using System;
using ln.snmp.types;
using System.Net;
using System.Collections.Generic;
using System.Linq;
using ln.snmp.channel;
using System.Reflection;

namespace ln.snmp
{
    public enum SnmpVersion : int { V1 = 0, V2c = 1, V3 = 3 }

    public abstract class SNMPInterface
    {
        public SNMPEngine SNMPEngine { get; }
        public IPEndPoint RemoteEndpoint { get; set; }

        public abstract SnmpVersion SnmpVersion { get; }

        public SNMPInterface(SNMPEngine snmpEngine,IPEndPoint remoteEndpoint)
        {
            SNMPEngine = snmpEngine;
            RemoteEndpoint = remoteEndpoint;
        }

        public abstract PDU snmpRequest(PDU pdu);

        private List<Sequence> snmpRequest<T>(IEnumerable<ObjectIdentifier> objectIdentifiers) where T: PDU, new()
        {
            PDU pdu = new T();
            foreach (ObjectIdentifier oid in objectIdentifiers)
            {
                pdu.Add(new Sequence(new Variable[] { oid, NullValue.Instance }));
            }

            PDU responsePDU = snmpRequest(pdu);

            if (responsePDU.Error.LongValue != 0)
            {
                string indicator = responsePDU.ErrorIndex > 0 && responsePDU.ErrorIndex <= pdu.VarBinds.Items.Length ? ((pdu.VarBinds.Items[(int)responsePDU.ErrorIndex - 1] as Sequence).Items[0] as ObjectIdentifier).AsString : "";
                throw new SnmpError(responsePDU.Error, responsePDU.ErrorIndex, indicator);
            }

            Sequence varBinds = responsePDU.VarBinds as Sequence;

            List<Sequence> results = new List<Sequence>();
            foreach (Variable varBind in varBinds.Items)
            {
                results.Add(varBind as Sequence);
            }
            return results;
        }

        public List<Sequence> snmpGet(IEnumerable<ObjectIdentifier> objectIdentifiers)
        {
            return snmpRequest<GetRequest>(objectIdentifiers);
        }
        public Variable snmpGet(ObjectIdentifier objectIdentifier)
        {
            return snmpGet(new ObjectIdentifier[] { objectIdentifier })[0].Items[1];
        }
        public Variable snmpGet(string objectIdentifier)
        {
            return snmpGet(new ObjectIdentifier[] { new ObjectIdentifier(objectIdentifier) })[0].Items[1];
        }
        public List<Sequence> snmpGet(IEnumerable<String> objectIdentifiers)
        {
            return snmpGet(objectIdentifiers.Select((x) => new ObjectIdentifier(x)));
        }

        public List<Sequence> snmpGetNext(IEnumerable<ObjectIdentifier> objectIdentifiers)
        {
            return snmpRequest<GetNextRequest>(objectIdentifiers);
        }
        public Sequence snmpGetNext(ObjectIdentifier objectIdentifier)
        {
            return snmpGetNext(new ObjectIdentifier[] { objectIdentifier })[0];
        }
        public Sequence snmpGetNext(string objectIdentifier)
        {
            return snmpGetNext(new ObjectIdentifier[] { new ObjectIdentifier(objectIdentifier) })[0];
        }
        public List<Sequence> snmpGetNext(IEnumerable<String> objectIdentifiers)
        {
            return snmpGetNext(objectIdentifiers.Select((x) => new ObjectIdentifier(x)));
        }

        private PDU TryBulk(GetBulkRequest bulkRequest)
        {
            try
            {
                return snmpRequest(bulkRequest);
            } catch (SnmpError se)
            {
                if ((se.Error == 1)&&(bulkRequest.MaxRepetitions.LongValue > 1))
                {
                    bulkRequest.MaxRepetitions.LongValue >>= 1;
                    return TryBulk(bulkRequest);
                }
                throw se;
            }
        }

        /*
         * ToDO: Algorithm is not perfect, when receiving an inclomplete "row", the already received partial row is ignored
         */
        public Sequence[][] snmpGetBulk(IEnumerable<ObjectIdentifier> objectIdentifiers, int maxRepetitions = 32)
        {
            ObjectIdentifier[] OIDs = objectIdentifiers.ToArray();
            int ncolumns = OIDs.Length;

            GetBulkRequest pdu = new GetBulkRequest();
            pdu.MaxRepetitions.LongValue = maxRepetitions;

            foreach (ObjectIdentifier oid in objectIdentifiers)
            {
                pdu.Add(new Sequence(new Variable[] { oid, NullValue.Instance }));
            }

            List<Sequence[]> result = new List<Sequence[]>();
            int nchunk;
            bool inTree = false;

            do
            {
                PDU responsePDU = TryBulk(pdu);
                Variable[] values = responsePDU.VarBinds.Items;

                nchunk = values.Length / ncolumns;
                inTree = false;

                for (int n = 0; n < nchunk; n++)
                {
                    Sequence[] row = new Sequence[ncolumns];
                    for (int c = 0; c < ncolumns; c++)
                    {
                        Sequence v = values[(n * ncolumns) + c] as Sequence;
                        if (OIDs[c].Contains(v.Items[0] as ObjectIdentifier))
                        {
                            row[c] = v;
                            inTree = true;
                        }
                    }
                    if (inTree)
                        result.Add(row);
                    else
                    {
                        break;
                    }
                }

                pdu.VarBinds.RemoveAll();
                for (int c = 0; c < ncolumns; c++)
                {
                    pdu.VarBinds.Add(new Sequence(new Variable[] { (responsePDU.VarBinds.Items[(ncolumns * (nchunk - 1)) + c] as Sequence).Items[0], NullValue.Instance }));
                }

                pdu.RequestID.LongValue++;

            } while (inTree);  //((nchunk == pdu.MaxRepetitions.LongValue) && inTree);


            return result.ToArray();
        }

        public List<Sequence> snmpGetBulk(ObjectIdentifier objectIdentifier)
        {
            List<Sequence> results = new List<Sequence>();
            List<Sequence> parts;

            do
            {
                parts = snmpRequest<GetBulkRequest>(new ObjectIdentifier[] { objectIdentifier });

                foreach (Sequence ps in parts)
                {
                    ObjectIdentifier oid = ps.Items[0] as ObjectIdentifier;
                    if (objectIdentifier.Contains(oid))
                        results.Add(ps);
                    else
                        return results;
                }


            } while (parts.Count >= 32);

            return results;
        }
        public List<Sequence> snmpGetBulk(String objectIdentifier)
        {
            return snmpGetBulk(new ObjectIdentifier(objectIdentifier));
        }


        public Sequence[][] snmpWalk(IEnumerable<ObjectIdentifier> objectIdentifiers)
        {
            if (SnmpVersion == SnmpVersion.V1)
            {
                ObjectIdentifier[] OIDs = objectIdentifiers.ToArray();
                ObjectIdentifier[] lastOIDs = objectIdentifiers.ToArray();
                List<Sequence[]> results = new List<Sequence[]>();

                bool cont = true;
                while (cont)
                {
                    cont = false;
                    List<Sequence> next = snmpGetNext(lastOIDs);

                    Sequence[] row = new Sequence[lastOIDs.Length];

                    for (int n = 0; n < lastOIDs.Length; n++)
                    {
                        lastOIDs[n] = next[n].Items[0] as ObjectIdentifier;
                        if (OIDs[n].Contains(lastOIDs[n]))
                        {
                            cont = true;
                            row[n] = next[n];
                        }
                        else
                        {
                            row[n] = null;
                        }
                    }
                    results.Add(row);
                }
                return results.ToArray();
            }
            else 
            {
                return snmpGetBulk(objectIdentifiers);
            }
        }
        public Sequence[][] snmpWalk(IEnumerable<String> objectIdentifiers)
        {
            return snmpWalk(objectIdentifiers.Select((x) => new ObjectIdentifier(x)));
        }

        public List<Sequence> snmpWalk(ObjectIdentifier objectIdentifier)
        {
            if (SnmpVersion == SnmpVersion.V1)
            {
                List<Sequence> results = new List<Sequence>();
                ObjectIdentifier oiLast = objectIdentifier;

                while (objectIdentifier.Contains(oiLast))
                {
                    Sequence next = snmpGetNext(oiLast);
                    oiLast = next.Items[0] as ObjectIdentifier;
                    if (objectIdentifier.Contains(oiLast))
                        results.Add(next);
                }
                return results;
            } else if (SnmpVersion == SnmpVersion.V2c)
            {
                return snmpGetBulk(objectIdentifier);
            }
            else
            {
                throw new NotImplementedException();
            }
        }
        public List<Sequence> snmpWalk(string objectIdentifier)
        {
            return snmpWalk(new ObjectIdentifier(objectIdentifier));
        }


    }
}