import { promises as fs } from 'node:fs'
import path from 'node:path'
import {
  downloadFile,
  uploadFiles,
  repoExists,
  createRepo,
  listFiles,
} from '@huggingface/hub'

/**
 * Durable storage for decks. Each deck persists two artifacts:
 *   decks/<id>.ydoc  — binary Yjs snapshot (lossless reload)
 *   decks/<id>.md    — human-readable markdown (= version history in git)
 *
 * Two backends: local filesystem (dev) and a git-backed HF Dataset repo (prod, since
 * HF Space disks are ephemeral). Chosen by env at startup.
 */
export interface DeckStorage {
  readonly kind: string
  load(deckId: string): Promise<Uint8Array | null>
  save(deckId: string, state: Uint8Array, markdown: string): Promise<void>
  listDecks(): Promise<string[]>
  /** Generic small text files (e.g. per-user deck index at users/<id>.json). */
  readText(path: string): Promise<string | null>
  writeText(path: string, content: string): Promise<void>
}

const safeId = (id: string): string =>
  id.replace(/[^a-zA-Z0-9_-]/g, '_').slice(0, 64) || 'default'

class LocalDeckStorage implements DeckStorage {
  readonly kind = 'local'
  constructor(private readonly dir: string) {}

  private file(id: string, ext: string) {
    return path.join(this.dir, safeId(id) + ext)
  }

  async load(deckId: string): Promise<Uint8Array | null> {
    try {
      return new Uint8Array(await fs.readFile(this.file(deckId, '.ydoc')))
    } catch {
      return null
    }
  }

  async save(deckId: string, state: Uint8Array, markdown: string): Promise<void> {
    await fs.mkdir(this.dir, { recursive: true })
    await fs.writeFile(this.file(deckId, '.ydoc'), Buffer.from(state))
    await fs.writeFile(this.file(deckId, '.md'), markdown, 'utf8')
  }

  async listDecks(): Promise<string[]> {
    try {
      const names = await fs.readdir(this.dir)
      return names.filter((n) => n.endsWith('.md')).map((n) => n.replace(/\.md$/, ''))
    } catch {
      return []
    }
  }

  // Generic files live next to the decks dir (base = parent of decks dir).
  private base() {
    return path.dirname(this.dir)
  }
  async readText(p: string): Promise<string | null> {
    try {
      return await fs.readFile(path.resolve(this.base(), p), 'utf8')
    } catch {
      return null
    }
  }
  async writeText(p: string, content: string): Promise<void> {
    const full = path.resolve(this.base(), p)
    await fs.mkdir(path.dirname(full), { recursive: true })
    await fs.writeFile(full, content, 'utf8')
  }
}

class HfDeckStorage implements DeckStorage {
  readonly kind = 'hf-dataset'
  private readonly repo: { type: 'dataset'; name: string }

  constructor(repoName: string, private readonly token: string) {
    this.repo = { type: 'dataset', name: repoName }
  }

  async ensureRepo(): Promise<void> {
    try {
      if (!(await repoExists({ repo: this.repo, accessToken: this.token }))) {
        await createRepo({ repo: this.repo, accessToken: this.token, visibility: 'private' })
        console.log(`[storage] created dataset repo ${this.repo.name}`)
      }
    } catch (e) {
      console.error('[storage] ensureRepo failed:', (e as Error)?.message)
    }
  }

  async load(deckId: string): Promise<Uint8Array | null> {
    try {
      const blob = await downloadFile({
        repo: this.repo,
        path: `decks/${safeId(deckId)}.ydoc`,
        accessToken: this.token,
      })
      if (!blob) return null
      return new Uint8Array(await blob.arrayBuffer())
    } catch (e) {
      console.error('[storage] load failed:', (e as Error)?.message)
      return null
    }
  }

  async save(deckId: string, state: Uint8Array, markdown: string): Promise<void> {
    const id = safeId(deckId)
    await uploadFiles({
      repo: this.repo,
      accessToken: this.token,
      commitTitle: `Update deck ${id}`,
      files: [
        { path: `decks/${id}.ydoc`, content: new Blob([new Uint8Array(state)]) },
        { path: `decks/${id}.md`, content: new Blob([new TextEncoder().encode(markdown)]) },
      ],
    })
  }

  async listDecks(): Promise<string[]> {
    try {
      const out: string[] = []
      for await (const f of listFiles({ repo: this.repo, path: 'decks', accessToken: this.token })) {
        if (f.path.endsWith('.md')) {
          out.push(f.path.replace(/^decks\//, '').replace(/\.md$/, ''))
        }
      }
      return out
    } catch {
      return []
    }
  }

  async readText(p: string): Promise<string | null> {
    try {
      const blob = await downloadFile({ repo: this.repo, path: p, accessToken: this.token })
      return blob ? await blob.text() : null
    } catch {
      return null
    }
  }
  async writeText(p: string, content: string): Promise<void> {
    await uploadFiles({
      repo: this.repo,
      accessToken: this.token,
      commitTitle: `Update ${p}`,
      files: [{ path: p, content: new Blob([new TextEncoder().encode(content)]) }],
    })
  }
}

export function createStorage(): DeckStorage {
  const repo = process.env.HF_DATASET_REPO
  const token = process.env.HF_TOKEN
  if (repo && token) {
    const storage = new HfDeckStorage(repo, token)
    void storage.ensureRepo()
    console.log(`[storage] using HF dataset: ${repo}`)
    return storage
  }
  const dir = process.env.DATA_DIR || './data/decks'
  console.log(`[storage] using local filesystem: ${dir}`)
  return new LocalDeckStorage(dir)
}