From 289bd4db13129c1e1ffd1660929da1aba931ccaf Mon Sep 17 00:00:00 2001
From: Ahmet Alp Balkan <ahmetb@google.com>
Date: Tue, 26 Jun 2018 12:54:36 -0700
Subject: [PATCH] frontend: view cart, add to cart, empty cart

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>
---
 src/checkoutservice/money.go        |  6 ++
 src/frontend/handlers.go            | 95 ++++++++++++++++++++++++++++-
 src/frontend/main.go                |  7 ++-
 src/frontend/money.go               | 50 +++++++++++++++
 src/frontend/rpc.go                 | 15 +++++
 src/frontend/templates/cart.html    | 53 ++++++++++++++++
 src/frontend/templates/header.html  |  2 +-
 src/frontend/templates/product.html |  2 +-
 8 files changed, 224 insertions(+), 6 deletions(-)
 create mode 100644 src/frontend/money.go
 create mode 100644 src/frontend/templates/cart.html

diff --git a/src/checkoutservice/money.go b/src/checkoutservice/money.go
index 4777d1d..584b72e 100644
--- a/src/checkoutservice/money.go
+++ b/src/checkoutservice/money.go
@@ -9,7 +9,13 @@ import (
 func sum(m1, m2 pb.MoneyAmount) pb.MoneyAmount {
 	f1, f2 := float64(m1.Fractional), float64(m2.Fractional)
 	lg1 := math.Max(1, math.Ceil(math.Log10(f1)))
+	if f1 == math.Pow(10, lg1) {
+		lg1++
+	}
 	lg2 := math.Max(1, math.Ceil(math.Log10(f2)))
+	if f2 == math.Pow(10, lg2) {
+		lg2++
+	}
 	lgMax := math.Max(lg1, lg2)
 
 	dSum := m1.Decimal + m2.Decimal
diff --git a/src/frontend/handlers.go b/src/frontend/handlers.go
index e0893f8..2170c1a 100644
--- a/src/frontend/handlers.go
+++ b/src/frontend/handlers.go
@@ -6,6 +6,7 @@ import (
 	"html/template"
 	"log"
 	"net/http"
+	"strconv"
 	"time"
 
 	"github.com/google/uuid"
@@ -43,7 +44,7 @@ func ensureSessionID(next http.HandlerFunc) http.HandlerFunc {
 }
 
 func (fe *frontendServer) homeHandler(w http.ResponseWriter, r *http.Request) {
-	log.Printf("[home] session_id=%+v", sessionID(r))
+	log.Printf("[home] session_id=%+v currency=%s", sessionID(r), currentCurrency(r))
 	currencies, err := fe.getCurrencies(r.Context())
 	if err != nil {
 		http.Error(w, fmt.Sprintf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
@@ -100,12 +101,16 @@ func (fe *frontendServer) productHandler(w http.ResponseWriter, r *http.Request)
 		http.Error(w, fmt.Sprintf("could not retrieve product: %+v", err), http.StatusInternalServerError)
 		return
 	}
-
 	currencies, err := fe.getCurrencies(r.Context())
 	if err != nil {
 		http.Error(w, fmt.Sprintf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
 		return
 	}
+	cart, err := fe.getCart(r.Context(), sessionID(r))
+	if err != nil {
+		http.Error(w, fmt.Sprintf("could not retrieve cart: %+v", err), http.StatusInternalServerError)
+		return
+	}
 
 	price, err := fe.convertCurrency(r.Context(), &pb.Money{
 		Amount:       p.GetPriceUsd(),
@@ -125,6 +130,92 @@ func (fe *frontendServer) productHandler(w http.ResponseWriter, r *http.Request)
 		"currencies":    currencies,
 		"product":       product,
 		"session_id":    sessionID(r),
+		"cart_size":     len(cart),
+	}); err != nil {
+		log.Println(err)
+	}
+}
+
+func (fe *frontendServer) addToCartHandler(w http.ResponseWriter, r *http.Request) {
+	quantity, _ := strconv.ParseUint(r.FormValue("quantity"), 10, 32)
+	productID := r.FormValue("product_id")
+	if productID == "" || quantity == 0 {
+		http.Error(w, "invalid form input", http.StatusBadRequest)
+		return
+	}
+	log.Printf("[addToCart] product_id=%s qty=%d session_id=%+v", productID, quantity, sessionID(r))
+
+	p, err := fe.getProduct(r.Context(), productID)
+	if err != nil {
+		http.Error(w, fmt.Sprintf("could not retrieve product: %+v", err), http.StatusInternalServerError)
+		return
+	}
+
+	if err := fe.insertCart(r.Context(), sessionID(r), p.GetId(), int32(quantity)); err != nil {
+		http.Error(w, fmt.Sprintf("failed to add to cart: %+v", err), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("location", "/cart")
+	w.WriteHeader(http.StatusFound)
+}
+
+func (fe *frontendServer) emptyCartHandler(w http.ResponseWriter, r *http.Request) {
+	log.Printf("[emptyCart] session_id=%+v", sessionID(r))
+
+	if err := fe.emptyCart(r.Context(), sessionID(r)); err != nil {
+		http.Error(w, fmt.Sprintf("failed to empty cart: %+v", err), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("location", "/")
+	w.WriteHeader(http.StatusFound)
+}
+
+func (fe *frontendServer) viewCartHandler(w http.ResponseWriter, r *http.Request) {
+	log.Printf("[viewCart] session_id=%+v", sessionID(r))
+	currencies, err := fe.getCurrencies(r.Context())
+	if err != nil {
+		http.Error(w, fmt.Sprintf("could not retrieve currencies: %+v", err), http.StatusInternalServerError)
+		return
+	}
+	cart, err := fe.getCart(r.Context(), sessionID(r))
+	if err != nil {
+		http.Error(w, fmt.Sprintf("could not retrieve cart: %+v", err), http.StatusInternalServerError)
+		return
+	}
+
+	type cartItemView struct {
+		Item     *pb.Product
+		Quantity int32
+		Price    *pb.Money
+	}
+	items := make([]cartItemView, len(cart))
+	for i, item := range cart {
+		p, err := fe.getProduct(r.Context(), item.GetProductId())
+		if err != nil {
+			http.Error(w, fmt.Sprintf("could not retrieve product #%s: %+v", item.GetProductId(), err), http.StatusInternalServerError)
+			return
+		}
+		price, err := fe.convertCurrency(r.Context(), &pb.Money{
+			Amount:       p.GetPriceUsd(),
+			CurrencyCode: defaultCurrency}, currentCurrency(r))
+		if err != nil {
+			http.Error(w, fmt.Sprintf("could not convert currency for product #%s: %+v", item.GetProductId(), err), http.StatusInternalServerError)
+			return
+		}
+
+		multPrice := multMoney(*price.GetAmount(), uint32(item.GetQuantity()))
+		items[i] = cartItemView{
+			Item:     p,
+			Quantity: item.GetQuantity(),
+			Price:    &pb.Money{Amount: &multPrice, CurrencyCode: price.GetCurrencyCode()}}
+	}
+
+	if err := templates.ExecuteTemplate(w, "cart", map[string]interface{}{
+		"user_currency": currentCurrency(r),
+		"currencies":    currencies,
+		"session_id":    sessionID(r),
+		"cart_size":     len(cart),
+		"items":         items,
 	}); err != nil {
 		log.Println(err)
 	}
diff --git a/src/frontend/main.go b/src/frontend/main.go
index 6b3584d..cda4a22 100644
--- a/src/frontend/main.go
+++ b/src/frontend/main.go
@@ -69,9 +69,12 @@ func main() {
 	r := mux.NewRouter()
 	r.HandleFunc("/", ensureSessionID(svc.homeHandler)).Methods(http.MethodGet, http.MethodHead)
 	r.HandleFunc("/product/{id}", ensureSessionID(svc.productHandler)).Methods(http.MethodGet, http.MethodHead)
-	r.PathPrefix("/static/").Handler(http.StripPrefix("/static/", http.FileServer(http.Dir("./static/"))))
-	r.HandleFunc("/logout", svc.logoutHandler).Methods(http.MethodGet)
+	r.HandleFunc("/cart", ensureSessionID(svc.viewCartHandler)).Methods(http.MethodGet, http.MethodHead)
+	r.HandleFunc("/cart", ensureSessionID(svc.addToCartHandler)).Methods(http.MethodPost)
+	r.HandleFunc("/cart/empty", ensureSessionID(svc.emptyCartHandler)).Methods(http.MethodPost)
 	r.HandleFunc("/setCurrency", ensureSessionID(svc.setCurrencyHandler)).Methods(http.MethodPost)
+	r.HandleFunc("/logout", svc.logoutHandler).Methods(http.MethodGet)
+	r.PathPrefix("/static/").Handler(http.StripPrefix("/static/", http.FileServer(http.Dir("./static/"))))
 	log.Printf("starting server on :" + srvPort)
 	log.Fatal(http.ListenAndServe("localhost:"+srvPort, r))
 }
diff --git a/src/frontend/money.go b/src/frontend/money.go
new file mode 100644
index 0000000..a97e1d3
--- /dev/null
+++ b/src/frontend/money.go
@@ -0,0 +1,50 @@
+package main
+
+import (
+	"math"
+
+	pb "frontend/genproto"
+)
+
+// TODO(ahmetb): any logic below is flawed because I just realized we have no
+// way of representing amounts like 17.07 because Fractional cannot store 07.
+func multMoney(m pb.MoneyAmount, n uint32) pb.MoneyAmount {
+	out := m
+	for n > 1 {
+		out = sum(out, m)
+		n--
+	}
+	return out
+}
+
+func sum(m1, m2 pb.MoneyAmount) pb.MoneyAmount {
+	// TODO(ahmetb) this is copied from ./checkoutservice/money.go, find a
+	// better mult function.
+	f1, f2 := float64(m1.Fractional), float64(m2.Fractional)
+	lg1 := math.Max(1, math.Ceil(math.Log10(f1)))
+	if f1 == math.Pow(10, lg1) {
+		lg1++
+	}
+	lg2 := math.Max(1, math.Ceil(math.Log10(f2)))
+	if f2 == math.Pow(10, lg2) {
+		lg2++
+	}
+	lgMax := math.Max(lg1, lg2)
+
+	dSum := m1.Decimal + m2.Decimal
+	o1 := f1 * math.Pow(10, lgMax-lg1)
+	o2 := f2 * math.Pow(10, lgMax-lg2)
+	fSum := o1 + o2
+	if fSum >= math.Pow(10, lgMax) {
+		fSum -= math.Pow(10, lgMax)
+		dSum++
+	}
+
+	for int(fSum)%10 == 0 && fSum != 0 {
+		fSum = float64(int(fSum) / 10)
+	}
+
+	return pb.MoneyAmount{
+		Decimal:    dSum,
+		Fractional: uint32(fSum)}
+}
diff --git a/src/frontend/rpc.go b/src/frontend/rpc.go
index 54c32bf..f295506 100644
--- a/src/frontend/rpc.go
+++ b/src/frontend/rpc.go
@@ -50,6 +50,21 @@ func (fe *frontendServer) getCart(ctx context.Context, userID string) ([]*pb.Car
 	return resp.GetItems(), err
 }
 
+func (fe *frontendServer) emptyCart(ctx context.Context, userID string) error {
+	_, err := pb.NewCartServiceClient(fe.cartSvcConn).EmptyCart(ctx, &pb.EmptyCartRequest{UserId: userID})
+	return err
+}
+
+func (fe *frontendServer) insertCart(ctx context.Context, userID, productID string, quantity int32) error {
+	_, err := pb.NewCartServiceClient(fe.cartSvcConn).AddItem(ctx, &pb.AddItemRequest{
+		UserId: userID,
+		Item: &pb.CartItem{
+			ProductId: productID,
+			Quantity:  quantity},
+	})
+	return err
+}
+
 func (fe *frontendServer) convertCurrency(ctx context.Context, money *pb.Money, currency string) (*pb.Money, error) {
 	if avoidNoopCurrencyConversionRPC && money.GetCurrencyCode() == currency {
 		return money, nil
diff --git a/src/frontend/templates/cart.html b/src/frontend/templates/cart.html
new file mode 100644
index 0000000..f20057c
--- /dev/null
+++ b/src/frontend/templates/cart.html
@@ -0,0 +1,53 @@
+{{ define "cart" }}
+    {{ template "header" . }}
+
+    <main role="main">
+        <div class="py-5">
+            <div class="container bg-light py-3 px-lg-5 py-lg-5">
+                <h1>Shopping Cart</h1>
+
+                {{ if eq (len $.items) 0 }}
+                <p>Your shopping cart is empty.</p>
+                <a class="btn btn-primary" href="/" role="button">Browse Products</a>
+                {{ end }}
+
+                {{ range $.items }}
+                <div class="row pt-2 mb-2">
+                    <div class="col text-right">
+                            <img class="img-fluid" style="width: auto; max-height: 60px;"
+                                src="{{.Item.Picture}}" />
+                    </div>
+                    <div class="col align-middle">
+                        <strong>{{.Item.Name}}</strong><br/>
+                        <small class="text-muted">SKU: #{{.Item.Id}}</small>
+                    </div>
+                    <div class="col text-left">
+                        Qty: {{.Quantity}}<br/>
+                        <strong>
+                            {{.Price.CurrencyCode}}
+                            {{.Price.Amount.Decimal}}.
+                            {{- .Price.Amount.Fractional}}{{- if lt .Price.Amount.Fractional 10}}0{{end}}
+                        </strong>
+                    </div>
+                </div>
+                {{ end }}
+
+                {{ if $.items }}
+                <div class="row mt-5">
+                    <div class="col-8 offset-2">
+                        <div class="d-flex justify-content-between align-items-center">
+                                <form method="POST" action="/cart/empty">
+                                    <button class="btn btn-secondary" type="submit">Empty Cart</button>
+                                </form>     
+                                <a class="btn btn-primary" href="/checkout" role="button">Proceed to Checkout</a>
+                        </div>
+                    </div>
+                </div>
+                {{ end }}
+
+            </div>
+        </div>
+    </main>
+
+    {{ template "footer" . }}
+{{ end }}
diff --git a/src/frontend/templates/header.html b/src/frontend/templates/header.html
index 51ba64b..76bb700 100644
--- a/src/frontend/templates/header.html
+++ b/src/frontend/templates/header.html
@@ -23,7 +23,7 @@
                         <option value="{{.}}" {{if eq . $.user_currency}}selected="selected"{{end}}>{{.}}</option>
                     {{end}}
                     </select>
-                    <a class="btn btn-primary ml-1" href="/cart" role="button">View Cart ({{$.cart_size}})</a>
+                    <a class="btn btn-primary ml-2" href="/cart" role="button">View Cart ({{$.cart_size}})</a>
                 </form>
             </div>
         </div>
diff --git a/src/frontend/templates/product.html b/src/frontend/templates/product.html
index 558e2a2..a4dae1d 100644
--- a/src/frontend/templates/product.html
+++ b/src/frontend/templates/product.html
@@ -24,7 +24,7 @@
                             </p>
                             <hr/>
 
-                            <form method="POST" action="/addToCart" class="form-inline text-muted">
+                            <form method="POST" action="/cart" class="form-inline text-muted">
                                 <input type="hidden" name="product_id" value="{{$.product.Item.Id}}"/>
                                 <div class="input-group">
                                     <div class="input-group-prepend">