1 files changed, 218 insertions, 0 deletions
diff --git a/src/bar.c b/src/bar.c
new file mode 100644
index 0000000..b928373
--- /dev/null
+++ b/src/bar.c
@@ -0,0 +1,218 @@
+// Copyright © Tavian Barnes <tavianator@tavianator.com>
+// SPDX-License-Identifier: 0BSD
+
+#include "prelude.h"
+#include "bar.h"
+#include "alloc.h"
+#include "atomic.h"
+#include "bfstd.h"
+#include "bit.h"
+#include "dstring.h"
+#include "sighook.h"
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/ioctl.h>
+
+struct bfs_bar {
+	int fd;
+	atomic unsigned int width;
+	atomic unsigned int height;
+
+	struct sighook *exit_hook;
+	struct sighook *winch_hook;
+};
+
+/** Get the terminal size, if possible. */
+static int bfs_bar_getsize(struct bfs_bar *bar) {
+#ifdef TIOCGWINSZ
+	struct winsize ws;
+	if (ioctl(bar->fd, TIOCGWINSZ, &ws) != 0) {
+		return -1;
+	}
+
+	store(&bar->width, ws.ws_col, relaxed);
+	store(&bar->height, ws.ws_row, relaxed);
+	return 0;
+#else
+	errno = ENOTSUP;
+	return -1;
+#endif
+}
+
+/** Write a string to the status bar (async-signal-safe). */
+static int bfs_bar_write(struct bfs_bar *bar, const char *str, size_t len) {
+	return xwrite(bar->fd, str, len) == len ? 0 : -1;
+}
+
+/** Write a string to the status bar (async-signal-safe). */
+static int bfs_bar_puts(struct bfs_bar *bar, const char *str) {
+	return bfs_bar_write(bar, str, strlen(str));
+}
+
+/** Number of decimal digits needed for terminal sizes. */
+#define ITOA_DIGITS ((USHRT_WIDTH + 2) / 3)
+
+/** Async Signal Safe itoa(). */
+static char *ass_itoa(char *str, unsigned int n) {
+	char *end = str + ITOA_DIGITS;
+	*end = '\0';
+
+	char *c = end;
+	do {
+		*--c = '0' + (n % 10);
+		n /= 10;
+	} while (n);
+
+	size_t len = end - c;
+	memmove(str, c, len + 1);
+	return str + len;
+}
+
+/** Update the size of the scrollable region. */
+static int bfs_bar_resize(struct bfs_bar *bar) {
+	static const char PREFIX[] =
+		"\033D"   // IND: Line feed, possibly scrolling
+		"\033[1A" // CUU: Move cursor up 1 row
+		"\0337"   // DECSC: Save cursor
+		"\033[;"; // DECSTBM: Set scrollable region
+	static const char SUFFIX[] =
+		"r"       // (end of DECSTBM)
+		"\0338"   // DECRC: Restore the cursor
+		"\033[J"; // ED: Erase display from cursor to end
+
+	char esc_seq[sizeof(PREFIX) + ITOA_DIGITS + sizeof(SUFFIX)];
+
+	// DECSTBM takes the height as the second argument
+	unsigned int height = load(&bar->height, relaxed) - 1;
+
+	char *cur = stpcpy(esc_seq, PREFIX);
+	cur = ass_itoa(cur, height);
+	cur = stpcpy(cur, SUFFIX);
+
+	return bfs_bar_write(bar, esc_seq, cur - esc_seq);
+}
+
+#ifdef SIGWINCH
+/** SIGWINCH handler. */
+static void bfs_bar_sigwinch(int sig, siginfo_t *info, void *arg) {
+	struct bfs_bar *bar = arg;
+	bfs_bar_getsize(bar);
+	bfs_bar_resize(bar);
+}
+#endif
+
+/** Reset the scrollable region and hide the bar. */
+static int bfs_bar_reset(struct bfs_bar *bar) {
+	return bfs_bar_puts(bar,
+		"\0337"  // DECSC: Save cursor
+		"\033[r" // DECSTBM: Reset scrollable region
+		"\0338"  // DECRC: Restore cursor
+		"\033[J" // ED: Erase display from cursor to end
+	);
+}
+
+/** Signal handler for process-terminating signals. */
+static void bfs_bar_sigexit(int sig, siginfo_t *info, void *arg) {
+	struct bfs_bar *bar = arg;
+	bfs_bar_reset(bar);
+}
+
+/** printf() to the status bar with a single write(). */
+attr(printf(2, 3))
+static int bfs_bar_printf(struct bfs_bar *bar, const char *format, ...) {
+	va_list args;
+	va_start(args, format);
+	dchar *str = dstrvprintf(format, args);
+	va_end(args);
+
+	if (!str) {
+		return -1;
+	}
+
+	int ret = bfs_bar_write(bar, str, dstrlen(str));
+	dstrfree(str);
+	return ret;
+}
+
+struct bfs_bar *bfs_bar_show(void) {
+	struct bfs_bar *bar = ALLOC(struct bfs_bar);
+	if (!bar) {
+		return NULL;
+	}
+
+	char term[L_ctermid];
+	ctermid(term);
+	if (strlen(term) == 0) {
+		errno = ENOTTY;
+		goto fail;
+	}
+
+	bar->fd = open(term, O_RDWR | O_CLOEXEC);
+	if (bar->fd < 0) {
+		goto fail;
+	}
+
+	if (bfs_bar_getsize(bar) != 0) {
+		goto fail_close;
+	}
+
+	bar->exit_hook = atsigexit(bfs_bar_sigexit, bar);
+	if (!bar->exit_hook) {
+		goto fail_close;
+	}
+
+#ifdef SIGWINCH
+	bar->winch_hook = sighook(SIGWINCH, bfs_bar_sigwinch, bar, 0);
+	if (!bar->winch_hook) {
+		goto fail_hook;
+	}
+#endif
+
+	bfs_bar_resize(bar);
+	return bar;
+
+fail_hook:
+	sigunhook(bar->exit_hook);
+fail_close:
+	close_quietly(bar->fd);
+fail:
+	free(bar);
+	return NULL;
+}
+
+unsigned int bfs_bar_width(const struct bfs_bar *bar) {
+	return load(&bar->width, relaxed);
+}
+
+int bfs_bar_update(struct bfs_bar *bar, const char *str) {
+	unsigned int height = load(&bar->height, relaxed);
+	return bfs_bar_printf(bar,
+		"\0337"      // DECSC: Save cursor
+		"\033[%u;0f" // HVP: Move cursor to row, column
+		"\033[K"     // EL: Erase line
+		"\033[7m"    // SGR reverse video
+		"%s"
+		"\033[27m"   // SGR reverse video off
+		"\0338",     // DECRC: Restore cursor
+		height,
+		str
+	);
+}
+
+void bfs_bar_hide(struct bfs_bar *bar) {
+	if (!bar) {
+		return;
+	}
+
+	sigunhook(bar->winch_hook);
+	sigunhook(bar->exit_hook);
+
+	bfs_bar_reset(bar);
+
+	xclose(bar->fd);
+	free(bar);
+}