theme album screens from their cover art

app/src/test/kotlin/com/subtracks/ui/AppScreenshotTest.kt

@@ -50,6 +50,7 @@ import com.subtracks.ui.settings.AddSourceScreen
 import com.subtracks.ui.settings.AddSourceState
 import com.subtracks.ui.settings.SettingsScreen
 import com.subtracks.ui.theme.SubtracksTheme
+import com.subtracks.ui.theme.artworkColorsFromSeed
 import kotlinx.coroutines.flow.flowOf
 import org.junit.After
 import org.junit.Before
@@ -120,6 +121,7 @@ class AppScreenshotTest {
                     album = Fixtures.albums.first(),
                     songs = Fixtures.songs,
                     coverArt = { id, _ -> id?.let { CoverArtRef(it, "test:$it") } },
+                    artwork = artworkColorsFromSeed(Color.rgb(120, 80, 200)),
                     onBack = {},
                     onSongClick = {},
                     playingSongId = Fixtures.songs.first().id,

app/src/test/kotlin/com/subtracks/ui/theme/ArtworkColorsTest.kt

@@ -0,0 +1,46 @@
+package com.subtracks.ui.theme
+
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.graphics.luminance
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class ArtworkColorsTest {
+    private val seeds =
+        listOf(
+            0xFF3A7BD5.toInt(),
+            0xFFD53A3A.toInt(),
+            0xFF3AD55F.toInt(),
+            0xFFB0B0B0.toInt(),
+            0x00000000,
+        )
+
+    @Test
+    fun darkBackgroundWithReadableText() {
+        for (seed in seeds) {
+            val scheme = artworkColorsFromSeed(seed).scheme
+            assertTrue("background for $seed", scheme.background.luminance() < 0.1f)
+            assertTrue("onBackground for $seed", contrast(scheme.background, scheme.onBackground) >= 4.5f)
+            assertTrue("primary text for $seed", contrast(scheme.primary, scheme.onPrimary) >= 3f)
+            assertTrue("onSurface for $seed", contrast(scheme.surface, scheme.onSurface) >= 4.5f)
+        }
+    }
+
+    @Test
+    fun independentOfAlphaBits() {
+        assertEquals(
+            artworkColorsFromSeed(0xFF3A7BD5.toInt()).scheme.primary,
+            artworkColorsFromSeed(0x3A7BD5).scheme.primary,
+        )
+    }
+
+    private fun contrast(
+        a: Color,
+        b: Color,
+    ): Float {
+        val hi = maxOf(a.luminance(), b.luminance())
+        val lo = minOf(a.luminance(), b.luminance())
+        return (hi + 0.05f) / (lo + 0.05f)
+    }
+}