using System;

namespace IslaApocalypse.Core
{
	/// <summary>
	/// A material's IDENTITY. → `Design - Data - Material Schema.md`, D-054.
	///
	/// ⚠⚠ IDENTITY IS A REGISTRY KEY, NEVER A POSITIONAL ORDINAL.
	///
	/// This is deliberately a stable string key and not an enum. The prototype's blueprint format
	/// keyed on enum ordinals, which made the enum's DECLARATION ORDER a wire format: inserting a
	/// value in the middle silently reinterpreted every world already generated
	/// (→ `Design - Tooling - Offline Generation.md`: "anything that changes its format or its enum
	/// ordinals breaks every world already generated"). The registry is also the mod surface
	/// (→ D-011, D-043) — a mod adds rows, and rows cannot be given ordinals by a third party.
	///
	/// So: adding a material is one new row, appended anywhere, in any order, by anyone, forever.
	///
	/// No serialization is built this phase. This type exists so that when it is, the identity it
	/// writes is already the key rather than a position.
	/// </summary>
	public readonly struct MaterialKey : IEquatable<MaterialKey>
	{
		/// <summary>The stable identity. Lowercase, dot-namespaced: "core.limestone", "mod.basalt".</summary>
		public readonly string Value;

		public MaterialKey(string value)
		{
			if (string.IsNullOrWhiteSpace(value))
				throw new ArgumentException("A material key may not be null or blank.", nameof(value));
			Value = value;
		}

		/// <summary>The unset key. Distinguishable from any real row; never registered.</summary>
		public static readonly MaterialKey None = default;

		public bool IsNone => Value == null;

		public bool Equals(MaterialKey other) => string.Equals(Value, other.Value, StringComparison.Ordinal);
		public override bool Equals(object obj) => obj is MaterialKey k && Equals(k);
		public override int GetHashCode() => Value == null ? 0 : StringComparer.Ordinal.GetHashCode(Value);
		public override string ToString() => Value ?? "<none>";

		public static bool operator ==(MaterialKey a, MaterialKey b) => a.Equals(b);
		public static bool operator !=(MaterialKey a, MaterialKey b) => !a.Equals(b);
	}
}