closes #14 - the /undefined padding bug (#15)

* fix bug in `pad(id)`

* add tests

* doc the injectable  + test it

* simpler english

README.md

@@ -54,6 +54,9 @@ that is 33 characters in length, by default `fixedLength` is `false`.
 If `{ fixedLength: true }` is passed in, the function will always generate an id
 that is 33 characters in length, by default `fixedLength` is `false`.  
 If `{ urlSafe: true }` is passed in, the function will generate url safe ids.
+If `{ startFrom: <int> }` is passed in, the first counter will start from that
+number, which must be beteen 0 and 2147483647. Fractions are discarded, only the
+integer part matters.
 
 ### instance()
 

hyperid.js

@@ -16,10 +16,21 @@ function hyperid (opts) {
     fixedLength = !!opts.fixedLength
   }
 
-  var count = 0
-
   generate.uuid = uuid()
+  generate.decode = decode
+
   var id = baseId(generate.uuid, urlSafe)
+  var count = Math.floor(opts.startFrom || 0)
+
+  if (isNaN(count) || !(maxInt > count && count >= 0)) {
+    throw new Error([
+      `when passed, opts.startFrom must be a number between 0 and ${maxInt}.`,
+      'Only the integer part matters.',
+      `- got: ${opts.startFrom}`
+    ].join('\n'))
+  }
+
+  return generate
 
   function generate () {
     var result = fixedLength
@@ -34,10 +45,6 @@ function hyperid (opts) {
 
     return result
   }
-
-  generate.decode = decode
-
-  return generate
 }
 
 function pad (count) {
@@ -50,6 +57,7 @@ function pad (count) {
   if (count < 10000000) return '000' + count
   if (count < 100000000) return '00' + count
   if (count < 1000000000) return '0' + count
+  return count
 }
 
 function baseId (id, urlSafe) {

test/test.js

@@ -95,3 +95,39 @@ test('decode url safe ids', function (t) {
     count: 0
   }, 'decode')
 })
+
+test('injecting opts.startFrom', function (t) {
+  t.plan(1)
+
+  const instance = hyperid({ startFrom: 999999999 })
+  const id = instance()
+
+  id.endsWith('999999999')
+    ? t.pass('generated as expected')
+    : t.fail('did not use injected id')
+})
+
+test('opts.fixedLength - passed 999999999 - pads correctly', function (t) {
+  t.plan(1)
+
+  const instance = hyperid({ startFrom: 999999999 })
+  instance()
+  const id = instance()
+
+  id.endsWith('1000000000')
+    ? t.pass('generated as expected')
+    : t.fail('did not use injected id')
+})
+
+test('opts.fixedLength - passed invalid value - throws a friendly error', function (t) {
+  t.plan(1)
+
+  try {
+    hyperid({ startFrom: 'not a number' })
+    t.fail('did not throw an expected error')
+  } catch (e) {
+    e.message.match(/startFrom must be a number/)
+      ? t.pass('thrown as expected')
+      : t.fail('this is not the error you\'re looking for')
+  }
+})