// +build wasm

package runtime

import "unsafe"

type timeUnit float64 // time in milliseconds, just like Date.now() in JavaScript

// Implements __wasi_ciovec_t and __wasi_iovec_t.
type wasiIOVec struct {
	buf    unsafe.Pointer
	bufLen uint
}

//go:wasm-module wasi_unstable
//export fd_write
func fd_write(id uint32, iovs *wasiIOVec, iovs_len uint, nwritten *uint) (errno uint)

func postinit() {}

//export _start
func _start() {
	// These need to be initialized early so that the heap can be initialized.
	heapStart = uintptr(unsafe.Pointer(&heapStartSymbol))
	heapEnd = uintptr(wasm_memory_size(0) * wasmPageSize)

	run()
}

// Using global variables to avoid heap allocation.
var (
	putcharBuf   = byte(0)
	putcharIOVec = wasiIOVec{
		buf:    unsafe.Pointer(&putcharBuf),
		bufLen: 1,
	}
)

func putchar(c byte) {
	// write to stdout
	const stdout = 1
	var nwritten uint
	putcharBuf = c
	fd_write(stdout, &putcharIOVec, 1, &nwritten)
}

var handleEvent func()

//go:linkname setEventHandler syscall/js.setEventHandler
func setEventHandler(fn func()) {
	handleEvent = fn
}

//export resume
func resume() {
	go func() {
		handleEvent()
	}()
	scheduler()
}

//export go_scheduler
func go_scheduler() {
	scheduler()
}

const asyncScheduler = true

func ticksToNanoseconds(ticks timeUnit) int64 {
	// The JavaScript API works in float64 milliseconds, so convert to
	// nanoseconds first before converting to a timeUnit (which is a float64),
	// to avoid precision loss.
	return int64(ticks * 1e6)
}

func nanosecondsToTicks(ns int64) timeUnit {
	// The JavaScript API works in float64 milliseconds, so convert to timeUnit
	// (which is a float64) first before dividing, to avoid precision loss.
	return timeUnit(ns) / 1e6
}

// This function is called by the scheduler.
// Schedule a call to runtime.scheduler, do not actually sleep.
//export runtime.sleepTicks
func sleepTicks(d timeUnit)

//export runtime.ticks
func ticks() timeUnit

// Abort executes the wasm 'unreachable' instruction.
func abort() {
	trap()
}

// TinyGo does not yet support any form of parallelism on WebAssembly, so these
// can be left empty.

//go:linkname procPin sync/atomic.runtime_procPin
func procPin() {
}

//go:linkname procUnpin sync/atomic.runtime_procUnpin
func procUnpin() {
}