frontend/src/utils/presetCache.js

/**
 * IndexedDB cache for preset stem PCM data.
 * Stores raw int16 bytes + metadata so preset loads are instant after first visit.
 *
 * Bump CACHE_VERSION whenever preset audio files change on the server —
 * old entries will be ignored and re-fetched.
 */

const DB_NAME = 'jam-tracks-presets'
const DB_VERSION = 1
const STORE_NAME = 'stems'
export const CACHE_VERSION = 1

function openDB() {
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB_NAME, DB_VERSION)
    req.onupgradeneeded = (e) => {
      const db = e.target.result
      if (!db.objectStoreNames.contains(STORE_NAME)) {
        db.createObjectStore(STORE_NAME)
      }
    }
    req.onsuccess = (e) => resolve(e.target.result)
    req.onerror = (e) => reject(e.target.error)
  })
}

function dbGet(db, key) {
  return new Promise((resolve, reject) => {
    const tx = db.transaction(STORE_NAME, 'readonly')
    const req = tx.objectStore(STORE_NAME).get(key)
    req.onsuccess = (e) => resolve(e.target.result)
    req.onerror = (e) => reject(e.target.error)
  })
}

function dbPut(db, key, value) {
  return new Promise((resolve, reject) => {
    const tx = db.transaction(STORE_NAME, 'readwrite')
    const req = tx.objectStore(STORE_NAME).put(value, key)
    req.onsuccess = () => resolve()
    req.onerror = (e) => reject(e.target.error)
  })
}

function stemKey(presetName, stemName) {
  return `v${CACHE_VERSION}:${presetName}:${stemName}`
}

/** Returns true if all stemNames for this preset are cached. */
export async function isCached(presetName, stemNames) {
  try {
    const db = await openDB()
    const checks = await Promise.all(stemNames.map(s => dbGet(db, stemKey(presetName, s))))
    return checks.every(v => v != null)
  } catch {
    return false
  }
}

/**
 * Returns cached data for all stems or null if any stem is missing.
 * Shape: { stemName: { bytes: ArrayBuffer, sampleRate, numChannels, numFrames } }
 */
export async function getCachedPreset(presetName, stemNames) {
  try {
    const db = await openDB()
    const result = {}
    for (const stemName of stemNames) {
      const entry = await dbGet(db, stemKey(presetName, stemName))
      if (!entry) return null
      result[stemName] = entry
    }
    return result
  } catch {
    return null
  }
}

/** Store a single stem's PCM data in IndexedDB. */
export async function cacheStem(presetName, stemName, data) {
  try {
    const db = await openDB()
    await dbPut(db, stemKey(presetName, stemName), data)
  } catch (err) {
    console.warn('[presetCache] Failed to cache stem:', err)
  }
}