grain.social/grain-android

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package social.grain

import androidx.test.ext.junit.runners.AndroidJUnit4
import kotlinx.serialization.json.Json
import okhttp3.OkHttpClient
import org.junit.Assert.assertEquals
import org.junit.Assert.assertNotNull
import org.junit.Assert.assertNull
import org.junit.Assert.assertTrue
import org.junit.Test
import org.junit.runner.RunWith
import social.grain.data.location.LocationServices

/**
 * The H3 cell is the grouping key for a location feed, so it has to agree with
 * every other Grain client exactly. These pin the resolution and the known
 * reference values rather than trusting that the binding loaded.
 */
@RunWith(AndroidJUnit4::class)
class H3Test {

    private val services = LocationServices(OkHttpClient(), Json { ignoreUnknownKeys = true })

    @Test
    fun theNativeBindingLoadsOnThisDevice() {
        assertTrue(
            "h3 ships arm and arm64 only — an x86 emulator has no binary",
            services.isAvailable,
        )
    }

    @Test
    fun theDocumentedReferenceCoordinateProducesItsKnownCell() {
        // The H3 project's own worked example: the Statue of Liberty at
        // resolution 10. An independent expected value is the only thing that
        // proves the binding agrees with other clients — asserting the
        // library's output against itself would prove nothing.
        assertEquals("8a2a1072b59ffff", services.cellFor(40.689247, -74.044502))
    }

    @Test
    fun aCellCentresBackOnThePointItCameFrom() {
        // The location feed's map has only the cell to work from, so the
        // reverse conversion has to land inside the ~65m cell it names.
        val center = services.coordinateFor("8a2a1072b59ffff")
        assertNotNull(center)
        assertEquals(40.689247, center!!.latitude, 0.001)
        assertEquals(-74.044502, center.longitude, 0.001)
        assertEquals("8a2a1072b59ffff", services.cellFor(center.latitude, center.longitude))
    }

    @Test
    fun aCellAddressThatIsNotOneYieldsNoCoordinate() {
        assertNull(services.coordinateFor("not-a-cell"))
    }

    @Test
    fun aCellAddressIsFifteenHexCharacters() {
        val cell = services.cellFor(51.5074, -0.1278)
        assertNotNull(cell)
        assertEquals(15, cell!!.length)
        assertTrue("not hex: $cell", cell.all { it.isDigit() || it in 'a'..'f' })
    }

    @Test
    fun nearbyPointsShareACellAndDistantOnesDoNot() {
        // Resolution 10 cells are roughly 65m across, so a few metres apart is
        // the same cell and a kilometre away is not.
        val base = services.cellFor(37.775938, -122.41795)
        assertEquals(base, services.cellFor(37.775940, -122.417952))
        assertTrue(base != services.cellFor(37.785938, -122.41795))
    }
}