Add config utils

This commit introduces utility functions for parsing and validating
CLI flags and YAML configuration files.

pkg/config/config.go

@@ -0,0 +1,71 @@
+package config
+
+import (
+	"fmt"
+	"github.com/jessevdk/go-flags"
+	"gopkg.in/yaml.v3"
+	"os"
+)
+
+// Config defines Icinga DB config.
+type Config struct {
+	Database *Database `yaml:"database"`
+	Redis    *Redis    `yaml:"redis"`
+}
+
+// Flags defines CLI flags.
+type Flags struct {
+	// Config is the path to the config file
+	Config string `short:"c" long:"config" description:"path to config file" required:"true" default:"./config.yml"`
+	// Datadir is the location of the data directory
+	Datadir string `long:"datadir" description:"path to the data directory" required:"true" default:"./"`
+}
+
+// FromYAMLFile returns a new Config value created from the given YAML config file.
+func FromYAMLFile(name string) (*Config, error) {
+	f, err := os.Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	c := &Config{}
+	d := yaml.NewDecoder(f)
+
+	if err := d.Decode(&c); err != nil {
+		return nil, err
+	}
+
+	return c, nil
+}
+
+// ValidateFile checks whether the given file name is a readable file.
+func ValidateFile(name string) error {
+	f, err := os.Stat(name)
+	if err != nil {
+		return err
+	}
+
+	if f.IsDir() {
+		return fmt.Errorf("'%s' is a directory", name)
+	}
+
+	return nil
+}
+
+// ParseFlags parses CLI flags and
+// returns a Flags value created from them.
+func ParseFlags() (*Flags, error) {
+	f := &Flags{}
+	parser := flags.NewParser(f, flags.Default)
+
+	if _, err := parser.Parse(); err != nil {
+		return nil, err
+	}
+
+	if err := ValidateFile(f.Config); err != nil {
+		return nil, err
+	}
+
+	return f, nil
+}