mtcute/packages/dispatcher/src/wizard.ts

import { MaybeAsync, Message } from '@mtcute/client'

import { Dispatcher } from './dispatcher'
import { UpdateState } from './state'
import { filters } from './filters'

/**
 * Action for the wizard scene.
 *
 * `Next`: Continue to the next registered step
 * (or exit, if this is the last step)
 *
 * `Stay`: Stay on the same step
 *
 * `Exit`: Exit from the wizard scene
 *
 * You can also return a `number` to jump to that step
 */
export enum WizardSceneAction {
    Next = 'next',
    Stay = 'stay',
    Exit = 'exit',
}

interface WizardInternalState {
    $step: number
}

/**
 * Wizard is a special type of Dispatcher
 * that can be used to simplify implementing
 * step-by-step scenes.
 */
export class WizardScene<
    State,
    SceneName extends string = string
> extends Dispatcher<State & WizardInternalState, SceneName> {
    private _steps = 0

    private _defaultState: State & WizardInternalState = {} as any

    setDefaultState(defaultState: State): void {
        this._defaultState = defaultState as State & WizardInternalState
    }

    /**
     * Get the total number of registered steps
     */
    get totalSteps(): number {
        return this._steps
    }

    /**
     * Add a step to the wizard
     */
    addStep(
        handler: (
            msg: Message,
            state: UpdateState<State, SceneName>
        ) => MaybeAsync<WizardSceneAction | number>
    ): void {
        const step = this._steps++

        const filter = filters.state<WizardInternalState>(
            (it) => it.$step === step
        )

        this.onNewMessage(
            step === 0 ? filters.or(filters.stateEmpty, filter) : filter,
            async (msg: Message, state) => {
                const result = await handler(msg, state)

                if (typeof result === 'number') {
                    await state.merge({ $step: result }, this._defaultState)
                    return
                }

                switch (result) {
                    case 'next': {
                        const next = step + 1
                        if (next === this._steps) {
                            await state.exit()
                        } else {
                            await state.merge(
                                { $step: next },
                                this._defaultState
                            )
                        }
                        break
                    }
                    case 'exit':
                        await state.exit()
                        break
                }
            }
        )
    }
}