Amount: add support for basic parsing from text.

core/src/main/kotlin/net/corda/core/contracts/FinanceTypes.kt

@@ -48,6 +48,58 @@ data class Amount<T>(val quantity: Long, val token: T) : Comparable<Amount<T>> {
             val longQuantity = quantity.movePointRight(currency.defaultFractionDigits).toLong()
             return Amount(longQuantity, currency)
         }
+
+        private val currencySymbols: Map<String, Currency> = mapOf(
+                "$" to USD,
+                "£" to GBP,
+                "€" to EUR
+        )
+        private val currencyCodes: Map<String, Currency> by lazy { Currency.getAvailableCurrencies().map { it.currencyCode to it }.toMap() }
+
+        /**
+         * Returns an amount that is equal to the given currency amount in text. Examples of what is supported:
+         *
+         * - 12 USD
+         * - 14.50 USD
+         * - 10 USD
+         * - 30 CHF
+         * - $10.24
+         * - £13
+         * - €5000
+         *
+         * Note this method does NOT respect internationalisation rules: it ignores commas and uses . as the
+         * decimal point separator, always. It also ignores the users locale: $ is special cased to be USD,
+         * £ is special cased to GBP and € is special cased to Euro. Thus an input of $12 expecting some other
+         * countries dollar will not work. Do your own parsing if you need correct handling of currency amounts
+         * with locale-sensitive handling.
+         *
+         * @throws IllegalArgumentException if the input string was not understood.
+         */
+        fun parseCurrency(input: String): Amount<Currency> {
+            val i = input.filter { it != ',' }
+            try {
+                // First check the symbols at the front.
+                for ((symbol, currency) in currencySymbols) {
+                    if (i.startsWith(symbol)) {
+                        val rest = i.substring(symbol.length)
+                        return fromDecimal(BigDecimal(rest), currency)
+                    }
+                }
+                // Now check the codes at the end.
+                val split = i.split(' ')
+                if (split.size == 2) {
+                    val (rest, code) = split
+                    for ((cc, currency) in currencyCodes) {
+                        if (cc == code) {
+                            return fromDecimal(BigDecimal(rest), currency)
+                        }
+                    }
+                }
+            } catch(e: Exception) {
+                throw IllegalArgumentException("Could not parse $input as a currency", e)
+            }
+            throw IllegalArgumentException("Did not recognise the currency in $input or could not parse")
+        }
     }
 
     init {

core/src/test/kotlin/net/corda/core/contracts/AmountTests.kt

@@ -23,4 +23,12 @@ class AmountTests {
         assertEquals(expected, amount.toDecimal())
         assertEquals(amount, Amount.fromDecimal(amount.toDecimal(), amount.token))
     }
+
+    @Test
+    fun parsing() {
+        assertEquals(Amount(1234L, GBP), Amount.parseCurrency("£12.34"))
+        assertEquals(Amount(1200L, GBP), Amount.parseCurrency("£12"))
+        assertEquals(Amount(1000L, USD), Amount.parseCurrency("$10"))
+        assertEquals(Amount(1500000000L, CHF), Amount.parseCurrency("15,000,000 CHF"))
+    }
 }