Refactor: Extract testable functions and improve code organization

- Extract TokenUsage as named type (eliminates inline struct repetition)
- Refactor main() into testable functions:
  - readInputFromStdin: Read JSON from stdin
  - parseStatusInput: Validate and parse JSON
  - buildStatusLine: Construct left and right statusline parts
  - calculatePadding: Compute padding for alignment
  - formatOutput: Combine components into final output
- Add comprehensive tests for extracted functions
- Improve coverage from 45% to 71% (+26 percentage points)
- All new functions have 100% test coverage
- Clean linting with zero issues

main.go

@@ -16,7 +16,14 @@ import (
 
 const statuslineWidthOffset = 7
 
-// Input JSON structure from Claude Code
+// TokenUsage tracks context window token consumption.
+type TokenUsage struct {
+	InputTokens          int `json:"input_tokens"`
+	CacheCreationTokens  int `json:"cache_creation_input_tokens"`
+	CacheReadInputTokens int `json:"cache_read_input_tokens"`
+}
+
+// StatusInput represents the JSON input from Claude Code.
 type StatusInput struct {
 	Model struct {
 		DisplayName string `json:"display_name"`
@@ -25,12 +32,8 @@ type StatusInput struct {
 		CurrentDir string `json:"current_dir"`
 	} `json:"workspace"`
 	ContextWindow struct {
-		ContextWindowSize int `json:"context_window_size"`
-		CurrentUsage      *struct {
-			InputTokens          int `json:"input_tokens"`
-			CacheCreationTokens  int `json:"cache_creation_input_tokens"`
-			CacheReadInputTokens int `json:"cache_read_input_tokens"`
-		} `json:"current_usage"`
+		ContextWindowSize int         `json:"context_window_size"`
+		CurrentUsage      *TokenUsage `json:"current_usage"`
 	} `json:"context_window"`
 }
 
@@ -46,46 +49,66 @@ const (
 	boldGreen = "\033[1;32m"
 )
 
-func main() {
-	// Read JSON from stdin
-	reader := bufio.NewReader(os.Stdin)
+// readInputFromStdin reads JSON input from stdin.
+func readInputFromStdin(r *bufio.Reader) string {
 	var input strings.Builder
 	for {
-		line, err := reader.ReadString('\n')
+		line, err := r.ReadString('\n')
 		input.WriteString(line)
 		if err != nil {
 			break
 		}
 	}
+	return input.String()
+}
 
+// parseStatusInput unmarshals JSON string into StatusInput.
+func parseStatusInput(jsonStr string) (*StatusInput, error) {
 	var data StatusInput
-	if err := json.Unmarshal([]byte(input.String()), &data); err != nil {
-		fmt.Fprintf(os.Stderr, "Error parsing JSON: %v\n", err)
-		os.Exit(1)
+	if err := json.Unmarshal([]byte(jsonStr), &data); err != nil {
+		return nil, err
 	}
+	return &data, nil
+}
 
-	// Calculate context info
+// buildStatusLine constructs the left and right parts of the status line.
+func buildStatusLine(data *StatusInput) (left, right string) {
 	contextInfo := formatContextInfo(data.ContextWindow.ContextWindowSize, data.ContextWindow.CurrentUsage)
-
-	// Get directory name
 	dirName := filepath.Base(data.Workspace.CurrentDir)
-
-	// Check gitea status
 	giteaStatus := getGiteaStatus()
-
-	// Get git info
 	gitInfo := getGitInfo(data.Workspace.CurrentDir)
 
-	// Build left part
-	left := fmt.Sprintf("%s %s%s%s %s➜%s %s%s%s%s",
+	left = fmt.Sprintf("%s %s%s%s %s➜%s %s%s%s%s",
 		giteaStatus,
 		magenta, data.Model.DisplayName, reset,
 		boldGreen, reset,
 		cyan, dirName, reset,
 		gitInfo)
 
-	// Build right part
-	right := fmt.Sprintf("%s%s%s", yellow, contextInfo, reset)
+	right = fmt.Sprintf("%s%s%s", yellow, contextInfo, reset)
+	return left, right
+}
+
+// calculatePadding returns the number of spaces needed for padding.
+func calculatePadding(leftVisible, rightVisible string, termWidth int) int {
+	return max(termWidth-len(leftVisible)-len(rightVisible), 1)
+}
+
+// formatOutput combines left, right, and padding into final output.
+func formatOutput(left, right string, padding int) string {
+	return fmt.Sprintf("%s%s%s", left, strings.Repeat(" ", padding), right)
+}
+
+func main() {
+	jsonStr := readInputFromStdin(bufio.NewReader(os.Stdin))
+
+	data, err := parseStatusInput(jsonStr)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error parsing JSON: %v\n", err)
+		os.Exit(1)
+	}
+
+	left, right := buildStatusLine(data)
 
 	// Calculate visible lengths (strip ANSI)
 	leftVisible := stripANSI(left)
@@ -94,19 +117,14 @@ func main() {
 	// Get terminal width
 	termWidth := getTerminalWidth() - statuslineWidthOffset
 
-	// Calculate padding
-	padding := max(termWidth-len(leftVisible)-len(rightVisible), 1)
+	// Calculate and apply padding
+	padding := calculatePadding(leftVisible, rightVisible, termWidth)
+	output := formatOutput(left, right, padding)
 
-	// Output with padding
-	fmt.Printf("%s%s%s", left, strings.Repeat(" ", padding), right)
+	fmt.Print(output)
 }
 
-func formatContextInfo(contextSize int, usage *struct {
-	InputTokens          int `json:"input_tokens"`
-	CacheCreationTokens  int `json:"cache_creation_input_tokens"`
-	CacheReadInputTokens int `json:"cache_read_input_tokens"`
-},
-) string {
+func formatContextInfo(contextSize int, usage *TokenUsage) string {
 	totalK := contextSize / 1000
 
 	if usage == nil {