Add mtgcard service

This service makes API calls to https://scryfall.com/docs/api/ and returns
information about "Magic: the Gathering" cards.

It provides a command:
!mtcard card name

And it provides expansion for:
[[card name]]

Both will return an html message with card information, links, and price.

I'm curious if you folks see it relevant to be added to go-neb or not.

If you want to see it live, hop to #magicthegathering:matrix.org (currently
running non-dedicated).

README.md

@@ -146,6 +146,7 @@ List of Services:
  - [JIRA](https://matrix-org.github.io/go-neb/pkg/github.com/matrix-org/go-neb/services/jira/) - Integration with JIRA
  - [RSS Bot](https://matrix-org.github.io/go-neb/pkg/github.com/matrix-org/go-neb/services/rssbot/) - An Atom/RSS feed reader
  - [Travis CI](https://matrix-org.github.io/go-neb/pkg/github.com/matrix-org/go-neb/services/travisci/) - Receive build notifications from Travis CI
+ - [Mtgcard](https://matrix-org.github.io/go-neb/pkg/github.com/matrix-org/go-neb/services/mtgcard/) - Query information about Magic: the Gathering card game
 
 
 ## Configuring Realms

src/github.com/matrix-org/go-neb/goneb.go

@@ -27,6 +27,7 @@ import (
 	_ "github.com/matrix-org/go-neb/services/guggy"
 	_ "github.com/matrix-org/go-neb/services/imgur"
 	_ "github.com/matrix-org/go-neb/services/jira"
+	_ "github.com/matrix-org/go-neb/services/mtgcard"
 	_ "github.com/matrix-org/go-neb/services/rssbot"
 	_ "github.com/matrix-org/go-neb/services/slackapi"
 	_ "github.com/matrix-org/go-neb/services/travisci"

src/github.com/matrix-org/go-neb/services/mtgcard/mtgcard.go

@@ -0,0 +1,168 @@
+// Package mtgcard implements a Service which adds !commands and mentions for scryfall api.
+package mtgcard
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"html"
+	"net/http"
+	"net/url"
+	"regexp"
+	"strings"
+
+	log "github.com/Sirupsen/logrus"
+	"github.com/matrix-org/go-neb/types"
+	"github.com/matrix-org/gomatrix"
+)
+
+// ServiceType of the Mtgcard service.
+const ServiceType = "mtgcard"
+
+// Matches [[ then word separated with spaces then ]]. E.g "[[card Name]]
+var cardRegex = regexp.MustCompile(`\[\[\w+(\s*\w+)*\]\]`)
+
+type scryfallSearch struct {
+	Name         string `json:"name"`
+	ScryfallURI  string `json:"scryfall_uri"`
+	Euro         string `json:"eur"`
+	PurchaseURIs struct {
+		Cardmarket string `json:cardmarket`
+	} `json:purchase_uris`
+	ImageURIs struct {
+		Normal string `json:"normal"`
+		Small  string `json:"small"`
+	} `json:"image_uris"`
+}
+
+// Service contains the Config fields for the Mtgcard Service.
+type Service struct {
+	types.DefaultService
+}
+
+// Commands supported:
+//   !mtgcard some search query without quotes
+// Responds with card information into the same room as the command.
+func (s *Service) Commands(client *gomatrix.Client) []types.Command {
+	return []types.Command{
+		types.Command{
+			Path: []string{"mtgcard"},
+			Command: func(roomID, userID string, args []string) (interface{}, error) {
+				return s.cmdScryfall(client, roomID, userID, args)
+			},
+		},
+	}
+}
+
+// Expansions expands card mentions represented as:
+//    [[ possible name of card ]]
+// and responds with card information into the same room as the expansion
+func (s *Service) Expansions(cli *gomatrix.Client) []types.Expansion {
+	return []types.Expansion{
+		types.Expansion{
+			Regexp: cardRegex,
+			Expand: func(roomID, userID string, cardMentions []string) interface{} {
+				return s.expandCard(roomID, userID, cardMentions)
+			},
+		},
+	}
+}
+
+// cmdScryfall processes a command by calling the query and returning a message with card info
+func (s *Service) cmdScryfall(client *gomatrix.Client, roomID, userID string, args []string) (interface{}, error) {
+	// only 1 arg which is the text to search for.
+	query := strings.Join(args, " ")
+
+	scryfallResult, err := s.searchScryfall(query)
+	if err != nil {
+		return nil, err
+	}
+	if scryfallResult != nil {
+		return createMessage(scryfallResult), err
+	}
+	return nil, err
+
+}
+
+// expandCard processes an expansion by calling the query and returning a message with card info
+func (s *Service) expandCard(roomID, userID string, cardMentions []string) interface{} {
+	// cardMentions => ["[[magic card]]"]
+
+	logger := log.WithField("cardMentions", cardMentions)
+	logger.WithFields(log.Fields{
+		"room_id": roomID,
+		"user_id": userID,
+	}).Print("Expanding card mention")
+
+	cardMentions[0] = strings.TrimPrefix(cardMentions[0], "[[")
+	cardMentions[0] = strings.TrimSuffix(cardMentions[0], "]]")
+	scryfallResult, err := s.searchScryfall(cardMentions[0])
+	if err != nil {
+		return err
+	}
+	if scryfallResult != nil {
+		return createMessage(scryfallResult)
+	}
+	return nil
+}
+
+// createMessage returns a nicely formatted matrix.HTMLMessage from a query result
+func createMessage(result *scryfallSearch) gomatrix.HTMLMessage {
+
+	var htmlBuffer bytes.Buffer
+	var plainBuffer bytes.Buffer
+	message := fmt.Sprintf(
+		"<ul><li><a href=%s>%s</a>\t<a href=%s>(SF)</a>\t<a href=%s>(%s&euro;)</a></li></ul>",
+		result.ImageURIs.Normal,
+		html.EscapeString(result.Name),
+		result.ScryfallURI,
+		result.PurchaseURIs.Cardmarket,
+		result.Euro,
+	)
+	htmlBuffer.WriteString(message)
+	plainBuffer.WriteString(fmt.Sprintf("$s, $s, $s", result.Name, result.ScryfallURI, result.Euro))
+
+	return gomatrix.HTMLMessage{
+		Body:          plainBuffer.String(),
+		MsgType:       "m.notice",
+		Format:        "org.matrix.custom.html",
+		FormattedBody: htmlBuffer.String(),
+	}
+}
+
+// searchScryfall queries Scryfall API for card info
+func (s *Service) searchScryfall(query string) (*scryfallSearch, error) {
+	log.Info("Searching scryfall for ", query)
+	u, err := url.Parse("https://api.scryfall.com/cards/named")
+	if err != nil {
+		return nil, err
+	}
+	q := u.Query()
+	q.Set("fuzzy", query)
+	u.RawQuery = q.Encode()
+	res, err := http.Get(u.String())
+	if res != nil {
+		defer res.Body.Close()
+	}
+	if err != nil {
+		log.Error("Problem searching scryfall: ", err)
+		return nil, err
+	}
+	if res.StatusCode == http.StatusNotFound {
+		return nil, nil
+	}
+	var search scryfallSearch
+	if err := json.NewDecoder(res.Body).Decode(&search); err != nil {
+		return nil, err
+	}
+	log.Info("Search scryfall returned ", search)
+	return &search, nil
+}
+
+func init() {
+	types.RegisterService(func(serviceID, serviceUserID, webhookEndpointURL string) types.Service {
+		return &Service{
+			DefaultService: types.NewDefaultService(serviceID, serviceUserID, ServiceType),
+		}
+	})
+}