Add time zone detection tests.

Author: alshan

plot-api/src/commonMain/kotlin/org/jetbrains/letsPlot/intern/ToSpecConverters.kt

@@ -453,7 +453,10 @@ private fun inferSeriesDType(data: Any?): String {
     }
 }
 
-private fun detectTimeZones(data: Any?): Map<String, String> {
+/**
+ * Not private to allow access from tests
+ */
+internal fun detectTimeZones(data: Any?): Map<String, String> {
     return if (data is Map<*, *>) {
         @Suppress("UNCHECKED_CAST")
         data.entries

plot-api/src/commonMain/kotlin/org/jetbrains/letsPlot/intern/standardizing/Standardizing.kt

@@ -13,7 +13,6 @@ import org.jetbrains.letsPlot.commons.intern.datetime.Instant
 import org.jetbrains.letsPlot.commons.intern.datetime.Time
 
 internal object Standardizing {
-//    private val UTC_LP by lazy { TimeZone("UTC") }
 
     fun standardizeValue(value: Any?): Any? {
         return when (value) {

plot-api/src/jvmTest/kotlin/org/jetbrains/letsPlot/intern/standardizing/TimeZoneDetectionTest.kt

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2021. JetBrains s.r.o.
+ * Use of this source code is governed by the MIT license that can be found in the LICENSE file.
+ */
+
+package org.jetbrains.letsPlot.intern.standardizing
+
+import org.jetbrains.letsPlot.intern.detectTimeZones
+import java.time.OffsetDateTime
+import java.time.ZoneId
+import java.time.ZoneOffset
+import java.time.ZonedDateTime
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import org.jetbrains.letsPlot.commons.intern.datetime.Instant as LPInstant
+import org.jetbrains.letsPlot.commons.intern.datetime.TimeZone as LPTimeZone
+
+
+class TimeZoneDetectionTest {
+
+    @Test
+    fun `detected timezone is recognized`() {
+        // This test verifies that:
+        // 1. `detectTimeZones` correctly extracts timezone IDs from `ZonedDateTime` and `OffsetDateTime` objects.
+        // 2. After standardizing to a timestamp and reconstructing with the detected timezone,
+        //    the resulting date-time components match the original objects.
+        val zdtUtc = ZonedDateTime.of(2023, 1, 1, 10, 0, 0, 0, ZoneId.of("UTC"))
+        val zdtMoscow = ZonedDateTime.of(2023, 1, 1, 10, 0, 0, 0, ZoneId.of("Europe/Moscow"))
+        val zdtNewYork = ZonedDateTime.of(2023, 1, 1, 10, 0, 0, 0, ZoneId.of("America/New_York"))
+
+        val odtUtc = OffsetDateTime.of(2024, 2, 2, 12, 30, 0, 0, ZoneOffset.UTC)
+        val odtMinus5h = OffsetDateTime.of(2024, 2, 2, 12, 30, 0, 0, ZoneOffset.ofHours(-5))
+        val odtPlus5h30m = OffsetDateTime.of(2024, 2, 2, 12, 30, 0, 0, ZoneOffset.ofHoursMinutes(5, 30))
+
+        val testData = mapOf(
+            "zdt_utc" to listOf(zdtUtc),
+            "zdt_moscow" to listOf(zdtMoscow),
+            "zdt_new_york" to listOf(zdtNewYork),
+            "odt_utc" to listOf(odtUtc),
+            "odt_minus_5h" to listOf(odtMinus5h),
+            "odt_plus_5h_30m" to listOf(odtPlus5h30m)
+        )
+
+        val detectedTimeZones = detectTimeZones(testData)
+
+        @Suppress("UNCHECKED_CAST")
+        val standardizedData = Standardizing.standardizeValue(testData) as Map<String, List<Double>>
+
+        fun check(original: ZonedDateTime, key: String) {
+            val timestamp = standardizedData.getValue(key).single()
+            val tzId = detectedTimeZones.getValue(key)
+            val lpDateTime = LPInstant(timestamp.toLong()).toDateTime(LPTimeZone(tzId))
+
+            assertEquals(original.year, lpDateTime.year)
+            assertEquals(original.monthValue, lpDateTime.month.ordinal + 1)
+            assertEquals(original.dayOfMonth, lpDateTime.day)
+            assertEquals(original.hour, lpDateTime.time.hours)
+            assertEquals(original.minute, lpDateTime.time.minutes)
+            assertEquals(original.second, lpDateTime.time.seconds)
+        }
+
+        fun check(original: OffsetDateTime, key: String) {
+            val timestamp = standardizedData.getValue(key).single()
+            val tzId = detectedTimeZones.getValue(key)
+            val lpDateTime = LPInstant(timestamp.toLong()).toDateTime(LPTimeZone(tzId))
+
+            assertEquals(original.year, lpDateTime.year)
+            assertEquals(original.monthValue, lpDateTime.month.ordinal + 1)
+            assertEquals(original.dayOfMonth, lpDateTime.day)
+            assertEquals(original.hour, lpDateTime.time.hours)
+            assertEquals(original.minute, lpDateTime.time.minutes)
+            assertEquals(original.second, lpDateTime.time.seconds)
+        }
+
+        check(zdtUtc, "zdt_utc")
+        check(zdtMoscow, "zdt_moscow")
+        check(zdtNewYork, "zdt_new_york")
+        check(odtUtc, "odt_utc")
+        check(odtMinus5h, "odt_minus_5h")
+        check(odtPlus5h30m, "odt_plus_5h_30m")
+    }
+}