AbsoluteCharacterFrequencies.cs

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

namespace Science.Cryptography.Ciphers.Analysis;

public readonly record struct AbsoluteCharacterFrequencies(IReadOnlyDictionary<char, int> Frequencies) : IReadOnlyDictionary<char, int>
{
	/// <summary>
	/// Gets the occurrences of a given <paramref name="character"/>.
	/// </summary>
	/// <param name="character"></param>
	/// <returns></returns>
	public readonly int this[char character]
	{
		get
		{
			Frequencies.TryGetValue(character, out int frequency);
			return frequency;
		}
	}


	public readonly RelativeCharacterFrequencies ToRelativeFrequencies()
	{
		var sum = Frequencies.Sum(f => f.Value);
		return new(
			Frequencies.ToFrozenDictionary(
				kv => kv.Key,
				kv => kv.Value / (double)sum
			)
		);
	}


	public readonly IReadOnlyDictionary<char, int> ToDictionary() => Frequencies;

	#region IReadOnlyDictionary<char, int>
	IEnumerable<char> IReadOnlyDictionary<char, int>.Keys => Frequencies.Keys;
	IEnumerable<int> IReadOnlyDictionary<char, int>.Values => Frequencies.Values;

	int IReadOnlyCollection<KeyValuePair<char, int>>.Count => Frequencies.Count;

	int IReadOnlyDictionary<char, int>.this[char key] => this[key];

	bool IReadOnlyDictionary<char, int>.ContainsKey(char key) => Frequencies.ContainsKey(key);

	bool IReadOnlyDictionary<char, int>.TryGetValue(char key, out int value) => Frequencies.TryGetValue(key, out value);

	IEnumerator<KeyValuePair<char, int>> IEnumerable<KeyValuePair<char, int>>.GetEnumerator() => Frequencies.GetEnumerator();

	IEnumerator IEnumerable.GetEnumerator() => Frequencies.GetEnumerator();
	#endregion
}