Improve the VcrSelfie to have better error messages.

Author: nedtwigg

jvm/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/Mode.kt

@@ -49,6 +49,11 @@ enum class Mode {
       msgSnapshotMismatch(expected.toQuotedPrintable(), actual.toQuotedPrintable())
   internal fun msgVcrKeyMismatch(key: String, expected: String, actual: String) =
       msg("VCR key $key " + SnapshotNotEqualErrorMsg.forUnequalStrings(expected, actual))
+  internal fun msgVcrKeyUnread(expected: Int, actual: Int) =
+      msg("VCR entries unread - only $actual were read out of $expected")
+  internal fun msgVcrKeyUnderflow(expected: Int) =
+      msg(
+          "VCR entries exhausted - only $expected are available but you tried to read ${expected + 1}")
   private fun ByteArray.toQuotedPrintable(): String {
     val sb = StringBuilder()
     for (byte in this) {

jvm/selfie-lib/src/commonMain/kotlin/com/diffplug/selfie/VcrSelfie.kt

@@ -22,7 +22,8 @@ import com.diffplug.selfie.guts.recordCall
 private const val OPEN = "«"
 private const val CLOSE = "»"
 
-class VcrSelfie(
+class VcrSelfie
+internal constructor(
     private val sub: String,
     private val call: CallStack,
     private val disk: DiskStorage,
@@ -60,7 +61,10 @@ class VcrSelfie(
   }
   override fun close() {
     if (state.readMode) {
-      check(state.count == state.sequence.size)
+      if (state.sequence.size != state.count) {
+        throw Selfie.system.fs.assertFailed(
+            Selfie.system.mode.msgVcrKeyUnread(state.sequence.size, state.count))
+      }
     } else {
       var snapshot = Snapshot.of("")
       var idx = 1
@@ -70,18 +74,24 @@ class VcrSelfie(
       disk.writeDisk(snapshot, sub, call)
     }
   }
-  private fun keyMismatch(expected: String, actual: String): Throwable =
-      Selfie.system.fs.assertFailed(
-          Selfie.system.mode.msgVcrKeyMismatch("$sub[$OPEN${state.count}$CLOSE]", expected, actual),
-          expected,
-          actual)
+  private fun nextValue(key: String): SnapshotValue {
+    val mode = Selfie.system.mode
+    val fs = Selfie.system.fs
+    if (state.sequence.size <= state.count) {
+      throw fs.assertFailed(mode.msgVcrKeyUnderflow(state.sequence.size))
+    }
+    val expected = state.sequence[state.count++]
+    if (expected.first != key) {
+      throw fs.assertFailed(
+          mode.msgVcrKeyMismatch("$sub[$OPEN${state.count}$CLOSE]", expected.first, key),
+          expected.first,
+          key)
+    }
+    return expected.second
+  }
   fun <V> next(key: String, roundtripValue: Roundtrip<V, String>, value: Cacheable<V>): V {
     if (state.readMode) {
-      val expected = state.sequence[state.count++]
-      if (expected.first != key) {
-        throw keyMismatch(expected.first, key)
-      }
-      return roundtripValue.parse(expected.second.valueString())
+      return roundtripValue.parse(nextValue(key).valueString())
     } else {
       val value = value.get()
       state.sequence.add(key to SnapshotValue.of(roundtripValue.serialize(value)))
@@ -93,11 +103,7 @@ class VcrSelfie(
       next(key, RoundtripJson.of<V>(), value)
   fun <V> nextBinary(key: String, roundtripValue: Roundtrip<V, ByteArray>, value: Cacheable<V>): V {
     if (state.readMode) {
-      val expected = state.sequence[state.count++]
-      if (expected.first != key) {
-        throw keyMismatch(expected.first, key)
-      }
-      return roundtripValue.parse(expected.second.valueBinary())
+      return roundtripValue.parse(nextValue(key).valueBinary())
     } else {
       val value = value.get()
       state.sequence.add(key to SnapshotValue.of(roundtripValue.serialize(value)))