#pragma once
// pitch_shift — a PURE, per-voice, duration-preserving pitch shifter: the S16 "Preserve"
// engine's DSP core. Time-domain delay-line shifter with CORRELATION-ALIGNED SPLICES
// (SOLA-style): one active read tap chases the write head at the shift ratio; when it drifts
// out of its safe delay band it is relocated by a nominal window jump REFINED BY A
// CROSS-CORRELATION SEARCH so the new read point is waveform-aligned, then the old and new
// taps are crossfaded (raised-cosine, amplitude-complementary). Source is consumed 1:1 and
// output produced 1:1 (duration held); only the PITCH changes — an octave up plays the same
// wall-clock length as the root note, unlike the Varispeed `readPos_ += ratio_` resample path.
//
// WHY CORRELATED SPLICES (GA-Preserve fix, 2026-07). The first S16 implementation was the
// naive two-tap OLA: taps hard-locked half a window apart, Hann-crossfaded by write-head
// distance. Its taps read the same stream at delays differing by exactly w/2, so their outputs
// carried a FIXED relative phase of 2*pi*f_src*(w/2) — arbitrary and source-frequency-
// dependent. Near anti-phase (roughly half of all frequencies) every crossfade midpoint
// nearly CANCELLED: deep periodic AM + phase slew = strong sidebands. A repitched pure sine
// came out mangled ("multiple partials" on a spectrogram) while the root stayed clean (unity
// freezes the crossfade). The fix is structural: splices must be PHASE-ALIGNED, so each jump
// is snapped to the best waveform match within a bounded lag search — a pure sine's jump
// lands on an integer period count and the output stays a single shifted tone.
//
// WHY A HAND-ROLLED PURE MODULE, NOT WDL (S16-F2, decided at build). The spec's lean was
// route (a) `WDL_SimplePitchShifter`. But its include chain
// (simple_pitchshift.h -> queue.h -> heapbuf.h -> wdltypes.h) does `#ifdef _WIN32 ->
// #include <windows.h>` unconditionally, which CANNOT enter the pure sampler_core module
// (CLAUDE.md load-bearing split: NO vendor/host/SDK types; sampler_core_tests links neither
// SDK and compiles outside the DAW). So the Preserve DSP lands as route (b): a house-native
// pure module alongside peaks / wav_trim, CTest-testable, RT-disciplined. Same
// PitchEngine::Preserve contract behind the seam — if WDL is ever preferred it swaps in at
// the SHELL, never in the pure core.
//
// PURE MODULE: NO VST3, NO REAPER, NO SWELL, NO vendor/ includes. Standard library only.
// Shares the `AudioSample` float alias from peaks (the one house precedent — sampler_core /
// wav_trim do the same).
//
// RT DISCIPLINE (S16 hard constraint). `configure()` sizes the ring ONCE (off the audio
// thread, at voice allocation). `warm()` pre-fills the ring with silence so steady-state
// latency is reached before the first real sample (no cold-start click). `process()` does
// NO allocation and NO locks — it reads/writes the pre-sized ring only. The splice-time
// correlation search is a bounded burst of multiply-adds (coarse+refine over a fixed lag
// range) that fires once per splice cadence (window / |ratio-1| frames), never per frame.

#include <cstddef>
#include <cstdint>
#include <vector>

#include "peaks.h"  // AudioSample (float)

namespace reasampler {

// A per-channel time-domain splice-aligned pitch shifter. One instance transposes ONE channel;
// a stereo voice owns two — the algorithm is per-sample and channel-count agnostic, matching
// the S7 "one read head, per-channel value" idiom of the core.
//
// The default-constructed shifter is INERT: with no configure() it passes input through
// unchanged (shift ratio 1.0, empty ring), so a Varispeed voice that never touches it is
// byte-identical to the pre-S16 engine.
class PitchShifter {
public:
    // Size the delay ring for `windowFrames` (the nominal splice-jump length; the ring is 2x
    // that for splice/search headroom) and derive the fade/search geometry. `windowFrames`
    // <= 1 degrades to pass-through (no ring), so a degenerate configure never divides by
    // zero or wraps a zero span. Called OFF the audio thread (allocates). Resets all running
    // state. A larger window = fewer splices and a deeper alignment search but more latency
    // (steady-state latency stays window/2); the shell picks it from kPreserveWindowMs.
    void configure(std::int64_t windowFrames);

    // Pre-fill the ring with silence (one full window of zero writes) so the read tap reaches
    // steady state before the first real sample. Removes the cold-start seam (the S16 "onset
    // click absent" requirement) — call once at voice allocation after configure(). No-op when
    // unconfigured (pass-through needs no warm-up).
    void warm();

    // The pitch shift ratio: 2^((note - root)/12) plus any per-frame pitch-envelope bias.
    // 1.0 = no shift (pass-through-equivalent output, no splices ever fire). Set per frame is
    // fine (cheap); the tap advance simply uses the current value. Values <= 0 are ignored
    // (kept at the last valid ratio) so a bad input never runs the tap backward or stalls it.
    void setShiftRatio(double ratio);

    // Transform ONE input frame into ONE output frame (duration-preserving: 1 in, 1 out).
    // RT-safe: reads/writes the pre-sized ring only, no allocation, no lock. When unconfigured
    // (window <= 1) returns `in` unchanged (pass-through). Otherwise writes `in` at the write
    // head, reads the active tap (crossfading against the outgoing tap while a splice fade is
    // live), then advances the write head by one and the tap(s) by the shift ratio. When the
    // active tap leaves its safe delay band, a correlation-aligned splice is scheduled.
    AudioSample process(AudioSample in);

    // Reset running state to a freshly-warmed-equivalent silence (ring zeroed, heads re-seeded)
    // WITHOUT reallocating — for voice reuse without a re-configure. Keeps the current window.
    void reset();

    // True once configure() sized a real ring (window > 1). A pass-through shifter is false.
    bool configured() const { return window_ > 1; }

    std::int64_t window() const { return window_; }

private:
    double readTap(double pos) const;               // fractional ring read, linear interp
    void splice(std::int64_t nominalJump);          // relocate the active tap, start the fade

    std::vector<AudioSample> ring_;  // delay line, length `ringLen_` == 2 * window_
    std::int64_t window_ = 0;        // nominal splice jump in frames; <= 1 = pass-through
    std::int64_t ringLen_ = 0;       // ring length (2 * window_): splice + search headroom
    std::int64_t writePos_ = 0;      // integer write head into the ring (source rate)
    double posA_ = 0.0;              // active read tap (advances at the shift ratio)
    double posB_ = 0.0;              // outgoing tap during a splice crossfade
    bool fading_ = false;            // a splice crossfade is in flight
    std::int64_t fadePos_ = 0;       // crossfade progress, [0, fadeLen_)
    std::int64_t fadeFrames_ = 0;    // NOMINAL crossfade length (window_/4)
    std::int64_t fadeLen_ = 0;       // LIVE crossfade length for the in-flight splice —
                                     // ratio-scaled at splice time so an up-shift's outgoing
                                     // tap can never drain into the writer mid-fade
    std::int64_t maxLag_ = 0;        // correlation search half-range (window_/4)
    std::int64_t corrFrames_ = 0;    // correlation segment length (dLow_-1, capped at 512, so
                                     // the reference read forward from the tap stays behind
                                     // the writer BY CONSTRUCTION at an up-splice)
    std::int64_t dLow_ = 0;          // splice trigger: active-tap delay below this (up-shift)
    std::int64_t dHigh_ = 0;         // splice trigger: active-tap delay above this (down-shift)
    double ratio_ = 1.0;             // current shift ratio (>0)
};

}  // namespace reasampler