// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: MIT

// The RPCSEC_GSSv3 structures of RFC 7861: the version three credential,
// the CREATE and LIST control procedures and the assertion payloads.

package rpc

import (
	"errors"

	"sourcedock.dev/petrbalvin/nfs/internal/xdr"
)

// Control procedure numbers of the rpc_gss_proc_t enumeration, RFC 7861
// section 5.1.
const (
	GSSProcCreate = 5
	GSSProcList   = 6
)

// The credential version that carries the new control procedures.
const GSSVersion3 = 3

// Assertion types of the rgss3_assertion_type enumeration.
const (
	AssertionLabel = 0
	AssertionPrivs = 1
)

// ErrGSSv3 marks a malformed version three control message.
var ErrGSSv3 = errors.New("rpc: malformed rpcsec gssv3 message")

// A GSSv3Cred is the version three credential: the version field rides
// in front of the version one shape, RFC 7861 section 5.1.
type GSSv3Cred struct {
	Proc    uint32
	Seq     uint32
	Service uint32
	Handle  []byte
}

// AppendGSSv3Cred encodes the version three credential body.
func AppendGSSv3Cred(b []byte, proc, seq, service uint32, handle []byte) []byte {
	b = xdr.AppendUint32(b, GSSVersion3)
	b = xdr.AppendUint32(b, proc)
	b = xdr.AppendUint32(b, seq)
	b = xdr.AppendUint32(b, service)
	return xdr.AppendVarOpaque(b, handle)
}

// DecodeGSSv3Cred decodes the version three credential body: the
// leading version field is checked and skipped before the credential
// proper.
func DecodeGSSv3Cred(body []byte) (GSSv3Cred, error) {
	d := xdr.NewDecoder(body)
	var c GSSv3Cred
	var err error
	if c.Proc, err = d.Uint32(); err != nil {
		return c, err
	}
	if c.Proc != GSSVersion3 {
		return c, ErrGSSv3
	}
	if c.Proc, err = d.Uint32(); err != nil {
		return c, err
	}
	if c.Seq, err = d.Uint32(); err != nil {
		return c, err
	}
	if c.Service, err = d.Uint32(); err != nil {
		return c, err
	}
	c.Handle, err = d.VarOpaque()
	return c, err
}

// A Label is the rgss3_label assertion: the label format specifier and
// the opaque label payload.
type Label struct {
	LfsId uint32
	PiId  uint32
	Bytes []byte
}

// Privs is the rgss3_privs structured privilege: who grants what.
type Privs struct {
	Who   string
	Grant string
	Bytes []byte
}

// An Assertion is one rgss3_assertion_u union member.
type Assertion struct {
	Type  uint32
	Label Label
	Privs Privs
	Ext   []byte
}

// appendLabel and appendPrivs encode the assertion payloads.
func appendLabel(b []byte, l Label) []byte {
	b = xdr.AppendUint32(b, l.LfsId)
	b = xdr.AppendUint32(b, l.PiId)
	return xdr.AppendVarOpaque(b, l.Bytes)
}

func appendPrivs(b []byte, p Privs) []byte {
	b = xdr.AppendString(b, p.Who)
	b = xdr.AppendString(b, p.Grant)
	return xdr.AppendVarOpaque(b, p.Bytes)
}

// AppendAssertion encodes one rgss3_assertion_u union.
func AppendAssertion(b []byte, a Assertion) []byte {
	b = xdr.AppendUint32(b, a.Type)
	switch a.Type {
	case AssertionLabel:
		return appendLabel(b, a.Label)
	case AssertionPrivs:
		return appendPrivs(b, a.Privs)
	default:
		return xdr.AppendVarOpaque(b, a.Ext)
	}
}

// DecodeAssertion decodes one rgss3_assertion_u union.
func DecodeAssertion(d *xdr.Decoder) (Assertion, error) {
	var a Assertion
	var err error
	if a.Type, err = d.Uint32(); err != nil {
		return a, err
	}
	switch a.Type {
	case AssertionLabel:
		if a.Label.LfsId, err = d.Uint32(); err != nil {
			return a, err
		}
		if a.Label.PiId, err = d.Uint32(); err != nil {
			return a, err
		}
		a.Label.Bytes, err = d.VarOpaque()
		return a, err
	case AssertionPrivs:
		if a.Privs.Who, err = d.String(); err != nil {
			return a, err
		}
		if a.Privs.Grant, err = d.String(); err != nil {
			return a, err
		}
		a.Privs.Bytes, err = d.VarOpaque()
		return a, err
	default:
		a.Ext, err = d.VarOpaque()
		return a, err
	}
}

// A MpAuth is the rgss3_gss_mp_auth multi-principal authentication
// payload: the inner context handle and a MIC of the RPC header made
// under the inner context.
type MpAuth struct {
	InnerHandle []byte
	HeaderMic   []byte
}

// appendOptional encodes an XDR optional: the presence flag and the
// payload.
func appendOptional(b []byte, present bool, enc func([]byte) []byte) []byte {
	b = xdr.AppendBool(b, present)
	if present {
		return enc(b)
	}
	return b
}

// AppendCreateArgs encodes the rgss3_create_args call data.
func AppendCreateArgs(b []byte, mpAuth *MpAuth, chanBinding []byte, assertions []Assertion) []byte {
	b = appendOptional(b, mpAuth != nil, func(x []byte) []byte {
		x = xdr.AppendVarOpaque(x, mpAuth.InnerHandle)
		return xdr.AppendVarOpaque(x, mpAuth.HeaderMic)
	})
	b = appendOptional(b, chanBinding != nil, func(x []byte) []byte {
		return xdr.AppendVarOpaque(x, chanBinding)
	})
	b = xdr.AppendUint32(b, uint32(len(assertions)))
	for _, a := range assertions {
		b = AppendAssertion(b, a)
	}
	return b
}

// DecodeCreateArgs decodes the rgss3_create_args call data.
func DecodeCreateArgs(payload []byte) (mpAuth *MpAuth, chanBinding []byte, assertions []Assertion, err error) {
	d := xdr.NewDecoder(payload)
	var present bool
	if present, err = d.Bool(); err != nil {
		return
	}
	if present {
		mpAuth = &MpAuth{}
		if mpAuth.InnerHandle, err = d.VarOpaque(); err != nil {
			return
		}
		if mpAuth.HeaderMic, err = d.VarOpaque(); err != nil {
			return
		}
	}
	if present, err = d.Bool(); err != nil {
		return
	}
	if present {
		if chanBinding, err = d.VarOpaque(); err != nil {
			return
		}
	}
	var n uint32
	if n, err = d.Uint32(); err != nil {
		return
	}
	for i := uint32(0); i < n; i++ {
		var a Assertion
		if a, err = DecodeAssertion(d); err != nil {
			return
		}
		assertions = append(assertions, a)
	}
	return
}

// AppendCreateRes encodes the rgss3_create_res reply: the child handle,
// the mirrored optional fields and the granted assertions in order.
func AppendCreateRes(b []byte, handle []byte, mpAuth *MpAuth, chanBinding []byte, assertions []Assertion) []byte {
	b = xdr.AppendVarOpaque(b, handle)
	b = appendOptional(b, mpAuth != nil, func(x []byte) []byte {
		x = xdr.AppendVarOpaque(x, mpAuth.InnerHandle)
		return xdr.AppendVarOpaque(x, mpAuth.HeaderMic)
	})
	b = appendOptional(b, chanBinding != nil, func(x []byte) []byte {
		return xdr.AppendVarOpaque(x, chanBinding)
	})
	b = xdr.AppendUint32(b, uint32(len(assertions)))
	for _, a := range assertions {
		b = AppendAssertion(b, a)
	}
	return b
}

// DecodeCreateRes decodes the rgss3_create_res reply.
func DecodeCreateRes(payload []byte) (handle []byte, mpAuth *MpAuth, chanBinding []byte, assertions []Assertion, err error) {
	d := xdr.NewDecoder(payload)
	if handle, err = d.VarOpaque(); err != nil {
		return
	}
	var present bool
	if present, err = d.Bool(); err != nil {
		return
	}
	if present {
		mpAuth = &MpAuth{}
		if mpAuth.InnerHandle, err = d.VarOpaque(); err != nil {
			return
		}
		if mpAuth.HeaderMic, err = d.VarOpaque(); err != nil {
			return
		}
	}
	if present, err = d.Bool(); err != nil {
		return
	}
	if present {
		if chanBinding, err = d.VarOpaque(); err != nil {
			return
		}
	}
	var n uint32
	if n, err = d.Uint32(); err != nil {
		return
	}
	for i := uint32(0); i < n; i++ {
		var a Assertion
		if a, err = DecodeAssertion(d); err != nil {
			return
		}
		assertions = append(assertions, a)
	}
	return
}

// AppendListRes encodes the RPCSEC_GSS_LIST reply: the supported
// assertion types, RFC 7861 section 5.3.
func AppendListRes(b []byte, types []uint32) []byte {
	b = xdr.AppendUint32(b, uint32(len(types)))
	for _, t := range types {
		b = xdr.AppendUint32(b, t)
	}
	return b
}