1 files changed, 47 insertions, 0 deletions
diff --git a/shared/backlog.c b/shared/backlog.c
new file mode 100644
index 0000000..926ccad
--- /dev/null
+++ b/shared/backlog.c
@@ -0,0 +1,47 @@
+#include <stdlib.h>
+
+#include "backlog.h"
+
+ws_s_backlog_database* g_ws_backlog_database = NULL;
+
+void ws_backlog_alloc(uint16_t record_amt) {
+	g_ws_backlog_database = malloc(sizeof(ws_s_backlog_database) + sizeof(ws_s_backlog_record) * record_amt);
+	g_ws_backlog_database->buffer_size = record_amt;
+	g_ws_backlog_database->buffer_start = 0;
+	g_ws_backlog_database->buffer_end = 0;
+}
+
+void ws_backlog_add_record(ws_s_backlog_record record) {
+	static uint16_t id = 0;
+
+	g_ws_backlog_database->records[g_ws_backlog_database->buffer_end].id = id++;
+	g_ws_backlog_database->records[g_ws_backlog_database->buffer_end].sens_atm_pressure = record.sens_atm_pressure;
+	g_ws_backlog_database->records[g_ws_backlog_database->buffer_end].sens_humidity = record.sens_humidity;
+	g_ws_backlog_database->records[g_ws_backlog_database->buffer_end].sens_temperature = record.sens_temperature;
+
+	// shift buffer start/end
+	g_ws_backlog_database->buffer_end = (g_ws_backlog_database->buffer_end + 1) % g_ws_backlog_database->buffer_size;
+	if (g_ws_backlog_database->buffer_end == g_ws_backlog_database->buffer_start)
+		g_ws_backlog_database->buffer_start = (g_ws_backlog_database->buffer_start + 1) % g_ws_backlog_database->buffer_size;
+}
+
+ws_s_backlog_record* ws_backlog_get_record(uint16_t record_index) {
+	return &g_ws_backlog_database->records[record_index];
+}
+
+ws_s_backlog_record* ws_backlog_get_last_record(uint16_t record_offset) {
+	return ws_backlog_get_record((g_ws_backlog_database->buffer_end - record_offset - 1) % g_ws_backlog_database->buffer_size);
+}
+
+static uint16_t mod(uint16_t a, uint16_t b) {
+	uint16_t m = a % b;
+	return m < 0 ? (b < 0) ? m - b : m + b : m;
+}
+
+uint16_t ws_backlog_get_record_count() {
+	// add buffer_size to the result of the modulo operation if it's result is negative
+	// (only works when buffer_size is less than 2^15)
+	// this is a consequence of the way in which c handles negative numbers in modulo operations
+	int16_t mod = (g_ws_backlog_database->buffer_end - g_ws_backlog_database->buffer_start) % g_ws_backlog_database->buffer_size;
+	return mod < 0 ? mod + g_ws_backlog_database->buffer_size : mod;
+}