// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: 2026 Martino Ferrari

#include <plot/plot/measure.hpp>

#include <cmath>

namespace plot {

Measurement Measure::evaluate(const data::Series& s, u64 begin, u64 end) {
  Measurement m;
  // Both guards run before any query, so an empty, inverted or out-of-range
  // interval returns an invalid result without touching the series.
  if (end <= begin || end > s.size()) return m;

  // Exact extremes and sums come from Series -- never from the pyramid's
  // *_buckets forms, which answer in whole buckets only and would drop up to two
  // partial edge buckets, silently returning wrong extrema and sums for any
  // interval that is not bucket-aligned. Each query here is O(kBucket) worst
  // case, so a measurement never scales with series length.
  const Range extremes = s.reduce(begin, end);
  const f64 total = s.sum(begin, end);
  const f64 squared = s.sumsq(begin, end);
  const f64 n = static_cast<f64>(end - begin);
  const f64 step = s.dx();

  m.ymin = extremes.min;
  m.ymax = extremes.max;
  m.mean = total / n;
  m.rms = std::sqrt(squared / n);
  m.integral = total * step;  // left-Riemann sum: see the note in measure.hpp

  if (end - begin >= 2) {
    // First and last sample of the interval: a single-sample query reduces to
    // that sample's value, and costs the same O(kBucket) as any other.
    const f64 first = s.reduce(begin, begin + 1).min;
    const f64 last = s.reduce(end - 1, end).min;
    m.dy = last - first;
    m.dx = static_cast<f64>(end - 1 - begin) * step;
    m.slope = m.dx != 0.0 ? m.dy / m.dx : 0.0;
  }
  m.valid = true;
  return m;
}

}  // namespace plot