///////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  File:   FsObject.sg
//

using Microsoft.Singularity.Channels;
using Microsoft.Singularity.Directory;

namespace Microsoft.Singularity.Services.Fat.Fs
{
    /// <remarks> Base class for file system objects.
    /// <para> Provides reference counting functionality and support for
    /// common directory and file operations, such as updating the
    /// last write time. </para>
    /// </remarks>
    internal abstract class FsObject
    {
        private Directory parent;
        private int shortEntryOffset;
        private int refcnt;

        public string cachedName     = null; // Debugging info
        public string cachedPathName = null; // Debugging info

        /// <remarks>
        /// Create an FsObject with a reference count of 1.
        /// </remarks>
        [ Microsoft.Contracts.NotDelayed ]
        internal FsObject(Directory! parent, int shortEntryOffset)
            requires shortEntryOffset > 0;
        {
            this.parent           = parent;
            this.shortEntryOffset = shortEntryOffset;
            this.refcnt           = 1;
        }

        internal FsObject()
        {
            this.refcnt           = 0;
            this.shortEntryOffset = -1;
            this.parent           = null;
        }

        [ Microsoft.Contracts.Pure ]
        internal bool HasParent { get { return parent != null; } }

        [ Microsoft.Contracts.Pure ]
        internal bool HasNoReferences { get { return this.refcnt == 0; } }

        [ Microsoft.Contracts.Pure ]
        internal bool HasOneReference { get { return this.refcnt == 1; } }

        [ Microsoft.Contracts.Pure ]
        internal int ShortEntryOffset
        {
            get { return this.shortEntryOffset; }
        }

        abstract internal int FirstCluster
        {
            get;
        }

        private void PopulateCachedName()
            requires this.cachedName == null;
            ensures  this.cachedName != null;
        {
            if (parent != null) {
                char[]! in ExHeap v = parent.GetName(this.shortEntryOffset);
                this.cachedName = Bitter.ToString2(v);
                delete v;
            }
            else {
                this.cachedName = "/";
            }
        }

        internal string Name
        {
            get {
                if (cachedName == null) {
                    PopulateCachedName();
                }
                return cachedName;
            }
        }

        internal bool GetShortDirectoryEntry(out DirectoryEntry de)
        {
            if (this.parent != null) {
                this.parent.GetShortDirectoryEntry(this.shortEntryOffset,
                                                   out de);
                return true;
            }
            de = new DirectoryEntry();
            return false;
        }

        private void PopulateCachedPathName()
            requires this.cachedPathName == null;
            ensures  this.cachedPathName != null;
        {
            if (parent != null) {
                if (this.parent.FullPathName == "/") {
                    this.cachedPathName = this.parent.FullPathName + this.Name;
                }
                else {
                    this.cachedPathName = this.parent.FullPathName + "/" + this.Name;
                }
            }
            else {
                this.cachedPathName = this.Name;
            }
        }

        internal string FullPathName
        {
            get {
                if (cachedPathName == null) {
                    PopulateCachedPathName();
                }
                return cachedPathName;
            }
        }

        internal void UpdateLastWriteTime()
        {
            if (parent != null && !FatVolume.IsReadOnly) {
                parent.UpdateLastWriteTime(this.shortEntryOffset);
            }
        }

        internal void UpdateLastAccessTime()
        {
            if (parent != null && !FatVolume.IsReadOnly) {
                parent.UpdateLastAccessTime(this.shortEntryOffset);
            }
        }

        /// <remarks> Update the file size field in the
        /// directory entry associated with a file object. This
        /// method also updates the last access and last update
        /// fields. </remarks>
        internal void UpdateFileSize(uint fileBytes)
        {
            if (parent != null && !FatVolume.IsReadOnly) {
                parent.UpdateFileSize(this.shortEntryOffset, fileBytes);
            }
        }

        /// <remarks> Update the first cluster field in the
        /// directory entry associated with a file object. This
        /// method also updates the last access and last update
        /// fields. It is called when a zero length file has been
        /// created and has no first cluster, and is subsequently
        /// grown</remarks>
        internal void UpdateFirstCluster(uint firstCluster)
        {
            if (parent != null && !FatVolume.IsReadOnly) {
                parent.UpdateFirstCluster(this.shortEntryOffset, firstCluster);
            }
        }

        internal void SetMutableAttributes(byte newAttributes)
            requires (newAttributes & ~DirectoryEntry.AttributeMutable) == 0;
        {
            if (parent != null && !FatVolume.IsReadOnly) {
                parent.SetMutableAttributes(this.shortEntryOffset,
                                            newAttributes);
            }
        }

        internal byte GetMutableAttributes()
        {
            if (parent != null) {
                return parent.GetMutableAttributes();
            }
            return 0;
        }

        internal void
        GetAttributes(ref FileAttributesRecord fileAttributes)
        {
            if (parent == null) {
                fileAttributes.Type  = NodeType.Directory;
                fileAttributes.FileSize = 0;
            }
            else {
                parent.GetAttributes(this.shortEntryOffset,
                                     ref fileAttributes);
            }
        }

        /// <remarks> Increment reference count by 1 </remarks>
        internal void AddRef()
        {
            this.refcnt++;
        }

        /// <remarks> Decrement reference count by 1 </remarks>
        internal void Release()
        {
            this.refcnt--;
        }

        internal void CloseInstance()
        {
            if (parent != null) {
                parent.CloseOpenFsObject(this);
            }
        }
    }
}