[wip] autogenerate numeric ids

index.js

@@ -48,6 +48,7 @@ function Cardboard(config) {
     if (!config.prefix) throw new Error('No s3 prefix set');
 
     var utils = require('./lib/utils')(config);
+    var ids = require('./lib/ids')(config.dyno);
 
     /**
      * A client configured to interact with a backend cardboard database

lib/ids.js

@@ -0,0 +1,50 @@
+module.exports = ids;
+
+var IDS_PER_RESERVATION = 1000;
+
+function ids(dyno) {
+    var reserved = {};
+    var numbers = {};
+
+    numbers.get = function(dataset, callback) {
+        if (reserved[dataset]) {
+            var val = reserved[dataset].get();
+            if (val) return callback(null, val);
+        }
+
+        numbers.reserve(dataset, function(err, values) {
+            if (err) return callback(err);
+            reserved[dataset] = new Range(values);
+            callback(null, reserved[dataset].get());
+        });
+    };
+
+    numbers.reserve = function(dataset, callback) {
+        dyno.updateItem({
+            Key: {
+                dataset: dataset,
+                id: 'autoid'
+            },
+            ExpressionAttributeNames: { '#v': 'value' },
+            ExpressionAttributeValues: { ':v': IDS_PER_RESERVATION },
+            UpdateExpression: 'add #v :v',
+            ReturnValues: 'ALL_NEW'
+        }, function(err, data) {
+            if (err) return callback(err);
+            var max = data.Attributes.value;
+            return callback(null, [max - (IDS_PER_RESERVATION - 1), max]);
+        });
+    };
+
+    return numbers;
+}
+
+function Range(values) {
+    this.next = values[0];
+    this.max = values[1];
+}
+
+Range.prototype.get = function() {
+    if (this.next + 1 > this.max) return null;
+    return ++this.next;
+};