// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

namespace System.Data.Entity.Core.Objects
{
    using System.Collections.Generic;
    using System.Data.Entity.Core.Common.Internal;
    using System.Data.Entity.Resources;
    using System.Data.Entity.Utilities;
    using System.Diagnostics;
    using System.Text;

    // <summary>
    // A collection of paths to determine which entities are spanned into a query.
    // </summary>
    internal sealed class Span
    {
        private readonly List<SpanPath> _spanList;
        private string _cacheKey;

        internal Span()
        {
            _spanList = new List<SpanPath>();
        }

        // <summary>
        // The list of paths that should be spanned into the query
        // </summary>
        internal List<SpanPath> SpanList
        {
            get { return _spanList; }
        }

        // <summary>
        // Checks whether relationship span needs to be performed. Currently this is only when the query is
        // not using MergeOption.NoTracking.
        // </summary>
        // <returns> True if the query needs a relationship span rewrite </returns>
        internal static bool RequiresRelationshipSpan(MergeOption mergeOption)
        {
            return (mergeOption != MergeOption.NoTracking);
        }

        // <summary>
        // Includes the specified span path in the specified span instance and returns the updated span instance.
        // If <paramref name="spanToIncludeIn" /> is null, a new span instance is constructed and returned that contains
        // the specified include path.
        // </summary>
        // <param name="spanToIncludeIn"> The span instance to which the include path should be added. May be null </param>
        // <param name="pathToInclude"> The include path to add </param>
        // <returns> A non-null span instance that contains the specified include path in addition to any paths ut already contained </returns>
        internal static Span IncludeIn(Span spanToIncludeIn, string pathToInclude)
        {
            if (null == spanToIncludeIn)
            {
                spanToIncludeIn = new Span();
            }

            spanToIncludeIn.Include(pathToInclude);
            return spanToIncludeIn;
        }

        // <summary>
        // Returns a span instance that is the union of the two specified span instances.
        // If <paramref name="span1" /> and <paramref name="span2" /> are both <c>null</c>,
        // then <c>null</c> is returned.
        // If <paramref name="span1" /> or <paramref name="span2" /> is null, but the remaining argument is non-null,
        // then the non-null argument is returned.
        // If neither <paramref name="span1" /> nor <paramref name="span2" /> are null, a new span instance is returned
        // that contains the merged span paths from both.
        // </summary>
        // <param name="span1">
        // The first span instance from which to include span paths; may be <c>null</c>
        // </param>
        // <param name="span2">
        // The second span instance from which to include span paths; may be <c>null</c>
        // </param>
        // <returns>
        // A span instance representing the union of the two arguments; may be <c>null</c> if both arguments are null
        // </returns>
        internal static Span CopyUnion(Span span1, Span span2)
        {
            if (null == span1)
            {
                return span2;
            }

            if (null == span2)
            {
                return span1;
            }

            var retSpan = span1.Clone();
            foreach (var path in span2.SpanList)
            {
                retSpan.AddSpanPath(path);
            }

            return retSpan;
        }

        internal string GetCacheKey()
        {
            if (null == _cacheKey)
            {
                if (_spanList.Count > 0)
                {
                    // If there is only a single Include path with a single property,
                    // then simply use the property name as the cache key rather than
                    // creating any new strings.
                    if (_spanList.Count == 1
                        &&
                        _spanList[0].Navigations.Count == 1)
                    {
                        _cacheKey = _spanList[0].Navigations[0];
                    }
                    else
                    {
                        var keyBuilder = new StringBuilder();
                        for (var pathIdx = 0; pathIdx < _spanList.Count; pathIdx++)
                        {
                            if (pathIdx > 0)
                            {
                                keyBuilder.Append(";");
                            }

                            var thisPath = _spanList[pathIdx];
                            keyBuilder.Append(thisPath.Navigations[0]);
                            for (var propIdx = 1; propIdx < thisPath.Navigations.Count; propIdx++)
                            {
                                keyBuilder.Append(".");
                                keyBuilder.Append(thisPath.Navigations[propIdx]);
                            }
                        }

                        _cacheKey = keyBuilder.ToString();
                    }
                }
            }

            return _cacheKey;
        }

        // <summary>
        // Adds a path to span into the query.
        // </summary>
        // <param name="path"> The path to span </param>
        public void Include(string path)
        {
            Check.NotEmpty(path, "path");

            var spanPath = new SpanPath(ParsePath(path));
            AddSpanPath(spanPath);
            _cacheKey = null;
        }

        // <summary>
        // Creates a new Span with the same SpanPaths as this Span
        // </summary>
        internal Span Clone()
        {
            var newSpan = new Span();
            newSpan.SpanList.AddRange(_spanList);
            newSpan._cacheKey = _cacheKey;

            return newSpan;
        }

        // <summary>
        // Adds the path if it does not already exist
        // </summary>
        internal void AddSpanPath(SpanPath spanPath)
        {
            if (ValidateSpanPath(spanPath))
            {
                RemoveExistingSubPaths(spanPath);
                _spanList.Add(spanPath);
            }
        }

        // <summary>
        // Returns true if the path can be added
        // </summary>
        private bool ValidateSpanPath(SpanPath spanPath)
        {
            // Check for dupliacte entries
            for (var i = 0; i < _spanList.Count; i++)
            {
                // make sure spanPath is not a sub-path of anything already in the list
                if (spanPath.IsSubPath(_spanList[i]))
                {
                    return false;
                }
            }
            return true;
        }

        private void RemoveExistingSubPaths(SpanPath spanPath)
        {
            var toDelete = new List<SpanPath>();
            for (var i = 0; i < _spanList.Count; i++)
            {
                // make sure spanPath is not a sub-path of anything already in the list
                if (_spanList[i].IsSubPath(spanPath))
                {
                    toDelete.Add(_spanList[i]);
                }
            }

            foreach (var path in toDelete)
            {
                _spanList.Remove(path);
            }
        }

        // <summary>
        // Storage for a span path
        // Currently this includes the list of navigation properties
        // </summary>
        internal class SpanPath
        {
            public readonly List<string> Navigations;

            public SpanPath(List<string> navigations)
            {
                Navigations = navigations;
            }

            public bool IsSubPath(SpanPath rhs)
            {
                // this is a subpath of rhs if it has fewer paths, and all the path element values are equal
                if (Navigations.Count
                    > rhs.Navigations.Count)
                {
                    return false;
                }

                for (var i = 0; i < Navigations.Count; i++)
                {
                    if (!Navigations[i].Equals(rhs.Navigations[i], StringComparison.OrdinalIgnoreCase))
                    {
                        return false;
                    }
                }

                return true;
            }
        }

        private static List<string> ParsePath(string path)
        {
            var navigations = MultipartIdentifier.ParseMultipartIdentifier(path, "[", "]", '.');

            for (var i = navigations.Count - 1; i >= 0; i--)
            {
                if (navigations[i] == null)
                {
                    navigations.RemoveAt(i);
                }
                else if (navigations[i].Length == 0)
                {
                    throw new ArgumentException(Strings.ObjectQuery_Span_SpanPathSyntaxError);
                }
            }

            Debug.Assert(navigations.Count > 0, "Empty path found");
            return navigations;
        }
    }
}
