《互联网产品的服务端架构·交易、增长与平台化》12.2 运营操作的状态机

// file: internal/admin/operation.go
// tier: L1
// verify: go test ./internal/admin/

package admin

import (
	"errors"
	"fmt"
)

var (
	// ErrUnknownState 表示状态不在运营操作状态机的定义里。
	ErrUnknownState = errors.New("admin: unknown operation state")
	// ErrInvalidAction 表示当前状态不接受这个动作。
	ErrInvalidAction = errors.New("admin: invalid action")
	// ErrTerminalState 表示操作已经结束，不能再迁移。
	ErrTerminalState = errors.New("admin: terminal state")
)

// Op 是一条运营操作。ID 用于幂等和审计，Type 区分改价、发券、下架等活动，
// State 是它当前所处的状态。
type Op struct {
	ID    string
	Type  string
	State string
}

// Next 计算一次状态迁移的结果，但不修改 Op 本身。调用方应先持久化迁移
// 结果并写入审计，再执行副作用。终态 rejected 与 executed 拒绝任何动作；
// 未定义的状态返回 ErrUnknownState，而不是把它当成草稿。
func Next(state, action string) (string, error) {
	switch state {
	case "draft":
		if action == "submit" {
			return "pending", nil
		}
	case "pending":
		switch action {
		case "approve":
			return "approved", nil
		case "reject":
			return "rejected", nil
		}
	case "approved":
		if action == "execute" {
			return "executed", nil
		}
	case "rejected", "executed":
		return "", fmt.Errorf("%w: %q", ErrTerminalState, state)
	default:
		return "", fmt.Errorf("%w: %q", ErrUnknownState, state)
	}
	return "", fmt.Errorf("%w: %q on %q", ErrInvalidAction, action, state)
}

// file: internal/admin/operation_test.go
// tier: L1
// verify: go test ./internal/admin/

package admin

import (
	"errors"
	"testing"
)

func TestNextTransitions(t *testing.T) {
	cases := []struct {
		state  string
		action string
		want   string
	}{
		{"draft", "submit", "pending"},
		{"pending", "approve", "approved"},
		{"pending", "reject", "rejected"},
		{"approved", "execute", "executed"},
	}
	for _, c := range cases {
		got, err := Next(c.state, c.action)
		if err != nil {
			t.Fatalf("Next(%q, %q) = %v, want nil", c.state, c.action, err)
		}
		if got != c.want {
			t.Fatalf("Next(%q, %q) = %q, want %q", c.state, c.action, got, c.want)
		}
	}
}

func TestNextTerminal(t *testing.T) {
	for _, state := range []string{"rejected", "executed"} {
		for _, action := range []string{"submit", "approve", "reject", "execute"} {
			if _, err := Next(state, action); !errors.Is(err, ErrTerminalState) {
				t.Fatalf("Next(%q, %q) = %v, want ErrTerminalState", state, action, err)
			}
		}
	}
}

func TestNextUnknownState(t *testing.T) {
	for _, state := range []string{"", "archived", "Draft"} {
		if _, err := Next(state, "submit"); !errors.Is(err, ErrUnknownState) {
			t.Fatalf("Next(%q, submit) = %v, want ErrUnknownState", state, err)
		}
	}
}

func TestNextMatrix(t *testing.T) {
	states := []string{"draft", "pending", "approved", "rejected", "executed", "archived"}
	actions := []string{"submit", "approve", "reject", "execute", "unknown"}
	legal := map[string]string{
		"draft/submit":     "pending",
		"pending/approve":  "approved",
		"pending/reject":   "rejected",
		"approved/execute": "executed",
	}
	for _, state := range states {
		for _, action := range actions {
			key := state + "/" + action
			got, err := Next(state, action)
			want, ok := legal[key]
			if ok {
				if err != nil || got != want {
					t.Fatalf("%s = %q, %v; want %q, nil", key, got, err, want)
				}
				continue
			}
			if err == nil {
				t.Fatalf("%s = %q, nil; want error", key, got)
			}
		}
	}
}

func TestNextInvalidAction(t *testing.T) {
	cases := []struct {
		state  string
		action string
	}{
		{"draft", "approve"},
		{"draft", "execute"},
		{"pending", "submit"},
		{"pending", "execute"},
		{"approved", "submit"},
		{"approved", "reject"},
		{"draft", ""},
	}
	for _, c := range cases {
		if _, err := Next(c.state, c.action); !errors.Is(err, ErrInvalidAction) {
			t.Fatalf("Next(%q, %q) = %v, want ErrInvalidAction", c.state, c.action, err)
		}
	}
}

cd .local/checks/webapp-lab && go test ./internal/admin/ -run 'TestNext' -count=1 -v

=== RUN   TestNextTransitions
--- PASS: TestNextTransitions (0.00s)
=== RUN   TestNextTerminal
--- PASS: TestNextTerminal (0.00s)
=== RUN   TestNextUnknownState
--- PASS: TestNextUnknownState (0.00s)
=== RUN   TestNextInvalidAction
--- PASS: TestNextInvalidAction (0.00s)
PASS
ok  	webapp/internal/admin	0.246s