Refactor how tsh lists apps as text (#49773)

This way it's going to be easier to add a column with target ports,
which should be displayed only if the list includes multi-port apps.

tool/tsh/common/app_test.go

@@ -24,9 +24,11 @@ import (
 	"crypto/tls"
 	"encoding/json"
 	"fmt"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"os/user"
+	"strings"
 	"testing"
 	"time"
 
@@ -44,6 +46,7 @@ import (
 	"github.com/gravitational/teleport/lib/client"
 	"github.com/gravitational/teleport/lib/events"
 	"github.com/gravitational/teleport/lib/service/servicecfg"
+	"github.com/gravitational/teleport/lib/tlsca"
 	testserver "github.com/gravitational/teleport/tool/teleport/testenv"
 )
 
@@ -597,3 +600,150 @@ uri: https://test-app.example.com:8443
 		})
 	}
 }
+
+func TestWriteAppTable(t *testing.T) {
+	defaultAppListings := []appListing{
+		appListing{
+			Proxy:   "example.com",
+			Cluster: "foo-cluster",
+			App: mustMakeNewAppV3(t, types.Metadata{Name: "root-app"}, types.AppSpecV3{
+				// Short URLs, because in tests the width of the term is just 80 characters and the public
+				// address column gets truncated very early.
+				PublicAddr: "https://root-app.example.com",
+				URI:        "http://localhost:8080",
+			}),
+		},
+		appListing{
+			Proxy:   "example.com",
+			Cluster: "bar-cluster",
+			App: mustMakeNewAppV3(t, types.Metadata{Name: "leaf-app"}, types.AppSpecV3{
+				PublicAddr: "https://leaf-app.example.com",
+				URI:        "http://localhost:4242",
+			}),
+		},
+	}
+
+	tests := []struct {
+		name          string
+		config        appTableConfig
+		appListings   []appListing
+		wantHeaders   []string
+		wantNoHeaders []string
+		wantValues    []string
+		wantNoValues  []string
+	}{
+		{
+			name: "regular list",
+			config: appTableConfig{
+				active:  []tlsca.RouteToApp{},
+				verbose: false,
+				listAll: false,
+			},
+			appListings: defaultAppListings,
+			wantHeaders: []string{"Application", "Public Address"},
+			// Public addresses are expected to be truncated when verbose mode is off.
+			wantValues:    []string{"https://root-app...", "https://leaf-app...", "root-app", "leaf-app"},
+			wantNoHeaders: []string{"URI", "Proxy", "Cluster"},
+			wantNoValues:  []string{"http://localhost:8080", "foo-cluster", "bar-cluster"},
+		},
+		{
+			name: "regular list with active app",
+			config: appTableConfig{
+				active: []tlsca.RouteToApp{
+					tlsca.RouteToApp{Name: "root-app"},
+				},
+				verbose: false,
+				listAll: false,
+			},
+			appListings: defaultAppListings,
+			wantHeaders: []string{"Application"},
+			wantValues:  []string{"> root-app", "leaf-app"},
+		},
+		{
+			name: "regular list with no apps",
+			config: appTableConfig{
+				active:  []tlsca.RouteToApp{},
+				verbose: false,
+				listAll: false,
+			},
+			appListings: []appListing{},
+			wantHeaders: []string{"Application", "Public Address"},
+		},
+		{
+			name: "verbose",
+			config: appTableConfig{
+				active:  []tlsca.RouteToApp{},
+				verbose: true,
+				listAll: false,
+			},
+			appListings: defaultAppListings,
+			wantHeaders: []string{"URI", "Application", "Public Address"},
+			wantValues: []string{"http://localhost:8080", "http://localhost:4242",
+				"https://root-app.example.com", "https://leaf-app.example.com", "root-app", "leaf-app"},
+			wantNoHeaders: []string{"Proxy", "Cluster"},
+			wantNoValues:  []string{"foo-cluster", "bar-cluster"},
+		},
+		{
+			name: "list all",
+			config: appTableConfig{
+				active:  []tlsca.RouteToApp{},
+				verbose: false,
+				listAll: true,
+			},
+			appListings: defaultAppListings,
+			wantHeaders: []string{"Proxy", "Cluster", "Application", "Public Address"},
+			// Public addresses are expected to be truncated when verbose mode is off.
+			wantValues:    []string{"foo-cluste...", "bar-cluste...", "example.co...", "https://ro...", "https://le...", "root-app", "leaf-app"},
+			wantNoHeaders: []string{"URI"},
+			wantNoValues:  []string{"http://localhost:8080"},
+		},
+		{
+			name: "verbose and list all",
+			config: appTableConfig{
+				active:  []tlsca.RouteToApp{},
+				verbose: true,
+				listAll: true,
+			},
+			appListings: defaultAppListings,
+			wantHeaders: []string{"Proxy", "Cluster", "URI", "Application", "Public Address"},
+			wantValues: []string{"foo-cluster", "bar-cluster", "http://localhost:8080", "http://localhost:4242",
+				"https://root-app.example.com", "https://leaf-app.example.com", "root-app", "leaf-app"},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			var b bytes.Buffer
+			w := io.Writer(&b)
+
+			err := writeAppTable(w, test.appListings, test.config)
+			require.NoError(t, err)
+
+			lines := strings.SplitN(b.String(), "\n", 3)
+			headers := lines[0]
+			// The second line contains header separators ("------"), that's why it's skipped here.
+			values := lines[2]
+
+			for _, wantHeader := range test.wantHeaders {
+				assert.Contains(t, headers, wantHeader)
+			}
+			for _, wantNoHeader := range test.wantNoHeaders {
+				assert.NotContains(t, headers, wantNoHeader)
+			}
+
+			for _, wantValue := range test.wantValues {
+				assert.Contains(t, values, wantValue)
+			}
+			for _, wantNoValue := range test.wantNoValues {
+				assert.NotContains(t, values, wantNoValue)
+			}
+		})
+	}
+}
+
+func mustMakeNewAppV3(t *testing.T, meta types.Metadata, spec types.AppSpecV3) *types.AppV3 {
+	t.Helper()
+	app, err := types.NewAppV3(meta, spec)
+	require.NoError(t, err)
+	return app
+}