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

#pragma once
#include <vector>

#include <plot/core/types.hpp>
#include <plot/data/minmax_pyramid.hpp>
#include <plot/data/series.hpp>

namespace plot::data {

/// Series over its own x array: sample i lives at `x()[i]`, and the samples are
/// sorted by ascending x. This is the store for data whose x is *not* on a
/// uniform grid -- scattered measurements, event times, a log-swept frequency
/// axis -- where `ArraySeries`' fixed `dx` cannot hold.
///
/// **Precondition: `x` is sorted ascending.** The O(log n) crosshair and
/// nearest-sample lookups are binary searches, which are only correct on sorted
/// input; the constructor and `reset()` assert sortedness in debug builds and
/// the behaviour with unsorted input is undefined in release ones. Callers with
/// a possibly-unsorted source sort it first (sorting the *pairs*, not the
/// arrays independently, or the samples get scrambled).
///
/// Everything the base `Series` contracts to holds, with the sample index as
/// the grid: the pyramid buckets samples by *index* (`kBucket` samples per
/// level-0 bucket, exactly as for a uniform series) and `gather()` emits x
/// relative to `x0()` -- `f32(x_at(i) - x0())`, never the absolute
/// coordinate -- so an epoch-scale x array narrows to f32 the same safe,
/// O(visible pixels) way a uniform one does. The queries that need a *uniform*
/// grid are overridden with the binary-search answer instead: `x_at()` reads
/// the array, `neighbours()` brackets with `upper_bound`/`lower_bound`, and
/// `snap_index()` compares the two candidates the search leaves. `dx()` is
/// meaningless here and returns 0: nothing that routes through
/// `x_at`/`neighbours`/`snap_index` consults it.
class XYSeries final : public Series {
 public:
  /// Takes both arrays by value. `x.size() == y.size()` and `x` sorted
  /// ascending (asserted in debug).
  XYSeries(std::vector<f64> x, std::vector<f32> y);
  /// Replaces both arrays, then rebuilds derived state (== commit()). Same
  /// preconditions as the constructor.
  void reset(std::vector<f64> x, std::vector<f32> y);
  /// Rebuilds the pyramid and the cached bounds from the arrays as they stand.
  void commit();

  u64 size() const override;
  /// x of sample 0: the first (smallest) x in the array.
  f64 x0() const override;
  /// Always 0: the grid is the x array, not a uniform step.
  f64 dx() const override;
  /// From the first and last x; a zero span for an empty series.
  Range x_bounds() const override;
  Range y_bounds() const override;
  const MinMaxPyramid& pyramid() const override;
  /// Same contract as `Series::gather`, with x emitted relative to `x_origin`.
  void gather(u32 level, u64 begin, u64 end, f64 x_origin, std::vector<f32>& out_xy,
              GatherMode mode = GatherMode::Envelope) const override;

  /// The sample's own x.
  f64 x_at(u64 i) const override;
  /// Binary-search bracket of data-space `x`: false outside
  /// `[x_at(0), x_at(size() - 1)]`, else the last sample at or left of `x` and
  /// the first at or right of it (equal on an exact hit).
  bool neighbours(f64 x, u64& i0, u64& i1) const override;
  /// Binary-search nearest sample, clamped to `[0, size() - 1]`; ties go to the
  /// lower index, and an empty series returns 0.
  u64 snap_index(f64 x) const override;

  /// The x array itself (sorted ascending).
  const std::vector<f64>& x() const noexcept { return x_; }

 protected:
  void copy_raw(u64 begin, u64 end, f32* out) const override;

 private:
  std::vector<f64> x_;
  std::vector<f32> y_;
  MinMaxPyramid pyramid_;
  Range x_bounds_{};
  Range y_bounds_{};
  /// False until a finite sample has been seen (see `ArraySeries`): the cached
  /// y bounds are then a placeholder, and the first finite sample seeds them.
  bool y_has_finite_ = false;
};

}  // namespace plot::data