Nuxt/packages/kit/src/module/define.ts

import defu from 'defu'
import { applyDefaults } from 'untyped'
import { useNuxt, nuxtCtx } from '../nuxt'
import type { Nuxt } from '../types/nuxt'
import type { NuxtModule, LegacyNuxtModule, ModuleOptions } from '../types/module'

/**
 * Define a Nuxt module, automatically merging defaults with user provided options, installing
 * any hooks that are provided, and calling an optional setup function for full control.
 */
export function defineNuxtModule<OptionsT extends ModuleOptions> (input: NuxtModule<OptionsT> | ((nuxt: Nuxt) => NuxtModule<OptionsT>)): LegacyNuxtModule {
  let mod: NuxtModule<OptionsT>

  function wrappedModule (inlineOptions: OptionsT) {
    // Get nuxt context
    const nuxt: Nuxt = this.nuxt || useNuxt()

    // Resolve function
    if (typeof input === 'function') {
      const fn = input
      mod = nuxtCtx.call(nuxt, () => fn(nuxt))
    } else {
      mod = input
    }

    // Install hooks
    if (mod.hooks) {
      nuxt.hooks.addHooks(mod.hooks)
    }

    // Stop if no install provided
    if (typeof mod.setup !== 'function') {
      return
    }

    // Resolve options
    const configKey = mod.configKey || mod.name
    const userOptions = defu(inlineOptions, nuxt.options[configKey]) as OptionsT
    const resolvedOptions = applyDefaults(mod.defaults as any, userOptions) as OptionsT

    // Call setup
    return nuxtCtx.call(nuxt, () => mod.setup.call(null, resolvedOptions, nuxt))
  }

  wrappedModule.meta = mod

  return wrappedModule
}