feat: read config, read history, hash files

most of the functionality exists now

src/data.js

@@ -0,0 +1,34 @@
+const fs = require('fs');
+const path = require('path');
+const mkdirp = require('mkdirp');
+
+const CONFIG_FILENAME = 'pkgcomp.json';
+
+exports.read = (fileRoot, ident) => {
+  const stats = fs.statSync(fileRoot);
+  const filePath = path.join(fileRoot, CONFIG_FILENAME);
+
+  // throw if pointing to a file
+  if (stats.isFile()) throw new Error(`getData expects a directory, got a file; ${fileRoot}`);
+
+  // create file if it's missing
+  if (!stats.isDirectory()) {
+    mkdirp.sync(fileRoot);
+  }
+
+  try {
+    const data = JSON.parse(fs.readFileSync(filePath));
+    return data[ident] || {};
+  } catch (err) {
+    if (err.code === 'ENOENT') {
+      fs.writeFileSync(filePath, JSON.stringify({}));
+      return {};
+    }
+    throw err;
+  }
+};
+
+exports.write = (fileRoot, ident, payload) => {
+  console.log('WRITE', { fileRoot, ident, payload });
+  throw new Error('Data write not implemented');
+};