SortedBucketCollection.cs

/**************************************************************************************

Storage.SortedBucketCollection
==============================

SortedBucketCollection stores items (TValue) which have 2 keys. Conceptually, a bucket stores items having the same 
value for TKey1. Within one bucket, each item must have a unique TKey2. However, internally, the items are not stored
in buckets, but a sorted linked list. SortedBucketCollection supports 3 indexers:
[TKey1]: returns an IEnumerable<TValue> looping over all items with the same TKey1
[TKey1a, TKey1b]: returns an IEnumerable<TValue> looping over all items with TKey1 in the range of TKey1a and TKey1b
[TKey1, TKey2]: returns one particular item.

Written in 2021 by Jürgpeter Huber 
Contact: PeterCode at Peterbox dot com

To the extent possible under law, the author(s) have dedicated all copyright and 
related and neighboring rights to this software to the public domain worldwide under
the Creative Commons 0 license (details see COPYING.txt file, see also
<http://creativecommons.org/publicdomain/zero/1.0/>). 

This software is distributed without any warranty. 
**************************************************************************************/
using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;


namespace StorageLib {

  #region IReadOnlySortedBucketCollection
  //      -------------------------------

  /// <summary>
  /// Provides readonly access to a BucketCollection, which works like a Dictionary, but each item needs 2 keys.
  /// </summary>
  public interface IReadOnlySortedBucketCollection<TKey1, TKey2, TValue>: IReadOnlyCollection<TValue> {

    #region Properties
    //      ----------

    /// <summary>
    /// A collection of all TKey1 values stored.
    /// </summary>
    ICollection<TKey1> Keys {get;}


    /// <summary>
    /// Number of all TKeys stored
    /// </summary>
    public int Key1Count {get;}


    /// <summary>
    /// Returns all items with TKey==key1
    /// </summary>
    public IEnumerable<TValue> this[TKey1 key1] {get;}


    /// <summary>
    /// Returns all items where TKey>=key1Lower && TKey<=key1Higher
    /// </summary>
    public IEnumerable<TValue> this[TKey1 key1Lower, TKey1 key1Higher] { get; }


    /// <summary>
    /// Returns the item stored for key1, key2
    /// </summary>
    public TValue? this[TKey1 key1, TKey2 key2] {get;}
    #endregion


    #region Methods
    //      -------

    /// <summary>
    /// Does at least 1 item exist in SortedBuckers with item.Key1==key1 ?
    /// </summary>
    public bool Contains(TKey1 key1);
    #endregion


    /// <summary>
    /// Does an item exist in SortedBuckers with item.Key1==key1 and item.Key2==key2 ?
    /// </summary>
    public bool Contains(TKey1 key1, TKey2 key2);


    /// <summary>
    /// Does an item with item.Key1==key1 and item.Key2==key2 exist in SortedBuckers ?
    /// </summary>
    public bool Contains(TValue item);


    /// <summary>
    /// Returns true if StoredBuckets stores an item with item.Key1==key1 and item Key2==key2
    /// </summary>
    public bool TryGetValue(TKey1 key1, TKey2 key2, [MaybeNullWhen(false)] out TValue value);
  }

  #endregion


  #region SortedBucketCollection
  //      ----------------------

  /// <summary>
  /// Like a SortedList, SortedBucketCollection stores TValue items which can be retrieved by their TKey1 value. In SortedList, 
  /// each TKey accesses at most 1 item. In SortedBucketCollection, each TKey1 accesses a bucket, which can contain 0 to many items 
  /// with the same TKey1, but different, unique TKey2. Items are sorted by TKey1, then TKey2. TKey1 and TKey2 are 
  /// properties within TValue.
  /// </summary>
  public class SortedBucketCollection<TKey1, TKey2, TValue>: ICollection<TValue>, IReadOnlySortedBucketCollection<TKey1, TKey2, TValue>
    where TKey1: notnull, IComparable<TKey1>
    where TKey2: notnull, IComparable<TKey2>
    where TValue: class
  {


    #region Properties
    //      ----------

    /// <summary>
    /// A collection of all TKey1 values stored.
    /// </summary>
    public ICollection<TKey1> Keys => buckets.Keys;


    /// <summary>
    /// Number of all TValues stored
    /// </summary>
    public int Count { get; private set;}


    /// <summary>
    /// Number of all TKeys stored
    /// </summary>
    public int Key1Count => buckets.Count;


    /// <summary>
    /// Readonly versions of SortedBucketCollection don't exist
    /// </summary>
    public bool IsReadOnly => false;


    /// <summary>
    /// Returns all items with TKey==key1
    /// </summary>
    public IEnumerable<TValue> this[TKey1 key1] => getValuesFor(key1);


    private IEnumerable<TValue> getValuesFor(TKey1 key1) {
      if (!buckets.TryGetValue(key1, out var bucketItem)) yield break;

      var versionCopy = version;
      do {
        yield return bucketItem.Item;

        if (versionCopy!=version) {
          throw new InvalidOperationException();
        }
        bucketItem = bucketItem.Next;
      } while (bucketItem is not null);
    }


    /// <summary>
    /// Returns all items where TKey>=key1Lower && TKey<=key1Higher
    /// </summary>
    public IEnumerable<TValue> this[TKey1 key1Lower, TKey1 key1Higher] => getValuesFor(key1Lower, key1Higher);


    private IEnumerable<TValue> getValuesFor(TKey1 key1Lower, TKey1 key1Higher) {
      var versionCopy = version;
      foreach (var keyValuePairBucketItem in buckets) {
        if (keyValuePairBucketItem.Key.CompareTo(key1Lower)<0) continue;

        if (keyValuePairBucketItem.Key.CompareTo(key1Higher)>0) break;

        var bucketItem = keyValuePairBucketItem.Value;
        yield return bucketItem.Item;

        if (versionCopy!=version) {
          throw new InvalidOperationException();
        }

        while (bucketItem.Next is not null) {
          bucketItem = bucketItem.Next;
          yield return bucketItem.Item;

          if (versionCopy!=version) {
            throw new InvalidOperationException();
          }
        }
      }
    }


    /// <summary>
    /// Returns the item stored for key1, key2
    /// </summary>
    public TValue? this[TKey1 key1, TKey2 key2] => getValueFor(key1, key2);


    private TValue? getValueFor(TKey1 key1, TKey2 key2) {
      if (!buckets.TryGetValue(key1, out var bucketItem)) return null;

      var compareResult = getKey2(bucketItem.Item).CompareTo(key2);
      while (compareResult==-1) {
        //Key2 is greater than bucketItem.Key2
        if (bucketItem.Next is null) return null;
        bucketItem = bucketItem.Next;
        compareResult = getKey2(bucketItem.Item).CompareTo(key2);
      }

      return compareResult==0 ? bucketItem.Item : null;
    }
    #endregion


    #region Bucket
    //      ------

    /// <summary>
    /// Basic storage unit in StoredBuckets.
    /// </summary>
    private class BucketItem{
      public readonly TValue Item;
      public BucketItem? Next;

      public BucketItem(TValue item, BucketItem? next) {
        Item = item;
        Next = next;
      }

      public override string ToString() {
        if (Next is null) {
          return $"{Item}; Next: ";
        } else {
          var nextItem = Next.Item; //bug in C# compiler with $"Next: {this.Next?.Item}"
          return $"{Item}; Next: {nextItem}";
        }
      }
    }
    #endregion


    #region Constructor
    //      -----------

    readonly Func<TValue, TKey1> getKey1;
    readonly Func<TValue, TKey2> getKey2;
    readonly SortedDictionary<TKey1, BucketItem> buckets;
    int version;


    /// <summary>
    /// The getKeyX() delegates provide access to the TKeyX property in TValue
    /// </summary>
    public SortedBucketCollection(Func<TValue, TKey1> getKey1, Func<TValue, TKey2> getKey2) {
      this.getKey1 = getKey1;
      this.getKey2 = getKey2;
      buckets = new();
      Count = 0;
    }
    #endregion


    #region Methods
    //      -------

    /// <summary>
    /// Adds value to SortedBucketCollection. It throws an exception if an item is stored already with value.Key1 and value.Key2.
    /// </summary>
    public void Add(TValue item) {
      var key1 = getKey1(item);
      if (buckets.TryGetValue(key1, out var foundBucketItem)) {
        var key2 = getKey2(item);
        var foundBucketItemKey2 = getKey2(foundBucketItem.Item);
        var compareResult = key2.CompareTo(foundBucketItemKey2);
        if (compareResult==0) throw new ArgumentException($"SortedBucketCollection.Add({item}): Key2 {key2} is used by already stored {foundBucketItem}.");

        if (compareResult<0) {
          //bucket.Key2<foundBucket.Key2
          //insert bucket into buckets, link foundBucket from bucket
          buckets[key1] = new BucketItem(item, foundBucketItem);

        } else {
          //bucket.Key2>foundBucket.Key2
          //find where in the linked list bucket needs to get inserted
          var nextBucketItem = foundBucketItem.Next;
          while (nextBucketItem is not null) {
            var nextBucketItemKey2 = getKey2(nextBucketItem.Item);
            compareResult = key2.CompareTo(nextBucketItemKey2);
            if (compareResult==0) throw new ArgumentException($"SortedBucketCollection.Add({item}): Key2 {key2} is used by already stored {nextBucketItem}.");

            if (compareResult<0) {
              //bucket.Key2<nextBucketItem.Key2
              //insert bucket between foundBucketItem and nextBucketItem
              foundBucketItem.Next = new BucketItem(item, nextBucketItem);
              Count++;
              version++;
              return;
            }

            foundBucketItem = nextBucketItem;
            foundBucketItemKey2 = nextBucketItemKey2;
            nextBucketItem = foundBucketItem.Next;
          }

          //bucket has bigger Key2 than any existing bucketItem with same Key1
          foundBucketItem.Next = new BucketItem(item, null);
        }

      } else {
        //first item for that Key1
        buckets.Add(key1, new BucketItem(item, null));
      }
      Count++;
      version++;
    }


    /// <summary>
    /// Does at least 1 item exist in SortedBuckers with item.Key1==key1 ?
    /// </summary>
    public bool Contains(TKey1 key1) {
      return buckets.ContainsKey(key1);
    }


    /// <summary>
    /// Does an item exist in SortedBuckers with item.Key1==key1 and item.Key2==key2 ?
    /// </summary>
    public bool Contains(TKey1 key1, TKey2 key2) {
      return this[key1, key2] is not null;
    }


    /// <summary>
    /// Does an item with item.Key1==key1 and item.Key2==key2 exist in SortedBuckers ?
    /// </summary>
    public bool Contains(TValue item) {
      var key1 = getKey1(item);
      var key2 = getKey2(item);
      return this[key1, key2] is not null;
    }


    /// <summary>
    /// Returns true if StoredBuckets stores an item with item.Key1==key1 and item Key2==key2
    /// </summary>
    public bool TryGetValue(TKey1 key1, TKey2 key2, [MaybeNullWhen(false)] out TValue value) {
      value = getValueFor(key1, key2);
      return value is not null;
    }


    /// <summary>
    /// Enumerates over all items in SortedBucketCollection, sorted by Key1, Key2
    /// </summary>
    public IEnumerator<TValue> GetEnumerator() {
      var versionCopy = version;

      foreach (var keyValuePairBucketItem in buckets) {
        var bucketItem = keyValuePairBucketItem.Value;
        yield return bucketItem.Item;

        if (versionCopy!=version) {
          throw new InvalidOperationException();
        }

        while (bucketItem.Next is not null) {
          bucketItem = bucketItem.Next;
          yield return bucketItem.Item;

          if (versionCopy!=version) {
            throw new InvalidOperationException();
          }
        }
      }
    }


    /// <summary>
    /// Enumerates over all items in SortedBucketCollection, sorted by Key1, Key2
    /// </summary>
    IEnumerator IEnumerable.GetEnumerator() {
      return GetEnumerator();
    }


    /// <summary>
    /// Returns true if an item with item.Key1==key1 and item.Key2==key2 was found. Item gets removed.
    /// </summary>
    public bool Remove(TValue item) {
      var key1 = getKey1(item);
      if (!buckets.TryGetValue(key1, out var existingBucketItem)) return false; //Key1 is completely missing in buckets

      var key2 = getKey2(item);
      var existingBucketItemKey2 = getKey2(existingBucketItem.Item);
      var compareResult = key2.CompareTo(existingBucketItemKey2);
      if (compareResult==0) {
        if (existingBucketItem.Next is null) {
          //only one item for Key1, remove it
          buckets.Remove(key1);
        } else {
          //replace found item with its next item
          buckets[key1] = existingBucketItem.Next;
        }
        Count--;
        version++;
        return true;

      } else if (compareResult<0) {
        //Key2<existingBucket.Key2, Key2 is missing
        return false;
      }

      //Key2>existingBucket.Key2
      //search linked list bucket for Key2
      var nextBucketItem = existingBucketItem.Next;
      while (nextBucketItem is not null) {
        var nextBucketItemKey2 = getKey2(nextBucketItem.Item);
        compareResult = key2.CompareTo(nextBucketItemKey2);
        if (compareResult<0) {
          //Key2<nextBucketItem.Key2
          //Key2 cannot be found
          return false;

        } else if (compareResult==0) {
          //item matching Key1 and Key2 found. Remove it from linked list
          existingBucketItem.Next = nextBucketItem.Next;
          Count--;
          version++;
          return true;
        }

        existingBucketItem = nextBucketItem;
        existingBucketItemKey2 = nextBucketItemKey2;
        nextBucketItem = existingBucketItem.Next;
      }

      //end of linked list reached, key2 not found
      return false;
    }


    /// <summary>
    /// Releases all items from SortedBucketCollection
    /// </summary>
    public void Clear() {
      buckets.Clear();//by removing the start of every linked list, all other items in the linked list become unreachable too
      Count = 0;
      version++;
    }


    /// <summary>
    /// Copies the elements of the SortedBucketCollection to an Array, starting at a particular Array index.
    /// </summary>
    public void CopyTo(TValue[] array, int arrayIndex) {
      if (array is null) throw new ArgumentNullException(nameof(array));

      if (arrayIndex<0) throw new ArgumentOutOfRangeException(nameof(array), $"value needs to be greater 0, but was {arrayIndex}.");

      if (array.Length - arrayIndex < Count) throw new ArgumentException("array is too small.");

      foreach (var item in this) {
        array[arrayIndex++] = item;
      }
    }
    #endregion
  }
  #endregion
}