// ----------------------------------------------------------------------------
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ----------------------------------------------------------------------------

// #define VERBOSE
// #define REALLY_VERBOSE

namespace Microsoft.Singularity.Security.AccessControl
{
    using System;
    using System.Text;
    using System.Text.RegularExpressions;
    using System.Collections;
    using Microsoft.SingSharp;
    using Microsoft.Singularity.Security;
    using Microsoft.Singularity.Channels;

    /// <summary>
    /// Converts an Access Control List description to a regular expression.
    /// Caches group expansions for improved performance.
    /// </summary>

    public class AclConverter
    {
        /// <summary>
        /// Regular expression matching an path fragment
        /// </summary>
        protected const string pathfrag = @"[a-zA-Z1-90_]+(\.[a-zA-Z1-90_]+)*";
        /// <summary>
        /// Regular expression matching the beginning of a string
        /// </summary>
        protected const string start = "^(";
        /// <summary>
        /// Regular expression matching the end of a string
        /// </summary>
        protected const string end = ")$";

        /// <summary>expression
        /// The reader of group definitions
        /// </summary>
        protected Cache! cache;
        private IAclCoreSupport support;

        /// <summary>
        /// Create new converter,
        /// </summary>

        private const int ExpnCachePrunePercent = 20;

        public AclConverter(IAclCoreSupport _support, int expnCacheMaxEntries, int expnCacheExpirySeconds)
        {
            this.support = _support;
            this.cache = new Cache(expnCacheMaxEntries, expnCacheExpirySeconds,
                                        ExpnCachePrunePercent, "Expansion Cache: ");
        }

        /// <summary>
        /// Convert the specified ACL to a regular expression
        /// </summary>
        /// <param name="acl">The access control list</param>
        /// <returns>An equivalent text regular expression</returns>

        public void DumpStats(StringBuilder! sb)
        {
            cache.DumpStats(sb);
        }

        public void ClearStats()
        {
            cache.ResetStats();
        }

        public void FlushCache()
        {
            cache.Prune(true);
        }

        public string! Convert(string! aclstr, bool bypassCache, out DateTime minExpiry)
        {
            StringBuilder! sb = new StringBuilder();
            Stack! stack = new Stack();
            int nSubExprs = 0;

            minExpiry = DateTime.MaxValue;
            sb.Append(start);
            DoExpand(aclstr, sb, "", stack, bypassCache, ref nSubExprs, ref minExpiry);
            sb.Append(end);
            return sb.ToString();
        }

        public string! ConvertTest(string! aclstr, out int nSubExprs)
        {
            DateTime minExpiry = DateTime.MaxValue;
            StringBuilder! sb = new StringBuilder();
            Stack! stack = new Stack();

            nSubExprs = 0;
            sb.Append(start);
            DoExpand(aclstr, sb, "", stack, false, ref nSubExprs, ref minExpiry);
            sb.Append(end);
            return sb.ToString();
        }

        internal class CacheEntry : ICacheValue
        {
            public string! expansion;
            public bool constant;
            public int nSubExprs;

            public CacheEntry(Cache! cache, string! expansion, bool constant,
                                           int nSubExprs, DateTime minExpiry)
            {
                base(cache, minExpiry);
                this.expansion = expansion;
                this.constant = constant;
                this.nSubExprs = nSubExprs;
            }
        }

        private void DoExpand(string! pattern, StringBuilder! sb, string! ns,
                               Stack! stack, bool bypassCache, ref int nSubExprs, ref DateTime minExpiry)
        {
            AclToken t;
            AclParser parser = new AclParser(pattern);

            CacheEntry ce = null;
            int eStart = sb.Length;
            int eSubExprs = nSubExprs;

            ce = (CacheEntry) cache.GetEntry(pattern);
            if (ce != null) {
                if (ce.Expired)
                    ce = null;
                else if (!bypassCache || ce.constant) {
#if VERBOSE
                    DebugStub.Print("DoExpand: Cache hit {0}\n", __arglist(path));
#endif
                    if (ce.expiry < minExpiry)
                        minExpiry = ce.expiry;
                    sb.Append(ce.expansion);
                    nSubExprs += ce.nSubExprs;
                    return;
                }
            }

            while ((t = parser.NextToken()) != null) {
                switch (t.Type) {
                    case AclTokenType.Literal:
#if REALLY_VERBOSE
                        DebugStub.Print("Literal: {0}\n", __arglist(t.Text));
#endif
                        sb.Append(t.Text);
                        break;
                    case AclTokenType.Arc:
#if REALLY_VERBOSE
                        DebugStub.Print("Arc: {0}\n", __arglist(t.Text));
#endif
                        // Arcs need no transformation   
                        sb.Append(t.Text);
                        break;
                    case AclTokenType.Any:
                        // Any matches any path fragment   
#if REALLY_VERBOSE
                        DebugStub.Print("Any: {0}\n", __arglist(t.Text));
#endif
                        sb.Append(pathfrag);
                        break;
                    case AclTokenType.Escape:
                        // Reserved regular expression symbol: escape it   
#if REALLY_VERBOSE
                        DebugStub.Print("Escape: {0}\n", __arglist(t.Text));
#endif
                        sb.AppendFormat("\\{0}", t.Text);
                        break;
                    case AclTokenType.GroupName:
                        //
                        //A sub-expression can have relative or absolute name.
                        //We resolve relative names by keeping track of the namespace
                        //of the last resolution.
                        //
                        bool isPath = true;
                        string path = t.Text;
                        nSubExprs++;
                        if (path.Length != 0) {
                            if (path[0] == '$') {
                                isPath = false;
                            }
                            else {
                                if (path[0] != '/') {
                                    // this is a relative path. append the namespace
                                    path = ns + "/" + path;
                                }

                                // update the namespace name:
                                int index = path.LastIndexOf('/');
                                if (index == -1) {
                                    ns = String.Empty;
                                }
                                else {
                                    ns = (!)path.Substring(0, index);
                                }
                            }

                            string subexpr = ReadSubexpression(path, isPath);
                            if (subexpr == null) {
#if VERBOSE
                                DebugStub.Print("Undefined subexpression: {0}\n", __arglist(t.Text));
#endif
                            }

                            if (stack.Contains(path)) {
                                throw new Exception("Infinite recursion detected while expanding acl.");
                            }

                            sb.Append('(');
                            stack.Push(path);
                            if (subexpr != null && subexpr.Length != 0)
                                DoExpand(subexpr, sb, ns, stack, bypassCache, ref nSubExprs, ref minExpiry);
                            stack.Pop();
                            sb.Append(')');
                        }
                        break;
                    case AclTokenType.Miscellaneous:
                        DebugStub.Print("Invalid token: {0} Skipping it\n", __arglist(t.Text));
                        break;
                }
            }
            // cache the results of the expansion at this level
            string expansion = sb.ToString(eStart, sb.Length-eStart);
            if (ce == null || expansion != ce.expansion) {
                ce = new CacheEntry(cache, expansion, false, nSubExprs-eSubExprs, minExpiry);
                cache.AddEntry(pattern, ce);
            }
            else if (ce != null) {
                // Old expansion was the same, update expiry.
                ce.ResetExpiry(cache, minExpiry);
            }
            if (ce.expiry < minExpiry)
                minExpiry = ce.expiry;
        }

        private string ReadSubexpression(string! path, bool isPath)
        {
            string result = null;
            if (isPath) {
                if (support == null)
                    DebugStub.Print("ReadSubexpression: AclCoreSupport object missing\n");
                else
                    result = support.Expand(path);
            }
            else
                result = Principal.ExpandAclIndirection(path);
            return result;
        }

        //
        //// this code has been moved to the client impl (e.g. DirAclCoreSupport.sg)
//
        //private string ReadGroup(string! path)
        //{
        //  return support.GetGroupContents(path);
        //}
//
        //// read the file size
        //  DirectoryServiceContract.Imp:Ready! ns = AcquireNSRoot();
        //  byte[] result =  ReadFromFile(path, ns);
        //  ReleaseNSRoot(ns);
//
        //  if (result == null)
        //      return null;
//
        //  string! subexpression = (!)encoder.GetString(result);
        //  return subexpression;
        //}
//
        //private DirectoryServiceContract.Imp:Ready! AcquireNSRoot()
        //{
//
        //  if (cachedRootNS == null)
        //      cachedRootNS =
        //          new TRef<DirectoryServiceContract.Imp:Ready>(support.GroupDirectoryRoot());
        //  return cachedRootNS.Acquire();
        //}
//
        //private void ReleaseNSRoot([Claims] DirectoryServiceContract.Imp:Ready! ns)
        //{
        //  cachedRootNS.Release(ns);
        //}
//
        //private byte[] ReadFromFile(string!path, DirectoryServiceContract.Imp:Ready! ns)
        //{
        //  ErrorCode errCode;
        //  byte[] result;
        //  long size = 0;
        //  int readSize = 4096;
        //  NodeType nodeType;
//
//
        //  try {
        //      bool temp = SdsUtils.GetAttributes(path, ns, out size, out nodeType, out errCode);
        //      if (!temp)
        //          // element does not exist or an error has occurred
        //          throw new Exception("Cannot get attributes - " + SdsUtils.ErrorCodeToString(errCode));
//
        //      result = new byte[size];
        //      byte[] in ExHeap buf = new[ExHeap] byte[readSize];
        //      if (result == null || buf == null)
        //          throw new Exception("Cannot allocate memory");
//
        //      FileContract.Imp! fileImp;
        //      FileContract.Exp! fileExp;
        //      FileContract.NewChannel(out fileImp, out fileExp);
        //      bool bindOk = SdsUtils.Bind(path, ns, fileExp, out errCode);
        //      if (!bindOk) {
        //          delete fileImp;
        //          throw new Exception("Can't read group - " + SdsUtils.ErrorCodeToString(errCode));
        //      }
        //      fileImp.RecvSuccess();
//
        //      long readOffset = 0;
        //      while (true) {
        //          fileImp.SendRead(buf, 0, readOffset, readSize);
        //          switch receive {
        //              case fileImp.AckRead(localbuf,  bytesRead,  error) :
        //                  // move the memory
        //                  Bitter.ToByteArray(localbuf, 0, (int)bytesRead, result, (int)readOffset);
        //                  if (bytesRead == readSize) {
        //                      // see if there is more
        //                      readOffset += bytesRead;
        //                      buf = localbuf;
        //                      continue;
        //                  }
        //                  delete localbuf;
        //                  break;
        //              case fileImp.ChannelClosed() :
        //                  break;
        //              case unsatisfiable :
        //                  break;
        //          }
        //          break;
        //      }
        //      delete fileImp;
        //  }
        //  catch (Exception e) {
        //      DebugStub.Print("An exception occurred while reading group definition: {0}\n",
        //                      __arglist(path));
        //      DebugStub.Print("Message: {0}\n", __arglist(e.Message));
        //      return null;
        //  }
        //  return result;
        //}
        //

    }
}