[#7] Add local tool for building database file

Added frostfs-locode-db CLI utility that can generate and view UN/LOCODE
database files. Go package
git.frostfs.info/TrueCloudLab/frostfs-node/pkg/util/locode copied to
this repository to eliminate interdependency between frostfs-node and
frostfs-locode-db projects. The process of building database files
reduced to starting make command.

Signed-off-by: George Bartolomey <george@bh4.ru>

pkg/locode/record.go

@@ -0,0 +1,83 @@
+package locode
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// LOCODE represents code from UN/LOCODE coding scheme.
+type LOCODE [2]string
+
+// Record represents a single record of the UN/LOCODE table.
+type Record struct {
+	// Change Indicator.
+	Ch string
+
+	// Combination of a 2-character country code and a 3-character location code.
+	LOCODE LOCODE
+
+	// Name of the locations which has been allocated a UN/LOCODE.
+	Name string
+
+	// Names of the locations which have been allocated a UN/LOCODE without diacritic signs.
+	NameWoDiacritics string
+
+	// ISO 1-3 character alphabetic and/or numeric code for the administrative division of the country concerned.
+	SubDiv string
+
+	// 8-digit function classifier code for the location.
+	Function string
+
+	// Status of the entry by a 2-character code.
+	Status string
+
+	// Last date when the location was updated/entered.
+	Date string
+
+	// The IATA code for the location if different from location code in column LOCODE.
+	IATA string
+
+	// Geographical coordinates (latitude/longitude) of the location, if there is any.
+	Coordinates string
+
+	// Some general remarks regarding the UN/LOCODE in question.
+	Remarks string
+}
+
+// ErrInvalidString is the error of incorrect string format of the LOCODE.
+var ErrInvalidString = errors.New("invalid string format in UN/Locode")
+
+// FromString parses string and returns LOCODE.
+//
+// If string has incorrect format, ErrInvalidString returns.
+func FromString(s string) (*LOCODE, error) {
+	const (
+		locationSeparator = " "
+		locodePartsNumber = 2
+	)
+
+	words := strings.Split(s, locationSeparator)
+	if ln := len(words); ln != locodePartsNumber {
+		return nil, fmt.Errorf(
+			"incorrect locode: it must consist of %d codes separated with a witespase, got: %d",
+			locodePartsNumber,
+			ln,
+		)
+	}
+
+	l := new(LOCODE)
+	copy(l[:], words)
+
+	return l, nil
+}
+
+// CountryCode returns a string representation of country code.
+func (l *LOCODE) CountryCode() string {
+	return l[0]
+}
+
+// LocationCode returns a string representation of location code.
+func (l *LOCODE) LocationCode() string {
+	return l[1]
+}