#include "Decimate.h"

#include <algorithm>

namespace udpscope {

void MinMaxDecimate(const double* t, const double* v, size_t n,
                    size_t maxPoints, Series& out) {
    out.clear();
    if (n == 0 || t == nullptr || v == nullptr) {
        return;
    }
    if (n <= maxPoints || maxPoints < 4) {
        out.t.assign(t, t + n);
        out.v.assign(v, v + n);
        return;
    }

    /* Two points per bucket, so the bucket count is half the budget. */
    const size_t buckets = maxPoints / 2;
    out.t.reserve(buckets * 2);
    out.v.reserve(buckets * 2);

    for (size_t b = 0; b < buckets; b++) {
        const size_t begin = (n * b) / buckets;
        size_t       end   = (n * (b + 1)) / buckets;
        if (end <= begin) { end = begin + 1; }
        if (end > n) { end = n; }

        size_t lo = begin, hi = begin;
        for (size_t i = begin + 1; i < end; i++) {
            if (v[i] < v[lo]) { lo = i; }
            if (v[i] > v[hi]) { hi = i; }
        }

        const size_t first  = std::min(lo, hi);
        const size_t second = std::max(lo, hi);
        out.t.push_back(t[first]);
        out.v.push_back(v[first]);
        if (second != first) {
            out.t.push_back(t[second]);
            out.v.push_back(v[second]);
        }
    }
}

} /* namespace udpscope */