package runtime

import (
	"unsafe"
)

const Compiler = "tgo"

// The compiler will fill this with calls to the initialization function of each
// package.
func initAll()

// The compiler will insert the call to main.main() here, depending on whether
// the scheduler is necessary.
//
// Without scheduler:
//
//     main.main()
//
// With scheduler:
//
//     coroutine := main.main(nil)
//     scheduler(coroutine)
func mainWrapper()

// Entry point for Go. Initialize all packages and call main.main().
//go:export main
func main() int {
	// Initialize memory etc.
	preinit()

	// Run initializers of all packages.
	initAll()

	// Enable interrupts etc.
	postinit()

	// Compiler-generated wrapper to main.main().
	mainWrapper()

	// For libc compatibility.
	return 0
}

func GOMAXPROCS(n int) int {
	// Note: setting GOMAXPROCS is ignored.
	return 1
}

func GOROOT() string {
	// TODO: don't hardcode but take the one at compile time.
	return "/usr/local/go"
}

//go:linkname os_runtime_args os.runtime_args
func os_runtime_args() []string {
	return nil
}

// Copy size bytes from src to dst. The memory areas must not overlap.
func memcpy(dst, src unsafe.Pointer, size uintptr) {
	for i := uintptr(0); i < size; i++ {
		*(*uint8)(unsafe.Pointer(uintptr(dst) + i)) = *(*uint8)(unsafe.Pointer(uintptr(src) + i))
	}
}

// Copy size bytes from src to dst. The memory areas may overlap and will do the
// correct thing.
func memmove(dst, src unsafe.Pointer, size uintptr) {
	if uintptr(dst) < uintptr(src) {
		// Copy forwards.
		memcpy(dst, src, size)
		return
	}
	// Copy backwards.
	i := size
	for {
		i--
		*(*uint8)(unsafe.Pointer(uintptr(dst) + i)) = *(*uint8)(unsafe.Pointer(uintptr(src) + i))
		if i == 0 {
			break
		}
	}
}

// Set the given number of bytes to zero.
func memzero(ptr unsafe.Pointer, size uintptr) {
	for i := uintptr(0); i < size; i++ {
		*(*byte)(unsafe.Pointer(uintptr(ptr) + i)) = 0
	}
}

// Compare two same-size buffers for equality.
func memequal(x, y unsafe.Pointer, n uintptr) bool {
	for i := uintptr(0); i < n; i++ {
		cx := *(*uint8)(unsafe.Pointer(uintptr(x) + i))
		cy := *(*uint8)(unsafe.Pointer(uintptr(y) + i))
		if cx != cy {
			return false
		}
	}
	return true
}

// Builtin copy(dst, src) function: copy bytes from dst to src.
func sliceCopy(dst, src unsafe.Pointer, dstLen, srcLen lenType, elemSize uintptr) lenType {
	// n = min(srcLen, dstLen)
	n := srcLen
	if n > dstLen {
		n = dstLen
	}
	memmove(dst, src, uintptr(n)*elemSize)
	return n
}

//go:linkname sleep time.Sleep
func sleep(d int64) {
	sleepTicks(timeUnit(d / tickMicros))
}