Add history graph API

[thirdparty/git.git] / graph.c

#include "cache.h"
#include "commit.h"
#include "graph.h"
#include "diff.h"
#include "revision.h"

/*
 * TODO:
 * - Add colors to the graph.
 *   Pick a color for each column, and print all characters
 *   in that column with the specified color.
 *
 * - Limit the number of columns, similar to the way gitk does.
 *   If we reach more than a specified number of columns, omit
 *   sections of some columns.
 *
 * - The output during the GRAPH_PRE_COMMIT and GRAPH_COLLAPSING states
 *   could be made more compact by printing horizontal lines, instead of
 *   long diagonal lines.  For example, during collapsing, something like
 *   this:          instead of this:
 *   | | | | |      | | | | |
 *   | |_|_|/       | | | |/
 *   |/| | |        | | |/|
 *   | | | |        | |/| |
 *                  |/| | |
 *                  | | | |
 *
 *   If there are several parallel diagonal lines, they will need to be
 *   replaced with horizontal lines on subsequent rows.
 */

struct column {
	/*
	 * The parent commit of this column.
	 */
	struct commit *commit;
	/*
	 * XXX: Once we add support for colors, struct column could also
	 * contain the color of its branch line.
	 */
};

enum graph_state {
	GRAPH_PADDING,
	GRAPH_SKIP,
	GRAPH_PRE_COMMIT,
	GRAPH_COMMIT,
	GRAPH_POST_MERGE,
	GRAPH_COLLAPSING
};

struct git_graph {
	/*
	 * The commit currently being processed
	 */
	struct commit *commit;
	/*
	 * The number of parents this commit has.
	 * (Stored so we don't have to walk over them each time we need
	 * this number)
	 */
	int num_parents;
	/*
	 * The next expansion row to print
	 * when state is GRAPH_PRE_COMMIT
	 */
	int expansion_row;
	/*
	 * The current output state.
	 * This tells us what kind of line graph_next_line() should output.
	 */
	enum graph_state state;
	/*
	 * The maximum number of columns that can be stored in the columns
	 * and new_columns arrays.  This is also half the number of entries
	 * that can be stored in the mapping and new_mapping arrays.
	 */
	int column_capacity;
	/*
	 * The number of columns (also called "branch lines" in some places)
	 */
	int num_columns;
	/*
	 * The number of columns in the new_columns array
	 */
	int num_new_columns;
	/*
	 * The number of entries in the mapping array
	 */
	int mapping_size;
	/*
	 * The column state before we output the current commit.
	 */
	struct column *columns;
	/*
	 * The new column state after we output the current commit.
	 * Only valid when state is GRAPH_COLLAPSING.
	 */
	struct column *new_columns;
	/*
	 * An array that tracks the current state of each
	 * character in the output line during state GRAPH_COLLAPSING.
	 * Each entry is -1 if this character is empty, or a non-negative
	 * integer if the character contains a branch line.  The value of
	 * the integer indicates the target position for this branch line.
	 * (I.e., this array maps the current column positions to their
	 * desired positions.)
	 *
	 * The maximum capacity of this array is always
	 * sizeof(int) * 2 * column_capacity.
	 */
	int *mapping;
	/*
	 * A temporary array for computing the next mapping state
	 * while we are outputting a mapping line.  This is stored as part
	 * of the git_graph simply so we don't have to allocate a new
	 * temporary array each time we have to output a collapsing line.
	 */
	int *new_mapping;
};

struct git_graph *graph_init(void)
{
	struct git_graph *graph = xmalloc(sizeof(struct git_graph));
	graph->commit = NULL;
	graph->num_parents = 0;
	graph->expansion_row = 0;
	graph->state = GRAPH_PADDING;
	graph->num_columns = 0;
	graph->num_new_columns = 0;
	graph->mapping_size = 0;

	/*
	 * Allocate a reasonably large default number of columns
	 * We'll automatically grow columns later if we need more room.
	 */
	graph->column_capacity = 30;
	graph->columns = xmalloc(sizeof(struct column) *
				 graph->column_capacity);
	graph->new_columns = xmalloc(sizeof(struct column) *
				     graph->column_capacity);
	graph->mapping = xmalloc(sizeof(int) * 2 * graph->column_capacity);
	graph->new_mapping = xmalloc(sizeof(int) * 2 * graph->column_capacity);

	return graph;
}

void graph_release(struct git_graph *graph)
{
	free(graph->columns);
	free(graph->new_columns);
	free(graph->mapping);
	free(graph);
}

static void graph_ensure_capacity(struct git_graph *graph, int num_columns)
{
	if (graph->column_capacity >= num_columns)
		return;

	do {
		graph->column_capacity *= 2;
	} while (graph->column_capacity < num_columns);

	graph->columns = xrealloc(graph->columns,
				  sizeof(struct column) *
				  graph->column_capacity);
	graph->new_columns = xrealloc(graph->new_columns,
				      sizeof(struct column) *
				      graph->column_capacity);
	graph->mapping = xrealloc(graph->mapping,
				  sizeof(int) * 2 * graph->column_capacity);
	graph->new_mapping = xrealloc(graph->new_mapping,
				      sizeof(int) * 2 * graph->column_capacity);
}

static void graph_insert_into_new_columns(struct git_graph *graph,
					  struct commit *commit,
					  int *mapping_index)
{
	int i;

	/*
	 * Ignore uinteresting and pruned commits
	 */
	if (commit->object.flags & (UNINTERESTING | TREESAME))
		return;

	/*
	 * If the commit is already in the new_columns list, we don't need to
	 * add it.  Just update the mapping correctly.
	 */
	for (i = 0; i < graph->num_new_columns; i++) {
		if (graph->new_columns[i].commit == commit) {
			graph->mapping[*mapping_index] = i;
			*mapping_index += 2;
			return;
		}
	}

	/*
	 * This commit isn't already in new_columns.  Add it.
	 */
	graph->new_columns[graph->num_new_columns].commit = commit;
	graph->mapping[*mapping_index] = graph->num_new_columns;
	*mapping_index += 2;
	graph->num_new_columns++;
}

static void graph_update_columns(struct git_graph *graph)
{
	struct commit_list *parent;
	struct column *tmp_columns;
	int max_new_columns;
	int mapping_idx;
	int i, seen_this;

	/*
	 * Swap graph->columns with graph->new_columns
	 * graph->columns contains the state for the previous commit,
	 * and new_columns now contains the state for our commit.
	 *
	 * We'll re-use the old columns array as storage to compute the new
	 * columns list for the commit after this one.
	 */
	tmp_columns = graph->columns;
	graph->columns = graph->new_columns;
	graph->num_columns = graph->num_new_columns;

	graph->new_columns = tmp_columns;
	graph->num_new_columns = 0;

	/*
	 * Now update new_columns and mapping with the information for the
	 * commit after this one.
	 *
	 * First, make sure we have enough room.  At most, there will
	 * be graph->num_columns + graph->num_parents columns for the next
	 * commit.
	 */
	max_new_columns = graph->num_columns + graph->num_parents;
	graph_ensure_capacity(graph, max_new_columns);

	/*
	 * Clear out graph->mapping
	 */
	graph->mapping_size = 2 * max_new_columns;
	for (i = 0; i < graph->mapping_size; i++)
		graph->mapping[i] = -1;

	/*
	 * Populate graph->new_columns and graph->mapping
	 *
	 * Some of the parents of this commit may already be in
	 * graph->columns.  If so, graph->new_columns should only contain a
	 * single entry for each such commit.  graph->mapping should
	 * contain information about where each current branch line is
	 * supposed to end up after the collapsing is performed.
	 */
	seen_this = 0;
	mapping_idx = 0;
	for (i = 0; i <= graph->num_columns; i++) {
		struct commit *col_commit;
		if (i == graph->num_columns) {
			if (seen_this)
				break;
			col_commit = graph->commit;
		} else {
			col_commit = graph->columns[i].commit;
		}

		if (col_commit == graph->commit) {
			seen_this = 1;
			for (parent = graph->commit->parents;
			     parent;
			     parent = parent->next) {
				graph_insert_into_new_columns(graph,
							      parent->item,
							      &mapping_idx);
			}
		} else {
			graph_insert_into_new_columns(graph, col_commit,
						      &mapping_idx);
		}
	}

	/*
	 * Shrink mapping_size to be the minimum necessary
	 */
	while (graph->mapping_size > 1 &&
	       graph->mapping[graph->mapping_size - 1] < 0)
		graph->mapping_size--;
}

void graph_update(struct git_graph *graph, struct commit *commit)
{
	struct commit_list *parent;

	/*
	 * Set the new commit
	 */
	graph->commit = commit;

	/*
	 * Count how many parents this commit has
	 */
	graph->num_parents = 0;
	for (parent = commit->parents; parent; parent = parent->next)
		graph->num_parents++;

	/*
	 * Call graph_update_columns() to update
	 * columns, new_columns, and mapping.
	 */
	graph_update_columns(graph);

	graph->expansion_row = 0;

	/*
	 * Update graph->state.
	 *
	 * If the previous commit didn't get to the GRAPH_PADDING state,
	 * it never finished its output.  Goto GRAPH_SKIP, to print out
	 * a line to indicate that portion of the graph is missing.
	 *
	 * Otherwise, if there are 3 or more parents, we need to print
	 * extra rows before the commit, to expand the branch lines around
	 * it and make room for it.
	 *
	 * If there are less than 3 parents, we can immediately print the
	 * commit line.
	 */
	if (graph->state != GRAPH_PADDING)
		graph->state = GRAPH_SKIP;
	else if (graph->num_parents >= 3)
		graph->state = GRAPH_PRE_COMMIT;
	else
		graph->state = GRAPH_COMMIT;
}

static int graph_is_mapping_correct(struct git_graph *graph)
{
	int i;

	/*
	 * The mapping is up to date if each entry is at its target,
	 * or is 1 greater than its target.
	 * (If it is 1 greater than the target, '/' will be printed, so it
	 * will look correct on the next row.)
	 */
	for (i = 0; i < graph->mapping_size; i++) {
		int target = graph->mapping[i];
		if (target < 0)
			continue;
		if (target == (i / 2))
			continue;
		return 0;
	}

	return 1;
}

static void graph_pad_horizontally(struct git_graph *graph, struct strbuf *sb)
{
	/*
	 * Add additional spaces to the end of the strbuf, so that all
	 * lines for a particular commit have the same width.
	 *
	 * This way, fields printed to the right of the graph will remain
	 * aligned for the entire commit.
	 *
	 * This computation results in 3 extra space to the right in most
	 * cases, but only 1 extra space if the commit doesn't have any
	 * children that have already been displayed in the graph (i.e.,
	 * if the current commit isn't in graph->columns).
	 */
	size_t extra;
	size_t final_width = graph->num_columns + graph->num_parents;
	if (graph->num_parents < 1)
		final_width++;
	final_width *= 2;

	if (sb->len >= final_width)
		return;

	extra = final_width - sb->len;
	strbuf_addf(sb, "%*s", (int) extra, "");
}

static void graph_output_padding_line(struct git_graph *graph,
				      struct strbuf *sb)
{
	int i;

	/*
	 * We could conceivable be called with a NULL commit
	 * if our caller has a bug, and invokes graph_next_line()
	 * immediately after graph_init(), without first calling
	 * graph_update().  Return without outputting anything in this
	 * case.
	 */
	if (!graph->commit)
		return;

	/*
	 * Output a padding row, that leaves all branch lines unchanged
	 */
	for (i = 0; i < graph->num_new_columns; i++) {
		strbuf_addstr(sb, "| ");
	}

	graph_pad_horizontally(graph, sb);
}

static void graph_output_skip_line(struct git_graph *graph, struct strbuf *sb)
{
	/*
	 * Output an ellipsis to indicate that a portion
	 * of the graph is missing.
	 */
	strbuf_addstr(sb, "...");
	graph_pad_horizontally(graph, sb);

	if (graph->num_parents >= 3)
		graph->state = GRAPH_PRE_COMMIT;
	else
		graph->state = GRAPH_COMMIT;
}

static void graph_output_pre_commit_line(struct git_graph *graph,
					 struct strbuf *sb)
{
	int num_expansion_rows;
	int i, seen_this;

	/*
	 * This function formats a row that increases the space around a commit
	 * with multiple parents, to make room for it.  It should only be
	 * called when there are 3 or more parents.
	 *
	 * We need 2 extra rows for every parent over 2.
	 */
	assert(graph->num_parents >= 3);
	num_expansion_rows = (graph->num_parents - 2) * 2;

	/*
	 * graph->expansion_row tracks the current expansion row we are on.
	 * It should be in the range [0, num_expansion_rows - 1]
	 */
	assert(0 <= graph->expansion_row &&
	       graph->expansion_row < num_expansion_rows);

	/*
	 * Output the row
	 */
	seen_this = 0;
	for (i = 0; i < graph->num_columns; i++) {
		struct column *col = &graph->columns[i];
		if (col->commit == graph->commit) {
			seen_this = 1;
			strbuf_addf(sb, "| %*s", graph->expansion_row, "");
		} else if (seen_this) {
			strbuf_addstr(sb, "\\ ");
		} else {
			strbuf_addstr(sb, "| ");
		}
	}

	graph_pad_horizontally(graph, sb);

	/*
	 * Increment graph->expansion_row,
	 * and move to state GRAPH_COMMIT if necessary
	 */
	graph->expansion_row++;
	if (graph->expansion_row >= num_expansion_rows)
		graph->state = GRAPH_COMMIT;
}

void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb)
{
	int seen_this = 0;
	int i, j;

	/*
	 * Output the row containing this commit
	 * Iterate up to and including graph->num_columns,
	 * since the current commit may not be in any of the existing
	 * columns.  (This happens when the current commit doesn't have any
	 * children that we have already processed.)
	 */
	seen_this = 0;
	for (i = 0; i <= graph->num_columns; i++) {
		struct commit *col_commit;
		if (i == graph->num_columns) {
			if (seen_this)
				break;
			col_commit = graph->commit;
		} else {
			col_commit = graph->columns[i].commit;
		}

		if (col_commit == graph->commit) {
			seen_this = 1;
			if (graph->num_parents > 1)
				strbuf_addch(sb, 'M');
			else
				strbuf_addch(sb, '*');

			if (graph->num_parents < 2)
				strbuf_addch(sb, ' ');
			else if (graph->num_parents == 2)
				strbuf_addstr(sb, "  ");
			else {
				int num_dashes =
					((graph->num_parents - 2) * 2) - 1;
				for (j = 0; j < num_dashes; j++)
					strbuf_addch(sb, '-');
				strbuf_addstr(sb, ". ");
			}
		} else if (seen_this && (graph->num_parents > 1)) {
			strbuf_addstr(sb, "\\ ");
		} else {
			strbuf_addstr(sb, "| ");
		}
	}

	graph_pad_horizontally(graph, sb);

	/*
	 * Update graph->state
	 */
	if (graph->num_parents > 1)
		graph->state = GRAPH_POST_MERGE;
	else if (graph_is_mapping_correct(graph))
		graph->state = GRAPH_PADDING;
	else
		graph->state = GRAPH_COLLAPSING;
}

void graph_output_post_merge_line(struct git_graph *graph, struct strbuf *sb)
{
	int seen_this = 0;
	int i, j;

	/*
	 * Output the post-merge row
	 */
	for (i = 0; i <= graph->num_columns; i++) {
		struct commit *col_commit;
		if (i == graph->num_columns) {
			if (seen_this)
				break;
			col_commit = graph->commit;
		} else {
			col_commit = graph->columns[i].commit;
		}

		if (col_commit == graph->commit) {
			seen_this = 1;
			strbuf_addch(sb, '|');
			for (j = 0; j < graph->num_parents - 1; j++)
				strbuf_addstr(sb, "\\ ");
			if (graph->num_parents == 2)
				strbuf_addch(sb, ' ');
		} else if (seen_this && (graph->num_parents > 2)) {
			strbuf_addstr(sb, "\\ ");
		} else {
			strbuf_addstr(sb, "| ");
		}
	}

	graph_pad_horizontally(graph, sb);

	/*
	 * Update graph->state
	 */
	if (graph_is_mapping_correct(graph))
		graph->state = GRAPH_PADDING;
	else
		graph->state = GRAPH_COLLAPSING;
}

void graph_output_collapsing_line(struct git_graph *graph, struct strbuf *sb)
{
	int i;
	int *tmp_mapping;

	/*
	 * Clear out the new_mapping array
	 */
	for (i = 0; i < graph->mapping_size; i++)
		graph->new_mapping[i] = -1;

	for (i = 0; i < graph->mapping_size; i++) {
		int target = graph->mapping[i];
		if (target < 0)
			continue;

		/*
		 * Since update_columns() always inserts the leftmost
		 * column first, each branch's target location should
		 * always be either its current location or to the left of
		 * its current location.
		 *
		 * We never have to move branches to the right.  This makes
		 * the graph much more legible, since whenever branches
		 * cross, only one is moving directions.
		 */
		assert(target * 2 <= i);

		if (target * 2 == i) {
			/*
			 * This column is already in the
			 * correct place
			 */
			assert(graph->new_mapping[i] == -1);
			graph->new_mapping[i] = target;
		} else if (graph->new_mapping[i - 1] < 0) {
			/*
			 * Nothing is to the left.
			 * Move to the left by one
			 */
			graph->new_mapping[i - 1] = target;
		} else if (graph->new_mapping[i - 1] == target) {
			/*
			 * There is a branch line to our left
			 * already, and it is our target.  We
			 * combine with this line, since we share
			 * the same parent commit.
			 *
			 * We don't have to add anything to the
			 * output or new_mapping, since the
			 * existing branch line has already taken
			 * care of it.
			 */
		} else {
			/*
			 * There is a branch line to our left,
			 * but it isn't our target.  We need to
			 * cross over it.
			 *
			 * The space just to the left of this
			 * branch should always be empty.
			 */
			assert(graph->new_mapping[i - 1] > target);
			assert(graph->new_mapping[i - 2] < 0);
			graph->new_mapping[i - 2] = target;
		}
	}

	/*
	 * The new mapping may be 1 smaller than the old mapping
	 */
	if (graph->new_mapping[graph->mapping_size - 1] < 0)
		graph->mapping_size--;

	/*
	 * Output out a line based on the new mapping info
	 */
	for (i = 0; i < graph->mapping_size; i++) {
		int target = graph->new_mapping[i];
		if (target < 0)
			strbuf_addch(sb, ' ');
		else if (target * 2 == i)
			strbuf_addch(sb, '|');
		else
			strbuf_addch(sb, '/');
	}

	graph_pad_horizontally(graph, sb);

	/*
	 * Swap mapping and new_mapping
	 */
	tmp_mapping = graph->mapping;
	graph->mapping = graph->new_mapping;
	graph->new_mapping = tmp_mapping;

	/*
	 * If graph->mapping indicates that all of the branch lines
	 * are already in the correct positions, we are done.
	 * Otherwise, we need to collapse some branch lines together.
	 */
	if (graph_is_mapping_correct(graph))
		graph->state = GRAPH_PADDING;
}

int graph_next_line(struct git_graph *graph, struct strbuf *sb)
{
	switch (graph->state) {
	case GRAPH_PADDING:
		graph_output_padding_line(graph, sb);
		return 0;
	case GRAPH_SKIP:
		graph_output_skip_line(graph, sb);
		return 0;
	case GRAPH_PRE_COMMIT:
		graph_output_pre_commit_line(graph, sb);
		return 0;
	case GRAPH_COMMIT:
		graph_output_commit_line(graph, sb);
		return 1;
	case GRAPH_POST_MERGE:
		graph_output_post_merge_line(graph, sb);
		return 0;
	case GRAPH_COLLAPSING:
		graph_output_collapsing_line(graph, sb);
		return 0;
	}

	assert(0);
	return 0;
}

void graph_padding_line(struct git_graph *graph, struct strbuf *sb)
{
	int i, j;

	if (graph->state != GRAPH_COMMIT) {
		graph_next_line(graph, sb);
		return;
	}

	/*
	 * Output the row containing this commit
	 * Iterate up to and including graph->num_columns,
	 * since the current commit may not be in any of the existing
	 * columns.  (This happens when the current commit doesn't have any
	 * children that we have already processed.)
	 */
	for (i = 0; i < graph->num_columns; i++) {
		struct commit *col_commit = graph->columns[i].commit;
		if (col_commit == graph->commit) {
			strbuf_addch(sb, '|');

			if (graph->num_parents < 3)
				strbuf_addch(sb, ' ');
			else {
				int num_spaces = ((graph->num_parents - 2) * 2);
				for (j = 0; j < num_spaces; j++)
					strbuf_addch(sb, ' ');
			}
		} else {
			strbuf_addstr(sb, "| ");
		}
	}

	graph_pad_horizontally(graph, sb);
}

int graph_is_commit_finished(struct git_graph const *graph)
{
	return (graph->state == GRAPH_PADDING);
}

void graph_show_commit(struct git_graph *graph)
{
	struct strbuf msgbuf;
	int shown_commit_line = 0;

	if (!graph)
		return;

	strbuf_init(&msgbuf, 0);

	while (!shown_commit_line) {
		shown_commit_line = graph_next_line(graph, &msgbuf);
		fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
		if (!shown_commit_line)
			putchar('\n');
		strbuf_setlen(&msgbuf, 0);
	}

	strbuf_release(&msgbuf);
}

void graph_show_oneline(struct git_graph *graph)
{
	struct strbuf msgbuf;

	if (!graph)
		return;

	strbuf_init(&msgbuf, 0);
	graph_next_line(graph, &msgbuf);
	fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
	strbuf_release(&msgbuf);
}

void graph_show_padding(struct git_graph *graph)
{
	struct strbuf msgbuf;

	if (!graph)
		return;

	strbuf_init(&msgbuf, 0);
	graph_padding_line(graph, &msgbuf);
	fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
	strbuf_release(&msgbuf);
}

int graph_show_remainder(struct git_graph *graph)
{
	struct strbuf msgbuf;
	int shown = 0;

	if (!graph)
		return 0;

	if (graph_is_commit_finished(graph))
		return 0;

	strbuf_init(&msgbuf, 0);
	for (;;) {
		graph_next_line(graph, &msgbuf);
		fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
		strbuf_setlen(&msgbuf, 0);
		shown = 1;

		if (!graph_is_commit_finished(graph))
			putchar('\n');
		else
			break;
	}
	strbuf_release(&msgbuf);

	return shown;
}


void graph_show_strbuf(struct git_graph *graph, struct strbuf const *sb)
{
	char *p;

	if (!graph) {
		fwrite(sb->buf, sizeof(char), sb->len, stdout);
		return;
	}

	/*
	 * Print the strbuf line by line,
	 * and display the graph info before each line but the first.
	 */
	p = sb->buf;
	while (p) {
		size_t len;
		char *next_p = strchr(p, '\n');
		if (next_p) {
			next_p++;
			len = next_p - p;
		} else {
			len = (sb->buf + sb->len) - p;
		}
		fwrite(p, sizeof(char), len, stdout);
		if (next_p && *next_p != '\0')
			graph_show_oneline(graph);
		p = next_p;
	}
}

void graph_show_commit_msg(struct git_graph *graph,
			   struct strbuf const *sb)
{
	int newline_terminated;

	if (!graph) {
		/*
		 * If there's no graph, just print the message buffer.
		 *
		 * The message buffer for CMIT_FMT_ONELINE and
		 * CMIT_FMT_USERFORMAT are already missing a terminating
		 * newline.  All of the other formats should have it.
		 */
		fwrite(sb->buf, sizeof(char), sb->len, stdout);
		return;
	}

	newline_terminated = (sb->len && sb->buf[sb->len - 1] == '\n');

	/*
	 * Show the commit message
	 */
	graph_show_strbuf(graph, sb);

	/*
	 * If there is more output needed for this commit, show it now
	 */
	if (!graph_is_commit_finished(graph)) {
		/*
		 * If sb doesn't have a terminating newline, print one now,
		 * so we can start the remainder of the graph output on a
		 * new line.
		 */
		if (!newline_terminated)
			putchar('\n');

		graph_show_remainder(graph);

		/*
		 * If sb ends with a newline, our output should too.
		 */
		if (newline_terminated)
			putchar('\n');
	}
}