using System.Diagnostics.CodeAnalysis;

namespace MeterVault.App;

/// <summary>
/// Unsaved dialog input that has to survive a detour to another page of the same circuit.
/// </summary>
/// <remarks>
/// A meter's source dialog sends the user off to create the connector the source needs, and the meter
/// page is disposed on the way. Keeping the draft here, keyed by what it belongs to, lets the dialog come
/// back with everything that was typed instead of empty. Scoped: it lives as long as the circuit and is
/// never shared between users.
/// </remarks>
public sealed class DraftStore
{
    private readonly Dictionary<string, object> _drafts = new(StringComparer.Ordinal);

    public void Save(string key, object draft) => _drafts[key] = draft;

    /// <summary>Hands back a draft once; it is gone afterwards.</summary>
    public bool TryTake<T>(string key, [NotNullWhen(true)] out T? draft)
        where T : class
    {
        if (_drafts.Remove(key, out var stored) && stored is T typed)
        {
            draft = typed;
            return true;
        }

        draft = null;
        return false;
    }

    public void Discard(string key) => _drafts.Remove(key);
}