using System;
using Microsoft.AspNetCore.Mvc;
using RestService.Model;
using RestService.Services;

namespace RestService.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class TaskController : ControllerBase
    {
        private readonly ICloudService _cloudService;

        public TaskController(ICloudService cloudService)
        {
            _cloudService = cloudService;
        }

        // POST: api/Task
        [HttpPost]
        public async Task<ActionResult> Post([FromBody] TaskItem item)
        {
            item.Id = Guid.NewGuid().ToString();
            await _cloudService.AddTaskAsync(item).ConfigureAwait(false);

            return Ok(item);
        }
    }
}

using System.Threading.Tasks;
using RestService.Model;

namespace RestService.Services
{
    public interface ICloudService
    {
        public Task AddTaskAsync(TaskItem item);
    }
}

using System.Threading.Tasks;
using RestService.Model;

namespace RestService.Services
{
    public class AzureCloudService : ICloudService
    {
        private readonly CosmosDbService _cosmosDb;

        public AzureCloudService(CosmosDbService cosmosDbService)
        {
            _cosmosDb = cosmosDbService;
        }

        public async Task AddTaskAsync(TaskItem item)
        {
            await _cosmosDb.AddTaskAsync(item).ConfigureAwait(false);
        }
    }
}

using System.Threading.Tasks;
using Microsoft.Azure.Cosmos;
using Microsoft.Azure.Cosmos.Fluent;
using Microsoft.Extensions.Configuration;
using Nito.AsyncEx;
using RestService.Model;

namespace RestService.Services
{
    public class CosmosDbService
    {
        private static IConfigurationSection _cosmosDbConfig;

        private readonly AsyncLazy<Container> _container = new AsyncLazy<Container>(async () =>
        {
            var databaseName = _cosmosDbConfig.GetSection("DatabaseName").Value;
            var containerName = _cosmosDbConfig.GetSection("ContainerName").Value;
            
            //...

            var container = client.GetContainer(databaseName, containerName);
            return container;
        });

        public CosmosDbService(IConfiguration configuration)
        {
            _cosmosDbConfig = configuration.GetSection("CosmosDb");
        }

        public async Task AddTaskAsync(TaskItem item)
        {
            await (await _container.ConfigureAwait(false)).
                CreateItemAsync(item, new PartitionKey(item.Id));
        }
    }
}

using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using Newtonsoft.Json;

namespace RestService.Model
{
    public class TaskItem
    {
        [Required]
        [JsonProperty(PropertyName = "id")]
        public string Id { get; set; }

        [Required]
        [JsonProperty(PropertyName = "name")]
        public string Name { get; set; }

        [Required]
        [JsonProperty(PropertyName = "priority")]
        public int Priority { get; set; }

        [JsonProperty(PropertyName = "description")]
        public string Description { get; set; }

        [JsonProperty(PropertyName = "attachments")]
        public List Attachments { get; set; }
        
    }
}