using System;
using System.Globalization;
using System.IO;
using System.Text.RegularExpressions;
using Newtonsoft.Json;

namespace Lskj.AgentBridge
{
    /// <summary>
    /// Publishes the local ERP bridge discovery document as one durable,
    /// atomic filesystem transition. Readers therefore observe either the
    /// previous complete generation or the new complete generation.
    /// </summary>
    public static class BridgeDiscoveryPublisher
    {
        internal const int MaximumDocumentBytes = 4096;
        private static readonly Regex SafePipeName = new Regex(
            "^[A-Za-z0-9_.-]{1,128}$",
            RegexOptions.Compiled | RegexOptions.CultureInvariant);
        private static readonly Regex SafeBridgeInstanceId = new Regex(
            "^[a-f0-9]{32}$",
            RegexOptions.Compiled | RegexOptions.CultureInvariant);

        public static string Publish(
            string directory,
            string pipeName,
            int processId,
            DateTime processStartedAtUtc,
            string bridgeInstanceId)
        {
            if (string.IsNullOrWhiteSpace(directory)
                || !Path.IsPathRooted(directory))
                throw new ArgumentException("发现目录必须是绝对路径。", "directory");
            if (string.IsNullOrWhiteSpace(pipeName)
                || !SafePipeName.IsMatch(pipeName))
                throw new ArgumentException("命名管道名称无效。", "pipeName");
            if (processId <= 0)
                throw new ArgumentOutOfRangeException("processId");
            if (string.IsNullOrWhiteSpace(bridgeInstanceId)
                || !SafeBridgeInstanceId.IsMatch(bridgeInstanceId))
                throw new ArgumentException("ERP 桥实例标识无效。", "bridgeInstanceId");
            string expectedPipeName = "lserp.agent."
                + processId.ToString(CultureInfo.InvariantCulture)
                + "."
                + bridgeInstanceId;
            if (!string.Equals(pipeName, expectedPipeName, StringComparison.Ordinal))
                throw new ArgumentException(
                    "命名管道名称必须绑定 ERP 进程号和桥实例。",
                    "pipeName");
            if (processStartedAtUtc.Kind != DateTimeKind.Utc)
                throw new ArgumentException("ERP 进程启动时间必须是 UTC。", "processStartedAtUtc");

            string fullDirectory = Path.GetFullPath(directory);
            Directory.CreateDirectory(fullDirectory);
            string destination = Path.Combine(
                fullDirectory,
                "agentbridge-" + processId.ToString(CultureInfo.InvariantCulture) + ".json");
            string temporary = Path.Combine(
                fullDirectory,
                ".agentbridge-" + processId.ToString(CultureInfo.InvariantCulture)
                    + "-" + Guid.NewGuid().ToString("N") + ".tmp");
            string json = JsonConvert.SerializeObject(new
            {
                protocolVersion = AgentBridgeRuntime.ProtocolVersion,
                pipeName = pipeName,
                processId = processId,
                startedAtUtc = processStartedAtUtc.ToString("o", CultureInfo.InvariantCulture),
                bridgeInstanceId = bridgeInstanceId
            });
            byte[] body = BridgeUtf8Codec.Encode(json);
            if (body.Length == 0 || body.Length > MaximumDocumentBytes)
                throw new InvalidDataException("ERP 桥发现文档长度无效。");

            try
            {
                using (FileStream stream = new FileStream(
                    temporary,
                    FileMode.CreateNew,
                    FileAccess.Write,
                    FileShare.None,
                    4096,
                    FileOptions.WriteThrough))
                {
                    stream.Write(body, 0, body.Length);
                    stream.Flush(true);
                }

                if (File.Exists(destination))
                    File.Replace(temporary, destination, null, true);
                else
                    File.Move(temporary, destination);
                return destination;
            }
            finally
            {
                try
                {
                    if (File.Exists(temporary)) File.Delete(temporary);
                }
                catch (IOException) { }
                catch (UnauthorizedAccessException) { }
            }
        }
    }
}