HealthStatsSync: stub buildWeekdayTypicalsFromData

Adds the helper signature and empty-input fast path. Subsequent commits
will fill in the binning algorithm test-by-test.

Author: aveao

libpebble3/src/commonMain/kotlin/io/rebble/libpebblecommon/services/HealthStatsSync.kt

@@ -21,6 +21,7 @@ import co.touchlab.kermit.Logger
 import io.rebble.libpebblecommon.database.dao.DailyMovementAggregate
 import io.rebble.libpebblecommon.database.dao.HealthAggregates
 import io.rebble.libpebblecommon.database.dao.HealthDao
+import io.rebble.libpebblecommon.database.entity.HealthDataEntity
 import io.rebble.libpebblecommon.database.entity.HealthStat
 import io.rebble.libpebblecommon.database.entity.HealthStatDao
 import io.rebble.libpebblecommon.util.DataBuffer
@@ -32,6 +33,7 @@ import kotlinx.datetime.TimeZone
 import kotlinx.datetime.atStartOfDayIn
 import kotlinx.datetime.minus
 import kotlinx.datetime.plus
+import kotlinx.datetime.toLocalDateTime
 
 private val logger = Logger.withTag("HealthStatsSync")
 
@@ -178,6 +180,23 @@ private fun movementPayload(dayStartEpochSec: Long, aggregates: HealthAggregates
     return buffer.array()
 }
 
+/**
+ * Bins a flat list of HealthDataEntity rows into per-weekday 15-minute typical-step payloads.
+ *
+ * For each weekday with at least MIN_DAYS_FOR_TYPICAL distinct matching days in the input,
+ * emits a 192-byte little-endian payload of 96 UShort values. A slot's value is the average
+ * step count across the distinct matching days that had at least one row overlapping that
+ * slot; if zero matching days covered the slot, the value is UNKNOWN_TYPICAL_STEPS so the
+ * watch sum-skips it. Weekdays below the threshold are omitted from the result.
+ */
+internal fun buildWeekdayTypicalsFromData(
+    allData: List<HealthDataEntity>,
+    timeZone: TimeZone,
+): Map<DayOfWeek, ByteArray> {
+    if (allData.isEmpty()) return emptyMap()
+    return emptyMap()
+}
+
 // Extension functions
 private fun Long.kilocalories(): Long = this / 1000L
 

libpebble3/src/commonTest/kotlin/io/rebble/libpebblecommon/services/HealthStatsSyncTest.kt

@@ -0,0 +1,26 @@
+package io.rebble.libpebblecommon.services
+
+import io.rebble.libpebblecommon.database.entity.HealthDataEntity
+import kotlinx.datetime.TimeZone
+import kotlin.test.Test
+import kotlin.test.assertTrue
+
+class HealthStatsSyncTest {
+    @Test
+    fun buildWeekdayTypicalsFromData_emptyInput_returnsEmptyMap() {
+        val result = buildWeekdayTypicalsFromData(emptyList(), TimeZone.UTC)
+        assertTrue(result.isEmpty(), "empty input should produce empty map, got keys=${result.keys}")
+    }
+}
+
+private fun row(timestamp: Long, steps: Int) = HealthDataEntity(
+    timestamp = timestamp,
+    steps = steps,
+    orientation = 0,
+    intensity = 0,
+    lightIntensity = 0,
+    activeMinutes = 0,
+    restingGramCalories = 0,
+    activeGramCalories = 0,
+    distanceCm = 0,
+)