import type { StarlightRouteData } from '@astrojs/starlight/route-data'

import type { StarlightSidebarTopicsSharedConfig } from './config'
import { isStarlightEntryWithTopic, type StarlightEntry } from './content'
import { getLocaleFromSlug, getLocalizedSlug } from './i18n'
import { arePathnamesEqual, stripLeadingAndTrailingSlashes } from './pathname'

const absoluteLinkRegex = /^https?:\/\//

export function getCurrentTopic(
  config: StarlightSidebarTopicsSharedConfig,
  sidebar: SidebarEntry[],
  currentSlug: string,
  entry: StarlightEntry,
): Topic | undefined {
  // If the current page has a topic ID, use it to find the topic.
  const topicId = getTopicIdFromEntry(entry)
  if (topicId) return getTopicById(config, sidebar, topicId)

  // Start by checking if the current page is a topic root.
  const topicFromSlug = getTopicFromSlug(config, sidebar, currentSlug)
  if (topicFromSlug) return topicFromSlug

  // Otherwise, find the current topic by looking for the current page in the sidebar.
  const currentSidebarTopic = getCurrentSidebarTopic(sidebar)
  if (!currentSidebarTopic) return

  const currentTopicConfig = config[Number.parseInt(currentSidebarTopic.label, 10)]
  if (!currentTopicConfig) return

  return { config: currentTopicConfig, sidebar: currentSidebarTopic.entries }
}

export function isTopicFirstPage(sidebar: SidebarEntry[], currentSlug: string): boolean {
  const currentSidebarTopic = getCurrentSidebarTopic(sidebar)
  if (!currentSidebarTopic) return false

  const firstPage = getSidebarFirstPage(currentSidebarTopic.entries)
  if (!firstPage) return false

  return arePathnamesEqual(stripLeadingAndTrailingSlashes(firstPage.href), currentSlug)
}

export function isTopicLastPage(sidebar: SidebarEntry[], currentSlug: string): boolean {
  const currentSidebarTopic = getCurrentSidebarTopic(sidebar)
  if (!currentSidebarTopic) return false

  const lastPage = getSidebarLastPage(currentSidebarTopic.entries)
  if (!lastPage) return false

  return arePathnamesEqual(stripLeadingAndTrailingSlashes(lastPage.href), currentSlug)
}

function getSidebarFirstPage(sidebar: SidebarEntry[]) {
  const entry = sidebar[0]
  if (!entry) return
  if (entry.type === 'link') return entry

  return getSidebarFirstPage(entry.entries)
}

function getSidebarLastPage(sidebar: SidebarEntry[]) {
  const entry = sidebar.at(-1)
  if (!entry) return
  if (entry.type === 'link') return entry

  return getSidebarLastPage(entry.entries)
}

function getTopicFromSlug(
  config: StarlightSidebarTopicsSharedConfig,
  sidebar: SidebarEntry[],
  slug: string,
): Topic | undefined {
  let topicConfig: Topic['config'] | undefined
  let topicSidebar: Topic['sidebar'] | undefined

  // Start by checking if the current page is a topic homepage.
  let groupTopicIndex = -1
  const slugLocale = getLocaleFromSlug(slug)

  for (const topic of config) {
    if (topic.type === 'group') groupTopicIndex++

    if (
      !absoluteLinkRegex.test(topic.link) &&
      arePathnamesEqual(getLocalizedSlug(stripLeadingAndTrailingSlashes(topic.link), slugLocale), slug) &&
      groupTopicIndex !== -1
    ) {
      const sidebarTopic = sidebar[groupTopicIndex]

      if (sidebarTopic?.type === 'group') {
        topicConfig = topic
        topicSidebar = sidebarTopic.entries
      }

      break
    }
  }

  if (!topicConfig || !topicSidebar) return

  return { config: topicConfig, sidebar: topicSidebar }
}

export function getTopicById(
  config: StarlightSidebarTopicsSharedConfig,
  sidebar: SidebarEntry[],
  id: string,
): Topic | undefined {
  let topicConfig: Topic['config'] | undefined
  let topicSidebar: Topic['sidebar'] | undefined

  let groupTopicIndex = -1

  for (const topic of config) {
    if (topic.type === 'group') groupTopicIndex++

    if (topic.type === 'group' && topic.id === id) {
      const sidebarTopic = sidebar[groupTopicIndex]

      if (sidebarTopic?.type === 'group') {
        topicConfig = topic
        topicSidebar = sidebarTopic.entries
      }

      break
    }
  }

  if (!topicConfig || !topicSidebar) return

  return { config: topicConfig, sidebar: topicSidebar }
}

function getCurrentSidebarTopic(sidebar: SidebarEntry[]): SidebarTopic | undefined {
  let currentSidebarTopic: SidebarTopic | undefined

  for (const topic of sidebar) {
    if (topic.type === 'link') continue

    const currentSidebarEntry = getCurrentSidebarEntry(topic.entries)

    if (currentSidebarEntry) {
      currentSidebarTopic = topic
      break
    }
  }

  return currentSidebarTopic
}

function getCurrentSidebarEntry(sidebar: SidebarEntry[]): SidebarEntry | undefined {
  return sidebar.find((entry) => {
    if (entry.type === 'link') {
      return entry.isCurrent
    }

    return getCurrentSidebarEntry(entry.entries)
  })
}

function getTopicIdFromEntry(entry: StarlightEntry): string | undefined {
  return isStarlightEntryWithTopic(entry) ? entry.data.topic : undefined
}

type SidebarEntry = StarlightRouteData['sidebar'][number]

interface SidebarTopic {
  label: string
  entries: SidebarEntry[]
}

export interface Topic {
  config: StarlightSidebarTopicsSharedConfig[number]
  sidebar: SidebarEntry[]
}