au_whisper_web/src/components/ModelPicker.tsx

import {
  estimateDefaultDownloadBytes,
  formatModelSize,
  type WhisperModel,
} from "../lib/models";
import type { DevicePreference, InferenceDevice } from "../worker/protocol";

interface ModelPickerProps {
  models: readonly WhisperModel[];
  selectedId: string;
  onSelect: (modelId: string) => void;
  devicePreference: DevicePreference;
  onDevicePreferenceChange: (preference: DevicePreference) => void;
  /** Backend the worker actually selected; null until the first load (D-004). */
  activeDevice: InferenceDevice | null;
  /** Model ids with weights already in the browser cache (D-005). */
  downloaded: ReadonlySet<string>;
  /** True when the service worker controls the page — app shell cached (M3). */
  offlineReady: boolean;
  /** True while a transcription is running — switching is disabled then. */
  disabled?: boolean;
  /** Explicitly download the selected model's weights (D-020). */
  onDownloadSelected: () => void;
  /** True while a model load/download is in flight. */
  downloading: boolean;
}

const DEVICE_OPTIONS: readonly { value: DevicePreference; label: string }[] = [
  { value: "auto", label: "Auto (WebNN → WebGPU → WASM)" },
  { value: "webgpu", label: "WebGPU" },
  { value: "webnn", label: "WebNN" },
  { value: "wasm", label: "WASM (CPU)" },
];

/** Human-readable backend names, shared with the active-device badge. */
export const DEVICE_LABELS: Record<InferenceDevice, string> = {
  webnn: "WebNN",
  webgpu: "WebGPU",
  wasm: "WASM",
};

/**
 * Curated model list (D-006): size estimate before download, English-only vs
 * multilingual grouping, downloaded badge from the Cache API (D-005), and a
 * device preference select (default "auto", D-004).
 */
export function ModelPicker({
  models,
  selectedId,
  onSelect,
  devicePreference,
  onDevicePreferenceChange,
  activeDevice,
  downloaded,
  offlineReady,
  disabled = false,
  onDownloadSelected,
  downloading,
}: ModelPickerProps) {
  // Size estimates depend on the dtype the worker will pick, which depends on
  // the device. Until the worker has reported one, assume WASM unless the
  // user explicitly asked for WebGPU.
  const estimateDevice: InferenceDevice =
    activeDevice ??
    (devicePreference === "webgpu"
      ? "webgpu"
      : devicePreference === "webnn"
        ? "webnn"
        : "wasm");

  const groups: { title: string; items: WhisperModel[] }[] = [
    {
      title: "English-only",
      items: models.filter((model) => !model.multilingual),
    },
    {
      title: "Multilingual",
      items: models.filter((model) => model.multilingual),
    },
  ];

  return (
    <section className="model-picker" aria-label="Model selection">
      <div className="model-picker-header">
        <h2>Model</h2>
        <label className="device-select">
          Backend
          <select
            value={devicePreference}
            disabled={disabled}
            onChange={(event) =>
              onDevicePreferenceChange(event.target.value as DevicePreference)
            }
          >
            {DEVICE_OPTIONS.map((option) => (
              <option key={option.value} value={option.value}>
                {option.label}
              </option>
            ))}
          </select>
        </label>
        {/* Which backend the worker actually selected (D-004/D-017) — the
            user's preference is only a preference, so show the outcome. */}
        {activeDevice && (
          <span
            className="model-badge device-active-badge"
            role="status"
            title="The inference backend the worker actually selected for this model."
          >
            Running on {DEVICE_LABELS[activeDevice]}
          </span>
        )}
      </div>
      {disabled && (
        <p className="model-picker-hint">
          Model switching is disabled while a transcription is running.
        </p>
      )}
      <p
        className={`offline-status${offlineReady && downloaded.size > 0 ? " offline-status-ready" : ""}`}
      >
        {offlineReady
          ? downloaded.size > 0
            ? "Offline ready — the app and the models marked “available offline” work without a network connection."
            : "The app is cached for offline use. Download a model (or run one on-device transcription) to make it available offline too."
          : "Offline support is not active yet (the service worker is still installing, or this browser does not support it)."}
      </p>
      {groups.map((group) => (
        <fieldset key={group.title} className="model-group" disabled={disabled}>
          <legend>{group.title}</legend>
          <ul>
            {group.items.map((model) => {
              const size = formatModelSize(
                estimateDefaultDownloadBytes(model, estimateDevice),
              );
              const isDownloaded = downloaded.has(model.id);
              const isSelected = model.id === selectedId;
              return (
                <li key={model.id}>
                  <label
                    className={`model-option${isSelected ? " model-option-selected" : ""}`}
                  >
                    <input
                      type="radio"
                      name="model"
                      value={model.id}
                      checked={isSelected}
                      disabled={disabled}
                      onChange={() => onSelect(model.id)}
                    />
                    <span className="model-option-name">{model.displayName}</span>
                    <span className="model-option-meta">
                      {isDownloaded && (
                        <span
                          className="model-badge"
                          title="Weights are cached in this browser — this model loads and transcribes without a network connection."
                        >
                          available offline
                        </span>
                      )}
                      <span className="model-option-size">~{size}</span>
                      {isSelected && !isDownloaded && (
                        <button
                          type="button"
                          className="model-download-button"
                          disabled={disabled || downloading}
                          title="Download this model now so it is available offline. Otherwise it downloads automatically when an on-device transcription starts."
                          onClick={onDownloadSelected}
                        >
                          {downloading ? "Downloading…" : "Download"}
                        </button>
                      )}
                    </span>
                  </label>
                </li>
              );
            })}
          </ul>
        </fieldset>
      ))}
    </section>
  );
}