export type JsonValue =
  null | boolean | number | string | JsonValue[] | { [key: string]: JsonValue }

export function jsonValue(value: unknown): JsonValue {
  if (value === null || typeof value === 'boolean') return value
  if (typeof value === 'string') {
    assertValidUnicode(value)
    return value
  }
  if (typeof value === 'number') {
    if (!Number.isFinite(value))
      throw new Error('canonical JSON does not permit non-finite numbers')
    return value
  }
  if (Array.isArray(value)) return value.map(jsonValue)
  if (typeof value === 'object') {
    const prototype = Object.getPrototypeOf(value)
    if (prototype !== Object.prototype && prototype !== null)
      throw new Error('value is not JSON')
    return Object.fromEntries(
      Object.entries(value).map(([key, member]) => {
        assertValidUnicode(key)
        return [key, jsonValue(member)]
      }),
    )
  }
  throw new Error('value is not JSON')
}

export function canonicalJson(value: JsonValue): string {
  if (
    value === null ||
    typeof value === 'boolean' ||
    typeof value === 'string'
  ) {
    if (typeof value === 'string') assertValidUnicode(value)
    return JSON.stringify(value)
  }
  if (typeof value === 'number') {
    if (!Number.isFinite(value))
      throw new Error('canonical JSON does not permit non-finite numbers')
    return JSON.stringify(value)
  }
  if (Array.isArray(value)) return `[${value.map(canonicalJson).join(',')}]`
  return `{${Object.keys(value)
    .map((key) => {
      assertValidUnicode(key)
      return key
    })
    .sort()
    .map((key) => `${JSON.stringify(key)}:${canonicalJson(value[key])}`)
    .join(',')}}`
}

function assertValidUnicode(value: string): void {
  for (let index = 0; index < value.length; index += 1) {
    const codeUnit = value.charCodeAt(index)
    if (codeUnit >= 0xd800 && codeUnit <= 0xdbff) {
      const next = value.charCodeAt(index + 1)
      if (index + 1 >= value.length || next < 0xdc00 || next > 0xdfff)
        throw new Error('canonical JSON does not permit lone surrogates')
      index += 1
    } else if (codeUnit >= 0xdc00 && codeUnit <= 0xdfff) {
      throw new Error('canonical JSON does not permit lone surrogates')
    }
  }
}

export async function requestFingerprint(value: JsonValue): Promise<string> {
  const digest = await crypto.subtle.digest(
    'SHA-256',
    new TextEncoder().encode(canonicalJson(value)),
  )
  return Array.from(new Uint8Array(digest), (byte) =>
    byte.toString(16).padStart(2, '0'),
  ).join('')
}