import { readFileSync, writeFileSync, existsSync } from 'fs'
import { relative, resolve } from 'path'
import type { SidebarItem } from './types'
import { parseFrontmatter, stringifyFrontmatter } from './frontmatter'
import { mergeSectionLinks, extractTopLevelLinks, extractItemsForPage } from './links'
import { normalizeLink } from './path-utils'
import { SectionLinkListItem } from '../../theme/components/SectionLinkList/SectionLinkList.types'

const removeDuplicates = (links: SectionLinkListItem[]) => {
  const result: SectionLinkListItem[] = []
  const seenLinks = new Set<string>()
  
  for (const link of links) {
    if (link.link) {
      const normalized = normalizeLink(link.link)
      if (!seenLinks.has(normalized)) {
        seenLinks.add(normalized)
        result.push(link)
      }
    }
  }
  
  return result
}

const hasChanges = (
  existingLinks: SectionLinkListItem[],
  mergedLinks: SectionLinkListItem[]
) => {
  if (existingLinks.length !== mergedLinks.length) return true

  const existingSet = new Set(
    existingLinks
      .filter(link => link.link)
      .map(link => `${normalizeLink(link.link!)}|${link.title}`)
  )

  const mergedSet = new Set(
    mergedLinks
      .filter(link => link.link)
      .map(link => `${normalizeLink(link.link!)}|${link.title}`)
  )

  if (existingSet.size !== mergedSet.size) return true

  for (const item of existingSet) {
    if (!mergedSet.has(item)) return true
  }

  return false
}

export const processIndexFile = (
  filePath: string,
  sidebarItems: SidebarItem[],
  srcDir: string
) => {
  if (!existsSync(filePath)) return false

  try {
    const fileContent = readFileSync(filePath, 'utf-8')
    const { frontmatter, content } = parseFrontmatter(fileContent)

    const relativePath = relative(srcDir, filePath).replace(/\\/g, '/')
    const normalizedPath = relativePath.startsWith('/') ? relativePath : `/${relativePath}`

    const existingLinks = removeDuplicates(
      Array.isArray(frontmatter.section_links) ? [...frontmatter.section_links] : []
    )
    const newLinks = extractTopLevelLinks(sidebarItems, normalizedPath, srcDir)

    if (!newLinks.length) return false

    const mergedLinks = removeDuplicates(mergeSectionLinks(existingLinks, newLinks))

    if (!hasChanges(existingLinks, mergedLinks)) return false

    frontmatter.section_links = mergedLinks
    writeFileSync(filePath, stringifyFrontmatter(frontmatter, content), 'utf-8')
    return true
  } catch {
    return false
  }
}

export const processPageWithItems = (
  filePath: string,
  sidebarItems: SidebarItem[],
  srcDir: string
) => {
  if (!existsSync(filePath)) return false

  try {
    const fileContent = readFileSync(filePath, 'utf-8')
    const { frontmatter, content } = parseFrontmatter(fileContent)

    const relativePath = relative(srcDir, filePath).replace(/\\/g, '/')
    const normalizedPath = relativePath.startsWith('/') ? relativePath : `/${relativePath}`

    const existingLinks = removeDuplicates(
      Array.isArray(frontmatter.section_links) ? [...frontmatter.section_links] : []
    )
    const newLinks = extractItemsForPage(sidebarItems, normalizedPath, srcDir)

    const mergedLinks = newLinks.length > 0
      ? removeDuplicates(mergeSectionLinks(existingLinks, newLinks))
      : []

    if (!hasChanges(existingLinks, mergedLinks)) return false

    frontmatter.section_links = mergedLinks
    writeFileSync(filePath, stringifyFrontmatter(frontmatter, content), 'utf-8')
    return true
  } catch {
    return false
  }
}