Rename healthcheck to preflight

lib/utils/preflight.js

@@ -0,0 +1,28 @@
+class Preflight {
+  constructor(kredits) {
+    this.kredits = kredits;
+  }
+
+  check() {
+    return this.kredits.ipfs._ipfsAPI.id()
+      .catch((error) => {
+        throw new Error(`IPFS node not available; config: ${JSON.stringify(this.kredits.ipfs.config)} - ${error.message}`);
+      })
+      .then(() => {
+        let promises = Object.keys(this.kredits.contracts).map((name) => {
+          let contractWrapper = this.kredits.contracts[name];
+          return this.kredits.provider.getCode(contractWrapper.contract.address).then((code) => {
+            // not sure if we always get the same return value if the code is not available
+            // so checking if it is < 5 long
+            if (code === '0x00' || code.length < 5) {
+              throw new Error(`Contract for: ${name} not found at ${contractWrapper.contract.address} on network ${this.kredits.provider.chainId}`);
+            }
+            return true;
+          });
+        });
+        return Promise.all(promises);
+      });
+  }
+}
+
+module.exports = Preflight;