Add exchange for currency in money exchange utils

src/main/kotlin/com/cubetiqs/libra/moneyutils/Money.kt

@@ -2,7 +2,7 @@ package com.cubetiqs.libra.moneyutils
 
 open class Money(
     var value: Double,
-    var currency: String = "USD"
+    private var currency: String = "USD"
 ) : StdMoney {
 
     //////////////////// - PROPERTIES - ////////////////////
@@ -20,4 +20,9 @@ open class Money(
     override fun toString(): String {
         return "Money(value=${getMoneyValue()}, currency='${getMoneyCurrency()}')"
     }
+
+    companion object {
+        val ZERO: StdMoney
+            get() = Money(value = 0.0)
+    }
 }

src/main/kotlin/com/cubetiqs/libra/moneyutils/MoneyConfig.kt

@@ -15,6 +15,8 @@ object MoneyConfig {
      * Value is the rate
      */
     private val config: MutableMap<String, Double> = mutableMapOf()
+    private var valid: Boolean = false
+    fun isValid() = valid
 
     /**
      * Money properties for money config format
@@ -56,6 +58,9 @@ object MoneyConfig {
                 throw MoneyCurrencyStateException("money config format is not valid!")
             }
         }
+
+        // validate the config is load or not
+        this.valid = this.config.isNotEmpty()
     }
 
     // all currencies with its rate

src/main/kotlin/com/cubetiqs/libra/moneyutils/MoneyExchangeUtils.kt

@@ -1,7 +1,13 @@
 package com.cubetiqs.libra.moneyutils
 
 object MoneyExchangeUtils {
-    fun computeRate(rateFrom: Double, rateTo: Double, baseRate: Double = 1.0, amountFrom: Double = 1.0): Double {
+    fun exchange(exchangeFrom: StdMoney, exchangeToCurrency: String): StdMoney {
+        val rateFrom = MoneyConfig.getRate(exchangeFrom.getMoneyCurrency())
+        val rateTo = MoneyConfig.getRate(exchangeToCurrency)
+        return Money(value = computeRate(rateFrom, rateTo, amountFrom = exchangeFrom.getMoneyValue()), currency = exchangeToCurrency)
+    }
+
+    private fun computeRate(rateFrom: Double, rateTo: Double, baseRate: Double = 1.0, amountFrom: Double = 1.0): Double {
         return amountFrom * ((baseRate / rateFrom) / (baseRate / rateTo))
     }
 }