// This is a helper for safely working with byte buffers returned from the Rust code.
// A rust-owned buffer is represented by its capacity, its current length, and a
// pointer to the underlying data.

@Structure.FieldOrder("capacity", "len", "data")
open class RustBuffer : Structure() {
    // Note: `capacity` and `len` are actually `ULong` values, but JVM only supports signed values.
    // When dealing with these fields, make sure to call `toULong()`.
    @JvmField var capacity: Long = 0
    @JvmField var len: Long = 0
    @JvmField var data: Pointer? = null

    class ByValue: RustBuffer(), Structure.ByValue
    class ByReference: RustBuffer(), Structure.ByReference

   internal fun setValue(other: RustBuffer) {
        capacity = other.capacity
        len = other.len
        data = other.data
    }

    companion object {
        internal fun alloc(size: ULong = 0UL) = uniffiRustCall() { status ->
            // Note: need to convert the size to a `Long` value to make this work with JVM.
            UniffiLib.INSTANCE.{{ ci.ffi_rustbuffer_alloc().name() }}(size.toLong(), status)
        }.also {
            if(it.data == null) {
               throw RuntimeException("RustBuffer.alloc() returned null data pointer (size=${size})")
           }
        }

        internal fun create(capacity: ULong, len: ULong, data: Pointer?): RustBuffer.ByValue {
            var buf = RustBuffer.ByValue()
            buf.capacity = capacity.toLong()
            buf.len = len.toLong()
            buf.data = data
            return buf
        }

        internal fun free(buf: RustBuffer.ByValue) = uniffiRustCall() { status ->
            UniffiLib.INSTANCE.{{ ci.ffi_rustbuffer_free().name() }}(buf, status)
        }
    }

    @Suppress("TooGenericExceptionThrown")
    fun asByteBuffer() =
        this.data?.getByteBuffer(0, this.len.toLong())?.also {
            it.order(ByteOrder.BIG_ENDIAN)
        }
}

/**
 * The equivalent of the `*mut RustBuffer` type.
 * Required for callbacks taking in an out pointer.
 *
 * Size is the sum of all values in the struct.
 */
class RustBufferByReference : ByReference(16) {
    /**
     * Set the pointed-to `RustBuffer` to the given value.
     */
    fun setValue(value: RustBuffer.ByValue) {
        // NOTE: The offsets are as they are in the C-like struct.
        val pointer = getPointer()
        pointer.setLong(0, value.capacity)
        pointer.setLong(8, value.len)
        pointer.setPointer(16, value.data)
    }

    /**
     * Get a `RustBuffer.ByValue` from this reference.
     */
    fun getValue(): RustBuffer.ByValue {
        val pointer = getPointer()
        val value = RustBuffer.ByValue()
        value.writeField("capacity", pointer.getLong(0))
        value.writeField("len", pointer.getLong(8))
        value.writeField("data", pointer.getLong(16))

        return value
    }
}

// This is a helper for safely passing byte references into the rust code.
// It's not actually used at the moment, because there aren't many things that you
// can take a direct pointer to in the JVM, and if we're going to copy something
// then we might as well copy it into a `RustBuffer`. But it's here for API
// completeness.

@Structure.FieldOrder("len", "data")
open class ForeignBytes : Structure() {
    @JvmField var len: Int = 0
    @JvmField var data: Pointer? = null

    class ByValue : ForeignBytes(), Structure.ByValue
}