1 files changed, 122 insertions, 0 deletions
diff --git a/BackEnd/Timeline/Services/BasicTimelineService.cs b/BackEnd/Timeline/Services/BasicTimelineService.cs
new file mode 100644
index 00000000..0d9f64a9
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+++ b/BackEnd/Timeline/Services/BasicTimelineService.cs
@@ -0,0 +1,122 @@
+using Microsoft.EntityFrameworkCore;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Timeline.Entities;
+using Timeline.Models;
+using Timeline.Models.Validation;
+using Timeline.Services.Exceptions;
+
+namespace Timeline.Services
+{
+    /// <summary>
+    /// This service provide some basic timeline functions, which should be used internally for other services.
+    /// </summary>
+    public interface IBasicTimelineService
+    {
+        /// <summary>
+        /// Get the timeline id by name.
+        /// </summary>
+        /// <param name="timelineName">Timeline name.</param>
+        /// <returns>Id of the timeline.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when <paramref name="timelineName"/> is null.</exception>
+        /// <exception cref="ArgumentException">Throw when <paramref name="timelineName"/> is of bad format.</exception>
+        /// <exception cref="TimelineNotExistException">
+        /// Thrown when timeline with name <paramref name="timelineName"/> does not exist.
+        /// If it is a personal timeline, then inner exception is <see cref="UserNotExistException"/>.
+        /// </exception>
+        /// <remarks>
+        /// If name is of personal timeline and the timeline does not exist, it will be created if user exists.
+        /// If the user does not exist,  <see cref="TimelineNotExistException"/> will be thrown with <see cref="UserNotExistException"/> as inner exception.
+        ///</remarks>
+        Task<long> GetTimelineIdByName(string timelineName);
+    }
+
+
+    public class BasicTimelineService : IBasicTimelineService
+    {
+        private readonly DatabaseContext _database;
+
+        private readonly IBasicUserService _basicUserService;
+        private readonly IClock _clock;
+
+        private readonly GeneralTimelineNameValidator _generalTimelineNameValidator = new GeneralTimelineNameValidator();
+
+        public BasicTimelineService(DatabaseContext database, IBasicUserService basicUserService, IClock clock)
+        {
+            _database = database;
+            _basicUserService = basicUserService;
+            _clock = clock;
+        }
+
+        protected TimelineEntity CreateNewTimelineEntity(string? name, long ownerId)
+        {
+            var currentTime = _clock.GetCurrentTime();
+
+            return new TimelineEntity
+            {
+                Name = name,
+                NameLastModified = currentTime,
+                OwnerId = ownerId,
+                Visibility = TimelineVisibility.Register,
+                CreateTime = currentTime,
+                LastModified = currentTime,
+                CurrentPostLocalId = 0,
+                Members = new List<TimelineMemberEntity>()
+            };
+        }
+
+        public async Task<long> GetTimelineIdByName(string timelineName)
+        {
+            if (timelineName == null)
+                throw new ArgumentNullException(nameof(timelineName));
+
+            if (!_generalTimelineNameValidator.Validate(timelineName, out var message))
+                throw new ArgumentException(message);
+
+            timelineName = TimelineHelper.ExtractTimelineName(timelineName, out var isPersonal);
+
+            if (isPersonal)
+            {
+                long userId;
+                try
+                {
+                    userId = await _basicUserService.GetUserIdByUsername(timelineName);
+                }
+                catch (UserNotExistException e)
+                {
+                    throw new TimelineNotExistException(timelineName, e);
+                }
+
+                var timelineEntity = await _database.Timelines.Where(t => t.OwnerId == userId && t.Name == null).Select(t => new { t.Id }).SingleOrDefaultAsync();
+
+                if (timelineEntity != null)
+                {
+                    return timelineEntity.Id;
+                }
+                else
+                {
+                    var newTimelineEntity = CreateNewTimelineEntity(null, userId);
+                    _database.Timelines.Add(newTimelineEntity);
+                    await _database.SaveChangesAsync();
+
+                    return newTimelineEntity.Id;
+                }
+            }
+            else
+            {
+                var timelineEntity = await _database.Timelines.Where(t => t.Name == timelineName).Select(t => new { t.Id }).SingleOrDefaultAsync();
+
+                if (timelineEntity == null)
+                {
+                    throw new TimelineNotExistException(timelineName);
+                }
+                else
+                {
+                    return timelineEntity.Id;
+                }
+            }
+        }
+    }
+}