Initial commit.

internal/configuration/config.go

@@ -0,0 +1,93 @@
+package configuration
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"gopkg.in/yaml.v2"
+)
+
+var (
+	ErrConfigurationFileDoesNotExist  = errors.New("configuration file does not exist")
+	ErrConfigurationFilePathUndefined = errors.New("configuration file path wasn't provided")
+)
+
+// Config is an application's configuration.
+type Config struct {
+	configPath string
+	// Applications describes configuration for remote application's endpoints.
+	// Key is an application's name.
+	Applications map[string]struct {
+		// Endpoint is a remote application endpoint which should give us metrics
+		// in Prometheus format.
+		Endpoint string
+		// TimeBetweenRequests is a minimal amount of time which should pass
+		// between requests.
+		TimeBetweenRequests time.Duration
+	}
+	// Datastore describes data storage configuration.
+	Datastore struct {
+		// ValidTimeout is a timeout for which every data entry will be considered
+		// as valid. After that timeout if value wasn't updated it will be considered
+		// as invalid and purged from memory.
+		ValidTimeout time.Duration `yaml:"valid_timeout"`
+	} `yaml:"datastore"`
+}
+
+// NewConfig returns new configuration.
+func NewConfig() *Config {
+	c := &Config{}
+	c.initialize()
+
+	return c
+}
+
+// Initializes configuration.
+func (c *Config) initialize() {
+	flag.StringVar(&c.configPath, "config", "", "Configuration file path.")
+}
+
+// Parse parses configuration.
+func (c *Config) Parse() error {
+	if c.configPath == "" {
+		return ErrConfigurationFilePathUndefined
+	}
+
+	if strings.HasPrefix(c.configPath, "~") {
+		userDir, err := os.UserHomeDir()
+		if err != nil {
+			return fmt.Errorf("%s: %w", "file path normalization: getting user's home directory", err)
+		}
+
+		c.configPath = strings.Replace(c.configPath, "~", userDir, 1)
+	}
+
+	cfgPath, err := filepath.Abs(c.configPath)
+	if err != nil {
+		return fmt.Errorf("%s: %w", "file path normalization: getting absolute path", err)
+	}
+
+	c.configPath = cfgPath
+
+	if c.configPath == "" {
+		return fmt.Errorf("%s: %w", "file path normalization", ErrConfigurationFilePathUndefined)
+	}
+
+	fileData, err := ioutil.ReadFile(c.configPath)
+	if err != nil {
+		return fmt.Errorf("%s: %w", "configuration file read", err)
+	}
+
+	err = yaml.Unmarshal(fileData, c)
+	if err != nil {
+		return fmt.Errorf("%s: %w", "configuration file parsing", err)
+	}
+
+	return nil
+}