//go:build wasm && go1.13
// +build wasm,go1.13

package wasm

import (
	"reflect"
	"runtime"
	"syscall/js"
	"unsafe"
)

func sliceToByteSlice(s interface{}) []byte {
	switch s := s.(type) {
	case []int8:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		return *(*[]byte)(unsafe.Pointer(h))
	case []int16:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 2
		h.Cap *= 2
		return *(*[]byte)(unsafe.Pointer(h))
	case []int32:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4
		h.Cap *= 4
		return *(*[]byte)(unsafe.Pointer(h))
	case []int64:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 8
		h.Cap *= 8
		return *(*[]byte)(unsafe.Pointer(h))
	case []uint8:
		return s
	case []uint16:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 2
		h.Cap *= 2
		return *(*[]byte)(unsafe.Pointer(h))
	case []uint32:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4
		h.Cap *= 4
		return *(*[]byte)(unsafe.Pointer(h))
	case []uint64:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 8
		h.Cap *= 8
		return *(*[]byte)(unsafe.Pointer(h))
	case []float32:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 4
		h.Cap *= 4
		return *(*[]byte)(unsafe.Pointer(h))
	case []float64:
		h := (*reflect.SliceHeader)(unsafe.Pointer(&s))
		h.Len *= 8
		h.Cap *= 8
		return *(*[]byte)(unsafe.Pointer(h))
	default:
		panic("jsutil: unexpected value at sliceToBytesSlice()")
	}
}

func SliceToTypedArray(s interface{}) (val js.Value, free func()) {
	free = func() {}
	switch s := s.(type) {
	case []int8:
		a := js.Global().Get("Uint8Array").New(len(s))
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Int8Array").New(buf, a.Get("byteOffset"), a.Get("byteLength")), free
	case []int16:
		a := js.Global().Get("Uint8Array").New(len(s) * 2)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Int16Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/2), free
	case []int32:
		a := js.Global().Get("Uint8Array").New(len(s) * 4)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Int32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4), free
	case []uint8:
		a := js.Global().Get("Uint8Array").New(len(s))
		js.CopyBytesToJS(a, s)
		runtime.KeepAlive(s)
		return a, free
	case []uint16:
		a := js.Global().Get("Uint8Array").New(len(s) * 2)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Uint16Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/2), free
	case []uint32:
		a := js.Global().Get("Uint8Array").New(len(s) * 4)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Uint32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4), free
	case []float32:
		a := js.Global().Get("Uint8Array").New(len(s) * 4)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Float32Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/4), free
	case []float64:
		a := js.Global().Get("Uint8Array").New(len(s) * 8)
		js.CopyBytesToJS(a, sliceToByteSlice(s))
		runtime.KeepAlive(s)
		buf := a.Get("buffer")
		return js.Global().Get("Float64Array").New(buf, a.Get("byteOffset"), a.Get("byteLength").Int()/8), free
	default:
		panic("jsutil: unexpected value at SliceToTypedArray()")
	}
}

func Equal(a, b js.Value) bool {
	return a.Equal(b)
}