/*
 * The statistics page counts each author's commits in the most recent periods
 * of the size asked for. It reads no diff and no blob contents, so the whole
 * thing costs about one rev-list.
 */

#define USE_THE_REPOSITORY_VARIABLE

#include "cgit.h"
#include "html.h"
#include "parsing.h"
#include "ui-shared.h"
#include "ui-stats.h"

#define DEFAULT_AUTHOR_ROWS 10

// How many periods the page shows side by side.
#define PERIOD_COLUMNS 4

struct cgit_period {
	const char code;
	const char *name;

	// Move a tm back to the first day of the period it falls in.
	void (*trunc)(struct tm *tm);

	// Step a truncated tm n whole periods, back when n is negative.
	void (*step)(struct tm *tm, int n);

	// Label the period a tm falls in. The buffer is reused, so a caller
	// that keeps a label copies it.
	char *(*pretty)(struct tm *tm);
};

// One author's share of the window. periods is keyed by the label of a period,
// with the commit count stored in the util field itself rather than behind
// another allocation.
struct authorstat {
	long total;
	struct string_list periods;
};

static void trunc_week(struct tm *tm)
{
	time_t t = timegm(tm);

	// tm_wday counts from Sunday, while the label comes from %V and %G,
	// which number the ISO weeks that start on Monday.
	t -= ((tm->tm_wday + 6) % 7) * SECONDS_PER_DAY;
	gmtime_r(&t, tm);
}

static void step_week(struct tm *tm, int n)
{
	time_t t = timegm(tm);

	t += n * SECONDS_PER_WEEK;
	gmtime_r(&t, tm);
}

static char *pretty_week(struct tm *tm)
{
	static char buf[10];

	// A year of five digits or more does not fit, and strftime then leaves
	// the buffer with contents the standard says nothing about, so empty it
	// rather than return whatever the last week left.
	if (!strftime(buf, sizeof(buf), "W%V %G", tm))
		buf[0] = '\0';
	return buf;
}

static void trunc_month(struct tm *tm)
{
	tm->tm_mday = 1;
}

static void step_month(struct tm *tm, int n)
{
	tm->tm_mon += n;
	if (tm->tm_mon < 0) {
		tm->tm_year--;
		tm->tm_mon += 12;
	} else if (tm->tm_mon > 11) {
		tm->tm_year++;
		tm->tm_mon -= 12;
	}
}

static char *pretty_month(struct tm *tm)
{
	static const char *months[] = {
		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
	};
	return cgit_fmt("%s %d", months[tm->tm_mon], tm->tm_year + 1900);
}

static void trunc_quarter(struct tm *tm)
{
	trunc_month(tm);
	tm->tm_mon -= tm->tm_mon % 3;
}

static void step_quarter(struct tm *tm, int n)
{
	step_month(tm, 3 * n);
}

static char *pretty_quarter(struct tm *tm)
{
	return cgit_fmt("Q%d %d", tm->tm_mon / 3 + 1, tm->tm_year + 1900);
}

static void trunc_year(struct tm *tm)
{
	trunc_month(tm);
	tm->tm_mon = 0;
}

static void step_year(struct tm *tm, int n)
{
	tm->tm_year += n;
}

static char *pretty_year(struct tm *tm)
{
	return cgit_fmt("%d", tm->tm_year + 1900);
}

// The order runs from the finest window to the coarsest, because a repository
// caps the page by storing an index into this table as its max-stats.
static const struct cgit_period periods[] = {
	{'w', "week", trunc_week, step_week, pretty_week},
	{'m', "month", trunc_month, step_month, pretty_month},
	{'q', "quarter", trunc_quarter, step_quarter, pretty_quarter},
	{'y', "year", trunc_year, step_year, pretty_year},
};

static void window_start(const struct cgit_period *period, struct tm *tm)
{
	// Read once, so the buckets and the column labels agree on the window
	// even when the clock crosses a period boundary between them.
	static time_t now;
	int i;

	if (!now)
		time(&now);
	gmtime_r(&now, tm);
	period->trunc(tm);
	// The window opens at midnight, not at the time of day it is now.
	tm->tm_hour = 0;
	tm->tm_min = 0;
	tm->tm_sec = 0;
	for (i = 1; i < PERIOD_COLUMNS; i++)
		period->step(tm, -1);
}

static void add_commit(struct string_list *authors, struct commitinfo *info,
	const struct cgit_period *period)
{
	struct string_list_item *author, *bucket;
	struct authorstat *stats;
	char *name, *label;
	struct tm date;
	time_t when;

	// A commit can lack an author header, so fall back rather than
	// handing xstrdup a NULL.
	name = xstrdup(info->author ? info->author : "(unknown)");
	author = string_list_insert(authors, name);
	if (!author->util)
		author->util = xcalloc(1, sizeof(struct authorstat));
	else
		free(name);
	stats = author->util;
	when = info->committer_date;
	// A crafted commit can carry a date outside the range gmtime_r can
	// represent, which would leave date uninitialised and later index the
	// month table out of bounds.
	if (!gmtime_r(&when, &date))
		return;
	period->trunc(&date);
	label = xstrdup(period->pretty(&date));
	bucket = string_list_insert(&stats->periods, label);
	if (bucket->util)
		free(label);
	bucket->util = (void *)((uintptr_t)bucket->util + 1);

	stats->total++;
}

/*
 * Count the commits in the displayed window into authors, whose util fields
 * hold a struct authorstat, and return non-zero once an error page has
 * answered instead. Merge commits are left out, so that pulling a branch in
 * does not credit the merger with its commits.
 */
static int collect_stats(const struct cgit_period *period, struct string_list *authors)
{
	struct rev_info rev;
	struct commit *commit;
	struct strvec argv = STRVEC_INIT;
	time_t since;
	struct tm tm;

	window_start(period, &tm);
	since = timegm(&tm);

	strvec_pushl(&argv, "stats", ctx.qry.head, NULL);
	if (ctx.qry.path)
		strvec_pushl(&argv, "--", ctx.qry.path, NULL);
	repo_init_revisions(the_repository, &rev, NULL);
	rev.max_parents = 1;
	setup_revisions(argv.nr, argv.v, &rev, NULL);
	// Prune the walk to the displayed window instead of traversing the
	// whole history and discarding older commits. The check below still
	// bounds the period edge exactly.
	rev.max_age = since;
	if (cgit_prepare_walk(&rev)) {
		strvec_clear(&argv);
		return -1;
	}
	while ((commit = get_revision(&rev))) {
		struct commitinfo *info = cgit_parse_commit(commit);

		if ((time_t)info->committer_date >= since)
			add_commit(authors, info, period);

		cgit_free_commitinfo(info);
		release_commit_memory(the_repository->parsed_objects, commit);
		commit->parents = NULL;
	}
	strvec_clear(&argv);
	return 0;
}

static int cmp_total_commits(const void *a, const void *b)
{
	const struct string_list_item *first = a;
	const struct string_list_item *second = b;
	const struct authorstat *first_stats = first->util;
	const struct authorstat *second_stats = second->util;

	// Report the sign only, since a long difference truncated to int
	// could flip and leave the comparator inconsistent.
	if (second_stats->total > first_stats->total)
		return 1;
	if (second_stats->total < first_stats->total)
		return -1;
	return 0;
}

/*
 * The column labels for the displayed window, oldest first. pretty hands back
 * a buffer it goes on to reuse, so the labels are copied here once and shared
 * by every table below.
 */
static struct string_list build_period_labels(const struct cgit_period *period)
{
	struct string_list labels = STRING_LIST_INIT_DUP;
	struct tm tm;
	int i;

	window_start(period, &tm);
	for (i = 0; i < PERIOD_COLUMNS; i++) {
		string_list_append(&labels, period->pretty(&tm));
		period->step(&tm, 1);
	}
	return labels;
}

/*
 * The run of authors to sum is given as a start and a count rather than as
 * two indices, so that an empty author list cannot describe a run that wraps.
 */
static void print_row(struct string_list *authors, size_t from, size_t count,
	const char *name, const char *nameclass, const char *cellclass,
	const struct string_list *labels)
{
	struct authorstat *stats;
	struct string_list_item *bucket;
	size_t i, column;
	long total, subtotal;

	total = 0;
	htmlf("<tr><td class='%s'>", nameclass);
	html_txt(name);
	html("</td>");
	for (column = 0; column < labels->nr; column++) {
		const char *label = labels->items[column].string;

		subtotal = 0;
		for (i = from; i < from + count; i++) {
			stats = authors->items[i].util;
			bucket = string_list_lookup(&stats->periods, label);
			if (bucket)
				subtotal += (uintptr_t)bucket->util;
		}
		if (cellclass)
			htmlf("<td class='%s'>%ld</td>", cellclass, subtotal);
		else
			htmlf("<td>%ld</td>", subtotal);
		total += subtotal;
	}
	htmlf("<td class='sum'>%ld</td></tr>\n", total);
}

static void print_authors(struct string_list *authors, int max_rows, const struct string_list *labels)
{
	size_t i, column, rows;

	html("<table class='stats'>\n<tr><th scope='col'>Author</th>");
	for (column = 0; column < labels->nr; column++)
		htmlf("<th scope='col'>%s</th>", labels->items[column].string);
	html("<th scope='col'>Total</th></tr>\n");

	// The row count arrives through ofs, which carries -1 for "all".
	rows = (max_rows <= 0 || (size_t)max_rows > authors->nr) ? authors->nr : (size_t)max_rows;

	for (i = 0; i < rows; i++)
		print_row(authors, i, 1, authors->items[i].string, "left", NULL, labels);

	if (rows < authors->nr)
		print_row(authors, rows, authors->nr - rows,
			cgit_fmt("Others (%ld)", (long)(authors->nr - rows)), "left", NULL, labels);

	print_row(authors, 0, authors->nr, "Total", "total", "sum", labels);
	html("</table>\n");
}

static void print_options_form(const struct cgit_period *period, int top)
{
	int choices, i;

	html("<div class='cgit-panel'>\n");
	html("<strong>Stat options</strong>");
	html("<form method='get' aria-label='Stat options'>");
	cgit_add_hidden_formfields(1, 0);
	html("<div class='fields'>");
	if (ctx.repo->max_stats > 1) {
		choices = ctx.repo->max_stats;
		html("<label for='stats-period'>period</label>");
		html("<select id='stats-period' name='period'>");
		for (i = 0; i < choices; i++)
			html_option(cgit_fmt("%c", periods[i].code), periods[i].name,
				cgit_fmt("%c", period->code));
		html("</select>\n");
	}
	html("<label for='stats-authors'>authors</label>");
	html("<select id='stats-authors' name='ofs'>");
	html_intoption(10, "10", top);
	html_intoption(25, "25", top);
	html_intoption(50, "50", top);
	html_intoption(100, "100", top);
	html_intoption(-1, "all", top);
	html("</select>\n");
	html("<input type='submit' value='reload'>");
	html("</div>");
	html("</form>\n");
	html("</div>\n");
}

int cgit_find_stats_period(const char *expr, const struct cgit_period **period)
{
	size_t i;
	char code = '\0';

	if (!expr)
		return 0;

	if (strlen(expr) == 1)
		code = expr[0];

	for (i = 0; i < ARRAY_SIZE(periods); i++)
		if (periods[i].code == code || !strcmp(periods[i].name, expr)) {
			if (period)
				*period = &periods[i];
			return i + 1;
		}
	return 0;
}

const char *cgit_find_stats_periodname(int idx)
{
	if (idx > 0 && idx <= (int)ARRAY_SIZE(periods))
		return periods[idx - 1].name;
	else
		return "";
}

void cgit_show_stats(void)
{
	struct string_list authors = STRING_LIST_INIT_NODUP;
	struct string_list labels;
	const struct cgit_period *period;
	int top, period_index;
	const char *code = "w";

	if (ctx.qry.period)
		code = ctx.qry.period;

	period_index = cgit_find_stats_period(code, &period);
	if (!period_index) {
		cgit_print_error_page(404, "Not Found", "Unknown statistics type: %c", code[0]);
		return;
	}
	if (period_index > ctx.repo->max_stats) {
		cgit_print_error_page(400, "Bad Request", "Statistics type disabled: %s", period->name);
		return;
	}
	// A leading colon makes git read the path as a pathspec with magic,
	// which can end the request inside git.
	if (ctx.qry.path && ctx.qry.path[0] == ':') {
		cgit_print_error_page(400, "Bad Request", "Invalid path");
		return;
	}
	if (collect_stats(period, &authors))
		return;
	QSORT(authors.items, authors.nr, cmp_total_commits);

	top = ctx.qry.ofs;
	if (!top)
		top = DEFAULT_AUTHOR_ROWS;

	cgit_print_layout_start();
	print_options_form(period, top);

	htmlf("<h2>Commits per author per %s", period->name);
	if (ctx.qry.path) {
		html(" (path '");
		html_txt(ctx.qry.path);
		html("')");
	}
	html("</h2>\n");

	labels = build_period_labels(period);
	print_authors(&authors, top, &labels);
	string_list_clear(&labels, 0);

	cgit_print_layout_end();
}