using Microsoft.Extensions.Localization;

using MongoDB.Driver;
using MongoDB.Entities;

using PrivaPub.ClientModels;
using PrivaPub.ClientModels.User;
using PrivaPub.Models;
using PrivaPub.Models.User;
using PrivaPub.Resources;
using PrivaPub.Infrastructure.Jobs;
using PrivaPub.Models.Jobs;
using PrivaPub.StaticServices;

using System.Globalization;
using System.Text.Json;

#pragma warning disable 8603
#pragma warning disable 8625

namespace PrivaPub.Services
{
	public class RootUsersService : IRootUsersService
	{
		readonly DbEntities DbEntities;
		readonly IPasswordHasher PasswordHasher;
		readonly IStringLocalizer Localizer;
		readonly ILogger<RootUsersService> Logger;
		readonly AppConfigurationService AppConfigurationService;
		readonly IJobQueue Jobs;
		readonly IRootSessions Sessions;
		readonly IRootRemoval Removal;

		public RootUsersService(
			IJobQueue jobs,
			IRootSessions sessions,
			IRootRemoval removal,
			IStringLocalizer<GenericRes> localizer,
			ILogger<RootUsersService> logger,
			IPasswordHasher passwordHasher,
			DbEntities dbEntities,
			AppConfigurationService appConfigurationService)
		{
			Jobs = jobs;
			Sessions = sessions;
			Removal = removal;
			DbEntities = dbEntities;
			PasswordHasher = passwordHasher;
			Localizer = localizer;
			Logger = logger;
			AppConfigurationService = appConfigurationService;
		}

		public const string NoMatch = "That username and password do not match.";
		static string _decoy;

		// a hash nobody's password matches, so an unknown login costs the same hashing as a wrong password
		string Decoy => _decoy ??= PasswordHasher.Hash(Convert.ToHexString(System.Security.Cryptography.RandomNumberGenerator.GetBytes(16)));

		public async Task<WebResult> SignUpAsync(LoginForm signUpForm)
		{
			var result = new WebResult();
			try
			{
				signUpForm.UserName = signUpForm.UserName.ToLower();
				if (await DbEntities.RootUsers.Match(u => u.UserName == signUpForm.UserName).ExecuteAnyAsync())
					return result.Invalidate(Localizer["Username '{0}' already taken.", signUpForm.UserName]);

				var signUpPasswordHashed = PasswordHasher.Hash(signUpForm.Password);
				var newUser = new RootUser
				{
					UserName = signUpForm.UserName,
					HashedPassword = signUpPasswordHashed
				};

				var cultureLanguage = CultureInfo.CurrentCulture.TwoLetterISOLanguageName;
				var language = await DbEntities.Languages.Match(l => l.International2Code == cultureLanguage).ExecuteFirstAsync();
				newUser.Settings = new RootUserSettings
				{
					LanguageCode = language?.International2Code ?? "en",
					LightThemeIndexColour = signUpForm.LightThemeIndexColour,
					DarkThemeIndexColour = signUpForm.DarkThemeIndexColour,
					IconsThemeIndexColour = signUpForm.IconsThemeIndexColour,
					ThemeIsDarkGray = signUpForm.ThemeIsDarkGray,
					ThemeIsLightGray = signUpForm.ThemeIsLightGray,
					PreferSystemTheming = signUpForm.PreferSystemTheming,
					ThemeIsDarkMode = signUpForm.ThemeIsDarkMode
				};
				await DB.Default.SaveAsync(newUser);

				result.Data = (newUser, ToViewSettings(newUser.Settings));

				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(SignUpAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public async Task<WebResult> LoginAsync(LoginForm loginForm)
		{
			var result = new WebResult();
			try
			{
				// One answer, after the same work, whether the login is unknown, deleted or the password wrong: sign-in must not
				// tell anyone which logins exist. Only someone who knows the password learns the login is banned.
				loginForm.UserName = loginForm.UserName.ToLower();
				var user = await DbEntities.RootUsers.Match(u => u.UserName == loginForm.UserName && u.DeletedAt == null).ExecuteFirstAsync();
				var (verified, needsUpgrade) = PasswordHasher.Check(user?.HashedPassword ?? Decoy, loginForm.Password);
				if (user?.HashedPassword == default || !verified)
					return result.Invalidate(Localizer[NoMatch]);
				if (user.IsBanned)
					return result.Invalidate(Localizer["User '{0}' banned.", user.UserName]);

				// hashed again at today's iterations; matched on the old hash, so two sign-ins at once never undo each other
				if (needsUpgrade)
				{
					var oldHash = user.HashedPassword;
					user.HashedPassword = PasswordHasher.Hash(loginForm.Password);
					await DB.Default.Update<RootUser>()
						.Match(u => u.ID == user.ID && u.HashedPassword == oldHash)
						.Modify(u => u.HashedPassword, user.HashedPassword)
						.ExecuteAsync();
				}

				var userSettingsResult = await GetUserSettingsAsync(user.ID, loginForm);
				var userSettings = (ViewUserSettings)userSettingsResult.Data;

				result.Data = (user, userSettings);

				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(LoginAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public async Task<WebResult> UpdateUserSettingsAsync(ViewUserSettings userSettings, string userId)
		{
			var result = new WebResult();
			try
			{
				var isSupportedLanguage = AppConfigurationService.AppConfiguration.SupportedLanguages.Contains(userSettings.LanguageCode);
				if (!isSupportedLanguage)
					return result.Invalidate(Localizer["Language code '{0}' unsupported.", userSettings.LanguageCode]);

				var languageCodeExists = await DbEntities.Languages
					.Match(l => l.International2Code == userSettings.LanguageCode).ExecuteAnyAsync();
				if (!languageCodeExists)
					return result.Invalidate(Localizer["Language code '{0}' doesn't exist.", userSettings.LanguageCode]);

				var language = await DbEntities.Languages.Match(l => l.International2Code == userSettings.LanguageCode)
					.ExecuteFirstAsync();
				_ = await DB.Default.Update<RootUser>()
					.MatchID(userId)
					.Modify(u => u.Settings.LanguageCode, language.International2Code)
					.Modify(u => u.Settings.LightThemeIndexColour, userSettings.LightThemeIndexColour)
					.Modify(u => u.Settings.DarkThemeIndexColour, userSettings.DarkThemeIndexColour)
					.Modify(u => u.Settings.PreferSystemTheming, userSettings.PreferSystemTheming)
					.Modify(u => u.Settings.ThemeIsDarkMode, userSettings.ThemeIsDarkMode)
					.Modify(u => u.Settings.ThemeIsDarkGray, userSettings.ThemeIsDarkGray)
					.Modify(u => u.Settings.ThemeIsLightGray, userSettings.ThemeIsLightGray)
					.Modify(u => u.Settings.IconsThemeIndexColour, userSettings.IconsThemeIndexColour)
					.Modify(u => u.Settings.SavedAt, DateTime.UtcNow)
					.Modify(u => u.UpdatedAt, DateTime.UtcNow)
					.ExecuteAsync();

				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(UpdateUserSettingsAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public async Task<WebResult> UpdateUserPasswordAsync(UserPasswordForm userPasswordForm, string userId)
		{
			var result = new WebResult();
			try
			{
				var user = await DbEntities.RootUsers.Match(u => u.ID == userId && u.DeletedAt == null).ExecuteFirstAsync();

				if (user == null)
					return result.Invalidate(Localizer["Username '{0}' not found.", userId]);

				var (verified, needsUpgrade) = PasswordHasher.Check(user.HashedPassword, userPasswordForm.OldPassword);

				if (!verified)
					return result.Invalidate(Localizer["Wrong password."]);

				await DB.Default.Update<RootUser>().MatchID(user.ID)
					.Modify(u => u.HashedPassword, PasswordHasher.Hash(userPasswordForm.NewPassword))
					.Modify(u => u.UpdatedAt, DateTime.UtcNow)
					.ExecuteAsync();
				// whoever else is signed in may be why the password changed: every session ends, and the caller gets a new one
				await Sessions.Revoke(user.ID, CancellationToken.None);
				user = await DbEntities.RootUsers.MatchID(user.ID).ExecuteFirstAsync();
				result.Data = (user, ToViewSettings(user.Settings));
				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(UpdateUserPasswordAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public async Task<WebResult> RemoveUserAsync(UsersIds usersIds)
		{
			var result = new WebResult();
			try
			{
				var removed = 0;
				foreach (var id in usersIds.UserIdList.Distinct())
					if (await Removal.Remove(id, CancellationToken.None))
						removed++;
				if (removed == 0)
					return result.Invalidate(Localizer["User already deleted."]);
				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(RemoveUserAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		// A root deletes itself only with its password, so a stolen session cannot.
		public async Task<WebResult> RemoveSelfAsync(string rootId, string password)
		{
			var result = new WebResult();
			try
			{
				var user = await DbEntities.RootUsers.MatchID(rootId).Match(u => u.DeletedAt == null).ExecuteFirstAsync();
				var (verified, _) = PasswordHasher.Check(user?.HashedPassword ?? Decoy, password ?? string.Empty);
				if (user?.HashedPassword == default || !verified)
					return result.Invalidate(Localizer[NoMatch], StatusCodes.Status403Forbidden);
				await Removal.Remove(user.ID, CancellationToken.None);
				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(RemoveSelfAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public async Task<WebResult> BanUserAsync(UsersIds usersIds)
		{
			var result = new WebResult();
			try
			{
				await DB.Default.Update<RootUser>()
					.Match(u => usersIds.UserIdList.Contains(u.ID))
					.Modify(u => u.IsBanned, true)
					.ExecuteAsync();

				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(BanUserAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public async Task<WebResult> UnbanUserAsync(UsersIds usersIds)
		{
			var result = new WebResult();
			try
			{
				await DB.Default.Update<RootUser>()
					.Match(u => usersIds.UserIdList.Contains(u.ID))
					.Modify(u => u.IsBanned, false)
					.ExecuteAsync();

				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(UnbanUserAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public async Task<WebResult> GetUserSettingsAsync(string userId, LoginForm loginForm = default)
		{
			var result = new WebResult();
			try
			{
				var user = await DbEntities.RootUsers.MatchID(userId).ExecuteFirstAsync();
				if (user == default)
					return result.Invalidate(Localizer["User not found."], StatusCodes.Status404NotFound);

				if (loginForm != default && loginForm.ThemeIsDarkMode != user.Settings.ThemeIsDarkMode)
				{
					user.Settings.ThemeIsDarkMode = loginForm.ThemeIsDarkMode;
					await DB.Default.Update<RootUser>()
						.MatchID(userId)
						.Modify(u => u.Settings.ThemeIsDarkMode, loginForm.ThemeIsDarkMode)
						.ExecuteAsync();
				}

				result.Data = ToViewSettings(user.Settings);
				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(GetUserSettingsAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public const string RecoverySent = "If that account has an email address, a recovery link is on its way. It works for one hour.";

		// The same answer, after the same work, whether the account exists, has an email or can be written to: recovery must
		// not tell anyone which logins or addresses exist. RecoveryJob does the rest, out of the request.
		public async Task<WebResult> SetupAndSendRecoveryEmail(PasswordRecoveryForm passwordRecoveryForm, string host)
		{
			var result = new WebResult();
			try
			{
				var userName = passwordRecoveryForm.UserName?.ToLowerInvariant();
				var user = passwordRecoveryForm.IsEmailDisabled
					? await DbEntities.RootUsers.Match(u => u.UserName == userName && u.DeletedAt == null).ExecuteFirstAsync()
					: await DbEntities.RootUsers.Match(u => u.Email == passwordRecoveryForm.Email && u.IsEmailValidated && u.DeletedAt == null).ExecuteFirstAsync();
				await Jobs.Enqueue(JobKind.SendRecovery, JsonSerializer.Serialize(new RecoveryPayload(user?.ID, host)), RecoveryJob.Host,
					dedupeKey: default, CancellationToken.None);
				result.Data = Localizer[RecoverySent].Value;
				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(SetupAndSendRecoveryEmail)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		Task<EmailRecovery> LiveRecovery(string recoveryCode)
		{
			var hash = RecoveryJob.Hash(recoveryCode);
			var now = DateTime.UtcNow;
			return DbEntities.EmailRecoveries.Match(er => er.CodeHash == hash && er.ExpiresAt > now).ExecuteFirstAsync();
		}

		public async Task<WebResult> IsValidRecoveryCode(string recoveryCode)
		{
			var result = new WebResult();
			try
			{
				result.Data = await LiveRecovery(recoveryCode) != default;
				return result;
			}
			catch (Exception ex)
			{
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		// A recovered password ends every session the root had: whoever had them may be why it was recovered.
		public async Task<WebResult> ChangePassword(NewPasswordForm newPasswordForm)
		{
			var result = new WebResult();
			try
			{
				var recovery = await LiveRecovery(newPasswordForm.RecoveryCode);
				var user = recovery == default ? default
					: await DbEntities.RootUsers.MatchID(recovery.RootUserId).Match(u => u.DeletedAt == null && !u.IsBanned).ExecuteFirstAsync();
				if (user == default)
					return result.Invalidate(Localizer["Invalid recovery code."], StatusCodes.Status404NotFound);

				await DB.Default.Update<RootUser>().MatchID(user.ID)
					.Modify(u => u.HashedPassword, PasswordHasher.Hash(newPasswordForm.NewPassword))
					.Modify(u => u.UpdatedAt, DateTime.UtcNow)
					.ExecuteAsync();
				await DB.Default.DeleteAsync<EmailRecovery>(er => er.RootUserId == user.ID);
				await Sessions.Revoke(user.ID, CancellationToken.None);
				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(ChangePassword)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		static ViewUserSettings ToViewSettings(RootUserSettings settings) => new()
		{
			LanguageCode = settings.LanguageCode,
			LightThemeIndexColour = settings.LightThemeIndexColour,
			DarkThemeIndexColour = settings.DarkThemeIndexColour,
			PreferSystemTheming = settings.PreferSystemTheming,
			ThemeIsDarkMode = settings.ThemeIsDarkMode,
			IconsThemeIndexColour = settings.IconsThemeIndexColour,
			ThemeIsDarkGray = settings.ThemeIsDarkGray,
			ThemeIsLightGray = settings.ThemeIsLightGray,
			SavedAt = settings.SavedAt
		};

		public const string EmailCodeSent = "If that address can be used, a code is on its way to it. It works for one hour.";
		public const string EmailCodeInvalid = "That code is not valid.";

		public async Task<WebResult> AccountAsync(string rootId)
		{
			var result = new WebResult();
			try
			{
				var user = await DbEntities.RootUsers.MatchID(rootId).Match(u => u.DeletedAt == null).ExecuteFirstAsync();
				if (user == default)
					return result.Invalidate(Localizer["User not found."], StatusCodes.Status404NotFound);
				var now = DateTime.UtcNow;
				var pending = await DB.Default.Find<EmailVerification>().Match(v => v.RootUserId == rootId && v.ExpiresAt > now).ExecuteFirstAsync();
				result.Data = new ViewAccount
				{
					UserName = user.UserName,
					Email = user.Email,
					IsEmailValidated = user.IsEmailValidated,
					PendingEmail = pending?.Email,
					CreatedAt = user.CreatedAt
				};
				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(AccountAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		// Only with the password, so a stolen session can't move recovery to its own inbox. The answer is the same sentence
		// whether or not the address is free; EmailVerificationJob sends the code, or nothing when another login holds it.
		public async Task<WebResult> RequestEmailChangeAsync(string rootId, EmailChangeForm form)
		{
			var result = new WebResult();
			try
			{
				var user = await DbEntities.RootUsers.MatchID(rootId).Match(u => u.DeletedAt == null).ExecuteFirstAsync();
				var (verified, _) = PasswordHasher.Check(user?.HashedPassword ?? Decoy, form.Password ?? string.Empty);
				if (user?.HashedPassword == default || !verified)
					return result.Invalidate(Localizer["Wrong password."], StatusCodes.Status403Forbidden);

				await DB.Default.DeleteAsync<EmailVerification>(v => v.RootUserId == user.ID);
				var pending = new EmailVerification
				{
					RootUserId = user.ID,
					Email = form.Email.Trim().ToLowerInvariant(),
					ExpiresAt = DateTime.UtcNow + EmailVerification.Lifetime
				};
				await DB.Default.SaveAsync(pending);
				await Jobs.Enqueue(JobKind.SendEmailVerification, JsonSerializer.Serialize(new EmailVerificationPayload(pending.ID)),
					EmailVerificationJob.Host, dedupeKey: default, CancellationToken.None);
				result.Data = Localizer[EmailCodeSent].Value;
				return result;
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(RequestEmailChangeAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		// One answer for every failure (wrong, expired, five tries spent, or the address verified by another login meanwhile)
		public async Task<WebResult> VerifyEmailAsync(string rootId, string code)
		{
			var result = new WebResult();
			try
			{
				var now = DateTime.UtcNow;
				var pending = await DB.Default.Find<EmailVerification>().Match(v => v.RootUserId == rootId && v.ExpiresAt > now).ExecuteFirstAsync();
				if (pending == default || string.IsNullOrEmpty(pending.CodeHash))
					return result.Invalidate(Localizer[EmailCodeInvalid]);
				if (pending.CodeHash != RecoveryJob.Hash(code?.Trim()))
				{
					if (pending.Attempts + 1 >= EmailVerification.MaxAttempts)
						await DB.Default.DeleteAsync<EmailVerification>(pending.ID);
					else
						await DB.Default.Update<EmailVerification>().MatchID(pending.ID).Modify(b => b.Inc(v => v.Attempts, 1)).ExecuteAsync();
					return result.Invalidate(Localizer[EmailCodeInvalid]);
				}
				await DB.Default.DeleteAsync<EmailVerification>(pending.ID);
				if (await DbEntities.RootUsers.Match(u => u.Email == pending.Email && u.IsEmailValidated && u.ID != rootId && u.DeletedAt == null).ExecuteAnyAsync())
					return result.Invalidate(Localizer[EmailCodeInvalid]);

				await DB.Default.Update<RootUser>().MatchID(rootId)
					.Modify(u => u.Email, pending.Email)
					.Modify(u => u.IsEmailValidated, true)
					.Modify(u => u.UpdatedAt, now)
					.ExecuteAsync();
				return await AccountAsync(rootId);
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(VerifyEmailAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}

		public async Task<WebResult> RemoveEmailAsync(string rootId, string password)
		{
			var result = new WebResult();
			try
			{
				var user = await DbEntities.RootUsers.MatchID(rootId).Match(u => u.DeletedAt == null).ExecuteFirstAsync();
				var (verified, _) = PasswordHasher.Check(user?.HashedPassword ?? Decoy, password ?? string.Empty);
				if (user?.HashedPassword == default || !verified)
					return result.Invalidate(Localizer["Wrong password."], StatusCodes.Status403Forbidden);

				await DB.Default.Update<RootUser>().MatchID(rootId)
					.Modify(u => u.Email, null)
					.Modify(u => u.IsEmailValidated, false)
					.Modify(u => u.UpdatedAt, DateTime.UtcNow)
					.ExecuteAsync();
				await DB.Default.DeleteAsync<EmailVerification>(v => v.RootUserId == rootId);
				await DB.Default.DeleteAsync<EmailRecovery>(r => r.RootUserId == rootId);
				return await AccountAsync(rootId);
			}
			catch (Exception ex)
			{
				Logger.LogError(ex, $"{nameof(RootUsersService)}.{nameof(RemoveEmailAsync)}()");
				return result.Invalidate(Localizer["Something went wrong."], exception: ex);
			}
		}
	}
}