Initial Commit

packages/ui/react/react-midi/src/midi-contract/reducers.ts

@@ -0,0 +1,173 @@
+import type {
+    CC14Change,
+    Channel,
+    ControlChangeMessage,
+    NRPNChange,
+    RPNChange,
+} from "./midi-message.types.js";
+
+const CC_NRPN_HIGH = 99;
+const CC_NRPN_LOW = 98;
+const CC_RPN_HIGH = 101;
+const CC_RPN_LOW = 100;
+const CC_DATA_HIGH = 6;
+const CC_DATA_LOW = 38;
+
+interface PartialState {
+    paramHigh: number | null;
+    paramLow: number | null;
+    valueHigh: number | null;
+    valueLow: number | null;
+}
+
+function emptyState(): PartialState {
+    return {
+        paramHigh: null,
+        paramLow: null,
+        valueHigh: null,
+        valueLow: null,
+    };
+}
+
+/**
+ * NRPN four-CC reducer. Feed channel-voice CC messages into `feed`;
+ * when CC 99/98/6/38 have all arrived on the same channel, the
+ * reducer emits a single `NRPNChange` event and resets that channel's
+ * partial state. Incomplete dances (e.g. missing LSB) remain pending
+ * until completion or are dropped when a fresh paramHigh arrives.
+ */
+export class NRPNReducer {
+    private readonly partials = new Map<Channel, PartialState>();
+
+    feed(msg: ControlChangeMessage): NRPNChange | null {
+        const state = this.partials.get(msg.channel) ?? emptyState();
+        switch (msg.controller) {
+            case CC_NRPN_HIGH:
+                state.paramHigh = msg.value;
+                state.paramLow = null;
+                state.valueHigh = null;
+                state.valueLow = null;
+                break;
+            case CC_NRPN_LOW:
+                state.paramLow = msg.value;
+                break;
+            case CC_DATA_HIGH:
+                state.valueHigh = msg.value;
+                break;
+            case CC_DATA_LOW:
+                state.valueLow = msg.value;
+                break;
+            default:
+                this.partials.set(msg.channel, state);
+                return null;
+        }
+        this.partials.set(msg.channel, state);
+        if (
+            state.paramHigh !== null &&
+            state.paramLow !== null &&
+            state.valueHigh !== null &&
+            state.valueLow !== null
+        ) {
+            const out: NRPNChange = {
+                type: "nrpnChange",
+                channel: msg.channel,
+                paramHigh: state.paramHigh,
+                paramLow: state.paramLow,
+                value: (state.valueHigh << 7) | state.valueLow,
+            };
+            this.partials.set(msg.channel, emptyState());
+            return out;
+        }
+        return null;
+    }
+}
+
+/**
+ * RPN four-CC reducer. Identical control flow as `NRPNReducer` but
+ * uses CC 101/100 for the parameter MSB/LSB selectors.
+ */
+export class RPNReducer {
+    private readonly partials = new Map<Channel, PartialState>();
+
+    feed(msg: ControlChangeMessage): RPNChange | null {
+        const state = this.partials.get(msg.channel) ?? emptyState();
+        switch (msg.controller) {
+            case CC_RPN_HIGH:
+                state.paramHigh = msg.value;
+                state.paramLow = null;
+                state.valueHigh = null;
+                state.valueLow = null;
+                break;
+            case CC_RPN_LOW:
+                state.paramLow = msg.value;
+                break;
+            case CC_DATA_HIGH:
+                state.valueHigh = msg.value;
+                break;
+            case CC_DATA_LOW:
+                state.valueLow = msg.value;
+                break;
+            default:
+                this.partials.set(msg.channel, state);
+                return null;
+        }
+        this.partials.set(msg.channel, state);
+        if (
+            state.paramHigh !== null &&
+            state.paramLow !== null &&
+            state.valueHigh !== null &&
+            state.valueLow !== null
+        ) {
+            const out: RPNChange = {
+                type: "rpnChange",
+                channel: msg.channel,
+                paramHigh: state.paramHigh,
+                paramLow: state.paramLow,
+                value: (state.valueHigh << 7) | state.valueLow,
+            };
+            this.partials.set(msg.channel, emptyState());
+            return out;
+        }
+        return null;
+    }
+}
+
+/**
+ * 14-bit CC reducer. Pairs CCs 0-31 with CCs 32-63 (MSB+LSB pair on
+ * the same channel). On reception of either half, the reducer
+ * remembers the partial value and, once both halves are observed,
+ * emits a single `CC14Change` event with the combined 14-bit value.
+ */
+export class CC14Reducer {
+    private readonly msbs = new Map<string, number>();
+    private readonly lsbs = new Map<string, number>();
+
+    feed(msg: ControlChangeMessage): CC14Change | null {
+        const isMsb = msg.controller < 32;
+        const isLsb = msg.controller >= 32 && msg.controller < 64;
+        if (!isMsb && !isLsb) {
+            return null;
+        }
+        const baseController = isMsb ? msg.controller : msg.controller - 32;
+        const key = `${msg.channel}:${baseController}`;
+        if (isMsb) {
+            this.msbs.set(key, msg.value);
+        } else {
+            this.lsbs.set(key, msg.value);
+        }
+        const msb = this.msbs.get(key);
+        const lsb = this.lsbs.get(key);
+        if (msb !== undefined && lsb !== undefined) {
+            const out: CC14Change = {
+                type: "cc14Change",
+                channel: msg.channel,
+                controller: baseController,
+                value: (msb << 7) | lsb,
+            };
+            this.msbs.delete(key);
+            this.lsbs.delete(key);
+            return out;
+        }
+        return null;
+    }
+}