How to do it...

These steps cover how to write and run your application:

1. From your Terminal or console application, create a new directory called ~/projects/go-programming-cookbook/chapter1/csvformat.
2. Navigate to this directory.
3. Run the following command:

$ go mod init github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter1/csvformat

You should see a file called go.mod that contains the following contents:

module github.com/PacktPublishing/Go-Programming-Cookbook-Second-Edition/chapter1/csvformat    

4. Copy the tests from ~/projects/go-programming-cookbook-original/chapter1/csvformat or use this as an exercise to write some of your own code!
5. Create a file called read_csv.go with the following contents:

        package csvformat
        
        import (
                "bytes"
                "encoding/csv"
                "fmt"
                "io"
                "strconv"
        )
        
        // Movie will hold our parsed CSV
        type Movie struct {
                Title string
                Director string
                Year int
        }
        
        // ReadCSV gives shows some examples of processing CSV
        // that is passed in as an io.Reader
        func ReadCSV(b io.Reader) ([]Movie, error) {
        
                r := csv.NewReader(b)
        
                // These are some optional configuration options
                r.Comma = ';'
                r.Comment = '-'
        
                var movies []Movie
        
                // grab and ignore the header for now
                // we may also want to use this for a dictionary key or
                // some other form of lookup
                _, err := r.Read()
                if err != nil && err != io.EOF {
                        return nil, err
                }
        
                // loop until it's all processed
                for {
                        record, err := r.Read()
                        if err == io.EOF {
                                break
                        } else if err != nil {
                                return nil, err
                        }
        
                        year, err := strconv.ParseInt(record[2], 10, 
                        64)
                        if err != nil {
                                return nil, err
                        }

                        m := Movie{record[0], record[1], int(year)}
                        movies = append(movies, m)
                }
                return movies, nil
        }

6. Add this additional function to read_csv.go, as follows:

        // AddMoviesFromText uses the CSV parser with a string
        func AddMoviesFromText() error {
                // this is an example of us taking a string, converting
                // it into a buffer, and reading it 
                // with the csv package
                in := `
                - first our headers
                movie title;director;year released
        
                - then some data
                Guardians of the Galaxy Vol. 2;James Gunn;2017
                Star Wars: Episode VIII;Rian Johnson;2017
                `
        
                b := bytes.NewBufferString(in)
                m, err := ReadCSV(b)
                if err != nil {
                        return err
                }
                fmt.Printf("%#vn", m)
                return nil
        }

7. Create a file called write_csv.go with the following contents:

        package csvformat
        
        import (
                "bytes"
                "encoding/csv"
                "io"
                "os"
        )
        
        // A Book has an Author and Title
        type Book struct {
                Author string
                Title string
        }
        
        // Books is a named type for an array of books
        type Books []Book
        
        // ToCSV takes a set of Books and writes to an io.Writer
        // it returns any errors
        func (books *Books) ToCSV(w io.Writer) error {
                n := csv.NewWriter(w)
                err := n.Write([]string{"Author", "Title"})
                if err != nil {
                        return err
                }
                for _, book := range *books {
                        err := n.Write([]string{book.Author, 
                        book.Title})
                        if err != nil {
                                return err
                        }
                }
        
                n.Flush()
                return n.Error()
        }

8. Add these additional functions to write_csv.go, as follows:

        // WriteCSVOutput initializes a set of books
        // and writes the to os.Stdout
        func WriteCSVOutput() error {
                b := Books{
                        Book{
                                Author: "F Scott Fitzgerald",
                                Title: "The Great Gatsby",
                        },
                        Book{
                                Author: "J D Salinger",
                                Title: "The Catcher in the Rye",
                        },
                }
        
                return b.ToCSV(os.Stdout)
        }

        // WriteCSVBuffer returns a buffer csv for
        // a set of books
        func WriteCSVBuffer() (*bytes.Buffer, error) {
                b := Books{
                        Book{
                                Author: "F Scott Fitzgerald",
                                Title: "The Great Gatsby",
                        },
                        Book{
                                Author: "J D Salinger",
                                Title: "The Catcher in the Rye",
                        },
                }
        
                w := &bytes.Buffer{}
                err := b.ToCSV(w)
                return w, err
        }

9. Create a new directory named example and navigate to it.
10. Create a main.go file with the following contents:

        package main
        
        import (
                "fmt"
        
                "github.com/PacktPublishing/
                 Go-Programming-Cookbook-Second-Edition/
                 chapter1/csvformat"
        )
        
        func main() {
                if err := csvformat.AddMoviesFromText(); err != nil {
                        panic(err)
                }
        
                if err := csvformat.WriteCSVOutput(); err != nil {
                        panic(err)
                }
        
                buffer, err := csvformat.WriteCSVBuffer()
                if err != nil {
                        panic(err)
                }
        
                fmt.Println("Buffer = ", buffer.String())
        }

11. Run go run ..
12. You may also run the following:

$ go build
$ ./example

You should see the following output:

$ go run . 
[]csvformat.Movie{csvformat.Movie{Title:"Guardians of the 
Galaxy Vol. 2", Director:"James Gunn", Year:2017},         
csvformat.Movie{Title:"Star Wars: Episode VIII", Director:"Rian 
Johnson", Year:2017}}
Author,Title
F Scott Fitzgerald,The Great Gatsby
J D Salinger,The Catcher in the Rye
Buffer = Author,Title
F Scott Fitzgerald,The Great Gatsby
J D Salinger,The Catcher in the Rye

13. If you copied or wrote your own tests, go up one directory and run go test, and ensure that all tests pass.