package std

import (
	"encoding"
	"iter"
	"strconv"
	"sync"
	"syscall"
)

// Syscalls returns an iterator over all wired syscalls.
func Syscalls() iter.Seq2[string, ScmpSyscall] {
	return func(yield func(string, ScmpSyscall) bool) {
		for name, num := range syscallNum {
			if !yield(name, num) {
				return
			}
		}
		for name, num := range syscallNumExtra {
			if !yield(name, num) {
				return
			}
		}
	}
}

// SyscallResolveName resolves a syscall number from its string representation.
func SyscallResolveName(name string) (num ScmpSyscall, ok bool) {
	if num, ok = syscallNum[name]; ok {
		return
	}
	num, ok = syscallNumExtra[name]
	return
}

// SchedPolicy denotes a scheduling policy defined in include/uapi/linux/sched.h.
type SchedPolicy int

// include/uapi/linux/sched.h
const (
	SCHED_NORMAL SchedPolicy = iota
	SCHED_FIFO
	SCHED_RR
	SCHED_BATCH
	_SCHED_ISO // SCHED_ISO: reserved but not implemented yet
	SCHED_IDLE
	SCHED_DEADLINE
	SCHED_EXT

	SCHED_LAST SchedPolicy = iota - 1
)

var _ encoding.TextMarshaler = SCHED_LAST
var _ encoding.TextUnmarshaler = new(SCHED_LAST)

// String returns a unique representation of policy, also used in encoding.
func (policy SchedPolicy) String() string {
	switch policy {
	case SCHED_NORMAL:
		return ""
	case SCHED_FIFO:
		return "fifo"
	case SCHED_RR:
		return "rr"
	case SCHED_BATCH:
		return "batch"
	case SCHED_IDLE:
		return "idle"
	case SCHED_DEADLINE:
		return "deadline"
	case SCHED_EXT:
		return "ext"

	default:
		return "invalid policy " + strconv.Itoa(int(policy))
	}
}

// MarshalText performs bounds checking and returns the result of String.
func (policy SchedPolicy) MarshalText() ([]byte, error) {
	if policy == _SCHED_ISO || policy < 0 || policy > SCHED_LAST {
		return nil, syscall.EINVAL
	}
	return []byte(policy.String()), nil
}

// InvalidSchedPolicyError is an invalid string representation of a [SchedPolicy].
type InvalidSchedPolicyError string

func (InvalidSchedPolicyError) Unwrap() error { return syscall.EINVAL }
func (e InvalidSchedPolicyError) Error() string {
	return "invalid scheduling policy " + strconv.Quote(string(e))
}

// UnmarshalText is the inverse of MarshalText.
func (policy *SchedPolicy) UnmarshalText(text []byte) error {
	switch string(text) {
	case "fifo":
		*policy = SCHED_FIFO
	case "rr":
		*policy = SCHED_RR
	case "batch":
		*policy = SCHED_BATCH
	case "idle":
		*policy = SCHED_IDLE
	case "deadline":
		*policy = SCHED_DEADLINE
	case "ext":
		*policy = SCHED_EXT

	case "":
		*policy = 0
		return nil
	default:
		return InvalidSchedPolicyError(text)
	}
	return nil
}

// for sched_get_priority_max and sched_get_priority_min
var (
	schedPriority     [SCHED_LAST + 1][2]Int
	schedPriorityErr  [SCHED_LAST + 1][2]error
	schedPriorityOnce [SCHED_LAST + 1][2]sync.Once
)

// GetPriorityMax returns the maximum priority value that can be used with the
// scheduling algorithm identified by policy.
func (policy SchedPolicy) GetPriorityMax() (Int, error) {
	schedPriorityOnce[policy][0].Do(func() {
		priority, _, errno := syscall.Syscall(
			syscall.SYS_SCHED_GET_PRIORITY_MAX,
			uintptr(policy),
			0, 0,
		)
		schedPriority[policy][0] = Int(priority)
		if schedPriority[policy][0] < 0 {
			schedPriorityErr[policy][0] = errno
		}
	})
	return schedPriority[policy][0], schedPriorityErr[policy][0]
}

// GetPriorityMin returns the minimum priority value that can be used with the
// scheduling algorithm identified by policy.
func (policy SchedPolicy) GetPriorityMin() (Int, error) {
	schedPriorityOnce[policy][1].Do(func() {
		priority, _, errno := syscall.Syscall(
			syscall.SYS_SCHED_GET_PRIORITY_MIN,
			uintptr(policy),
			0, 0,
		)
		schedPriority[policy][1] = Int(priority)
		if schedPriority[policy][1] < 0 {
			schedPriorityErr[policy][1] = errno
		}
	})
	return schedPriority[policy][1], schedPriorityErr[policy][1]

}