compose-jb/components/resources/library/src/wasmJsMain/kotlin/org/jetbrains/compose/resources/ResourceReader.wasmJs.kt

package org.jetbrains.compose.resources

import kotlinx.browser.window
import kotlinx.coroutines.await
import org.khronos.webgl.ArrayBuffer
import org.khronos.webgl.Int8Array
import org.w3c.fetch.Response
import kotlin.wasm.unsafe.UnsafeWasmMemoryApi
import kotlin.wasm.unsafe.withScopedMemoryAllocator

/**
 * Reads the content of the resource file at the specified path and returns it as a byte array.
 *
 * @param path The path of the file to read in the resource's directory.
 * @return The content of the file as a byte array.
 */
@OptIn(ExperimentalResourceApi::class)
@InternalResourceApi
actual suspend fun readResourceBytes(path: String): ByteArray {
    val resPath = WebResourcesConfiguration.getResourcePath(path)
    val response = window.fetch(resPath).await<Response>()
    if (!response.ok) {
        throw MissingResourceException(resPath)
    }
    return response.arrayBuffer().await<ArrayBuffer>().toByteArray()
}

private fun ArrayBuffer.toByteArray(): ByteArray  {
    val source = Int8Array(this, 0, byteLength)
    return jsInt8ArrayToKotlinByteArray(source)
}

@JsFun(
    """ (src, size, dstAddr) => {
        const mem8 = new Int8Array(wasmExports.memory.buffer, dstAddr, size);
        mem8.set(src);
    }
"""
)
internal external fun jsExportInt8ArrayToWasm(src: Int8Array, size: Int, dstAddr: Int)

internal fun jsInt8ArrayToKotlinByteArray(x: Int8Array): ByteArray {
    val size = x.length

    @OptIn(UnsafeWasmMemoryApi::class)
    return withScopedMemoryAllocator { allocator ->
        val memBuffer = allocator.allocate(size)
        val dstAddress = memBuffer.address.toInt()
        jsExportInt8ArrayToWasm(x, size, dstAddress)
        ByteArray(size) { i -> (memBuffer + i).loadByte() }
    }
}