import fs from 'fs'
import path from 'path'
import matter from 'gray-matter'
import { remark } from 'remark'
import remarkParse from 'remark-parse'
import remarkGfm from 'remark-gfm'
import remarkMath from 'remark-math'
import remarkRehype from 'remark-rehype'
import rehypeHighlight from 'rehype-highlight'
import rehypeKatex from 'rehype-katex'
import rehypeReact from 'rehype-react'
import {
  cache,
  cloneElement,
  isValidElement,
  type ReactElement,
  Fragment,
  type ReactNode,
} from 'react'
import { jsx, jsxs } from 'react/jsx-runtime'
import { rehypeCodeMeta } from '@/lib/rehype-code-meta'
import { CodeWrapper } from '@/components/content/CodeWrapper'
import { ImageWrapper } from '@/components/content/ImageWrapper'
import { ExternalLink } from '@/components/ui/ExternalLink'
import readingTime from 'reading-time'
import { rehypeUnwrapImages } from '@/lib/rehype-unwrap-images'
import { rehypeMermaidSsg } from '@/lib/rehype-mermaid-ssg'
import { getTextContent, stripLeadingMatch } from '@/lib/react-node-text'
import { BlockquoteWrapper } from '@/components/content/BlockquoteWrapper'
import type { NoteType } from '@/types/Note.type'
import { rehypeMark } from '@/lib/rehype-mark'
import { rehypeDefinition } from '@/lib/rehype-definition'
import { slugify } from '@/utils/slug'
import { PostMeta } from '@/types/Post.type'
import Link from 'next/link'

const postsDirectory = path.join(process.cwd(), 'content/posts')
const pagesDirectory = path.join(process.cwd(), 'content/pages')

const includeDrafts = process.env.NODE_ENV !== 'production'

type TocItem = { text: string; id: string; level: number }

function readMarkdownFile(directory: string, slug: string) {
  return matter(fs.readFileSync(path.join(directory, `${slug}.md`), 'utf8'))
}

/**
 * Validates post frontmatter and normalizes dates to ISO strings.
 * Throws at build time with the offending file and field instead of rendering a broken post.
 */
function parsePostFrontmatter(slug: string, data: Record<string, unknown>) {
  const fail = (message: string): never => {
    throw new Error(`Invalid frontmatter in content/posts/${slug}.md: ${message}`)
  }
  const requireString = (key: string) => {
    const value = data[key]
    return typeof value === 'string' && value.trim() !== ''
      ? value
      : fail(`"${key}" is required and must be a non-empty string`)
  }
  const optionalString = (key: string) => {
    const value = data[key]
    return value === undefined || typeof value === 'string'
      ? value
      : fail(`"${key}" must be a string`)
  }
  // YAML parses bare dates (2024-08-04) into Date objects, anything with a time stays a string
  const optionalDate = (key: string) => {
    const value = data[key]
    if (value === undefined) return undefined
    const date = value instanceof Date ? value : new Date(String(value))
    return Number.isNaN(date.getTime()) ? fail(`"${key}" is not a valid date`) : date.toISOString()
  }

  const tags = data.tags ?? []
  if (!Array.isArray(tags) || tags.some((tag) => typeof tag !== 'string')) {
    fail('"tags" must be a list of strings')
  }

  return {
    title: requireString('title'),
    description: requireString('description'),
    date: optionalDate('date') ?? fail('"date" is required'),
    updated: optionalDate('updated'),
    category: requireString('category'),
    tags: tags as string[],
    math: data.math === true,
    mermaid: data.mermaid === true,
    draft: data.draft === true,
    coverImage: optionalString('coverImage'),
    coverImageAlt: optionalString('coverImageAlt'),
  }
}

export function getPostMeta(slug: string): PostMeta {
  const { data, content } = readMarkdownFile(postsDirectory, slug)
  return {
    slug,
    ...parsePostFrontmatter(slug, data),
    readingTimeText: readingTime(content).text,
  }
}

export function getAllPostsMeta(): PostMeta[] {
  return fs
    .readdirSync(postsDirectory)
    .filter((f) => f.endsWith('.md'))
    .map((f) => getPostMeta(f.replace(/\.md$/, '')))
    .filter((post) => includeDrafts || !post.draft)
    .toSorted((a, b) => (a.date < b.date ? 1 : -1))
}

export function getAllPostSlugs(): string[] {
  return getAllPostsMeta().map((post) => post.slug)
}

export function getNextAndPreviousPosts(slug: string): {
  next: PostMeta | null
  previous: PostMeta | null
} {
  const posts = getAllPostsMeta()
  const index = posts.findIndex((post) => post.slug === slug)
  const previous = index < posts.length - 1 ? posts[index + 1] : null
  const next = index > 0 ? posts[index - 1] : null
  return { next, previous }
}

// Cached so generateMetadata and the page share one render per request/build
export const getPostBySlug = cache(async (slug: string) => {
  const meta = getPostMeta(slug)
  const { content } = readMarkdownFile(postsDirectory, slug)
  return { meta, ...(await renderMarkdown(content, meta)) }
})

/** Loads a standalone page (about, projects, ...) from content/pages. */
export const getPageBySlug = cache(async (slug: string) => {
  const { data, content } = readMarkdownFile(pagesDirectory, slug)
  const meta = { title: String(data.title), description: String(data.description) }
  return { meta, ...(await renderMarkdown(content, data)) }
})

async function renderMarkdown(
  content: string,
  options: { math?: boolean; mermaid?: boolean },
): Promise<{ content: ReactNode; tableOfContents: TocItem[] }> {
  let processor = remark().use(remarkParse).use(remarkGfm)

  if (options.math) {
    processor = processor.use(remarkMath)
  }

  processor = processor
    .use(remarkRehype, { allowDangerousHtml: true })
    .use(rehypeHighlight)
    .use(rehypeCodeMeta)
    .use(rehypeMark)
    .use(rehypeDefinition)

  if (options.math) {
    processor = processor.use(rehypeKatex)
  }

  if (options.mermaid) {
    processor = processor.use(rehypeMermaidSsg)
  }

  processor = processor.use(rehypeUnwrapImages).use(rehypeReact, {
    Fragment,
    jsx,
    jsxs,
    components: {
      pre: ({ children, ...props }: { children: ReactNode; [key: string]: unknown }) => {
        const language =
          typeof props['data-language'] === 'string' ? props['data-language'] : undefined
        return <CodeWrapper language={language}>{children}</CodeWrapper>
      },
      img: ({ src, alt, title }: { src: string; alt: string; title?: string }) => (
        <ImageWrapper src={src} alt={alt} caption={title} />
      ),
      a: ({ href, children, ...props }: { href?: string; children: ReactNode }) => {
        if (href?.startsWith('http')) return <ExternalLink href={href}>{children}</ExternalLink>
        // Only internal routes go through next/link; anchors, mailto:, footnotes etc. stay plain
        if (href?.startsWith('/')) return <Link href={href}>{children}</Link>
        return (
          <a href={href} {...props}>
            {children}
          </a>
        )
      },
      blockquote: ({ children }: { children: ReactNode }) => {
        const textContent = getTextContent(children).trimStart()
        const type = textContent.match(/^\[!(\w+)\]/)?.[1]?.toLowerCase() as NoteType | undefined
        return (
          <BlockquoteWrapper type={type}>
            {stripLeadingMatch(children, /^\[!(\w+)\]/)}
          </BlockquoteWrapper>
        )
      },
    },
  })

  const file = await processor.process(content)
  const rawContentNode = file.result as ReactNode

  const tableOfContents: TocItem[] = []
  const seenIds = new Map<string, number>()

  function withHeadingIds(node: ReactNode): ReactNode {
    if (!isValidElement(node)) return node

    const element = node as ReactElement<{ children?: ReactNode; id?: string }>
    if (element.type === 'h2' || element.type === 'h3') {
      const text = getTextContent(element.props.children ?? [])
      let id = slugify(text)

      const seenCount = seenIds.get(id) ?? 0
      seenIds.set(id, seenCount + 1)
      if (seenCount > 0) id = `${id}-${seenCount}`

      const level = element.type === 'h2' ? 2 : 3
      tableOfContents.push({ text, id, level })

      return cloneElement(element, { id })
    }

    return node
  }

  const rawChildren = isValidElement(rawContentNode)
    ? (rawContentNode.props as { children?: ReactNode }).children
    : rawContentNode
  const childrenArray = Array.isArray(rawChildren) ? rawChildren : [rawChildren]

  const processedChildren = childrenArray.map(withHeadingIds)

  const processedContent = isValidElement(rawContentNode)
    ? cloneElement(rawContentNode, {}, processedChildren)
    : rawContentNode

  return { content: processedContent, tableOfContents }
}