bash-complete

#!/usr/bin/bash

# Ensure that bash-completion is properly set up
. /usr/share/bash-completion/bash_completion

# bash function that gets the completion function for a given command if it exists
get_completion_function() {
	local candidates=$(complete | grep $1)
	# Unfortunately, I do not know how to handle this line-wise. Therefore,
	# I have to do a dirty little hack:
	# Handle the whole output word-wise, whenever we find "complete" and after
	# the loop has finished, we know that we have finished a line :(
	for candidate in $candidates # automatically splits by ' '
	do
		if [ "$nextIsFunction" == "1" ]
		then
			local localFunctionName="$candidate"
			local nextIsFunction=0
		fi
		if [ "$candidate" == "-F" ]
		then
			local nextIsFunction=1
		fi
		if [ "$candidate" == "complete" ]
		then
			if [ "$lastWord" == "$1" ]
			then
				# Success (not last line)
				functionName=$localFunctionName
				return 0
			fi
		fi
		local lastWord="$candidate"
	done
	if [ "$lastWord" == "$1" ]
	then
		# Success (last line)
		functionName=$localFunctionName
		return 0
	fi
	return 1
}
load_completion_function() {
	local candidates=$(complete | grep -- -D)
	# See above
	for candidate in $candidates # automatically splits by ' '
	do
		if [ "$nextIsFunction" == "1" ]
		then
			local functionName="$candidate"
			local hasFunction=1
			local nextIsFunction=0
			if [ "$isDefault" == "1" ]
			then
				$functionName $1 "" $1 # call loader function
				return 0
			fi
		fi
		if [ "$candidate" == "-F" ]
		then
			local nextIsFunction=1
		fi
		if [ "$candidate" == "-D" ]
		then
			local isDefault=1
			if [ "$hasFunction" == "1" ]
			then
				$functionName $1 "" $1 # call loader function
				return 0
			fi
		fi
		if [ "$candidate" == "complete" ]
		then
			local hasFunction=0
			local isDefault=0
		fi
	done
	return 1
}
# Attention: load_and_get... must not be called with $(...) syntax because it
# changes bash state and $(...) seems to be executed in its own ... scope?
# Therefore, the name of the completionFunction is not "returned" by echo but
# by setting a global variable instead. Yeah, bash scripting :)
load_and_get_completion_function() {
	if get_completion_function $1
	then
		completionFunction=$functionName
		return 0
	fi
	load_completion_function $1
	if get_completion_function $1
	then
		completionFunction=$functionName
		return 0
	fi
	return 1
}

# If we are in the first word, we complete commands or fallback to directories
# because those could expand to a command path (bash default seems to be to
# only return commands from PATH if there are any found and directories otherwise)
if [ $1 == 0 ]
then
	commands=$(compgen -c $2) # Try commands first
	if [ "$commands" ]
	then
		echo $commands
		exit
	else
		dirs=$(compgen -d $2) # Try directories as fallback
		slashdirs=()
		for dir in $dirs
		do
			slashdirs+=($dir"/") # Append / to each directory
		done
		echo ${slashdirs[@]}
	fi
	exit # Do not try function completion
fi

if load_and_get_completion_function $2
then
	# Since my bash-scripting skills are so lacking, I have to do everything step
	# by step here:
	# From all arguments, extract the current word position (first argument
	# after this script's name, i.e. $1) and the current command-line which should
	# by completed (all following arguments)
	allArgs=($@)
	argLen=${#allArgs[@]}
	wordPos=${allArgs[0]}
	argsWithoutPos=(${allArgs[@]:1:$argLen})
	# Set the 6 environment variables which are used by the completion scripts
	COMP_LINE=${argsWithoutPos[@]}
	COMP_POINT=0 # We have to calculate COMP_POINT by counting all words until $wordPos
	wordIter=0
	while [ $wordIter -le $wordPos ]
	do
		word=${argsWithoutPos[$wordIter]}
		wordLen=${#word}
		COMP_POINT=$((COMP_POINT+wordLen))
		if [ $wordIter -gt 0 ] # For all following words, include the whitespace between the two words
		then
			COMP_POINT=$((COMP_POINT+1))
		fi
		((wordIter++))
	done
	COMP_WORDS=(${argsWithoutPos[@]})
	COMP_CWORD=$wordPos
	COMP_KEY=9   # we hold those two ...
	COMP_TYPE=33 # ... fix for the moment
	COMPREPLY=() # Reset COMPREPLY ... :(
	# Set the three arguments to the completion function
	cmdname=$2
	curWord=${argsWithoutPos[$wordPos]}
	prevWordPos=$((wordPos-1))
	prevWord=${argsWithoutPos[$prevWordPos]}
	# Call the completion function
	: '# Output debug info
	echo $completionFunction
	echo $cmdname
	echo $curWord
	echo $prevWord
	'
	# If we have found a meaningful completion function, call it. Otherwise, 
	# do file and directory completion.
	if [ "$completionFunction" != "_minimal" ]
	then
		$completionFunction "$cmdname" "$curWord" "$prevWord"
		echo ${COMPREPLY[@]}
	else # file & directory completion
		results=()
		files=$(compgen -f $curWord)
		for file in $files
		do
			results+=($file)
		done
		dirs=$(compgen -d $curWord) # Try directories as fallback
		for dir in $dirs
		do
			results+=($dir"/") # Append / to each directory
		done
		echo ${results[@]}
	fi
else
	exit 1
fi

#
# Starting here: Just testing stuff
#

# Register a function _custom_complete() for (hopefully) nonexistent command
# 'asdf' which just prints the variables/parameters
: '
_custom_complete() {
	echo "" # Just a newline for nicer output
	echo "COMP_LINE='"$COMP_LINE"'"
	echo "COMP_POINT='"$COMP_POINT"'"
	echo "COMP_KEY='"$COMP_KEY"'"
	echo "COMP_TYPE='"$COMP_TYPE"'"
	echo "COMP_WORDS='"${COMP_WORDS[@]}"'"
	echo "COMP_CWORD='"$COMP_CWORD"'"
	echo "p1='"$1"'"
	echo "p2='"$2"'"
	echo "p3='"$3"'"
}
complete -F _custom_complete asdf
'

# Try to manually call the _known_hosts function which provides completion for
# dig, ftp ...
: '
COMP_LINE="ftp "
COMP_POINT=4
COMP_KEY=9
COMP_TYPE=33
COMP_WORDS=(ftp )
COMP_CWORD=1
_known_hosts ftp "" ftp
length=${#COMPREPLY[@]}
for reply in ${COMPREPLY[@]}
do
	#suppress output of: echo $reply
	true # bash does not like empty loops?
done
echo $length
'

# Try to dynamically load the completion code for git
: '
echo "Completion function for git before calling _completion_loader:"
complete | grep git
COMP_LINE="git "
COMP_POINT=4
COMP_KEY=9
COMP_TYPE=33
COMP_WORDS=(git )
COMP_CWORD=1
_completion_loader git "" git
echo "Completion function for git after calling _completion_loader:"
complete | grep git
'

# Let's call it :)
: '
COMP_LINE="git ch file"
COMP_POINT=6
COMP_KEY=9
COMP_TYPE=33
COMP_WORDS=(git ch file)
COMP_CWORD=1
COMPREPLY=() # Reset COMPREPLY ... :(
__git_wrap__git_main git ch git
echo ${COMPREPLY[@]}
'

# Let's try something more
: '
COMP_LINE="cd ~/"
COMP_POINT=5
COMP_KEY=9
COMP_TYPE=33
COMP_WORDS=(cd ~/)
COMP_CWORD=1
_cd cd ~/ cd
echo ${COMPREPLY[@]}
'