Add initial declpac CLI tool implementation

pkg/input/input.go

@@ -0,0 +1,66 @@
+package input
+
+import (
+	"bufio"
+	"os"
+	"strings"
+)
+
+func ReadPackages(stateFiles []string) (map[string]bool, error) {
+	packages := make(map[string]bool)
+
+	for _, file := range stateFiles {
+		if err := readStateFile(file, packages); err != nil {
+			return nil, err
+		}
+	}
+
+	if err := readStdin(packages); err != nil {
+		return nil, err
+	}
+
+	return packages, nil
+}
+
+func readStateFile(path string, packages map[string]bool) error {
+	file, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		name := normalizePackageName(scanner.Text())
+		if name != "" {
+			packages[name] = true
+		}
+	}
+
+	return scanner.Err()
+}
+
+func readStdin(packages map[string]bool) error {
+	info, err := os.Stdin.Stat()
+	if err != nil {
+		return err
+	}
+
+	if (info.Mode() & os.ModeCharDevice) != 0 {
+		return nil
+	}
+
+	scanner := bufio.NewScanner(os.Stdin)
+	for scanner.Scan() {
+		name := normalizePackageName(scanner.Text())
+		if name != "" {
+			packages[name] = true
+		}
+	}
+
+	return scanner.Err()
+}
+
+func normalizePackageName(name string) string {
+	return strings.TrimSpace(name)
+}