using System.Text.Json;
using System.Collections.Generic;
using System.Linq;
using Lskj.AgentPet.Host.Core.Configuration;

namespace Lskj.AgentPet.Host.Core.ErpBridge;

public sealed class SessionBoundErpBridgeClient : IErpBridgeClient
{
    private readonly IErpBridgeClient _inner;
    private readonly ErpSessionScopeBinding _scope;

    public SessionBoundErpBridgeClient(
        IErpBridgeClient inner,
        ErpSessionScopeBinding scope)
    {
        _inner = inner ?? throw new ArgumentNullException(nameof(inner));
        _scope = scope ?? throw new ArgumentNullException(nameof(scope));
    }

    public async Task<JsonDocument> SendAsync(
        JsonElement request,
        CancellationToken cancellationToken = default)
    {
        string method = RequiredString(request, "method", 128);
        if (string.Equals(method, "context.get", StringComparison.Ordinal))
        {
            using JsonDocument boundRequest = BindRequest(request);
            JsonDocument context = await _inner.SendAsync(
                    boundRequest.RootElement,
                    cancellationToken)
                .ConfigureAwait(false);
            try
            {
                _scope.VerifyContextResponse(context.RootElement);
                return context;
            }
            catch
            {
                context.Dispose();
                throw;
            }
        }

        string protocol = RequiredString(request, "protocolVersion", 16);
        string clientSessionId = RequiredString(request, "clientSessionId", 128);
        ErpSessionScopeSnapshot before = await ReadContextAsync(
            protocol,
            clientSessionId,
            cancellationToken).ConfigureAwait(false);
        JsonDocument? result = null;
        try
        {
            using JsonDocument boundRequest = BindRequest(request);
            result = await _inner.SendAsync(
                    boundRequest.RootElement,
                    cancellationToken)
                .ConfigureAwait(false);
            ErpSessionScopeSnapshot after;
            try
            {
                after = await ReadContextAsync(
                    protocol,
                    clientSessionId,
                    cancellationToken).ConfigureAwait(false);
            }
            catch (HostError error) when (error.Code == "erp_session_scope_mismatch")
            {
                throw new HostError(
                    "erp_session_scope_changed",
                    "ERP 会话在桌宠操作期间发生切换，操作结果不会交给页面继续使用。",
                    error);
            }
            bool targetMayChangeUi = string.Equals(
                method,
                "command.execute",
                StringComparison.Ordinal);
            if (!before.SameSessionIdentity(after)
                || (!targetMayChangeUi && !before.SameUiState(after)))
            {
                throw new HostError(
                    "erp_session_scope_changed",
                    "ERP 会话在桌宠操作期间发生切换，操作结果不会交给页面继续使用。");
            }
            JsonDocument accepted = result;
            result = null;
            return accepted;
        }
        finally
        {
            result?.Dispose();
        }
    }

    private async Task<ErpSessionScopeSnapshot> ReadContextAsync(
        string protocol,
        string clientSessionId,
        CancellationToken cancellationToken)
    {
        string requestId = Guid.NewGuid().ToString("N");
        string correlationId = "scope-" + Guid.NewGuid().ToString("N");
        using JsonDocument request = JsonSerializer.SerializeToDocument(new
        {
            protocolVersion = protocol,
            requestId,
            correlationId,
            clientSessionId,
            sessionScopeToken = _scope.Token,
            method = "context.get",
            payload = new { }
        });
        using JsonDocument response = await _inner.SendAsync(
            request.RootElement,
            cancellationToken).ConfigureAwait(false);
        return _scope.VerifyContextResponse(response.RootElement);
    }

    private JsonDocument BindRequest(JsonElement request)
    {
        if (request.ValueKind != JsonValueKind.Object)
            throw new HostError(
                "bridge_request_invalid",
                "ERP 桥请求必须是 JSON 对象。");

        Dictionary<string, JsonElement> fields = new(StringComparer.Ordinal);
        foreach (JsonProperty property in request.EnumerateObject())
        {
            if (!fields.TryAdd(property.Name, property.Value.Clone()))
                throw new HostError(
                    "bridge_request_invalid",
                    "ERP 桥请求包含重复字段。");
        }

        // 浏览器页面不能声明或覆盖会话令牌；Host 只使用启动时绑定的
        // ERP 登录范围重新注入它，然后才把请求交给命名管道客户端。
        fields["sessionScopeToken"] = JsonSerializer.SerializeToElement(
            _scope.Token);
        return JsonSerializer.SerializeToDocument(fields);
    }

    private static string RequiredString(JsonElement source, string name, int maximumLength)
    {
        if (source.ValueKind != JsonValueKind.Object
            || !source.TryGetProperty(name, out JsonElement value)
            || value.ValueKind != JsonValueKind.String)
        {
            throw new HostError("bridge_request_invalid", "ERP 桥请求缺少会话绑定字段。");
        }
        string result = value.GetString() ?? string.Empty;
        if (string.IsNullOrWhiteSpace(result)
            || result.Length > maximumLength
            || result.Any(char.IsControl))
            throw new HostError("bridge_request_invalid", "ERP 桥请求会话绑定字段无效。");
        return result;
    }
}