Rewrite the entire code-base

The following changes are focused upon:
- Modularity
- Doing away with globals
- No heap allocations
- Better command line interface
- Switch from Xlib to XCB
- More verbose type definitions
- Implement a single-file config by utilising X-macros

src/timer.c

@@ -0,0 +1,56 @@
+#include "timer.h"
+
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "block.h"
+#include "main.h"
+#include "util.h"
+
+static unsigned int compute_tick(void) {
+    unsigned int tick = 0;
+
+    for (unsigned short i = 0; i < LEN(blocks); ++i) {
+        const block *const block = &blocks[i];
+        tick = gcd(block->interval, tick);
+    }
+
+    return tick;
+}
+
+static unsigned int compute_reset_value(void) {
+    unsigned int reset_value = 1;
+
+    for (unsigned short i = 0; i < LEN(blocks); ++i) {
+        const block *const block = &blocks[i];
+        reset_value = MAX(block->interval, reset_value);
+    }
+
+    return reset_value;
+}
+
+timer timer_new(void) {
+    timer timer = {
+        .time = 0,
+        .tick = compute_tick(),
+        .reset_value = compute_reset_value(),
+    };
+
+    return timer;
+}
+
+int timer_arm(timer *const timer) {
+    errno = 0;
+    (void)alarm(timer->tick);
+
+    if (errno != 0) {
+        (void)fprintf(stderr, "error: could not arm timer\n");
+        return 1;
+    }
+
+    // Wrap `time` to the interval [1, reset_value].
+    timer->time = (timer->time + timer->tick) % timer->reset_value + 1;
+
+    return 0;
+}