using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Channels;
using System.Threading.Tasks;
using System.Diagnostics;
using AudibleApi;
using AudibleApi.Common;
using Dinah.Core;
using Polly;
using Polly.Retry;
using System.Threading;

#nullable enable
namespace AudibleUtilities
{
	/// <summary>USE THIS from within Libation. It wraps the call with correct JSONPath</summary>
	public class ApiExtended
	{
		public static Func<Account, ILoginChoiceEager>? LoginChoiceFactory { get; set; }
		public Api Api { get; private set; }

		private const int MaxConcurrency = 10;
		private const int BatchSize = 50;

		private ApiExtended(Api api) => Api = api;

		/// <summary>Get api from existing tokens else login with 'eager' choice. External browser url is provided. Response can be external browser login or continuing with native api callbacks.</summary>
		public static async Task<ApiExtended> CreateAsync(Account account)
		{
			ArgumentValidator.EnsureNotNull(account, nameof(account));
			ArgumentValidator.EnsureNotNull(account.AccountId, nameof(account.AccountId));
			ArgumentValidator.EnsureNotNull(account.Locale, nameof(account.Locale));

			try
			{
				Serilog.Log.Logger.Information("{@DebugInfo}", new
				{
					AccountMaskedLogEntry = account.MaskedLogEntry
				});

				var api = await EzApiCreator.GetApiAsync(
						account.Locale,
						AudibleApiStorage.AccountsSettingsFile,
						account.GetIdentityTokensJsonPath());
				return new ApiExtended(api);
			}
			catch
			{
				if (LoginChoiceFactory is null)
					throw new InvalidOperationException($"The UI module must first set {nameof(LoginChoiceFactory)} before attempting to create the api");

				Serilog.Log.Logger.Information("{@DebugInfo}", new
				{
					LoginType = nameof(ILoginChoiceEager),
					Account = account.MaskedLogEntry ?? "[null]",
					LocaleName = account.Locale?.Name
				});

				var api = await EzApiCreator.GetApiAsync(
					LoginChoiceFactory(account),
					account.Locale,
					AudibleApiStorage.AccountsSettingsFile,
					account.GetIdentityTokensJsonPath());

				return new ApiExtended(api);
			}
		}	

		private static AsyncRetryPolicy policy { get; }
			= Policy.Handle<Exception>()
			// 2 retries == 3 total
			.RetryAsync(2);

		public Task<List<Item>> GetLibraryValidatedAsync(LibraryOptions libraryOptions, bool importEpisodes = true)
		{
			// bug on audible's side. the 1st time after a long absence, a query to get library will return without titles or authors. a subsequent identical query will be successful. this is true whether or not tokens are refreshed
			// worse, this 1st dummy call doesn't seem to help:
			//    var page = await api.GetLibraryAsync(new AudibleApi.LibraryOptions { NumberOfResultPerPage = 1, PageNumber = 1, PurchasedAfter = DateTime.Now.AddYears(-20), ResponseGroups = AudibleApi.LibraryOptions.ResponseGroupOptions.ALL_OPTIONS });
			// i don't want to incur the cost of making a full dummy call every time because it fails sometimes
			return policy.ExecuteAsync(() => getItemsAsync(libraryOptions, importEpisodes));
		}

		private async Task<List<Item>> getItemsAsync(LibraryOptions libraryOptions, bool importEpisodes)
		{
			Serilog.Log.Logger.Debug("Beginning library scan.");

			List<Item> items = new();
			var sw = Stopwatch.StartNew();
			var totalTime = TimeSpan.Zero;
			using var semaphore = new SemaphoreSlim(MaxConcurrency);

			var episodeChannel = Channel.CreateUnbounded<string>(new UnboundedChannelOptions { SingleReader = true, SingleWriter = true });
			var batchReaderTask = readAllAsinsAsync(episodeChannel.Reader, semaphore);

			//Scan the library for all added books.
			//Get relationship asins from episode-type items and write them to episodeChannel where they will be batched and queried.
			await foreach (var item in Api.GetLibraryItemsPagesAsync(libraryOptions, BatchSize, semaphore))
			{
				if (importEpisodes)
				{
					var episodes = item.Where(i => i.IsEpisodes).ToList();
					var series = item.Where(i => i.IsSeriesParent).ToList();

					var parentAsins = episodes
						.SelectMany(i => i.Relationships)
						.Where(r => r.RelationshipToProduct == RelationshipToProduct.Parent)
						.Select(r => r.Asin);

					var episodeAsins = series
						.SelectMany(i => i.Relationships)
						.Where(r => r.RelationshipToProduct == RelationshipToProduct.Child && r.RelationshipType == RelationshipType.Episode)
						.Select(r => r.Asin);

					foreach (var asin in parentAsins.Concat(episodeAsins))
						episodeChannel.Writer.TryWrite(asin);

					items.AddRange(episodes);
					items.AddRange(series);
				}

				items.AddRange(item.Where(i => !i.IsSeriesParent && !i.IsEpisodes));
			}

			sw.Stop();
			totalTime += sw.Elapsed;
			Serilog.Log.Logger.Debug("Library scan complete after {elappsed_ms} ms. Found {count} books and series. Waiting on series episode scans to complete.", sw.ElapsedMilliseconds, items.Count);
			sw.Restart();

			//Signal that we're done adding asins
			episodeChannel.Writer.Complete();

			//Wait for all episodes/parents to be retrived
			var allEps = await batchReaderTask;

			sw.Stop();
			totalTime += sw.Elapsed;
			Serilog.Log.Logger.Debug("Episode scan complete after {elappsed_ms} ms. Found {count} episodes and series .", sw.ElapsedMilliseconds, allEps.Count);
			sw.Restart();

			Serilog.Log.Logger.Debug("Begin indexing series episodes");
			items.AddRange(allEps);

			//Set the Item.Series info for episodes and parents.
			foreach (var parent in items.Where(i => i.IsSeriesParent))
			{
				var children = items.Where(i => i.IsEpisodes && i.Relationships.Any(r => r.Asin == parent.Asin));
				SetSeries(parent, children);
			}

			int orphansRemoved = items.RemoveAll(i => (i.IsEpisodes || i.IsSeriesParent) && i.Series is null);
			if (orphansRemoved > 0)
				Serilog.Log.Debug("{orphansRemoved} podcast orphans not imported", orphansRemoved);

			sw.Stop();
			totalTime += sw.Elapsed;
			Serilog.Log.Logger.Information("Completed indexing series episodes after {elappsed_ms} ms.", sw.ElapsedMilliseconds);
			Serilog.Log.Logger.Information($"Completed library scan in {totalTime.TotalMilliseconds:F0} ms.");

			var allExceptions = IValidator.GetAllValidators().SelectMany(v => v.Validate(items)).ToList();
			if (allExceptions?.Count > 0)
				throw new ImportValidationException(items, allExceptions);

			return items;
		}

		#region episodes and podcasts

		/// <summary>
		/// Read asins from the channel and request catalog item info in batches of <see cref="BatchSize"/>. Blocks until <paramref name="channelReader"/> is closed.
		/// </summary>
		/// <param name="channelReader">Input asins to batch</param>
		/// <param name="semaphore">Shared semaphore to limit concurrency</param>
		/// <returns>All <see cref="Item"/>s of asins written to the channel.</returns>
		private async Task<List<Item>> readAllAsinsAsync(ChannelReader<string> channelReader, SemaphoreSlim semaphore)
		{
			int batchNum = 1;
			List<Task<List<Item>>> getTasks = new();

			while (await channelReader.WaitToReadAsync())
			{
				List<string> asins = new();

				while (asins.Count < BatchSize && await channelReader.WaitToReadAsync())
				{
					var asin = await channelReader.ReadAsync();

					if (!asins.Contains(asin))
						asins.Add(asin);
				}
				await semaphore.WaitAsync();
				getTasks.Add(getProductsAsync(batchNum++, asins, semaphore));
			}

			var completed = await Task.WhenAll(getTasks);
			//We only want Series parents and Series episodes. Explude other relationship types (e.g. 'season')
			return completed.SelectMany(l => l).Where(i => i.IsSeriesParent || i.IsEpisodes).ToList();
		}

		private async Task<List<Item>> getProductsAsync(int batchNum, List<string> asins, SemaphoreSlim semaphore)
		{
			Serilog.Log.Logger.Debug($"Batch {batchNum} Begin: Fetching {asins.Count} asins");
			try
			{
				var sw = Stopwatch.StartNew();
				var items = await Api.GetCatalogProductsAsync(asins, CatalogOptions.ResponseGroupOptions.Rating | CatalogOptions.ResponseGroupOptions.Media
					| CatalogOptions.ResponseGroupOptions.Relationships | CatalogOptions.ResponseGroupOptions.ProductDesc
					| CatalogOptions.ResponseGroupOptions.Contributors | CatalogOptions.ResponseGroupOptions.ProvidedReview
					| CatalogOptions.ResponseGroupOptions.ProductPlans | CatalogOptions.ResponseGroupOptions.Series
					| CatalogOptions.ResponseGroupOptions.CategoryLadders | CatalogOptions.ResponseGroupOptions.ProductExtendedAttrs);
				sw.Stop();

				Serilog.Log.Logger.Debug($"Batch {batchNum} End: Retrieved {items.Count} items in {sw.ElapsedMilliseconds} ms");

				return items;
			}
			catch (Exception ex)
			{
				Serilog.Log.Logger.Error(ex, "Error fetching batch of episodes. {@DebugInfo}", new { asins });
				throw;
			}
			finally { semaphore.Release(); }
		}

		public static void SetSeries(Item parent, IEnumerable<Item> children)
		{
			ArgumentValidator.EnsureNotNull(parent, nameof(parent));
			ArgumentValidator.EnsureNotNull(children, nameof(children));

			//A series parent will always have exactly 1 Series
			parent.Series = new[]
			{
				new Series
				{
					Asin = parent.Asin,
					Sequence = "-1",
					Title = parent.TitleWithSubtitle
				}
			};

			if (parent.PurchaseDate == default)
			{
				parent.PurchaseDate = children.Select(c => c.PurchaseDate).Order().FirstOrDefault(d => d != default);

				if (parent.PurchaseDate == default)
				{
					Serilog.Log.Logger.Warning("{series} doesn't have a purchase date. Using UtcNow", parent);
					parent.PurchaseDate = DateTimeOffset.UtcNow;
				}
			}

			int lastEpNum = -1, dupeCount = 0;
			foreach (var child in children.OrderBy(i => i.EpisodeNumber).ThenBy(i => i.PublicationDateTime))
			{
				string sequence;
				if (child.EpisodeNumber is null)
				{
					// This should properly be Single() not FirstOrDefault(), but FirstOrDefault is defensive for malformed data from audible
					sequence = parent.Relationships.FirstOrDefault(r => r.Asin == child.Asin)?.Sort?.ToString() ?? "0";
				}
				else
				{
					//multipart episodes may have the same episode number
					if (child.EpisodeNumber == lastEpNum)
						dupeCount++;
					else
						lastEpNum = child.EpisodeNumber.Value;

					sequence = (lastEpNum + dupeCount).ToString();
				}

				// use parent's 'DateAdded'. DateAdded is just a convenience prop for: PurchaseDate.UtcDateTime
				child.PurchaseDate = parent.PurchaseDate;
				// parent is essentially a series
				child.Series = new[]
				{
					new Series
					{
						Asin = parent.Asin,
						Sequence = sequence,
						Title = parent.TitleWithSubtitle
					}
				};
			}
		}
		#endregion
	}
}