import { promises as fs } from "fs"
import path from "path"
import { randomBytes } from "crypto"
import {
  S3Client,
  PutObjectCommand,
  GetObjectCommand,
  DeleteObjectCommand,
  ListObjectsV2Command,
  type GetObjectCommandOutput,
} from "@aws-sdk/client-s3"
import { getSignedUrl } from "@aws-sdk/s3-request-presigner"

// Local-disk fallback root. Used only when object storage is not configured.
// Kept OUTSIDE the public web root so files are only served through /api/files.
const STORAGE_DIR = path.resolve(process.cwd(), process.env.STORAGE_DIR ?? "./storage")

const MIME_BY_EXT: Record<string, string> = {
  pdf: "application/pdf",
  png: "image/png",
  jpg: "image/jpeg",
  jpeg: "image/jpeg",
  gif: "image/gif",
  webp: "image/webp",
  doc: "application/msword",
  docx: "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
  xls: "application/vnd.ms-excel",
  xlsx: "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
  csv: "text/csv",
  txt: "text/plain",
}

export function contentTypeForKey(key: string): string {
  const ext = key.split(".").pop()?.toLowerCase() ?? ""
  return MIME_BY_EXT[ext] ?? "application/octet-stream"
}

// Single source of truth for what users may upload. Deliberately excludes svg
// and any html/script types, which can execute JavaScript when served inline
// from our origin. Enforce this at EVERY upload entry point (see /api/upload
// and /api/documents) — divergence is how an allowlist gets bypassed.
export const ALLOWED_UPLOAD_EXTENSIONS = [
  "pdf", "png", "jpg", "jpeg", "gif", "webp",
  "doc", "docx", "xls", "xlsx", "csv", "txt",
] as const

export function extOf(filename: string): string {
  return filename.split(".").pop()?.toLowerCase() ?? ""
}

export function isAllowedUploadExt(filename: string): boolean {
  return (ALLOWED_UPLOAD_EXTENSIONS as readonly string[]).includes(extOf(filename))
}

// ── Object storage (DigitalOcean Spaces / S3-compatible) ──────────────────────
// When SPACES_* are configured, uploads and serving use the bucket instead of
// local disk. The key scheme (`<userId>/<scope>/<file>`) is identical either
// way, so existing /api/files/<key> URLs stored in the DB keep working after the
// backend switch — only the bytes move.
const SPACES_BUCKET = process.env.SPACES_BUCKET ?? ""

export function usingSpaces(): boolean {
  return Boolean(process.env.SPACES_KEY && process.env.SPACES_SECRET && SPACES_BUCKET)
}

/**
 * Thrown when a write is attempted in production without object storage
 * configured. The local-disk fallback is EPHEMERAL on App Platform, so silently
 * using it means uploads vanish on the next deploy. We fail loud instead.
 */
export class StorageNotConfiguredError extends Error {
  constructor() {
    super(
      "Object storage (SPACES_*) is not configured. Refusing to write uploads to " +
        "ephemeral local disk in production — files would be lost on the next deploy."
    )
    this.name = "StorageNotConfiguredError"
  }
}

function newClient(endpoint: string | undefined): S3Client {
  return new S3Client({
    region: process.env.SPACES_REGION || "us-east-1",
    endpoint,
    forcePathStyle: false,
    credentials: {
      accessKeyId: process.env.SPACES_KEY!,
      secretAccessKey: process.env.SPACES_SECRET!,
    },
  })
}

// Origin client — used for all mutating/reading operations (PUT/GET/DELETE/HEAD).
let _s3: S3Client | null = null
function s3(): S3Client {
  if (!_s3) _s3 = newClient(process.env.SPACES_ENDPOINT) // e.g. https://nyc3.digitaloceanspaces.com
  return _s3
}

// Rewrite a presigned origin URL to the Spaces CDN edge host when the CDN is
// enabled. The URL is signed against the ORIGIN host; the CDN forwards requests
// to origin with the origin Host header, so the SigV4 signature still validates.
// (Signing directly against the CDN host is rejected by origin with 403.)
function toCdnUrl(signedUrl: string): string {
  const cdn = process.env.SPACES_CDN_ENDPOINT
  const origin = process.env.SPACES_ENDPOINT
  if (!cdn || !origin) return signedUrl
  try {
    const originHost = new URL(origin).host // e.g. nyc3.digitaloceanspaces.com
    const cdnHost = new URL(cdn).host // e.g. nyc3.cdn.digitaloceanspaces.com
    const u = new URL(signedUrl)
    if (u.host.endsWith(originHost)) {
      u.host = u.host.slice(0, u.host.length - originHost.length) + cdnHost
      return u.toString()
    }
    return signedUrl
  } catch {
    return signedUrl
  }
}

// ── key helpers ───────────────────────────────────────────────────────────────
/** Validate a storage key, refusing empty/traversal segments. Returns it cleaned. */
function assertSafeKey(key: string): string {
  const clean = key.replace(/^\/+/, "")
  if (!clean || clean.split(/[\\/]+/).some((seg) => seg === "" || seg === "." || seg === "..")) {
    throw new Error("Invalid storage path")
  }
  return clean
}

/** Resolve a key to an absolute local path (local-disk backend only). */
function resolveKey(key: string): string {
  const clean = assertSafeKey(key)
  const abs = path.resolve(STORAGE_DIR, clean)
  if (abs !== STORAGE_DIR && !abs.startsWith(STORAGE_DIR + path.sep)) {
    throw new Error("Invalid storage path")
  }
  return abs
}

function sanitizeSegment(s: string): string {
  return s.replace(/[^a-zA-Z0-9_-]/g, "_")
}

/**
 * True iff a storage key lives in the given owner's namespace (`<ownerId>/…`).
 * Keys are generated server-side as `<sanitized ownerId>/<scope>/<file>`, so any
 * client-supplied key/path whose first segment differs belongs to another tenant
 * (or is malformed) and must be rejected.
 */
export function keyBelongsToOwner(key: string | null | undefined, ownerId: string): boolean {
  if (!key || !ownerId) return false
  const first = key.replace(/^\/+/, "").split(/[\\/]+/)[0]
  return first === sanitizeSegment(ownerId)
}

/**
 * Lightweight magic-byte check: reject a file whose real content doesn't match
 * its claimed extension (e.g. an HTML/script payload renamed to `.pdf`). Types
 * without a reliable file signature (csv/txt) are allowed through. `head` should
 * be the first ~16 bytes of the file.
 */
export function contentMatchesExtension(head: Buffer, ext: string): boolean {
  const at = (offset: number, sig: number[]) =>
    head.length >= offset + sig.length && sig.every((b, i) => head[offset + i] === b)
  switch (ext) {
    case "pdf":
      return at(0, [0x25, 0x50, 0x44, 0x46]) // %PDF
    case "png":
      return at(0, [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a])
    case "jpg":
    case "jpeg":
      return at(0, [0xff, 0xd8, 0xff])
    case "gif":
      return at(0, [0x47, 0x49, 0x46, 0x38]) // GIF8
    case "webp":
      return at(0, [0x52, 0x49, 0x46, 0x46]) && at(8, [0x57, 0x45, 0x42, 0x50]) // RIFF…WEBP
    case "docx":
    case "xlsx":
      return at(0, [0x50, 0x4b, 0x03, 0x04]) || at(0, [0x50, 0x4b, 0x05, 0x06]) // zip (PK)
    case "doc":
    case "xls":
      return at(0, [0xd0, 0xcf, 0x11, 0xe0, 0xa1, 0xb1, 0x1a, 0xe1]) || at(0, [0x50, 0x4b]) // OLE or zip
    case "csv":
    case "txt":
      return true // no reliable signature
    default:
      return true
  }
}

async function bodyToBuffer(body: GetObjectCommandOutput["Body"]): Promise<Buffer> {
  if (!body) return Buffer.alloc(0)
  // The AWS SDK v3 Node runtime adds transformToByteArray() to the stream body.
  const stream = body as { transformToByteArray?: () => Promise<Uint8Array> }
  if (typeof stream.transformToByteArray === "function") {
    return Buffer.from(await stream.transformToByteArray())
  }
  const chunks: Buffer[] = []
  for await (const chunk of body as AsyncIterable<Uint8Array>) chunks.push(Buffer.from(chunk))
  return Buffer.concat(chunks)
}

/**
 * Persist an uploaded File under `${userId}/${scope}/<random>.<ext>` and return
 * the storage key (relative path). Optionally pass `fixedName` to make the file
 * name deterministic (e.g. one photo per property).
 */
export async function saveFile(
  file: File,
  opts: { userId: string; scope: string; fixedName?: string }
): Promise<{ key: string; size: number; type: string }> {
  const ext = (file.name.split(".").pop() ?? "bin").toLowerCase().replace(/[^a-z0-9]/g, "")
  const base = opts.fixedName
    ? sanitizeSegment(opts.fixedName)
    : `${Date.now()}-${randomBytes(6).toString("hex")}`
  const key = `${sanitizeSegment(opts.userId)}/${sanitizeSegment(opts.scope)}/${base}.${ext}`
  const buffer = Buffer.from(await file.arrayBuffer())
  const type = file.type || contentTypeForKey(key)

  if (usingSpaces()) {
    await s3().send(
      new PutObjectCommand({
        Bucket: SPACES_BUCKET,
        Key: key,
        Body: buffer,
        ContentType: type,
        ACL: "private",
      })
    )
  } else {
    // In production the local-disk backend is ephemeral (lost on redeploy), so a
    // misconfigured Spaces setup must fail loudly rather than silently drop data.
    if (process.env.NODE_ENV === "production") throw new StorageNotConfiguredError()
    const abs = resolveKey(key)
    await fs.mkdir(path.dirname(abs), { recursive: true })
    await fs.writeFile(abs, buffer)
  }

  return { key, size: file.size, type }
}

/**
 * Persist raw bytes under `${userId}/${scope}/<random>.<ext>` (server-generated,
 * so the key is always in the owner's namespace) and return the storage key.
 * Used for server-side artifacts like signed e-sign PDFs.
 */
export async function saveBuffer(
  buffer: Buffer,
  opts: { userId: string; scope: string; ext: string }
): Promise<{ key: string }> {
  const ext = opts.ext.replace(/[^a-z0-9]/gi, "").toLowerCase() || "bin"
  const key = `${sanitizeSegment(opts.userId)}/${sanitizeSegment(opts.scope)}/${Date.now()}-${randomBytes(6).toString("hex")}.${ext}`
  if (usingSpaces()) {
    await s3().send(
      new PutObjectCommand({
        Bucket: SPACES_BUCKET,
        Key: key,
        Body: buffer,
        ContentType: contentTypeForKey(key),
        ACL: "private",
      })
    )
  } else {
    if (process.env.NODE_ENV === "production") throw new StorageNotConfiguredError()
    const abs = resolveKey(key)
    await fs.mkdir(path.dirname(abs), { recursive: true })
    await fs.writeFile(abs, buffer)
  }
  return { key }
}

export async function readFile(key: string): Promise<Buffer> {
  if (usingSpaces()) {
    const res = await s3().send(new GetObjectCommand({ Bucket: SPACES_BUCKET, Key: assertSafeKey(key) }))
    return bodyToBuffer(res.Body)
  }
  return fs.readFile(resolveKey(key))
}

/**
 * Presigned, time-limited GET URL for an object in Spaces — lets the browser
 * fetch the bytes directly from the bucket (offloading them from the app) while
 * access stays gated: the caller must pass auth + ownership checks before this
 * is issued, and the URL expires. `ResponseContent*` control how the browser
 * treats the file (inline image vs. attachment download) with the right type.
 */
export async function presignGetUrl(
  key: string,
  opts: { expiresIn?: number; disposition?: "inline" | "attachment"; filename?: string } = {}
): Promise<string> {
  const safe = assertSafeKey(key)
  // The key's basename is already generated/sanitized at upload; keep only
  // filename-safe characters for the Content-Disposition header.
  const filename = (opts.filename ?? safe.split("/").pop() ?? "file").replace(/[^A-Za-z0-9._-]/g, "_")
  const cmd = new GetObjectCommand({
    Bucket: SPACES_BUCKET,
    Key: safe,
    ResponseContentType: contentTypeForKey(safe),
    ResponseContentDisposition: `${opts.disposition ?? "inline"}; filename="${filename}"`,
  })
  const signed = await getSignedUrl(s3(), cmd, { expiresIn: opts.expiresIn ?? 3600 })
  return toCdnUrl(signed)
}

export async function deleteFile(key: string, ownerId: string): Promise<void> {
  // Defense in depth: never delete an object outside the caller's own namespace,
  // even if a stored storage_path was tampered with to point at another tenant.
  if (!keyBelongsToOwner(key, ownerId)) return
  try {
    if (usingSpaces()) {
      await s3().send(new DeleteObjectCommand({ Bucket: SPACES_BUCKET, Key: assertSafeKey(key) }))
    } else {
      await fs.unlink(resolveKey(key))
    }
  } catch {
    // Already gone — ignore.
  }
}

/**
 * Permanently delete EVERY stored object in a user's namespace (`<userId>/…`),
 * across whichever backend is active. Used by GDPR account deletion — there is
 * no undo. Returns the number of objects removed (best effort; local-disk
 * removals aren't counted individually).
 */
export async function deleteUserStorage(userId: string): Promise<number> {
  const prefix = `${sanitizeSegment(userId)}/`

  if (usingSpaces()) {
    let deleted = 0
    let token: string | undefined
    do {
      const res = await s3().send(
        new ListObjectsV2Command({ Bucket: SPACES_BUCKET, Prefix: prefix, ContinuationToken: token })
      )
      for (const obj of res.Contents ?? []) {
        if (!obj.Key) continue
        await s3().send(new DeleteObjectCommand({ Bucket: SPACES_BUCKET, Key: obj.Key }))
        deleted++
      }
      token = res.IsTruncated ? res.NextContinuationToken : undefined
    } while (token)
    return deleted
  }

  await fs.rm(path.join(STORAGE_DIR, sanitizeSegment(userId)), { recursive: true, force: true })
  return 0
}

async function walkDirSize(dir: string): Promise<number> {
  let entries
  try {
    entries = await fs.readdir(dir, { withFileTypes: true })
  } catch {
    return 0 // directory doesn't exist yet → 0 bytes
  }
  let total = 0
  for (const e of entries) {
    const full = path.join(dir, e.name)
    if (e.isDirectory()) total += await walkDirSize(full)
    else if (e.isFile()) {
      try {
        total += (await fs.stat(full)).size
      } catch {
        // File vanished between readdir and stat — ignore.
      }
    }
  }
  return total
}

/**
 * Total bytes currently stored for a user, across whichever backend is active.
 * Files are namespaced under `<userId>/…`, so we sum that prefix. Used to
 * enforce per-plan storage quotas at upload time.
 */
export async function getUserStorageBytes(userId: string): Promise<number> {
  const prefix = `${sanitizeSegment(userId)}/`

  if (usingSpaces()) {
    let total = 0
    let token: string | undefined
    do {
      const res = await s3().send(
        new ListObjectsV2Command({ Bucket: SPACES_BUCKET, Prefix: prefix, ContinuationToken: token })
      )
      for (const obj of res.Contents ?? []) total += obj.Size ?? 0
      token = res.IsTruncated ? res.NextContinuationToken : undefined
    } while (token)
    return total
  }

  return walkDirSize(path.join(STORAGE_DIR, sanitizeSegment(userId)))
}