// Nauka Czytania
;(function () {
  // ms between line advances for each speed level (0 = manual)
  const SPEEDS_MS    = [0, 3500, 2000, 1000]
  const SPEED_LABELS = ['Pauza', 'Wolno', 'Średnio', 'Szybko']

  let yOffset   = 0
  let lineH     = 80   // recalculated after render
  let maxOffset = 0
  let speedIdx  = 0
  let autoTimer = null

  const listWrap      = document.getElementById('list-wrap')
  const readWrap      = document.getElementById('read-wrap')
  const textList      = document.getElementById('text-list')
  const customInput   = document.getElementById('custom-input')
  const customStartBtn = document.getElementById('custom-start-btn')
  const readBackBtn   = document.getElementById('read-back-btn')
  const readTitleEl   = document.getElementById('read-title')
  const speedBtn      = document.getElementById('speed-btn')
  const readViewport  = document.getElementById('read-viewport')
  const readTextEl    = document.getElementById('read-text')
  const nextLineBtn   = document.getElementById('next-line-btn')
  const progressBar   = document.getElementById('read-progress-bar-inner')

  // ── Load text list from dyktanda.json ────────────────────────────────────
  fetch('json/dyktanda.json')
    .then(r => r.json())
    .then(data => {
      data.forEach(item => {
        const btn = document.createElement('button')
        btn.className = 'list-item-btn'
        btn.textContent = item.name
        btn.addEventListener('click', () => startReading(item.name, item.text))
        textList.appendChild(btn)
      })
    })
    .catch(() => {
      textList.innerHTML = '<p style="color:var(--muted);padding:8px 0">Nie udało się wczytać tekstów.</p>'
    })

  customStartBtn.addEventListener('click', () => {
    const txt = customInput.value.trim()
    if (!txt) return
    startReading('Własny', txt)
  })

  // ── Start reading ─────────────────────────────────────────────────────────
  function startReading(title, text) {
    yOffset  = 0
    speedIdx = 0
    clearInterval(autoTimer)
    autoTimer = null

    readTitleEl.textContent     = title
    readTextEl.textContent      = text
    readTextEl.style.transform  = 'translateY(0)'
    speedBtn.textContent        = SPEED_LABELS[0]
    progressBar.style.width     = '0%'

    listWrap.classList.add('hidden')
    readWrap.classList.remove('hidden')

    // measure real line height after layout
    requestAnimationFrame(() => {
      requestAnimationFrame(() => {
        const cs = getComputedStyle(readTextEl)
        const lhVal = cs.lineHeight
        lineH = (lhVal === 'normal')
          ? parseFloat(cs.fontSize) * 1.35
          : parseFloat(lhVal)

        maxOffset = Math.max(0, readTextEl.offsetHeight - lineH)
        updateNextBtn()
        updateProgressBar()
      })
    })
  }

  // ── Back to list ──────────────────────────────────────────────────────────
  readBackBtn.addEventListener('click', () => {
    const active = yOffset > 0 || autoTimer !== null
    if (active && !confirm('Wrócić do listy tekstów?')) return
    clearInterval(autoTimer)
    autoTimer = null
    readWrap.classList.add('hidden')
    listWrap.classList.remove('hidden')
    // Reset speed to manual on exit
    speedIdx = 0;
  })

  // ── Speed selector ────────────────────────────────────────────────────────
  speedBtn.addEventListener('click', () => {
    clearInterval(autoTimer)
    autoTimer = null
    speedIdx = (speedIdx + 1) % SPEEDS_MS.length
    speedBtn.textContent = SPEED_LABELS[speedIdx]
    if (SPEEDS_MS[speedIdx] > 0 && yOffset < maxOffset) {
      autoTimer = setInterval(advanceLine, SPEEDS_MS[speedIdx])
    }
  })

  // ── Manual line advance ───────────────────────────────────────────────────
  nextLineBtn.addEventListener('click', advanceLine)

  // ── Core scroll logic ─────────────────────────────────────────────────────
  function advanceLine() {
    if (yOffset >= maxOffset) {
      stopAutoAtEnd()
      return
    }
    yOffset = Math.min(yOffset + lineH, maxOffset)
    readTextEl.style.transform = `translateY(${-yOffset}px)`
    updateNextBtn()
    updateProgressBar()
    if (yOffset >= maxOffset) stopAutoAtEnd()
  }

  function stopAutoAtEnd() {
    if (autoTimer !== null) {
      clearInterval(autoTimer)
      autoTimer = null
      speedIdx = 0
      speedBtn.textContent = SPEED_LABELS[0]
    }
    updateNextBtn()
  }

  function updateNextBtn() {
    nextLineBtn.disabled = yOffset >= maxOffset
  }

  function updateProgressBar() {
    const progress = maxOffset > 0 ? (yOffset / maxOffset) * 100 : 100
    progressBar.style.width = `${progress}%`
  }
})()