Replace wlr_log with sway_log

This commit mostly duplicates the wlr_log functions, although
with a sway_* prefix. (This is very similar to PR #2009.)
However, the logging function no longer needs to be replaceable,
so sway_log_init's second argument is used to set the exit
callback for sway_abort.

wlr_log_init is still invoked in sway/main.c

This commit makes it easier to remove the wlroots dependency for
the helper programs swaymsg, swaybg, swaybar, and swaynag.

common/log.c

@@ -1,16 +1,20 @@
+#define _POSIX_C_SOURCE 199506L
 #include <signal.h>
 #include <stdarg.h>
+#include <stdio.h>
 #include <stdlib.h>
+#include <time.h>
+#include <unistd.h>
 #include "log.h"
 
-void sway_terminate(int code);
+static terminate_callback_t log_terminate = exit;
 
 void _sway_abort(const char *format, ...) {
 	va_list args;
 	va_start(args, format);
-	_wlr_vlog(WLR_ERROR, format, args);
+	_sway_vlog(SWAY_ERROR, format, args);
 	va_end(args);
-	sway_terminate(EXIT_FAILURE);
+	log_terminate(EXIT_FAILURE);
 }
 
 bool _sway_assert(bool condition, const char *format, ...) {
@@ -20,7 +24,7 @@ bool _sway_assert(bool condition, const char *format, ...) {
 
 	va_list args;
 	va_start(args, format);
-	_wlr_vlog(WLR_ERROR, format, args);
+	_sway_vlog(SWAY_ERROR, format, args);
 	va_end(args);
 
 #ifndef NDEBUG
@@ -29,3 +33,80 @@ bool _sway_assert(bool condition, const char *format, ...) {
 
 	return false;
 }
+
+static bool colored = true;
+static sway_log_importance_t log_importance = SWAY_ERROR;
+
+static const char *verbosity_colors[] = {
+	[SWAY_SILENT] = "",
+	[SWAY_ERROR ] = "\x1B[1;31m",
+	[SWAY_INFO  ] = "\x1B[1;34m",
+	[SWAY_DEBUG ] = "\x1B[1;30m",
+};
+
+static void sway_log_stderr(sway_log_importance_t verbosity, const char *fmt,
+		va_list args) {
+	if (verbosity > log_importance) {
+		return;
+	}
+	// prefix the time to the log message
+	struct tm result;
+	time_t t = time(NULL);
+	struct tm *tm_info = localtime_r(&t, &result);
+	char buffer[26];
+
+	// generate time prefix
+	strftime(buffer, sizeof(buffer), "%F %T - ", tm_info);
+	fprintf(stderr, "%s", buffer);
+
+	unsigned c = (verbosity < SWAY_LOG_IMPORTANCE_LAST) ? verbosity :
+		SWAY_LOG_IMPORTANCE_LAST - 1;
+
+	if (colored && isatty(STDERR_FILENO)) {
+		fprintf(stderr, "%s", verbosity_colors[c]);
+	}
+
+	vfprintf(stderr, fmt, args);
+
+	if (colored && isatty(STDERR_FILENO)) {
+		fprintf(stderr, "\x1B[0m");
+	}
+	fprintf(stderr, "\n");
+}
+
+void sway_log_init(sway_log_importance_t verbosity, terminate_callback_t callback) {
+	if (verbosity < SWAY_LOG_IMPORTANCE_LAST) {
+		log_importance = verbosity;
+	}
+	if (callback) {
+		log_terminate = callback;
+	}
+}
+
+void _sway_vlog(sway_log_importance_t verbosity, const char *fmt, va_list args) {
+	sway_log_stderr(verbosity, fmt, args);
+}
+
+void _sway_log(sway_log_importance_t verbosity, const char *fmt, ...) {
+	va_list args;
+	va_start(args, fmt);
+	sway_log_stderr(verbosity, fmt, args);
+	va_end(args);
+}
+
+// strips the path prefix from filepath
+// will try to strip SWAY_SRC_DIR as well as a relative src dir
+// e.g. '/src/build/sway/util/log.c' and
+// '../util/log.c' will both be stripped to
+// 'util/log.c'
+const char *_sway_strip_path(const char *filepath) {
+	static int srclen = sizeof(SWAY_SRC_DIR);
+	if (strstr(filepath, SWAY_SRC_DIR) == filepath) {
+		filepath += srclen;
+	} else if (*filepath == '.') {
+		while (*filepath == '.' || *filepath == '/') {
+			++filepath;
+		}
+	}
+	return filepath;
+}