// 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 System.Collections.Immutable;

namespace Microsoft.CodeAnalysis.Options
{
    /// <inheritdoc cref="Option2{T}"/>
    public class Option<T> : ILanguageSpecificOption<T>
    {
        private readonly OptionDefinition _optionDefinition;

        /// <inheritdoc cref="OptionDefinition.Feature"/>
        public string Feature => _optionDefinition.Feature;

        /// <inheritdoc cref="OptionDefinition.Group"/>
        internal OptionGroup Group => _optionDefinition.Group;

        /// <inheritdoc cref="OptionDefinition.Name"/>
        public string Name => _optionDefinition.Name;

        /// <inheritdoc cref="OptionDefinition.DefaultValue"/>
        public T DefaultValue => (T)_optionDefinition.DefaultValue!;

        /// <inheritdoc cref="OptionDefinition.Type"/>
        public Type Type => _optionDefinition.Type;

        /// <inheritdoc cref="Option2{T}.StorageLocations"/>
        public ImmutableArray<OptionStorageLocation> StorageLocations { get; }

        [Obsolete("Use a constructor that specifies an explicit default value.")]
        public Option(string feature, string name)
            : this(feature, name, default!)
        {
            // This constructor forwards to the next one; it exists to maintain source-level compatibility with older callers.
        }

        public Option(string feature, string name, T defaultValue)
            : this(feature, name, defaultValue, storageLocations: Array.Empty<OptionStorageLocation>())
        {
        }

        public Option(string feature, string name, T defaultValue, params OptionStorageLocation[] storageLocations)
            : this(feature, group: OptionGroup.Default, name, defaultValue, storageLocations)
        {
        }

        internal Option(string feature, OptionGroup group, string name, T defaultValue, params OptionStorageLocation[] storageLocations)
            : this(feature, group, name, defaultValue, storageLocations.ToImmutableArray())
        {
        }

        internal Option(string feature, OptionGroup group, string name, T defaultValue, ImmutableArray<OptionStorageLocation> storageLocations)
            : this(new OptionDefinition(feature, group, name, defaultValue, typeof(T), isPerLanguage: false), storageLocations)
        {
        }

        internal Option(OptionDefinition optionDefinition, ImmutableArray<OptionStorageLocation> storageLocations)
        {
            _optionDefinition = optionDefinition;
            this.StorageLocations = storageLocations;
        }

        OptionGroup IOptionWithGroup.Group => this.Group;

        object? IOption.DefaultValue => this.DefaultValue;

        bool IOption.IsPerLanguage => false;

        OptionDefinition IOption2.OptionDefinition => _optionDefinition;

        bool IEquatable<IOption2?>.Equals(IOption2? other) => Equals(other);

        public override string ToString() => _optionDefinition.ToString();

        public override int GetHashCode() => _optionDefinition.GetHashCode();

        public override bool Equals(object? obj) => Equals(obj as IOption2);

        private bool Equals(IOption2? other)
        {
            if (ReferenceEquals(this, other))
            {
                return true;
            }

            return _optionDefinition == other?.OptionDefinition;
        }

        public static implicit operator OptionKey(Option<T> option)
            => new(option);
    }
}
