// 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.Expressions;

namespace Microsoft.AspNetCore.Components.Forms;

/// <summary>
/// Holds validation messages for an <see cref="EditContext"/>.
/// </summary>
public sealed class ValidationMessageStore
{
    private readonly EditContext _editContext;
    private readonly Dictionary<FieldIdentifier, List<string>> _messages = new Dictionary<FieldIdentifier, List<string>>();

    /// <summary>
    /// Creates an instance of <see cref="ValidationMessageStore"/>.
    /// </summary>
    /// <param name="editContext">The <see cref="EditContext"/> with which this store should be associated.</param>
    public ValidationMessageStore(EditContext editContext)
    {
        _editContext = editContext ?? throw new ArgumentNullException(nameof(editContext));
    }

    /// <summary>
    /// Adds a validation message for the specified field.
    /// </summary>
    /// <param name="fieldIdentifier">The identifier for the field.</param>
    /// <param name="message">The validation message.</param>
    public void Add(in FieldIdentifier fieldIdentifier, string message)
        => GetOrCreateMessagesListForField(fieldIdentifier).Add(message);

    /// <summary>
    /// Adds a validation message for the specified field.
    /// </summary>
    /// <param name="accessor">Identifies the field for which to add the message.</param>
    /// <param name="message">The validation message.</param>
    public void Add(Expression<Func<object>> accessor, string message)
        => Add(FieldIdentifier.Create(accessor), message);

    /// <summary>
    /// Adds the messages from the specified collection for the specified field.
    /// </summary>
    /// <param name="fieldIdentifier">The identifier for the field.</param>
    /// <param name="messages">The validation messages to be added.</param>
    public void Add(in FieldIdentifier fieldIdentifier, IEnumerable<string> messages)
        => GetOrCreateMessagesListForField(fieldIdentifier).AddRange(messages);

    /// <summary>
    /// Adds the messages from the specified collection for the specified field.
    /// </summary>
    /// <param name="accessor">Identifies the field for which to add the messages.</param>
    /// <param name="messages">The validation messages to be added.</param>
    public void Add(Expression<Func<object>> accessor, IEnumerable<string> messages)
        => Add(FieldIdentifier.Create(accessor), messages);

    /// <summary>
    /// Gets the validation messages within this <see cref="ValidationMessageStore"/> for the specified field.
    ///
    /// To get the validation messages across all validation message stores, use <see cref="EditContext.GetValidationMessages(FieldIdentifier)"/> instead
    /// </summary>
    /// <param name="fieldIdentifier">The identifier for the field.</param>
    /// <returns>The validation messages for the specified field within this <see cref="ValidationMessageStore"/>.</returns>
    public IEnumerable<string> this[FieldIdentifier fieldIdentifier]
        => _messages.TryGetValue(fieldIdentifier, out var messages) ? messages : Array.Empty<string>();

    /// <summary>
    /// Gets the validation messages within this <see cref="ValidationMessageStore"/> for the specified field.
    ///
    /// To get the validation messages across all validation message stores, use <see cref="EditContext.GetValidationMessages(FieldIdentifier)"/> instead
    /// </summary>
    /// <param name="accessor">The identifier for the field.</param>
    /// <returns>The validation messages for the specified field within this <see cref="ValidationMessageStore"/>.</returns>
    public IEnumerable<string> this[Expression<Func<object>> accessor]
        => this[FieldIdentifier.Create(accessor)];

    /// <summary>
    /// Removes all messages within this <see cref="ValidationMessageStore"/>.
    /// </summary>
    public void Clear()
    {
        foreach (var fieldIdentifier in _messages.Keys)
        {
            DissociateFromField(fieldIdentifier);
        }

        _messages.Clear();
    }

    /// <summary>
    /// Removes all messages within this <see cref="ValidationMessageStore"/> for the specified field.
    /// </summary>
    /// <param name="accessor">Identifies the field for which to remove the messages.</param>
    public void Clear(Expression<Func<object>> accessor)
        => Clear(FieldIdentifier.Create(accessor));

    /// <summary>
    /// Removes all messages within this <see cref="ValidationMessageStore"/> for the specified field.
    /// </summary>
    /// <param name="fieldIdentifier">The identifier for the field.</param>
    public void Clear(in FieldIdentifier fieldIdentifier)
    {
        DissociateFromField(fieldIdentifier);
        _messages.Remove(fieldIdentifier);
    }

    private List<string> GetOrCreateMessagesListForField(in FieldIdentifier fieldIdentifier)
    {
        if (!_messages.TryGetValue(fieldIdentifier, out var messagesForField))
        {
            messagesForField = new List<string>();
            _messages.Add(fieldIdentifier, messagesForField);
            AssociateWithField(fieldIdentifier);
        }

        return messagesForField;
    }

    private void AssociateWithField(in FieldIdentifier fieldIdentifier)
        => _editContext.GetOrAddFieldState(fieldIdentifier).AssociateWithValidationMessageStore(this);

    private void DissociateFromField(in FieldIdentifier fieldIdentifier)
        => _editContext.GetFieldState(fieldIdentifier)?.DissociateFromValidationMessageStore(this);
}
