29WxOrder/OrderSupportTicket/ViewModels/ChatMessageViewModel.cs

using OrderSupportTicket.Models.Api;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Globalization;
using System.Linq;
using System.Threading.Tasks;
using WPFCommon.Models;

namespace OrderSupportTicket.ViewModels;

/// <summary>
/// 工单留言板中的单条消息。
/// </summary>
public sealed class ChatMessageViewModel : BindableBaseEx
{
    private string _messageId;
    private int _sequenceNo;
    private string _senderType;
    private string _senderDisplayName;
    private string _content;
    private bool _isRecalled;
    private DateTimeOffset _createdAt;

    public ChatMessageViewModel(TicketMessageDto dto)
    {
        if (dto == null)
            throw new ArgumentNullException(nameof(dto));
        Attachments = new ObservableCollection<ChatAttachmentViewModel>();
        MessageId = dto.MessageId;
        SequenceNo = dto.SequenceNo;
        SenderType = dto.SenderType;
        IsRecalled = dto.Recalled;
        SenderDisplayName = string.IsNullOrWhiteSpace(dto.SenderName)
            ? (IsCustomer ? "我" : "客服")
            : dto.SenderName;
        Content = dto.Recalled
            ? "该消息已撤回"
            : (dto.Text ?? string.Empty);
        CreatedAt = ParseTimestamp(dto.CreatedAt);
        ReplaceAttachments(dto.Attachments);
    }

    /// <summary>
    /// 消息唯一 ID。
    /// </summary>
    public string MessageId
    {
        get => _messageId;
        private set => SetValue(ref _messageId, value);
    }

    /// <summary>
    /// 工单内连续递增的消息序号。
    /// </summary>
    public int SequenceNo
    {
        get => _sequenceNo;
        private set => SetValue(ref _sequenceNo, value);
    }

    /// <summary>
    /// 消息发送方类型。
    /// </summary>
    public string SenderType
    {
        get => _senderType;
        private set
        {
            if (SetValue(ref _senderType, value))
                RaisePropertyChanged(nameof(IsCustomer));
        }
    }

    /// <summary>
    /// 消息发送方显示名称。
    /// </summary>
    public string SenderDisplayName
    {
        get => _senderDisplayName;
        private set => SetValue(ref _senderDisplayName, value);
    }

    /// <summary>
    /// 消息展示内容；撤回消息显示固定提示文本。
    /// </summary>
    public string Content
    {
        get => _content;
        private set
        {
            if (SetValue(ref _content, value))
                RaisePropertyChanged(nameof(HasText));
        }
    }

    /// <summary>
    /// 是否有可展示的文字内容。
    /// </summary>
    public bool HasText => !string.IsNullOrWhiteSpace(Content);

    /// <summary>
    /// 消息是否已撤回。
    /// </summary>
    public bool IsRecalled
    {
        get => _isRecalled;
        private set => SetValue(ref _isRecalled, value);
    }

    /// <summary>
    /// 消息发送时间。
    /// </summary>
    public DateTimeOffset CreatedAt
    {
        get => _createdAt;
        private set
        {
            if (SetValue(ref _createdAt, value))
                RaisePropertyChanged(nameof(CreatedAtText));
        }
    }

    /// <summary>
    /// 消息中的公开图片附件。
    /// </summary>
    public ObservableCollection<ChatAttachmentViewModel> Attachments { get; }

    /// <summary>
    /// 是否包含图片附件。
    /// </summary>
    public bool HasAttachments => Attachments.Count > 0;

    /// <summary>
    /// 当前消息是否由客户发送。
    /// </summary>
    public bool IsCustomer =>
        string.Equals(SenderType, "customer", StringComparison.OrdinalIgnoreCase);

    /// <summary>
    /// 适合聊天界面展示的本地时间文本。
    /// </summary>
    public string CreatedAtText =>
        CreatedAt == default
            ? string.Empty
            : CreatedAt.ToLocalTime().ToString("MM-dd HH:mm", CultureInfo.CurrentCulture);

    /// <summary>
    /// 使用服务端最新数据更新消息。短时图片地址会随每次查询变化，因此需要刷新附件。
    /// </summary>
    public void UpdateFrom(TicketMessageDto dto)
    {
        if (dto == null)
            return;

        SenderDisplayName = string.IsNullOrWhiteSpace(dto.SenderName)
            ? (IsCustomer ? "我" : "客服")
            : dto.SenderName;
        IsRecalled = dto.Recalled;
        Content = dto.Recalled
            ? "该消息已撤回"
            : (dto.Text ?? string.Empty);
        CreatedAt = ParseTimestamp(dto.CreatedAt);
        ReplaceAttachments(dto.Attachments);
    }

    private void ReplaceAttachments(IEnumerable<TicketAttachmentDto> attachments)
    {
        Attachments.Clear();
        foreach (var dto in attachments ?? Enumerable.Empty<TicketAttachmentDto>())
        {
            if (dto == null)
                continue;
            Attachments.Add(new ChatAttachmentViewModel(dto));
        }
        RaisePropertyChanged(nameof(HasAttachments));
        _ = LoadAttachmentsAsync();
    }

    private async Task LoadAttachmentsAsync()
    {
        try
        {
            await Task.WhenAll(Attachments.Select(item => item.LoadAsync()));
        }
        catch
        {
            // 单张图片加载失败时保留占位提示，不影响文字留言显示。
        }
    }

    private static DateTimeOffset ParseTimestamp(string value)
    {
        if (DateTimeOffset.TryParse(
            value,
            CultureInfo.InvariantCulture,
            DateTimeStyles.AssumeUniversal,
            out var parsed))
        {
            return parsed;
        }
        return default;
    }
}