Add Amazon support (#3)

This commit introduces the Amazon support with calls to the Product Advertising
API (PA API). For now, I was only able to use the "www.amazon.fr" marketplace.
I will add more marketplaces when my Amazon Associate accounts will be
validated.

Signed-off-by: Julien Riou <julien@riou.xyz>

parser_amazon.go

@@ -0,0 +1,158 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+	paapi5 "github.com/spiegel-im-spiegel/pa-api"
+	"github.com/spiegel-im-spiegel/pa-api/entity"
+	"github.com/spiegel-im-spiegel/pa-api/query"
+)
+
+// NewAmazonServer creates an Amazon Server function based on the Marketplace.
+// The paapi5 marketplaceEnum is not exported, so this type cannot be used in simple map.
+func NewAmazonServer(marketplace string) *paapi5.Server {
+	switch marketplace {
+	case "www.amazon.fr":
+		return paapi5.New(paapi5.WithMarketplace(paapi5.LocaleFrance))
+	case "www.amazon.com":
+		return paapi5.New(paapi5.WithMarketplace(paapi5.LocaleUnitedStates))
+	default:
+		return paapi5.New() // default Marketplace
+	}
+}
+
+// Map of messages to detect availability
+var availabilityMessages = []string{"En stock."}
+
+// AmazonParser structure to handle Amazon parsing logic
+type AmazonParser struct {
+	client          paapi5.Client
+	searches        []string
+	includeRegex    *regexp.Regexp
+	excludeRegex    *regexp.Regexp
+	amazonFulfilled bool
+	amazonMerchant  bool
+	affiliateLinks  bool
+}
+
+// NewAmazonParser to create a new AmazonParser instance
+func NewAmazonParser(marketplace string, partnerTag string, accessKey string, secretKey string, searches []string, includeRegex string, excludeRegex string, amazonFulfilled bool, amazonMerchant bool, affiliateLinks bool) (*AmazonParser, error) {
+	var err error
+	var includeRegexCompiled, excludeRegexCompiled *regexp.Regexp
+
+	log.Debugf("compiling include name regex")
+	if includeRegex != "" {
+		includeRegexCompiled, err = regexp.Compile(includeRegex)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	log.Debugf("compiling exclude name regex")
+	if excludeRegex != "" {
+		excludeRegexCompiled, err = regexp.Compile(excludeRegex)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return &AmazonParser{
+		client:          NewAmazonServer(marketplace).CreateClient(partnerTag, accessKey, secretKey),
+		searches:        searches,
+		includeRegex:    includeRegexCompiled,
+		excludeRegex:    excludeRegexCompiled,
+		amazonFulfilled: amazonFulfilled,
+		amazonMerchant:  amazonMerchant,
+		affiliateLinks:  affiliateLinks,
+	}, nil
+}
+
+// Parse Amazon API to return list of products
+// Implements Parser interface
+func (p *AmazonParser) Parse() ([]*Product, error) {
+
+	var products []*Product
+
+	for _, search := range p.searches {
+
+		log.Debugf("searching for '%s' on %s", search, p.client.Marketplace())
+
+		// create search request on API
+		q := query.NewSearchItems(
+			p.client.Marketplace(),
+			p.client.PartnerTag(),
+			p.client.PartnerType(),
+		).Search(query.Keywords, search).EnableItemInfo().EnableOffers()
+		body, err := p.client.Request(q)
+		if err != nil {
+			return nil, err
+		}
+
+		// decode response
+		res, err := entity.DecodeResponse(body)
+		if err != nil {
+			return nil, err
+		}
+
+		// decode products
+		for _, item := range res.SearchResult.Items {
+
+			product := &Product{}
+			if !p.affiliateLinks {
+				product.URL = fmt.Sprintf("https://%s/dp/%s", p.client.Marketplace(), item.ASIN)
+
+			} else {
+				product.URL = item.DetailPageURL // includes partner tag
+			}
+			product.Name = item.ItemInfo.Title.DisplayValue
+
+			if item.Offers != nil && *item.Offers.Listings != nil {
+				for _, offer := range *item.Offers.Listings {
+					// detect if product is packaged by Amazon
+					if p.amazonFulfilled && !offer.DeliveryInfo.IsAmazonFulfilled {
+						log.Debugf("excluding offer by '%s' for product '%s' because not fulfilled by Amazon", offer.MerchantInfo.Name, product.Name)
+						continue
+					}
+
+					// detect if product is sold by Amazon
+					if p.amazonMerchant && !strings.HasPrefix(offer.MerchantInfo.Name, "Amazon") {
+						log.Debugf("excluding offer by '%s' for product '%s' because not sold by Amazon", offer.MerchantInfo.Name, product.Name)
+						continue
+					}
+
+					// detect price
+					product.Price = offer.Price.Amount
+					product.PriceCurrency = offer.Price.Currency
+
+					// detect availability
+					if ContainsString(availabilityMessages, offer.Availability.Message) {
+						product.Available = true
+						break
+					}
+				}
+			}
+
+			products = append(products, product)
+		}
+	}
+
+	// apply filters
+	products = filterInclusive(p.includeRegex, products)
+	products = filterExclusive(p.excludeRegex, products)
+
+	return products, nil
+}
+
+// String to print AmazonParser
+// Implements the Parser interface
+func (p *AmazonParser) String() string {
+	return fmt.Sprintf("AmazonParser<%s@%s>", p.client.PartnerTag(), p.client.Marketplace())
+}
+
+// ShopName returns shop name from Amazon Marketplace
+func (p *AmazonParser) ShopName() string {
+	return strings.ReplaceAll(p.client.Marketplace(), "www.", "")
+}