Create NumberFormatter for Statistics Values (EXPOSUREAPP-4652) #2118

* Implement StatisticsNumberValueFormatter.kt and add tests

* Fix ktlint issues

* Improve StatisticsNumberValueFormatter.kt

* Reduce parameters for formatter, adapt test

* Define formatting function as top-level function instead of a function in object

Corona-Warn-App/src/main/java/de/rki/coronawarnapp/statistics/util/StatisticsNumberValueFormatter.kt

+package de.rki.coronawarnapp.statistics.util
+
+import android.content.Context
+import de.rki.coronawarnapp.R
+import de.rki.coronawarnapp.contactdiary.util.getLocale
+import java.text.DecimalFormat
+import java.text.DecimalFormatSymbols
+
+fun formatStatisticalValue(
+    context: Context,
+    value: Double,
+    decimals: Int
+): String {
+
+    val locale = context.getLocale()
+
+    // return strings like "12.7 Mio" for large values
+    if (value >= 10_000_000) {
+        return DecimalFormat("#,###.0", DecimalFormatSymbols(locale))
+            .format(value / 1_000_000) + " ${context.getString(R.string.statistics_value_suffix_million)}"
+    }
+
+    return when (decimals) {
+        in Int.MIN_VALUE..0 -> DecimalFormat("#,###", DecimalFormatSymbols(locale))
+        1 -> DecimalFormat("#,###.#", DecimalFormatSymbols(locale))
+        else -> DecimalFormat("#,###.##", DecimalFormatSymbols(locale))
+    }.format(value)
+}

Corona-Warn-App/src/test/java/de/rki/coronawarnapp/statistics/util/StatisticsNumberValueFormatterTest.kt

+package de.rki.coronawarnapp.statistics.util
+
+import android.content.Context
+import de.rki.coronawarnapp.R
+import de.rki.coronawarnapp.contactdiary.util.getLocale
+import io.kotest.matchers.shouldBe
+import io.mockk.MockKAnnotations
+import io.mockk.every
+import io.mockk.impl.annotations.MockK
+import io.mockk.mockkStatic
+import io.mockk.unmockkAll
+import org.junit.jupiter.api.AfterAll
+import org.junit.jupiter.api.BeforeAll
+import org.junit.jupiter.api.TestInstance
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.Arguments
+import org.junit.jupiter.params.provider.MethodSource
+import java.util.Locale
+
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+internal class StatisticsNumberValueFormatterTest {
+
+    @MockK
+    private lateinit var context: Context
+
+    @BeforeAll
+    fun setUp() {
+        MockKAnnotations.init(this)
+        mockkStatic("de.rki.coronawarnapp.contactdiary.util.ContactDiaryExtensionsKt")
+        every { context.getString(R.string.statistics_value_suffix_million) } returns "Mio."
+    }
+
+    @ParameterizedTest
+    @MethodSource("provideArguments")
+    fun `getFormattedNumberValue() should return correctly formatted number`(
+        value: Double,
+        decimals: Int,
+        locale: Locale,
+        expected: String
+    ) {
+
+        every { context.getLocale() } returns locale
+
+        formatStatisticalValue(context, value, decimals) shouldBe expected
+    }
+
+    companion object {
+
+        @Suppress("unused")
+        @JvmStatic
+        fun provideArguments() = listOf(
+
+            Arguments.of(12.3456, -1, Locale.GERMANY, "12"),
+            Arguments.of(12.3456, 0, Locale.GERMANY, "12"),
+            Arguments.of(12.3456, 1, Locale.GERMANY, "12,3"),
+            Arguments.of(12.3456, 2, Locale.GERMANY, "12,35"),
+
+            Arguments.of(12.3456, 1, Locale.UK, "12.3"),
+
+            Arguments.of(12.6543, -1, Locale.GERMANY, "13"),
+            Arguments.of(12.6543, 0, Locale.GERMANY, "13"),
+            Arguments.of(12.6543, 1, Locale.GERMANY, "12,7"),
+            Arguments.of(12.6543, 2, Locale.GERMANY, "12,65"),
+
+            Arguments.of(9_999_999, 0, Locale.GERMANY, "9.999.999"),
+            Arguments.of(9_999_999, 0, Locale.UK, "9,999,999"),
+
+            Arguments.of(10_000_000, 0, Locale.GERMANY, "10,0 Mio."),
+            Arguments.of(12_345_678, 0, Locale.GERMANY, "12,3 Mio."),
+            Arguments.of(12_654_321, 0, Locale.GERMANY, "12,7 Mio."),
+            Arguments.of(12_654_321, 0, Locale.UK, "12.7 Mio.")
+        )
+    }
+
+    @AfterAll
+    fun cleanUp() {
+        unmockkAll()
+    }
+}