Updated the demo for some functions

src/main/kotlin/com/example/demo/DemoApplication.kt

@@ -1,7 +1,13 @@
 package com.example.demo
 
+import com.example.demo.domain.Currency
+import com.example.demo.domain.Money
 import com.example.demo.domain.MoneyConfig
 import com.example.demo.domain.MoneyDyn
+import com.example.demo.domain.addMoney
+import com.example.demo.domain.exchange
+import com.example.demo.domain.plus
+import com.example.demo.domain.toStdMoneyFormatable
 import org.springframework.boot.CommandLineRunner
 import org.springframework.boot.autoconfigure.SpringBootApplication
 import org.springframework.boot.runApplication
@@ -23,14 +29,22 @@ class DemoApplication : CommandLineRunner {
 
         MoneyConfig.parse("USD=1,KHR=4000,EUR=0.99")
 
-        val value1 = MoneyDyn(value = 2.0, currency = "USD")
-        val value2 = MoneyDyn(value = 20000.0, currency = "KHR")
-        val value3 = MoneyDyn(value = 0.99, currency = "EUR")
-        value1.addMoney(value2)
-        value1.addMoney(value3)
+        // val value1 = MoneyDyn(value = 2.0, currency = "USD")
+        // val value2 = MoneyDyn(value = 20000.0, currency = "KHR")
+        // val value3 = MoneyDyn(value = 0.99, currency = "EUR")
+        // value1.addMoney(value2)
+        // value1.addMoney(value3)
+        //
+        // // val result = value1.exchange("KHR")
+        // println(value1.exchangeTo("KHR")) // 7
 
-        // val result = value1.exchange("KHR")
-        println(value1.exchangeTo("KHR")) // 7
+        val moneyUsd = Money(2.0)
+            .addMoney(20000.0, "USD")
+            .exchange("KHR")
+            .toStdMoneyFormatable()
+            .formatMoneyDisplay()
+
+        println(moneyUsd)
     }
 }
 

src/main/kotlin/com/example/demo/domain/Money.kt

@@ -3,7 +3,7 @@ package com.example.demo.domain
 class Money (
     var value: Double = 0.0,
     var currency: Currency = Currency.USD
-) {
+) : StdMoneyFormatable {
     companion object {
         private const val MONEY_SPLITTER = ':'
         fun parse(value: String): Money {
@@ -16,25 +16,19 @@ class Money (
         }
     }
 
+    override fun getMoneyValue() = value
+
+    override fun getMoneyCurrency() = this.currency.name
+
     override fun toString(): String {
-        return "Money(value=$value, currency=$currency)"
-    }
-
-    fun addMoney(value: Money): Money {
-        if (value.currency == this.currency) {
-            this.value = this.value.plus(value.value)
-        } else {
-            throw IllegalArgumentException("currency ${value.currency.name} is not matched!")
-        }
-
-        return this
+        return "Money(value=${formatMoneyValue()}, currency=$currency)"
     }
 }
 
 enum class Currency (val symbol: Char, val displayName: String) {
     USD('$', "Dollar"),
     KHR('R', "Riel");
-    
+
     companion object {
         fun create(value: String): Currency {
             return try {

src/main/kotlin/com/example/demo/domain/MoneyExtension.kt

@@ -0,0 +1,38 @@
+package com.example.demo.domain
+
+operator fun StdMoney.plus(other: StdMoney): StdMoney {
+    if (!this.getMoneyCurrency().equals(other.getMoneyCurrency(), ignoreCase = true)) {
+        throw IllegalStateException("money currency is not valid")
+    }
+    return Money(this.getMoneyValue().plus(other.getMoneyValue()), currency = Currency.create(this.getMoneyCurrency()))
+}
+
+fun StdMoney.addMoney(other: StdMoney): StdMoney {
+    if (this.getMoneyCurrency() == other.getMoneyCurrency()) {
+        return this + other
+    }
+
+    // this = USD
+    // other = KHR
+
+    // other (20000) -> this (5)
+
+    // exchange
+    val otherExchange = other.exchange(this.getMoneyCurrency())
+    return this + otherExchange
+}
+
+fun StdMoney.addMoney(value: Double, currency: String): StdMoney {
+    return this.addMoney(Money(value = value, currency = Currency.create(currency)))
+}
+
+fun StdMoney.exchange(toCurrency: String): StdMoney {
+    val rateFrom = MoneyConfig.getRate(this.getMoneyCurrency())
+    val rateTo = MoneyConfig.getRate(toCurrency)
+    val resultAmount = this.getMoneyValue() * ((1 / rateFrom) / (1 / rateTo))
+    return Money(value = resultAmount, currency = Currency.create(toCurrency))
+}
+
+fun StdMoney.toStdMoneyFormatable(): StdMoneyFormatable {
+    return this as StdMoneyFormatable
+}

src/main/kotlin/com/example/demo/domain/StdMoney.kt

@@ -0,0 +1,6 @@
+package com.example.demo.domain
+
+interface StdMoney {
+    fun getMoneyValue(): Double
+    fun getMoneyCurrency(): String
+}

src/main/kotlin/com/example/demo/domain/StdMoneyFormatable.kt

@@ -0,0 +1,18 @@
+package com.example.demo.domain
+
+import java.text.DecimalFormat
+
+interface StdMoneyFormatable : StdMoney {
+    companion object {
+        const val MONEY_FORMAT = "#,##0.##"
+    }
+
+    fun formatMoneyValue(): String {
+        val df = DecimalFormat(MONEY_FORMAT)
+        return df.format(getMoneyValue())
+    }
+
+    fun formatMoneyDisplay(): String {
+        return "${formatMoneyValue()} ${getMoneyCurrency()}"
+    }
+}