namespace OECS;

/// <summary>
/// Describes a query over the ECS world.
/// Composed of a set of required component types ("with") and
/// a set of excluded component types ("without").
/// </summary>
public class QueryDescriptor
{
    /// <summary>
    /// Component types that must be present on matching entities.
    /// </summary>
    public IReadOnlySet<Type> With { get; }

    /// <summary>
    /// Component types that must NOT be present on matching entities.
    /// </summary>
    public IReadOnlySet<Type> Without { get; }

    private readonly int _hashCode;

    internal QueryDescriptor(HashSet<Type> with, HashSet<Type> without)
    {
        With = with;
        Without = without;
        _hashCode = ComputeHashCode();
    }

    /// <summary>
    /// Returns true if this query has no "with" components (matches nothing).
    /// </summary>
    internal bool IsEmpty => With.Count == 0;

    public override bool Equals(object? obj)
    {
        if (obj is not QueryDescriptor other) return false;
        if (With.Count != other.With.Count || Without.Count != other.Without.Count)
            return false;
        return With.SetEquals(other.With) && Without.SetEquals(other.Without);
    }

    public override int GetHashCode() => _hashCode;

    private int ComputeHashCode()
    {
        var hash = new HashCode();
        foreach (var t in With.OrderBy(t => t.GUID.ToString()))
            hash.Add(t);
        foreach (var t in Without.OrderBy(t => t.GUID.ToString()))
            hash.Add(t);
        return hash.ToHashCode();
    }
}