using System;

sealed class AssemblyBuffer
{  
  public readonly QRP_Sock Sock;
  public readonly int PageSize;
  public readonly UInt64 Cookie;

  private enum PageStatus : byte { Initial, Requested, Sent, TimedOut, Done }
  private byte [] Buf;
  private PageStatus [] Status;  
  private long [] Time;
  private int InFlight;
  private int InFlightHigh;
  private int NotDone;

  private int TimeoutTotal;

  public bool ProgressOk()
  {
    return TimeoutTotal < 3;
  }
 
  public bool Add( int PageNum, DnsRx Rx )
  {
    InFlight -= 1;
    if ( Status[PageNum] != PageStatus.Done )
    {
      int Offset = PageNum * PageSize;   
      Buffer.BlockCopy( Rx.Buffer, Rx.Ix, Buf, Offset, Rx.N-Rx.Ix );
      Status[PageNum] = PageStatus.Done;
      NotDone -= 1;
    }
    else
    {
      #if (Trace)
        Cache.Log( "QRP Duplicate, PageNum=" + PageNum );
      #endif
    }
    if ( NotDone == 0 )
    {
      Rx.Buffer = Buf;
      Rx.N = Buf.Length;
      Rx.Ix = 0;
      return true;
    }    
    return false;
  }

  public void NoteSent( int PageNum, int Sent, int Requested, long Now )
  {
    InFlight -= Requested - Sent;
    int j = PageNum + Sent;
    for ( int i=PageNum; i<j; i+=1 )
    {
      Status[i] = PageStatus.Sent;
      Time[i] = Now;
    }
    int k = PageNum+Requested; 
    if ( k > Status.Length ) k = Status.Length;
    for ( int i=j; i<k; i+=1 )
    {
      Status[i] = PageStatus.Initial;
      Time[i] = Now;
    }
  }

  public void RequestMore( SimpleQuery Sq )
  {
    long Now = System.DateTime.Now.Ticks;
    long Timeout = Sock.LinkInfo.GetTimeout( Now, InFlightHigh );
    Now -= Sq.StartTicks; // Convert to relative time for this SimpleQuery
    int i;

    // Look for timed out (lost) pages    
    for ( i=0; i<Status.Length; i+=1 )
    {
      if ( Status[i] == PageStatus.Requested || Status[i] == PageStatus.Sent )
      {
        long Age = Now - Time[i];
        if ( Age > Timeout )
        {
          InFlight -= 1;
          Status[i] = PageStatus.TimedOut;
          TimeoutTotal += 1;
        }
      }
    }

    int MaxInFlight = Sock.LinkInfo.GetMaxInFlight();
    int N = MaxInFlight - InFlight;
    if ( N <= 1 ) return; // Note : using 1 means we wait until we can request 2 pages.
    
    i = 0;
    while ( true )
    {
      // Send Follow-up requests for pages that have not yet been requested
      while ( i < Status.Length && Status[i] != PageStatus.Initial ) i += 1;
      if ( i >= Status.Length ) break;
      int j = i;
      int Stop = j + ( N > 255 ? 255 : N );           
      if ( Stop > Status.Length ) Stop = Status.Length;         
      while ( j < Stop && Status[j] == PageStatus.Initial ) 
      {
        Status[j] = PageStatus.Requested;
        Time[j] = Now;
        j += 1;         
      }        
      int Count = j - i;
      InFlight += Count;
      if ( InFlight > InFlightHigh ) InFlightHigh = InFlight;
      N -= Count;
      Sock.FollowUp( Sq, i, (byte)Count );
      if ( N == 0 ) return;
    }

    while ( true )
    {
      // Look for oldest timeout
      long Oldest = 0;
      int Page = 0;
      bool Found = false;
      for ( i=0; i<Status.Length; i+=1 )
      {
        if ( Status[i] == PageStatus.TimedOut )
        {
          if ( !Found || Time[i] < Oldest ) { Oldest = Time[i]; Found = true; Page = i; }
        }             
      }        
      if ( !Found ) return;       
      Status[ Page ] = PageStatus.Requested;
      Time[ Page ] = Now;
      InFlight += 1;
      if ( InFlight > InFlightHigh ) InFlightHigh = InFlight;
      N -= 1;
      Sock.FollowUp( Sq, Page, 1 );
      if ( N == 0 ) return;
    }
  }

  public AssemblyBuffer( int _InFlight, int _PageSize, int Total, UInt64 _Cookie, QRP_Sock _Sock )
  { 
    InFlight = _InFlight;
    InFlightHigh = _InFlight;
    PageSize = _PageSize;
    Cookie = _Cookie;
    Sock = _Sock;
    Buf = new byte[ Total ];
    NotDone = 1 + ( Total - 1 ) / PageSize;
    Status = new PageStatus[NotDone];
    Time = new long[NotDone];
  }
}