using System.Text.Json;
using Microsoft.Extensions.Options;
using Microsoft.Identity.Client;

namespace OASystem.API.OAMethodLib.MicrosoftGraphMailbox;

/// <summary>
/// 后台轮询收件箱：仅当 <see cref="MicrosoftGraphMailboxOptions.Enabled"/> 为 true 时才会登录并访问 Graph。
/// 首次无缓存时会通过交互式浏览器完成授权（重定向 URI 与配置一致）。
/// </summary>
public sealed class MicrosoftGraphInboxPollerHostedService : BackgroundService
{
    private readonly IOptionsMonitor<MicrosoftGraphMailboxOptions> _optionsMonitor;
    private readonly IMicrosoftGraphMailboxService _graphMailbox;
    private readonly ILogger<MicrosoftGraphInboxPollerHostedService> _logger;

    private readonly HashSet<string> _processedMessageIds = new(StringComparer.Ordinal);
    private DateTime? _monitorStartUtc;
    private bool _startupProfileLogged;

    public MicrosoftGraphInboxPollerHostedService(
        IOptionsMonitor<MicrosoftGraphMailboxOptions> optionsMonitor,
        IMicrosoftGraphMailboxService graphMailbox,
        ILogger<MicrosoftGraphInboxPollerHostedService> logger)
    {
        _optionsMonitor = optionsMonitor;
        _graphMailbox = graphMailbox;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            var options = _optionsMonitor.CurrentValue;

            if (!options.Enabled)
            {
                await Task.Delay(TimeSpan.FromSeconds(5), stoppingToken).ConfigureAwait(false);
                continue;
            }

            if (_monitorStartUtc == null)
                _monitorStartUtc = DateTime.UtcNow;

            try
            {
                if (!_startupProfileLogged && options.LogProfileOnStartup)
                {
                    var meJson = await _graphMailbox.GetMeRawJsonAsync(stoppingToken).ConfigureAwait(false);
                    if (!string.IsNullOrEmpty(meJson))
                        _logger.LogInformation("Graph 邮箱：当前用户 /me 响应（节选） {Snippet}",
                            meJson.Length > 500 ? meJson[..500] + "…" : meJson);
                    _startupProfileLogged = true;
                }

                await PollInboxAsync(stoppingToken).ConfigureAwait(false);
            }
            catch (MsalException ex)
            {
                _logger.LogError(ex, "Graph 邮箱 MSAL 认证失败");
            }
            catch (HttpRequestException ex)
            {
                _logger.LogError(ex, "Graph 邮箱 HTTP 请求失败");
            }
            catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
            {
                throw;
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Graph 邮箱轮询异常");
            }

            var interval = TimeSpan.FromSeconds(Math.Clamp(options.PollIntervalSeconds, 5, 3600));
            await Task.Delay(interval, stoppingToken).ConfigureAwait(false);
        }
    }

    private async Task PollInboxAsync(CancellationToken cancellationToken)
    {
        var options = _optionsMonitor.CurrentValue;
        var startUtc = _monitorStartUtc ?? DateTime.UtcNow;

        var json = await _graphMailbox.GetInboxMessagesJsonSinceAsync(startUtc, cancellationToken)
            .ConfigureAwait(false);

        if (string.IsNullOrEmpty(json))
        {
            _logger.LogWarning("Graph 邮箱：未收到响应正文。");
            return;
        }

        using var doc = JsonDocument.Parse(json);
        if (!doc.RootElement.TryGetProperty("value", out var messages) ||
            messages.ValueKind != JsonValueKind.Array)
        {
            if (json.Contains("error", StringComparison.OrdinalIgnoreCase))
                _logger.LogWarning("Graph 邮箱接口错误响应: {Json}", json);
            else
                _logger.LogWarning("Graph 邮箱：响应中无 value 数组。");
            return;
        }

        var newCount = 0;

        foreach (var mail in messages.EnumerateArray())
        {
            var id = GetString(mail, "id");
            if (string.IsNullOrWhiteSpace(id))
                continue;

            if (!_processedMessageIds.Add(id))
                continue;

            newCount++;

            var subject = GetString(mail, "subject");
            var from = GetNestedString(mail, "from", "emailAddress", "address");
            var receivedDateTime = GetString(mail, "receivedDateTime");
            var bodyPreview = GetString(mail, "bodyPreview");
            var conversationId = GetString(mail, "conversationId");

            _logger.LogInformation(
                "Graph 新邮件 Id={Id} From={From} Subject={Subject} Received={Received} ConversationId={Conv} Preview={Preview}",
                id, from, subject, receivedDateTime, conversationId, bodyPreview);

            if (!string.IsNullOrWhiteSpace(subject) &&
                subject.StartsWith("Re:", StringComparison.OrdinalIgnoreCase))
            {
                _logger.LogInformation("Graph 新邮件检测到回复主题: {Subject}", subject);
            }
        }

        if (newCount == 0 && options.LogEachPollWhenEmpty)
            _logger.LogDebug("Graph 邮箱轮询：无新邮件（起点 UTC {Start:O}）", startUtc);
    }

    private static string GetString(JsonElement element, string propertyName)
    {
        if (element.TryGetProperty(propertyName, out var value))
        {
            return value.ValueKind switch
            {
                JsonValueKind.String => value.GetString() ?? string.Empty,
                JsonValueKind.Null => string.Empty,
                _ => value.ToString()
            };
        }

        return string.Empty;
    }

    private static string GetNestedString(JsonElement element, params string[] propertyPath)
    {
        var current = element;

        foreach (var property in propertyPath)
        {
            if (!current.TryGetProperty(property, out current))
                return string.Empty;
        }

        return current.ValueKind == JsonValueKind.String
            ? current.GetString() ?? string.Empty
            : current.ToString();
    }
}