FabledScribe/frontend/src/composables/useOnnxPreloader.ts

import { ref, readonly } from 'vue'

/**
 * Idle-preload the Silero VAD ONNX model and its companion assets.
 *
 * `@ricky0123/vad-web` pulls ~2MB of ONNX model + ~5MB of onnxruntime-web
 * WASM the first time `MicVAD.new()` runs. Calling `defaultModelFetcher`
 * during page idle warms the browser cache so the first mic click feels
 * instant. If the preload fails, VAD simply loads lazily on first click.
 */
const ready = ref(false)
let loading = false

export function useOnnxPreloader() {
  async function preload() {
    if (ready.value || loading) return
    loading = true
    try {
      const { defaultModelFetcher } = await import('@ricky0123/vad-web')
      // Asset lives at site root because vite-plugin-static-copy drops it
      // there. Match whatever path MicVAD will use at call time (see useVad).
      await defaultModelFetcher('/silero_vad_v5.onnx')
      ready.value = true
    } catch {
      // Non-fatal — MicVAD will load the model itself on first use.
    } finally {
      loading = false
    }
  }

  function schedulePreload() {
    if (ready.value) return
    if (typeof window === 'undefined') return
    if ('requestIdleCallback' in window) {
      (window as Window & { requestIdleCallback: (cb: () => void, opts: { timeout: number }) => void })
        .requestIdleCallback(() => void preload(), { timeout: 5000 })
    } else {
      setTimeout(() => void preload(), 5000)
    }
  }

  return { ready: readonly(ready), schedulePreload }
}