feat(overmind): new transition API and allow async exit transitions

BREAKING CHANGE:
explicit transition API

Author: christianalfoni

packages/node_modules/overmind/src/statemachine.test.ts

@@ -41,7 +41,7 @@ describe('Statemachine', () => {
       state: 'FOO'
     })
     const transition: Action = ({ state }) => {
-      state.BAR()
+      state.transition('BAR')
     }
 
     const config = {
@@ -72,7 +72,7 @@ describe('Statemachine', () => {
       state: 'FOO'
     })
     const transition: Action = ({ state }) => {
-      state.BAR()
+      state.transition('BAR')
     }
 
     const config = {
@@ -88,7 +88,7 @@ describe('Statemachine', () => {
     overmind.actions.transition()
     expect(overmind.state.state).toBe('FOO')
   })
-  test('should run entry and exit transition', () => {
+  test('should run entry and exit transition', async () => {
     expect.assertions(3)
     type States = {
       state: 'FOO'
@@ -104,9 +104,9 @@ describe('Statemachine', () => {
       })
 
     const transition: Action = ({ state }) => {
-      state.BAR(() => {
+      return state.transition('BAR', () => {
         expect(state.state).toBe('BAR')
-        state.FOO()
+        state.transition('FOO')
       }, () => {
         expect(state.state).toBe('BAR')
       })
@@ -119,10 +119,10 @@ describe('Statemachine', () => {
       }
     } 
 
-    interface Action extends IAction<typeof config, void, void> {}
+    interface Action extends IAction<typeof config, void, void | Promise<void>> {}
 
     const overmind = createOvermindMock(config)
-    overmind.actions.transition()
+    await overmind.actions.transition()
     expect(overmind.state.state).toBe('FOO')
   })
   test('should flush changes to transitions', () => {
@@ -142,7 +142,7 @@ describe('Statemachine', () => {
       })
 
     const transition: Action = ({ state }) => {
-      state.BAR()
+      state.transition('BAR')
     }
 
     const config = {
@@ -177,7 +177,7 @@ describe('Statemachine', () => {
         state: 'FOO'
       })
     const transition: Action = ({ state }) => {
-      return state.BAR(async () => {
+      return state.transition('BAR', async () => {
         await Promise.resolve()
         expect(state[PROXY_TREE].master.mutationTree.isBlocking).toBe(true)
       })
@@ -214,7 +214,7 @@ describe('Statemachine', () => {
       })
 
     const transition: Action = ({ state }) => {
-      state.BAR()
+      state.transition('BAR')
     }
 
     const config = {
@@ -252,8 +252,8 @@ describe('Statemachine', () => {
       })
 
     const transition: Action = ({ state }) => {
-      state.BAR(() => {
-        state.FOO((current) => {
+      return state.transition('BAR', () => {
+        state.transition('FOO', (current) => {
           current.foo = 'bar2'
         })
       }, (current) => {
@@ -268,7 +268,7 @@ describe('Statemachine', () => {
       }
     } 
 
-    interface Action extends IAction<typeof config, void, void> {}
+    interface Action extends IAction<typeof config, void, void | Promise<void>> {}
 
     const overmind = createOvermind(config)
     overmind.actions.transition()
@@ -278,4 +278,52 @@ describe('Statemachine', () => {
     // @ts-ignore
     expect(overmind.state.bar).toBe('baz2')
   })
+
+  test('should allow async exit transition', async () => {
+    expect.assertions(3)
+
+    type States = {
+      state: 'FOO'
+      foo: string
+    } | {
+      state: 'BAR'
+      bar: string
+    }
+
+    const state = statemachine<States>({
+      FOO: ['BAR'],
+      BAR: ['FOO']
+      }, {
+        state: 'FOO',
+        foo: 'bar'
+      })
+    
+    const transition: Action = ({ state }) => {
+      return state.transition('BAR', async () => {
+        await Promise.resolve()
+        state.transition('FOO', (current) => {
+          current.foo = 'bar2'
+        })
+      }, (current) => {
+        current.bar = 'baz2'
+      })
+    }
+
+    const config = {
+      state,
+      actions: {
+        transition
+      }
+    } 
+
+    interface Action extends IAction<typeof config, void, void | Promise<void>> {}
+
+    const overmind = createOvermind(config)
+    await overmind.actions.transition()
+    expect(overmind.state.state).toBe('FOO')
+    // @ts-ignore
+    expect(overmind.state.foo).toBe('bar2')
+    // @ts-ignore
+    expect(overmind.state.bar).toBe('baz2')
+  })
 })

packages/node_modules/overmind/src/statemachine.ts

@@ -15,15 +15,19 @@ export interface MachineMethods<States extends TStates> {
   matches<T extends States["state"][]>(...states: T): this is Statemachine<States> & (States extends {
     state: T extends Array<infer S> ? S : never;
 } ? States : never);
+  transition<State extends States["state"], >(
+    state: State,
+    entry?:  (current: Statemachine<States> & (States extends { state: State } ? States : never)) => void,
+    exit?: (current: Statemachine<States> & (States extends { state: State } ? States : never)) => void
+  ): Promise<void>
   whenTransitioned: (state: States["state"]) => Promise<void>
 }
 
-export type Statemachine<States extends TStates> = States & MachineMethods<States> & {
-  [State in States["state"]]: <O>(entry?:  (current: Statemachine<States> & (States extends { state: State } ? States : never)) => O, exit?: (current: Statemachine<States> & (States extends { state: State } ? States : never)) => void) => O
-}
+export type Statemachine<States extends TStates> = States & MachineMethods<States>
 
 const CURRENT_EXIT = Symbol('CURRENT_EXIT')
 const INITIAL_STATE = Symbol('INITIAL_STATE')
+const TRANSITIONS = Symbol('TRANSITIONS')
 const PENDING_TRANSITIONS = Symbol('PENDING_TRANSITIONS')
 
 class StateMachine<States extends TStates>  {
@@ -33,31 +37,36 @@ class StateMachine<States extends TStates>  {
   private [PENDING_TRANSITIONS]: { [key: string]: Function[] } = {}
   constructor(transitions: StatemachineTransitions<States>, definition: States) {
     this[INITIAL_STATE] = definition.state
+    this[TRANSITIONS] = transitions
     Object.assign(this, definition)
+  }
+  transition(state, entry, exit) {
+    const transitions = this[VALUE][TRANSITIONS]
+    if (transitions[this.state].includes(state)) {
+      const tree = (this[PROXY_TREE].master.mutationTree || this[PROXY_TREE])
+      let exitResult
+      tree.enableMutations()
+      
+      if (this[CURRENT_EXIT]) this[CURRENT_EXIT]!()
+      if (exit) {
+        exitResult = new Promise((resolve) => {
+          this[VALUE][CURRENT_EXIT] = () => resolve(exit(this))
+        })
+      } else {
+        this[VALUE][CURRENT_EXIT] = undefined
+      }
+      this.state = state
+      const entryResult = entry && entry(this)
 
-    Object.keys(transitions).reduce((aggr, key) => {
-      aggr[key] = function (entry, exit) {
-        if (transitions[this.state].includes(key as any)) {
-          const tree = (this[PROXY_TREE].master.mutationTree || this[PROXY_TREE])
-
-          tree.enableMutations()
-          if (this[CURRENT_EXIT]) this[CURRENT_EXIT](this)
-          this[VALUE][CURRENT_EXIT] = exit
-          this.state = key as any
-          const result = entry && entry(this)
-          tree.blockMutations()
-
-          if (this[VALUE][PENDING_TRANSITIONS][this.state]) {
-            this[VALUE][PENDING_TRANSITIONS][this.state].forEach((resolve) => resolve())
-            this[VALUE][PENDING_TRANSITIONS][this.state] = []
-          }
+      tree.blockMutations()
 
-          return result
-        }
+      if (this[VALUE][PENDING_TRANSITIONS][this.state]) {
+        this[VALUE][PENDING_TRANSITIONS][this.state].forEach((resolve) => resolve())
+        this[VALUE][PENDING_TRANSITIONS][this.state] = []
       }
-  
-      return aggr
-    }, this)
+
+      return exitResult || entryResult
+    }
   }
   matches(...states) {
     if (states.includes(this.state)) {