reasampler/src/shell/actions/instrument_drop_win.cpp

// instrument_drop_win — the REAPER shell for S17 drop-and-load. See instrument_drop_win.h.
//
// Compiled into the reaper_reasampler MODULE. Includes reaper_plugin_functions.h WITHOUT
// REAPERAPI_IMPLEMENT (main.cpp owns the pointers; here they are extern via the WANT list).

#include "shell/actions/instrument_drop_win.h"

#include <atomic>
#include <cstdint>
#include <filesystem>
#include <fstream>
#include <string>
#include <system_error>
#include <vector>

#include "core/version/app_version.h"      // vstPluginName() — the CHANNEL-correct FX name (stable/beta pairing)
#include "core/wire/instrument_drop.h"  // infoNamesFxHotspot — the PURE, unit-tested hotspot classifier

#include "reaper_plugin.h"

#define REAPERAPI_MINIMAL
#define REAPERAPI_WANT_GetThingFromPoint
#define REAPERAPI_WANT_TrackFX_AddByName
#define REAPERAPI_WANT_TrackFX_Delete
#define REAPERAPI_WANT_TrackFX_SetPreset
#define REAPERAPI_WANT_Undo_BeginBlock2
#define REAPERAPI_WANT_Undo_EndBlock2
#include "reaper_plugin_functions.h"

namespace reasampler {

// Real-namespace-home using-declarations (Q-W6: the namespaces.h shim is retired).
using version::vstPluginName;
using wire::infoNamesFxHotspot;

namespace {

// Write `bytes` to a fresh uniquely-named .vstpreset in the OS temp dir and return its path;
// returns an empty path on any failure. The .vstpreset extension is load-bearing —
// TrackFX_SetPreset's full-path form is documented for .vstpreset files (VST3). The file is
// transient: the caller deletes it right after the SetPreset call.
//
// The temp filename embeds the process ID so two concurrent REAPER instances (e.g. stable +
// beta) cannot collide in the shared OS temp dir, and one instance's cleanup cannot
// accidentally delete another's in-flight file.
//
// Non-throwing: every std::filesystem call uses the error_code overload. The whole body is
// wrapped in try/catch to guarantee no exception crosses the REAPER C callback boundary
// (the same discipline the prune shell uses — see prune_fs.cpp's non-throwing scan comment).
//
// Returns the path object (not a narrow string) so the caller can:
//   (a) pass path.u8string() to TrackFX_SetPreset — UTF-8 on MSVC, not ACP-converted,
//       so a temp dir with accented or CJK user-name bytes is handled correctly;
//   (b) delete via the retained path object — not via re-parsing the narrow string —
//       so the cleanup cannot leak if the conversion above were to round-trip incorrectly.
std::filesystem::path writeTempPreset(const std::vector<std::uint8_t>& bytes) {
    try {
        static std::atomic<unsigned> counter{0};
        std::error_code ec;
        const std::filesystem::path dir = std::filesystem::temp_directory_path(ec);
        if (ec) return {};
        // PID in the name keeps files from distinct REAPER instances distinct in the shared
        // temp dir — prevents cross-instance collisions and spurious post-apply deletions.
        const std::string name =
            "reasampler_drop_" + std::to_string(GetCurrentProcessId()) +
            "_" + std::to_string(counter.fetch_add(1)) + ".vstpreset";
        const std::filesystem::path path = dir / name;
        std::ofstream out(path, std::ios::binary | std::ios::trunc);
        if (!out) return {};
        out.write(reinterpret_cast<const char*>(bytes.data()),
                  static_cast<std::streamsize>(bytes.size()));
        out.close();
        if (!out) {  // short write / flush failure -> don't hand REAPER a truncated preset
            std::filesystem::remove(path, ec);
            return {};
        }
        return path;
    } catch (...) {
        return {};
    }
}

}  // namespace

FxDropTarget resolveFxDropTarget(int screenX, int screenY) {
    FxDropTarget out;
    char info[256] = {0};
    // GetThingFromPoint returns the track under the point (may be null for a non-track thing)
    // and fills `info` with what was hit. A non-empty info OR a non-null track means the point
    // is over REAPER's own UI; a null track with an empty info means the pointer has left
    // REAPER entirely (over another app / the desktop) — the OsDrag boundary.
    MediaTrack* track = GetThingFromPoint(screenX, screenY, info, sizeof(info));
    out.track = track;
    out.overReaperUi = (track != nullptr) || (info[0] != '\0');
    // The hotspot is either the FX chain/floating window ("fx_*") OR the FX-button family of
    // the track/mixer panel ("tcp.fx*"/"mcp.fx*"). The pure classifier owns the rule.
    out.overFxHotspot = (track != nullptr) && infoNamesFxHotspot(info);
    return out;
}

bool loadInstrumentOntoTrack(MediaTrack* track, const std::vector<std::uint8_t>& presetBytes) {
    if (!track || presetBytes.empty()) return false;

    // Materialize the .vstpreset FIRST so an I/O failure leaves the track untouched (no FX
    // added yet — nothing to roll back).
    const std::filesystem::path presetPath = writeTempPreset(presetBytes);
    if (presetPath.empty()) return false;

    // The CHANNEL-correct FX name: "VST3:ReaSampler 9000" on stable, "VST3:ReaSampler 9000
    // beta" on beta. Sourcing it from app_version::vstPluginName() (the same accessor the VST
    // factory display name derives from) keeps the pairing invariant intact — a beta extension
    // drops the beta VST, a stable extension the stable VST — with no literal to drift. (The
    // preset's class ID forks by the same channel bit inside buildInstrumentDropPreset.)
    const std::string fxName = "VST3:" + vstPluginName();

    // Negative `instantiate` => always create a NEW instance (verified in the header). recFX
    // = false: a normal track FX chain instance, not a record/monitoring FX.
    const int fxIndex = TrackFX_AddByName(track, fxName.c_str(), /*recFX=*/false,
                                          /*instantiate=*/-1);
    bool ok = fxIndex >= 0;

    // Apply the dragged capture's component state through the DOCUMENTED channel: a full
    // .vstpreset path handed to TrackFX_SetPreset (SDK: "Full paths to .vstpreset files are
    // also supported for VST3 plug-ins"). REAPER parses the Steinberg container and feeds the
    // 'Comp' chunk to the instance's setState — the same bytes the instrument's own
    // serializer produced (instrument_drop::buildInstrumentDropPreset ->
    // sample_map::serializeComponentState). Unlike the former "vst_chunk" named-config-parm
    // write, a failure here is REPORTED (false), not silently ignored.
    //
    // u8string() gives UTF-8 bytes on MSVC (not ACP-converted), so a temp dir under an
    // accented or CJK user-name is handled correctly by REAPER's path APIs.
    if (ok) ok = TrackFX_SetPreset(track, fxIndex, presetPath.u8string().c_str());

    // The preset file is transient regardless of outcome; delete via the retained path object
    // (not a re-parsed narrow string) so cleanup cannot leak even if the UTF-8 conversion
    // round-trip were incorrect.
    std::error_code ec;
    std::filesystem::remove(presetPath, ec);

    if (!ok && fxIndex >= 0) {
        // All-or-nothing: if the preset apply fails, remove the empty FX instance we just
        // added so the track is left exactly as it was. TrackFX_Delete signature (verified
        // in reaper_plugin_functions.h:7236): bool TrackFX_Delete(MediaTrack*, int fx).
        TrackFX_Delete(track, fxIndex);
    }
    return ok;
}

bool performInstrumentDrop(MediaTrack* track, const std::vector<std::uint8_t>& presetBytes) {
    if (!track || presetBytes.empty()) return false;

    // One undo point for the whole gesture (mirrors the bank-verb undo discipline). Both the
    // FX add and the state apply are REAPER-undoable, so Ctrl-Z removes the instance cleanly.
    Undo_BeginBlock2(nullptr);
    const bool ok = loadInstrumentOntoTrack(track, presetBytes);
    // The undo label reflects the placement-of-the-player framing (not a capture, not an insert).
    Undo_EndBlock2(nullptr, "ReaSampler: drop capture onto FX chain", -1);
    return ok;
}

}  // namespace reasampler