using System;
using System.Collections.Concurrent;
using System.Collections.Generic;

namespace LibSearchBox
{
	public class InvertedIndex
	{
		// Gotta be public to allow Newtonsoft.JSON to do it's job. Don't interact with it directly!
		public ConcurrentDictionary<string, ConcurrentDictionary<int, List<int>>> invertedIndex = new ConcurrentDictionary<string, ConcurrentDictionary<int, List<int>>>();

		public InvertedIndex()
		{
		}

		public bool AddIndex(int pageId, Index newIndex)
		{
			foreach (KeyValuePair<string, List<int>> token in newIndex)
			{
				if (!invertedIndex.ContainsKey(token.Key) &&
					!invertedIndex.TryAdd(token.Key, new ConcurrentDictionary<int, List<int>>()))
					return false;

				if (!invertedIndex[token.Key].TryAdd(pageId, token.Value))
					return false;
			}
			return true;
		}

		public bool RemoveIndex(int pageId, Index oldIndex)
		{
			foreach (string token in oldIndex.Tokens()) {
				if (!invertedIndex.ContainsKey(token) || !invertedIndex[token].ContainsKey(pageId)) continue;

				if (!invertedIndex[token].TryRemove(pageId, out List<int> noop))
					return false;
			}
			return false;
		}

		public bool ReplaceIndex(int pageId, Index oldIndex, Index newIndex)
		{
			if (!RemoveIndex(pageId, oldIndex)) return false;
			if (!AddIndex(pageId, newIndex)) return false;
			return true;
		}

		public bool RemoveById(int pageId)
		{
			foreach (KeyValuePair<string, ConcurrentDictionary<int, List<int>>> pair in invertedIndex) {
				if (!pair.Value.ContainsKey(pageId)) continue;
				if (!pair.Value.TryRemove(pageId, out List<int> noop))
					return false;
				if (pair.Value.Count == 0 && !invertedIndex.TryRemove(pair.Key, out var noopAgain))
					return false;
			}
			return true;
		}

		public ConcurrentDictionary<int, List<int>> Query(string normalisedToken)
		{
			invertedIndex.TryGetValue(normalisedToken, out ConcurrentDictionary<int, List<int>> result);
			return result;
		}
	}
}