WebView.kt

private fun getClient(): WebViewClient {
        return object : WebViewClient() {
            override fun shouldInterceptRequest(
                view: WebView?,
                request: WebResourceRequest?
            ): WebResourceResponse? {
                return super.shouldInterceptRequest(view, request)
            }

            override fun shouldInterceptRequest(view: WebView?, url: String?): WebResourceResponse? {
                if (url == null) {
                    return super.shouldInterceptRequest(view, url as String)
                }

                val interceptedUrl = url.toLowerCase(Locale.ROOT)
                val cachableImage = CachableImage.getMatchingImage(interceptedUrl)

                return when {
                    cachableImage != null -> {
                        val bitmap = Glide.with(webView)
                            .asBitmap()
                            .diskCacheStrategy(DiskCacheStrategy.ALL)
                            .load(interceptedUrl)
                            .submit()
                            .get()

                        WebResourceResponse(
                            cachableImage.mimeType,
                            "UTF-8",
                            getBitmapInputStream(
                                bitmap,
                                cachableImage.compressFormat,
                            )
                        )
                    }
                    else -> super.shouldInterceptRequest(view, interceptedUrl)
                }
            }
        }
    }

enum class CachableImage(
    val suffixes: Set<String>,
    val mimeType: String,
    val compressFormat: Bitmap.CompressFormat,
) {
    JPG(setOf("jpg", "jpeg"), "image/jpg", Bitmap.CompressFormat.JPEG),
    PNG(setOf("png"), "image/png", Bitmap.CompressFormat.PNG),
    WEBP(setOf("webp"), "image/webp", Bitmap.CompressFormat.WEBP_LOSSY);

    companion object {
        fun getMatchingImage(url: String): CachableImage? = values().find { image ->
            image.suffixes.any { url.contains(".$it") }
        }
    }
}

private fun getBitmapInputStream(bitmap: Bitmap, compressFormat: Bitmap.CompressFormat): InputStream =
        ByteArrayInputStream(
            ByteArrayOutputStream().apply {
                bitmap.compress(compressFormat, 80, this)
            }.toByteArray()
        )