Add command to list available assignments

* lists available exercises for a given language and explains how to fetch them
* returns error for unknown languages
* Resolves issue #89
* Fetches the track for a specific language using the /tracks/:language endopoint on the XAPI.

Author: lcowell

api/api.go

@@ -3,8 +3,10 @@ package api
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
+	"strings"
 
 	"github.com/exercism/cli/config"
 )
@@ -13,6 +15,8 @@ var (
 	// UserAgent lets the API know where the call is being made from.
 	// It's set from main() so that we have access to the version.
 	UserAgent string
+
+	UnknownLanguageError = errors.New("the language is unknown")
 )
 
 // PayloadError represents an error message from the API.
@@ -128,6 +132,40 @@ func Submit(url string, iter *Iteration) (*Submission, error) {
 	return ps.Submission, nil
 }
 
+// List available problems for a language
+func List(language, host string) ([]string, error) {
+	url := fmt.Sprintf("%s/tracks/%s", host, language)
+
+	req, err := http.NewRequest("GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("User-Agent", UserAgent)
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer res.Body.Close()
+	if res.StatusCode != http.StatusOK {
+		return nil, UnknownLanguageError
+	}
+
+	var payload struct {
+		Track Track
+	}
+	if err := json.NewDecoder(res.Body).Decode(&payload); err != nil {
+		return nil, err
+	}
+	problems := make([]string, len(payload.Track.Problems))
+	prefix := language + "/"
+
+	for n, p := range payload.Track.Problems {
+		problems[n] = strings.TrimPrefix(p, prefix)
+	}
+
+	return problems, nil
+}
+
 // Unsubmit deletes a submission.
 func Unsubmit(url string) error {
 	req, err := http.NewRequest("DELETE", url, nil)

api/api_test.go

@@ -0,0 +1,42 @@
+package api
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestListTrack(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// check that we correctly built the URI path
+		assert.Equal(t, "/tracks/clojure", r.RequestURI)
+
+		f, err := os.Open("../fixtures/tracks.json")
+		if err != nil {
+			t.Fatal(err)
+		}
+		io.Copy(w, f)
+		f.Close()
+	}))
+	defer ts.Close()
+
+	problems, err := List("clojure", ts.URL)
+	assert.NoError(t, err)
+
+	assert.Equal(t, len(problems), 34)
+	assert.Equal(t, problems[0], "bob")
+}
+
+func TestUnknownLanguage(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.NotFound(w, r)
+	}))
+	defer ts.Close()
+
+	_, err := List("rubbbby", ts.URL)
+	assert.Equal(t, err, UnknownLanguageError)
+}

cmd/list.go

@@ -0,0 +1,41 @@
+package cmd
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/codegangsta/cli"
+	"github.com/exercism/cli/api"
+	"github.com/exercism/cli/config"
+)
+
+const msgExplainFetch = "In order to fetch a specific assignment, call the fetch command with a specific assignment.\n\nexercism fetch ruby matrix"
+
+// List returns the full list of assignments for a given language
+func List(ctx *cli.Context) {
+	c, err := config.New(ctx.GlobalString("config"))
+	if err != nil {
+		log.Fatal(err)
+	}
+	args := ctx.Args()
+
+	if len(args) != 1 {
+		msg := "Usage: execism list LANGUAGE"
+		log.Fatal(msg)
+	}
+
+	language := args[0]
+
+	problems, err := api.List(language, c.XAPI)
+	if err != nil {
+		if err == api.UnknownLanguageError {
+			log.Fatalf("The requested language '%s' is unknown", language)
+		}
+		log.Fatal(err)
+	}
+
+	for _, p := range problems {
+		fmt.Printf("%s\n", p)
+	}
+	fmt.Printf("\n%s\n\n", msgExplainFetch)
+}

exercism/main.go

@@ -29,6 +29,7 @@ const (
 
 	descLongRestore = "Restore will pull the latest revisions of exercises that have already been submitted. It will *not* overwrite existing files. If you have made changes to a file and have not submitted it, and you're trying to restore the last submitted version, first move that file out of the way, then call restore."
 	descDownload    = "Downloads and saves a specified submission into the local system"
+	descList        = "Lists all available assignments for a given language"
 )
 
 func main() {
@@ -120,6 +121,12 @@ func main() {
 			Usage:     descDownload,
 			Action:    cmd.Download,
 		},
+		{
+			Name:      "list",
+			ShortName: "li",
+			Usage:     descList,
+			Action:    cmd.List,
+		},
 	}
 	if err := app.Run(os.Args); err != nil {
 

fixtures/tracks.json

@@ -0,0 +1,45 @@
+{
+  "track":{
+    "language":"Clojure",
+    "active":true,
+    "id":"clojure",
+    "slug":"clojure",
+    "problems":[
+      "clojure/bob",
+      "clojure/rna-transcription",
+      "clojure/word-count",
+      "clojure/anagram",
+      "clojure/beer-song",
+      "clojure/nucleotide-count",
+      "clojure/point-mutations",
+      "clojure/phone-number",
+      "clojure/grade-school",
+      "clojure/robot-name",
+      "clojure/leap",
+      "clojure/etl",
+      "clojure/meetup",
+      "clojure/space-age",
+      "clojure/grains",
+      "clojure/gigasecond",
+      "clojure/triangle",
+      "clojure/scrabble-score",
+      "clojure/roman-numerals",
+      "clojure/binary",
+      "clojure/prime-factors",
+      "clojure/raindrops",
+      "clojure/allergies",
+      "clojure/atbash-cipher",
+      "clojure/bank-account",
+      "clojure/crypto-square",
+      "clojure/kindergarten-garden",
+      "clojure/robot-simulator",
+      "clojure/queen-attack",
+      "clojure/accumulate",
+      "clojure/binary-search-tree",
+      "clojure/difference-of-squares",
+      "clojure/hexadecimal",
+      "clojure/largest-series-product"
+    ],
+    "repository":"https://github.com/exercism/xclojure"
+  }
+}