#pragma once
#include <vector>

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

namespace plot::data {

/// A uniform-grid series of y samples: sample i lives at x = x0() + i*dx().
///
/// Every concrete series answers range queries exactly, and never by scanning the
/// whole range: the bucket-aligned interior comes from the pyramid (O(log n)
/// bucket aggregates) and at most two partial edge buckets are read through
/// copy_raw() and scanned. Cost is independent of series length and no query
/// allocates.
///
/// Indexing is over the series' own window: index 0 is the oldest sample the
/// series currently holds (for a ring-backed series that is the oldest retained
/// one), so reduce(start, end) and gather() are in the same coordinates as
/// size(), x0() and pyramid().
class Series {
 public:
  virtual ~Series() = default;

  virtual u64 size() const = 0;
  /// x of sample 0, i.e. of the oldest sample currently held.
  virtual f64 x0() const = 0;
  /// Uniform x spacing between consecutive samples.
  virtual f64 dx() const = 0;
  virtual Range x_bounds() const = 0;
  virtual Range y_bounds() const = 0;
  virtual const MinMaxPyramid& pyramid() const = 0;

  /// Appends interleaved (x, y) pairs in data coordinates for level `level`.
  ///
  /// Level 0 emits the raw samples of [begin, end). Level >= 1 emits one (min, max)
  /// envelope pair per *complete* level bucket wholly inside the retained window,
  /// bounded by the two partial buckets at the edges of the requested range — the
  /// bucket the window starts inside and the bucket the newest samples are in —
  /// which it emits as raw samples through copy_raw(). A bucket that is only partly
  /// retained holds aggregates of samples the window no longer has and a partial
  /// trailing bucket is not stored at all, so neither may be drawn as an envelope.
  ///
  /// The emitted geometry therefore always spans [begin, end) exactly, for at most
  /// two buckets of extra raw work (about two pixels at the level level_for()
  /// picks), and never reaches outside the retained window. Pairs are appended to
  /// out_xy, which is never cleared.
  virtual void gather(u32 level, u64 begin, u64 end, std::vector<f32>& out_xy) const = 0;

  /// Exact min/max, sum and sum-of-squares over [begin, end).
  /// Preconditions: begin < end, end <= size(); a degenerate range yields a
  /// zero-span Range and zero sums. Implemented once, non-virtually, over
  /// copy_raw() in src/data/series.cpp.
  Range reduce(u64 begin, u64 end) const;
  f64 sum(u64 begin, u64 end) const;
  f64 sumsq(u64 begin, u64 end) const;

 protected:
  /// Copies raw y samples for [begin, end) into `out`, which the caller sized to
  /// (end - begin). Handles ring wraparound. Only ever called with the small edge
  /// spans of the queries above, never on a per-sample path. Out-of-range spans
  /// are clamped and the unwritten tail is zero-filled.
  virtual void copy_raw(u64 begin, u64 end, f32* out) const = 0;

  /// The shared body of the concrete gather() overrides: raw samples at level 0,
  /// bucket min/max envelope above it.
  void gather_impl(u32 level, u64 begin, u64 end, std::vector<f32>& out_xy) const;

 private:
  /// [begin, end) split into the bucket-aligned interior the pyramid can answer
  /// exactly, plus the at most two partial edge spans it cannot.
  struct QueryParts {
    u64 interior_begin = 0, interior_end = 0;   // whole level-0 buckets, may be empty
    u64 left_begin = 0, left_end = 0;           // partial head bucket
    u64 right_begin = 0, right_end = 0;         // partial tail bucket
  };
  /// Needs the pyramid's window base: the bucket grid it aligns to is absolute,
  /// while begin/end are window coordinates.
  QueryParts split_query(u64 begin, u64 end) const;
  /// Reads both edge spans through copy_raw() into `out` (which must hold at
  /// least 2*kBucket samples) and returns how many were written.
  u64 copy_edges(const QueryParts& parts, f32* out) const;
  /// Appends the raw samples of [begin, end) as (x, y) pairs, in copy_raw()'s
  /// bounded chunks. The one path that reads samples rather than aggregates: level
  /// 0 is entirely this, and a level >= 1 gather uses it for the two partial edge
  /// buckets a pyramid of complete buckets cannot answer for. Precondition:
  /// begin < end, end <= size().
  void gather_raw(u64 begin, u64 end, std::vector<f32>& out_xy) const;
};

}  // namespace plot::data