Use a formatter to display Btc/MilliBtc amounts (#90)

Display at most 8 decimals, instead of the default which may even use the exponent display occasionnally.

Author: pm47

src/main/scala/fr/acinq/bitcoin/scalacompat/BtcAmount.scala

@@ -1,5 +1,10 @@
 package fr.acinq.bitcoin.scalacompat
 
+import fr.acinq.bitcoin.scalacompat.BtcAmount.{btcFormat, milliBtcFormat}
+
+import java.text.{DecimalFormat, DecimalFormatSymbols}
+import java.util.Locale
+
 sealed trait BtcAmount
 
 case class Satoshi(private val underlying: Long) extends BtcAmount with Ordered[Satoshi] {
@@ -52,7 +57,7 @@ case class MilliBtc(private val underlying: BigDecimal) extends BtcAmount with O
   def toBigDecimal: BigDecimal = underlying
   def toDouble: Double = underlying.toDouble
   def toLong: Long = underlying.toLong
-  override def toString = s"$underlying mBTC"
+  override def toString = s"${milliBtcFormat.format(underlying)} mBTC"
   // @formatter:on
 }
 
@@ -82,12 +87,14 @@ case class Btc(private val underlying: BigDecimal) extends BtcAmount with Ordere
   def toBigDecimal: BigDecimal = underlying
   def toDouble: Double = underlying.toDouble
   def toLong: Long = underlying.toLong
-  override def toString = s"$underlying BTC"
+  override def toString = s"${btcFormat.format(underlying)} BTC"
   // @formatter:on
 }
 
 object BtcAmount {
   val Coin = 100000000L
   val Cent = 1000000L
   val MaxMoney: Double = 21e6 * Coin
-}
+  val milliBtcFormat = new DecimalFormat("#.#####", new DecimalFormatSymbols(Locale.US))
+  val btcFormat = new DecimalFormat("#.########", new DecimalFormatSymbols(Locale.US))
+}

src/test/scala/fr/acinq/bitcoin/scalacompat/BtcAmountSpec.scala

@@ -2,6 +2,8 @@ package fr.acinq.bitcoin.scalacompat
 
 import org.scalatest.FunSuite
 
+import java.util.Locale
+
 class BtcAmountSpec extends FunSuite {
 
   test("btc/millibtc/satoshi conversions") {
@@ -94,4 +96,23 @@ class BtcAmountSpec extends FunSuite {
     assert((1.1 btc).min(90000000 sat) === Btc(0.9))
   }
 
+  test("toString formatting") {
+    assert((0.00000000 btc).toString == "0 BTC")
+    assert((10.00000000 btc).toString == "10 BTC")
+    assert((1.23456789 btc).toString == "1.23456789 BTC")
+    assert((-1.23456789 btc).toString == "-1.23456789 BTC")
+    assert((1.2345 btc).toString == "1.2345 BTC")
+    assert((-1.2345 btc).toString == "-1.2345 BTC")
+
+    assert((0 btc).toMilliBtc.toString == "0 mBTC")
+    assert((10.00000000 btc).toMilliBtc.toString == "10000 mBTC")
+    assert((1.23456789 btc).toMilliBtc.toString == "1234.56789 mBTC")
+    assert((-1.23456789 btc).toMilliBtc.toString == "-1234.56789 mBTC")
+    assert((1.2345 btc).toMilliBtc.toString == "1234.5 mBTC")
+    assert((-1.2345 btc).toMilliBtc.toString == "-1234.5 mBTC")
+    assert((1.234 btc).toMilliBtc.toString == "1234 mBTC")
+    assert((-1.234 btc).toMilliBtc.toString == "-1234 mBTC")
+
+  }
+
 }