/*
This file is part of the Notesnook Sync Server project (https://notesnook.com/)

Copyright (C) 2023 Streetwriters (Private) Limited

This program is free software: you can redistribute it and/or modify
it under the terms of the Affero GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
Affero GNU General Public License for more details.

You should have received a copy of the Affero GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using Amazon;
using Amazon.S3;
using Amazon.S3.Model;
using Microsoft.Extensions.Logging;
using MongoDB.Driver;
using Notesnook.API.Helpers;
using Notesnook.API.Interfaces;
using Notesnook.API.Models;
using Streetwriters.Common;
using Streetwriters.Common.Accessors;

namespace Notesnook.API.Services
{
    enum S3ClientMode
    {
        INTERNAL = 0,
        EXTERNAL = 1
    }

    public class S3Service : IS3Service
    {
        private readonly string BUCKET_NAME = Constants.S3_BUCKET_NAME;
        private readonly string INTERNAL_BUCKET_NAME = Constants.S3_INTERNAL_BUCKET_NAME ?? Constants.S3_BUCKET_NAME;
        private readonly S3FailoverHelper S3Client;
        private ISyncItemsRepositoryAccessor Repositories { get; }
        private WampServiceAccessor ServiceAccessor { get; }

        // When running in a dockerized environment the sync server doesn't have access
        // to the host's S3 Service URL. It can only talk to S3 server via its own internal
        // network. This creates the issue where the client needs host-level access while
        // the sync server needs only internal access.
        // This wouldn't be a big issue (just map one to the other right?) but the signed
        // URLs generated by S3 are host specific. Changing their hostname on the fly causes
        // SignatureDoesNotMatch error.
        // That is why we create 2 separate S3 clients. One for internal traffic and one for external.
        private readonly S3FailoverHelper S3InternalClient;
        private readonly HttpClient httpClient = new();
        private readonly ILogger<S3Service> logger;

        public S3Service(ISyncItemsRepositoryAccessor syncItemsRepositoryAccessor, WampServiceAccessor wampServiceAccessor, ILogger<S3Service> logger)
        {
            this.logger = logger;
            Repositories = syncItemsRepositoryAccessor;
            ServiceAccessor = wampServiceAccessor;
            S3Client = new S3FailoverHelper(
                S3ClientFactory.CreateS3Clients(
                    Constants.S3_SERVICE_URL,
                    Constants.S3_REGION,
                    Constants.S3_ACCESS_KEY_ID,
                    Constants.S3_ACCESS_KEY,
                    forcePathStyle: true
                ),
                logger: logger
            );

            if (!string.IsNullOrEmpty(Constants.S3_INTERNAL_SERVICE_URL) && !string.IsNullOrEmpty(Constants.S3_INTERNAL_BUCKET_NAME))
            {
                S3InternalClient = new S3FailoverHelper(
                    S3ClientFactory.CreateS3Clients(
                        Constants.S3_INTERNAL_SERVICE_URL,
                        Constants.S3_REGION,
                        Constants.S3_ACCESS_KEY_ID,
                        Constants.S3_ACCESS_KEY,
                        forcePathStyle: true
                    ),
                    logger: logger
                );
            }
            else S3InternalClient = S3Client;

            AWSConfigsS3.UseSignatureVersion4 = true;
        }

        public async Task DeleteObjectAsync(string userId, string name)
        {
            var objectName = GetFullObjectName(userId, name) ?? throw new Exception("Invalid object name.");

            var response = await S3InternalClient.ExecuteWithFailoverAsync((client) => client.DeleteObjectAsync(INTERNAL_BUCKET_NAME, objectName), operationName: "DeleteObject", isWriteOperation: true);

            if (!IsSuccessStatusCode((int)response.HttpStatusCode))
                throw new Exception("Could not delete object.");
        }

        public async Task DeleteObjectsAsync(string userId, string[] names)
        {
            var objectsToDelete = new List<KeyVersion>();

            foreach (var name in names)
            {
                var objectName = GetFullObjectName(userId, name);
                if (objectName == null) continue;

                objectsToDelete.Add(new KeyVersion { Key = objectName });
            }

            if (objectsToDelete.Count == 0)
            {
                return;
            }

            // S3 DeleteObjectsRequest supports max 1000 keys per request
            var batchSize = 1000;
            var deleteErrors = new List<DeleteError>();
            var failedBatches = 0;

            for (int i = 0; i < objectsToDelete.Count; i += batchSize)
            {
                var batch = objectsToDelete.Skip(i).Take(batchSize).ToList();
                var deleteObjectsResponse = await S3InternalClient.ExecuteWithFailoverAsync(
                    (client) => client.DeleteObjectsAsync(new DeleteObjectsRequest
                    {
                        BucketName = INTERNAL_BUCKET_NAME,
                        Objects = batch,
                    }),
                    operationName: "DeleteObjects",
                    isWriteOperation: true
                );

                if (!IsSuccessStatusCode((int)deleteObjectsResponse.HttpStatusCode))
                {
                    failedBatches++;
                }

                if (deleteObjectsResponse.DeleteErrors.Count > 0)
                {
                    deleteErrors.AddRange(deleteObjectsResponse.DeleteErrors);
                }
            }

            if (failedBatches > 0 || deleteErrors.Count > 0)
            {
                var errorParts = new List<string>();

                if (failedBatches > 0)
                {
                    errorParts.Add($"{failedBatches} batch(es) failed with unsuccessful status code");
                }

                if (deleteErrors.Count > 0)
                {
                    errorParts.Add(string.Join(", ", deleteErrors.Select(e => $"{e.Key}: {e.Message}")));
                }

                throw new Exception(string.Join("; ", errorParts));
            }
        }

        public async Task DeleteDirectoryAsync(string userId)
        {
            var request = new ListObjectsV2Request
            {
                BucketName = INTERNAL_BUCKET_NAME,
                Prefix = userId,
            };

            var response = new ListObjectsV2Response();
            var keys = new List<KeyVersion>();
            do
            {
                response = await S3InternalClient.ExecuteWithFailoverAsync((client) => client.ListObjectsV2Async(request), operationName: "ListObjectsV2");
                response.S3Objects.ForEach(obj => keys.Add(new KeyVersion
                {
                    Key = obj.Key,
                }));

                request.ContinuationToken = response.NextContinuationToken;
            }
            while (response.IsTruncated);

            if (keys.Count <= 0) return;

            var deleteObjectsResponse = await S3InternalClient.ExecuteWithFailoverAsync((client) => client.DeleteObjectsAsync(new DeleteObjectsRequest
            {
                BucketName = INTERNAL_BUCKET_NAME,
                Objects = keys,
            }), operationName: "DeleteObjects", isWriteOperation: true);

            if (!IsSuccessStatusCode((int)deleteObjectsResponse.HttpStatusCode))
                throw new Exception("Could not delete directory.");
        }

        public async Task<long> GetObjectSizeAsync(string userId, string name)
        {
            var url = await this.GetPresignedURLAsync(userId, name, HttpVerb.HEAD, S3ClientMode.INTERNAL);
            if (url == null) return 0;

            var request = new HttpRequestMessage(HttpMethod.Head, url);
            var response = await httpClient.SendAsync(request);
            return response.Content.Headers.ContentLength ?? 0;
        }


        public async Task<string?> GetUploadObjectUrlAsync(string userId, string name)
        {
            return await this.GetPresignedURLAsync(userId, name, HttpVerb.PUT);
        }

        public async Task<string?> GetInternalUploadObjectUrlAsync(string userId, string name)
        {
            return await this.GetPresignedURLAsync(userId, name, HttpVerb.PUT, S3ClientMode.INTERNAL);
        }

        public async Task<string?> GetDownloadObjectUrlAsync(string userId, string name)
        {
            // var subscriptionService = await WampServers.SubscriptionServer.GetServiceAsync<IUserSubscriptionService>(SubscriptionServerTopics.UserSubscriptionServiceTopic);
            // var subscription = await subscriptionService.GetUserSubscriptionAsync(Clients.Notesnook.Id, userId);

            // var size = await GetObjectSizeAsync(userId, name);
            // if (StorageHelper.IsFileSizeExceeded(subscription, size))
            // {
            //     var fileSizeLimit = StorageHelper.GetFileSizeLimitForPlan(subscription);
            //     throw new Exception($"You cannot download files larger than {StorageHelper.FormatBytes(fileSizeLimit)} on this plan.");
            // }

            var url = await this.GetPresignedURLAsync(userId, name, HttpVerb.GET);
            if (url == null) return null;
            return url;
        }

        public async Task<MultipartUploadMeta> StartMultipartUploadAsync(string userId, string name, int parts, string? uploadId = null)
        {
            var objectName = GetFullObjectName(userId, name);
            if (userId == null || objectName == null) throw new Exception("Could not initiate multipart upload.");

            if (string.IsNullOrEmpty(uploadId))
            {
                var response = await S3InternalClient.ExecuteWithFailoverAsync((client) => client.InitiateMultipartUploadAsync(INTERNAL_BUCKET_NAME, objectName), operationName: "InitiateMultipartUpload", isWriteOperation: true);
                if (!IsSuccessStatusCode((int)response.HttpStatusCode)) throw new Exception("Failed to initiate multipart upload.");

                uploadId = response.UploadId;
            }

            var signedUrls = new string[parts];
            for (var i = 0; i < parts; ++i)
            {
                signedUrls[i] = await GetPresignedURLForUploadPartAsync(objectName, uploadId, i + 1);
            }

            return new MultipartUploadMeta
            {
                UploadId = uploadId,
                Parts = signedUrls
            };
        }

        public async Task AbortMultipartUploadAsync(string userId, string name, string uploadId)
        {
            var objectName = GetFullObjectName(userId, name);
            if (userId == null || objectName == null) throw new Exception("Could not abort multipart upload.");

            var response = await S3InternalClient.ExecuteWithFailoverAsync((client) => client.AbortMultipartUploadAsync(INTERNAL_BUCKET_NAME, objectName, uploadId), operationName: "AbortMultipartUpload", isWriteOperation: true);
            if (!IsSuccessStatusCode(((int)response.HttpStatusCode))) throw new Exception("Failed to abort multipart upload.");
        }

        private async Task<long> GetMultipartUploadSizeAsync(string userId, string key, string uploadId)
        {
            var objectName = GetFullObjectName(userId, key) ?? throw new Exception("Invalid object name.");
            long totalSize = 0;
            var marker = 0;
            while (true)
            {
                var request = new ListPartsRequest
                {
                    BucketName = INTERNAL_BUCKET_NAME,
                    Key = objectName,
                    UploadId = uploadId,
                    PartNumberMarker = marker.ToString()
                };
                var parts = await S3InternalClient.ExecuteWithFailoverAsync(
                    (client) => client.ListPartsAsync(request),
                    operationName: "ListParts",
                    isWriteOperation: true);
                foreach (var part in parts.Parts)
                {
                    totalSize = checked(totalSize + part.Size);
                }

                if (!parts.IsTruncated)
                    break;
                if (parts.NextPartNumberMarker <= marker)
                    throw new Exception("S3 returned an invalid parts page.");
                marker = parts.NextPartNumberMarker;
            }
            return totalSize;
        }

        public async Task CompleteMultipartUploadAsync(string userId, CompleteMultipartUploadRequest uploadRequest)
        {
            var objectName = GetFullObjectName(userId, uploadRequest.Key);
            if (userId == null || objectName == null) throw new Exception("Could not abort multipart upload.");

            var userSettings = await Repositories.UsersSettings.FindOneAsync((u) => u.UserId == userId);
            if (userSettings == null)
            {
                await this.AbortMultipartUploadAsync(userId, uploadRequest.Key, uploadRequest.UploadId);
                throw new Exception("User settings not found.");
            }
            var observedStorageLimit = userSettings.StorageLimit;
            userSettings.StorageLimit = StorageHelper.RolloverStorageLimit(userSettings.StorageLimit);
            long fileSize = 0;

            if (!Constants.IS_SELF_HOSTED)
            {
                var subscription = await ServiceAccessor.UserSubscriptionService.GetUserSubscriptionAsync(Clients.Notesnook.Id, userId) ?? throw new Exception("User subscription not found.");

                fileSize = await GetMultipartUploadSizeAsync(userId, uploadRequest.Key, uploadRequest.UploadId);
                if (StorageHelper.IsFileSizeExceeded(subscription, fileSize))
                {
                    await this.AbortMultipartUploadAsync(userId, uploadRequest.Key, uploadRequest.UploadId);
                    throw new Exception("Max file size exceeded.");
                }

                if (StorageHelper.IsStorageLimitReached(subscription, userSettings.StorageLimit.Value + fileSize))
                {
                    await this.AbortMultipartUploadAsync(userId, uploadRequest.Key, uploadRequest.UploadId);
                    throw new Exception("Storage limit reached.");
                }
            }

            uploadRequest.Key = objectName;
            uploadRequest.BucketName = INTERNAL_BUCKET_NAME;
            var response = await S3InternalClient.ExecuteWithFailoverAsync((client) => client.CompleteMultipartUploadAsync(uploadRequest), operationName: "CompleteMultipartUpload", isWriteOperation: true);
            if (!IsSuccessStatusCode((int)response.HttpStatusCode)) throw new Exception("Failed to complete multipart upload.");

            if (!Constants.IS_SELF_HOSTED)
            {
                try
                {
                    await IncrementStorageUsageAsync(userId, fileSize, observedStorageLimit);
                }
                catch (Exception ex)
                {
                    // The object is already committed. Accounting is best effort so
                    // a Mongo failure cannot turn a successful upload into a retry.
                    logger.LogError(ex, "Failed to account for multipart attachment usage for user {UserId}.", userId);
                }
            }
        }

        public async Task IncrementStorageUsageAsync(string userId, long fileSize, Limit? observedStorageLimit)
        {
            var collection = Repositories.UsersSettings.Collection;
            var userFilter = Builders<UserSettings>.Filter.Eq(u => u.UserId, userId);

            for (var attempt = 0; attempt < 3; attempt++)
            {
                var now = DateTimeOffset.UtcNow;
                var monthStart = new DateTimeOffset(now.Year, now.Month, 1, 0, 0, 0, TimeSpan.Zero);
                var nextMonthStart = monthStart.AddMonths(1);
                var nowMilliseconds = now.ToUnixTimeMilliseconds();
                var monthStartMilliseconds = monthStart.ToUnixTimeMilliseconds();
                var nextMonthStartMilliseconds = nextMonthStart.ToUnixTimeMilliseconds();
                var currentStorageLimit = observedStorageLimit;

                if (attempt > 0)
                {
                    currentStorageLimit = (await collection.Find(userFilter).FirstOrDefaultAsync())?.StorageLimit;
                }

                var isCurrentMonth = currentStorageLimit != null
                    && currentStorageLimit.UpdatedAt >= monthStartMilliseconds
                    && currentStorageLimit.UpdatedAt < nextMonthStartMilliseconds;

                if (!isCurrentMonth)
                {
                    var observedFilter = currentStorageLimit == null
                        ? Builders<UserSettings>.Filter.Eq(u => u.StorageLimit, null)
                        : Builders<UserSettings>.Filter.Eq("StorageLimit.UpdatedAt", currentStorageLimit.UpdatedAt);

                    var resetResult = await collection.UpdateOneAsync(
                        Builders<UserSettings>.Filter.And(userFilter, observedFilter),
                        Builders<UserSettings>.Update.Set(
                            "StorageLimit",
                            new Limit { Value = 0, UpdatedAt = nowMilliseconds }));

                    if (resetResult.MatchedCount == 0)
                        continue;
                }

                var result = await collection.UpdateOneAsync(
                    Builders<UserSettings>.Filter.And(
                        userFilter,
                        Builders<UserSettings>.Filter.Gte("StorageLimit.UpdatedAt", monthStartMilliseconds),
                        Builders<UserSettings>.Filter.Lt("StorageLimit.UpdatedAt", nextMonthStartMilliseconds)),
                    Builders<UserSettings>.Update.Combine(
                        Builders<UserSettings>.Update.Inc("StorageLimit.Value", fileSize),
                        Builders<UserSettings>.Update.Set("StorageLimit.UpdatedAt", nowMilliseconds)));

                if (result.MatchedCount > 0)
                    return;
            }

            throw new Exception("Storage usage counter was not available after rollover retries.");
        }

        private async Task<string?> GetPresignedURLAsync(string userId, string name, HttpVerb httpVerb, S3ClientMode mode = S3ClientMode.EXTERNAL)
        {
            var objectName = GetFullObjectName(userId, name);
            if (userId == null || objectName == null) return null;

            var client = mode == S3ClientMode.INTERNAL ? S3InternalClient : S3Client;
            var bucketName = mode == S3ClientMode.INTERNAL ? INTERNAL_BUCKET_NAME : BUCKET_NAME;

            return await client.ExecuteWithFailoverAsync(client =>
            {
                var request = new GetPreSignedUrlRequest
                {
                    BucketName = bucketName,
                    Expires = System.DateTime.Now.AddHours(1),
                    Verb = httpVerb,
                    Key = objectName,
                    Protocol = client.Config.ServiceURL.StartsWith("http://") ? Protocol.HTTP : Protocol.HTTPS,
                };
                return client.GetPreSignedURLAsync(request);
            }, operationName: "GetPreSignedURL");
        }

        private Task<string> GetPresignedURLForUploadPartAsync(string objectName, string uploadId, int partNumber, S3ClientMode mode = S3ClientMode.EXTERNAL)
        {

            var client = mode == S3ClientMode.INTERNAL ? S3InternalClient : S3Client;
            var bucketName = mode == S3ClientMode.INTERNAL ? INTERNAL_BUCKET_NAME : BUCKET_NAME;

            return client.ExecuteWithFailoverAsync(c => c.GetPreSignedURLAsync(new GetPreSignedUrlRequest
            {
                BucketName = bucketName,
                Expires = System.DateTime.Now.AddHours(1),
                Verb = HttpVerb.PUT,
                Key = objectName,
                PartNumber = partNumber,
                UploadId = uploadId,
                Protocol = c.Config.ServiceURL.StartsWith("http://") ? Protocol.HTTP : Protocol.HTTPS,
            }), operationName: "GetPreSignedURL");
        }

        private static string? GetFullObjectName(string userId, string name)
        {
            if (userId == null || !Regex.IsMatch(name, "[0-9a-zA-Z!" + Regex.Escape("-") + "_.*'()]")) return null;
            return $"{userId}/{name}";
        }

        static bool IsSuccessStatusCode(int statusCode)
        {
            return ((int)statusCode >= 200) && ((int)statusCode <= 299);
        }
    }
}