[PATCH v7 04/10] column: add dense layout support

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Normally, all items will be gone through once. The largest cell will set
column width for all columns. With this strategy, one long item will
stretch out all columns, wasting space in between them.

With COL_DENSE enabled, it shrinks all columns to minimum, then attempts
to push the last row's cells over to the next column with hope that
everything still fits even there's one row less. The process is repeated
until the new layout cannot fit in given width anymore, or there's only
one row left (perfect!).

Apparently, this mode consumes more cpu than the former, but makes
better use of terminal space. For layouting one or two screens, cpu
usage should not be a problem.

Thanks-to: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 column.c          |   80 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 column.h          |    2 +
 t/t9002-column.sh |   48 +++++++++++++++++++++++++++++++
 3 files changed, 130 insertions(+), 0 deletions(-)

diff --git a/column.c b/column.c
index 6aaa829..95faec5 100644
--- a/column.c
+++ b/column.c
@@ -19,6 +19,7 @@ struct column_data {
 
 	int rows, cols;
 	int *len;			/* cell length */
+	int *width;			/* index to the longest row in column */
 };
 
 /* return length of 's' in letters, ANSI escapes stripped */
@@ -63,6 +64,69 @@ static void layout(struct column_data *data, int *width)
 	data->rows = DIV_ROUND_UP(data->list->nr, data->cols);
 }
 
+static void compute_column_width(struct column_data *data)
+{
+	int i, x, y;
+	for (x = 0; x < data->cols; x++) {
+		data->width[x] = XY2LINEAR(data, x, 0);
+		for (y = 0; y < data->rows; y++) {
+			i = XY2LINEAR(data, x, y);
+			if (i >= data->list->nr)
+				continue;
+			if (data->len[data->width[x]] < data->len[i])
+				data->width[x] = i;
+		}
+	}
+}
+
+/*
+ * Shrink all columns by shortening them one row each time (and adding
+ * more columns along the way). Hopefully the longest cell will be
+ * moved to the next column, column is shrunk so we have more space
+ * for new columns. The process ends when the whole thing no longer
+ * fits in data->total_width.
+ */
+static void shrink_columns(struct column_data *data)
+{
+	int x, y, total_width, cols, rows;
+
+	data->width = xrealloc(data->width,
+			       sizeof(*data->width) * data->cols);
+	for (x = 0; x < data->cols; x++) {
+		data->width[x] = 0;
+		for (y = 0; y < data->rows; y++) {
+			int len1 = data->len[data->width[x]];
+			int len2 = data->len[XY2LINEAR(data, x, y)];
+			if (len1 < len2)
+				data->width[x] = y;
+		}
+	}
+
+	while (data->rows > 1) {
+		rows = data->rows;
+		cols = data->cols;
+
+		data->rows--;
+		data->cols = DIV_ROUND_UP(data->list->nr, data->rows);
+		if (data->cols != cols)
+			data->width = xrealloc(data->width, sizeof(*data->width) * data->cols);
+
+		compute_column_width(data);
+
+		total_width = strlen(data->indent);
+		for (x = 0; x < data->cols; x++) {
+			total_width += data->len[data->width[x]];
+			total_width += data->padding;
+		}
+		if (total_width > data->total_width) {
+			data->rows = rows;
+			data->cols = cols;
+			compute_column_width(data);
+			break;
+		}
+	}
+}
+
 /* Display without layout when COL_ENABLED is not set */
 static void display_plain(const struct string_list *list,
 			  const char *indent, const char *nl)
@@ -82,7 +146,18 @@ static int display_cell(struct column_data *data, int initial_width,
 	i = XY2LINEAR(data, x, y);
 	if (i >= data->list->nr)
 		return -1;
+
 	len = data->len[i];
+	if (data->width && data->len[data->width[x]] < initial_width) {
+		/*
+		 * empty_cell has initial_width chars, if real column
+		 * is narrower, increase len a bit so we fill less
+		 * space.
+		 */
+		len += initial_width - data->len[data->width[x]];
+		len -= data->padding;
+	}
+
 	if (MODE(data->mode) == COL_MODE_COLUMN)
 		newline = i + data->rows >= data->list->nr;
 	else
@@ -119,6 +194,9 @@ static void display_table(const struct string_list *list,
 
 	layout(&data, &initial_width);
 
+	if (mode & COL_DENSE)
+		shrink_columns(&data);
+
 	empty_cell = xmalloc(initial_width + 1);
 	memset(empty_cell, ' ', initial_width);
 	empty_cell[initial_width] = '\0';
@@ -129,6 +207,7 @@ static void display_table(const struct string_list *list,
 	}
 
 	free(data.len);
+	free(data.width);
 	free(empty_cell);
 }
 
@@ -227,6 +306,7 @@ static int parse_option(const char *arg, int len,
 		{ MODE,   "column", COL_MODE_COLUMN },
 		{ MODE,   "row",    COL_MODE_ROW },
 		{ OPTION, "color",  COL_ANSI },
+		{ OPTION, "dense",  COL_DENSE },
 	};
 	int i;
 
diff --git a/column.h b/column.h
index d9d27c6..eb03c6c 100644
--- a/column.h
+++ b/column.h
@@ -7,6 +7,8 @@
 #define COL_ENABLED      (1 << 4)
 #define COL_ENABLED_SET  (1 << 5)  /* Has COL_ENABLED been set by config? */
 #define COL_ANSI         (1 << 6)  /* Remove ANSI escapes from string length */
+#define COL_DENSE        (1 << 7)  /* Shrink columns when possible,
+				      making space for more columns */
 #define COL_PARSEOPT     (1 << 8)  /* --column is given */
 
 #define explicitly_enable_column(c) \
diff --git a/t/t9002-column.sh b/t/t9002-column.sh
index cffb029..fe7a30e 100755
--- a/t/t9002-column.sh
+++ b/t/t9002-column.sh
@@ -71,6 +71,30 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success '20 columns, nodense' '
+	cat >expected <<\EOF &&
+one    seven
+two    eight
+three  nine
+four   ten
+five   eleven
+six
+EOF
+	git column --mode=column,nodense < lista > actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '20 columns, dense' '
+	cat >expected <<\EOF &&
+one   five  nine
+two   six   ten
+three seven eleven
+four  eight
+EOF
+	git column --mode=column,dense < lista > actual &&
+	test_cmp expected actual
+'
+
 test_expect_success '20 columns, padding 2' '
 	cat >expected <<\EOF &&
 one     seven
@@ -110,4 +134,28 @@ EOF
 	test_cmp expected actual
 '
 
+test_expect_success '20 columns, row first, nodense' '
+	cat >expected <<\EOF &&
+one    two
+three  four
+five   six
+seven  eight
+nine   ten
+eleven
+EOF
+	git column --mode=row,nodense <lista >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success '20 columns, row first, dense' '
+	cat >expected <<\EOF &&
+one   two    three
+four  five   six
+seven eight  nine
+ten   eleven
+EOF
+	git column --mode=row,dense <lista >actual &&
+	test_cmp expected actual
+'
+
 test_done
-- 
1.7.8.36.g69ee2