import { defineStore } from 'pinia'
import { ref } from 'vue'
import { useApi } from '../composables/useApi.js'
import { useAsyncAction } from '../composables/useAsyncAction.js'

// IR reader.js "viewport-center-in-third" rule, pure for unit tests.
// metrics: [{page_number, top, height}] in page order.
export function currentPageFromScroll(metrics, scrollTop, viewportH) {
  if (!metrics.length) return 1
  const target = scrollTop + viewportH / 3
  let cur = metrics[0].page_number
  for (const m of metrics) {
    if (target >= m.top) cur = m.page_number
  }
  return cur
}

export function progressPct(scrollTop, scrollHeight, clientHeight) {
  const denom = scrollHeight - clientHeight
  if (denom <= 0) return 0
  const pct = (scrollTop / denom) * 100
  return Math.min(100, Math.max(0, pct))
}

export function clampPage(n, total) {
  if (!total || total < 1) return 1
  if (!Number.isFinite(n) || n < 1) return 1
  if (n > total) return total
  return Math.floor(n)
}

export const useSeriesReaderStore = defineStore('seriesReader', () => {
  const api = useApi()

  const series = ref(null)
  const pages = ref([])
  const { loading, error, run } = useAsyncAction({ errorAs: 'message' })

  async function load(tagId) {
    series.value = null  // cleared upfront so they stay reset on error
    pages.value = []
    await run(async () => {
      const body = await api.get(`/api/series/${tagId}/pages`)
      series.value = body.series
      pages.value = body.pages
    })
  }

  return { series, pages, loading, error, load }
})