feat: Add expect/actual for blurhash and base64Image in commons

- Create PlatformImage expect/actual abstracting Bitmap/BufferedImage
- Move pure blurhash algorithms (Base83, SRGB, CosineCache, BlurHashEncoder) to commonMain
- Rewrite BlurHashDecoder to return PlatformImage instead of Bitmap
- Add PlatformImage.toBlurhash() extension in commonMain
- Add platform-specific Bitmap.toBlurhash() and BufferedImage.toBlurhash()
- Add base64Image toPlatformImage() for both Android and JVM

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

commons/src/androidMain/kotlin/com/vitorpamplona/amethyst/commons/base64Image/Base64ImageBitmap.kt

@@ -22,6 +22,8 @@ package com.vitorpamplona.amethyst.commons.base64Image
 
 import android.graphics.Bitmap
 import android.graphics.BitmapFactory
+import com.vitorpamplona.amethyst.commons.blurhash.PlatformImage
+import com.vitorpamplona.amethyst.commons.blurhash.toPlatformImage
 import java.util.Base64
 
 fun Base64Image.toBitmap(content: String): Bitmap {
@@ -35,3 +37,9 @@ fun Base64Image.toBitmap(content: String): Bitmap {
 
     throw Exception("Unable to convert base64 to image $content")
 }
+
+/**
+ * Converts a base64 image data URI to a PlatformImage.
+ * Delegates to toBitmap and wraps the result.
+ */
+fun Base64Image.toPlatformImage(content: String): PlatformImage = toBitmap(content).toPlatformImage()

commons/src/androidMain/kotlin/com/vitorpamplona/amethyst/commons/blurhash/BitmapUtils.kt

@@ -21,41 +21,9 @@
 package com.vitorpamplona.amethyst.commons.blurhash
 
 import android.graphics.Bitmap
-import kotlin.math.roundToInt
 
-fun Bitmap.toBlurhash(): String {
+/**
-    val aspectRatio = this.width.toFloat() / this.height.toFloat()
+ * Encodes this Android Bitmap to a blurhash string.
-
+ * Delegates to PlatformImage.toBlurhash() for the actual encoding.
-    if (this.width > 100 && this.height > 100) {
+ */
-        return Bitmap.createScaledBitmap(this, 100, (100 / aspectRatio).toInt(), false).toBlurhash()
+fun Bitmap.toBlurhash(): String = this.toPlatformImage().toBlurhash()
-    }
-
-    val intArray = IntArray(width * height)
-    this.getPixels(intArray, 0, width, 0, 0, width, height)
-
-    val numX =
-        if (aspectRatio > 1) {
-            9
-        } else if (aspectRatio < 1) {
-            (9 * aspectRatio).roundToInt()
-        } else {
-            4
-        }
-
-    val numY =
-        if (aspectRatio > 1) {
-            (9 * (1 / aspectRatio)).roundToInt()
-        } else if (aspectRatio < 1) {
-            9
-        } else {
-            4
-        }
-
-    return BlurHashEncoder().encode(
-        intArray,
-        width,
-        height,
-        numX,
-        numY,
-    )
-}

commons/src/androidMain/kotlin/com/vitorpamplona/amethyst/commons/blurhash/PlatformImage.android.kt

@@ -0,0 +1,65 @@
+/**
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.blurhash
+
+import android.graphics.Bitmap
+
+actual class PlatformImage(
+    val bitmap: Bitmap,
+) {
+    actual val width: Int get() = bitmap.width
+    actual val height: Int get() = bitmap.height
+
+    actual fun getPixels(
+        pixels: IntArray,
+        offset: Int,
+        stride: Int,
+        x: Int,
+        y: Int,
+        width: Int,
+        height: Int,
+    ) {
+        bitmap.getPixels(pixels, offset, stride, x, y, width, height)
+    }
+
+    actual fun scale(
+        width: Int,
+        height: Int,
+    ): PlatformImage = PlatformImage(Bitmap.createScaledBitmap(bitmap, width, height, false))
+
+    actual companion object {
+        actual fun create(
+            pixels: IntArray,
+            width: Int,
+            height: Int,
+        ): PlatformImage = PlatformImage(Bitmap.createBitmap(pixels, width, height, Bitmap.Config.ARGB_8888))
+    }
+}
+
+/**
+ * Extension to convert Android Bitmap to PlatformImage.
+ */
+fun Bitmap.toPlatformImage(): PlatformImage = PlatformImage(this)
+
+/**
+ * Extension to get the underlying Android Bitmap.
+ */
+fun PlatformImage.toAndroidBitmap(): Bitmap = this.bitmap

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/blurhash/BlurHashDecoder.kt

@@ -20,7 +20,6 @@
  */
 package com.vitorpamplona.amethyst.commons.blurhash
 
-import android.graphics.Bitmap
 import com.vitorpamplona.amethyst.commons.blurhash.SRGB.Companion.linearToSrgb
 import com.vitorpamplona.amethyst.commons.blurhash.SRGB.Companion.srgbToLinear
 import kotlin.math.pow
@@ -66,7 +65,7 @@ object BlurHashDecoder {
     }
 
     /**
-     * Decode a blur hash into a new bitmap.
+     * Decode a blur hash into a new PlatformImage.
      *
      * @param useCache use in memory cache for the calculated math, reused by images with same size.
      *   if the cache does not exist yet it will be created and populated with new calculations. By
@@ -76,7 +75,7 @@ object BlurHashDecoder {
         blurHash: String?,
         width: Int,
         useCache: Boolean = true,
-    ): Bitmap? {
+    ): PlatformImage? {
         if (blurHash == null || blurHash.length < 6) {
             return null
         }
@@ -87,7 +86,7 @@ object BlurHashDecoder {
         val height = (width * (1 / (numCompX.toFloat() / numCompY.toFloat()))).roundToInt()
         val colors = computeColors(numCompX, numCompY, blurHash)
         val imageArray = composeImageArray(width, height, numCompX, numCompY, colors, useCache)
-        return Bitmap.createBitmap(imageArray, width, height, Bitmap.Config.ARGB_8888)
+        return PlatformImage.create(imageArray, width, height)
     }
 
     private fun decodeDc(colorEnc: Int): FloatArray {

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/blurhash/BlurHashEncoderExt.kt

@@ -0,0 +1,64 @@
+/**
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.blurhash
+
+import kotlin.math.roundToInt
+
+/**
+ * Encodes this PlatformImage to a blurhash string.
+ * The image will be scaled down if larger than 100x100 for performance.
+ */
+fun PlatformImage.toBlurhash(): String {
+    val aspectRatio = this.width.toFloat() / this.height.toFloat()
+
+    if (this.width > 100 && this.height > 100) {
+        return this.scale(100, (100 / aspectRatio).toInt()).toBlurhash()
+    }
+
+    val intArray = IntArray(width * height)
+    this.getPixels(intArray, 0, width, 0, 0, width, height)
+
+    val numX =
+        if (aspectRatio > 1) {
+            9
+        } else if (aspectRatio < 1) {
+            (9 * aspectRatio).roundToInt()
+        } else {
+            4
+        }
+
+    val numY =
+        if (aspectRatio > 1) {
+            (9 * (1 / aspectRatio)).roundToInt()
+        } else if (aspectRatio < 1) {
+            9
+        } else {
+            4
+        }
+
+    return BlurHashEncoder().encode(
+        intArray,
+        width,
+        height,
+        numX,
+        numY,
+    )
+}

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/blurhash/CosineCache.kt

@@ -21,6 +21,7 @@
 package com.vitorpamplona.amethyst.commons.blurhash
 
 import androidx.collection.LruCache
+import kotlin.math.PI
 import kotlin.math.cos
 
 object CosineCache {
@@ -54,7 +55,7 @@ object CosineCache {
             DoubleArray(height * numCompY) {
                 val y = it / numCompY
                 val j = it % numCompY
-                cos(Math.PI * y * j / height)
+                cos(PI * y * j / height)
             }.also {
                 cacheCosinesY.put(height * numCompY, it)
             }
@@ -73,7 +74,7 @@ object CosineCache {
             DoubleArray(width * numCompX) {
                 val x = it / numCompX
                 val i = it % numCompX
-                cos(Math.PI * x * i / width)
+                cos(PI * x * i / width)
             }.also { cacheCosinesX.put(width * numCompX, it) }
         }
         else -> cacheCosinesX[width * numCompX]!!

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/blurhash/PlatformImage.kt

@@ -0,0 +1,65 @@
+/**
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.blurhash
+
+/**
+ * Platform-agnostic image wrapper for blurhash encoding/decoding.
+ *
+ * On Android: wraps android.graphics.Bitmap
+ * On Desktop JVM: wraps java.awt.image.BufferedImage
+ */
+expect class PlatformImage {
+    val width: Int
+    val height: Int
+
+    /**
+     * Read ARGB pixels into the provided array.
+     * Pixels are in ARGB format (0xAARRGGBB).
+     */
+    fun getPixels(
+        pixels: IntArray,
+        offset: Int,
+        stride: Int,
+        x: Int,
+        y: Int,
+        width: Int,
+        height: Int,
+    )
+
+    /**
+     * Create a scaled copy of this image.
+     */
+    fun scale(
+        width: Int,
+        height: Int,
+    ): PlatformImage
+
+    companion object {
+        /**
+         * Create a new image from ARGB pixel array.
+         */
+        fun create(
+            pixels: IntArray,
+            width: Int,
+            height: Int,
+        ): PlatformImage
+    }
+}

commons/src/jvmMain/kotlin/com/vitorpamplona/amethyst/commons/base64Image/Base64ImagePlatform.jvm.kt

@@ -0,0 +1,45 @@
+/**
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.base64Image
+
+import com.vitorpamplona.amethyst.commons.blurhash.PlatformImage
+import com.vitorpamplona.amethyst.commons.blurhash.toPlatformImage
+import java.io.ByteArrayInputStream
+import java.util.Base64
+import javax.imageio.ImageIO
+
+/**
+ * Converts a base64 image data URI to a PlatformImage (BufferedImage wrapper).
+ */
+fun Base64Image.toPlatformImage(content: String): PlatformImage {
+    val matcher = pattern.matcher(content)
+
+    if (matcher.find()) {
+        val base64String = matcher.group(2)
+        val byteArray = Base64.getDecoder().decode(base64String)
+        val bufferedImage =
+            ImageIO.read(ByteArrayInputStream(byteArray))
+                ?: throw Exception("Unable to decode base64 image: $content")
+        return bufferedImage.toPlatformImage()
+    }
+
+    throw Exception("Unable to convert base64 to image $content")
+}

commons/src/jvmMain/kotlin/com/vitorpamplona/amethyst/commons/blurhash/BitmapUtils.jvm.kt

@@ -0,0 +1,29 @@
+/**
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.blurhash
+
+import java.awt.image.BufferedImage
+
+/**
+ * Encodes this BufferedImage to a blurhash string.
+ * Delegates to PlatformImage.toBlurhash() for the actual encoding.
+ */
+fun BufferedImage.toBlurhash(): String = this.toPlatformImage().toBlurhash()

commons/src/jvmMain/kotlin/com/vitorpamplona/amethyst/commons/blurhash/PlatformImage.jvm.kt

@@ -0,0 +1,75 @@
+/**
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.blurhash
+
+import java.awt.Image
+import java.awt.image.BufferedImage
+
+actual class PlatformImage(
+    val image: BufferedImage,
+) {
+    actual val width: Int get() = image.width
+    actual val height: Int get() = image.height
+
+    actual fun getPixels(
+        pixels: IntArray,
+        offset: Int,
+        stride: Int,
+        x: Int,
+        y: Int,
+        width: Int,
+        height: Int,
+    ) {
+        image.getRGB(x, y, width, height, pixels, offset, stride)
+    }
+
+    actual fun scale(
+        width: Int,
+        height: Int,
+    ): PlatformImage {
+        val scaled = image.getScaledInstance(width, height, Image.SCALE_FAST)
+        val buffered = BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB)
+        buffered.graphics.drawImage(scaled, 0, 0, null)
+        return PlatformImage(buffered)
+    }
+
+    actual companion object {
+        actual fun create(
+            pixels: IntArray,
+            width: Int,
+            height: Int,
+        ): PlatformImage {
+            val image = BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB)
+            image.setRGB(0, 0, width, height, pixels, 0, width)
+            return PlatformImage(image)
+        }
+    }
+}
+
+/**
+ * Extension to convert BufferedImage to PlatformImage.
+ */
+fun BufferedImage.toPlatformImage(): PlatformImage = PlatformImage(this)
+
+/**
+ * Extension to get the underlying BufferedImage.
+ */
+fun PlatformImage.toBufferedImage(): BufferedImage = this.image