+/*
+ * '--color-words' algorithm can be described as:
+ *
+ * 1. collect a the minus/plus lines of a diff hunk, divided into
+ * minus-lines and plus-lines;
+ *
+ * 2. break both minus-lines and plus-lines into words and
+ * place them into two mmfile_t with one word for each line;
+ *
+ * 3. use xdiff to run diff on the two mmfile_t to get the words level diff;
+ *
+ * And for the common parts of the both file, we output the plus side text.
+ * diff_words->current_plus is used to trace the current position of the plus file
+ * which printed. diff_words->last_minus is used to trace the last minus word
+ * printed.
+ *
+ * For '--graph' to work with '--color-words', we need to output the graph prefix
+ * on each line of color words output. Generally, there are two conditions on
+ * which we should output the prefix.
+ *
+ * 1. diff_words->last_minus == 0 &&
+ * diff_words->current_plus == diff_words->plus.text.ptr
+ *
+ * that is: the plus text must start as a new line, and if there is no minus
+ * word printed, a graph prefix must be printed.
+ *
+ * 2. diff_words->current_plus > diff_words->plus.text.ptr &&
+ * *(diff_words->current_plus - 1) == '\n'
+ *
+ * that is: a graph prefix must be printed following a '\n'
+ */
+static int color_words_output_graph_prefix(struct diff_words_data *diff_words)
+{
+ if ((diff_words->last_minus == 0 &&
+ diff_words->current_plus == diff_words->plus.text.ptr) ||
+ (diff_words->current_plus > diff_words->plus.text.ptr &&
+ *(diff_words->current_plus - 1) == '\n')) {
+ return 1;
+ } else {
+ return 0;
+ }
+}
+