Kick off (#1)

* Kick off
* Update LICENSE copyright

src/checks/http.ts

@@ -0,0 +1,82 @@
+import type { HttpCheckRequest, CheckResult } from '../types.js';
+import { sleep } from './utils.js';
+
+const DEFAULT_HEADERS: Record<string, string> = {
+  'User-Agent': 'atalaya-uptime',
+};
+
+export async function executeHttpCheck(check: HttpCheckRequest): Promise<CheckResult> {
+  const startTime = Date.now();
+  let attempts = 0;
+  let lastError = '';
+  const headers = { ...DEFAULT_HEADERS, ...check.headers };
+
+  for (let i = 0; i <= check.retries; i++) {
+    attempts++;
+    const controller = new AbortController();
+    let timeout: ReturnType<typeof setTimeout> | undefined;
+
+    try {
+      timeout = setTimeout(() => {
+        controller.abort();
+      }, check.timeoutMs);
+
+      const response = await fetch(check.target, {
+        method: check.method ?? 'GET',
+        headers,
+        signal: controller.signal,
+      });
+
+      clearTimeout(timeout);
+      timeout = undefined;
+
+      const responseTime = Date.now() - startTime;
+
+      if (check.expectedStatus && response.status !== check.expectedStatus) {
+        lastError = `Expected status ${check.expectedStatus}, got ${response.status}`;
+        if (i < check.retries) {
+          await sleep(check.retryDelayMs);
+          continue;
+        }
+
+        return {
+          name: check.name,
+          status: 'down',
+          responseTimeMs: responseTime,
+          error: lastError,
+          attempts,
+        };
+      }
+
+      return {
+        name: check.name,
+        status: 'up',
+        responseTimeMs: responseTime,
+        error: '',
+        attempts,
+      };
+    } catch (error) {
+      if (timeout) {
+        clearTimeout(timeout);
+        timeout = undefined;
+      }
+
+      lastError = error instanceof Error ? error.message : 'Unknown error';
+      if (i < check.retries) {
+        await sleep(check.retryDelayMs);
+      }
+    } finally {
+      if (timeout) {
+        clearTimeout(timeout);
+      }
+    }
+  }
+
+  return {
+    name: check.name,
+    status: 'down',
+    responseTimeMs: Date.now() - startTime,
+    error: lastError,
+    attempts,
+  };
+}