Make arguments simpler to deal with in action functions

<source> was an optional argument, and the second out of three passed,
meaning when only two arguments were given, the action functions would
have to know to use the second argument as <target>, instead of the the
third. Now the second argument is always <target>, and the <source>
argument is always the third, if given.

src/lib/dotify-action.sh

@@ -1,17 +1,26 @@
 dotify-action() {
   local action="$1"
-  local source="$2"
-  local target="$3"
+
+  if [ $# -lt 3 ]; then
+    local target="$2"
+  else
+    local source="$2"
+    local target="$3"
+  fi
 
   if [ "$action" == "default" ]; then
     action="$DOTIFY_OPT_DEFAULT_ACTION"
   fi
 
-  ! valid_action="$(command -v "dotify-action-${action}")"
+  ! local valid_action="$(command -v "dotify-action-${action}")"
   if [ -z "$valid_action" ]; then
     echo "ERROR: \"$action\" is not a valid action." >&2
     return 1
   fi
 
-  dotify-action-${action} "$source" "$target"
+  if [ -n "$source" ]; then
+    dotify-action-${action} "$DOTIFY_RUN_MODE" "$target" "$source"
+  else
+    dotify-action-${action} "$DOTIFY_RUN_MODE" "$target"
+  fi
 }

test/lib/dotify-action-test.sh

@@ -6,7 +6,8 @@ source "../../src/lib/dotify-action.sh"
 # dotify-action() tests
 #
 
-# Set required option ENV
+# Set required environment variables.
+DOTIFY_RUN_MODE="install"
 DOTIFY_OPT_DEFAULT_ACTION="link"
 
 # Simple mock for link action.
@@ -16,10 +17,17 @@ dotify-action-link() {
 
 
 # Given a specific action.
-assert "dotify-action link ackrc .ackrc" "link stub: ackrc .ackrc"
+assert "dotify-action link ackrc .ackrc" "link stub: install .ackrc ackrc"
+
+# Given a specific action without a <source>.
+assert "dotify-action link .ackrc" "link stub: install .ackrc"
 
 # Given "default" action, it uses configured default action.
-assert "dotify-action default ackrc .ackrc" "link stub: ackrc .ackrc"
+assert "dotify-action default ackrc .ackrc" "link stub: install .ackrc ackrc"
+
+# Given "default" action without a <source>, it uses configured default
+# action.
+assert "dotify-action default .ackrc" "link stub: install .ackrc"
 
 # Given a invalid action.
 assert_raises "dotify-action foo ackrc .ackrc" 1