//! SNMP Parser
//!
//! SNMP is defined in the following RFCs:
//!   - [RFC1157](https://tools.ietf.org/html/rfc1157): SNMP v1
//!   - [RFC1902](https://tools.ietf.org/html/rfc1902): SNMP v2 SMI
//!   - [RFC3416](https://tools.ietf.org/html/rfc3416): SNMP v2
//!   - [RFC2570](https://tools.ietf.org/html/rfc2570): Introduction to SNMP v3

use std::{fmt,str};
use std::net::Ipv4Addr;
use std::slice::Iter;
use nom::{IResult,ErrorKind};
use der_parser::*;
use der_parser::oid::Oid;

#[derive(Clone, Copy, Eq, PartialEq)]
pub struct PduType(pub u8);

#[allow(non_upper_case_globals)]
impl PduType {
    pub const GetRequest     : PduType = PduType(0);
    pub const GetNextRequest : PduType = PduType(1);
    pub const Response       : PduType = PduType(2);
    pub const SetRequest     : PduType = PduType(3);
    pub const TrapV1         : PduType = PduType(4); // Obsolete, was the old Trap-PDU in SNMPv1
    pub const GetBulkRequest : PduType = PduType(5);
    pub const InformRequest  : PduType = PduType(6);
    pub const TrapV2         : PduType = PduType(7);
    pub const Report         : PduType = PduType(8);
}

impl fmt::Debug for PduType {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.0 {
           0 => f.write_str("GetRequest"),
           1 => f.write_str("GetNextRequest"),
           2 => f.write_str("Response"),
           3 => f.write_str("SetRequest"),
           4 => f.write_str("TrapV1"),
           5 => f.write_str("GetBulkRequest"),
           6 => f.write_str("InformRequest"),
           7 => f.write_str("TrapV2"),
           8 => f.write_str("Report"),
           n => f.debug_tuple("PduType").field(&n).finish(),
        }
    }
}

#[derive(Clone, Copy, Eq, PartialEq)]
pub struct TrapType(pub u8);

impl TrapType {
    pub const COLD_START             : TrapType = TrapType(0);
    pub const WARM_START             : TrapType = TrapType(1);
    pub const LINK_DOWN              : TrapType = TrapType(2);
    pub const LINK_UP                : TrapType = TrapType(3);
    pub const AUTHENTICATION_FAILURE : TrapType = TrapType(4);
    pub const EGP_NEIGHBOR_LOSS      : TrapType = TrapType(5);
    pub const ENTERPRISE_SPECIFIC    : TrapType = TrapType(6);
}

impl fmt::Debug for TrapType {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.0 {
           0 => f.write_str("coldStart"),
           1 => f.write_str("warmStart"),
           2 => f.write_str("linkDown"),
           3 => f.write_str("linkUp"),
           4 => f.write_str("authenticationFailure"),
           5 => f.write_str("egpNeighborLoss"),
           6 => f.write_str("enterpriseSpecific"),
           n => f.debug_tuple("TrapType").field(&n).finish(),
        }
    }
}

/// This CHOICE represents an address from one of possibly several
/// protocol families.  Currently, only one protocol family, the Internet
/// family, is present in this CHOICE.
#[derive(Copy, Clone, Debug, PartialEq)]
pub enum NetworkAddress {
    IPv4(Ipv4Addr),
}

/// This application-wide type represents a non-negative integer which
/// monotonically increases until it reaches a maximum value, when it
/// wraps around and starts increasing again from zero.  This memo
/// specifies a maximum value of 2^32-1 (4294967295 decimal) for
/// counters.
pub type Counter = u32;

/// This application-wide type represents a non-negative integer, which
/// may increase or decrease, but which latches at a maximum value.  This
/// memo specifies a maximum value of 2^32-1 (4294967295 decimal) for
/// gauges.
pub type Gauge = u32;

/// This application-wide type represents a non-negative integer which
/// counts the time in hundredths of a second since some epoch.  When
/// object types are defined in the MIB which use this ASN.1 type, the
/// description of the object type identifies the reference epoch.
pub type TimeTicks = u32;

#[derive(Clone, Copy, Eq, PartialEq)]
pub struct ErrorStatus(pub u32);

#[allow(non_upper_case_globals)]
impl ErrorStatus {
    pub const NoError    : ErrorStatus = ErrorStatus(0);
    pub const TooBig     : ErrorStatus = ErrorStatus(1);
    pub const NoSuchName : ErrorStatus = ErrorStatus(2);
    pub const BadValue   : ErrorStatus = ErrorStatus(3);
    pub const ReadOnly   : ErrorStatus = ErrorStatus(4);
    pub const GenErr     : ErrorStatus = ErrorStatus(5);
}

impl fmt::Debug for ErrorStatus {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.0 {
           0 => f.write_str("NoError"),
           1 => f.write_str("TooBig"),
           2 => f.write_str("NoSuchName"),
           3 => f.write_str("BadValue"),
           4 => f.write_str("ReadOnly"),
           5 => f.write_str("GenErr"),
           n => f.debug_tuple("ErrorStatus").field(&n).finish(),
        }
    }
}

#[derive(Debug,PartialEq)]
pub struct SnmpGenericPdu<'a> {
    pub pdu_type: PduType,
    pub req_id: u32,
    pub err: ErrorStatus,
    pub err_index: u32,
    pub var: Vec<SnmpVariable<'a>>,
}

#[derive(Debug,PartialEq)]
pub struct SnmpTrapPdu<'a> {
    pub enterprise: Oid,
    pub agent_addr: NetworkAddress,
    pub generic_trap: TrapType,
    pub specific_trap: u32,
    pub timestamp: TimeTicks,
    pub var: Vec<SnmpVariable<'a>>,
}

#[derive(Debug,PartialEq)]
pub enum SnmpPdu<'a> {
    Generic(SnmpGenericPdu<'a>),
    TrapV1(SnmpTrapPdu<'a>),
}

#[derive(Debug,PartialEq)]
pub struct SnmpMessage<'a> {
    pub version: u32,
    pub community: String,
    pub pdu: SnmpPdu<'a>,
}

impl<'a> SnmpGenericPdu<'a> {
    pub fn vars_iter(&'a self) -> Iter<SnmpVariable> {
        self.var.iter()
    }
}

impl<'a> SnmpTrapPdu<'a> {
    pub fn vars_iter(&'a self) -> Iter<SnmpVariable> {
        self.var.iter()
    }
}

impl<'a> SnmpPdu<'a> {
    pub fn pdu_type(&self) -> PduType {
        match *self {
            SnmpPdu::Generic(ref pdu) => pdu.pdu_type,
            SnmpPdu::TrapV1(_)        => PduType::TrapV1,
        }
    }

    pub fn vars_iter(&'a self) -> Iter<SnmpVariable> {
        match *self {
            SnmpPdu::Generic(ref pdu) => pdu.var.iter(),
            SnmpPdu::TrapV1(ref pdu)  => pdu.var.iter(),
        }
    }
}

impl<'a> SnmpMessage<'a> {
    pub fn pdu_type(&self) -> PduType {
        self.pdu.pdu_type()
    }

    pub fn vars_iter(&'a self) -> Iter<SnmpVariable> {
        self.pdu.vars_iter()
    }
}

#[derive(Debug,PartialEq)]
pub struct SnmpVariable<'a> {
    pub oid: Oid,
    pub val: ObjectSyntax<'a>
}

#[derive(Debug,PartialEq)]
pub enum ObjectSyntax<'a> {
    Number(DerObject<'a>),
    String(&'a[u8]),
    Object(Oid),
    Empty,
    Address(NetworkAddress),
    Counter(Counter),
    Gauge(Gauge),
    Ticks(TimeTicks),
    Arbitrary(DerObject<'a>),
}

pub fn parse_der_octetstring_as_slice(i:&[u8]) -> IResult<&[u8],&[u8]> {
    match parse_der_octetstring(i) {
        IResult::Done(rem,ref obj) => {
            match obj.content {
                DerObjectContent::OctetString(s) => {
                    IResult::Done(rem, s)
                }
                _ => IResult::Error(error_code!(ErrorKind::Custom(DER_TAG_ERROR))),
            }
        }
        IResult::Incomplete(i) => IResult::Incomplete(i),
        IResult::Error(e) => IResult::Error(e)
    }
}

fn parse_objectsyntax<'a>(i:&'a[u8]) -> IResult<&'a[u8],ObjectSyntax> {
    match der_read_element_header(i) {
        IResult::Done(rem,hdr) => {
            if hdr.is_application() {
                match hdr.tag {
                    0 => {
                        map_res!(
                            rem,
                            apply!(der_read_element_content_as,DerTag::OctetString as u8, hdr.len as usize),
                            |x:DerObjectContent| {
                                match x {
                                    DerObjectContent::OctetString(s) if s.len() == 4 => {
                                        Ok(ObjectSyntax::Address(NetworkAddress::IPv4(Ipv4Addr::new(s[0],s[1],s[2],s[3]))))
                                    },
                                    _ => Err(DER_TAG_ERROR),
                                }
                            }
                        )
                    },
                    1 ... 3 => {
                        map_res!(
                            rem,
                            apply!(der_read_element_content_as, DerTag::Integer as u8, hdr.len as usize),
                            |x:DerObjectContent| {
                                x.as_u32().map(|x| {
                                    match hdr.tag {
                                        1 => ObjectSyntax::Counter(x),
                                        2 => ObjectSyntax::Gauge(x),
                                        3 => ObjectSyntax::Ticks(x),
                                        _ => unreachable!(),
                                    }
                                })
                            }
                        )
                    },
                    4 => {
                        let r = der_read_element_content_as(rem, DerTag::OctetString as u8, hdr.len as usize);
                        r.map(|x| ObjectSyntax::Arbitrary(DerObject::from_obj(x)))
                    },
                    _ => IResult::Error(error_code!(ErrorKind::Custom(DER_TAG_ERROR))),
                }
            } else {
                        map_res!(
                            rem,
                            apply!(der_read_element_content_as, hdr.tag, hdr.len as usize),
                            |x:DerObjectContent<'a>| {
                                match x {
                                    DerObjectContent::Integer(_)     => Ok(ObjectSyntax::Number(DerObject::from_obj(x))),
                                    DerObjectContent::OctetString(s) => Ok(ObjectSyntax::String(s)),
                                    DerObjectContent::OID(o)         => Ok(ObjectSyntax::Object(o)),
                                    DerObjectContent::Null           => Ok(ObjectSyntax::Empty),
                                    _                                => Err(DER_TAG_ERROR),
                                }
                            }
                        )
            }
        },
        IResult::Incomplete(i) => IResult::Incomplete(i),
        IResult::Error(e)      => IResult::Error(e)
    }
}

#[inline]
fn parse_varbind(i:&[u8]) -> IResult<&[u8],SnmpVariable> {
    parse_der_struct!(
        i,
        TAG DerTag::Sequence,
        oid: map_res!(parse_der_oid, |x:DerObject| x.as_oid_val()) >>
        val: parse_objectsyntax >>
             // eof!() >>
        (
            SnmpVariable{ oid, val }
        )
    ).map(|x| x.1)
}

#[inline]
fn parse_varbind_list(i:&[u8]) -> IResult<&[u8],Vec<SnmpVariable>> {
    parse_der_struct!(
        i,
        TAG DerTag::Sequence,
        l: many0!(parse_varbind) >>
           // eof!() >>
        ( l )
    ).map(|x| x.1)
}

/// <pre>
///  NetworkAddress ::=
///      CHOICE {
///          internet
///              IpAddress
///      }
/// IpAddress ::=
///     [APPLICATION 0]          -- in network-byte order
///         IMPLICIT OCTET STRING (SIZE (4))
/// </pre>
fn parse_networkaddress(i:&[u8]) -> IResult<&[u8],NetworkAddress> {
    match parse_der(i) {
        IResult::Done(rem,obj) => {
            if obj.tag != 0 || obj.class != 0b01 {
                return IResult::Error(error_code!(ErrorKind::Custom(DER_TAG_ERROR)));
            }
            match obj.content {
                DerObjectContent::Unknown(s) if s.len() == 4 => {
                    IResult::Done(rem, NetworkAddress::IPv4(Ipv4Addr::new(s[0],s[1],s[2],s[3])))
                },
                _ => IResult::Error(error_code!(ErrorKind::Custom(DER_TAG_ERROR))),
            }
        },
        IResult::Incomplete(i) => IResult::Incomplete(i),
        IResult::Error(e)      => IResult::Error(e),
    }
}

/// <pre>
/// TimeTicks ::=
///     [APPLICATION 3]
///         IMPLICIT INTEGER (0..4294967295)
/// </pre>
fn parse_timeticks(i:&[u8]) -> IResult<&[u8],TimeTicks> {
    fn der_read_integer_content(i:&[u8], _tag:u8, len: usize) -> IResult<&[u8],DerObjectContent,u32> {
        der_read_element_content_as(i, DerTag::Integer as u8, len)
    }
    map_res!(i, apply!(parse_der_implicit, 3, der_read_integer_content), |x: DerObject| {
        match x.as_context_specific() {
            Ok((_,Some(x))) => x.as_u32(),
            _               => Err(DerError::DerTypeError),
        }
    })
}




fn parse_snmp_v1_generic_pdu(pdu: &[u8], tag:PduType) -> IResult<&[u8],SnmpPdu> {
    do_parse!(pdu,
              req_id:       parse_der_u32 >>
              err:          parse_der_u32 >>
              err_index:    parse_der_u32 >>
                            error_if!(true == false, ErrorKind::Custom(128)) >>
              var_bindings: parse_varbind_list >>
              (
                  SnmpPdu::Generic(
                      SnmpGenericPdu {
                          pdu_type:  tag,
                          req_id,
                          err:       ErrorStatus(err),
                          err_index,
                          var:       var_bindings
                      }
                  )
              ))
}

fn parse_snmp_v1_trap_pdu(pdu: &[u8]) -> IResult<&[u8],SnmpPdu> {
    do_parse!(
        pdu,
        enterprise:    map_res!(parse_der_oid, |x: DerObject| x.as_oid_val()) >>
        agent_addr:    parse_networkaddress >>
        generic_trap:  parse_der_u32 >>
        specific_trap: parse_der_u32 >>
        timestamp:     parse_timeticks >>
        var_bindings:  parse_varbind_list >>
        (
            SnmpPdu::TrapV1(
                SnmpTrapPdu {
                    enterprise,
                    agent_addr,
                    generic_trap:  TrapType(generic_trap as u8),
                    specific_trap,
                    timestamp,
                    var:           var_bindings
                }
            )
        )
    )
}

/// Top-level message
///
/// <pre>
/// Message ::=
///         SEQUENCE {
///             version          -- version-1 for this RFC
///                 INTEGER {
///                     version-1(0)
///                 },
///
///             community        -- community name
///                 OCTET STRING,
///
///             data             -- e.g., PDUs if trivial
///                 ANY          -- authentication is being used
///         }
/// </pre>
pub fn parse_snmp_v1(i:&[u8]) -> IResult<&[u8],SnmpMessage> {
    parse_der_struct!(
        i,
        TAG DerTag::Sequence,
        version:   parse_der_u32 >>
        community: map_res!(
            parse_der_octetstring_as_slice,
            |s| str::from_utf8(s)
        ) >>
        pdu:       parse_snmp_v1_pdu >>
        (
            SnmpMessage{
                version,
                community: community.to_string(),
                pdu
            }
        )
    ).map(|x| x.1)
}

pub fn parse_snmp_v1_pdu(i:&[u8]) -> IResult<&[u8],SnmpPdu> {
    match der_read_element_header(i) {
        IResult::Done(rem,hdr) => {
            match PduType(hdr.tag) {
                PduType::GetRequest |
                PduType::GetNextRequest |
                PduType::Response |
                PduType::SetRequest |
                PduType::Report     => parse_snmp_v1_generic_pdu(rem, PduType(hdr.tag)),
                PduType::TrapV1     => parse_snmp_v1_trap_pdu(rem),
                _                   => IResult::Error(error_code!(ErrorKind::Custom(128))),
                // _                   => { return IResult::Error(error_code!(ErrorKind::Custom(SnmpError::InvalidPdu))); },
            }
        },
        IResult::Incomplete(i) => IResult::Incomplete(i),
        IResult::Error(_)      => IResult::Error(error_code!(ErrorKind::Custom(129))),
        // IResult::Error(_)      => IResult::Error(error_code!(ErrorKind::Custom(SnmpError::InvalidScopedPduData))),
    }
}