import { getDirective, MapperKind, mapSchema } from '@graphql-tools/utils'
import type { GraphQLSchema } from 'graphql'

import type { Directive } from './index'

const NAME = 'cacheControl'

export interface CacheControl {
  sMaxAge?: number
  staleWhileRevalidate?: number
  scope?: string
}

export const stringify = (
  cacheControl: CacheControl,
  forcePrivate?: boolean
): string => {
  const {
    scope = 'private',
    sMaxAge = 0,
    staleWhileRevalidate = 0,
  } = cacheControl
  const finalScope = forcePrivate ? 'private' : scope
  return `${finalScope}, s-maxage=${sMaxAge}, stale-while-revalidate=${staleWhileRevalidate}`
}

const min = (a: number | undefined, b: number | undefined) => {
  if (typeof a === 'number' && typeof b === 'number') {
    return a > b ? b : a
  }

  if (typeof a === 'number') {
    return a
  }

  return b
}

const minScope = (a: string | undefined, b: string | undefined) => {
  if (typeof a === 'string' && typeof b === 'string') {
    return a === 'public' && b === 'public' ? 'public' : 'private'
  }

  return a || b
}

const directive: Directive = {
  typeDefs: `directive @cacheControl(sMaxAge: Int, staleWhileRevalidate: Int, scope: String) on FIELD_DEFINITION`,
  transformer: (schema: GraphQLSchema) =>
    mapSchema(schema, {
      [MapperKind.OBJECT_FIELD]: (fieldConfig) => {
        const cacheControl = getDirective(schema, fieldConfig, NAME)?.[0] as
          | CacheControl
          | undefined

        if (cacheControl) {
          const { sMaxAge, staleWhileRevalidate, scope } = cacheControl

          const resolver = fieldConfig.resolve

          fieldConfig.resolve = (obj, args, ctx, info) => {
            ctx.cacheControl = {
              sMaxAge: min(ctx.cacheControl?.sMaxAge, sMaxAge),
              staleWhileRevalidate: min(
                ctx.cacheControl?.staleWhileRevalidate,
                staleWhileRevalidate
              ),
              scope: minScope(ctx.cacheControl?.scope, scope),
            }

            return resolver?.(obj, args, ctx, info)
          }
        }

        return fieldConfig
      },
    }),
}

export default directive