Withdrawal script (#4)

* Withdrawal script. Added a script that lets you withdraw through Kraken API if the charged fees are under a certain level

* refactored code and added validation functionality

* Enhanced README to reflect the option to also withdraw in an automated manner

* fixed typo

withdraw.js

@@ -0,0 +1,47 @@
+const assert = require('assert')
+const Kraken = require('kraken-api')
+
+const {
+  KRAKEN_API_KEY: key,
+  KRAKEN_API_SECRET: secret,
+  KRAKEN_MAX_REL_FEE: max_fee,
+  KRAKEN_WITHDRAW_KEY: wdr_key
+} = process.env
+
+assert(key && secret, 'Provide the KRAKEN_API_KEY and KRAKEN_API_SECRET environment variables.')
+assert(max_fee && wdr_key, 'Provide the KRAKEN_MAX_REL_FEE and KRAKEN_WITHDRAW_KEY environment variables.')
+
+// https://www.kraken.com/features/api
+const kraken = new Kraken(key, secret)
+const crypto = 'XBT'
+const validate = process.argv[2] === '--validate'
+
+;(async () => {
+    // Get withdrawal information
+    // URL: https://api.kraken.com/0/private/WithdrawInfo
+    const withdrawdetails = { asset: crypto, key: wdr_key, amount: 0 } 
+    try {
+        const { result: { method, limit, fee } } = await kraken.api('WithdrawInfo', withdrawdetails);
+        const rel_fee = 1/parseFloat(limit)*parseFloat(fee)
+        console.log(`💡  Relative fee of withdrawal amount: ${(rel_fee*100).toFixed(2)}%`)
+
+        // Place withdrawal when fee is low enough (relatively)
+        if (rel_fee < max_fee/100) {
+            console.log(`⏏️  Withdraw ${limit} ${crypto} now.`)
+            const withdraw = { asset: crypto, key: wdr_key, amount: limit } 
+            if (!validate) {
+                try {
+                    const { result: { refid } } = await kraken.api('Withdraw', withdraw)
+                    if (refid) console.log(`📎  Withdrawal reference ID: ${refid}`)
+                } catch (err) {
+                    console.log(`\n🚨  Failure:`, err.message)
+                }
+            }
+        }else{
+            console.log(`\n❌ Don\'t withdraw now. Fee is too high. Max rel. fee: ${parseFloat(max_fee).toFixed(2)}%`);
+        }
+    } catch (err) {
+        console.log(`\n🚨  Failure:`, err.message)
+    }
+    if (validate) console.log('\n🚨  THIS WAS JUST A VALIDATION RUN, NO WITHDRAWAL HAS BEEN PLACED!')
+})()