import { Message, MessageAttributes } from '@node-ts/bus-messages'
import { ClassConstructor } from '../util'
import {
  WorkflowAlreadyHandlesMessage,
  WorkflowAlreadyStartedByMessage
} from './error'
import { MessageWorkflowMapping } from './message-workflow-mapping'
import { WorkflowState, WorkflowStatus } from './workflow-state'

export type WorkflowHandler<
  TMessage extends Message,
  TMessageAttributes extends MessageAttributes,
  WorkflowStateType extends WorkflowState
> = (
  message?: TMessage,
  attributes?: TMessageAttributes,
  workflowState?: WorkflowStateType
) =>
  | void
  | Partial<WorkflowStateType>
  | Promise<void | Partial<WorkflowStateType>>

export type WhenHandler<
  WorkflowStateType extends WorkflowState,
  WorkflowType extends Workflow<WorkflowStateType>
> = (
  workflow: WorkflowType
) => WorkflowHandler<Message, MessageAttributes, WorkflowStateType>

type KeyOfType<T, U> = { [P in keyof T]: T[P] extends U ? P : never }[keyof T]

export type OnWhenHandler<
  WorkflowStateType extends WorkflowState = WorkflowState,
  WorkflowType extends Workflow<WorkflowStateType> = Workflow<WorkflowStateType>
> = {
  workflowCtor: ClassConstructor<Workflow<WorkflowState>>
  workflowHandler: KeyOfType<WorkflowType, Function>
  customLookup: MessageWorkflowMapping | undefined
}

/**
 * A workflow configuration that describes how to map incoming messages to handlers within the workflow.
 */
export class WorkflowMapper<
  WorkflowStateType extends WorkflowState,
  WorkflowType extends Workflow<WorkflowStateType>
> {
  readonly onStartedBy = new Map<
    ClassConstructor<Message>,
    {
      workflowCtor: ClassConstructor<Workflow<WorkflowState>>
      workflowHandler: KeyOfType<WorkflowType, Function>
    }
  >()
  readonly onWhen = new Map<
    ClassConstructor<Message>,
    OnWhenHandler<WorkflowStateType, WorkflowType>
  >()
  private workflowStateType: ClassConstructor<WorkflowStateType> | undefined

  constructor(
    private readonly workflow: ClassConstructor<Workflow<WorkflowState>>
  ) {}

  get workflowStateCtor(): ClassConstructor<WorkflowStateType> | undefined {
    return this.workflowStateType
  }

  withState(workflowStateType: ClassConstructor<WorkflowStateType>): this {
    this.workflowStateType = workflowStateType
    return this
  }

  startedBy<MessageType extends Message>(
    message: ClassConstructor<MessageType>,
    workflowHandler: KeyOfType<WorkflowType, Function>
    // workflowHandler: (workflow: WorkflowType) => WorkflowHandler<MessageType, WorkflowStateType>
  ): this {
    if (this.onStartedBy.has(message)) {
      throw new WorkflowAlreadyStartedByMessage(this.workflow.name, message)
    }
    this.onStartedBy.set(message, {
      workflowHandler,
      workflowCtor: this.workflow
    })
    return this
  }

  when<MessageType extends Message>(
    message: ClassConstructor<MessageType>,
    workflowHandler: KeyOfType<WorkflowType, Function>,
    customLookup?: MessageWorkflowMapping<MessageType, WorkflowStateType>
  ): this {
    if (this.onWhen.has(message)) {
      throw new WorkflowAlreadyHandlesMessage(this.workflow.name, message)
    }
    this.onWhen.set(message, {
      workflowHandler,
      workflowCtor: this.workflow,
      customLookup: customLookup as MessageWorkflowMapping<
        Message,
        WorkflowState
      >
    })
    return this
  }
}

export abstract class Workflow<WorkflowStateType extends WorkflowState> {
  abstract configureWorkflow(
    mapper: WorkflowMapper<WorkflowStateType, any>
  ): void

  /**
   * Ends the workflow and optionally sets any final state. After this is returned,
   * the workflow instance will no longer be activated for subsequent messages.
   */
  protected completeWorkflow(workflowState?: Partial<WorkflowStateType>) {
    return {
      ...workflowState,
      $status: WorkflowStatus.Complete
    }
  }

  /**
   * Prevents a new workflow from starting, and prevents the persistence of
   * the workflow state. This should only be used in `startedBy` workflow handlers.
   */
  protected discardWorkflow() {
    return { $status: WorkflowStatus.Discard }
  }
}