20-pdf

Gophercises - 20 - Building PDFs

Problem

• https://github.com/gophercises/pdf
• https://gophercises.com/exercises/pdf

Solution

• main.go: Certificate of completion.
• learn-gofpdf/main.go: Learning how the package works.
• corp: Contains a corp package that is used to create invoices.
  • consts.go: Constants used in the PDF. Pretty much every position and color in the PDF is customizable here.
  • invoice.go: Invoice represents an invoice. Inside each invoice add client information and a slice of items. For each item, add description, amount, and price per unit. Everything else is calculated automatically (or with methods).
  • corp.go: Has methods for generating the invoice PDF. Different methods for page banner and footer, invoice header, and item list.
• generate-invoice/main.go: Generates an invoice almost exactly as the one in the example using the corp package. Look at main for usage of the corp package.

Generated Invoice

See image of generate invoice by generate-invoice/main.go. See a copy at generate-invoice/invoice.go

Lessons Learned

gofpdf Package

See inside gofpdflearn/main.go.

Access Struct Fields with the Reflect Package

Don't use relfection I guess. But this is fun.

In this case, our struct only has string fields so we only check for empty string.

v := reflect.ValueOf(c)
for i := 0; i < v.NumField(); i++ {
    if v.Field(i).Interface() == "" {
        return fmt.Errorf("Corp not initialized. Set value of %s", v.Type().Field(i).Name)
    }
}

We can access the value of a field with v.Field(i).Interface() and its name with v.Type().Field(i).Name.

Convert Float to String with Two Floating Points

Change 2 to get more floating points.

func FloatToString(f float64) string {
	return strconv.FormatFloat(f, 'f', 2, 64)
}

Corp Package Usage

Sample usage to generate the invoice PDF for the lesson.

package main

import (
	"fmt"

	"github.com/jung-kurt/gofpdf"
	"github.com/parsiya/Parsia-Code/gophercises/20-pdf/corp"
)

func main() {

	// Create a new corporation.
	co := corp.Company{
		Address: `123 Fake St.
		Some Town, PA
		12345`,
		ContactInfo: `(555)555-5555
		test@example.net
		example.net`,
		Logo: "img/logo.png",
	}

	// Create a new invoice.
	in := corp.Invoice{
		ClientName: "Client Name",
		ClientAddress: `1 Client Address
		City, State, Country
		Postal Code`,
		InvoiceNumber: "0000000123",
		Date:          "10/06/2018",
	}

	// Create items.
	it := []corp.Item{
		{
			"2x6 Lumber - 8'", 3.75, 220,
		},
		{
			"2x6 Lumber - 10'", 5.55, 18,
		},
		{
			"2x4 Lumber - 8'", 2.99, 80,
		},
		{
			"Drywall Sheet", 8.22, 50,
		},
		{
			"Paint", 14.55, 3,
		},
		{
			"Some item with a super long unit name to test our word wrapping",
			9.99, 22,
		},
	}

	// Add items to invoice.
	for _, i := range it {
		if err := in.AddItem(i); err != nil {
			panic(err)
		}
	}

	// Change papersize to letter because 'Murica is special!
	pdf := gofpdf.New(gofpdf.OrientationPortrait, gofpdf.UnitPoint, gofpdf.PageSizeLetter, "")

	// Set Header.
	if err := co.SetHeader(pdf); err != nil {
		panic(err)
	}
	co.SetFooter(pdf)

	pdf.AddPage()
	pdf.MoveTo(0, 0)

	// Draw invoice header.
	if err := co.InvoiceHeader(pdf, in); err != nil {
		panic(err)
	}

	// Draw item list.
	if err := co.ItemList(pdf, in); err != nil {
		panic(err)
	}

	// corp.DrawGrid(pdf)
	if err := pdf.OutputFileAndClose("invoice.pdf"); err != nil {
		panic(err)
	}
	fmt.Println("Done")
}