using System.Diagnostics.Metrics;
using System.Globalization;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using Data.SeaHavenIndustries.Enums;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using SeaHaven.DataServices.Interfaces;
using SeaHaven.Services.Configuration;
using SeaHaven.Services.Constants;
using SeaHaven.Services.Helpers;
using SeaHaven.Services.Interfaces;

namespace SeaHaven.Services.Implementation
{
    public sealed class WorkOrderWebhookService : IWorkOrderWebhookService
    {
        private static readonly Meter Meter = new("SeaHaven.WorkOrderWebhook", "1.0");
        private static readonly Counter<long> Accepted = Meter.CreateCounter<long>("work_order_webhook.accepted");
        private static readonly Counter<long> Duplicates = Meter.CreateCounter<long>("work_order_webhook.duplicate");
        private static readonly Counter<long> Rejected = Meter.CreateCounter<long>("work_order_webhook.rejected");
        private static readonly Counter<long> Invalid = Meter.CreateCounter<long>("work_order_webhook.invalid");
        private static readonly Counter<long> Failed = Meter.CreateCounter<long>("work_order_webhook.failed");
        private static readonly JsonSerializerOptions JsonOptions = new()
        {
            PropertyNameCaseInsensitive = false,
            PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower
        };

        private readonly IWorkOrderWebhookSecretProvider _secretProvider;
        private readonly IWorkOrderWebhookDataService _dataService;
        private readonly IOptionsMonitor<WorkOrderWebhookOptions> _options;
        private readonly TimeProvider _timeProvider;
        private readonly ILogger<WorkOrderWebhookService> _logger;

        public WorkOrderWebhookService(
            IWorkOrderWebhookSecretProvider secretProvider,
            IWorkOrderWebhookDataService dataService,
            IOptionsMonitor<WorkOrderWebhookOptions> options,
            TimeProvider timeProvider,
            ILogger<WorkOrderWebhookService> logger)
        {
            _secretProvider = secretProvider;
            _dataService = dataService;
            _options = options;
            _timeProvider = timeProvider;
            _logger = logger;
        }

        public int MaximumBodyBytes =>
            Math.Clamp(_options.CurrentValue.MaxBodyBytes, 1, 1_048_576);

        public async Task<WorkOrderWebhookResult> ProcessAsync(
            WorkOrderWebhookRequest request,
            CancellationToken cancellationToken)
        {
            var options = _options.CurrentValue;
            if (!options.Enabled)
                return new WorkOrderWebhookResult(WorkOrderWebhookStatus.Disabled);

            if (!TryReadTimestamp(request.Timestamp, options.AllowedClockSkewSeconds, out var timestamp)
                || string.IsNullOrWhiteSpace(request.KeyId)
                || request.KeyId.Length > 128
                || string.IsNullOrWhiteSpace(request.Signature))
            {
                Rejected.Add(1);
                return Unauthorized();
            }

            WorkOrderWebhookSecretResult secretResult;
            try
            {
                secretResult = await _secretProvider.GetSecretAsync(request.KeyId, cancellationToken);
            }
            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
            {
                throw;
            }
            catch (Exception)
            {
                Failed.Add(1);
                _logger.LogError("Work-order webhook signing secret could not be loaded.");
                return new WorkOrderWebhookResult(WorkOrderWebhookStatus.Unavailable);
            }

            if (secretResult.Status == WorkOrderWebhookSecretStatus.Unavailable)
            {
                Failed.Add(1);
                return new WorkOrderWebhookResult(WorkOrderWebhookStatus.Unavailable);
            }

            if (secretResult.Status != WorkOrderWebhookSecretStatus.Found
                || secretResult.Secret is not { Length: > 0 })
            {
                Rejected.Add(1);
                return Unauthorized();
            }

            var signatureValid = false;
            try
            {
                signatureValid = VerifySignature(
                    request.Timestamp!,
                    request.Body,
                    request.Signature!,
                    secretResult.Secret);
            }
            finally
            {
                CryptographicOperations.ZeroMemory(secretResult.Secret);
            }

            if (!signatureValid)
            {
                Rejected.Add(1);
                return Unauthorized();
            }

            WorkOrderWebhookEnvelope? envelope;
            try
            {
                envelope = JsonSerializer.Deserialize<WorkOrderWebhookEnvelope>(request.Body, JsonOptions);
            }
            catch (JsonException)
            {
                Invalid.Add(1);
                return new WorkOrderWebhookResult(WorkOrderWebhookStatus.InvalidEnvelope);
            }

            if (!TryCreateMutation(envelope, request.Body, out var mutation))
            {
                Invalid.Add(1);
                return new WorkOrderWebhookResult(WorkOrderWebhookStatus.InvalidEnvelope);
            }

            try
            {
                var persisted = await _dataService.ApplyAsync(mutation!, cancellationToken);
                switch (persisted.Status)
                {
                    case WorkOrderWebhookPersistenceStatus.Applied:
                        Accepted.Add(1);
                        _logger.LogInformation(
                            "Work-order webhook delivery {DeliveryId} was accepted. State mutation skipped: {StateMutationSkipped}.",
                            mutation!.DeliveryId,
                            persisted.StateMutationSkipped);
                        return new WorkOrderWebhookResult(
                            WorkOrderWebhookStatus.Applied,
                            persisted.StateMutationSkipped);
                    case WorkOrderWebhookPersistenceStatus.Duplicate:
                        Duplicates.Add(1);
                        _logger.LogInformation(
                            "Work-order webhook delivery {DeliveryId} was already processed.",
                            mutation!.DeliveryId);
                        return new WorkOrderWebhookResult(WorkOrderWebhookStatus.Duplicate);
                    case WorkOrderWebhookPersistenceStatus.HashConflict:
                        Rejected.Add(1);
                        _logger.LogWarning(
                            "Work-order webhook delivery {DeliveryId} conflicts with an existing delivery.",
                            mutation!.DeliveryId);
                        return new WorkOrderWebhookResult(WorkOrderWebhookStatus.HashConflict);
                    default:
                        throw new InvalidOperationException("Unknown persistence result.");
                }
            }
            catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested)
            {
                throw;
            }
            catch (Exception ex)
            {
                Failed.Add(1);
                _logger.LogError(
                    ex,
                    "Work-order webhook delivery {DeliveryId} could not be persisted.",
                    mutation!.DeliveryId);
                return new WorkOrderWebhookResult(WorkOrderWebhookStatus.Unavailable);
            }
        }

        private bool TryReadTimestamp(
            string? value,
            int allowedClockSkewSeconds,
            out DateTimeOffset timestamp)
        {
            timestamp = default;
            if (string.IsNullOrEmpty(value)
                || value.Any(c => c is < '0' or > '9')
                || !long.TryParse(value, NumberStyles.None, CultureInfo.InvariantCulture, out var seconds))
                return false;

            try
            {
                timestamp = DateTimeOffset.FromUnixTimeSeconds(seconds);
            }
            catch (ArgumentOutOfRangeException)
            {
                return false;
            }

            var skew = (_timeProvider.GetUtcNow() - timestamp).Duration();
            return skew <= TimeSpan.FromSeconds(Math.Clamp(allowedClockSkewSeconds, 0, 3600));
        }

        private static bool VerifySignature(
            string timestamp,
            byte[] body,
            string signature,
            byte[] secret)
        {
            const string prefix = "v1=";
            if (!signature.StartsWith(prefix, StringComparison.Ordinal)
                || signature.Length != prefix.Length + 64)
                return false;

            byte[] supplied;
            try
            {
                supplied = Convert.FromHexString(signature[prefix.Length..]);
            }
            catch (FormatException)
            {
                return false;
            }

            var timestampBytes = Encoding.UTF8.GetBytes(timestamp);
            var signed = new byte[timestampBytes.Length + 1 + body.Length];
            timestampBytes.CopyTo(signed, 0);
            signed[timestampBytes.Length] = (byte)'.';
            body.CopyTo(signed, timestampBytes.Length + 1);
            var expected = HMACSHA256.HashData(secret, signed);
            return CryptographicOperations.FixedTimeEquals(expected, supplied);
        }

        private bool TryCreateMutation(
            WorkOrderWebhookEnvelope? envelope,
            byte[] body,
            out WorkOrderWebhookMutation? mutation)
        {
            mutation = null;
            if (envelope == null
                || envelope.SchemaVersion != 1
                || string.IsNullOrWhiteSpace(envelope.DeliveryId)
                || envelope.DeliveryId.Length > 128
                || string.IsNullOrWhiteSpace(envelope.EventType)
                || envelope.EventType.Length > 64
                || envelope.OccurredAt == null
                 || !string.Equals(envelope.Source, WorkOrderSourceIdentity.WireSource, StringComparison.Ordinal)
                || envelope.Replay == null
                || envelope.Data == null
                || string.IsNullOrWhiteSpace(envelope.Data.WorkOrderId)
                || envelope.Data.WorkOrderId.Length > 450
                || !KnownEvents.Contains(envelope.EventType))
                return false;

            var isComment = envelope.EventType == "work_order.comment_added";
            if (isComment
                && (string.IsNullOrWhiteSpace(envelope.Data.CommentId)
                    || envelope.Data.CommentId.Length > 450
                    || string.IsNullOrWhiteSpace(envelope.Data.Text)))
                return false;

            var updatedAt = envelope.Data.UpdatedAt
                ?? envelope.Data.IngestedAt
                ?? envelope.OccurredAt;
            if (updatedAt == null)
                return false;

            var bodyHash = Convert.ToHexString(SHA256.HashData(body)).ToLowerInvariant();
            var versionHash = isComment
                ? WorkOrderExternalVersion.ComputeComment(new WorkOrderExternalVersion.Comment(
                    envelope.Data.WorkOrderId,
                    envelope.Data.CommentId!,
                    envelope.Data.RecordType,
                    envelope.Data.Commenter,
                    envelope.Data.Text,
                    envelope.Data.CreatedAt,
                    envelope.Data.IngestedAt,
                    envelope.Data.SourceEmailS3Key))
                : WorkOrderExternalVersion.ComputeWorkOrder(new WorkOrderExternalVersion.WorkOrder(
                envelope.Data.WorkOrderId,
                envelope.Data.WoStatus ?? envelope.Data.Status,
                envelope.Data.Description,
                envelope.Data.Customer,
                envelope.Data.SiteCode,
                envelope.Data.Building,
                envelope.Data.Address,
                envelope.Data.Severity,
                envelope.Data.Priority,
                envelope.Data.AssignedTo,
                envelope.Data.DateReported,
                envelope.Data.ScheduledStart,
                envelope.Data.DueDate,
                envelope.Data.RecordType,
                envelope.Data.CreatedAt,
                envelope.Data.SourceEmailS3Key));
            var statusSource = envelope.Data.WoStatus ?? envelope.Data.Status;
            var status = WorkOrderIngestFieldMapper.MapStatus(statusSource);
            mutation = new WorkOrderWebhookMutation
            {
                DeliveryId = envelope.DeliveryId,
                EventType = envelope.EventType,
                OccurredAt = envelope.OccurredAt.Value,
                ProcessedAt = _timeProvider.GetUtcNow(),
                BodySha256 = bodyHash,
                ExternalWorkOrderId = envelope.Data.WorkOrderId,
                WorkerOrderNumber = envelope.Data.WorkOrderId,
                Source = WorkOrderSourceIdentity.CanonicalSource,
                UpdatedAt = updatedAt.Value,
                VersionHash = versionHash,
                IsStateEvent = !isComment,
                IsCancelled = envelope.EventType == "work_order.cancelled",
                Title = envelope.Data.Title,
                Description = envelope.Data.Description,
                Status = status,
                LifecycleStatus = envelope.EventType == "work_order.cancelled"
                    ? LifecycleStatus.Canceled
                    : LifecycleStatusMapper.FromLegacyStatus(status),
                Severity = envelope.Data.Severity,
                Priority = envelope.Data.Priority
                    ?? WorkOrderIngestFieldMapper.MapSeverityToPriority(envelope.Data.Severity),
                AssignedTo = envelope.Data.AssignedTo,
                RecordType = envelope.Data.RecordType,
                SourceEmailS3Key = envelope.Data.SourceEmailS3Key,
                Customer = envelope.Data.Customer,
                SiteCode = envelope.Data.SiteCode,
                Building = envelope.Data.Building,
                Address = envelope.Data.Address,
                DueDate = envelope.Data.DueDate?.UtcDateTime,
                DateReported = envelope.Data.DateReported?.UtcDateTime,
                ScheduledStart = envelope.Data.ScheduledStart?.UtcDateTime,
                CreatedAt = envelope.Data.CreatedAt?.UtcDateTime,
                CommentId = isComment ? envelope.Data.CommentId : null,
                CommentText = isComment ? envelope.Data.Text : null,
                Commenter = isComment ? envelope.Data.Commenter : null,
                CommentType = isComment ? envelope.Data.CommentType : null
            };
            return true;
        }

        private static WorkOrderWebhookResult Unauthorized() =>
            new(WorkOrderWebhookStatus.Unauthorized);

        private static readonly HashSet<string> KnownEvents = new(StringComparer.Ordinal)
        {
            "work_order.created",
            "work_order.updated",
            "work_order.cancelled",
            "work_order.comment_added"
        };

        private sealed class WorkOrderWebhookEnvelope
        {
            [JsonPropertyName("schema_version")]
            public int? SchemaVersion { get; set; }

            [JsonPropertyName("delivery_id")]
            public string? DeliveryId { get; set; }

            [JsonPropertyName("event_type")]
            public string? EventType { get; set; }

            [JsonPropertyName("occurred_at")]
            public DateTimeOffset? OccurredAt { get; set; }

            public string? Source { get; set; }
            public bool? Replay { get; set; }
            public WorkOrderWebhookData? Data { get; set; }
        }

        private sealed class WorkOrderWebhookData
        {
            [JsonPropertyName("work_order_id")]
            public string? WorkOrderId { get; set; }

            public string? Description { get; set; }
            public string? Title { get; set; }

            [JsonPropertyName("wo_status")]
            public string? WoStatus { get; set; }

            public string? Status { get; set; }
            public string? Severity { get; set; }
            public string? Priority { get; set; }
            public string? Customer { get; set; }
            [JsonPropertyName("assigned_to")]
            public string? AssignedTo { get; set; }

            [JsonPropertyName("site_code")]
            public string? SiteCode { get; set; }

            public string? Building { get; set; }
            public string? Address { get; set; }

            [JsonPropertyName("due_date")]
            public DateTimeOffset? DueDate { get; set; }

            [JsonPropertyName("date_reported")]
            public DateTimeOffset? DateReported { get; set; }

            [JsonPropertyName("scheduled_start")]
            public DateTimeOffset? ScheduledStart { get; set; }

            [JsonPropertyName("created_at")]
            public DateTimeOffset? CreatedAt { get; set; }

            [JsonPropertyName("updated_at")]
            public DateTimeOffset? UpdatedAt { get; set; }

            [JsonPropertyName("ingested_at")]
            public DateTimeOffset? IngestedAt { get; set; }

            [JsonPropertyName("record_type")]
            public string? RecordType { get; set; }

            [JsonPropertyName("source_email_s3_key")]
            public string? SourceEmailS3Key { get; set; }

            [JsonPropertyName("comment_id")]
            public string? CommentId { get; set; }

            public string? Text { get; set; }
            public string? Commenter { get; set; }

            [JsonPropertyName("comment_type")]
            public string? CommentType { get; set; }
        }
    }
}