feat(view): D2 view shell — apply mode toggle plan to live project

Reads I_FOLDERDEPTH into a FolderTree (pure view_tree helper, unit-tested),
snapshots to-be-parked tracks before parking, runs the D1 planner, and applies
park/restore flag + per-FX-offline writes under an undo block. Master and
mute/solo untouched; acts only on tagged tracks.

CMakeLists.txt

@@ -45,6 +45,17 @@ target_include_directories(capture_paths PUBLIC src)
 add_library(view_mode_model STATIC src/view_mode_model.cpp)
 target_include_directories(view_mode_model PUBLIC src)
 
+# ---------------------------------------------------------------------------
+# 2d) Pure view_tree library — NO REAPER, NO SWELL. The one testable-outside-DAW
+#     piece of the D2 view shell: turning REAPER's linear I_FOLDERDEPTH stream into
+#     the parent<->child FolderTree the model consumes. The REAPER reads stay in
+#     view.cpp; this fiddly folder-depth walk is unit-tested here (mirrors
+#     capture_paths splitting the path math out of the capture shell).
+# ---------------------------------------------------------------------------
+add_library(view_tree STATIC src/view_tree.cpp)
+target_include_directories(view_tree PUBLIC src)
+target_link_libraries(view_tree PUBLIC view_mode_model)
+
 # ---------------------------------------------------------------------------
 # 3) Standalone tests for the pure modules (run without launching REAPER).
 # ---------------------------------------------------------------------------
@@ -65,6 +76,10 @@ add_executable(view_mode_model_tests tests/test_view_mode_model.cpp)
 target_link_libraries(view_mode_model_tests PRIVATE view_mode_model)
 add_test(NAME view_mode_model_tests COMMAND view_mode_model_tests)
 
+add_executable(view_tree_tests tests/test_view_tree.cpp)
+target_link_libraries(view_tree_tests PRIVATE view_tree)
+add_test(NAME view_tree_tests COMMAND view_tree_tests)
+
 # ---------------------------------------------------------------------------
 # 4) The REAPER extension — a loadable module (dlopen'd by REAPER, not linked).
 # ---------------------------------------------------------------------------
@@ -73,6 +88,8 @@ add_library(reaper_reasampler MODULE
     src/capture.cpp
     src/persist.cpp
     src/view_mode_model.cpp
+    src/view_tree.cpp
+    src/view.cpp
 )
 target_link_libraries(reaper_reasampler PRIVATE bank_model capture_paths)
 target_include_directories(reaper_reasampler PRIVATE ${SDK_INC} ${WDL_INC})

src/view.cpp

@@ -0,0 +1,188 @@
+// view.cpp — REAPER-facing Design View shell (Phase D2). See view.h.
+//
+// Compiled into the reaper_reasampler MODULE. Includes reaper_plugin_functions.h
+// WITHOUT REAPERAPI_IMPLEMENT — main.cpp is the one TU that defines the API
+// pointers; here they are extern (CLAUDE.md §contract).
+//
+// The tree arithmetic (I_FOLDERDEPTH -> FolderTree) lives in the pure view_tree
+// module so it is unit-tested outside the DAW; this file owns only the REAPER
+// reads/writes and the snapshot-before-park ordering.
+
+#include "view.h"
+
+#include <string>
+#include <vector>
+
+#include "view_tree.h"
+
+#define REAPERAPI_MINIMAL
+#define REAPERAPI_WANT_CountTracks
+#define REAPERAPI_WANT_GetTrack
+#define REAPERAPI_WANT_GetTrackGUID
+#define REAPERAPI_WANT_guidToString
+#define REAPERAPI_WANT_GetMediaTrackInfo_Value
+#define REAPERAPI_WANT_SetMediaTrackInfo_Value
+#define REAPERAPI_WANT_TrackFX_GetCount
+#define REAPERAPI_WANT_TrackFX_GetOffline
+#define REAPERAPI_WANT_TrackFX_SetOffline
+#define REAPERAPI_WANT_Undo_BeginBlock2
+#define REAPERAPI_WANT_Undo_EndBlock2
+#include "reaper_plugin_functions.h"
+
+namespace reasampler {
+
+namespace {
+
+// REAPER's GUID -> string form. guidToString needs a 64-byte destination (SDK
+// contract); the canonical "{XXXXXXXX-...}" string is the membership-index key the
+// actions layer tags with, so the tree keys and the model keys align exactly.
+std::string trackGuidString(MediaTrack* tr) {
+    GUID* g = GetTrackGUID(tr);
+    if (!g) return {};
+    char buf[64] = {0};
+    guidToString(g, buf);
+    return std::string(buf);
+}
+
+// The parmname for each planner Flag. All four are documented bool*/int* track
+// info params driven through the double-valued Get/SetMediaTrackInfo_Value API.
+const char* flagParm(Flag f) {
+    switch (f) {
+        case Flag::ShowInTcp:   return "B_SHOWINTCP";
+        case Flag::ShowInMixer: return "B_SHOWINMIXER";
+        case Flag::MainSend:    return "B_MAINSEND";
+        case Flag::FxEnable:    return "I_FXEN";
+    }
+    return "B_SHOWINTCP";  // unreachable; keeps the compiler quiet
+}
+
+// Reads the arrange-ordered track list and their I_FOLDERDEPTH, keyed by GUID.
+// The master track is NOT enumerated by GetTrack (index space is the non-master
+// tracks), so it can never enter the tree — the master-untouched invariant holds
+// by construction. Also caches the MediaTrack* per GUID so later apply steps
+// resolve a GUID back to its handle without a second linear scan.
+std::vector<TrackFolderEntry> readFolderEntries(
+        ReaProject* proj,
+        std::vector<std::pair<std::string, MediaTrack*>>& handleByGuid) {
+    std::vector<TrackFolderEntry> entries;
+    int count = CountTracks(proj);
+    entries.reserve(static_cast<std::size_t>(count));
+    handleByGuid.reserve(static_cast<std::size_t>(count));
+    for (int i = 0; i < count; ++i) {
+        MediaTrack* tr = GetTrack(proj, i);
+        if (!tr) continue;
+        std::string guid = trackGuidString(tr);
+        if (guid.empty()) continue;
+        int depth = static_cast<int>(GetMediaTrackInfo_Value(tr, "I_FOLDERDEPTH"));
+        entries.push_back(TrackFolderEntry{guid, depth});
+        handleByGuid.emplace_back(guid, tr);
+    }
+    return entries;
+}
+
+MediaTrack* resolve(const std::vector<std::pair<std::string, MediaTrack*>>& handleByGuid,
+                    const std::string& guid) {
+    for (const auto& kv : handleByGuid) {
+        if (kv.first == guid) return kv.second;
+    }
+    return nullptr;  // stale/deleted GUID — pruned by being skipped
+}
+
+// Captures a track's prior driven-flag state BEFORE it is parked. Reads only the
+// four owned flags + per-FX offline; never B_MUTE/I_SOLO, never the master (not
+// reachable here). ints preserve whatever REAPER reported (defensive per D1's
+// TrackSnapshot contract).
+TrackSnapshot snapshotTrack(MediaTrack* tr) {
+    TrackSnapshot snap;
+    snap.showInTcp   = static_cast<int>(GetMediaTrackInfo_Value(tr, "B_SHOWINTCP"));
+    snap.showInMixer = static_cast<int>(GetMediaTrackInfo_Value(tr, "B_SHOWINMIXER"));
+    snap.mainSend    = static_cast<int>(GetMediaTrackInfo_Value(tr, "B_MAINSEND"));
+    snap.fxEnable    = static_cast<int>(GetMediaTrackInfo_Value(tr, "I_FXEN"));
+
+    int fxCount = TrackFX_GetCount(tr);
+    snap.fxOffline.reserve(static_cast<std::size_t>(fxCount));
+    for (int fx = 0; fx < fxCount; ++fx) {
+        snap.fxOffline.push_back(TrackFX_GetOffline(tr, fx) ? 1 : 0);
+    }
+    return snap;
+}
+
+// Applies the planner's scalar-flag writes. B_* are bool* params, I_FXEN is int*,
+// all driven through the double API — marshal the plan's int value to double.
+void applyFlags(MediaTrack* tr, const std::vector<TrackFlagOp>& flags) {
+    for (const TrackFlagOp& op : flags) {
+        SetMediaTrackInfo_Value(tr, flagParm(op.flag), static_cast<double>(op.value));
+    }
+}
+
+// Parks a track's FX offline: the pure park plan leaves fxOffline empty by design;
+// the shell expands it from the live FX count and offlines every slot.
+void parkFxOffline(MediaTrack* tr) {
+    int fxCount = TrackFX_GetCount(tr);
+    for (int fx = 0; fx < fxCount; ++fx) {
+        TrackFX_SetOffline(tr, fx, true);
+    }
+}
+
+// Restores per-FX offline from the snapshot verbatim — each slot back to its
+// captured value, never a blanket "online". Bounds-checked against the live FX
+// count in case the plugin chain changed while parked (prune-safe).
+void restoreFxOffline(MediaTrack* tr, const std::vector<FxOfflineOp>& fxOffline) {
+    int fxCount = TrackFX_GetCount(tr);
+    for (const FxOfflineOp& op : fxOffline) {
+        if (op.fxIndex < 0 || op.fxIndex >= fxCount) continue;
+        TrackFX_SetOffline(tr, op.fxIndex, op.offline);
+    }
+}
+
+} // namespace
+
+bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject* proj) {
+    // Reject an unregistered target before touching the project (no partial apply).
+    if (!model.modes().contains(targetModeId)) {
+        return false;
+    }
+
+    std::vector<std::pair<std::string, MediaTrack*>> handleByGuid;
+    std::vector<TrackFolderEntry> entries = readFolderEntries(proj, handleByGuid);
+    FolderTree tree = buildFolderTree(entries);
+
+    TogglePlan plan = model.planToggle(tree, targetModeId);
+
+    Undo_BeginBlock2(proj);
+
+    // PARK: snapshot BEFORE mutating, store into the model (so restore survives a
+    // save-while-parked), then apply the park writes + expand the FX-offline loop.
+    for (const TrackPlan& tp : plan.park) {
+        // Every op in a TrackPlan targets the same track; take the guid from the
+        // first flag op (the pure park plan always emits the four flag ops).
+        if (tp.flags.empty()) continue;
+        const std::string& guid = tp.flags.front().guid;
+        MediaTrack* tr = resolve(handleByGuid, guid);
+        if (!tr) continue;  // stale GUID — prune
+
+        model.storeSnapshot(guid, snapshotTrack(tr));
+        applyFlags(tr, tp.flags);
+        parkFxOffline(tr);
+    }
+
+    // RESTORE: apply the snapshot-sourced flag + per-FX offline writes verbatim,
+    // then drop the now-consumed snapshot so a re-park recaptures fresh state.
+    for (const TrackPlan& tp : plan.restore) {
+        if (tp.flags.empty()) continue;
+        const std::string& guid = tp.flags.front().guid;
+        MediaTrack* tr = resolve(handleByGuid, guid);
+        if (!tr) continue;  // stale GUID — prune
+
+        applyFlags(tr, tp.flags);
+        restoreFxOffline(tr, tp.fxOffline);
+        model.clearSnapshot(guid);
+    }
+
+    model.setActiveMode(targetModeId);
+
+    Undo_EndBlock2(proj, "ReaSampler: apply Design View mode", -1);
+    return true;
+}
+
+} // namespace reasampler

src/view.h

@@ -0,0 +1,50 @@
+#pragma once
+// view — the REAPER-facing shell of the Design View feature (Phase D2). It is the
+// mirror of the capture shell: the ViewModeModel (pure, D1) holds the mode/
+// membership/snapshot state and emits the toggle plan; this shell reads the live
+// project's folder tree, snapshots the tracks it is about to park, runs the model's
+// planner, and applies the resulting flag + per-FX-offline writes to REAPER.
+//
+// It includes view_mode_model (pure) but NO REAPER headers — the .cpp is the one
+// REAPER-facing translation unit (CLAUDE.md §contract: only main.cpp defines the
+// API pointers; every other .cpp gets them extern). Callers (persist, actions)
+// depend on this seam without dragging the SDK into their include sites.
+//
+// Hard invariants this shell enforces (CONTEXT.md §Design View, precision
+// invariants) — verified in self-review, never crossed:
+//   * Never touches the master track's visibility (SDK forbids B_SHOWINTCP/
+//     B_SHOWINMIXER on master); the master is never a node in the tree.
+//   * Never reads or writes B_MUTE / I_SOLO on any track.
+//   * Acts only on tracks the model owns (tagged leaves the planner names) plus
+//     derived parents' visibility — never an untagged track's owned flags.
+//   * Snapshots every to-be-parked track's prior flags BEFORE parking, storing
+//     them into the model so restore is faithful and survives a save-while-parked.
+
+#include <string>
+
+#include "view_mode_model.h"
+
+// REAPER's opaque project handle. Forward-declared to keep this header SDK-free;
+// the .cpp includes reaper_plugin_functions.h and sees the real class.
+class ReaProject;
+
+namespace reasampler {
+
+// Applies `targetModeId` to the live project `proj`:
+//   1. Reads the arrange-ordered track list, builds the FolderTree from
+//      I_FOLDERDEPTH (via the pure buildFolderTree helper).
+//   2. Runs model.planToggle(tree, targetModeId).
+//   3. For each track about to be PARKED: snapshots its current B_SHOWINTCP /
+//      B_SHOWINMIXER / B_MAINSEND / I_FXEN and per-FX offline state, stores the
+//      snapshot into the model, THEN applies the park writes (expanding the
+//      per-FX offline loop from TrackFX_GetCount, which the pure plan leaves empty).
+//   4. For each track to RESTORE: applies the plan's snapshot-sourced flag + per-FX
+//      offline writes verbatim.
+//   5. Sets the model's active mode to `targetModeId`.
+// All track mutations are wrapped in Undo_BeginBlock2 / Undo_EndBlock2.
+//
+// Returns false (no mutation, active mode unchanged) if `targetModeId` is not a
+// registered mode. `proj` may be nullptr to mean REAPER's current project.
+bool applyMode(ViewModeModel& model, const std::string& targetModeId, ReaProject* proj);
+
+} // namespace reasampler

src/view_tree.cpp

@@ -0,0 +1,41 @@
+// view_tree — pure folder-depth walk. See view_tree.h.
+
+#include "view_tree.h"
+
+namespace reasampler {
+
+FolderTree buildFolderTree(const std::vector<TrackFolderEntry>& entries) {
+    FolderTree tree;
+    tree.nodes.reserve(entries.size());
+
+    // Stack of currently-open folder-parent GUIDs. The top is the immediate parent
+    // of the next track. A folder-parent track opens its folder AFTER contributing
+    // its own node (its own parent is the enclosing folder), so the push trails the
+    // assignment. A closing track belongs to the folder it closes, so the pop also
+    // trails the assignment.
+    std::vector<std::string> open;
+
+    for (const TrackFolderEntry& e : entries) {
+        FolderNode node;
+        node.guid       = e.guid;
+        node.parentGuid = open.empty() ? std::string{} : open.back();
+        node.isParent   = e.folderDepth == 1;
+        tree.nodes.push_back(node);
+
+        if (e.folderDepth == 1) {
+            open.push_back(e.guid);  // this track's folder opens for what follows
+        } else if (e.folderDepth < 0) {
+            // Closes |folderDepth| levels after this (already-assigned) track.
+            // Clamp to the stack size so a malformed/stale depth stream can't
+            // underflow — the walk stays total.
+            int levels = -e.folderDepth;
+            while (levels-- > 0 && !open.empty()) {
+                open.pop_back();
+            }
+        }
+    }
+
+    return tree;
+}
+
+} // namespace reasampler

src/view_tree.h

@@ -0,0 +1,33 @@
+#pragma once
+// view_tree — the ONE genuinely pure piece of the D2 view shell: turning REAPER's
+// linear I_FOLDERDEPTH stream into the parent<->child FolderTree the pure model
+// consumes. The REAPER reads (GetTrack / GetTrackGUID / I_FOLDERDEPTH) stay in
+// view.cpp; this tree arithmetic is REAPER-free so the fiddly folder-depth walk is
+// unit-tested outside the DAW (mirrors capture_paths splitting the path math out).
+//
+// PURE MODULE (CLAUDE.md §load-bearing split): NO REAPER types, NO SWELL, NO
+// vendor/ includes. Standard library + view_mode_model.h (for FolderTree) only.
+
+#include <string>
+#include <vector>
+
+#include "view_mode_model.h"
+
+namespace reasampler {
+
+// One track's contribution to the folder walk, read from REAPER in arrange order.
+// folderDepth is I_FOLDERDEPTH verbatim: 0 = normal, 1 = folder parent (opens a
+// folder after this track), <0 = closes |folderDepth| folder levels after this
+// track (-1 last in innermost, -2 last in innermost + next-innermost, ...).
+struct TrackFolderEntry {
+    std::string guid;
+    int         folderDepth = 0;
+};
+
+// Walks the ordered entries, tracking the open-folder stack, and assigns each
+// node its immediate parentGuid (empty = top level) and isParent (opens a folder).
+// Pure and total: tolerates malformed depth streams (a close deeper than the stack
+// is clamped to empty) so a corrupt/stale project can never fault the shell.
+FolderTree buildFolderTree(const std::vector<TrackFolderEntry>& entries);
+
+} // namespace reasampler

tests/test_view_tree.cpp

@@ -0,0 +1,119 @@
+// Standalone tests for reasampler::buildFolderTree — no REAPER, no framework.
+// The D2 view shell is DAW-bound and only verifiable in REAPER; this covers the
+// one genuinely pure piece: the I_FOLDERDEPTH walk that turns REAPER's linear
+// track stream into the parent<->child FolderTree the pure model consumes.
+
+#include "../src/view_tree.h"
+
+#include <cstdio>
+#include <string>
+
+using namespace reasampler;
+
+static int g_fail = 0;
+#define CHECK(cond) do { if(!(cond)) { \
+    std::printf("FAIL line %d: %s\n", __LINE__, #cond); ++g_fail; } } while(0)
+
+// Find a node by guid; returns nullptr if absent.
+static const FolderNode* nodeOf(const FolderTree& t, const std::string& guid) {
+    for (const auto& n : t.nodes)
+        if (n.guid == guid) return &n;
+    return nullptr;
+}
+
+// All top-level leaves: three depth-0 tracks, no folders. Every parentGuid empty,
+// nothing is a parent, order preserved.
+static void testFlatLeaves() {
+    FolderTree t = buildFolderTree({{"a", 0}, {"b", 0}, {"c", 0}});
+    CHECK(t.nodes.size() == 3);
+    CHECK(t.nodes[0].guid == "a" && t.nodes[1].guid == "b" && t.nodes[2].guid == "c");
+    for (const auto& n : t.nodes) {
+        CHECK(n.parentGuid.empty());
+        CHECK(!n.isParent);
+    }
+}
+
+// One folder: parent P (depth 1) contains child C, which closes the folder (-1).
+// P is a parent and is itself top-level; C's parent is P.
+static void testSingleFolder() {
+    FolderTree t = buildFolderTree({{"P", 1}, {"C", -1}});
+    const FolderNode* p = nodeOf(t, "P");
+    const FolderNode* c = nodeOf(t, "C");
+    CHECK(p && c);
+    CHECK(p->isParent);
+    CHECK(p->parentGuid.empty());     // the folder parent is itself top-level
+    CHECK(!c->isParent);
+    CHECK(c->parentGuid == "P");      // child sits under the folder
+}
+
+// Folder with two children; a following top-level leaf must land back at the root,
+// proving the close (-1) popped the folder off the stack.
+static void testFolderThenSibling() {
+    FolderTree t = buildFolderTree({{"P", 1}, {"C1", 0}, {"C2", -1}, {"S", 0}});
+    CHECK(nodeOf(t, "C1")->parentGuid == "P");
+    CHECK(nodeOf(t, "C2")->parentGuid == "P");
+    CHECK(nodeOf(t, "S")->parentGuid.empty());  // popped back to root
+}
+
+// Nested folders: P > Q > leaf. The inner leaf closes BOTH folders at once (-2).
+// A sibling after it returns to the root.
+static void testNestedDeepClose() {
+    FolderTree t = buildFolderTree({{"P", 1}, {"Q", 1}, {"L", -2}, {"S", 0}});
+    CHECK(nodeOf(t, "P")->isParent && nodeOf(t, "P")->parentGuid.empty());
+    CHECK(nodeOf(t, "Q")->isParent && nodeOf(t, "Q")->parentGuid == "P");
+    CHECK(nodeOf(t, "L")->parentGuid == "Q");   // deepest leaf under Q
+    CHECK(!nodeOf(t, "L")->isParent);
+    CHECK(nodeOf(t, "S")->parentGuid.empty());  // both levels popped
+}
+
+// Nested with a stepwise close: inner folder closes (-1), then a sibling at the
+// OUTER level, then that folder closes (-1). Proves partial pops track correctly.
+static void testNestedStepwiseClose() {
+    FolderTree t = buildFolderTree(
+        {{"P", 1}, {"Q", 1}, {"L", -1}, {"M", -1}});
+    CHECK(nodeOf(t, "Q")->parentGuid == "P");
+    CHECK(nodeOf(t, "L")->parentGuid == "Q");   // L inside inner folder Q
+    CHECK(nodeOf(t, "M")->parentGuid == "P");   // after Q closed, M is under P
+}
+
+// Malformed stream: a close deeper than the open stack must clamp to empty, never
+// underflow. A following leaf is still top-level and the walk stays total.
+static void testMalformedCloseClamps() {
+    FolderTree t = buildFolderTree({{"P", 1}, {"C", -5}, {"S", 0}});
+    CHECK(nodeOf(t, "C")->parentGuid == "P");
+    CHECK(nodeOf(t, "S")->parentGuid.empty());  // clamped, not underflowed
+    CHECK(t.nodes.size() == 3);
+}
+
+// Empty input yields an empty tree (no fault).
+static void testEmpty() {
+    FolderTree t = buildFolderTree({});
+    CHECK(t.nodes.empty());
+}
+
+// An empty folder (parent immediately closes itself, depth accounting P=1 then a
+// child that both belongs to and closes it). Here P opens and the sole child
+// closes; verifies a folder with exactly one leaf child.
+static void testSingleChildFolder() {
+    FolderTree t = buildFolderTree({{"P", 1}, {"only", -1}});
+    CHECK(nodeOf(t, "only")->parentGuid == "P");
+    CHECK(nodeOf(t, "P")->isParent);
+}
+
+int main() {
+    testFlatLeaves();
+    testSingleFolder();
+    testFolderThenSibling();
+    testNestedDeepClose();
+    testNestedStepwiseClose();
+    testMalformedCloseClamps();
+    testEmpty();
+    testSingleChildFolder();
+
+    if (g_fail == 0) {
+        std::printf("view_tree: all tests passed\n");
+        return 0;
+    }
+    std::printf("view_tree: %d checks FAILED\n", g_fail);
+    return 1;
+}