using System;
using Microsoft.CodeAnalysis.CSharp;

namespace Vellum.Generator
{
    /// <summary>
    /// Describes a saved field or auto-property as plain data, which an incremental generator step can compare between
    /// runs.
    /// </summary>
    public sealed class MemberShape : IEquatable<MemberShape>
    {
        /// <summary>
        /// Holds the member's name, which is the key it's saved under.
        /// </summary>
        public readonly string Key;

        /// <summary>
        /// Holds the member's type, spelled so generated code names it from anywhere.
        /// </summary>
        public readonly string TypeName;

        /// <summary>
        /// Holds whether C# lets code in the type assign the member outside a constructor.  A readonly field and a
        /// property with no setter, or only an init setter, don't.
        /// </summary>
        public readonly bool AssignsDirectly;

        public MemberShape(string key, string typeName)
            : this(key, typeName, assignsDirectly: true)
        {
        }

        public MemberShape(string key, string typeName, bool assignsDirectly)
        {
            Key = key;
            TypeName = typeName;
            AssignsDirectly = assignsDirectly;
        }

        /// <summary>
        /// Returns the member read through <paramref name="instance"/>, with an @ if its name is a keyword.
        /// </summary>
        public string On(string instance)
        {
            if (SyntaxFacts.GetKeywordKind(Key) != SyntaxKind.None)
            {
                return instance + ".@" + Key;
            }

            return instance + "." + Key;
        }

        public bool Equals(MemberShape other)
        {
            return other != null
                && Key == other.Key
                && TypeName == other.TypeName
                && AssignsDirectly == other.AssignsDirectly;
        }

        public override bool Equals(object obj)
        {
            return Equals(obj as MemberShape);
        }

        public override int GetHashCode()
        {
            return Key.GetHashCode() * 31 + TypeName.GetHashCode();
        }
    }
}