// ---- Types ------------------------------------------------------------------

export type ServerType = "vanilla" | "paper" | "spigot" | "fabric" | "forge" | "bedrock"

export interface VersionInfo {
  id: string
  type?: string
  releaseTime?: string
  url?: string
}

// ---- In-memory cache --------------------------------------------------------

interface CacheEntry<T> {
  data: T
  expiresAt: number
}

const CACHE_TTL_MS = 5 * 60 * 1000 // 5 minutes
const cache = new Map<string, CacheEntry<unknown>>()

function cacheGet<T>(key: string): T | null {
  const entry = cache.get(key)
  if (!entry) return null
  if (Date.now() > entry.expiresAt) {
    cache.delete(key)
    return null
  }
  return entry.data as T
}

function cacheSet<T>(key: string, data: T): void {
  cache.set(key, { data, expiresAt: Date.now() + CACHE_TTL_MS })
}

// ---- Vanilla ----------------------------------------------------------------

interface MojangManifest {
  latest: { release: string; snapshot: string }
  versions: Array<{
    id: string
    type: string
    url: string
    releaseTime: string
    sha1: string
  }>
}

/** Fetch all versions from the official Mojang version manifest. */
export async function fetchVanillaVersions(): Promise<VersionInfo[]> {
  const key = "vanilla:versions"
  const cached = cacheGet<VersionInfo[]>(key)
  if (cached) return cached

  const res = await fetch(
    "https://piston-meta.mojang.com/mc/game/version_manifest_v2.json",
  )
  if (!res.ok) {
    throw new Error(`Failed to fetch Mojang manifest: ${res.status} ${res.statusText}`)
  }

  const manifest: MojangManifest = await res.json()
  const versions: VersionInfo[] = manifest.versions.map((v) => ({
    id: v.id,
    type: v.type,
    releaseTime: v.releaseTime,
    url: v.url,
  }))

  cacheSet(key, versions)
  return versions
}

// ---- Paper ------------------------------------------------------------------

interface PaperBuildsResponse {
  project_id: string
  project_name: string
  version: string
  builds: number[]
}

/** Fetch all Paper MC versions from the PaperMC API. */
export async function fetchPaperVersions(): Promise<VersionInfo[]> {
  const key = "paper:versions"
  const cached = cacheGet<VersionInfo[]>(key)
  if (cached) return cached

  const res = await fetch("https://api.papermc.io/v2/projects/paper")
  if (!res.ok) {
    throw new Error(`Failed to fetch Paper versions: ${res.status} ${res.statusText}`)
  }

  const data: { versions: string[] } = await res.json()
  const versions: VersionInfo[] = data.versions.map((id) => ({ id }))

  cacheSet(key, versions)
  return versions
}

// ---- Fabric -----------------------------------------------------------------

interface FabricGameVersion {
  version: string
  stable: boolean
}

/** Fetch all Fabric-supported Minecraft versions. */
export async function fetchFabricVersions(): Promise<VersionInfo[]> {
  const key = "fabric:versions"
  const cached = cacheGet<VersionInfo[]>(key)
  if (cached) return cached

  const res = await fetch("https://meta.fabricmc.net/v2/versions/game")
  if (!res.ok) {
    throw new Error(`Failed to fetch Fabric versions: ${res.status} ${res.statusText}`)
  }

  const data: FabricGameVersion[] = await res.json()
  const versions: VersionInfo[] = data.map((v) => ({
    id: v.version,
    type: v.stable ? "release" : "snapshot",
  }))

  cacheSet(key, versions)
  return versions
}

// ---- Download URL resolution ------------------------------------------------

/**
 * Resolve the direct download URL for a given server type + version.
 * Throws if the type/version combination cannot be resolved.
 */
export async function getDownloadUrl(
  type: ServerType,
  version: string,
): Promise<string> {
  validateVersion(version)

  switch (type) {
    case "vanilla":
      return getVanillaDownloadUrl(version)
    case "paper":
      return getPaperDownloadUrl(version)
    case "fabric":
      return getFabricDownloadUrl(version)
    case "spigot":
      throw new Error(
        "Spigot cannot be downloaded directly; use BuildTools instead.",
      )
    case "forge":
      throw new Error(
        "Forge installers must be downloaded from files.minecraftforge.net.",
      )
    case "bedrock":
      throw new Error(
        "Bedrock server downloads require manual acceptance of Microsoft's EULA.",
      )
    default:
      throw new Error(`Unsupported server type: ${type}`)
  }
}

async function getVanillaDownloadUrl(version: string): Promise<string> {
  const versions = await fetchVanillaVersions()
  const entry = versions.find((v) => v.id === version)
  if (!entry?.url) throw new Error(`Vanilla version not found: ${version}`)

  // The URL points to a version JSON; fetch it to get the server jar URL
  const cacheKey = `vanilla:jar-url:${version}`
  const cached = cacheGet<string>(cacheKey)
  if (cached) return cached

  const res = await fetch(entry.url)
  if (!res.ok) {
    throw new Error(`Failed to fetch version manifest for ${version}: ${res.status}`)
  }

  const versionData: {
    downloads: { server?: { url: string } }
  } = await res.json()

  const url = versionData.downloads.server?.url
  if (!url) throw new Error(`No server download available for vanilla ${version}`)

  cacheSet(cacheKey, url)
  return url
}

async function getPaperDownloadUrl(version: string): Promise<string> {
  const cacheKey = `paper:jar-url:${version}`
  const cached = cacheGet<string>(cacheKey)
  if (cached) return cached

  // Get the latest build number for this version
  const buildsRes = await fetch(
    `https://api.papermc.io/v2/projects/paper/versions/${encodeURIComponent(version)}`,
  )
  if (!buildsRes.ok) {
    throw new Error(`Paper version ${version} not found: ${buildsRes.status}`)
  }

  const buildsData: PaperBuildsResponse = await buildsRes.json()
  const latestBuild = buildsData.builds.at(-1)
  if (latestBuild === undefined) {
    throw new Error(`No builds found for Paper ${version}`)
  }

  const url = `https://api.papermc.io/v2/projects/paper/versions/${encodeURIComponent(version)}/builds/${latestBuild}/downloads/paper-${version}-${latestBuild}.jar`
  cacheSet(cacheKey, url)
  return url
}

async function getFabricDownloadUrl(version: string): Promise<string> {
  const cacheKey = `fabric:jar-url:${version}`
  const cached = cacheGet<string>(cacheKey)
  if (cached) return cached

  // Get latest loader and installer versions
  const [loadersRes, installersRes] = await Promise.all([
    fetch("https://meta.fabricmc.net/v2/versions/loader"),
    fetch("https://meta.fabricmc.net/v2/versions/installer"),
  ])

  if (!loadersRes.ok || !installersRes.ok) {
    throw new Error("Failed to fetch Fabric loader/installer versions")
  }

  const loaders: Array<{ version: string; stable: boolean }> = await loadersRes.json()
  const installers: Array<{ version: string; stable: boolean }> = await installersRes.json()

  const latestLoader = loaders.find((l) => l.stable)
  const latestInstaller = installers.find((i) => i.stable)

  if (!latestLoader || !latestInstaller) {
    throw new Error("Could not determine latest stable Fabric loader/installer")
  }

  const url = `https://meta.fabricmc.net/v2/versions/loader/${encodeURIComponent(version)}/${encodeURIComponent(latestLoader.version)}/${encodeURIComponent(latestInstaller.version)}/server/jar`
  cacheSet(cacheKey, url)
  return url
}

// ---- Download ---------------------------------------------------------------

/**
 * Download a server jar to `destPath`.
 * @param onProgress - optional callback receiving bytes downloaded and total bytes
 */
export async function downloadServer(
  type: ServerType,
  version: string,
  destPath: string,
  onProgress?: (downloaded: number, total: number) => void,
): Promise<void> {
  validateDestPath(destPath)

  const url = await getDownloadUrl(type, version)

  const res = await fetch(url)
  if (!res.ok) {
    throw new Error(`Failed to download server jar: ${res.status} ${res.statusText}`)
  }

  const contentLength = Number(res.headers.get("content-length") ?? "0")
  const body = res.body
  if (!body) throw new Error("Response body is empty")

  const file = Bun.file(destPath)
  const writer = file.writer()

  let downloaded = 0
  const reader = body.getReader()

  try {
    while (true) {
      const { done, value } = await reader.read()
      if (done) break

      writer.write(value)
      downloaded += value.byteLength

      if (onProgress && contentLength > 0) {
        onProgress(downloaded, contentLength)
      }
    }
    await writer.end()
  } catch (err) {
    writer.end()
    throw err
  } finally {
    reader.releaseLock()
  }

  console.log(
    `[Versions] Downloaded ${type} ${version} → ${destPath} (${downloaded} bytes)`,
  )
}

// ---- Input validation -------------------------------------------------------

/** Minecraft version strings are like "1.21.4", "24w44a" - allow alphanumeric + dots + dashes */
function validateVersion(version: string): void {
  if (!version || typeof version !== "string") {
    throw new Error("Version must be a non-empty string")
  }
  if (!/^[\w.\-+]{1,64}$/.test(version)) {
    throw new Error(`Invalid version string: ${version}`)
  }
}

/** Prevent path traversal in destination paths */
function validateDestPath(destPath: string): void {
  if (!destPath || typeof destPath !== "string") {
    throw new Error("Destination path must be a non-empty string")
  }
  if (destPath.includes("..")) {
    throw new Error("Destination path must not contain '..'")
  }
  if (!destPath.endsWith(".jar")) {
    throw new Error("Destination path must end with .jar")
  }
}