using System.Net;
using System.Net.Http.Headers;
using System.Net.Http.Json;
using System.Runtime.CompilerServices;
using System.Text.Json;
using System.Text.RegularExpressions;
using Lskj.AgentPet.Host.Core.Configuration;
using Lskj.AgentPet.Host.Core.Security;

namespace Lskj.AgentPet.Host.Core.AstrBot;

public sealed record AstrBotStreamEvent(
    string Type,
    JsonElement Data,
    string? ChainType,
    bool Streaming,
    string? RunId,
    string? SessionId);

public sealed record AstrBotChatAttachment(
    string AttachmentId,
    string FileName,
    string Type);

public sealed record AstrBotChatRequest(
    string Text,
    IReadOnlyList<AstrBotChatAttachment> Attachments)
{
    /// <summary>
    /// Host-generated, already-sanitized ERP execution evidence. Browser input
    /// can never populate this property.
    /// </summary>
    public string? TrustedContext { get; init; }
}

public interface IAstrBotChatClient
{
    IAsyncEnumerable<AstrBotStreamEvent> StreamAsync(
        AstrBotChatRequest request,
        CancellationToken cancellationToken = default);
}

public sealed class AstrBotChatClient : IAstrBotChatClient
{
    private static readonly Regex SafeType = new(
        "^[a-zA-Z0-9_.:-]{1,64}$",
        RegexOptions.Compiled | RegexOptions.CultureInvariant);
    private static readonly Regex SafeAttachmentId = new(
        "^[A-Za-z0-9_-]{8,128}$",
        RegexOptions.Compiled | RegexOptions.CultureInvariant);
    private static readonly Regex SafeRunId = new(
        "^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$",
        RegexOptions.Compiled | RegexOptions.CultureInvariant);
    private readonly HttpClient _httpClient;
    private readonly HostConfiguration _configuration;

    public AstrBotChatClient(HttpClient httpClient, HostConfiguration configuration)
    {
        _httpClient = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
        _configuration = configuration ?? throw new ArgumentNullException(nameof(configuration));
    }

    public async IAsyncEnumerable<AstrBotStreamEvent> StreamAsync(
        AstrBotChatRequest chatRequest,
        [EnumeratorCancellation] CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(chatRequest);
        string text = (chatRequest.Text ?? string.Empty).Trim();
        IReadOnlyList<AstrBotChatAttachment> attachments =
            chatRequest.Attachments ?? Array.Empty<AstrBotChatAttachment>();
        if (text.Length > 2000 || (text.Length == 0 && attachments.Count == 0))
            throw new HostError("chat_text_invalid", "聊天内容为空或超过 2000 个字符。");
        string? trustedContext = chatRequest.TrustedContext;
        if (trustedContext is not null
            && !TrustedDiagnosticContextStore.IsWellFormedPrompt(trustedContext))
            throw new HostError(
                "trusted_context_invalid",
                "本机 ERP 诊断上下文格式无效。");
        if (attachments.Count > _configuration.MaximumAttachmentCount)
            throw new HostError("attachment_count_exceeded", "聊天附件数量超过允许范围。");
        object message = BuildMessage(text, attachments, trustedContext);

        using CancellationTokenSource timeout = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
        timeout.CancelAfter(_configuration.ChatTimeout);
        using HttpRequestMessage request = new(
            HttpMethod.Post,
            new Uri(_configuration.AstrBotBaseUri, "api/v1/chat"));
        request.Headers.TryAddWithoutValidation("X-API-Key", _configuration.AstrBotApiKey);
        request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("text/event-stream"));
        request.Content = JsonContent.Create(new
        {
            session_id = _configuration.AstrBotSessionId,
            message,
            flags = new
            {
                enable_inline_genui = false,
                enable_default_system_prompt = true,
                enable_streaming = true
            }
        });

        using HttpResponseMessage response = await _httpClient.SendAsync(
            request,
            HttpCompletionOption.ResponseHeadersRead,
            timeout.Token).ConfigureAwait(false);
        if (response.StatusCode is HttpStatusCode.Unauthorized or HttpStatusCode.Forbidden)
            throw new HostError("astrbot_auth_failed", "AstrBot API Key 无效或缺少 chat scope。");
        if (!response.IsSuccessStatusCode)
            throw new HostError("astrbot_http_error", "AstrBot 对话服务暂时不可用。");
        string mediaType = response.Content.Headers.ContentType?.MediaType ?? string.Empty;
        if (!string.Equals(mediaType, "text/event-stream", StringComparison.OrdinalIgnoreCase))
            throw new HostError("astrbot_protocol_error", "AstrBot 未返回 SSE 对话流。");

        await using Stream stream = await response.Content.ReadAsStreamAsync(timeout.Token).ConfigureAwait(false);
        bool sessionBound = false;
        string? boundRunId = null;
        await foreach (SseFrame frame in SseParser.ReadAsync(stream, timeout.Token).ConfigureAwait(false))
        {
            if (string.IsNullOrWhiteSpace(frame.Data)) continue;
            JsonDocument document;
            try
            {
                document = JsonDocument.Parse(frame.Data, new JsonDocumentOptions
                {
                    AllowTrailingCommas = false,
                    CommentHandling = JsonCommentHandling.Disallow,
                    MaxDepth = 64
                });
            }
            catch (JsonException error)
            {
                throw new HostError("astrbot_protocol_error", "AstrBot SSE 包含无效 JSON。", error);
            }
            using (document)
            {
                JsonElement root = document.RootElement;
                if (root.ValueKind != JsonValueKind.Object)
                    throw new HostError("astrbot_protocol_error", "AstrBot SSE 事件必须是 JSON 对象。");
                EnsureUniqueProperties(root);
                string type = RequiredProtocolString(root, "type", 64);
                if (!SafeType.IsMatch(type))
                    throw new HostError("astrbot_protocol_error", "AstrBot SSE 事件类型无效。");
                string? chainType = OptionalProtocolString(root, "chain_type", 64);
                string? sessionId = OptionalProtocolString(root, "session_id", 256);
                string? messageId = OptionalProtocolString(root, "message_id", 128);
                string? legacyRunId = OptionalProtocolString(root, "run_id", 128);
                string? runId = ResolveRunId(messageId, legacyRunId);

                if (!sessionBound)
                {
                    if (!string.Equals(type, "session_id", StringComparison.Ordinal))
                        throw new HostError(
                            "astrbot_session_binding_required",
                            "AstrBot SSE 未先回显本轮会话标识。");
                    ValidateSessionId(sessionId);
                    sessionBound = true;
                }
                else if (sessionId is not null)
                {
                    ValidateSessionId(sessionId);
                }

                if (runId is not null)
                {
                    if (!SafeRunId.IsMatch(runId))
                        throw new HostError(
                            "astrbot_protocol_error",
                            "AstrBot SSE 运行标识格式无效。");
                    if (boundRunId is null)
                        boundRunId = runId;
                    else if (!string.Equals(boundRunId, runId, StringComparison.Ordinal))
                        throw new HostError(
                            "astrbot_run_mismatch",
                            "AstrBot SSE 混入了另一轮运行事件。");
                }

                if (RequiresRunBinding(type, chainType) && runId is null)
                    throw new HostError(
                        "astrbot_run_binding_required",
                        "AstrBot SSE 关键事件缺少本轮运行标识。");
                JsonElement data = root.TryGetProperty("data", out JsonElement value)
                    ? value.Clone()
                    : JsonSerializer.SerializeToElement<object?>(null);
                yield return new AstrBotStreamEvent(
                    type,
                    data,
                    chainType,
                    Boolean(root, "streaming"),
                    runId,
                    sessionId);
            }
        }
    }

    private void ValidateSessionId(string? sessionId)
    {
        if (!string.Equals(
                sessionId,
                _configuration.AstrBotSessionId,
                StringComparison.Ordinal))
            throw new HostError(
                "astrbot_session_mismatch",
                "AstrBot SSE 会话标识与请求不一致。");
    }

    private static string? ResolveRunId(string? messageId, string? legacyRunId)
    {
        if (messageId is not null
            && legacyRunId is not null
            && !string.Equals(messageId, legacyRunId, StringComparison.Ordinal))
            throw new HostError(
                "astrbot_run_mismatch",
                "AstrBot SSE 同时返回了冲突的运行标识。");
        return messageId ?? legacyRunId;
    }

    private static bool RequiresRunBinding(string type, string? chainType)
    {
        return string.Equals(type, "end", StringComparison.Ordinal)
            || string.Equals(chainType, "tool_call", StringComparison.OrdinalIgnoreCase)
            || string.Equals(chainType, "tool_call_result", StringComparison.OrdinalIgnoreCase);
    }

    private static void EnsureUniqueProperties(JsonElement value)
    {
        HashSet<string> names = new(StringComparer.Ordinal);
        foreach (JsonProperty property in value.EnumerateObject())
        {
            if (!names.Add(property.Name))
                throw new HostError(
                    "astrbot_protocol_error",
                    "AstrBot SSE 事件包含重复字段。");
        }
    }

    private static string RequiredProtocolString(
        JsonElement value,
        string name,
        int maximumLength)
    {
        return OptionalProtocolString(value, name, maximumLength)
            ?? throw new HostError(
                "astrbot_protocol_error",
                "AstrBot SSE 事件缺少必要字段。");
    }

    private static string? OptionalProtocolString(
        JsonElement value,
        string name,
        int maximumLength)
    {
        if (!value.TryGetProperty(name, out JsonElement item)) return null;
        if (item.ValueKind != JsonValueKind.String)
            throw new HostError(
                "astrbot_protocol_error",
                "AstrBot SSE 身份字段类型无效。");
        string result = item.GetString() ?? string.Empty;
        if (result.Length is < 1
            || result.Length > maximumLength
            || result.Any(char.IsControl)
            || !string.Equals(result, result.Trim(), StringComparison.Ordinal))
            throw new HostError(
                "astrbot_protocol_error",
                "AstrBot SSE 身份字段内容无效。");
        return result;
    }

    private static bool Boolean(JsonElement value, string name)
    {
        return value.TryGetProperty(name, out JsonElement item)
            && item.ValueKind is JsonValueKind.True;
    }

    private static object BuildMessage(
        string text,
        IReadOnlyList<AstrBotChatAttachment> attachments,
        string? trustedContext)
    {
        if (attachments.Count == 0 && trustedContext is null) return text;
        List<object> parts = new();
        if (text.Length > 0) parts.Add(new { type = "plain", text });
        if (trustedContext is not null)
            parts.Add(new { type = "plain", text = trustedContext });
        foreach (AstrBotChatAttachment attachment in attachments)
        {
            string fileName = (attachment.FileName ?? string.Empty).Trim();
            if (!SafeAttachmentId.IsMatch(attachment.AttachmentId ?? string.Empty)
                || (attachment.Type != "image" && attachment.Type != "file")
                || fileName.Length is < 1 or > 128
                || fileName.Any(char.IsControl)
                || fileName.Contains('/')
                || fileName.Contains('\\'))
                throw new HostError("attachment_invalid", "聊天附件字段无效。");
            parts.Add(new
            {
                type = attachment.Type,
                attachment_id = attachment.AttachmentId,
                filename = fileName
            });
        }
        return parts;
    }
}