/*
   Copyright 2024 Josh Deprez

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package aurp

import (
	"encoding/binary"
	"fmt"
	"io"
	"strings"
)

type RIReqPacket struct {
	Header
}

type RIRspPacket struct {
	Header

	Networks NetworkTuples
}

func (p *RIRspPacket) WriteTo(w io.Writer) (int64, error) {
	a := acc(w)
	a.writeTo(&p.Header)
	a.writeTo(p.Networks)
	return a.ret()
}

func parseRIRsp(p []byte) (*RIRspPacket, error) {
	n, err := parseNetworkTuples(p)
	if err != nil {
		return nil, err
	}
	return &RIRspPacket{
		Networks: n,
	}, nil
}

type RIAckPacket struct {
	Header
}

type RIUpdPacket struct {
	Header

	Events EventTuples
}

func (p *RIUpdPacket) WriteTo(w io.Writer) (int64, error) {
	a := acc(w)
	a.writeTo(&p.Header)
	a.writeTo(p.Events)
	return a.ret()
}

func parseRIUpd(p []byte) (*RIUpdPacket, error) {
	e, err := parseEventTuples(p)
	if err != nil {
		return nil, err
	}
	return &RIUpdPacket{
		Events: e,
	}, nil
}

type NetworkTuples []NetworkTuple

func (n NetworkTuples) String() string {
	var sb strings.Builder
	for i, nt := range n {
		if i > 0 {
			sb.WriteString(", ")
		}
		fmt.Fprintf(&sb, "%d-%d dist %d", nt.RangeStart, nt.RangeEnd, nt.Distance)
	}
	return sb.String()
}

func (n NetworkTuples) WriteTo(w io.Writer) (int64, error) {
	a := acc(w)
	for _, nt := range n {
		a.writeTo(&nt)
	}
	return a.ret()
}

func parseNetworkTuples(p []byte) (NetworkTuples, error) {
	// Each network tuple is at least 3 bytes, so we need to store at most
	// len(p)/3 of them.
	n := make(NetworkTuples, 0, len(p)/3)
	for len(p) > 0 {
		nt, nextp, err := parseNetworkTuple(p)
		if err != nil {
			return nil, fmt.Errorf("parsing network tuple %d: %w", len(n), err)
		}
		n = append(n, nt)
		p = nextp
	}
	return n, nil
}

type NetworkTuple struct {
	Extended   bool
	RangeStart uint16
	Distance   uint8
	RangeEnd   uint16
	// 0x00 for extended tuples
}

func (nt *NetworkTuple) WriteTo(w io.Writer) (int64, error) {
	a := acc(w)
	a.write16(nt.RangeStart)
	if !nt.Extended {
		// non-extended tuple
		a.write8(nt.Distance)
		return a.ret()
	}
	// extended tuple
	a.write8(nt.Distance | 0x80)
	a.write16(nt.RangeEnd)
	a.write8(0x00)
	return a.ret()
}

func parseNetworkTuple(p []byte) (NetworkTuple, []byte, error) {
	if len(p) < 3 {
		return NetworkTuple{}, p, fmt.Errorf("insufficient input length %d for network tuple", len(p))
	}

	var nt NetworkTuple
	nt.RangeStart = binary.BigEndian.Uint16(p[:2])
	nt.RangeEnd = nt.RangeStart
	nt.Distance = p[2]
	nt.Extended = nt.Distance&0x80 != 0

	if !nt.Extended {
		return nt, p[3:], nil
	}

	if len(p) < 6 {
		return NetworkTuple{}, p, fmt.Errorf("insufficient input length %d for extended network tuple", len(p))
	}

	nt.Distance &^= 0x80
	nt.RangeEnd = binary.BigEndian.Uint16(p[3:5])
	return nt, p[6:], nil
}

type EventTuples []EventTuple

func (e EventTuples) WriteTo(w io.Writer) (int64, error) {
	a := acc(w)
	for _, et := range e {
		a.writeTo(&et)
	}
	return a.ret()
}

func parseEventTuples(p []byte) (EventTuples, error) {
	// Each event tuple is at least 4 bytes, so we need to store at most
	// len(p)/4 of them.
	e := make(EventTuples, 0, len(p)/4)
	for len(p) > 0 {
		et, nextp, err := parseEventTuple(p)
		if err != nil {
			return nil, fmt.Errorf("parsing event tuple %d: %w", len(e), err)
		}
		e = append(e, et)
		p = nextp
	}
	return e, nil
}

type EventTuple struct {
	EventCode  EventCode
	Extended   bool
	RangeStart uint16
	Distance   uint8
	RangeEnd   uint16
}

func (et *EventTuple) WriteTo(w io.Writer) (int64, error) {
	a := acc(w)
	a.write8(uint8(et.EventCode))
	a.write16(et.RangeStart)
	if !et.Extended {
		// non-extended tuple
		a.write8(et.Distance)
		return a.ret()
	}
	// extended tuple
	a.write8(et.Distance | 0x80)
	a.write16(et.RangeEnd)
	return a.ret()
}

func parseEventTuple(p []byte) (EventTuple, []byte, error) {
	if len(p) < 4 {
		return EventTuple{}, p, fmt.Errorf("insufficient input length %d for network event tuple", len(p))
	}

	var et EventTuple
	et.EventCode = EventCode(p[0])
	et.RangeStart = binary.BigEndian.Uint16(p[1:3])
	et.RangeEnd = et.RangeStart
	et.Distance = p[3]
	et.Extended = et.Distance&0x80 != 0

	if !et.Extended {
		return et, p[4:], nil
	}

	if len(p) < 6 {
		return EventTuple{}, p, fmt.Errorf("insufficient input length %d for extended network event tuple", len(p))
	}

	et.Distance &^= 0x80
	et.RangeEnd = binary.BigEndian.Uint16(p[4:6])
	return et, p[6:], nil
}

type EventCode uint8

const (
	EventCodeNull EventCode = 0
	EventCodeNA   EventCode = 1
	EventCodeND   EventCode = 2
	EventCodeNRC  EventCode = 3
	EventCodeNDC  EventCode = 4
	EventCodeZC   EventCode = 5
)

func (ec EventCode) String() string {
	return map[EventCode]string{
		EventCodeNull: "null",
		EventCodeNA:   "network added",
		EventCodeND:   "network deleted",
		EventCodeNRC:  "network route change",
		EventCodeNDC:  "network distance change",
		EventCodeZC:   "zone name change",
	}[ec]
}