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Telegram/SourceFiles/data/data_abstract_sparse_ids.h

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+/*
+This file is part of Telegram Desktop,
+the official desktop application for the Telegram messaging service.
+
+For license and copyright information please follow this link:
+https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
+*/
+#pragma once
+
+template <typename IdsContainer>
+class AbstractSparseIds {
+public:
+	using Id = typename IdsContainer::value_type;
+
+	AbstractSparseIds() = default;
+	AbstractSparseIds(
+		const IdsContainer &ids,
+		std::optional<int> fullCount,
+		std::optional<int> skippedBefore,
+		std::optional<int> skippedAfter)
+	: _ids(ids)
+	, _fullCount(fullCount)
+	, _skippedBefore(skippedBefore)
+	, _skippedAfter(skippedAfter) {
+	}
+
+	[[nodiscard]] std::optional<int> fullCount() const {
+		return _fullCount;
+	}
+	[[nodiscard]] std::optional<int> skippedBefore() const {
+		return _skippedBefore;
+	}
+	[[nodiscard]] std::optional<int> skippedAfter() const {
+		return _skippedAfter;
+	}
+	[[nodiscard]] std::optional<int> indexOf(Id id) const {
+		const auto it = ranges::find(_ids, id);
+		if (it != _ids.end()) {
+			return (it - _ids.begin());
+		}
+		return std::nullopt;
+	}
+	[[nodiscard]] int size() const {
+		return _ids.size();
+	}
+	[[nodiscard]] Id operator[](int index) const {
+		Expects(index >= 0 && index < size());
+
+		return *(_ids.begin() + index);
+	}
+	[[nodiscard]] std::optional<int> distance(Id a, Id b) const {
+		if (const auto i = indexOf(a)) {
+			if (const auto j = indexOf(b)) {
+				return *j - *i;
+			}
+		}
+		return std::nullopt;
+	}
+	[[nodiscard]] std::optional<Id> nearest(Id id) const {
+		static_assert(std::is_same_v<IdsContainer, base::flat_set<Id>>);
+		if (const auto it = ranges::lower_bound(_ids, id); it != _ids.end()) {
+			return *it;
+		} else if (_ids.empty()) {
+			return std::nullopt;
+		}
+		return _ids.back();
+	}
+	void reverse() {
+		ranges::reverse(_ids);
+		std::swap(_skippedBefore, _skippedAfter);
+	}
+
+	friend inline bool operator==(
+		const AbstractSparseIds&,
+		const AbstractSparseIds&) = default;
+
+private:
+	IdsContainer _ids;
+	std::optional<int> _fullCount;
+	std::optional<int> _skippedBefore;
+	std::optional<int> _skippedAfter;
+
+};