internal/api: implement module versions endpoint

- Implement module versions endpoint using ds.GetVersionsForPath
- Introduce paginate helper to generalize paginaton logic
- Update fakedatasource to correctly use V1Path to return all versions

Change-Id: Icc028bf8ca9c13978bb6eba84afe9736ccd6bcee
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/754862
Reviewed-by: Jonathan Amsterdam <jba@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ethan Lee <ethanalee@google.com>
kokoro-CI: kokoro <noreply+kokoro@google.com>

2 files changed, 139 insertions, 1 deletions

diff --git a/internal/api/api.go b/internal/api/api.go
index 2b0f3f4f..3b653fd8 100644
--- a/internal/api/api.go
+++ b/internal/api/api.go
@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"errors"
 	"net/http"
+	"strconv"
 	"strings"
 
 	"golang.org/x/pkgsite/internal"
@@ -210,7 +211,35 @@ func ServeModule(w http.ResponseWriter, r *http.Request, ds internal.DataSource)
 		}
 	}
 
-	// Future: handle licenses param.
+	return serveJSON(w, http.StatusOK, resp)
+}
+
+// ServeModuleVersions handles requests for the v1 module versions endpoint.
+func ServeModuleVersions(w http.ResponseWriter, r *http.Request, ds internal.DataSource) (err error) {
+	defer derrors.Wrap(&err, "ServeModuleVersions")
+
+	path := strings.TrimPrefix(r.URL.Path, "/v1/versions/")
+	if path == "" {
+		return serveErrorJSON(w, http.StatusBadRequest, "missing path", nil)
+	}
+
+	var params VersionsParams
+	if err := ParseParams(r.URL.Query(), &params); err != nil {
+		return serveErrorJSON(w, http.StatusBadRequest, err.Error(), nil)
+	}
+
+	infos, err := ds.GetVersionsForPath(r.Context(), path)
+	if err != nil {
+		if errors.Is(err, derrors.NotFound) {
+			return serveErrorJSON(w, http.StatusNotFound, err.Error(), nil)
+		}
+		return err
+	}
+
+	resp, err := paginate(infos, params.ListParams, 100)
+	if err != nil {
+		return serveErrorJSON(w, http.StatusBadRequest, err.Error(), nil)
+	}
 
 	return serveJSON(w, http.StatusOK, resp)
 }
@@ -238,3 +267,38 @@ func serveErrorJSON(w http.ResponseWriter, status int, message string, candidate
 		Candidates: candidates,
 	})
 }
+
+func paginate[T any](all []T, lp ListParams, defaultLimit int) (PaginatedResponse[T], error) {
+	limit := lp.Limit
+	if limit <= 0 {
+		limit = defaultLimit
+	}
+
+	offset := 0
+	if lp.Token != "" {
+		var err error
+		offset, err = strconv.Atoi(lp.Token)
+		if err != nil || offset < 0 {
+			return PaginatedResponse[T]{}, errors.New("invalid token")
+		}
+	}
+
+	if offset > len(all) {
+		offset = len(all)
+	}
+	end := offset + limit
+	if end > len(all) {
+		end = len(all)
+	}
+
+	var nextToken string
+	if end < len(all) {
+		nextToken = strconv.Itoa(end)
+	}
+
+	return PaginatedResponse[T]{
+		Items:         all[offset:end],
+		Total:         len(all),
+		NextPageToken: nextToken,
+	}, nil
+}
diff --git a/internal/api/api_test.go b/internal/api/api_test.go
index f61c8581..9112c576 100644
--- a/internal/api/api_test.go
+++ b/internal/api/api_test.go
@@ -247,3 +247,77 @@ func TestServeModule(t *testing.T) {
 		})
 	}
 }
+
+func TestServeModuleVersions(t *testing.T) {
+	ctx := context.Background()
+	ds := fakedatasource.New()
+
+	ds.MustInsertModule(ctx, &internal.Module{
+		ModuleInfo: internal.ModuleInfo{ModulePath: "example.com", Version: "v1.0.0"},
+		Units:      []*internal.Unit{{UnitMeta: internal.UnitMeta{Path: "example.com"}}},
+	})
+	ds.MustInsertModule(ctx, &internal.Module{
+		ModuleInfo: internal.ModuleInfo{ModulePath: "example.com", Version: "v1.1.0"},
+		Units:      []*internal.Unit{{UnitMeta: internal.UnitMeta{Path: "example.com"}}},
+	})
+	ds.MustInsertModule(ctx, &internal.Module{
+		ModuleInfo: internal.ModuleInfo{ModulePath: "example.com/v2", Version: "v2.0.0"},
+		Units:      []*internal.Unit{{UnitMeta: internal.UnitMeta{Path: "example.com/v2"}}},
+	})
+
+	for _, test := range []struct {
+		name       string
+		url        string
+		wantStatus int
+		wantCount  int
+	}{
+		{
+			name:       "all versions (cross-major)",
+			url:        "/v1/versions/example.com",
+			wantStatus: http.StatusOK,
+			wantCount:  3,
+		},
+		{
+			name:       "with limit",
+			url:        "/v1/versions/example.com?limit=1",
+			wantStatus: http.StatusOK,
+			wantCount:  1,
+		},
+		{
+			name:       "pagination",
+			url:        "/v1/versions/example.com?limit=1&token=1",
+			wantStatus: http.StatusOK,
+			wantCount:  1,
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			r := httptest.NewRequest("GET", test.url, nil)
+			w := httptest.NewRecorder()
+
+			err := ServeModuleVersions(w, r, ds)
+			if err != nil {
+				t.Fatalf("ServeModuleVersions returned error: %v", err)
+			}
+
+			if w.Code != test.wantStatus {
+				t.Errorf("status = %d, want %d", w.Code, test.wantStatus)
+			}
+
+			if test.wantStatus == http.StatusOK {
+				var got PaginatedResponse[internal.ModuleInfo]
+				if err := json.Unmarshal(w.Body.Bytes(), &got); err != nil {
+					t.Fatalf("json.Unmarshal: %v", err)
+				}
+				if len(got.Items) != test.wantCount {
+					t.Errorf("count = %d, want %d", len(got.Items), test.wantCount)
+				}
+				if test.name == "with limit" && got.NextPageToken != "1" {
+					t.Errorf("nextPageToken = %q, want %q", got.NextPageToken, "1")
+				}
+				if test.name == "pagination" && got.NextPageToken != "2" {
+					t.Errorf("nextPageToken = %q, want %q", got.NextPageToken, "2")
+				}
+			}
+		})
+	}
+}