// Web MIDI input manager: enumerates inputs, follows hot-plug through
// statechange, and forwards note on/off events from the selected input
// (or from every input) to subscribers.

export interface NoteInputEvent {
  on: boolean;
  pitch: number;
  velocity: number; // 1..127 for on
  source: string;
}

export interface MidiState {
  supported: boolean;
  requested: boolean;
  error: string | null;
  inputs: { id: string; name: string }[];
  selectedId: string; // 'all' or an input id
}

type Listener = (e: NoteInputEvent) => void;

class MidiManager {
  private access: MIDIAccess | null = null;
  private listeners = new Set<Listener>();
  private stateListeners = new Set<() => void>();
  private state: MidiState = { supported: typeof navigator !== 'undefined' && 'requestMIDIAccess' in navigator, requested: false, error: null, inputs: [], selectedId: 'all' };

  getState(): MidiState { return this.state; }

  subscribeState(cb: () => void): () => void {
    this.stateListeners.add(cb);
    return () => this.stateListeners.delete(cb);
  }

  subscribe(cb: Listener): () => void {
    this.listeners.add(cb);
    return () => this.listeners.delete(cb);
  }

  private setState(patch: Partial<MidiState>) {
    this.state = { ...this.state, ...patch };
    for (const cb of this.stateListeners) cb();
  }

  async request(): Promise<void> {
    if (!this.state.supported || this.access) return;
    this.setState({ requested: true });
    try {
      this.access = await navigator.requestMIDIAccess({ sysex: false });
      this.access.onstatechange = () => this.refresh();
      this.refresh();
    } catch (err) {
      this.setState({ error: err instanceof Error ? err.message : String(err) });
    }
  }

  select(id: string) {
    this.setState({ selectedId: id });
    this.refresh();
  }

  private refresh() {
    if (!this.access) return;
    const inputs: { id: string; name: string }[] = [];
    for (const input of this.access.inputs.values()) {
      inputs.push({ id: input.id, name: input.name ?? input.id });
      const active = this.state.selectedId === 'all' || this.state.selectedId === input.id;
      input.onmidimessage = active ? (ev: MIDIMessageEvent) => this.onMessage(input.name ?? input.id, ev) : null;
    }
    this.setState({ inputs });
  }

  private onMessage(source: string, ev: MIDIMessageEvent) {
    const d = ev.data;
    if (!d || d.length < 3) return;
    const kind = d[0] >> 4;
    if (kind === 0x9 && d[2] > 0) this.emit({ on: true, pitch: d[1], velocity: d[2], source });
    else if (kind === 0x8 || (kind === 0x9 && d[2] === 0)) this.emit({ on: false, pitch: d[1], velocity: 0, source });
  }

  private emit(e: NoteInputEvent) {
    for (const cb of this.listeners) cb(e);
  }
}

export const midiManager = new MidiManager();