frontend/src/hooks/usePresetCache.js

import { useState, useEffect, useCallback } from 'react'
import { isCached, cacheStem } from '../utils/presetCache'

const STEM_NAMES = ['guitar', 'drums', 'bass', 'synth', 'click_record']

/**
 * Checks IndexedDB for cached presets on mount, then background-fetches
 * any that are missing using the stateless /api/preset-stem endpoint.
 *
 * Returns cacheStatus: { [presetName]: 'cached' | 'loading' | 'uncached' }
 */
export function usePresetCache() {
  const [cacheStatus, setCacheStatus] = useState({})

  const prefetchPreset = useCallback(async (presetName) => {
    setCacheStatus(prev => ({ ...prev, [presetName]: 'loading' }))
    try {
      const results = await Promise.all(
        STEM_NAMES.map(async (stemName) => {
          const response = await fetch(`/api/preset-stem/${presetName}/${stemName}`)
          if (!response.ok) return false

          const sampleRate = parseInt(response.headers.get('X-Sample-Rate'))
          const numChannels = parseInt(response.headers.get('X-Channels'))
          const numFrames = parseInt(response.headers.get('X-Frames'))
          const bytes = await response.arrayBuffer()

          await cacheStem(presetName, stemName, { bytes, sampleRate, numChannels, numFrames })
          return true
        })
      )

      const allOk = results.every(Boolean)
      setCacheStatus(prev => ({ ...prev, [presetName]: allOk ? 'cached' : 'uncached' }))
    } catch {
      setCacheStatus(prev => ({ ...prev, [presetName]: 'uncached' }))
    }
  }, [])

  useEffect(() => {
    let cancelled = false

    async function init() {
      try {
        const res = await fetch('/api/presets')
        const { presets } = await res.json()
        if (cancelled || !presets?.length) return

        // Check which presets are already in IndexedDB
        const statuses = {}
        await Promise.all(
          presets.map(async (name) => {
            statuses[name] = (await isCached(name, STEM_NAMES)) ? 'cached' : 'uncached'
          })
        )
        if (cancelled) return
        setCacheStatus(statuses)

        // Background-fetch uncached presets one at a time to avoid saturating bandwidth
        for (const name of presets) {
          if (cancelled) break
          if (statuses[name] === 'uncached') {
            await prefetchPreset(name)
          }
        }
      } catch {
        // Prefetch is best-effort — silently fail
      }
    }

    init()
    return () => { cancelled = true }
  }, [prefetchPreset])

  return { cacheStatus }
}