From 72a89be8c1450d77c526aab523b8c02187ea9e80 Mon Sep 17 00:00:00 2001
From: dudaodong <dudaodong@gmail.com>
Date: Sat, 11 Dec 2021 13:30:11 +0800
Subject: [PATCH] feat: add function package for funcational programming

---
 function/function.go      | 72 +++++++++++++++++++++++++++++
 function/function_test.go | 95 +++++++++++++++++++++++++++++++++++++++
 function/function_util.go | 23 ++++++++++
 3 files changed, 190 insertions(+)
 create mode 100644 function/function.go
 create mode 100644 function/function_test.go
 create mode 100644 function/function_util.go

diff --git a/function/function.go b/function/function.go
new file mode 100644
index 00000000..873579e9
--- /dev/null
+++ b/function/function.go
@@ -0,0 +1,72 @@
+// Copyright 2021 dudaodong@gmail.com. All rights reserved.
+// Use of this source code is governed by MIT license
+
+// Package function implements some functions for functional programming.
+
+package function
+
+import (
+	"reflect"
+	"time"
+)
+
+// After creates a function that invokes func once it's called n or more times
+func After(n int, fn interface{}) func(args ...interface{}) []reflect.Value {
+	return func(args ...interface{}) []reflect.Value {
+		n--
+		if n < 1 {
+			return invokeFunc(fn, args...)
+		}
+		return nil
+	}
+}
+
+// Before creates a function that invokes func once it's called less than n times
+func Before(n int, fn interface{}) func(args ...interface{}) []reflect.Value {
+	var res []reflect.Value
+
+	return func(args ...interface{}) []reflect.Value {
+		if n > 0 {
+			res = invokeFunc(fn, args...)
+		}
+		if n <= 0 {
+			fn = nil
+		}
+		n--
+		return res
+	}
+}
+
+type Fn func(...interface{}) interface{}
+
+// Curry make a curryed function
+func (f Fn) Curry(i interface{}) func(...interface{}) interface{} {
+	return func(values ...interface{}) interface{} {
+		v := append([]interface{}{i}, values...)
+		return f(v...)
+	}
+}
+
+// Delay make the function excution after delayed time
+func Delay(delay time.Duration, fn interface{}, args ...interface{}) {
+	time.Sleep(delay)
+	invokeFunc(fn, args...)
+}
+
+// Schedule invoke function every duration time, util close the returned bool chan
+func Schedule(d time.Duration, fn interface{}, args ...interface{}) chan bool {
+	quit := make(chan bool)
+
+	go func() {
+		for {
+			invokeFunc(fn, args...)
+			select {
+			case <-time.After(d):
+			case <-quit:
+				return
+			}
+		}
+	}()
+
+	return quit
+}
diff --git a/function/function_test.go b/function/function_test.go
new file mode 100644
index 00000000..93f271cd
--- /dev/null
+++ b/function/function_test.go
@@ -0,0 +1,95 @@
+package function
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+	"time"
+)
+
+func TestAfter(t *testing.T) {
+	arr := []string{"a", "b"}
+	f := After(len(arr), func(i int) int {
+		fmt.Println("print done")
+		return i
+	})
+	type cb func(args ...interface{}) []reflect.Value
+	print := func(i int, s string, fn cb) {
+		fmt.Printf("print: arr[%d] is %s \n", i, s)
+		v := fn(i)
+		if v != nil {
+			vv := v[0].Int()
+			if vv != 1 {
+				t.FailNow()
+			}
+		}
+	}
+	fmt.Println("print: arr is", arr)
+	for i := 0; i < len(arr); i++ {
+		print(i, arr[i], f)
+	}
+}
+
+func TestBefore(t *testing.T) {
+	arr := []string{"a", "b", "c", "d", "e"}
+	f := Before(3, func(i int) int {
+		return i
+	})
+
+	var res []int64
+	type cb func(args ...interface{}) []reflect.Value
+	appendStr := func(i int, s string, fn cb) {
+		fmt.Printf("appendStr: arr[%d] is %s \n", i, s)
+		v := fn(i)
+		res = append(res, v[0].Int())
+	}
+
+	for i := 0; i < len(arr); i++ {
+		appendStr(i, arr[i], f)
+	}
+
+	expect := []int64{0, 1, 2, 2, 2}
+	if !reflect.DeepEqual(expect, res) {
+		t.FailNow()
+	}
+}
+
+func TestCurry(t *testing.T) {
+	add := func(a, b int) int {
+		return a + b
+	}
+	var addCurry Fn = func(values ...interface{}) interface{} {
+		return add(values[0].(int), values[1].(int))
+	}
+
+	add1 := addCurry.Curry(1)
+	v := add1(2)
+	if v != 3 {
+		t.FailNow()
+	}
+}
+
+func TestDelay(t *testing.T) {
+	var print = func(s string) {
+		fmt.Println(s)
+	}
+	Delay(2*time.Second, print, "test delay")
+}
+
+func TestSchedule(t *testing.T) {
+	var res []string
+	appendStr := func(s string) {
+		fmt.Println(s)
+		res = append(res, s)
+	}
+
+	stop := Schedule(1*time.Second, appendStr, "*")
+	time.Sleep(5 * time.Second)
+	close(stop)
+
+	expect := []string{"*", "*", "*", "*", "*"}
+	if !reflect.DeepEqual(expect, res) {
+		t.FailNow()
+	}
+	fmt.Println("done")
+}
diff --git a/function/function_util.go b/function/function_util.go
new file mode 100644
index 00000000..b809c566
--- /dev/null
+++ b/function/function_util.go
@@ -0,0 +1,23 @@
+package function
+
+import (
+	"fmt"
+	"reflect"
+)
+
+func invokeFunc(fn interface{}, args ...interface{}) []reflect.Value {
+	fv := functionValue(fn)
+	params := make([]reflect.Value, len(args))
+	for i, item := range args {
+		params[i] = reflect.ValueOf(item)
+	}
+	return fv.Call(params)
+}
+
+func functionValue(function interface{}) reflect.Value {
+	v := reflect.ValueOf(function)
+	if v.Kind() != reflect.Func {
+		panic(fmt.Sprintf("Invalid function type, value of type %T", function))
+	}
+	return v
+}