import BaseScene from './base'
import Composer from '../composer'
import Context from '../context'
import d from 'debug'
import { SessionContext } from '../session'
const debug = d('telegraf:scenes:context')

const noop = () => Promise.resolve()
const now = () => Math.floor(Date.now() / 1000)

export interface SceneContext<D extends SceneSessionData = SceneSessionData>
  extends Context {
  session: SceneSession<D>
  scene: SceneContextScene<SceneContext<D>, D>
}

export interface SceneSessionData {
  current?: string
  expires?: number
  state?: object
}

export interface SceneSession<S extends SceneSessionData = SceneSessionData> {
  __scenes: S
}

export interface SceneContextSceneOptions<D extends SceneSessionData> {
  ttl?: number
  default?: string
  defaultSession: D
}

export default class SceneContextScene<
  C extends SessionContext<SceneSession<D>>,
  D extends SceneSessionData = SceneSessionData
> {
  private readonly options: SceneContextSceneOptions<D>

  constructor(
    private readonly ctx: C,
    private readonly scenes: Map<string, BaseScene<C>>,
    options: Partial<SceneContextSceneOptions<D>>
  ) {
    // @ts-expect-error {} might not be assignable to D
    const fallbackSessionDefault: D = {}

    this.options = { defaultSession: fallbackSessionDefault, ...options }
  }

  get session(): D {
    const defaultSession = this.options.defaultSession

    let session = this.ctx.session?.__scenes ?? defaultSession
    if (session.expires !== undefined && session.expires < now()) {
      session = defaultSession
    }
    if (this.ctx.session === undefined) {
      this.ctx.session = { __scenes: session }
    } else {
      this.ctx.session.__scenes = session
    }
    return session
  }

  get state() {
    return (this.session.state ??= {})
  }

  set state(value) {
    this.session.state = { ...value }
  }

  get current() {
    const sceneId = this.session.current ?? this.options.default
    return sceneId === undefined || !this.scenes.has(sceneId)
      ? undefined
      : this.scenes.get(sceneId)
  }

  reset() {
    if (this.ctx.session !== undefined)
      this.ctx.session.__scenes = this.options.defaultSession
  }

  async enter(
    sceneId: string,
    initialState: object = {},
    silent: boolean = false
  ) {
    if (!this.scenes.has(sceneId)) {
      throw new Error(`Can't find scene: ${sceneId}`)
    }
    if (!silent) {
      await this.leave()
    }
    debug('Entering scene', sceneId, initialState, silent)
    this.session.current = sceneId
    this.state = initialState
    const ttl = this.current?.ttl ?? this.options.ttl
    if (ttl !== undefined) {
      this.session.expires = now() + ttl
    }
    if (this.current === undefined || silent) {
      return
    }
    const handler =
      'enterMiddleware' in this.current &&
      typeof this.current.enterMiddleware === 'function'
        ? this.current.enterMiddleware()
        : this.current.middleware()
    return await handler(this.ctx, noop)
  }

  reenter() {
    return this.session.current === undefined
      ? undefined
      : this.enter(this.session.current, this.state)
  }

  private leaving = false
  async leave() {
    if (this.leaving) return
    debug('Leaving scene')
    try {
      this.leaving = true
      if (this.current === undefined) {
        return
      }
      const handler =
        'leaveMiddleware' in this.current &&
        typeof this.current.leaveMiddleware === 'function'
          ? this.current.leaveMiddleware()
          : Composer.passThru()
      await handler(this.ctx, noop)
      return this.reset()
    } finally {
      this.leaving = false
    }
  }
}