feat: add help text via --help, version via --version (#6)

* feat: add help text via --help

* feat: add --version flag

main.go

@@ -50,11 +50,33 @@ type Config struct {
 	tracePath  string
 	verbosity  int
 	depthLimit int
+	help       bool
+	version    bool
 }
 
+var rVersionFlag = regexp.MustCompile("^--version$")
+var rHelpFlag = regexp.MustCompile("^--help$")
 var rVerboseFlag = regexp.MustCompile("^-(?P<verbosity>(v{1,2}))$")
 var rDepthPattern = regexp.MustCompile("--depth=(?P<depth>([1-9][0-9]*|0))")
 
+var helpText = fmt.Sprintf(`
+Doggo (version %s)
+
+🐕🔎 Inspecting big Datadog traces in the CLI
+
+Usage:
+
+doggo <trace_path> <resource_name or partial string> [-vv] [--depth=<depthLimit>]
+
+Given a trace_path leading to tracedata json and a query (either a resource name or a partial resource name), displays the spans and children of the sections of the trace that match.
+
+By default, timing information for each span is shown.
+
+-v adds more resource-related information for each span;
+-vv adds even more resource-related information, including tags, for each span;
+--depth=<depthLimit> allows limiting how many levels down each match the display should go.
+`, Version)
+
 // Prints traces recursively with increasing ident levels.
 // More data is printed until there are no more traces available
 // i.e. until the ChildrenIds key yields an empty array.
@@ -143,10 +165,22 @@ func parseTraceJsonFromFile(path string) TraceData {
 // Parses command-line arguments to extract flags and
 // other useful contextual details.
 func parseArgs(args []string) Config {
-	rootOfInterest := os.Args[2]
+	rootOfInterest := ""
-	tracePath := os.Args[1]
+
+	if len(os.Args) >= 3 {
+		rootOfInterest = os.Args[2]
+	}
+
+	tracePath := ""
+
+	if len(os.Args) >= 2 {
+		tracePath = os.Args[1]
+	}
+
 	verbosity := 0
 	depth := 9999
+	help := false
+	version := false
 
 	verbosityMatchIndex := rVerboseFlag.SubexpIndex("verbosity")
 	for _, arg := range os.Args {
@@ -173,15 +207,33 @@ func parseArgs(args []string) Config {
 			depth = depthLimit
 			continue
 		}
+
+		if rHelpFlag.MatchString(arg) {
+			help = true
 		}
 
-	return Config{rootOfInterest, tracePath, verbosity, depth}
+		if rVersionFlag.MatchString(arg) {
+			version = true
+		}
+
+	}
+
+	return Config{rootOfInterest, tracePath, verbosity, depth, help, version}
 }
 
 func main() {
-	log.Println("Doggo version: ", Version)
 	config := parseArgs(os.Args)
 
+	if config.help {
+		fmt.Println(helpText)
+		return
+	}
+
+	if config.version {
+		fmt.Println(Version)
+		return
+	}
+
 	fullTrace := parseTraceJsonFromFile(config.tracePath)
 
 	spansById, spanIdsByResourceName := buildSpanIndexes(fullTrace)