package main

import (
	"fmt"
	"io"
	"strings"
	"sync"
	"time"
)

func main() {
	comment := "Package io provides basic interfaces to I/O primitives. " +
		"Its primary job is to wrap existing implementations of such primitives, " +
		"such as those in package os, " +
		"into shared public interfaces that abstract the functionality, " +
		"plus some other related primitives."

	// 示例1。
	fmt.Println("New a string reader and name it \"reader1\" ...")
	reader1 := strings.NewReader(comment)
	buf1 := make([]byte, 7)
	n, err := reader1.Read(buf1)
	var offset1, index1 int64
	executeIfNoErr(err, func() {
		fmt.Printf("Read(%d): %q\n", n, buf1[:n])
		offset1 = int64(53)
		index1, err = reader1.Seek(offset1, io.SeekCurrent)
	})
	executeIfNoErr(err, func() {
		fmt.Printf("The new index after seeking from current with offset %d: %d\n",
			offset1, index1)
		n, err = reader1.Read(buf1)
	})
	executeIfNoErr(err, func() {
		fmt.Printf("Read(%d): %q\n", n, buf1[:n])
	})
	fmt.Println()

	// 示例2。
	reader1.Reset(comment)
	num1 := int64(7)
	fmt.Printf("New a limited reader with reader1 and number %d ...\n", num1)
	reader2 := io.LimitReader(reader1, 7)
	buf2 := make([]byte, 10)
	for i := 0; i < 3; i++ {
		n, err = reader2.Read(buf2)
		executeIfNoErr(err, func() {
			fmt.Printf("Read(%d): %q\n", n, buf2[:n])
		})
	}
	fmt.Println()

	// 示例3。
	reader1.Reset(comment)
	offset2 := int64(56)
	num2 := int64(72)
	fmt.Printf("New a section reader with reader1, offset %d and number %d ...\n", offset2, num2)
	reader3 := io.NewSectionReader(reader1, offset2, num2)
	buf3 := make([]byte, 20)
	for i := 0; i < 5; i++ {
		n, err = reader3.Read(buf3)
		executeIfNoErr(err, func() {
			fmt.Printf("Read(%d): %q\n", n, buf3[:n])
		})
	}
	fmt.Println()

	// 示例4。
	reader1.Reset(comment)
	writer1 := new(strings.Builder)
	fmt.Println("New a tee reader with reader1 and writer1 ...")
	reader4 := io.TeeReader(reader1, writer1)
	buf4 := make([]byte, 40)
	for i := 0; i < 8; i++ {
		n, err = reader4.Read(buf4)
		executeIfNoErr(err, func() {
			fmt.Printf("Read(%d): %q\n", n, buf4[:n])
		})
	}
	fmt.Println()

	// 示例5。
	reader5a := strings.NewReader(
		"MultiReader returns a Reader that's the logical concatenation of " +
			"the provided input readers.")
	reader5b := strings.NewReader("They're read sequentially.")
	reader5c := strings.NewReader("Once all inputs have returned EOF, " +
		"Read will return EOF.")
	reader5d := strings.NewReader("If any of the readers return a non-nil, " +
		"non-EOF error, Read will return that error.")
	fmt.Println("New a multi-reader with 4 readers ...")
	reader5 := io.MultiReader(reader5a, reader5b, reader5c, reader5d)
	buf5 := make([]byte, 50)
	for i := 0; i < 8; i++ {
		n, err = reader5.Read(buf5)
		executeIfNoErr(err, func() {
			fmt.Printf("Read(%d): %q\n", n, buf5[:n])
		})
	}
	fmt.Println()

	// 示例6。
	fmt.Println("New a synchronous in-memory pipe ...")
	pReader, pWriter := io.Pipe()
	_ = interface{}(pReader).(io.ReadCloser)
	_ = interface{}(pWriter).(io.WriteCloser)

	comments := [][]byte{
		[]byte("Pipe creates a synchronous in-memory pipe."),
		[]byte("It can be used to connect code expecting an io.Reader "),
		[]byte("with code expecting an io.Writer."),
	}

	// 这里添加这个同步工具纯属为了保证下面示例中的打印语句都能够执行完成。
	// 在实际使用中没有必要这样做。
	var wg sync.WaitGroup
	wg.Add(2)

	go func() {
		defer wg.Done()
		for _, d := range comments {
			time.Sleep(time.Millisecond * 1000)
			n, err := pWriter.Write(d)
			if err != nil {
				fmt.Printf("write error: %v\n", err)
				break
			}
			fmt.Printf("Written(%d) time(%d): %q\n", n, time.Now().UnixNano(), d)
		}
		pWriter.Close()
	}()
	go func() {
		defer wg.Done()
		wBuf := make([]byte, 55)
		for {
			n, err := pReader.Read(wBuf)
			if err != nil {
				fmt.Printf("read error: %v\n", err)
				break
			}
			fmt.Printf("Read(%d) time(%d): %q\n", n, time.Now().UnixNano(), wBuf[:n])
		}
	}()
	wg.Wait()
}

func executeIfNoErr(err error, f func()) {
	if err != nil {
		fmt.Printf("error: %v\n", err)
		return
	}
	f()
}