Add Single Customer endpoint

lib/customers.js

@@ -21,6 +21,11 @@ function get (phone) {
   })
 }
 
+function getById (id) {
+  const sql = 'select * from customers where id=$1'
+  return db.oneOrNone(sql, [id])
+}
+
 function getDailyVolume (id) {
   return Promise.all([
     db.one(`select coalesce(sum(fiat), 0) as total from cash_in_txs 
@@ -41,4 +46,4 @@ function batch () {
   return db.any(sql, [ anonymous.uuid, NUM_RESULTS ])
 }
 
-module.exports = { add, get, batch }
+module.exports = { add, get, batch, getById }