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

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;
    }
}