KeyProvider.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace ClassTranscribeDatabase.Services.MSTranscription
{
    /// <summary>
    /// Each object of this class represents an azure subscription key.
    /// </summary>
    public class Key
    {
        public string ApiKey { get; set; }
        public string Region { get; set; }
        /// <summary>
        /// This value indicates the number of tasks that are already using this key currently.
        /// </summary>
        public int Load { get; set; }
    }

    /// <summary>
    /// This class "provides" azure subscription keys for transcription tasks.
    /// It reads its key values from configuration variable "AZURE_SUBSCRIPTION_KEYS"
    /// </summary>
    public class KeyProvider
    {
        private readonly AppSettings _appSettings;
        private readonly List<Key> Keys;
        private readonly HashSet<string> CurrentVideoIds;

        public KeyProvider(AppSettings appSettings)
        {
            _appSettings = appSettings;
            string subscriptionKeys = _appSettings.AZURE_SUBSCRIPTION_KEYS ?? "";
            Keys = new List<Key>();
            CurrentVideoIds = new HashSet<string>();

            foreach (string subscriptionKey in subscriptionKeys.Split(';'))
            {
                if (!subscriptionKeys.Contains(","))
                {
                    continue;
                }
                string[] keyregion = subscriptionKey.Split(',');
                if (keyregion.Length != 2)
                {
                    throw new Exception("AZURE_SUBSCRIPTION_KEYS should be in the form key,region;key,region");
                }
                Keys.Add(new Key
                {
                    ApiKey = keyregion[0].Trim(),
                    Region = keyregion[1].Trim(),
                    Load = 0
                });
            }

        }

        /// <summary>
        /// To obtain a new key for a task
        /// </summary>
        public Key GetKey(string videoId)
        {
            if (!CurrentVideoIds.Contains(videoId))
            {
                Key key = Keys.OrderBy(k => k.Load).First();
                key.Load += 1;
                CurrentVideoIds.Add(videoId);
                return key;
            }
            else
            {
                throw new Exception("Video already being transcribed");
            }
        }

        /// <summary>
        /// To release a key that was being used.
        /// </summary>
        public void ReleaseKey(Key key, string videoId)
        {
            Keys.Find(k => k.ApiKey == key.ApiKey).Load -= 1;
            CurrentVideoIds.Remove(videoId);
        }
    }
}