	read -r hash _drop <<- EOH
		$(
			hash_paths="${CONFIGS}:${APPLICATIONS_DIRS}"
			{
				# cache 'version', change to invalidate when format changes
				echo 3
				echo "${XDG_CURRENT_DESKTOP-}"
				IFS=':'
				# shellcheck disable=SC2086
				debug ">     hashing '${XDG_CURRENT_DESKTOP-}' and listing of:" $hash_paths "^     end of hash listing"
				# shellcheck disable=SC2012,SC2086
				LANG=C ls -LRl ${hash_paths} 2> /dev/null
			} | md5sum 2> /dev/null
		)
	EOH
	case "$hash" in
	[0-9a-f]??????????????????????????????[0-9a-f])
		debug "got fresh hash '$hash'"
		echo "$hash"
		return 0
		;;
	*)
		debug "failed to get fresh hash, got '$hash'"
		return 1
		;;
	esac
}

read_cache() {
	# reads $cached_hash, $cached_cmd, $cached_exec_usep, $cached_execarg, and others from cache file,
	# checks if cache is actual and applies it, otherwise returns 1
	# tries to bail out as soon as possible if something does not fit
	if [ -f "${CACHE_FILE}" ]; then
		line_num=0
		line_limit=50
		cached_exec_usep=
		finished=0
		while IFS='' read -r line; do
			line_num=$((line_num + 1))
			case "${line_num}" in
			1) cached_hash=$line ;;
			2) cached_cmd=$line ;;
			3) cached_execarg=$line ;;
			4) cached_appidarg=$line ;;
			5) cached_titlearg=$line ;;
			6) cached_dirarg=$line ;;
			7) cached_holdarg=$line ;;
			"$line_limit")
				debug "reached cache line limit ($line_limit)"
				return 1
				;;
			# Line 8 starts command
			*)
				# Command is stored as raw expanded and tokenized $USEP-separated command,
				# technically it can contain newline characters.
				# Reconstruct newlines, use ${RSEP}END_OF_EXEC_USEP string as terminator.
				cached_exec_usep=${cached_exec_usep}${cached_exec_usep:+$N}${line}
				case "${line}" in
				*"${RSEP}END_OF_EXEC_USEP")
					cached_exec_usep=${cached_exec_usep%"${RSEP}END_OF_EXEC_USEP"}
					finished=1
					break
					;;
				esac
				;;
			esac
		done < "${CACHE_FILE}"
		if [ "$finished" = "1" ]; then
			debug "got cache:" \
				"hash=${cached_hash}" \
				"cmd=${cached_cmd}" \
				"execarg=${cached_execarg}" \
				"appidarg=${cached_appidarg}" \
				"titlearg=${cached_titlearg}" \
				"dirarg=${cached_dirarg}" \
				"holdarg=${cached_holdarg}" \
				"exec_usep=${cached_exec_usep}"
			HASH=$(gen_hash) || return 1
			if [ "$HASH" = "$cached_hash" ] && command -v "$cached_cmd" > /dev/null; then
				debug "cache is actual"
				EXEC_USEP=${cached_exec_usep}
				EXECARG=${cached_execarg}
				APPIDARG=${cached_appidarg}
				TITLEARG=${cached_titlearg}
				DIRARG=${cached_dirarg}
				HOLDARG=${cached_holdarg}
				return 0
			else
				debug "cache is out-of-date"
				return 1
			fi
		else
			debug "invalid cache data"
			return 1
		fi
	else
		debug "no cache data"
		return 1
	fi
}

save_cache() {
	# saves $HASH, $1 (executable), $EXEC_USEP, $EXECARG, other supported args to cache file or removes it if CACHE_ENABLED is false
	if check_bool "$CACHE_ENABLED"; then
		[ ! -d "${XDG_CACHE_HOME}" ] && mkdir -p "${XDG_CACHE_HOME}"
		if [ -z "${HASH-}" ]; then
			HASH=$(gen_hash) || {
				error "could not hash listing of files, removing '${CACHE_FILE}'"
				rm -f "${CACHE_FILE}"
				return 0
			}
		fi
		case "${HASH}${1}${EXECARG}${APPIDARG}${TITLEARG}${DIRARG}${HOLDARG}" in
		"$N")
			error "One or more of terminal's arguments contains a newline, removing '${CACHE_FILE}'"
			rm -f "${CACHE_FILE}"
			return 0
			;;
		esac
		UM=$(umask)
		umask 0077
		printf '%s\n' \
			"${HASH}" \
			"${1}" \
			"${EXECARG}" \
			"${APPIDARG}" \
			"${TITLEARG}" \
			"${DIRARG}" \
			"${HOLDARG}" \
			"${EXEC_USEP}${RSEP}END_OF_EXEC_USEP" > "${CACHE_FILE}"
		umask "$UM"
		debug ">     saved cache:" "${HASH}" "${EXEC_USEP}" "${EXECARG}" "${1}" "^     end of saved cache"
	else
		debug "cache is disabled, removing '${CACHE_FILE}'"
		rm -f "${CACHE_FILE}"
		return 0
	fi
}

list_contains() {
	# checks if list $1 contains item $2 delimited by $3 (default $N)
	delimiter=${3:-$N}
	case "${delimiter}${1}${delimiter}" in
	*"${delimiter}${2}${delimiter}"*) return 0 ;;
	*) return 1 ;;
	esac
}

# Parse all config files and populate $ENTRY_IDS with read desktop entry IDs
read_config_paths() {
	# All config files are read immediatelly, rather than on demand, even if it's more IO intensive
	# This way all IDs are already known, and in order of preference, before iterating over them
	IFS=':'
	for config_path in ${CONFIGS}; do
		debug "reading config '$config_path'"
		# Nonexistant file is not an error
		[ -f "$config_path" ] || continue
		# Let `read` trim leading/trailing whitespace from the line
		while IFS="$OIFS" read -r line; do
			#debug "read line '$line'"
			case $line in

			# Catch directives first

			# cache control
			/enable_cache)
				debug "found '$line' directive${CACHE_CONFIGURED:+ (ignored)}"
				[ -z "$CACHE_CONFIGURED" ] || continue
				CACHE_ENABLED=true
				CACHE_CONFIGURED=1
				;;
			/disable_cache)
				debug "found '$line' directive${CACHE_CONFIGURED:+ (ignored)}"
				[ -z "$CACHE_CONFIGURED" ] || continue
				CACHE_ENABLED=false
				CACHE_CONFIGURED=1
				;;

			# compat mode
			/execarg_compat)
				debug "found '$line' directive${EXECARG_COMPAT_CONFIGURED:+ (ignored)}"
				[ -z "$EXECARG_COMPAT_CONFIGURED" ] || continue
				EXECARG_COMPAT=true
				EXECARG_COMPAT_CONFIGURED=1
				;;
			/execarg_strict)
				debug "found '$line' directive${EXECARG_COMPAT_CONFIGURED:+ (ignored)}"
				[ -z "$EXECARG_COMPAT_CONFIGURED" ] || continue
				EXECARG_COMPAT=false
				EXECARG_COMPAT_CONFIGURED=1
				;;

			# default TerminalArgExec overrides
			/execarg_default:*:*)
				if ! check_bool "$EXECARG_COMPAT"; then
					debug "ignored directive '$line' (strict mode)"
					continue
				fi
				IFS=':' read -r _directive entry_id execarg_default <<- EOF
					$line
				EOF
				if validate_entry_id "${entry_id}"; then
					debug "added TerminalArgExec default '${execarg_default}' for '${entry_id}'"
					# do not bother with deduplication, first entry ID will win
					EXECARG_DEFAULTS=${EXECARG_DEFAULTS}${EXECARG_DEFAULTS:+$N}${entry_id}:${execarg_default}
				fi
				;;

			# `[The extensionless entry filename] should be a valid D-Bus well-known name.`
			# `a sequence of non-empty elements separated by dots (U+002E FULL STOP),
			# none of which starts with a digit, and each of which contains only characters from the set [a-zA-Z0-9-_]`
			# Stricter parts seem to be related only to reversed DNS notation but not common naming
			# i.e. there is `2048-qt.desktop`.
			# I do not know of any terminal that starts with a number, but it's valid.

			# Catch and validate potential entry ID with action ID (be graceful about an empty one)
			[a-zA-Z0-9_]* | [+-][a-zA-Z0-9_]*)
				case "$line" in
				[+-]*)
					# save and cut exclusion marker
					_line=${line#[+-]}
					exclusion=${line%"$_line"}
					line=$_line
					;;
				*) exclusion='' ;;
				esac
				# consider only the first ':' as a delimiter
				IFS=':' read -r entry_id action_id <<- EOL
					$line
				EOL
				if validate_entry_id "${entry_id}" && validate_action_id "${action_id}"; then
					case "$exclusion" in
					'')
						ENTRY_IDS=${ENTRY_IDS:+${ENTRY_IDS}${N}}$line
						debug "added entry ID with action ID '$line'"
						;;
					'+')
						if list_contains "${EXCLUDED_ENTRY_IDS}" "${entry_id}"; then
							debug "entry '${entry_id}' was already excluded from fallback"
						elif list_contains "${INCLUDED_ENTRY_IDS}" "${entry_id}"; then
							debug "entry '${entry_id}' fallback exclusion was already prevented"
						else
							debug "preventing fallback exclusion for entry '${entry_id}'"
							INCLUDED_ENTRY_IDS=${INCLUDED_ENTRY_IDS:+${INCLUDED_ENTRY_IDS}${N}}${entry_id}
						fi
						;;
					'-')
						if list_contains "${INCLUDED_ENTRY_IDS}" "${entry_id}"; then
							debug "entry '${entry_id}' fallback exclusion was already prevented"
						elif list_contains "${EXCLUDED_ENTRY_IDS}" "${entry_id}"; then
							debug "entry '${entry_id}' was already excluded from fallback"
						else
							debug "excluding entry '${entry_id}' from fallback"
							EXCLUDED_ENTRY_IDS=${EXCLUDED_ENTRY_IDS:+${EXCLUDED_ENTRY_IDS}${N}}${entry_id}
						fi
						;;
					esac
				else
					error "Discarded possibly misspelled entry '$line'"
				fi
				;;

			esac
			# By default empty lines and comments get ignored
		done < "$config_path"
	done
}
# Mask IFS withing function to allow temporary changes
alias read_config_paths='IFS= read_config_paths'

replace() {
	# takes $1, replaces $2 with $3
	# does it in large chunks
	# writes result to global REPLACED_STR to avoid $() newline issues

	# right part of string
	r_remainder=${1}
	REPLACED_STR=
	while [ -n "$r_remainder" ]; do
		# left part before first encounter of $2
		r_left=${r_remainder%%"$2"*}
		# append
		REPLACED_STR=${REPLACED_STR}$r_left
		if [ "$r_left" = "$r_remainder" ]; then
			# nothing left to cut
			break
		fi
		# append replace substring
		REPLACED_STR=${REPLACED_STR}$3
		# cut remainder
		r_remainder=${r_remainder#*"$2"}
	done
}

de_expand_str() {
	# expands \s, \n, \t, \r, \\
	# https://specifications.freedesktop.org/desktop-entry-spec/latest/value-types.html
	# writes result to global $EXPANDED_STR in place to avoid $() expansion newline issues
	debug "expander received: $1"
	EXPANDED_STR=
	exp_remainder=$1
	while [ -n "$exp_remainder" ]; do
		# left is substring of remainder before the first encountered backslash
		exp_left=${exp_remainder%%\\*}

		# append left to EXPANDED_STR
		EXPANDED_STR=${EXPANDED_STR}${exp_left}
		debug "expander appended: $exp_left"

		if [ "$exp_left" = "$exp_remainder" ]; then
			debug "expander ended: $EXPANDED_STR"
			# no more backslashes left
			break
		fi

		# remove left substring and backslash from remainder
		exp_remainder=${exp_remainder#"$exp_left"\\}

		case "$exp_remainder" in
		# expand and append to EXPANDED_STR
		s*)
			EXPANDED_STR=${EXPANDED_STR}' '
			exp_remainder=${exp_remainder#?}
			debug "expander substituted space"
			;;
		n*)
			EXPANDED_STR=${EXPANDED_STR}$N
			exp_remainder=${exp_remainder#?}
			debug "expander substituted newline"
			;;
		t*)
			EXPANDED_STR=${EXPANDED_STR}'	'
			exp_remainder=${exp_remainder#?}
			debug "expander substituted tab"
			;;
		r*)
			EXPANDED_STR=${EXPANDED_STR}$(printf '%b' '\r')
			exp_remainder=${exp_remainder#?}
			debug "expander substituted caret return"
			;;
		\\*)
			EXPANDED_STR=${EXPANDED_STR}\\
			exp_remainder=${exp_remainder#?}
			debug "expander substituted backslash"
			;;
		# unsupported sequence, reappend backslash
		#*)
		#	EXPANDED_STR=${EXPANDED_STR}\\
		#	debug 'expander reappended backslash'
		#	;;
		esac
	done
}

de_tokenize_exec() {
	# Shell-based DE Exec string tokenizer.
	# https://specifications.freedesktop.org/desktop-entry-spec/latest/exec-variables.html
	# How hard can it be?
	# Fills global EXEC_USEP var with $USEP-separated command array in place to avoid $() expansion newline issues
	debug "tokenizer received: $1"
	EXEC_USEP=
	tok_remainder=$1
	tok_quoted=0
	tok_in_space=0
	while [ -n "$tok_remainder" ]; do
		# left is substring of remainder before the first encountered special char
		tok_left=${tok_remainder%%[[:space:]\"\`\$\\\'\>\<\~\|\&\;\*\?\#\(\)]*}

		# left should be safe to append right away
		EXEC_USEP=${EXEC_USEP}${tok_left}
		debug "tokenizer appended: >$tok_left<"

		# end of the line
		case "$tok_remainder" in
		"$tok_left")
			debug "tokenizer is out of special chars"
			break
			;;
		esac

		# isolate special char
		tok_remainder=${tok_remainder#"$tok_left"}
		cut=${tok_remainder#?}
		tok_char=${tok_remainder%"$cut"}
		unset cut
		# cut it from remainder
		tok_remainder=${tok_remainder#"$tok_char"}

		# check if still in space
		case "${tok_in_space}${tok_left}${tok_char}" in
		1[[:space:]])
			debug "tokenizer still in space :) skipping space character"
			continue
			;;
		1*)
			debug "tokenizer no longer in space :("
			tok_in_space=0
			;;
		esac

		## decide what to do with the character
		# doublequote while quoted
		case "${tok_quoted}${tok_char}" in
		'1"')
			tok_quoted=0
			debug "tokenizer closed double quotes"
			continue
			;;
		# doublequote while unquoted
		'0"')
			tok_quoted=1
			debug "tokenizer opened double quotes"
			continue
			;;
		# error out on unquoted special chars
		0[\`\$\\\'\>\<\~\|\&\;\*\?\#\(\)])
			debug "${entry_id}: Encountered unquoted character: '$tok_char'"
			return 1
			;;
		# error out on quoted but unescaped chars
		1[\`\$])
			debug "${entry_id}: Encountered unescaped quoted character: '$tok_char'"
			return 1
			;;
		# process quoted escapes
		1\\)
			case "$tok_remainder" in
			# if there is no next char, fail
			'')
				debug "${entry_id}: Dangling backslash encountered!"
				return 1
				;;
			# cut and append the next char right away
			# or a half of multibyte char, the other half should go into the next
			# 'tok_left' hopefully...
			*)
				cut=${tok_remainder#?}
				tok_char=${tok_remainder%"$cut"}
				tok_remainder=${cut}
				unset cut
				EXEC_USEP=${EXEC_USEP}${tok_char}
				debug "tokenizer appended escaped: >$tok_char<"
				;;
			esac
			;;
		# Consider Cosmos
		0[[:space:]])
			case "${tok_remainder}" in
			# there is non-space to follow
			*[![:space:]]*)
				# append separator
				EXEC_USEP=${EXEC_USEP}${USEP}
				tok_in_space=1
				debug "tokenizer entered spaaaaaace!!!! separator appended"
				;;
			# ignore unquoted space at the end of string
			*)
				debug "tokenizer entered outer spaaaaaace!!!! separator skipped, this is the end"
				break
				;;
			esac
			;;
		# append quoted chars
		1[[:space:]\'\>\<\~\|\&\;\*\?\#\(\)])
			EXEC_USEP=${EXEC_USEP}${tok_char}
			debug "tokenizer appended quoted char: >$tok_char<"
			;;
		# this should not happen
		*)
			debug "${entry_id}: parsing error at char '$tok_char', (quoted: $tok_quoted)"
			return 1
			;;
		esac
	done
	case "$tok_quoted" in
	1)
		debug "${entry_id}: Double quote was not closed!"
		return 1
		;;
	esac
	# shellcheck disable=SC2086
	debug "tokenizer ended:" "$(
		IFS=$USEP
		printf 'D:     >%s<\n' $EXEC_USEP
	)"
}

de_strip_fields() {
	# Operates on $EXEC_USEP
	# modifies according to args/fields
	# no arguments, erase fields from $EXEC_USEP
	exec_usep=''
	fu_found=false
	IFS=$USEP
	for arg in $EXEC_USEP; do
		case "$arg" in
		# remove deprecated fields
		*[!%]'%'[dDnNvm]* | '%'[dDnNvm]*) debug "injector removed deprecated '$arg'" ;;
		# treat file fields
		*[!%]'%'[fFuU]* | '%'[fFuU]*)
			if [ "$fu_found" = "true" ]; then
				debug "${entry_id}: Encountered more than one %[fFuU] field!"
				return 1
			fi
			fu_found=true
			debug "injector removed '$arg'"
			continue
			;;
		# other fields
		*[!%]'%i'* | '%i'* | *[!%]'%c'* | '%c'*)
			debug "injector removed '$arg'"
			continue
			;;
		# literal %
		*[!%]%%* | %%*)
			replace "$arg" "%%" "%"
			rarg=$REPLACED_STR
			debug "injector replacing '%%': '$arg' -> '$rarg'"
			exec_usep=${exec_usep}${exec_usep:+$USEP}${rarg}
			;;
		# invalid field
		*%?* | *[!%]%)
			debug "${entry_id}: unknown % field in argument '${arg}'"
			return 1
			;;
		*)
			debug "injector keeped: '$arg'"
			exec_usep=${exec_usep}${exec_usep:+$USEP}${arg}
			;;
		esac
	done
	EXEC_USEP=$exec_usep
	IFS=$OIFS
}
# Mask IFS withing function to allow temporary changes
alias de_strip_fields='IFS= de_strip_fields'

reset_keys() {
	# init vars used in entry checks
	IS_TERMINAL=''
	EXEC_USEP=''
	EXECARG='-e'
	EXECARG_DEFINED=false
	APPIDARG=''
	TITLEARG=''
	DIRARG=''
	HOLDARG=''
}

# Find and map all desktop entry files from standardised paths into aliases
find_entry_paths() {
	debug "registering entries"

	# Append application directory paths to be searched
	IFS=':'
	for directory in $APPLICATIONS_DIRS; do
		# Append '.' to delimit start of entry ID
		set -- "$@" "$directory".
	done

	# Find all files
	set -- "$@" -type f

	# Append path conditions per directory
	or_arg=''
	for directory in $APPLICATIONS_DIRS; do
		# Match full path with proper first character of entry ID and .desktop extension
		# Reject paths with invalid characters in entry ID
		set -- "$@" ${or_arg} '(' -path "$directory"'./[a-zA-Z0-9_]*.desktop' ! -path "$directory"'./*[^a-zA-Z0-9_./-]*' ')'
		or_arg='-o'
	done

	# Loop through found entry paths and IDs
	IFS=$N
	while read -r entry_path && read -r entry_id; do
		# exclude entries based on EXCLUDED_ENTRY_IDS
		if list_contains "$EXCLUDED_ENTRY_IDS" "$entry_id"; then
			debug "entry '${entry_id}' was excluded from fallback"
			continue
		fi
		# Entries are checked in ascending order of preference, so use last found if duplicate
		# shellcheck disable=SC2139
		alias "$entry_id"="entry_path='$entry_path'"
		debug "registered '$entry_path' as entry '$entry_id'"
		# Add as a fallback ID regardles if it's a duplicate
		FALLBACK_ENTRY_IDS=${entry_id}${FALLBACK_ENTRY_IDS:+${N}${FALLBACK_ENTRY_IDS}}
		debug "added fallback ID '$entry_id'"
	done <<- EOE
		$(
			# Don't complain about nonexistent directories
			find -L "$@" 2> /dev/null |
				# Print entry path and convert it into an ID and print that too
				awk '{ print; sub(".*/[.]/", ""); gsub("/", "-"); print }'
		)
	EOE
}
# Mask IFS withing function to allow temporary changes
alias find_entry_paths='IFS= find_entry_paths'

# Check validity of a given entry key - value pair
# Modifies following global variables:
# EXEC_USEP : Program to execute, possibly with arguments, delimited by ASCII Unit Separator.
# EXECARG : Execution argument for the terminal emulator.
# IS_TERMINAL : Set if application has been categorized as a terminal emulator
check_entry_key() {
	key="$1"
	value="$2"
	action="$3"
	read_exec="$4"
	de_checks="$5"

	# Order of checks is important
	case $key in
	'Categories'*=*)
		debug "checking for 'TerminalEmulator' in Categories '$value'"
		IFS=';'
		for category in $value; do
			[ "$category" = "TerminalEmulator" ] && {
				IS_TERMINAL=true
				return 0
			}
		done
		# Default in this case is to fail
		return 1
		;;
	'Actions'*=*)
		# `It is not valid to have an action group for an action identifier not mentioned in the Actions key.
		# Such an action group must be ignored by implementors.`
		# ignore if no action requested
		[ -z "$action" ] && return 0
		debug "checking for '$action' in Actions '$value'"
		IFS=';'
		for check_action in $value; do
			if [ "$check_action" = "$action" ]; then
				action_listed=true
				return 0
			fi
		done
		# Default in this case is to fail
		return 1
		;;
	'OnlyShowIn'*=*)
		case "$de_checks" in
		true) debug "checking for intersecion between '${XDG_CURRENT_DESKTOP-}' and OnlyShowIn '$value'" ;;
		false)
			debug "skipping OnlyShowIn check"
			return 0
			;;
		esac
		IFS=';'
		for target in $value; do
			IFS=':'
			for desktop in ${XDG_CURRENT_DESKTOP-}; do
				[ "$desktop" = "$target" ] && return 0
			done
		done
		# Default in this case is to fail
		return 1
		;;
	'NotShowIn'*=*)
		case "$de_checks" in
		true) debug "checking for intersecion between '${XDG_CURRENT_DESKTOP-}' and NotShowIn '$value'" ;;
		false)
			debug "skipping NotShowIn check"
			return 0
			;;
		esac
		IFS=';'
		for target in $value; do
			IFS=':'
			for desktop in ${XDG_CURRENT_DESKTOP-}; do
				debug "checking NotShowIn match '$desktop'='$target'"
				[ "$desktop" = "$target" ] && return 1
			done
		done
		# Default in this case is to succeed
		return 0
		;;
	'X-TerminalArgExec'*=* | 'TerminalArgExec'*=*)
		# Set global variable
		# values of type string should support escape sequences
		de_expand_str "$value"
		EXECARG=$EXPANDED_STR
		EXECARG_DEFINED=true
		debug "read TerminalArgExec '$EXECARG'"
		;;
	'X-ExecArg'*=* | 'ExecArg'*=*)
		# ignore old ExecArg in strict mode
		case "${EXECARG_COMPAT}" in
		false) return 0 ;;
		esac
		# Set global variable
		# values of type string should support escape sequences
		de_expand_str "$value"
		EXECARG=$EXPANDED_STR
		EXECARG_DEFINED=true
		debug "read TerminalArgExec '$EXECARG'"
		;;
	'X-TerminalArgAppId'*=* | 'TerminalArgAppId'*=*)
		# Set global variable
		# values of type string should support escape sequences
		de_expand_str "$value"
		APPIDARG=$EXPANDED_STR
		debug "read TerminalArgAppId '$APPIDARG'"
		;;
	'X-TerminalArgTitle'*=* | 'TerminalArgTitle'*=*)
		# Set global variable
		# values of type string should support escape sequences
		de_expand_str "$value"
		TITLEARG=$EXPANDED_STR
		debug "read TerminalArgTitle '$TITLEARG'"
		;;
	'X-TerminalArgDir'*=* | 'TerminalArgDir'*=*)
		# Set global variable
		# values of type string should support escape sequences
		de_expand_str "$value"
		DIRARG=$EXPANDED_STR
		debug "read TerminalArgDir '$DIRARG'"
		;;
	'X-TerminalArgHold'*=* | 'TerminalArgHold'*=*)
		# Set global variable
		# values of type string should support escape sequences
		de_expand_str "$value"
		HOLDARG=$EXPANDED_STR
		debug "read TerminalArgHold '$HOLDARG'"
		;;
	'TryExec'*=*)
		de_expand_str "$value"
		debug "checking TryExec executable '$EXPANDED_STR'"
		command -v "$(printf '%b' "$EXPANDED_STR")" > /dev/null || return 1
		;;
	'Hidden'*=*)
		debug "checking boolean Hidden '$value'"
		case "$value" in
		true)
			debug "ignored Hidden entry"
			return 1
			;;
		esac
		;;
	'Exec'*=*)
		case "$read_exec" in
		false)
			debug "ignored Exec from wrong section"
			return 0
			;;
		esac
		debug "read Exec '$value'"
		# Escape sequences of DE string value (sets $EXPANDED_STR)
		de_expand_str "$value"
		# Tokenize resulting string (sets $EXEC_USEP)
		de_tokenize_exec "$EXPANDED_STR"
		# Expand % fields
		de_strip_fields
		# Get first word from read Exec value
		EXEC0=${EXEC_USEP%%"$USEP"*}
		debug "checking Exec[0] executable '$EXEC0'"
		command -v "$EXEC0" > /dev/null || return 1
		;;
	esac
	# By default unrecognised keys, empty lines and comments get ignored
}
# Mask IFS withing function to allow temporary changes
alias check_entry_key='IFS= check_entry_key'

# Read entry from given path
read_entry_path() {
	entry_path="$1"
	entry_action="$2"
	de_checks="$3"
	read_exec=false
	action_listed=false
	# shellcheck disable=SC2016
	debug "reading desktop entry '$entry_path'${entry_action:+ action '}$entry_action${entry_action:+'}"
	# Let `read` trim leading/trailing whitespace from the line
	while IFS="$OIFS" read -r line; do
		case $line in
		# `There should be nothing preceding [the Desktop Entry group] in the desktop entry file but [comments]`
		# if entry_action is not requested, allow reading Exec right away from the main group
		'[Desktop Entry]'*) [ -z "$entry_action" ] && read_exec=true ;;
		# A `Key=Value` pair
		[a-zA-Z0-9-]*)
			# Split value from pair
			value=${line#*=}
			# Remove all but leading spaces, and trim that from the value
			value=${value#"${value%%[! ]*}"}
			# Check the key, continue to next line on success
			check_entry_key "$line" "$value" "$entry_action" "$read_exec" "$de_checks" && continue
			# Reset values that might have been set
			reset_keys
			# shellcheck disable=SC2016
			debug "entry discarded"
			return 1
			;;
		# found requested action, allow reading Exec
		"[Desktop Action ${entry_action}]"*)
			if [ "$action_listed" = "true" ]; then
				read_exec=true
			else
				debug "action '$entry_action' was not listed in Actions"
				return 1
			fi
			;;
		# Start of the next group header, stop if already read exec
		'['*) [ "$read_exec" = "true" ] && break ;;
		esac
		# By default empty lines and comments get ignored
	done < "$entry_path"
}

validate_entry_id() {
	# validates entry ID ($1)

	case "$1" in
	# invalid characters or degrees of emptiness
	*[!a-zA-Z0-9_.-]* | *[!a-zA-Z0-9_.-] | [!a-zA-Z0-9_.-]* | [!a-zA-Z0-9_.-] | '' | .desktop)
		debug "string not valid as Entry ID: '$1'"
		return 1
		;;
	# all that left with .desktop
	*.desktop) return 0 ;;
	# and without
	*)
		debug "string not valid as Entry ID '$1'"
		return 1
		;;
	esac
}

validate_action_id() {
	# validates action ID ($1)

	case "$1" in
	# empty is ok
	'') return 0 ;;
	# invalid characters
	*[!a-zA-Z0-9-]* | *[!a-zA-Z0-9-] | [!a-zA-Z0-9-]* | [!a-zA-Z0-9-])
		debug "string not valid as Action ID: '$1'"
		return 1
		;;
	# all that left
	*) return 0 ;;
	esac
}

# Loop through IDs and try to find a valid entry
find_entry() {
	# for explicitly listed entries do not apply DE *ShowIn limits
	de_checks=false
	IFS="$N"
	for entry_id in ${ENTRY_IDS}${N}//fallback_start//${N}$FALLBACK_ENTRY_IDS; do
		case "$entry_id" in
		# entry has an action appended
		*:*)
			entry_action=${entry_id#*:}
			entry_id=${entry_id%:*}
			;;
		# skip empty line
		'') continue ;;
		# fallback entries ahead, enable *ShowIn checks
		'//fallback_start//')
			de_checks=true
			continue
			;;
		# nullify action
		*) entry_action='' ;;
		esac

		debug "matching path for entry ID '$entry_id'"
		# Check if a matching path was found for ID
		alias "$entry_id" > /dev/null 2>&1 || continue
		# Evaluates the alias, it sets $entry_path
		eval "$entry_id"
		# Unset the alias, so duplicate entries are skipped
		unalias "$entry_id"
		read_entry_path "$entry_path" "$entry_action" "$de_checks" || continue
		# Check that the entry is actually executable
		[ -z "${EXEC_USEP}" ] && continue
		# ensure entry is a Terminal Emulator
		[ -z "${IS_TERMINAL}" ] && continue
		# if entry lacks TerminalArgExec
		if [ "$EXECARG_DEFINED" != "true" ]; then
			# get (custom) default in compat mode
			if check_bool "$EXECARG_COMPAT"; then
				EXECARG=$(get_default_execarg "$entry_id")
			# discard entry in strict mode
			else
				continue
			fi
		fi
		# Entry is valid, stop
		return 0
	done
	# shellcheck disable=SC2086
	IFS=':' error "No valid terminal entry was found in:" ${APPLICATIONS_DIRS}
	return 1
}
# Mask IFS withing function to allow temporary changes
alias find_entry='IFS= find_entry'

get_default_execarg() {
	# based on entry_id ($1) return TerminalArgExec from EXECARG_DEFAULTS
	check_entry=$1
	while IFS=':' read -r entry_id execarg_default; do
		case "$entry_id" in
		"$check_entry")
			printf '%s' "$execarg_default"
			debug "custom default TerminalArgExec '$execarg_default' for '$check_entry'"
			return 0
			;;
		esac
	done <<- EOF
		$EXECARG_DEFAULTS
	EOF
	printf '%s' '-e'
	debug "using default TerminalArgExec '-e' for '$check_entry'"
}

## globals
LOWERCASE_XDG_CURRENT_DESKTOP=$(printf '%s' "${XDG_CURRENT_DESKTOP-}" | tr '[:upper:]' '[:lower:]')

# compat mode
EXECARG_COMPAT=${XTE_EXECARG_COMPAT-true}
# flag reused in directive encounter
EXECARG_COMPAT_CONFIGURED=${XTE_EXECARG_COMPAT-}

EXEC_USEP=''
EXPANDED_STR=''

# this will receive proper value later
APPLICATIONS_DIRS=''

# this will be filled with values from /execarg_default:*:* directives
EXECARG_DEFAULTS=''

# this (re)sets vars to be filled from desktop entry
reset_keys

# path iterators
make_paths

# At this point we have no way of telling if cache is enabled or not, unless
# XTE_CACHE_ENABLED is set, so just try reading it by default, otherwise do the
# usual thing. Editing config to disable cache should invalidate the cache.
CACHE_ENABLED=${XTE_CACHE_ENABLED-true}
# flag reused for directive encounter
CACHE_CONFIGURED=${XTE_CACHE_ENABLED-}

# HASH can be reused
HASH=''

if check_bool "${CACHE_ENABLED}" && read_cache; then
	CACHE_USED=true
else
	# continue with globals
	CACHE_USED=false

	# All desktop entry ids in descending order of preference from *xdg-terminals.list configs,
	# with duplicates removed
	ENTRY_IDS=''
	# All desktop entry ids found in data dirs in descending order of preference,
	# with duplicates (including those in $ENTRY_IDS) removed
	FALLBACK_ENTRY_IDS=''

	# Entry IDs excluded from fallback by '-entry.desktop' directives
	EXCLUDED_ENTRY_IDS=''
	# Entry IDS included (exclusion prevented) by '+entry.desktop' directives
	INCLUDED_ENTRY_IDS=''

	# Modifies $ENTRY_IDS
	read_config_paths
	# Modifies $ENTRY_IDS and sets global aliases
	find_entry_paths

	# shellcheck disable=SC2086
	IFS="$N" debug ">     final entry ID list:" ${ENTRY_IDS} "^     end of final entry ID list"
	# shellcheck disable=SC2086
	IFS="$N" debug ">     final fallback entry ID list:" ${FALLBACK_ENTRY_IDS} "^     end of final fallback entry ID list"

	# walk ID lists and find first applicable
	find_entry || exit 1
fi

# Store original argument list, before it's modified
debug ">     original args:" "$@" "^     end of original args" "EXEC_USEP=$EXEC_USEP" "EXECARG=$EXECARG"

# process/discard options
debug "option processing"
APPIDVAL=''
TITLEVAL=''
DIRVAL=''
HOLD=false
TEST_MODE=false
while [ "$#" -gt "0" ]; do
	case "$1" in
	--)
		debug "found explicit end of options $1"
		shift
		break
		;;
	-e | "$EXECARG")
		debug "found exec arg $1"
		shift
		break
		;;
	--app-id=*)
		debug "found option $1"
		IFS='=' read -r _opt APPIDVAL <<- EOF
			$1
		EOF
		debug "set app-id option to $APPIDVAL"
		shift
		;;
	--title=*)
		debug "found option $1"
		IFS='=' read -r _opt TITLEVAL <<- EOF
			$1
		EOF
		debug "set title option to $DIRVAL"
		shift
		;;
	--dir=*)
		debug "found option $1"
		IFS='=' read -r _opt DIRVAL <<- EOF
			$1
		EOF
		debug "set dir option to $DIRVAL"
		shift
		;;
	--hold)
		debug "found option $1"
		HOLD=true
		debug "set HOLD=true"
		shift
		;;
	--test)
		debug "found option $1"
		TEST_MODE=true
		debug "set TEST_MODE=true"
		shift
		;;
	[!-]*)
		debug "found non-option $1"
		break
		;;
	-*)
		debug "discarding unknown option $1"
		shift
		;;
	esac
done
debug "end of option processing, prependig options"

# option prepend
if [ "$#" -gt 0 ] && [ -n "$EXECARG" ]; then
	set -- "$EXECARG" "$@"
	debug "prepended $1"
fi

if [ -n "$HOLDARG" ] && check_bool "$HOLD"; then
	set -- "${HOLDARG}" "$@"
	debug "prepended $1"
elif [ -z "$HOLDARG" ] && check_bool "$HOLD"; then
	debug "terminal entry has no TerminalArgHold="
fi

if [ -n "$DIRARG" ] && [ -n "$DIRVAL" ]; then
	case "$DIRARG" in
	*=)
		set -- "${DIRARG}${DIRVAL}" "$@"
		debug "prepended $1"
		;;
	*)
		set -- "${DIRARG}" "${DIRVAL}" "$@"
		debug "prepended $1 $2"
		;;
	esac
elif [ -z "$DIRARG" ] && [ -n "$DIRVAL" ]; then
	debug "terminal entry has no TerminalArgDir="
fi

if [ -n "$TITLEARG" ] && [ -n "$TITLEVAL" ]; then
	case "$TITLEARG" in
	*=)
		set -- "${TITLEARG}${TITLEVAL}" "$@"
		debug "prepended $1"
		;;
	*)
		set -- "${TITLEARG}" "${TITLEVAL}" "$@"
		debug "prepended $1 $2"
		;;
	esac
elif [ -z "$TITLEARG" ] && [ -n "$TITLEVAL" ]; then
	debug "terminal entry has no TerminalArgTitle="
fi

if [ -n "$APPIDARG" ] && [ -n "$APPIDVAL" ]; then
	case "$APPIDARG" in
	*=)
		set -- "${APPIDARG}${APPIDVAL}" "$@"
		debug "prepended $1"
		;;
	*)
		set -- "${APPIDARG}" "${APPIDVAL}" "$@"
		debug "prepended $1 $2"
		;;
	esac
elif [ -z "$APPIDARG" ] && [ -n "$APPIDVAL" ]; then
	debug "terminal entry has no TerminalArgAppId="
fi

debug "end of option prepending"

# prepend Exec
IFS=$USEP
# shellcheck disable=SC2086
set -- $EXEC_USEP "$@"
IFS=$OIFS

debug ">     final args:" "$@" "^     end of final args"

if [ "$CACHE_USED" = "false" ]; then
	# saves or removes cache, forked out of the way
	save_cache "$1" &
fi

case "$TEST_MODE" in
true)
	printf '%s\n' 'Command and arguments:'
	printf '  >%s<\n' "$@"
	exit 0
	;;
esac

exec "$@"