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// vim:set sw=2 ts=2 sts et:
//
// Copyright 2024 Rutger Broekhoff. Licensed under the EUPL.
#ifndef OEUF_QUERYKV1_DATERANGE_HPP
#define OEUF_QUERYKV1_DATERANGE_HPP
#include <cassert>
#include <chrono>
#include <concepts>
#include <iterator>
#include <utility>
#include <vector>
// DateRange expresses the date range [from, thru].
class DateRange {
public:
class Iterator {
friend class DateRange;
public:
Iterator &operator++();
std::chrono::year_month_day operator*() const;
std::chrono::year_month_day ymd() const;
private:
explicit Iterator(std::chrono::year_month_day ymd);
std::chrono::year_month_day ymd_;
};
explicit DateRange(std::chrono::year_month_day from, std::chrono::year_month_day thru);
Iterator begin() const;
Iterator end() const;
bool valid() const;
std::chrono::year_month_day from() const;
std::chrono::year_month_day thru() const;
private:
std::chrono::year_month_day from_;
std::chrono::year_month_day thru_;
};
bool operator==(const DateRange::Iterator a, const DateRange::Iterator b);
template<typename Tp, typename T>
concept DerefsTo = requires(Tp p) {
{ *p } -> std::convertible_to<T>;
};
class DateRangeSeq {
// The way LE and GE are ordered makes a difference for how the sorting
// (insertion based on lower_bound) works. Do not carelessly reorder this.
enum LeGe {
GE, // >=
LE, // <=
};
std::vector<DateRange> ranges_;
public:
template<std::input_iterator InputIt>
requires DerefsTo<InputIt, DateRange>
explicit DateRangeSeq(InputIt begin, InputIt end) {
// We convert every inclusive date range [x, y] into (x, >=) and (y, <=)
// and put these into a list, using binary search to make sure that these
// stay ordered. We then reduce this list, removing tautological
// predicates, giving us a final list of ranges that do not overlap.
std::vector<std::pair<std::chrono::year_month_day, LeGe>> preds;
size_t n = 0;
for (auto it = begin; it != end; it++) {
auto &range = *it;
if (!range.valid()) continue;
auto a = std::make_pair(range.from(), GE);
auto b = std::make_pair(range.thru(), LE);
preds.insert(std::lower_bound(preds.begin(), preds.end(), a), a);
preds.insert(std::lower_bound(preds.begin(), preds.end(), b), b);
n++;
}
if (preds.empty())
return;
assert(preds.size() >= 2);
assert(preds.front().second == GE);
assert(preds.back().second == LE);
std::chrono::year_month_day begin_ymd = preds[0].first;
for (size_t i = 1; i < preds.size(); i++) {
if (preds[i].second == LE && (i + 1 == preds.size() || preds[i + 1].second == GE)) {
std::chrono::year_month_day end_ymd = preds[i].first;
if (!ranges_.empty() && ranges_.back().thru() == begin_ymd)
ranges_.back() = DateRange(ranges_.back().from(), end_ymd);
else
ranges_.push_back(DateRange(begin_ymd, end_ymd));
if (i + 1 != preds.size()) {
begin_ymd = preds[i + 1].first;
i++;
}
}
}
}
explicit DateRangeSeq(std::initializer_list<DateRange> ranges);
DateRangeSeq clampFrom(std::chrono::year_month_day from) const;
DateRangeSeq clampThru(std::chrono::year_month_day thru) const;
public:
std::vector<DateRange>::const_iterator begin() const;
std::vector<DateRange>::const_iterator end() const;
};
#endif // OEUF_QUERYKV1_DATERANGE_HPP
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