reasampler/src/view_mode_model.h

#pragma once
// view_mode_model — the pure core of the Design View feature, deliberately free of any
// REAPER type so it compiles and unit-tests OUTSIDE the DAW. It is the mirror of
// bank_model: it owns the mode registry, the GUID-keyed membership index, the
// folder-tree-aware visibility derivation, the parking/restore planner, and the
// JSON round-trip of all of it.
//
// PURE MODULE (CLAUDE.md §load-bearing split): NO REAPER types, NO SWELL, NO
// vendor/ includes. Standard library only. The folder structure is an INPUT
// supplied by the D2 shell (which reads REAPER's I_FOLDERDEPTH); this model never
// fetches or stores REAPER's live tree — folder structure is REAPER's truth and
// changes underneath us, so it is passed in per query, not held.
//
// -- Representation decisions (design latitude exercised; invariants below) -----
//
// * A mode is (stable string id, display name, ordinal). Arrange (id "arrange",
//   ordinal 0) and Design (id "design", ordinal 1) are seeded. Arrange is the
//   fallback home for every untagged leaf; structurally it is just another mode.
//
// * Membership is GUID -> { mode ids } (a set, not a bool) plus a per-track
//   show-both flag. Normally a leaf is in exactly one mode; multiple only via the
//   parent-derivation rule (computed, not stored) or the show-both escape hatch.
//   An untagged GUID is NOT in the index and belongs to Arrange by default.
//
// * The planner drives exactly four scalar flags (showInTcp, showInMixer,
//   mainSend, fxEnable) plus a per-FX offline list. Park values are fixed zeros
//   (defined by the parking contract), so PARK ops need no snapshot. RESTORE ops
//   come entirely FROM a TrackSnapshot captured before parking — never a hardcoded
//   default. This is where the restore-contract invariant lives and is tested.
//
// * The snapshot stores the full prior per-FX offline vector so a save-while-parked
//   project round-trips and restores each FX to its exact prior offline state. The
//   pure model does NOT need REAPER FX counts to plan a park (park offlines all N,
//   which the shell expands from TrackFX_GetCount); it only needs them to restore,
//   and it gets them from the snapshot it captured.

#include <cstdint>
#include <map>
#include <optional>
#include <set>
#include <string>
#include <vector>

namespace reasampler {

// Stable seed-mode ids. Arrange is the default home for untagged leaves.
inline constexpr const char* kArrangeModeId = "arrange";
inline constexpr const char* kDesignModeId  = "design";

// A display "stance" the user adopts. Modes are ordered by `ordinal` for tab order.
struct Mode {
    std::string id;           // stable, persisted; never reused for a different mode
    std::string displayName;
    int         ordinal = 0;  // tab order

    bool operator==(const Mode& o) const;
};

// Ordered registry of modes. Arrange + Design are seeded on construction. Add more
// to prove the model is N-mode, not boolean. Ids are unique; adding a duplicate id
// is rejected.
class ModeRegistry {
public:
    ModeRegistry();  // seeds Arrange (ordinal 0) + Design (ordinal 1)

    // Adds a mode. Rejects (returns false, no mutation) an empty or duplicate id.
    bool add(const Mode& mode);

    // Returns the mode with `id`, or nullptr. Invalidated by any mutating call.
    const Mode* query(const std::string& id) const;

    bool contains(const std::string& id) const { return query(id) != nullptr; }

    // All modes in ordinal order (ties broken by insertion order).
    const std::vector<Mode>& all() const { return modes_; }

    std::size_t size() const { return modes_.size(); }

    bool operator==(const ModeRegistry& o) const { return modes_ == o.modes_; }

    // An empty registry (no seed modes). Deserialization parses the persisted mode
    // set into this and then owns it; the default ctor's seed would otherwise make
    // the serialized Arrange/Design collide on add() and fail to round-trip.
    static ModeRegistry makeEmpty() { return ModeRegistry(EmptyTag{}); }

private:
    struct EmptyTag {};
    explicit ModeRegistry(EmptyTag) {}  // no seed

    std::vector<Mode> modes_;  // kept sorted by ordinal, then insertion
};

// The membership record for one tagged leaf track, keyed externally by GUID.
struct Membership {
    std::set<std::string> modeIds;   // the mode(s) this leaf opted into
    bool                  showBoth = false;  // pinned visible + running in every mode

    bool operator==(const Membership& o) const {
        return modeIds == o.modeIds && showBoth == o.showBoth;
    }
};

// GUID-keyed membership index. Untagged GUIDs are absent and belong to Arrange.
// Keyed by track GUID string, never index (reorder-safe).
class MembershipIndex {
public:
    // Tags `guid` into `modeId`, replacing any prior mode set (a leaf lives in one
    // mode; use showBoth for the cross-mode case). No-op-safe on repeated calls.
    // Returns false if guid or modeId is empty.
    bool tag(const std::string& guid, const std::string& modeId);

    // Removes `guid` from the index entirely (returns it to the Arrange default).
    // Returns true if it was present.
    bool untag(const std::string& guid);

    // Sets the show-both flag for `guid`. Tags the guid into no new mode; if the
    // guid is untagged it is created with an empty mode set (Arrange default) so
    // show-both alone is representable. Returns false if guid is empty.
    bool setShowBoth(const std::string& guid, bool showBoth);

    // Installs a complete membership record verbatim (multi-mode set + show-both),
    // replacing any existing entry for `guid`. Used by deserialization to rebuild a
    // trusted, already-valid entry without tag()'s single-mode clobbering. Returns
    // false if guid is empty.
    bool restore(const std::string& guid, const Membership& membership);

    // Returns the membership for `guid`, or nullptr if untagged. Invalidated by any
    // mutating call.
    const Membership* query(const std::string& guid) const;

    bool isShowBoth(const std::string& guid) const {
        const Membership* m = query(guid);
        return m && m->showBoth;
    }

    // The mode ids `guid` belongs to. Empty for an untagged guid (⇒ Arrange).
    std::set<std::string> modesOf(const std::string& guid) const;

    const std::map<std::string, Membership>& all() const { return entries_; }

    std::size_t size() const { return entries_.size(); }
    bool empty() const { return entries_.empty(); }

    bool operator==(const MembershipIndex& o) const { return entries_ == o.entries_; }

private:
    std::map<std::string, Membership> entries_;  // guid -> membership
};

// -- Folder tree (INPUT, not stored) ----------------------------------------
//
// The shell builds this from I_FOLDERDEPTH each time and passes it to a visibility
// query. A node is a leaf or a parent; a parent is visible in every mode any of
// its descendant leaves belongs to, and is never parked. The master track is
// modeled implicitly (always visible, never touched) and is NOT a node here.
struct FolderNode {
    std::string guid;
    std::string parentGuid;  // empty ⇒ top-level (child of master / project root)
    bool        isParent = false;  // true if this node has descendant tracks (a folder)
};

// A flat parent↔child description of the current track tree. Order is arrange-view
// order; parentGuid links each node to its immediate parent folder.
struct FolderTree {
    std::vector<FolderNode> nodes;
};

// -- Snapshot + planner ------------------------------------------------------

// The prior value of every tool-driven flag on one track, captured BEFORE parking.
// Restore uses these values verbatim — the restore contract's source of truth.
// Flags mirror REAPER's numeric representation (0/1 for the bools) so the shell
// applies them without translation; ints, not bools, so a snapshot faithfully
// round-trips whatever REAPER reported (defensive against non-0/1 values).
struct TrackSnapshot {
    int showInTcp   = 0;   // B_SHOWINTCP prior value
    int showInMixer = 0;   // B_SHOWINMIXER prior value
    int mainSend    = 0;   // B_MAINSEND  prior value
    int fxEnable    = 0;   // I_FXEN      prior value

    // Prior per-FX offline state, index = fx slot. Lets restore return each FX to
    // exactly its captured offline value rather than a blanket "online".
    std::vector<int> fxOffline;

    bool operator==(const TrackSnapshot& o) const {
        return showInTcp == o.showInTcp && showInMixer == o.showInMixer &&
               mainSend == o.mainSend && fxEnable == o.fxEnable &&
               fxOffline == o.fxOffline;
    }
};

// Which scalar flag a TrackFlagOp drives. FX-offline is carried separately (it is
// per-slot, variable length), see TrackParkPlan::fxOffline.
enum class Flag {
    ShowInTcp,    // B_SHOWINTCP
    ShowInMixer,  // B_SHOWINMIXER
    MainSend,     // B_MAINSEND
    FxEnable,     // I_FXEN
};

// One scalar-flag write the shell must apply: SetMediaTrackInfo_Value(guid, flag, value).
struct TrackFlagOp {
    std::string guid;
    Flag        flag = Flag::ShowInTcp;
    int         value = 0;

    bool operator==(const TrackFlagOp& o) const {
        return guid == o.guid && flag == o.flag && value == o.value;
    }
};

// One per-FX offline write: TrackFX_SetOffline(guid, fxIndex, offline).
struct FxOfflineOp {
    std::string guid;
    int         fxIndex = 0;
    bool        offline = false;

    bool operator==(const FxOfflineOp& o) const {
        return guid == o.guid && fxIndex == o.fxIndex && offline == o.offline;
    }
};

// The complete set of operations to park one inactive leaf, or restore one leaf.
// Park uses fixed zeros (parking contract); restore uses a snapshot's values.
// fxOffline is emitted per known FX slot: on park, from the snapshot's slot count
// (all -> offline); on restore, each slot back to its captured value.
struct TrackPlan {
    std::vector<TrackFlagOp>  flags;
    std::vector<FxOfflineOp>  fxOffline;
};

// The plan for a whole toggle to a target mode: which tracks to park, and which to
// restore from their snapshots. Parents and show-both leaves never appear here —
// they are derived-visible and never parked (visibility is answered separately by
// visibleTracks). Untagged LEAVES DO appear: an untagged leaf is an Arrange member,
// so it parks in every non-Arrange mode and restores in Arrange — the mode system
// manages all leaves, not only tagged ones.
struct TogglePlan {
    std::vector<TrackPlan> park;     // inactive leaves -> parked (fixed zeros)
    std::vector<TrackPlan> restore;  // active leaves returning -> snapshot values
};

// -- The view mode model -----------------------------------------------------
//
// Owns the mode registry, the membership index, the active mode, and the durable
// per-track snapshots (kept for tracks currently parked so a save-while-parked
// project restores correctly). Visibility and the toggle plan are computed against
// a supplied FolderTree — the tree is never stored.
class ViewModeModel {
public:
    ViewModeModel();  // Arrange + Design seeded; active mode = Arrange

    ModeRegistry&           modes()       { return modes_; }
    const ModeRegistry&     modes() const { return modes_; }
    MembershipIndex&        membership()       { return membership_; }
    const MembershipIndex&  membership() const { return membership_; }

    const std::string& activeModeId() const { return activeModeId_; }
    // Sets the active mode. Returns false (no change) if the id is not registered.
    bool setActiveMode(const std::string& modeId);

    // Records / clears the pre-park snapshot for a track. The shell calls store
    // before it parks a track; the model persists it so restore survives a save.
    void storeSnapshot(const std::string& guid, const TrackSnapshot& snap);
    void clearSnapshot(const std::string& guid);
    const TrackSnapshot* snapshot(const std::string& guid) const;
    const std::map<std::string, TrackSnapshot>& snapshots() const { return snapshots_; }

    // Does `guid` belong to `modeId`? A leaf belongs if it is tagged into modeId,
    // is show-both (belongs everywhere), or is untagged and modeId is Arrange (the
    // default). Parent derivation is NOT applied here — this is the LEAF rule; use
    // visibleTracks for the tree-aware answer.
    bool leafBelongsToMode(const std::string& guid, const std::string& modeId) const;

    // The set of track GUIDs visible in `modeId`, tree-aware: active leaves,
    // show-both leaves, and every parent with at least one descendant leaf in the
    // mode. Untagged leaves count as Arrange. Stale GUIDs in the tree are tolerated.
    // The master is not represented (always visible; the shell never touches it).
    std::set<std::string> visibleTracks(const FolderTree& tree,
                                        const std::string& modeId) const;

    // Plans a toggle to `targetMode` by enumerating EVERY leaf in the supplied tree.
    // A leaf inactive in the target mode — tagged into another mode, or untagged and
    // the target isn't Arrange — is parked with fixed zeros; a leaf that becomes
    // active AND has a stored snapshot is restored from it. Parents (visibility-only)
    // and show-both leaves (always visible) are never parked; the master is not in
    // the tree. Untagged leaves ARE managed: they are Arrange members, so they park
    // in non-Arrange modes and restore in Arrange. Tree membership is the enumeration
    // source, so stale membership GUIDs absent from the tree are naturally ignored.
    //
    // Note: park plans emitted here have an empty fxOffline vector. The D2 shell
    // expands per-FX offline writes using TrackFX_GetCount — the pure model has no
    // access to REAPER FX counts at plan time.
    TogglePlan planToggle(const FolderTree& tree, const std::string& targetMode) const;

    bool operator==(const ViewModeModel& o) const;

    std::string serialize() const;

    // Parses a JSON string produced by serialize(). std::nullopt on malformed
    // input. On success deserialize(serialize(x)) == x.
    static std::optional<ViewModeModel> deserialize(const std::string& json);

private:
    ModeRegistry    modes_;
    MembershipIndex membership_;
    std::string     activeModeId_;                       // always a registered id
    std::map<std::string, TrackSnapshot> snapshots_;     // guid -> pre-park snapshot
};

// Builds the fixed-zero park plan for one leaf. Offlines `fxCount` slots. Exposed
// for the shell and for direct testing of the parking contract.
TrackPlan makeParkPlan(const std::string& guid, int fxCount);

// Builds the restore plan for one leaf from its snapshot — every flag set to its
// captured value, never a default. Exposed for the shell and for testing the
// restore-contract invariant directly.
TrackPlan makeRestorePlan(const std::string& guid, const TrackSnapshot& snap);

// The next mode id in the registry's ordinal order, cycling past `currentModeId`
// and wrapping to the first mode after the last (Arrange -> Design -> Arrange with
// the two seed modes; the same cycle scales to N modes with no call-site change).
// This is the pure decision behind the "toggle active mode" action: the shell reads
// the model's active mode, asks for the next one, and applies it.
//   * empty registry           -> "" (nothing to cycle to)
//   * currentModeId not present -> the first mode's id (a sane home to jump to)
// Exposed as a free function (not a model member) so it is unit-testable against a
// bare ModeRegistry without a full ViewModeModel.
std::string nextModeId(const ModeRegistry& modes, const std::string& currentModeId);

} // namespace reasampler