import { bytesToHex } from '@noble/hashes/utils'
import { sha256 } from '@noble/hashes/sha256'
import { base64 } from '@scure/base'
import { Event, EventTemplate, verifyEvent } from './pure.ts'
import { utf8Decoder, utf8Encoder } from './utils.ts'
import { HTTPAuth } from './kinds.ts'

const _authorizationScheme = 'Nostr '

export function hashPayload(payload: any): string {
  const hash = sha256(utf8Encoder.encode(JSON.stringify(payload)))
  return bytesToHex(hash)
}

/**
 * Generate token for NIP-98 flow.
 *
 * @example
 * const sign = window.nostr.signEvent
 * await nip98.getToken('https://example.com/login', 'post', (e) => sign(e), true)
 */
export async function getToken(
  loginUrl: string,
  httpMethod: string,
  sign: (e: EventTemplate) => Promise<Event> | Event,
  includeAuthorizationScheme: boolean = false,
  payload?: Record<string, any>,
): Promise<string> {
  const event: EventTemplate = {
    kind: HTTPAuth,
    tags: [
      ['u', loginUrl],
      ['method', httpMethod],
    ],
    created_at: Math.round(new Date().getTime() / 1000),
    content: '',
  }

  if (payload) {
    event.tags.push(['payload', bytesToHex(sha256(utf8Encoder.encode(JSON.stringify(payload))))])
  }

  const signedEvent = await sign(event)
  const authorizationScheme = includeAuthorizationScheme ? _authorizationScheme : ''

  return authorizationScheme + base64.encode(utf8Encoder.encode(JSON.stringify(signedEvent)))
}

/**
 * Validate token for NIP-98 flow.
 *
 * @example
 * await nip98.validateToken('Nostr base64token', 'https://example.com/login', 'post')
 */
export async function validateToken(token: string, url: string, method: string): Promise<boolean> {
  const event = await unpackEventFromToken(token).catch(error => {
    throw error
  })
  const valid = await validateEvent(event, url, method).catch(error => {
    throw error
  })

  return valid
}

export async function unpackEventFromToken(token: string): Promise<Event> {
  if (!token) {
    throw new Error('Missing token')
  }
  token = token.replace(_authorizationScheme, '')

  const eventB64 = utf8Decoder.decode(base64.decode(token))
  if (!eventB64 || eventB64.length === 0 || !eventB64.startsWith('{')) {
    throw new Error('Invalid token')
  }

  const event = JSON.parse(eventB64) as Event

  return event
}

export async function validateEvent(event: Event, url: string, method: string, body?: any): Promise<boolean> {
  if (!event) {
    throw new Error('Invalid nostr event')
  }
  if (!verifyEvent(event)) {
    throw new Error('Invalid nostr event, signature invalid')
  }
  if (event.kind !== HTTPAuth) {
    throw new Error('Invalid nostr event, kind invalid')
  }

  if (!event.created_at) {
    throw new Error('Invalid nostr event, created_at invalid')
  }

  // Event must be less than 60 seconds old
  if (Math.round(new Date().getTime() / 1000) - event.created_at > 60) {
    throw new Error('Invalid nostr event, expired')
  }

  const urlTag = event.tags.find(t => t[0] === 'u')
  if (urlTag?.length !== 1 && urlTag?.[1] !== url) {
    throw new Error('Invalid nostr event, url tag invalid')
  }

  const methodTag = event.tags.find(t => t[0] === 'method')
  if (methodTag?.length !== 1 && methodTag?.[1].toLowerCase() !== method.toLowerCase()) {
    throw new Error('Invalid nostr event, method tag invalid')
  }

  if (Boolean(body) && Object.keys(body).length > 0) {
    const payloadTag = event.tags.find(t => t[0] === 'payload')
    const payloadHash = bytesToHex(sha256(utf8Encoder.encode(JSON.stringify(body))))
    if (payloadTag?.[1] !== payloadHash) {
      throw new Error('Invalid payload tag hash, does not match request body hash')
    }
  }

  return true
}