# This script can be run in two different contexts:
#
#   - From git, when the user invokes the "vimdiff" merge tool. In this context
#     this script expects the following environment variables (among others) to
#     be defined (which is something "git" takes care of):
#
#       - $BASE
#       - $LOCAL
#       - $REMOTE
#       - $MERGED
#
#     In this mode, all this script does is to run the next command:
#
#         vim -f -c ... $LOCAL $BASE $REMOTE $MERGED
#
#     ...where the "..." string depends on the value of the
#     "mergetool.vimdiff.layout" configuration variable and is used to open vim
#     with a certain layout of buffers, windows and tabs.
#
#   - From a script inside the unit tests framework folder ("t" folder) by
#     sourcing this script and then manually calling "run_unit_tests", which
#     will run a battery of unit tests to make sure nothing breaks.
#     In this context this script does not expect any particular environment
#     variable to be set.


################################################################################
## Internal functions (not meant to be used outside this script)
################################################################################

debug_print () {
	# Send message to stderr if global variable GIT_MERGETOOL_VIMDIFF is set
	# to "true"

	if test -n "$GIT_MERGETOOL_VIMDIFF_DEBUG"
	then
		>&2 echo "$@"
	fi
}

substring () {
	# Return a substring of $1 containing $3 characters starting at
	# zero-based offset $2.
	#
	# Examples:
	#
	#   substring "Hello world" 0 4  --> "Hell"
	#   substring "Hello world" 3 4  --> "lo w"
	#   substring "Hello world" 3 10 --> "lo world"

	STRING=$1
	START=$2
	LEN=$3

	echo "$STRING" | cut -c$(( START + 1 ))-$(( START + $LEN ))
}

gen_cmd_aux () {
	# Auxiliary function used from "gen_cmd()".
	# Read that other function documentation for more details.

	LAYOUT=$1
	CMD=$2  # This is a second (hidden) argument used for recursion

	debug_print
	debug_print "LAYOUT    : $LAYOUT"
	debug_print "CMD       : $CMD"

	if test -z "$CMD"
	then
		CMD="echo" # vim "nop" operator
	fi

	start=0
	end=${#LAYOUT}

	nested=0
	nested_min=100


	# Step 1:
	#
	# Increase/decrease "start"/"end" indices respectively to get rid of
	# outer parenthesis.
	#
	# Example:
	#
	#   - BEFORE: (( LOCAL , BASE ) / MERGED )
	#   - AFTER :  ( LOCAL , BASE ) / MERGED

	oldIFS=$IFS
	IFS=#
	for c in $(echo "$LAYOUT" | sed 's:.:&#:g')
	do
		if test "$c" = " "
		then
			continue
		fi

		if test "$c" = "("
		then
			nested=$(( nested + 1 ))
			continue
		fi

		if test "$c" = ")"
		then
			nested=$(( nested - 1 ))
			continue
		fi

		if test "$nested" -lt "$nested_min"
		then
			nested_min=$nested
		fi
	done
	IFS=$oldIFS

	debug_print "NESTED MIN: $nested_min"

	while test "$nested_min" -gt "0"
	do
		start=$(( start + 1 ))
		end=$(( end - 1 ))

		start_minus_one=$(( start - 1 ))

		while ! test "$(substring "$LAYOUT" "$start_minus_one" 1)" = "("
		do
			start=$(( start + 1 ))
			start_minus_one=$(( start_minus_one + 1 ))
		done

		while ! test "$(substring "$LAYOUT" "$end" 1)" = ")"
		do
			end=$(( end - 1 ))
		done

		nested_min=$(( nested_min - 1 ))
	done

	debug_print "CLEAN     : $(substring "$LAYOUT" "$start" "$(( end - start ))")"


	# Step 2:
	#
	# Search for all valid separators ("+", "/" or ",") which are *not*
	# inside parenthesis. Save the index at which each of them makes the
	# first appearance.

	index_new_tab=""
	index_horizontal_split=""
	index_vertical_split=""

	nested=0
	i=$(( start - 1 ))

	oldIFS=$IFS
	IFS=#
	for c in $(substring "$LAYOUT" "$start" "$(( end - start ))" | sed 's:.:&#:g');
	do
		i=$(( i + 1 ))

		if test "$c" = " "
		then
			continue
		fi

		if test "$c" = "("
		then
			nested=$(( nested + 1 ))
			continue
		fi

		if test "$c" = ")"
		then
			nested=$(( nested - 1 ))
			continue
		fi

		if test "$nested" = 0
		then
			current=$c

			if test "$current" = "+"
			then
				if test -z "$index_new_tab"
				then
					index_new_tab=$i
				fi

			elif test "$current" = "/"
			then
				if test -z "$index_horizontal_split"
				then
					index_horizontal_split=$i
				fi

			elif test "$current" = ","
			then
				if test -z "$index_vertical_split"
				then
					index_vertical_split=$i
				fi
			fi
		fi
	done
	IFS=$oldIFS


	# Step 3:
	#
	# Process the separator with the highest order of precedence
	# (";" has the highest precedence and "|" the lowest one).
	#
	# By "process" I mean recursively call this function twice: the first
	# one with the substring at the left of the separator and the second one
	# with the one at its right.

	terminate="false"

	if ! test -z "$index_new_tab"
	then
		before="-tabnew"
		after="tabnext"
		index=$index_new_tab
		terminate="true"

	elif ! test -z "$index_horizontal_split"
	then
		before="leftabove split"
		after="wincmd j"
		index=$index_horizontal_split
		terminate="true"

	elif ! test -z "$index_vertical_split"
	then
		before="leftabove vertical split"
		after="wincmd l"
		index=$index_vertical_split
		terminate="true"
	fi

	if  test "$terminate" = "true"
	then
		CMD="$CMD | $before"
		CMD=$(gen_cmd_aux "$(substring "$LAYOUT" "$start" "$(( index - start ))")" "$CMD")
		CMD="$CMD | $after"
		CMD=$(gen_cmd_aux "$(substring "$LAYOUT" "$(( index + 1 ))" "$(( ${#LAYOUT} - index ))")" "$CMD")
		echo "$CMD"
		return
	fi


	# Step 4:
	#
	# If we reach this point, it means there are no separators and we just
	# need to print the command to display the specified buffer

	target=$(substring "$LAYOUT" "$start" "$(( end - start ))" | sed 's:[ @();|-]::g')

	if test "$target" = "LOCAL"
	then
		CMD="$CMD | 1b"

	elif test "$target" = "BASE"
	then
		CMD="$CMD | 2b"

	elif test "$target" = "REMOTE"
	then
		CMD="$CMD | 3b"

	elif test "$target" = "MERGED"
	then
		CMD="$CMD | 4b"

	else
		CMD="$CMD | ERROR: >$target<"
	fi

	echo "$CMD"
	return
}


gen_cmd () {
	# This function returns (in global variable FINAL_CMD) the string that
	# you can use when invoking "vim" (as shown next) to obtain a given
	# layout:
	#
	#   $ vim -f $FINAL_CMD "$LOCAL" "$BASE" "$REMOTE" "$MERGED"
	#
	# It takes one single argument: a string containing the desired layout
	# definition.
	#
	# The syntax of the "layout definitions" is explained in "Documentation/
	# mergetools/vimdiff.txt" but you can already intuitively understand how
	# it works by knowing that...
	#
	#   * "+" means "a new vim tab"
	#   * "/" means "a new vim horizontal split"
	#   * "," means "a new vim vertical split"
	#
	# It also returns (in global variable FINAL_TARGET) the name ("LOCAL",
	# "BASE", "REMOTE" or "MERGED") of the file that is marked with an "@",
	# or "MERGED" if none of them is.
	#
	# Example:
	#
	#     gen_cmd "@LOCAL , REMOTE"
	#     |
	#     `-> FINAL_CMD    == "-c \"echo | leftabove vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
	#         FINAL_TARGET == "LOCAL"

	LAYOUT=$1


	# Search for a "@" in one of the files identifiers ("LOCAL", "BASE",
	# "REMOTE", "MERGED"). If not found, use "MERGE" as the default file
	# where changes will be saved.

	if echo "$LAYOUT" | grep @LOCAL >/dev/null
	then
		FINAL_TARGET="LOCAL"
	elif echo "$LAYOUT" | grep @BASE >/dev/null
	then
		FINAL_TARGET="BASE"
	else
		FINAL_TARGET="MERGED"
	fi


	# Obtain the first part of vim "-c" option to obtain the desired layout

	CMD=$(gen_cmd_aux "$LAYOUT")


	# Adjust the just obtained script depending on whether more than one
	# windows are visible or not

	if echo "$LAYOUT" | grep ",\|/" >/dev/null
	then
		CMD="$CMD | tabdo windo diffthis"
	else
		CMD="$CMD | bufdo diffthis"
	fi


	# Add an extra "-c" option to move to the first tab (notice that we
	# can't simply append the command to the previous "-c" string as
	# explained here: https://github.com/vim/vim/issues/9076

	FINAL_CMD="-c \"$CMD\" -c \"tabfirst\""
}


################################################################################
## API functions (called from "git-mergetool--lib.sh")
################################################################################

diff_cmd () {
	"$merge_tool_path" -R -f -d \
		-c 'wincmd l' -c 'cd $GIT_PREFIX' "$LOCAL" "$REMOTE"
}


diff_cmd_help () {
	TOOL=$1

	case "$TOOL" in
	nvimdiff*)
		printf "Use Neovim"
		;;
	gvimdiff*)
		printf "Use gVim (requires a graphical session)"
		;;
	vimdiff*)
		printf "Use Vim"
		;;
	esac

	return 0
}


merge_cmd () {
	layout=$(git config mergetool.vimdiff.layout)

	case "$1" in
	*vimdiff)
		if test -z "$layout"
		then
			# Default layout when none is specified
			layout="(LOCAL,BASE,REMOTE)/MERGED"
		fi
		;;
	*vimdiff1)
		layout="@LOCAL,REMOTE"
		;;
	*vimdiff2)
		layout="LOCAL,MERGED,REMOTE"
		;;
	*vimdiff3)
		layout="MERGED"
		;;
	esac

	gen_cmd "$layout"

	debug_print ""
	debug_print "FINAL CMD : $FINAL_CMD"
	debug_print "FINAL TAR : $FINAL_TARGET"

	if $base_present
	then
		eval "$merge_tool_path" \
			-f "$FINAL_CMD" "$LOCAL" "$BASE" "$REMOTE" "$MERGED"
	else
		# If there is no BASE (example: a merge conflict in a new file
		# with the same name created in both braches which didn't exist
		# before), close all BASE windows using vim's "quit" command

		FINAL_CMD=$(echo "$FINAL_CMD" | \
			sed -e 's:2b:quit:g' -e 's:3b:2b:g' -e 's:4b:3b:g')

		eval "$merge_tool_path" \
			-f "$FINAL_CMD" "$LOCAL" "$REMOTE" "$MERGED"
	fi

	ret="$?"

	if test "$ret" -eq 0
	then
		case "$FINAL_TARGET" in
		LOCAL)
			source_path="$LOCAL"
			;;
		REMOTE)
			source_path="$REMOTE"
			;;
		MERGED|*)
			# Do nothing
			source_path=
			;;
		esac

		if test -n "$source_path"
		then
			cp "$source_path" "$MERGED"
		fi
	fi

	return "$ret"
}


merge_cmd_help () {
	TOOL=$1

	case "$TOOL" in
	nvimdiff*)
		printf "Use Neovim "
		;;
	gvimdiff*)
		printf "Use gVim (requires a graphical session) "
		;;
	vimdiff*)
		printf "Use Vim "
		;;
	esac

	case "$TOOL" in
	*1)
		echo "with a 2 panes layout (LOCAL and REMOTE)"
		;;
	*2)
		echo "with a 3 panes layout (LOCAL, MERGED and REMOTE)"
		;;
	*3)
		echo "where only the MERGED file is shown"
		;;
	*)
		echo "with a custom layout (see \`git help mergetool\`'s \`BACKEND SPECIFIC HINTS\` section)"
		;;
	esac

	return 0
}


translate_merge_tool_path () {
	case "$1" in
	nvimdiff*)
		echo nvim
		;;
	gvimdiff*)
		echo gvim
		;;
	vimdiff*)
		echo vim
		;;
	esac
}


exit_code_trustable () {
	true
}


list_tool_variants () {
	if test "$TOOL_MODE" = "diff"
	then
		for prefix in '' g n
		do
			echo "${prefix}vimdiff"
		done
	else
		for prefix in '' g n
		do
			for suffix in '' 1 2 3
			do
				echo "${prefix}vimdiff${suffix}"
			done
		done
	fi
}


################################################################################
## Unit tests (called from scripts inside the "t" folder)
################################################################################

run_unit_tests () {
	# Function to make sure that we don't break anything when modifying this
	# script.

	NUMBER_OF_TEST_CASES=16

	TEST_CASE_01="(LOCAL,BASE,REMOTE)/MERGED"   # default behaviour
	TEST_CASE_02="@LOCAL,REMOTE"                # when using vimdiff1
	TEST_CASE_03="LOCAL,MERGED,REMOTE"          # when using vimdiff2
	TEST_CASE_04="MERGED"                       # when using vimdiff3
	TEST_CASE_05="LOCAL/MERGED/REMOTE"
	TEST_CASE_06="(LOCAL/REMOTE),MERGED"
	TEST_CASE_07="MERGED,(LOCAL/REMOTE)"
	TEST_CASE_08="(LOCAL,REMOTE)/MERGED"
	TEST_CASE_09="MERGED/(LOCAL,REMOTE)"
	TEST_CASE_10="(LOCAL/BASE/REMOTE),MERGED"
	TEST_CASE_11="(LOCAL,BASE,REMOTE)/MERGED+BASE,LOCAL+BASE,REMOTE+(LOCAL/BASE/REMOTE),MERGED"
	TEST_CASE_12="((LOCAL,REMOTE)/BASE),MERGED"
	TEST_CASE_13="((LOCAL,REMOTE)/BASE),((LOCAL/REMOTE),MERGED)"
	TEST_CASE_14="BASE,REMOTE+BASE,LOCAL"
	TEST_CASE_15="  ((  (LOCAL , BASE , REMOTE) / MERGED))   +(BASE)   , LOCAL+ BASE , REMOTE+ (((LOCAL / BASE / REMOTE)) ,    MERGED   )  "
	TEST_CASE_16="LOCAL,BASE,REMOTE / MERGED + BASE,LOCAL + BASE,REMOTE + (LOCAL / BASE / REMOTE),MERGED"

	EXPECTED_CMD_01="-c \"echo | leftabove split | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_02="-c \"echo | leftabove vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_03="-c \"echo | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 4b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_04="-c \"echo | 4b | bufdo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_05="-c \"echo | leftabove split | 1b | wincmd j | leftabove split | 4b | wincmd j | 3b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_06="-c \"echo | leftabove vertical split | leftabove split | 1b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_07="-c \"echo | leftabove vertical split | 4b | wincmd l | leftabove split | 1b | wincmd j | 3b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_08="-c \"echo | leftabove split | leftabove vertical split | 1b | wincmd l | 3b | wincmd j | 4b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_09="-c \"echo | leftabove split | 4b | wincmd j | leftabove vertical split | 1b | wincmd l | 3b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_10="-c \"echo | leftabove vertical split | leftabove split | 1b | wincmd j | leftabove split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_11="-c \"echo | -tabnew | leftabove split | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 3b | tabnext | leftabove vertical split | leftabove split | 1b | wincmd j | leftabove split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_12="-c \"echo | leftabove vertical split | leftabove split | leftabove vertical split | 1b | wincmd l | 3b | wincmd j | 2b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_13="-c \"echo | leftabove vertical split | leftabove split | leftabove vertical split | 1b | wincmd l | 3b | wincmd j | 2b | wincmd l | leftabove vertical split | leftabove split | 1b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_14="-c \"echo | -tabnew | leftabove vertical split | 2b | wincmd l | 3b | tabnext | leftabove vertical split | 2b | wincmd l | 1b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_15="-c \"echo | -tabnew | leftabove split | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 3b | tabnext | leftabove vertical split | leftabove split | 1b | wincmd j | leftabove split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""
	EXPECTED_CMD_16="-c \"echo | -tabnew | leftabove split | leftabove vertical split | 1b | wincmd l | leftabove vertical split | 2b | wincmd l | 3b | wincmd j | 4b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 1b | tabnext | -tabnew | leftabove vertical split | 2b | wincmd l | 3b | tabnext | leftabove vertical split | leftabove split | 1b | wincmd j | leftabove split | 2b | wincmd j | 3b | wincmd l | 4b | tabdo windo diffthis\" -c \"tabfirst\""

	EXPECTED_TARGET_01="MERGED"
	EXPECTED_TARGET_02="LOCAL"
	EXPECTED_TARGET_03="MERGED"
	EXPECTED_TARGET_04="MERGED"
	EXPECTED_TARGET_05="MERGED"
	EXPECTED_TARGET_06="MERGED"
	EXPECTED_TARGET_07="MERGED"
	EXPECTED_TARGET_08="MERGED"
	EXPECTED_TARGET_09="MERGED"
	EXPECTED_TARGET_10="MERGED"
	EXPECTED_TARGET_11="MERGED"
	EXPECTED_TARGET_12="MERGED"
	EXPECTED_TARGET_13="MERGED"
	EXPECTED_TARGET_14="MERGED"
	EXPECTED_TARGET_15="MERGED"
	EXPECTED_TARGET_16="MERGED"

	at_least_one_ko="false"

	for i in $(seq -w 1 99)
	do
		if test "$i" -gt $NUMBER_OF_TEST_CASES
		then
			break
		fi

		gen_cmd "$(eval echo \${TEST_CASE_"$i"})"

		if test "$FINAL_CMD" = "$(eval echo \${EXPECTED_CMD_"$i"})" \
			&& test "$FINAL_TARGET" = "$(eval echo \${EXPECTED_TARGET_"$i"})"
		then
			printf "Test Case #%02d: OK\n" "$(echo "$i" | sed 's/^0*//')"
		else
			printf "Test Case #%02d: KO !!!!\n" "$(echo "$i" | sed 's/^0*//')"
			echo "  FINAL_CMD              : $FINAL_CMD"
			echo "  FINAL_CMD (expected)   : $(eval echo \${EXPECTED_CMD_"$i"})"
			echo "  FINAL_TARGET           : $FINAL_TARGET"
			echo "  FINAL_TARGET (expected): $(eval echo \${EXPECTED_TARGET_"$i"})"
			at_least_one_ko="true"
		fi
	done

	if test "$at_least_one_ko" = "true"
	then
		return 255
	else
		return 0
	fi
}