Add more flexibility in LocalDateTime parsing (#40)

Author: seljabali

src/main/kotlin/javatimefun/localdatetime/extensions/LocalDateTimeParsingExtensions.kt

@@ -6,6 +6,8 @@ import java.time.LocalTime
 import java.time.format.DateTimeFormatter
 import java.time.format.DateTimeParseException
 
+private const val flexibleIso8601Format = "yyyy-MM-dd'T'HH:mm:ss[.SSSSSS][.SSSS][.SSS][.SS][.S]['Z']"
+
 /**
  * Works off of String representations of date(time) and parses through the following attempts in order when
  * no format is present:
@@ -20,18 +22,19 @@ import java.time.format.DateTimeParseException
  * @return LocalDateTime? Null means couldn't parse, else parsed LocalDateTime.
  */
 fun String.toLocalDateTime(format: String? = null): LocalDateTime? {
-    val localDateTime = parseLocalDateTimeHelper(this, format)
-    if (localDateTime != null) {
-        return localDateTime
-    }
+    var localDateTime = parseLocalDateTimeOrNull(this, format)
+    if (localDateTime != null) return localDateTime
+
+    localDateTime = parseLocalDateTimeOrNull(this, flexibleIso8601Format)
+    if (localDateTime != null) return localDateTime
+
     val localDate = this.toLocalDate(format)
-    if (localDate != null) {
-        return LocalDateTime.of(localDate, LocalTime.MIN)
-    }
+    if (localDate != null) return LocalDateTime.of(localDate, LocalTime.MIN)
+
     return null
 }
 
-private fun parseLocalDateTimeHelper(dateText: String, format: String?): LocalDateTime? =
+private fun parseLocalDateTimeOrNull(dateText: String, format: String?): LocalDateTime? =
     if (format.isNullOrEmpty())
         try {
             LocalDateTime.parse(dateText)

src/test/kotlin/localdatetime/LocalDateTimeParsingExtensionsTest.kt

@@ -0,0 +1,99 @@
+package localdatetime
+
+import javatimefun.localdatetime.extensions.print
+import javatimefun.localdatetime.extensions.toLocalDateTime
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+import java.lang.RuntimeException
+import java.time.LocalDateTime
+
+class LocalDateTimeParsingExtensionsTest {
+
+    companion object {
+        private const val ISO_8601 = "yyyy-MM-dd'T'HH:mm:ss'Z'"
+        private const val ISO_8601_S = "yyyy-MM-dd'T'HH:mm:ss.S'Z'"
+        private const val ISO_8601_SS = "yyyy-MM-dd'T'HH:mm:ss.SS'Z'"
+        private const val ISO_8601_SSS = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'"
+        private const val ISO_8601_SSSS = "yyyy-MM-dd'T'HH:mm:ss.SSSS'Z'"
+        private const val ISO_8601_SSSSSS = "yyyy-MM-dd'T'HH:mm:ss.SSSSSS'Z'"
+    }
+    
+    @Test
+    fun `given date in ISO_8601, when parsed without format & converted to date, then should match when printed back to text`() {
+        // given
+        val dateInText = "2023-07-26T12:34:56Z"
+
+        // when
+        val dateParsed: LocalDateTime = dateInText.toLocalDateTime() ?: throw RuntimeException("Failed to parse")
+
+        // then
+        assertEquals(dateInText, dateParsed.print(ISO_8601))
+        assertEquals("2023-07-26T12:34:56.000000Z", dateParsed.print(ISO_8601_SSSSSS))
+    }
+
+    @Test
+    fun `given date in ISO_8601_S, when parsed without format & converted to date, then should match when printed back to text`() {
+        // given
+        val dateInText = "2023-07-26T12:34:56.1Z"
+
+        // when
+        val dateParsed: LocalDateTime = dateInText.toLocalDateTime() ?: throw RuntimeException("Failed to parse")
+
+        // then
+        assertEquals(dateInText, dateParsed.print(ISO_8601_S))
+        assertEquals("2023-07-26T12:34:56.100000Z", dateParsed.print(ISO_8601_SSSSSS))
+    }
+
+    @Test
+    fun `given date in ISO_8601_SS, when parsed without format & converted to date, then should match when printed back to text`() {
+        // given
+        val dateInText = "2023-07-26T12:34:56.12Z"
+
+        // when
+        val dateParsed: LocalDateTime = dateInText.toLocalDateTime() ?: throw RuntimeException("Failed to parse")
+
+        // then
+        assertEquals(dateInText, dateParsed.print(ISO_8601_SS))
+        assertEquals("2023-07-26T12:34:56.120000Z", dateParsed.print(ISO_8601_SSSSSS))
+    }
+
+    @Test
+    fun `given date in ISO_8601_SSS, when parsed without format & converted to date, then should match when printed back to text`() {
+        // given
+        val dateInText = "2023-07-26T12:34:56.123Z"
+
+        // when
+        val dateParsed: LocalDateTime = dateInText.toLocalDateTime() ?: throw RuntimeException("Failed to parse")
+
+        // then
+        assertEquals(dateInText, dateParsed.print(ISO_8601_SSS))
+        assertEquals("2023-07-26T12:34:56.123000Z", dateParsed.print(ISO_8601_SSSSSS))
+    }
+
+    @Test
+    fun `given date in ISO_8601_SSSS, when parsed without format & converted to date, then should match when printed back to text`() {
+        // given
+        val dateInText = "2023-07-26T12:34:56.1234Z"
+
+        // when
+        val dateParsed: LocalDateTime = dateInText.toLocalDateTime() ?: throw RuntimeException("Failed to parse")
+
+        // then
+        assertEquals(dateInText, dateParsed.print(ISO_8601_SSSS))
+        assertEquals("2023-07-26T12:34:56.123400Z", dateParsed.print(ISO_8601_SSSSSS))
+    }
+
+    @Test
+    fun `given date in ISO_8601_SSSSSS, when parsed without format & converted to date, then should match when printed back to text`() {
+        // given
+        val dateInText = "2023-07-26T12:34:56.123456Z"
+
+        // when
+        val dateParsed: LocalDateTime = dateInText.toLocalDateTime() ?: throw RuntimeException("Failed to parse")
+
+        // then
+        assertEquals(dateInText, dateParsed.print(ISO_8601_SSSSSS))
+        assertEquals("2023-07-26T12:34:56.123456Z", dateParsed.print(ISO_8601_SSSSSS))
+    }
+
+}