package link

import (
	"errors"
	"unsafe"

	"github.com/cilium/ebpf"
	"github.com/cilium/ebpf/asm"
	"github.com/cilium/ebpf/internal"
	"github.com/cilium/ebpf/internal/unix"
)

// Type is the kind of link.
type Type uint32

// Valid link types.
//
// Equivalent to enum bpf_link_type.
const (
	UnspecifiedType Type = iota
	RawTracepointType
	TracingType
	CgroupType
	IterType
	NetNsType
	XDPType
)

var haveProgAttach = internal.FeatureTest("BPF_PROG_ATTACH", "4.10", func() error {
	prog, err := ebpf.NewProgram(&ebpf.ProgramSpec{
		Type:       ebpf.CGroupSKB,
		AttachType: ebpf.AttachCGroupInetIngress,
		License:    "MIT",
		Instructions: asm.Instructions{
			asm.Mov.Imm(asm.R0, 0),
			asm.Return(),
		},
	})
	if err != nil {
		return internal.ErrNotSupported
	}

	// BPF_PROG_ATTACH was introduced at the same time as CGgroupSKB,
	// so being able to load the program is enough to infer that we
	// have the syscall.
	prog.Close()
	return nil
})

var haveProgAttachReplace = internal.FeatureTest("BPF_PROG_ATTACH atomic replacement", "5.5", func() error {
	if err := haveProgAttach(); err != nil {
		return err
	}

	prog, err := ebpf.NewProgram(&ebpf.ProgramSpec{
		Type:       ebpf.CGroupSKB,
		AttachType: ebpf.AttachCGroupInetIngress,
		License:    "MIT",
		Instructions: asm.Instructions{
			asm.Mov.Imm(asm.R0, 0),
			asm.Return(),
		},
	})
	if err != nil {
		return internal.ErrNotSupported
	}
	defer prog.Close()

	// We know that we have BPF_PROG_ATTACH since we can load CGroupSKB programs.
	// If passing BPF_F_REPLACE gives us EINVAL we know that the feature isn't
	// present.
	attr := internal.BPFProgAttachAttr{
		// We rely on this being checked after attachFlags.
		TargetFd:    ^uint32(0),
		AttachBpfFd: uint32(prog.FD()),
		AttachType:  uint32(ebpf.AttachCGroupInetIngress),
		AttachFlags: uint32(flagReplace),
	}

	err = internal.BPFProgAttach(&attr)
	if errors.Is(err, unix.EINVAL) {
		return internal.ErrNotSupported
	}
	if errors.Is(err, unix.EBADF) {
		return nil
	}
	return err
})

type bpfLinkCreateAttr struct {
	progFd     uint32
	targetFd   uint32
	attachType ebpf.AttachType
	flags      uint32
}

func bpfLinkCreate(attr *bpfLinkCreateAttr) (*internal.FD, error) {
	ptr, err := internal.BPF(internal.BPF_LINK_CREATE, unsafe.Pointer(attr), unsafe.Sizeof(*attr))
	if err != nil {
		return nil, err
	}
	return internal.NewFD(uint32(ptr)), nil
}

type bpfLinkUpdateAttr struct {
	linkFd    uint32
	newProgFd uint32
	flags     uint32
	oldProgFd uint32
}

func bpfLinkUpdate(attr *bpfLinkUpdateAttr) error {
	_, err := internal.BPF(internal.BPF_LINK_UPDATE, unsafe.Pointer(attr), unsafe.Sizeof(*attr))
	return err
}

var haveBPFLink = internal.FeatureTest("bpf_link", "5.7", func() error {
	prog, err := ebpf.NewProgram(&ebpf.ProgramSpec{
		Type:       ebpf.CGroupSKB,
		AttachType: ebpf.AttachCGroupInetIngress,
		License:    "MIT",
		Instructions: asm.Instructions{
			asm.Mov.Imm(asm.R0, 0),
			asm.Return(),
		},
	})
	if err != nil {
		return internal.ErrNotSupported
	}
	defer prog.Close()

	attr := bpfLinkCreateAttr{
		// This is a hopefully invalid file descriptor, which triggers EBADF.
		targetFd:   ^uint32(0),
		progFd:     uint32(prog.FD()),
		attachType: ebpf.AttachCGroupInetIngress,
	}
	_, err = bpfLinkCreate(&attr)
	if errors.Is(err, unix.EINVAL) {
		return internal.ErrNotSupported
	}
	if errors.Is(err, unix.EBADF) {
		return nil
	}
	return err
})

type bpfIterCreateAttr struct {
	linkFd uint32
	flags  uint32
}

func bpfIterCreate(attr *bpfIterCreateAttr) (*internal.FD, error) {
	ptr, err := internal.BPF(internal.BPF_ITER_CREATE, unsafe.Pointer(attr), unsafe.Sizeof(*attr))
	if err == nil {
		return internal.NewFD(uint32(ptr)), nil
	}
	return nil, err
}

type bpfRawTracepointOpenAttr struct {
	name internal.Pointer
	fd   uint32
	_    uint32
}

func bpfRawTracepointOpen(attr *bpfRawTracepointOpenAttr) (*internal.FD, error) {
	ptr, err := internal.BPF(internal.BPF_RAW_TRACEPOINT_OPEN, unsafe.Pointer(attr), unsafe.Sizeof(*attr))
	if err == nil {
		return internal.NewFD(uint32(ptr)), nil
	}
	return nil, err
}