import { visit } from 'unist-util-visit'
import { Node } from 'unist'

interface LinkNode extends Node {
  type: 'link'
  url: string
  children: Node[]
}

/**
 * Detects internal blog post links:
 * - Relative paths (no http/https)
 * - Not absolute paths (doesn't start with /)
 * - Ends with .md
 */
function isInternalBlogLink(url: string): boolean {
  return (
    !url.startsWith('http://') &&
    !url.startsWith('https://') &&
    !url.startsWith('/') &&
    url.includes('.md')
  )
}

/**
 * Transforms internal .md links to blog routes:
 * - tech/article.md → /blog/tech/article
 * - article.md#section → /blog/article#section
 * - nested/path/post.md?ref=foo → /blog/nested/path/post?ref=foo
 */
function transformToBlogPath(url: string): string {
  // Split into path, hash, and query
  const hashIndex = url.indexOf('#')
  const queryIndex = url.indexOf('?')

  let path = url
  let hash = ''
  let query = ''

  if (hashIndex !== -1) {
    path = url.substring(0, hashIndex)
    hash = url.substring(hashIndex)
  }

  if (queryIndex !== -1 && queryIndex < (hashIndex === -1 ? url.length : hashIndex)) {
    path = url.substring(0, queryIndex)
    query = url.substring(queryIndex, hashIndex === -1 ? url.length : hashIndex)
  }

  // Remove .md extension
  const cleanPath = path.replace(/\.md$/, '')

  // Build final URL
  return `/blog/${cleanPath}${query}${hash}`
}

export function remarkInternalLinks() {
  return (tree: Node) => {
    visit(tree, 'link', (node: Node) => {
      const linkNode = node as LinkNode

      if (isInternalBlogLink(linkNode.url)) {
        linkNode.url = transformToBlogPath(linkNode.url)
      }
    })
  }
}