package pkg

import (
	"archive/zip"
	"bytes"
	"context"
	"errors"
	"fmt"
	"github.com/julienschmidt/httprouter"
	"html/template"
	"io"
	"log"
	"math"
	"net/http"
	"os"
	"os/exec"
	"sort"
	"strconv"
	"strings"
	"time"
)

type InvoiceEntry struct {
	Slug         string
	Date         time.Time
	Number       string
	Total        string
	CustomerName string
	Tags         []string
	Status       string
	StatusLabel  string
}

type InvoicesIndexPage struct {
	Invoices        []*InvoiceEntry
	InvoiceStatuses map[string]string
}

func IndexInvoices(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
	conn := getConn(r)
	locale := getLocale(r)
	tag := r.URL.Query().Get("tag")
	page := &InvoicesIndexPage{
		Invoices:        mustCollectInvoiceEntries(r.Context(), conn, mustGetCompany(r), locale, tag),
		InvoiceStatuses: mustCollectInvoiceStatuses(r.Context(), conn, locale),
	}
	mustRenderMainTemplate(w, r, "invoices/index.gohtml", page)
}

func mustCollectInvoiceEntries(ctx context.Context, conn *Conn, company *Company, locale *Locale, tag string) []*InvoiceEntry {
	rows := conn.MustQuery(ctx, `
		select invoice.slug
		     , invoice_date
		     , invoice_number
		     , contact.business_name
		     , array_agg(coalesce(tag.name::text, ''))
		     , invoice.invoice_status
		     , isi18n.name
		     , to_price(total, decimal_digits)
		from invoice
		left join invoice_tag using (invoice_id)
		left join tag using(tag_id)
		join contact using (contact_id)
		join invoice_status_i18n isi18n on invoice.invoice_status = isi18n.invoice_status and isi18n.lang_tag = $2
		join invoice_amount using (invoice_id)
		join currency using (currency_code)
		where invoice.company_id = $1 and (($3 = '') or (tag.name = $3))
		group by invoice.slug
		       , invoice_date
		       , invoice_number
		       , contact.business_name
		       , invoice.invoice_status
		       , isi18n.name
		       , total
		       , decimal_digits
		order by invoice_date desc
		       , invoice_number desc
	`, company.Id, locale.Language.String(), tag)
	defer rows.Close()

	var entries []*InvoiceEntry
	for rows.Next() {
		entry := &InvoiceEntry{}
		if err := rows.Scan(&entry.Slug, &entry.Date, &entry.Number, &entry.CustomerName, &entry.Tags, &entry.Status, &entry.StatusLabel, &entry.Total); err != nil {
			panic(err)
		}
		entries = append(entries, entry)
	}
	if rows.Err() != nil {
		panic(rows.Err())
	}

	return entries
}

func mustCollectInvoiceStatuses(ctx context.Context, conn *Conn, locale *Locale) map[string]string {
	rows := conn.MustQuery(ctx, "select invoice_status.invoice_status, isi18n.name from invoice_status join invoice_status_i18n isi18n using(invoice_status) where isi18n.lang_tag = $1 order by invoice_status", locale.Language.String())
	defer rows.Close()

	statuses := map[string]string{}
	for rows.Next() {
		var key, name string
		if err := rows.Scan(&key, &name); err != nil {
			panic(err)
		}
		statuses[key] = name
	}
	if rows.Err() != nil {
		panic(rows.Err())
	}

	return statuses
}

func ServeInvoice(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
	conn := getConn(r)
	company := mustGetCompany(r)
	slug := params[0].Value
	if slug == "new" {
		locale := getLocale(r)
		form := newInvoiceForm(r.Context(), conn, locale, company)
		if invoiceToDuplicate := r.URL.Query().Get("duplicate"); invoiceToDuplicate != "" {
			form.MustFillFromDatabase(r.Context(), conn, invoiceToDuplicate)
			form.InvoiceStatus.Selected = []string{"created"}
			form.Number.Val = ""
		}
		form.Date.Val = time.Now().Format("2006-01-02")
		w.WriteHeader(http.StatusOK)
		mustRenderNewInvoiceForm(w, r, form)
		return
	}

	pdf := false
	if strings.HasSuffix(slug, ".pdf") {
		pdf = true
		slug = slug[:len(slug)-len(".pdf")]
	}
	inv := mustGetInvoice(r.Context(), conn, company, slug)
	if inv == nil {
		http.NotFound(w, r)
		return
	}
	if pdf {
		w.Header().Set("Content-Type", "application/pdf")
		mustWriteInvoicePdf(w, r, inv)
	} else {
		mustRenderAppTemplate(w, r, "invoices/view.gohtml", inv)
	}
}

func mustWriteInvoicePdf(w io.Writer, r *http.Request, inv *invoice) {
	cmd := exec.Command("weasyprint", "--format", "pdf", "--stylesheet", "web/static/invoice.css", "-", "-")
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	stdin, err := cmd.StdinPipe()
	if err != nil {
		panic(err)
	}
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		panic(err)
	}
	defer func() {
		err := stdout.Close()
		if !errors.Is(err, os.ErrClosed) {
			panic(err)
		}
	}()
	if err = cmd.Start(); err != nil {
		panic(err)
	}
	go func() {
		defer mustClose(stdin)
		mustRenderAppTemplate(stdin, r, "invoices/view.gohtml", inv)
	}()
	if _, err = io.Copy(w, stdout); err != nil {
		panic(err)
	}
	if err := cmd.Wait(); err != nil {
		log.Printf("ERR - %v\n", stderr.String())
		panic(err)
	}
}

func mustClose(closer io.Closer) {
	if err := closer.Close(); err != nil {
		panic(err)
	}
}

type invoice struct {
	Number              string
	Slug                string
	Date                time.Time
	Invoicer            taxDetails
	Invoicee            taxDetails
	Notes               string
	PaymentInstructions string
	Products            []*invoiceProduct
	Subtotal            string
	Taxes               [][]string
	TaxClasses          []string
	HasDiscounts        bool
	Total               string
	LegalDisclaimer     string
}

type taxDetails struct {
	Name       string
	VATIN      string
	Address    string
	City       string
	PostalCode string
	Province   string
	Email      string
	Phone      string
}

type invoiceProduct struct {
	Name        string
	Description string
	Price       string
	Discount    int
	Quantity    int
	Taxes       map[string]int
	Subtotal    string
	Total       string
}

func mustGetInvoice(ctx context.Context, conn *Conn, company *Company, slug string) *invoice {
	inv := &invoice{
		Slug: slug,
	}
	var invoiceId int
	var decimalDigits int
	if notFoundErrorOrPanic(conn.QueryRow(ctx, "select invoice_id, decimal_digits, invoice_number, invoice_date, notes, instructions, business_name, vatin, phone, email, address, city, province, postal_code, to_price(subtotal, decimal_digits), to_price(total, decimal_digits) from invoice join payment_method using (payment_method_id) join contact using (contact_id) join invoice_amount using (invoice_id) join currency using (currency_code) where invoice.slug = $1", slug).Scan(&invoiceId, &decimalDigits, &inv.Number, &inv.Date, &inv.Notes, &inv.PaymentInstructions, &inv.Invoicee.Name, &inv.Invoicee.VATIN, &inv.Invoicee.Phone, &inv.Invoicee.Email, &inv.Invoicee.Address, &inv.Invoicee.City, &inv.Invoicee.Province, &inv.Invoicee.PostalCode, &inv.Subtotal, &inv.Total)) {
		return nil
	}
	if err := conn.QueryRow(ctx, "select business_name, vatin, phone, email, address, city, province, postal_code, legal_disclaimer from company where company_id = $1", company.Id).Scan(&inv.Invoicer.Name, &inv.Invoicer.VATIN, &inv.Invoicer.Phone, &inv.Invoicer.Email, &inv.Invoicer.Address, &inv.Invoicer.City, &inv.Invoicer.Province, &inv.Invoicer.PostalCode, &inv.LegalDisclaimer); err != nil {
		panic(err)
	}
	if err := conn.QueryRow(ctx, "select array_agg(array[name, to_price(amount, $2)]) from invoice_tax_amount join tax using (tax_id) where invoice_id = $1", invoiceId, decimalDigits).Scan(&inv.Taxes); err != nil {
		panic(err)
	}
	rows := conn.MustQuery(ctx, "select invoice_product.name, description, to_price(price, $2), (discount_rate * 100)::integer, quantity, to_price(subtotal, $2), to_price(total, $2), array_agg(array[tax_class.name, (tax_rate * 100)::integer::text]) from invoice_product join invoice_product_amount using (invoice_product_id) left join invoice_product_tax using (invoice_product_id) left join tax using (tax_id) left join tax_class using (tax_class_id) where invoice_id = $1 group by invoice_product.name, description, discount_rate, price, quantity, subtotal, total", invoiceId, decimalDigits)
	defer rows.Close()
	taxClasses := map[string]bool{}
	for rows.Next() {
		product := &invoiceProduct{
			Taxes: make(map[string]int),
		}
		var taxes [][]string
		if err := rows.Scan(&product.Name, &product.Description, &product.Price, &product.Discount, &product.Quantity, &product.Subtotal, &product.Total, &taxes); err != nil {
			panic(err)
		}
		for _, tax := range taxes {
			taxClass := tax[0]
			taxClasses[taxClass] = true
			product.Taxes[taxClass], _ = strconv.Atoi(tax[1])
		}
		if product.Discount > 0 {
			inv.HasDiscounts = true
		}
		inv.Products = append(inv.Products, product)
	}
	for taxClass := range taxClasses {
		inv.TaxClasses = append(inv.TaxClasses, taxClass)
	}
	sort.Strings(inv.TaxClasses)
	if rows.Err() != nil {
		panic(rows.Err())
	}

	return inv
}

type newInvoicePage struct {
	Form     *invoiceForm
	Subtotal string
	Taxes    [][]string
	Total    string
}

func newNewInvoicePage(form *invoiceForm, r *http.Request) *newInvoicePage {
	page := &newInvoicePage{
		Form: form,
	}
	conn := getConn(r)
	company := mustGetCompany(r)
	err := conn.QueryRow(r.Context(), "select subtotal, taxes, total from compute_new_invoice_amount($1, $2)", company.Id, NewInvoiceProductArray(form.Products)).Scan(&page.Subtotal, &page.Taxes, &page.Total)
	if err != nil {
		panic(err)
	}
	return page
}

func mustRenderNewInvoiceForm(w http.ResponseWriter, r *http.Request, form *invoiceForm) {
	locale := getLocale(r)
	form.Customer.EmptyLabel = gettext("Select a customer to bill.", locale)
	page := newNewInvoicePage(form, r)
	mustRenderAppTemplate(w, r, "invoices/new.gohtml", page)
}

func mustRenderNewInvoiceProductsForm(w http.ResponseWriter, r *http.Request, action string, form *invoiceForm) {
	conn := getConn(r)
	company := mustGetCompany(r)
	page := newInvoiceProductsPage{
		Action:   companyURI(company, action),
		Form:     form,
		Products: mustGetProductChoices(r.Context(), conn, company),
	}
	mustRenderAppTemplate(w, r, "invoices/products.gohtml", page)
}

func mustGetProductChoices(ctx context.Context, conn *Conn, company *Company) []*productChoice {
	rows := conn.MustQuery(ctx, "select product.product_id, product.name, to_price(price, decimal_digits) from product join company using (company_id) join currency using (currency_code) where company_id = $1 order by name", company.Id)
	defer rows.Close()

	var choices []*productChoice
	for rows.Next() {
		entry := &productChoice{}
		if err := rows.Scan(&entry.Id, &entry.Name, &entry.Price); err != nil {
			panic(err)
		}
		choices = append(choices, entry)
	}
	if rows.Err() != nil {
		panic(rows.Err())
	}

	return choices
}

type newInvoiceProductsPage struct {
	Action   string
	Form     *invoiceForm
	Products []*productChoice
}

type productChoice struct {
	Id    int
	Name  string
	Price string
}

func HandleAddInvoice(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
	locale := getLocale(r)
	conn := getConn(r)
	company := mustGetCompany(r)
	form := newInvoiceForm(r.Context(), conn, locale, company)
	if err := form.Parse(r); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if err := verifyCsrfTokenValid(r); err != nil {
		http.Error(w, err.Error(), http.StatusForbidden)
		return
	}
	if !form.Validate() {
		w.WriteHeader(http.StatusUnprocessableEntity)
		mustRenderNewInvoiceForm(w, r, form)
		return
	}
	slug := conn.MustGetText(r.Context(), "", "select add_invoice($1, $2, $3, $4, $5, $6, $7, $8)", company.Id, form.Number, form.Date, form.Customer, form.Notes, form.PaymentMethod, form.Tags, NewInvoiceProductArray(form.Products))
	http.Redirect(w, r, companyURI(company, "/invoices/"+slug), http.StatusSeeOther)
}

func HandleNewInvoiceAction(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
	switch params[0].Value {
	case "new":
		handleInvoiceAction(w, r, "/invoices/new", mustRenderNewInvoiceForm)
	case "batch":
		HandleBatchInvoiceAction(w, r, params)
	default:
		http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
	}
}

func HandleBatchInvoiceAction(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
	if err := r.ParseForm(); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if err := verifyCsrfTokenValid(r); err != nil {
		http.Error(w, err.Error(), http.StatusForbidden)
		return
	}
	slugs := r.Form["invoice"]
	if len(slugs) == 0 {
		http.Redirect(w, r, companyURI(mustGetCompany(r), "/invoices"), http.StatusSeeOther)
		return
	}
	locale := getLocale(r)
	switch r.Form.Get("action") {
	case "download":
		invoices := mustWriteInvoicesPdf(r, slugs)
		w.Header().Set("Content-Type", "application/zip")
		w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=%s", gettext("invoices.zip", locale)))
		w.WriteHeader(http.StatusOK)
		if _, err := w.Write(invoices); err != nil {
			panic(err)
		}
	default:
		http.Error(w, gettext("Invalid action", locale), http.StatusBadRequest)
	}
}

func mustWriteInvoicesPdf(r *http.Request, slugs []string) []byte {
	conn := getConn(r)
	company := mustGetCompany(r)
	buf := new(bytes.Buffer)
	w := zip.NewWriter(buf)
	for _, slug := range slugs {
		inv := mustGetInvoice(r.Context(), conn, company, slug)
		if inv == nil {
			continue
		}
		f, err := w.Create(inv.Number + ".pdf")
		if err != nil {
			panic(err)
		}
		mustWriteInvoicePdf(f, r, inv)
	}
	mustClose(w)
	return buf.Bytes()
}

type invoiceForm struct {
	locale        *Locale
	company       *Company
	InvoiceStatus *SelectField
	Customer      *SelectField
	Number        *InputField
	Date          *InputField
	Notes         *InputField
	PaymentMethod *SelectField
	Tags          *TagsField
	Products      []*invoiceProductForm
}

func newInvoiceForm(ctx context.Context, conn *Conn, locale *Locale, company *Company) *invoiceForm {
	return &invoiceForm{
		locale:  locale,
		company: company,
		InvoiceStatus: &SelectField{
			Name:     "invoice_status",
			Required: true,
			Label:    pgettext("input", "Invoice Status", locale),
			Selected: []string{"created"},
			Options:  MustGetOptions(ctx, conn, "select invoice_status.invoice_status, isi18n.name from invoice_status join invoice_status_i18n isi18n using(invoice_status) where isi18n.lang_tag = $1 order by invoice_status", locale.Language.String()),
		},
		Customer: &SelectField{
			Name:     "customer",
			Label:    pgettext("input", "Customer", locale),
			Required: true,
			Options:  MustGetOptions(ctx, conn, "select contact_id::text, business_name from contact where company_id = $1 order by business_name", company.Id),
		},
		Number: &InputField{
			Name:  "number",
			Label: pgettext("input", "Number", locale),
			Type:  "text",
		},
		Date: &InputField{
			Name:     "date",
			Label:    pgettext("input", "Invoice Date", locale),
			Type:     "date",
			Required: true,
		},
		Notes: &InputField{
			Name:  "notes",
			Label: pgettext("input", "Notes", locale),
			Type:  "textarea",
		},
		Tags: &TagsField{
			Name:  "tags",
			Label: pgettext("input", "Tags", locale),
		},
		PaymentMethod: &SelectField{
			Name:     "payment_method",
			Required: true,
			Label:    pgettext("input", "Payment Method", locale),
			Selected: []string{conn.MustGetText(ctx, "", "select default_payment_method_id::text from company where company_id = $1", company.Id)},
			Options:  MustGetOptions(ctx, conn, "select payment_method_id::text, name from payment_method where company_id = $1", company.Id),
		},
	}
}

func (form *invoiceForm) Parse(r *http.Request) error {
	if err := r.ParseForm(); err != nil {
		return err
	}
	form.InvoiceStatus.FillValue(r)
	form.Customer.FillValue(r)
	form.Number.FillValue(r)
	form.Date.FillValue(r)
	form.Notes.FillValue(r)
	form.Tags.FillValue(r)
	form.PaymentMethod.FillValue(r)
	if _, ok := r.Form["product.id.0"]; ok {
		taxOptions := mustGetTaxOptions(r.Context(), getConn(r), form.company)
		for index := 0; true; index++ {
			if _, ok := r.Form["product.id."+strconv.Itoa(index)]; !ok {
				break
			}
			productForm := newInvoiceProductForm(index, form.company, form.locale, taxOptions)
			if err := productForm.Parse(r); err != nil {
				return err
			}
			form.Products = append(form.Products, productForm)
		}
	}
	return nil
}

func (form *invoiceForm) Validate() bool {
	validator := newFormValidator()

	validator.CheckValidSelectOption(form.InvoiceStatus, gettext("Selected invoice status is not valid.", form.locale))
	validator.CheckValidSelectOption(form.Customer, gettext("Selected customer is not valid.", form.locale))
	if validator.CheckRequiredInput(form.Date, gettext("Invoice date can not be empty.", form.locale)) {
		validator.CheckValidDate(form.Date, gettext("Invoice date must be a valid date.", form.locale))
	}
	validator.CheckValidSelectOption(form.PaymentMethod, gettext("Selected payment method is not valid.", form.locale))

	allOK := validator.AllOK()
	for _, product := range form.Products {
		allOK = product.Validate() && allOK
	}
	return allOK
}

func (form *invoiceForm) Update() {
	products := form.Products
	form.Products = nil
	for n, product := range products {
		if product.Quantity.Val != "0" {
			if n != len(form.Products) {
				product.Reindex(len(form.Products))
			}
			form.Products = append(form.Products, product)
		}
	}
}

func (form *invoiceForm) AddProducts(ctx context.Context, conn *Conn, productsId []string) {
	form.mustAddProductsFromQuery(ctx, conn, "select '', product_id, name, description, to_price(price, decimal_digits), 1 as quantity, 0 as discount, array_remove(array_agg(tax_id), null) from product join company using (company_id) join currency using (currency_code) left join product_tax using (product_id) where product_id = any ($1) group by product_id, name, description, price, decimal_digits", productsId)
}

func (form *invoiceForm) mustAddProductsFromQuery(ctx context.Context, conn *Conn, sql string, args ...interface{}) {
	index := len(form.Products)
	taxOptions := mustGetTaxOptions(ctx, conn, form.company)
	rows := conn.MustQuery(ctx, sql, args...)
	defer rows.Close()
	for rows.Next() {
		product := newInvoiceProductForm(index, form.company, form.locale, taxOptions)
		if err := rows.Scan(product.InvoiceProductId, product.ProductId, product.Name, product.Description, product.Price, product.Quantity, product.Discount, product.Tax); err != nil {
			panic(err)
		}
		form.Products = append(form.Products, product)
		index++
	}
	if rows.Err() != nil {
		panic(rows.Err())
	}
}

func (form *invoiceForm) MustFillFromDatabase(ctx context.Context, conn *Conn, slug string) bool {
	var invoiceId int
	selectedInvoiceStatus := form.InvoiceStatus.Selected
	form.InvoiceStatus.Clear()
	selectedPaymentMethod := form.PaymentMethod.Selected
	form.PaymentMethod.Clear()
	if notFoundErrorOrPanic(conn.QueryRow(ctx, `
		select invoice_id
		     , invoice_status
		     , contact_id
		     , invoice_number
		     , invoice_date
		     , notes
		     , payment_method_id
		     , string_agg(tag.name, ',')
		from invoice
		left join invoice_tag using (invoice_id)
		left join tag using(tag_id) where slug = $1
		group by invoice_id
		       , contact_id
		       , invoice_number
		       , invoice_date
		       , notes
		       , payment_method_id
	`, slug).Scan(&invoiceId, form.InvoiceStatus, form.Customer, form.Number, form.Date, form.Notes, form.PaymentMethod, form.Tags)) {
		form.PaymentMethod.Selected = selectedPaymentMethod
		form.InvoiceStatus.Selected = selectedInvoiceStatus
		return false
	}
	form.Products = []*invoiceProductForm{}
	form.mustAddProductsFromQuery(ctx, conn, "select invoice_product_id::text, product_id, name, description, to_price(price, $2), quantity, (discount_rate * 100)::integer, array_remove(array_agg(tax_id), null) from invoice_product left join invoice_product_tax using (invoice_product_id) where invoice_id = $1 group by invoice_product_id, product_id, name, description, discount_rate, price, quantity", invoiceId, form.company.DecimalDigits)
	return true
}

func mustGetTaxOptions(ctx context.Context, conn *Conn, company *Company) []*SelectOption {
	return MustGetGroupedOptions(ctx, conn, "select tax_id::text, tax.name, tax_class.name from tax join tax_class using (tax_class_id) where tax.company_id = $1 order by tax_class.name, tax.name", company.Id)
}

type invoiceProductForm struct {
	locale           *Locale
	company          *Company
	InvoiceProductId *InputField
	ProductId        *InputField
	Name             *InputField
	Description      *InputField
	Price            *InputField
	Quantity         *InputField
	Discount         *InputField
	Tax              *SelectField
}

func newInvoiceProductForm(index int, company *Company, locale *Locale, taxOptions []*SelectOption) *invoiceProductForm {
	form := &invoiceProductForm{
		locale:  locale,
		company: company,
		InvoiceProductId: &InputField{
			Label:    pgettext("input", "Id", locale),
			Type:     "hidden",
			Required: true,
		},
		ProductId: &InputField{
			Label:    pgettext("input", "Id", locale),
			Type:     "hidden",
			Required: true,
		},
		Name: &InputField{
			Label:    pgettext("input", "Name", locale),
			Type:     "text",
			Required: true,
		},
		Description: &InputField{
			Label: pgettext("input", "Description", locale),
			Type:  "textarea",
		},
		Price: &InputField{
			Label:    pgettext("input", "Price", locale),
			Type:     "number",
			Required: true,
			Attributes: []template.HTMLAttr{
				`min="0"`,
				template.HTMLAttr(fmt.Sprintf(`step="%v"`, company.MinCents())),
			},
		},
		Quantity: &InputField{
			Label:    pgettext("input", "Quantity", locale),
			Type:     "number",
			Required: true,
			Attributes: []template.HTMLAttr{
				`min="0"`,
			},
		},
		Discount: &InputField{
			Label:    pgettext("input", "Discount (%)", locale),
			Type:     "number",
			Required: true,
			Attributes: []template.HTMLAttr{
				`min="0"`,
				`max="100"`,
			},
		},
		Tax: &SelectField{
			Label:    pgettext("input", "Taxes", locale),
			Multiple: true,
			Options:  taxOptions,
		},
	}
	form.Reindex(index)
	return form
}

func (form *invoiceProductForm) Reindex(index int) {
	suffix := "." + strconv.Itoa(index)
	form.InvoiceProductId.Name = "product.invoice_product_id" + suffix
	form.ProductId.Name = "product.id" + suffix
	form.Name.Name = "product.name" + suffix
	form.Description.Name = "product.description" + suffix
	form.Price.Name = "product.price" + suffix
	form.Quantity.Name = "product.quantity" + suffix
	form.Discount.Name = "product.discount" + suffix
	form.Tax.Name = "product.tax" + suffix
}

func (form *invoiceProductForm) Parse(r *http.Request) error {
	if err := r.ParseForm(); err != nil {
		return err
	}
	form.InvoiceProductId.FillValue(r)
	form.ProductId.FillValue(r)
	form.Name.FillValue(r)
	form.Description.FillValue(r)
	form.Price.FillValue(r)
	form.Quantity.FillValue(r)
	form.Discount.FillValue(r)
	form.Tax.FillValue(r)
	return nil
}

func (form *invoiceProductForm) Validate() bool {
	validator := newFormValidator()
	validator.CheckRequiredInput(form.ProductId, gettext("Product ID can not be empty.", form.locale))
	validator.CheckRequiredInput(form.Name, gettext("Name can not be empty.", form.locale))
	if validator.CheckRequiredInput(form.Price, gettext("Price can not be empty.", form.locale)) {
		validator.CheckValidDecimal(form.Price, form.company.MinCents(), math.MaxFloat64, gettext("Price must be a number greater than zero.", form.locale))
	}
	if validator.CheckRequiredInput(form.Quantity, gettext("Quantity can not be empty.", form.locale)) {
		validator.CheckValidInteger(form.Quantity, 1, math.MaxInt32, gettext("Quantity must be a number greater than zero.", form.locale))
	}
	if validator.CheckRequiredInput(form.Discount, gettext("Discount can not be empty.", form.locale)) {
		validator.CheckValidInteger(form.Discount, 0, 100, gettext("Discount must be a percentage between 0 and 100.", form.locale))
	}
	validator.CheckValidSelectOption(form.Tax, gettext("Selected tax is not valid.", form.locale))
	validator.CheckAtMostOneOfEachGroup(form.Tax, gettext("You can only select a tax of each class.", form.locale))
	return validator.AllOK()
}

func HandleUpdateInvoice(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
	locale := getLocale(r)
	conn := getConn(r)
	company := mustGetCompany(r)
	form := newInvoiceForm(r.Context(), conn, locale, company)
	if err := form.Parse(r); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if err := verifyCsrfTokenValid(r); err != nil {
		http.Error(w, err.Error(), http.StatusForbidden)
		return
	}
	if r.FormValue("quick") == "status" {
		slug := conn.MustGetText(r.Context(), "", "update invoice set invoice_status = $1 where slug = $2 returning slug", form.InvoiceStatus, params[0].Value)
		if slug == "" {
			http.NotFound(w, r)
		}
		http.Redirect(w, r, companyURI(mustGetCompany(r), "/invoices"), http.StatusSeeOther)
	} else {
		slug := params[0].Value
		if !form.Validate() {
			w.WriteHeader(http.StatusUnprocessableEntity)
			mustRenderEditInvoiceForm(w, r, slug, form)
			return
		}
		slug = conn.MustGetText(r.Context(), "", "select edit_invoice($1, $2, $3, $4, $5, $6, $7)", slug, form.InvoiceStatus, form.Customer, form.Notes, form.PaymentMethod, form.Tags, EditedInvoiceProductArray(form.Products))
		if slug == "" {
			http.NotFound(w, r)
			return
		}
		http.Redirect(w, r, companyURI(company, "/invoices/"+slug), http.StatusSeeOther)
	}
}

func ServeEditInvoice(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
	conn := getConn(r)
	company := mustGetCompany(r)
	slug := params[0].Value
	locale := getLocale(r)
	form := newInvoiceForm(r.Context(), conn, locale, company)
	if !form.MustFillFromDatabase(r.Context(), conn, slug) {
		http.NotFound(w, r)
		return
	}
	w.WriteHeader(http.StatusOK)
	mustRenderEditInvoiceForm(w, r, slug, form)
}

type editInvoicePage struct {
	*newInvoicePage
	Slug   string
	Number string
}

func newEditInvoicePage(slug string, form *invoiceForm, r *http.Request) *editInvoicePage {
	return &editInvoicePage{
		newNewInvoicePage(form, r),
		slug,
		form.Number.String(),
	}
}

func mustRenderEditInvoiceForm(w http.ResponseWriter, r *http.Request, slug string, form *invoiceForm) {
	page := newEditInvoicePage(slug, form, r)
	mustRenderAppTemplate(w, r, "invoices/edit.gohtml", page)
}

func HandleEditInvoiceAction(w http.ResponseWriter, r *http.Request, params httprouter.Params) {
	slug := params[0].Value
	actionUri := fmt.Sprintf("/invoices/%s/edit", slug)
	handleInvoiceAction(w, r, actionUri, func(w http.ResponseWriter, r *http.Request, form *invoiceForm) {
		mustRenderEditInvoiceForm(w, r, slug, form)
	})
}

type renderFormFunc func(w http.ResponseWriter, r *http.Request, form *invoiceForm)

func handleInvoiceAction(w http.ResponseWriter, r *http.Request, action string, renderForm renderFormFunc) {
	locale := getLocale(r)
	conn := getConn(r)
	company := mustGetCompany(r)
	form := newInvoiceForm(r.Context(), conn, locale, company)
	if err := form.Parse(r); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if err := verifyCsrfTokenValid(r); err != nil {
		http.Error(w, err.Error(), http.StatusForbidden)
		return
	}
	switch r.Form.Get("action") {
	case "update":
		form.Update()
		w.WriteHeader(http.StatusOK)
		renderForm(w, r, form)
	case "select-products":
		w.WriteHeader(http.StatusOK)
		mustRenderNewInvoiceProductsForm(w, r, action, form)
	case "add-products":
		form.AddProducts(r.Context(), conn, r.Form["id"])
		w.WriteHeader(http.StatusOK)
		renderForm(w, r, form)
	default:
		http.Error(w, gettext("Invalid action", locale), http.StatusBadRequest)
	}
}