import { randomBytes } from "crypto"

const prefixes = {

job: "job",

event: "evt",

session: "ses",

message: "msg",

permission: "per",

question: "que",

part: "prt",

pty: "pty",

tool: "tool",

workspace: "wrk",

} as const

const LENGTH = 26

// State for monotonic ID generation

let lastTimestamp = 0

let counter = 0

export function ascending(prefix: keyof typeof prefixes, given?: string) {

return generateID(prefix, "ascending", given)

}

export function descending(prefix: keyof typeof prefixes, given?: string) {

return generateID(prefix, "descending", given)

}

function generateID(prefix: keyof typeof prefixes, direction: "descending" | "ascending", given?: string): string {

if (!given) {

return create(prefixes[prefix], direction)

}

if (!given.startsWith(prefixes[prefix])) {

throw new Error(`ID ${given} does not start with ${prefixes[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"