import { randomBytes } from "crypto"

export type Prefix = "evt" | "ses" | "msg" | "per" | "que" | "prt" | "pty" | "tool" | "wrk"

const LENGTH = 26

// State for monotonic ID generation
let lastTimestamp = 0
let counter = 0

export function ascending(prefix: Prefix, given?: string) {
  return generateID(prefix, "ascending", given)
}

export function descending(prefix: Prefix, given?: string) {
  return generateID(prefix, "descending", given)
}

function generateID(prefix: Prefix, direction: "descending" | "ascending", given?: string): string {
  if (!given) {
    return create(prefix, direction)
  }

  if (!given.startsWith(prefix)) {
    throw new Error(`ID ${given} does not start with ${prefix}`)
  }
  return given
}

function randomBase62(length: number): string {
  const chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
  let result = ""
  const bytes = randomBytes(length)
  for (let i = 0; i < length; i++) {
    result += chars[bytes[i] % 62]
  }
  return result
}

export function create(prefix: string, direction: "descending" | "ascending", timestamp?: number): string {
  const currentTimestamp = timestamp ?? Date.now()

  if (currentTimestamp !== lastTimestamp) {
    lastTimestamp = currentTimestamp
    counter = 0
  }
  counter++

  let now = BigInt(currentTimestamp) * BigInt(0x1000) + BigInt(counter)

  now = direction === "descending" ? ~now : now

  const timeBytes = Buffer.alloc(6)
  for (let i = 0; i < 6; i++) {
    timeBytes[i] = Number((now >> BigInt(40 - 8 * i)) & BigInt(0xff))
  }

  return prefix + "_" + timeBytes.toString("hex") + randomBase62(LENGTH - 12)
}

/** Extract timestamp from an ascending ID. Does not work with descending IDs. */
export function timestamp(id: string): number {
  const prefix = id.split("_")[0]
  const hex = id.slice(prefix.length + 1, prefix.length + 13)
  const encoded = BigInt("0x" + hex)
  return Number(encoded / BigInt(0x1000))
}

export * as Identifier from "./id"