// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.FindSymbols;

internal struct SearchQuery : IDisposable
{
    /// <summary>The name being searched for.  Is null in the case of custom predicate searching..  But 
    /// can be used for faster index based searching when it is available.</summary> 
    public readonly string? Name;

    ///<summary>The kind of search this is.  Faster index-based searching can be used if the 
    /// SearchKind is not <see cref="SearchKind.Custom"/>.</summary>
    public readonly SearchKind Kind;

    ///<summary>The predicate to fall back on if faster index searching is not possible.</summary>
    private readonly Func<string, bool> _predicate;

    /// <summary>
    /// Not readonly as this is mutable struct.
    /// </summary>
    private WordSimilarityChecker _wordSimilarityChecker;

    private SearchQuery(string name, SearchKind kind)
    {
        Name = name ?? throw new ArgumentNullException(nameof(name));
        Kind = kind;

        switch (kind)
        {
            case SearchKind.Exact:
                _predicate = s => StringComparer.Ordinal.Equals(name, s);
                break;
            case SearchKind.ExactIgnoreCase:
                _predicate = s => CaseInsensitiveComparison.Comparer.Equals(name, s);
                break;
            case SearchKind.Fuzzy:
                // Create a single WordSimilarityChecker and capture a delegate reference to 
                // its 'AreSimilar' method. That way we only create the WordSimilarityChecker
                // once and it can cache all the information it needs while it does the AreSimilar
                // check against all the possible candidates.
                _wordSimilarityChecker = new WordSimilarityChecker(name, substringsAreSimilar: false);
                _predicate = _wordSimilarityChecker.AreSimilar;
                break;
            default:
                throw ExceptionUtilities.UnexpectedValue(kind);
        }
    }

    private SearchQuery(Func<string, bool> predicate)
    {
        Kind = SearchKind.Custom;
        _predicate = predicate ?? throw new ArgumentNullException(nameof(predicate));
    }

    public readonly void Dispose()
        => _wordSimilarityChecker.Dispose();

    public static SearchQuery Create(string name, SearchKind kind)
        => new(name, kind);

    public static SearchQuery Create(string name, bool ignoreCase)
        => new(name, ignoreCase ? SearchKind.ExactIgnoreCase : SearchKind.Exact);

    public static SearchQuery CreateFuzzy(string name)
        => new(name, SearchKind.Fuzzy);

    public static SearchQuery CreateCustom(Func<string, bool> predicate)
        => new(predicate);

    public readonly Func<string, bool> GetPredicate()
        => _predicate;
}