refactor: implement unidirectional data flow with dispatcher pattern

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

dispatcher.h

@@ -0,0 +1,166 @@
+#ifndef DISPATCHER_H
+#define DISPATCHER_H
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <stdatomic.h>
+#include <jack/jack.h>
+#include <pthread.h>
+
+// ============================================================
+// Application State - contains ALL application state
+// ============================================================
+
+#define MAX_SCENES 8
+#define MAX_CHANNELS 8
+#define MAX_CLIPS (MAX_SCENES * MAX_CHANNELS)  // 64
+#define MAX_BUFFER_SIZE 441000  // 10 seconds at 44.1kHz
+#define MAX_UNDO_HISTORY 256
+
+#define CLIP_INDEX(scene, channel) ((scene) * MAX_CHANNELS + (channel))
+
+typedef enum {
+    CLIP_EMPTY,
+    CLIP_RECORDING,
+    CLIP_LOOPING,
+    CLIP_STOPPED
+} ClipState;
+
+typedef enum {
+    QUANTIZE_OFF,
+    QUANTIZE_BEAT,
+    QUANTIZE_BAR
+} QuantizeMode;
+
+typedef enum {
+    TRANSPORT_STOPPED,
+    TRANSPORT_PLAYING,
+    TRANSPORT_PAUSED
+} TransportState;
+
+typedef enum {
+    CLOCK_SOURCE_INTERNAL,
+    CLOCK_SOURCE_MIDI
+} ClockSource;
+
+typedef struct {
+    ClipState state;
+    float *buffer;
+    size_t buffer_size;
+    size_t write_position;
+    size_t read_position;
+} Clip;
+
+typedef struct {
+    // Transport state
+    TransportState transport_state;
+    ClockSource clock_source;
+    uint32_t clock_count;
+    uint32_t beat_position;
+    uint32_t bar_position;
+    uint32_t sample_position;
+    double bpm;
+    double samples_per_beat;
+    double sample_accumulator;
+    
+    // Quantization
+    QuantizeMode quantize_mode;
+    jack_nframes_t quantize_threshold;
+    
+    // Clips
+    Clip clips[MAX_CLIPS];
+    
+    // Undo history
+    struct {
+        int undo_index;
+        int redo_index;
+        int count;
+        ClipState prev_clip_states[MAX_UNDO_HISTORY];
+        int prev_clip_indices[MAX_UNDO_HISTORY];
+        size_t prev_buffer_sizes[MAX_UNDO_HISTORY];
+        size_t prev_write_positions[MAX_UNDO_HISTORY];
+        size_t prev_read_positions[MAX_UNDO_HISTORY];
+    } undo;
+    
+    // JACK info (needed by audio thread)
+    jack_nframes_t sample_rate;
+    bool running;
+} AppState;
+
+// ============================================================
+// Actions
+// ============================================================
+
+typedef enum {
+    ACTION_TRIGGER_CLIP,
+    ACTION_TRIGGER_SCENE,
+    ACTION_RESET_CLIP,
+    ACTION_SET_QUANTIZE_MODE,
+    ACTION_SET_QUANTIZE_THRESHOLD,
+    ACTION_TRANSPORT_PLAY,
+    ACTION_TRANSPORT_PAUSE,
+    ACTION_TRANSPORT_STOP,
+    ACTION_TRANSPORT_TOGGLE_PLAY,
+    ACTION_SET_CLOCK_SOURCE,
+    ACTION_SET_BPM,
+    ACTION_RESET_TRANSPORT,
+    ACTION_UNDO,
+    ACTION_REDO,
+    ACTION_SAVE_CLIP,
+    ACTION_LOAD_CLIP,
+    ACTION_MIDI_NOTE_ON,
+    ACTION_MIDI_SCENE_LAUNCH,
+    ACTION_PROCESS_AUDIO,
+    ACTION_QUIT
+} ActionType;
+
+typedef struct {
+    ActionType type;
+    union {
+        struct { int clip_index; } trigger_clip;
+        struct { int scene_index; } trigger_scene;
+        struct { int clip_index; } reset_clip;
+        struct { QuantizeMode mode; } set_quantize_mode;
+        struct { jack_nframes_t threshold; } set_quantize_threshold;
+        struct { ClockSource source; } set_clock_source;
+        struct { double bpm; } set_bpm;
+        struct { int clip_index; } save_clip;
+        struct { int clip_index; char filename[256]; } load_clip;
+        struct { int note; int velocity; int channel; jack_nframes_t time; } midi_note_on;
+        struct { int scene_index; jack_nframes_t time; } midi_scene_launch;
+        struct { jack_nframes_t nframes; } process_audio;
+    } data;
+} Action;
+
+// ============================================================
+// Dispatcher API
+// ============================================================
+
+// Thread-safe dispatch function - called by any thread
+typedef void (*DispatchFn)(Action action);
+
+// Subscriber callback - called after each state update (from dispatcher thread)
+typedef void (*SubscriberFn)(AppState *state, void *user_data);
+
+// Initialize the dispatcher with initial state
+// Returns the dispatch function that consumers can call
+DispatchFn dispatcher_init(AppState *initial_state);
+
+// Register a subscriber (call before dispatcher_start)
+void dispatcher_subscribe(SubscriberFn fn, void *user_data);
+
+// Start the dispatcher thread
+void dispatcher_start(void);
+
+// Stop the dispatcher and cleanup
+void dispatcher_stop(void);
+
+// Get current state (thread-safe snapshot)
+AppState dispatcher_get_state(void);
+
+// ============================================================
+// Reducer - pure function
+// ============================================================
+AppState reducer(AppState state, Action action);
+
+#endif // DISPATCHER_H