// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Linq;

namespace Microsoft.AspNetCore.Components.Forms;

/// <summary>
/// Supplies CSS class names for form fields to represent their validation state or other
/// state information from an <see cref="EditContext"/>.
/// </summary>
public class FieldCssClassProvider
{
    internal static readonly FieldCssClassProvider Instance = new FieldCssClassProvider();

    /// <summary>
    /// Gets a string that indicates the status of the specified field as a CSS class.
    /// The result is one of <c>"valid"</c>, <c>"invalid"</c>, <c>"pending"</c>, or <c>"faulted"</c>,
    /// optionally prefixed with <c>"modified "</c> when
    /// <see cref="EditContext.IsModified(in FieldIdentifier)"/> is <c>true</c>.
    /// <list type="bullet">
    /// <item><c>"pending"</c> is emitted while an async validation task registered via
    /// <see cref="EditContext.AddValidationTask"/> is in flight, and supersedes valid/invalid
    /// since the outcome is not yet known.</item>
    /// <item><c>"faulted"</c> is emitted when the field's last async validation threw a
    /// non-cancellation exception, and supersedes valid/invalid since the infrastructure
    /// failed to determine validity.</item>
    /// <item><c>"valid"</c> or <c>"invalid"</c> reflects whether any validation messages exist
    /// for the field once no pending or faulted state applies.</item>
    /// </list>
    /// </summary>
    /// <param name="editContext">The <see cref="EditContext"/>.</param>
    /// <param name="fieldIdentifier">The <see cref="FieldIdentifier"/>.</param>
    /// <returns>A CSS class name string.</returns>
    public virtual string GetFieldCssClass(EditContext editContext, in FieldIdentifier fieldIdentifier)
    {
        var modified = editContext.IsModified(fieldIdentifier);

        if (editContext.IsValidationPending(fieldIdentifier))
        {
            return modified ? "modified pending" : "pending";
        }

        if (editContext.IsValidationFaulted(fieldIdentifier))
        {
            return modified ? "modified faulted" : "faulted";
        }

        var isValid = !editContext.GetValidationMessages(fieldIdentifier).Any();
        if (modified)
        {
            return isValid ? "modified valid" : "modified invalid";
        }

        return isValid ? "valid" : "invalid";
    }
}