Add CLI interface

Fixes #5

log.h

@@ -0,0 +1,59 @@
+/**
+ * Copyright 2021 Johannes Marbach
+ *
+ * This file is part of unl0kr, hereafter referred to as the program.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+
+#ifndef UL_LOG_H
+#define UL_LOG_H
+
+#include <stdio.h>
+
+/**
+ * Log levels
+ */
+typedef enum {
+    /* Errors only */
+    UL_LOG_LEVEL_ERROR   = 0,
+    /* Include non-errors in log */
+    UL_LOG_LEVEL_VERBOSE = 1
+} ul_log_level;
+
+/**
+ * Set the log level.
+ * 
+ * @param level new log level value
+ */
+void ul_set_log_level(ul_log_level level);
+
+/**
+ * Log a message.
+ * 
+ * @param level log level of the message
+ * @param format message format string
+ * @param ... parameters to fill into the format string
+ */
+void ul_log(ul_log_level level, const char *format, ...);
+
+/**
+ * Handle an LVGL log message.
+ * 
+ * @param msg message to print
+ */
+void ul_print_cb(const char *msg);
+
+#endif /* UL_LOG_H */