// Package maxmind provides utilities for downloading and managing MaxMind GeoIP databases.
//
// This package handles downloading GeoIP databases from MaxMind's servers,
// extracting them from compressed archives, and validating database editions.
// It supports both commercial GeoIP2 and free GeoLite2 database editions.
//
// The implementation is based on the approach used in the Kubernetes ingress-nginx project.
// See: https://github.com/kubernetes/ingress-nginx/pull/4896/files
package maxmind

import (
	"archive/tar"
	"compress/gzip"
	"fmt"
	"io"
	"net/http"
	"os"
	"path"
	"strings"
)

// LicenseKey is the MaxMind license key used to download databases.
// This must be set to a valid license key obtained from MaxMind.
var LicenseKey = ""

// EditionIDs is a comma-separated list of MaxMind database editions to download.
// Examples: "GeoLite2-City,GeoLite2-Country" or "GeoIP2-ISP".
var EditionIDs = ""

// EditionFiles contains the list of database files that have been downloaded.
// This slice is populated by DownloadGeoLite2DB after successful downloads.
var EditionFiles []string

// Path specifies the directory where MaxMind databases should be stored.
// If empty, a default system path will be used.
var Path string

const (
	dbExtension = ".mmdb"
	maxmindURL  = "https://download.maxmind.com/app/geoip_download?license_key=%v&edition_id=%v&suffix=tar.gz"
)

// GeoLite2DBExists checks if all required MaxMind databases exist in the filesystem.
// It verifies that all databases specified in EditionIDs are present in the Path directory.
// Returns true only if all specified databases are found.
func GeoLite2DBExists() bool {
	for _, dbName := range strings.Split(EditionIDs, ",") {
		if !fileExists(path.Join(Path, dbName+dbExtension)) {
			return false
		}
	}

	return true
}

// DownloadGeoLite2DB downloads all databases specified in EditionIDs from MaxMind.
// It requires a valid LicenseKey and updates EditionFiles with successfully downloaded files.
// Returns an error if any download fails.
func DownloadGeoLite2DB() error {
	for _, dbName := range strings.Split(EditionIDs, ",") {
		err := downloadDatabase(dbName)
		if err != nil {
			return err
		}
		EditionFiles = append(EditionFiles, dbName+dbExtension)
	}
	return nil
}

// downloadDatabase downloads a single MaxMind database by name.
// It fetches the database archive from MaxMind, extracts the .mmdb file,
// and saves it to the specified Path directory.
func downloadDatabase(dbName string) error {
	url := fmt.Sprintf(maxmindURL, LicenseKey, dbName)
	req, err := http.NewRequest(http.MethodGet, url, nil)
	if err != nil {
		return err
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}

	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("HTTP status %v", resp.Status)
	}

	archive, err := gzip.NewReader(resp.Body)
	if err != nil {
		return err
	}
	defer archive.Close()

	mmdbFile := dbName + dbExtension

	tarReader := tar.NewReader(archive)
	for true {
		header, err := tarReader.Next()
		if err == io.EOF {
			break
		}

		if err != nil {
			return err
		}

		switch header.Typeflag {
		case tar.TypeReg:
			if !strings.HasSuffix(header.Name, mmdbFile) {
				continue
			}

			outFile, err := os.Create(path.Join(Path, mmdbFile))
			if err != nil {
				return err
			}

			defer outFile.Close()

			if _, err := io.Copy(outFile, tarReader); err != nil {
				return err
			}

			return nil
		}
	}

	return fmt.Errorf("the URL %v does not contains the database %v",
		fmt.Sprintf(maxmindURL, "XXXXXXX", dbName), mmdbFile)
}

// ValidateGeoLite2DBEditions validates that all specified database editions are recognized.
// It checks each edition in EditionIDs against a list of known MaxMind database editions.
// Returns an error if any unknown edition names are found.
func ValidateGeoLite2DBEditions() error {
	allowedEditions := map[string]bool{
		"GeoIP2-Anonymous-IP":    true,
		"GeoIP2-Country":         true,
		"GeoIP2-City":            true,
		"GeoIP2-Connection-Type": true,
		"GeoIP2-Domain":          true,
		"GeoIP2-ISP":             true,
		"GeoIP2-ASN":             true,
		"GeoLite2-ASN":           true,
		"GeoLite2-Country":       true,
		"GeoLite2-City":          true,
	}

	for _, edition := range strings.Split(EditionIDs, ",") {
		if !allowedEditions[edition] {
			return fmt.Errorf("unknown Maxmind GeoIP2 edition name: '%s'", edition)
		}
	}
	return nil
}

// fileExists checks if a file exists at the given path and is not a directory.
// It returns true only if the path points to an existing regular file.
func fileExists(filePath string) bool {
	info, err := os.Stat(filePath)
	if os.IsNotExist(err) {
		return false
	}

	return !info.IsDir()
}