#include "loops.hpp"

#include <algorithm>
#include <ranges>

namespace control_flow {

auto sum_range(const int from, const int to) -> int {
    return std::ranges::fold_left(
        std::views::iota(from, to + 1), // End-exclusive
        0,
        [](const int acc, const int x) { return acc + x; }
    );
}

auto factorial(const int n) -> long long
    pre(n >= 0)
{
    if (n == 0 || n == 1) return 1;
    return std::ranges::fold_left(
        std::views::iota(2, n + 1), // End-exclusive
        1LL,
        [](const long long acc, const int x) { return acc * x; }
    );
}

auto count_occurrences(const std::vector<int>& data, const int target) -> int {
    int count = 0;
    std::ranges::for_each(data, [target, &count](const int x) {
        if (x == target) ++count;
    });
    return count;
}

auto first_index_of(const std::vector<int>& data, const int target) -> int {
    const auto it = std::ranges::find(data, target);
    if (it == data.end()) return -1;
    return static_cast<int>(std::distance(data.begin(), it));
}

}  // namespace control_flow