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/watcher.c

@@ -0,0 +1,53 @@
+#include "watcher.h"
+
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <sys/poll.h>
+
+#include "main.h"
+#include "util.h"
+
+int watcher_init(watcher* const watcher, const int signal_fd) {
+    if (signal_fd == -1) {
+        fprintf(stderr,
+                "error: invalid signal file descriptor passed to watcher\n");
+        return 1;
+    }
+
+    watcher_fd* const fd = &watcher->fds[SIGNAL_FD];
+    fd->fd = signal_fd;
+    fd->events = POLLIN;
+
+    for (unsigned short i = 0; i < LEN(blocks); ++i) {
+        const int block_fd = blocks[i].pipe[READ_END];
+        if (block_fd == -1) {
+            fprintf(
+                stderr,
+                "error: invalid block file descriptors passed to watcher\n");
+            return 1;
+        }
+
+        watcher_fd* const fd = &watcher->fds[i];
+        fd->fd = block_fd;
+        fd->events = POLLIN;
+    }
+
+    return 0;
+}
+
+int watcher_poll(watcher* watcher, const int timeout_ms) {
+    const int event_count = poll(watcher->fds, LEN(watcher->fds), timeout_ms);
+
+    // Don't return non-zero status for signal interruptions.
+    if (event_count == -1 && errno != EINTR) {
+        (void)fprintf(stderr, "error: watcher could not poll blocks\n");
+        return -1;
+    }
+
+    return event_count;
+}
+
+bool watcher_fd_is_readable(const watcher_fd* const watcher_fd) {
+    return (watcher_fd->revents & POLLIN) != 0;
+}