using System.Collections.ObjectModel;

namespace Prefab.Base;

/// <summary>
/// Provides a customizable attribute bag with change tracking for Prefab domain objects.
/// </summary>
public class GenericAttributes : ICanBeCustomized
{
    private readonly Dictionary<string, object> _attributes = new();
    private readonly List<GenericAttributeChange> _changes = new();

    /// <inheritdoc />
    IReadOnlyDictionary<string, object> IHasGenericAttributes.GenericAttributes => new ReadOnlyDictionary<string, object>(_attributes);

    /// <summary>
    /// Gets the ordered list of attribute mutations recorded since the last call to <see cref="ClearChanges"/>.
    /// </summary>
    public IReadOnlyList<GenericAttributeChange> Changes => _changes.AsReadOnly();

    /// <summary>
    /// Provides an extension point for enforcing key/value requirements before persisting the attribute.
    /// </summary>
    /// <param name="key">The attribute key being modified.</param>
    /// <param name="value">The proposed attribute value.</param>
    protected virtual void ValidateAttribute(string key, object value)
    {
        // Default: no validation. Override in derived classes for custom logic.
    }

    /// <summary>
    /// Sets or replaces an attribute value and records the mutation.
    /// </summary>
    /// <param name="key">The attribute key to set.</param>
    /// <param name="value">The attribute value.</param>
    public void SetAttribute(string key, object value)
    {
        _attributes.TryGetValue(key, out var oldValue);
        ValidateAttribute(key, value);
        _attributes[key] = value;
        _changes.Add(new GenericAttributeChange(key, oldValue, value));
    }

    /// <summary>
    /// Removes an attribute if present and records the removal.
    /// </summary>
    /// <param name="key">The attribute key to remove.</param>
    /// <returns><c>true</c> when the key existed and was removed; otherwise <c>false</c>.</returns>
    public bool RemoveAttribute(string key)
    {
        if (_attributes.TryGetValue(key, out var oldValue) && _attributes.Remove(key))
        {
            _changes.Add(new GenericAttributeChange(key, oldValue, null));
            return true;
        }

        return false;
    }

    /// <summary>
    /// Attempts to read an attribute value and cast it to the requested type.
    /// </summary>
    /// <param name="key">The attribute key to read.</param>
    /// <param name="value">Receives the typed attribute value when successful.</param>
    /// <typeparam name="T">The expected attribute type.</typeparam>
    /// <returns><c>true</c> when the attribute exists and matches the requested type.</returns>
    public bool TryGetAttribute<T>(string key, out T value)
    {
        if (_attributes.TryGetValue(key, out var obj) && obj is T t)
        {
            value = t;
            return true;
        }

        value = default!;
        return false;
    }

    /// <summary>
    /// Creates an immutable snapshot copy of the current attributes.
    /// </summary>
    public IReadOnlyDictionary<string, object> Snapshot() => new ReadOnlyDictionary<string, object>(new Dictionary<string, object>(_attributes));

    /// <summary>
    /// Clears all recorded attribute changes while keeping the current attribute values intact.
    /// </summary>
    public void ClearChanges() => _changes.Clear();
}