/*
   Copyright 2014 CoreOS, Inc.

   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 network

import (
	"fmt"
	"net"
	"strconv"
	"strings"
)

type stanza interface{}

type stanzaAuto struct {
	interfaces []string
}

type stanzaInterface struct {
	name         string
	kind         interfaceKind
	auto         bool
	configMethod configMethod
	options      map[string][]string
}

type interfaceKind int

const (
	interfaceBond = interfaceKind(iota)
	interfacePhysical
	interfaceVLAN
)

type route struct {
	destination net.IPNet
	gateway     net.IP
}

type configMethod interface{}

type configMethodStatic struct {
	addresses   []net.IPNet
	nameservers []net.IP
	routes      []route
	hwaddress   net.HardwareAddr
}

type configMethodLoopback struct{}

type configMethodManual struct{}

type configMethodDHCP struct {
	hwaddress net.HardwareAddr
}

func parseStanzas(lines []string) (stanzas []stanza, err error) {
	rawStanzas, err := splitStanzas(lines)
	if err != nil {
		return nil, err
	}

	stanzas = make([]stanza, 0, len(rawStanzas))
	for _, rawStanza := range rawStanzas {
		if stanza, err := parseStanza(rawStanza); err == nil {
			stanzas = append(stanzas, stanza)
		} else {
			return nil, err
		}
	}

	autos := make([]string, 0)
	interfaceMap := make(map[string]*stanzaInterface)
	for _, stanza := range stanzas {
		switch c := stanza.(type) {
		case *stanzaAuto:
			autos = append(autos, c.interfaces...)
		case *stanzaInterface:
			interfaceMap[c.name] = c
		}
	}

	// Apply the auto attribute
	for _, auto := range autos {
		if iface, ok := interfaceMap[auto]; ok {
			iface.auto = true
		}
	}

	return stanzas, nil
}

func splitStanzas(lines []string) ([][]string, error) {
	var curStanza []string
	stanzas := make([][]string, 0)
	for _, line := range lines {
		if isStanzaStart(line) {
			if curStanza != nil {
				stanzas = append(stanzas, curStanza)
			}
			curStanza = []string{line}
		} else if curStanza != nil {
			curStanza = append(curStanza, line)
		} else {
			return nil, fmt.Errorf("missing stanza start %q", line)
		}
	}

	if curStanza != nil {
		stanzas = append(stanzas, curStanza)
	}

	return stanzas, nil
}

func isStanzaStart(line string) bool {
	switch strings.Split(line, " ")[0] {
	case "auto":
		fallthrough
	case "iface":
		fallthrough
	case "mapping":
		return true
	}

	if strings.HasPrefix(line, "allow-") {
		return true
	}

	return false
}

func parseStanza(rawStanza []string) (stanza, error) {
	if len(rawStanza) == 0 {
		panic("empty stanza")
	}
	tokens := strings.Fields(rawStanza[0])
	if len(tokens) < 2 {
		return nil, fmt.Errorf("malformed stanza start %q", rawStanza[0])
	}

	kind := tokens[0]
	attributes := tokens[1:]

	switch kind {
	case "auto":
		return parseAutoStanza(attributes, rawStanza[1:])
	case "iface":
		return parseInterfaceStanza(attributes, rawStanza[1:])
	default:
		return nil, fmt.Errorf("unknown stanza %q", kind)
	}
}

func parseAutoStanza(attributes []string, options []string) (*stanzaAuto, error) {
	return &stanzaAuto{interfaces: attributes}, nil
}

func parseInterfaceStanza(attributes []string, options []string) (*stanzaInterface, error) {
	if len(attributes) != 3 {
		return nil, fmt.Errorf("incorrect number of attributes")
	}

	iface := attributes[0]
	confMethod := attributes[2]

	optionMap := make(map[string][]string, 0)
	for _, option := range options {
		if strings.HasPrefix(option, "post-up") {
			tokens := strings.SplitAfterN(option, " ", 2)
			if len(tokens) != 2 {
				continue
			}
			if v, ok := optionMap["post-up"]; ok {
				optionMap["post-up"] = append(v, tokens[1])
			} else {
				optionMap["post-up"] = []string{tokens[1]}
			}
		} else if strings.HasPrefix(option, "pre-down") {
			tokens := strings.SplitAfterN(option, " ", 2)
			if len(tokens) != 2 {
				continue
			}
			if v, ok := optionMap["pre-down"]; ok {
				optionMap["pre-down"] = append(v, tokens[1])
			} else {
				optionMap["pre-down"] = []string{tokens[1]}
			}
		} else {
			tokens := strings.Fields(option)
			optionMap[tokens[0]] = tokens[1:]
		}
	}

	var conf configMethod
	switch confMethod {
	case "static":
		config := configMethodStatic{
			addresses:   make([]net.IPNet, 1),
			routes:      make([]route, 0),
			nameservers: make([]net.IP, 0),
		}
		if addresses, ok := optionMap["address"]; ok {
			if len(addresses) == 1 {
				config.addresses[0].IP = net.ParseIP(addresses[0])
			}
		}
		if netmasks, ok := optionMap["netmask"]; ok {
			if len(netmasks) == 1 {
				config.addresses[0].Mask = net.IPMask(net.ParseIP(netmasks[0]).To4())
			}
		}
		if config.addresses[0].IP == nil || config.addresses[0].Mask == nil {
			return nil, fmt.Errorf("malformed static network config for %q", iface)
		}
		if gateways, ok := optionMap["gateway"]; ok {
			if len(gateways) == 1 {
				config.routes = append(config.routes, route{
					destination: net.IPNet{
						IP:   net.IPv4(0, 0, 0, 0),
						Mask: net.IPv4Mask(0, 0, 0, 0),
					},
					gateway: net.ParseIP(gateways[0]),
				})
			}
		}
		if hwaddress, err := parseHwaddress(optionMap, iface); err == nil {
			config.hwaddress = hwaddress
		} else {
			return nil, err
		}
		for _, nameserver := range optionMap["dns-nameservers"] {
			config.nameservers = append(config.nameservers, net.ParseIP(nameserver))
		}
		for _, postup := range optionMap["post-up"] {
			if strings.HasPrefix(postup, "route add") {
				route := route{}
				fields := strings.Fields(postup)
				for i, field := range fields[:len(fields)-1] {
					switch field {
					case "-net":
						if _, dst, err := net.ParseCIDR(fields[i+1]); err == nil {
							route.destination = *dst
						} else {
							route.destination.IP = net.ParseIP(fields[i+1])
						}
					case "netmask":
						route.destination.Mask = net.IPMask(net.ParseIP(fields[i+1]).To4())
					case "gw":
						route.gateway = net.ParseIP(fields[i+1])
					}
				}
				if route.destination.IP != nil && route.destination.Mask != nil && route.gateway != nil {
					config.routes = append(config.routes, route)
				}
			}
		}
		conf = config
	case "loopback":
		conf = configMethodLoopback{}
	case "manual":
		conf = configMethodManual{}
	case "dhcp":
		config := configMethodDHCP{}
		if hwaddress, err := parseHwaddress(optionMap, iface); err == nil {
			config.hwaddress = hwaddress
		} else {
			return nil, err
		}
		conf = config
	default:
		return nil, fmt.Errorf("invalid config method %q", confMethod)
	}

	if _, ok := optionMap["vlan_raw_device"]; ok {
		return parseVLANStanza(iface, conf, attributes, optionMap)
	}

	if strings.Contains(iface, ".") {
		return parseVLANStanza(iface, conf, attributes, optionMap)
	}

	if _, ok := optionMap["bond-slaves"]; ok {
		return parseBondStanza(iface, conf, attributes, optionMap)
	}

	return parsePhysicalStanza(iface, conf, attributes, optionMap)
}

func parseHwaddress(options map[string][]string, iface string) (net.HardwareAddr, error) {
	if hwaddress, ok := options["hwaddress"]; ok && len(hwaddress) == 2 {
		switch hwaddress[0] {
		case "ether":
			if address, err := net.ParseMAC(hwaddress[1]); err == nil {
				return address, nil
			}
			return nil, fmt.Errorf("malformed hwaddress option for %q", iface)
		}
	}
	return nil, nil
}

func parseBondStanza(iface string, conf configMethod, attributes []string, options map[string][]string) (*stanzaInterface, error) {
	return &stanzaInterface{name: iface, kind: interfaceBond, configMethod: conf, options: options}, nil
}

func parsePhysicalStanza(iface string, conf configMethod, attributes []string, options map[string][]string) (*stanzaInterface, error) {
	return &stanzaInterface{name: iface, kind: interfacePhysical, configMethod: conf, options: options}, nil
}

func parseVLANStanza(iface string, conf configMethod, attributes []string, options map[string][]string) (*stanzaInterface, error) {
	var id string
	if strings.Contains(iface, ".") {
		tokens := strings.Split(iface, ".")
		id = tokens[len(tokens)-1]
	} else if strings.HasPrefix(iface, "vlan") {
		id = strings.TrimPrefix(iface, "vlan")
	} else {
		return nil, fmt.Errorf("malformed vlan name %q", iface)
	}

	if _, err := strconv.Atoi(id); err != nil {
		return nil, fmt.Errorf("malformed vlan name %q", iface)
	}
	options["id"] = []string{id}
	options["raw_device"] = options["vlan_raw_device"]

	return &stanzaInterface{name: iface, kind: interfaceVLAN, configMethod: conf, options: options}, nil
}