--wip-- [skip ci]

internal/pkg/templer/middleware.go

@@ -2,8 +2,10 @@ package templer
 
 import (
 	"context"
+	"fmt"
 	"log/slog"
 	"net/http"
+	"net/url"
 	"strings"
 )
 
@@ -25,12 +27,38 @@ func Middleware(next http.Handler) http.HandlerFunc {
 	}
 }
 
-// Path returns the current path without a leading slash
+// Path returns the current path with a leading slash
 func Path(ctx context.Context) string {
 	path, ok := ctx.Value(pathKey).(string)
 	if !ok {
 		slog.Error("could not extract request path from context")
 		return ""
 	}
-	return strings.TrimPrefix(path, "/")
+	return path
+}
+
+func RelativePath(ctx context.Context, relPath string) (path string, err error) {
+	baseStr := Path(ctx)
+
+	if baseStr != "" && !strings.HasSuffix(baseStr, "/") {
+		baseStr += "/"
+	}
+
+	base, err := url.Parse(baseStr)
+	if err != nil {
+		err = fmt.Errorf("could not parse base path: %w", err)
+		return
+	}
+	rel, err := url.Parse(relPath)
+	if err != nil {
+		err = fmt.Errorf("could not parse relative path: %w", err)
+		return
+	}
+
+	// Resolve the relative path against the base
+	path = base.ResolveReference(rel).Path
+	if strings.HasSuffix(path, "/") {
+		path = path[:len(path)-1]
+	}
+	return
 }

internal/pkg/templer/middleware_test.go

@@ -0,0 +1,75 @@
+package templer
+
+import (
+	"context"
+	"testing"
+)
+
+func TestRelativePath(t *testing.T) {
+	tests := []struct {
+		name string // description of this test case
+		// Named input parameters for target function.
+		base    string
+		relPath string
+		want    string
+		wantErr bool
+	}{
+		// TODO: Add test cases.
+		{
+			name:    "with no relative path stays the same",
+			base:    "/foo/bar",
+			relPath: "",
+			want:    "/foo/bar",
+			wantErr: false,
+		},
+		{
+			name:    "with . relative path stays the same",
+			base:    "/foo/bar",
+			relPath: ".",
+			want:    "/foo/bar",
+			wantErr: false,
+		},
+		{
+			name:    "with ./ relative path stays the same",
+			base:    "/foo/bar",
+			relPath: "./",
+			want:    "/foo/bar",
+			wantErr: false,
+		},
+
+		{
+			name:    "with .. relative path goes one up",
+			base:    "/foo/bar",
+			relPath: "..",
+			want:    "/foo",
+			wantErr: false,
+		},
+
+		{
+			name:    "with ../baz relative path replaces last element with baz",
+			base:    "/foo/bar",
+			relPath: "../baz",
+			want:    "/foo/baz",
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx := context.WithValue(t.Context(), pathKey, tt.base)
+			got, gotErr := RelativePath(ctx, tt.relPath)
+			if gotErr != nil {
+				if !tt.wantErr {
+					t.Errorf("RelativePath() failed: %v", gotErr)
+				}
+				return
+			}
+			if tt.wantErr {
+				t.Fatal("RelativePath() succeeded unexpectedly")
+			}
+			// TODO: update the condition below to compare got with tt.want.
+			if got != tt.want {
+				t.Errorf("RelativePath() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}