const fs = require('fs')
const Path = require('path')
const async = require('async')
const { promisify } = require('util')
const Settings = require('@overleaf/settings')
const Views = require('./Views')
const _ = require('lodash')

const MODULE_BASE_PATH = Path.join(__dirname, '/../../../modules')

const _modules = []
let _modulesLoaded = false
const _hooks = {}
const _middleware = {}
let _viewIncludes = {}

async function modules() {
  if (!_modulesLoaded) {
    await loadModules()
  }
  return _modules
}

async function loadModulesImpl() {
  const settingsCheckModuleCjs = Path.join(
    MODULE_BASE_PATH,
    'settings-check',
    'index.js'
  )
  const settingsCheckModuleEsm = Path.join(
    MODULE_BASE_PATH,
    'settings-check',
    'index.mjs'
  )
  if (fs.existsSync(settingsCheckModuleCjs)) {
    await import(settingsCheckModuleCjs)
  } else if (fs.existsSync(settingsCheckModuleEsm)) {
    await import(settingsCheckModuleEsm)
  }
  for (const moduleName of Settings.moduleImportSequence || []) {
    let path
    if (fs.existsSync(Path.join(MODULE_BASE_PATH, moduleName, 'index.mjs'))) {
      path = Path.join(MODULE_BASE_PATH, moduleName, 'index.mjs')
    } else {
      path = Path.join(MODULE_BASE_PATH, moduleName, 'index.js')
    }
    const module = await import(path)
    const loadedModule = module.default || module

    loadedModule.name = moduleName
    _modules.push(loadedModule)
    if (loadedModule.viewIncludes) {
      throw new Error(
        `${moduleName}: module.viewIncludes moved into Settings.viewIncludes`
      )
    }
    if (loadedModule.dependencies) {
      for (const dependency of loadedModule.dependencies) {
        if (!Settings.moduleImportSequence.includes(dependency)) {
          throw new Error(
            `Module '${dependency}' listed as a dependency of '${moduleName}' is missing in the moduleImportSequence. Please also verify that it is available in the current environment.`
          )
        }
      }
    }
  }
  _modulesLoaded = true
  await attachHooks()
  await attachMiddleware()
}

const loadModules = _.memoize(loadModulesImpl)

async function applyRouter(webRouter, privateApiRouter, publicApiRouter) {
  for (const module of await modules()) {
    if (module.router && module.router.apply) {
      await module.router.apply(webRouter, privateApiRouter, publicApiRouter)
    }
  }
}

async function applyNonCsrfRouter(
  webRouter,
  privateApiRouter,
  publicApiRouter
) {
  for (const module of await modules()) {
    if (module.nonCsrfRouter != null) {
      module.nonCsrfRouter.apply(webRouter, privateApiRouter, publicApiRouter)
    }
    if (module.router && module.router.applyNonCsrfRouter) {
      module.router.applyNonCsrfRouter(
        webRouter,
        privateApiRouter,
        publicApiRouter
      )
    }
  }
}

async function start() {
  for (const module of await modules()) {
    await module.start?.()
  }
}

function loadViewIncludes(app) {
  _viewIncludes = Views.compileViewIncludes(app)
}

async function applyMiddleware(appOrRouter, middlewareName, options) {
  if (!middlewareName) {
    throw new Error(
      'middleware name must be provided to register module middleware'
    )
  }
  for (const module of await modules()) {
    if (module[middlewareName]) {
      module[middlewareName](appOrRouter, options)
    }
  }
}

function moduleIncludes(view, locals) {
  const compiledPartials = _viewIncludes[view] || []
  let html = ''
  for (const compiledPartial of compiledPartials) {
    html += compiledPartial(locals)
  }
  return html
}

function moduleIncludesAvailable(view) {
  return (_viewIncludes[view] || []).length > 0
}

async function linkedFileAgentsIncludes() {
  const agents = {}
  for (const module of await modules()) {
    for (const name in module.linkedFileAgents) {
      const agentFunction = module.linkedFileAgents[name]
      agents[name] = agentFunction()
    }
  }
  return agents
}

async function attachHooks() {
  for (const module of await modules()) {
    for (const hook in module.hooks || {}) {
      const method = module.hooks[hook]
      attachHook(hook, method)
    }
  }
}

function attachHook(name, method) {
  if (_hooks[name] == null) {
    _hooks[name] = []
  }
  _hooks[name].push(method)
}

async function attachMiddleware() {
  for (const module of await modules()) {
    for (const middleware in module.middleware || {}) {
      const method = module.middleware[middleware]
      if (_middleware[middleware] == null) {
        _middleware[middleware] = []
      }
      _middleware[middleware].push(method)
    }
  }
}

function fireHook(name, ...rest) {
  const adjustedLength = Math.max(rest.length, 1)
  const args = rest.slice(0, adjustedLength - 1)
  const callback = rest[adjustedLength - 1]
  function fire() {
    const methods = _hooks[name] || []
    const callMethods = methods.map(method => cb => method(...args, cb))
    async.series(callMethods, function (error, results) {
      if (error) {
        return callback(error)
      }
      callback(null, results)
    })
  }

  // ensure that modules are loaded if we need to fire a hook
  // this can happen if a script calls a method that fires a hook
  if (!_modulesLoaded) {
    loadModules()
      .then(() => {
        fire()
      })
      .catch(err => callback(err))
  } else {
    fire()
  }
}

async function getMiddleware(name) {
  // ensure that modules are loaded if we need to call a middleware
  if (!_modulesLoaded) {
    await loadModules()
  }
  return _middleware[name] || []
}

module.exports = {
  applyNonCsrfRouter,
  applyRouter,
  linkedFileAgentsIncludes,
  loadViewIncludes,
  moduleIncludes,
  moduleIncludesAvailable,
  applyMiddleware,
  start,
  hooks: {
    attach: attachHook,
    fire: fireHook,
  },
  middleware: getMiddleware,
  promises: {
    hooks: {
      fire: promisify(fireHook),
    },
  },
}