// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq.Expressions;
using Microsoft.AspNetCore.Components.Rendering;
 
namespace Microsoft.AspNetCore.Components.Forms;
 
/// <summary>
/// Displays the display name for a specified field, reading from <see cref="DisplayAttribute"/>
/// or <see cref="DisplayNameAttribute"/> if present, or falling back to the property name.
/// </summary>
/// <typeparam name="TValue">The type of the field.</typeparam>
public class DisplayName<TValue> : IComponent
{
 
    private RenderHandle _renderHandle;
    private Expression<Func<TValue>>? _previousFieldAccessor;
    private string? _displayName;
 
    /// <summary>
    /// Specifies the field for which the display name should be shown.
    /// </summary>
    [Parameter, EditorRequired]
    public Expression<Func<TValue>>? For { get; set; }
    /// <inheritdoc />
    void IComponent.Attach(RenderHandle renderHandle)
    {
        _renderHandle = renderHandle;
    }
 
    /// <inheritdoc />
    Task IComponent.SetParametersAsync(ParameterView parameters)
    {
        parameters.SetParameterProperties(this);
 
        if (For is null)
        {
            throw new InvalidOperationException($"{GetType()} requires a value for the " +
                $"{nameof(For)} parameter.");
        }
 
        // Only recalculate if the expression changed
        if (For != _previousFieldAccessor)
        {
            var newDisplayName = ExpressionMemberAccessor.GetDisplayName(For);
 
            if (newDisplayName != _displayName)
            {
                _displayName = newDisplayName;
                _renderHandle.Render(BuildRenderTree);
            }
 
            _previousFieldAccessor = For;
        }
 
        return Task.CompletedTask;
    }
 
    private void BuildRenderTree(RenderTreeBuilder builder)
    {
        builder.AddContent(0, _displayName);
    }
}