using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;
using System.Reflection;
using System.Linq;
using System.Diagnostics;

namespace System.Data.Linq {
    using System.Data.Linq.Mapping;
    using System.Data.Linq.Provider;
    using System.Diagnostics.CodeAnalysis;

    public sealed class ChangeConflictCollection : ICollection<ObjectChangeConflict>, ICollection, IEnumerable<ObjectChangeConflict>, IEnumerable {
        private List<ObjectChangeConflict> conflicts;

        internal ChangeConflictCollection() {
            this.conflicts = new List<ObjectChangeConflict>();
        }

        /// <summary>
        /// The number of conflicts in the collection
        /// </summary>
        public int Count {
            get { return this.conflicts.Count; }
        }

        public ObjectChangeConflict this[int index] {
            get { return this.conflicts[index]; }
        }

        bool ICollection<ObjectChangeConflict>.IsReadOnly {
            get { return true; }
        }

        void ICollection<ObjectChangeConflict>.Add(ObjectChangeConflict item) {
            throw Error.CannotAddChangeConflicts();
        }

        /// <summary>
        /// Removes the specified conflict from the collection.
        /// </summary>
        /// <param name="item">The conflict to remove</param>
        /// <returns></returns>
        public bool Remove(ObjectChangeConflict item) {
            return this.conflicts.Remove(item);
        }

        /// <summary>
        /// Removes all conflicts from the collection
        /// </summary>
        public void Clear() {
            this.conflicts.Clear();
        }

        /// <summary>
        /// Returns true if the specified conflict is a member of the collection.
        /// </summary>
        /// <param name="item"></param>
        /// <returns></returns>
        public bool Contains(ObjectChangeConflict item) {
            return this.conflicts.Contains(item);
        }

        public void CopyTo(ObjectChangeConflict[] array, int arrayIndex) {
            this.conflicts.CopyTo(array, arrayIndex);
        }

        /// <summary>
        /// Returns the enumerator for the collection.
        /// </summary>
        /// <returns></returns>
        public IEnumerator<ObjectChangeConflict> GetEnumerator() {
            return this.conflicts.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator() {
            return this.conflicts.GetEnumerator();
        }

        bool ICollection.IsSynchronized {
            get { return false; }
        }

        object ICollection.SyncRoot {
            get { return null; }
        }

        void ICollection.CopyTo(Array array, int index) {
            ((ICollection)this.conflicts).CopyTo(array, index);
        }

        /// <summary>
        /// Resolves all conflicts in the collection using the specified strategy.
        /// </summary>
        /// <param name="mode">The strategy to use to resolve the conflicts.</param>
        public void ResolveAll(RefreshMode mode) {
            this.ResolveAll(mode, true);
        }

        /// <summary>
        /// Resolves all conflicts in the collection using the specified strategy.
        /// </summary>
        /// <param name="mode">The strategy to use to resolve the conflicts.</param>
        /// <param name="autoResolveDeletes">If true conflicts resulting from the modified
        /// object no longer existing in the database will be automatically resolved.</param>
        public void ResolveAll(RefreshMode mode, bool autoResolveDeletes) {
            foreach (ObjectChangeConflict c in this.conflicts) {
                if (!c.IsResolved) {
                    c.Resolve(mode, autoResolveDeletes);
                }
            }
        }

        internal void Fill(List<ObjectChangeConflict> conflictList) {
            this.conflicts = conflictList;
        }
    }

    internal sealed class ChangeConflictSession {
        private DataContext context;
        private DataContext refreshContext;

        internal ChangeConflictSession(DataContext context) {
            this.context = context;
        }

        internal DataContext Context {
            get { return this.context; }
        }

        internal DataContext RefreshContext {
            get {
                if (this.refreshContext == null) {
                    this.refreshContext = this.context.CreateRefreshContext();
                }
                return this.refreshContext;
            }
        }
    }

    /// <summary>
    /// Represents an update with one or more optimistic concurrency conflicts.
    /// </summary>
    public sealed class ObjectChangeConflict {
        private ChangeConflictSession session;
        private TrackedObject trackedObject;
        private bool isResolved;
        private ReadOnlyCollection<MemberChangeConflict> memberConflicts;
        private object database;
        private object original;
        private bool? isDeleted;

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="session">The session in which the conflicts occurred.</param>
        /// <param name="trackedObject">The tracked item in conflict.</param>
        internal ObjectChangeConflict(ChangeConflictSession session, TrackedObject trackedObject) {
            this.session = session;
            this.trackedObject = trackedObject;
            this.original = trackedObject.CreateDataCopy(trackedObject.Original);
        }

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="session">The session in which the conflicts occurred.</param>
        /// <param name="trackedObject">The tracked item in conflict.</param>
        /// <param name="isDeleted">True if the item in conflict no longer exists in the database.</param>
        internal ObjectChangeConflict(ChangeConflictSession session, TrackedObject trackedObject, bool isDeleted)
            : this(session, trackedObject) {
            this.isDeleted = isDeleted;
        }

        internal ChangeConflictSession Session {
            get { return this.session; }
        }

        internal TrackedObject TrackedObject {
            get { return this.trackedObject; }
        }

        /// <summary>
        /// The object in conflict.
        /// </summary>
        public object Object {
            get { return this.trackedObject.Current; }
        }

        /// <summary>
        /// An instance containing the baseline original values used to perform the concurrency check.
        /// </summary>
        internal object Original {
            get { return this.original; }
        }

        /// <summary>
        /// True if the conflicts for this object have already been resovled.
        /// </summary>
        public bool IsResolved {
            get { return this.isResolved; }
        }
       
        /// <summary>
        /// True if the object in conflict has been deleted from the database.
        /// </summary>
        public bool IsDeleted {
            get { 
                if (this.isDeleted.HasValue) {
                    return this.isDeleted.Value;
                }
                return (this.Database == null); 
            }
        }

        /// <summary>
        /// An instance containing the most recent values from the database
        /// </summary>
        internal object Database {
            get {
                if (this.database == null) {
                    // use the 'refresh' context to retrieve the current database state
                    DataContext ctxt = this.session.RefreshContext;
                    object[] keyValues = CommonDataServices.GetKeyValues(this.trackedObject.Type, this.original);
                    this.database = ctxt.Services.GetObjectByKey(this.trackedObject.Type, keyValues);
                }
                return this.database;
            }
        }

        /// <summary>
        /// Resolve member conflicts keeping current values and resetting the baseline 'Original' values
        /// to match the more recent 'Database' values.
        /// </summary>
        public void Resolve() {
            this.Resolve(RefreshMode.KeepCurrentValues, true);
        }

        /// <summary>
        /// Resolve member conflicts using the mode specified and resetting the baseline 'Original' values
        /// to match the more recent 'Database' values.
        /// </summary>  
        /// <param name="refreshMode">The mode that determines how the current values are 
        /// changed in order to resolve the conflict</param>
        public void Resolve(RefreshMode refreshMode) {
            this.Resolve(refreshMode, false);
        }

        /// <summary>
        /// Resolve member conflicts using the mode specified and resetting the baseline 'Original' values
        /// to match the more recent 'Database' values.
        /// </summary>
        /// <param name="refreshMode">The mode that determines how the current values are 
        /// changed in order to resolve the conflict</param>
        /// <param name="autoResolveDeletes">If true conflicts resulting from the modified
        /// object no longer existing in the database will be automatically resolved.</param>
        public void Resolve(RefreshMode refreshMode, bool autoResolveDeletes) {
            if (autoResolveDeletes && this.IsDeleted) {
                this.ResolveDelete();
            }
            else {
                // We make these calls explicity rather than simply calling
                // DataContext.Refresh (which does virtually the same thing)
                // since we want to cache the database value read.
                if (this.Database == null) {
                    throw Error.RefreshOfDeletedObject();
                }
                trackedObject.Refresh(refreshMode, this.Database);
                this.isResolved = true;
            }
        }

        /// <summary>
        /// Resolve a conflict where we have updated an entity that no longer exists
        /// in the database.
        /// </summary>
        private void ResolveDelete() {
            Debug.Assert(this.IsDeleted);
            // If the user is attempting to update an entity that no longer exists 
            // in the database, we first need to [....] the delete into the local cache.
            if (!trackedObject.IsDeleted) {
                trackedObject.ConvertToDeleted();
            }

            // As the object have been deleted, it needs to leave the cache
            this.Session.Context.Services.RemoveCachedObjectLike(trackedObject.Type, trackedObject.Original);

            // Now that our cache is in [....], we accept the changes
            this.trackedObject.AcceptChanges();
            this.isResolved = true;
        }

        /// <summary>
        /// Returns a collection of all member conflicts that caused the update to fail.
        /// </summary>       
        public ReadOnlyCollection<MemberChangeConflict> MemberConflicts {
            get {
                if (this.memberConflicts == null) {
                    var list = new List<MemberChangeConflict>();
                    if (this.Database != null) {
                        // determine which members are in conflict                   
                        foreach (MetaDataMember metaMember in trackedObject.Type.PersistentDataMembers) {
                            if (!metaMember.IsAssociation && this.HasMemberConflict(metaMember)) {
                                list.Add(new MemberChangeConflict(this, metaMember));
                            }
                        }
                    }
                    this.memberConflicts = list.AsReadOnly();
                }
                return this.memberConflicts;
            }
        }

        private bool HasMemberConflict(MetaDataMember member) {
            object oValue = member.StorageAccessor.GetBoxedValue(this.original);
            if (!member.DeclaringType.Type.IsAssignableFrom(this.database.GetType())) {
                return false;
            }
            object dValue = member.StorageAccessor.GetBoxedValue(this.database);
            return !this.AreEqual(member, oValue, dValue);
        }

        private bool AreEqual(MetaDataMember member, object v1, object v2) {
            if (v1 == null && v2 == null)
                return true;
            if (v1 == null || v2 == null)
                return false;
            if (member.Type == typeof(char[])) {
                return this.AreEqual((char[])v1, (char[])v2);
            }
            else if (member.Type == typeof(byte[])) {
                return this.AreEqual((byte[])v1, (byte[])v2);
            }
            else {
                return object.Equals(v1, v2);
            }
        }

        [SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic", Justification="Unknown reason.")]
        private bool AreEqual(char[] a1, char[] a2) {
            if (a1.Length != a2.Length)
                return false;
            for (int i = 0, n = a1.Length; i < n; i++) {
                if (a1[i] != a2[i])
                    return false;
            }
            return true;
        }

        [SuppressMessage("Microsoft.Performance", "CA1822:MarkMembersAsStatic", Justification="Unknown reason.")]
        private bool AreEqual(byte[] a1, byte[] a2) {
            if (a1.Length != a2.Length)
                return false;
            for (int i = 0, n = a1.Length; i < n; i++) {
                if (a1[i] != a2[i])
                    return false;
            }
            return true;
        }

        internal void OnMemberResolved() {
            if (!this.IsResolved) {
                int nResolved = this.memberConflicts.AsEnumerable().Count(m => m.IsResolved);
                if (nResolved == this.memberConflicts.Count) {
                    this.Resolve(RefreshMode.KeepCurrentValues, false);
                }
            }
        }
    }

    /// <summary>
    /// Represents a single optimistic concurrency member conflict.
    /// </summary>
    public sealed class MemberChangeConflict {
        private ObjectChangeConflict conflict;
        private MetaDataMember metaMember;
        private object originalValue;
        private object databaseValue;
        private object currentValue;
        bool isResolved;

        internal MemberChangeConflict(ObjectChangeConflict conflict, MetaDataMember metaMember) {
            this.conflict = conflict;            
            this.metaMember = metaMember;
            this.originalValue = metaMember.StorageAccessor.GetBoxedValue(conflict.Original);
            this.databaseValue = metaMember.StorageAccessor.GetBoxedValue(conflict.Database);
            this.currentValue = metaMember.StorageAccessor.GetBoxedValue(conflict.TrackedObject.Current);
        }

        /// <summary>
        /// The previous client value.
        /// </summary>
        public object OriginalValue {
            get { return this.originalValue; }
        }

        /// <summary>
        /// The current database value.
        /// </summary>
        public object DatabaseValue {
            get { return this.databaseValue; }
        }

        /// <summary>
        /// The current client value.
        /// </summary>
        public object CurrentValue {
            get { return this.currentValue; }
        }

        /// <summary>
        /// MemberInfo for the member in conflict.
        /// </summary>
        public MemberInfo Member {
            get { return this.metaMember.Member; }
        }

        /// <summary>
        /// Updates the current value to the specified value.
        /// </summary>       
        public void Resolve(object value) {
            this.conflict.TrackedObject.RefreshMember(this.metaMember, RefreshMode.OverwriteCurrentValues, value);
            this.isResolved = true;
            this.conflict.OnMemberResolved();
        }

        /// <summary>
        /// Updates the current value using the specified strategy.
        /// </summary>        
        public void Resolve(RefreshMode refreshMode) {
            this.conflict.TrackedObject.RefreshMember(this.metaMember, refreshMode, this.databaseValue);
            this.isResolved = true;
            this.conflict.OnMemberResolved();
        }

        /// <summary>
        /// True if the value was modified by the client.
        /// </summary>
        public bool IsModified {
            get { return this.conflict.TrackedObject.HasChangedValue(this.metaMember); }
        }

        /// <summary>
        /// True if the member conflict has been resolved.
        /// </summary>
        public bool IsResolved {
            get { return this.isResolved; }
        }
    }
}