package geoip

import (
	"compress/gzip"
	"context"
	"fmt"
	"io"
	"net/http"
	"os"
	"path/filepath"
	"strings"
)

// DownloadMMDB downloads an MMDB URL to destPath. If the URL ends with `.gz`, the body is gunzipped.
// Otherwise the response body is written as-is (raw `.mmdb`, e.g. GitHub raw).
func DownloadMMDB(ctx context.Context, client *http.Client, url, destPath string) error {
	if strings.HasSuffix(strings.ToLower(strings.TrimSpace(url)), ".gz") {
		return downloadGzippedMMDB(ctx, client, url, destPath)
	}
	return downloadRawMMDB(ctx, client, url, destPath)
}

func downloadRawMMDB(ctx context.Context, client *http.Client, url, destPath string) error {
	if client == nil {
		client = http.DefaultClient
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return err
	}
	resp, err := client.Do(req)
	if err != nil {
		return fmt.Errorf("geoip download: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("geoip download: http %s", resp.Status)
	}
	dir := filepath.Dir(destPath)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return fmt.Errorf("geoip mkdir %q: %w (directory must exist or be creatable by the process)", dir, err)
	}
	tmp, err := os.CreateTemp(dir, "geolite-*.mmdb.part")
	if err != nil {
		return fmt.Errorf("geoip temp file in %q: %w", dir, err)
	}
	tmpPath := tmp.Name()
	_, copyErr := io.Copy(tmp, resp.Body)
	closeErr := tmp.Close()
	if copyErr != nil {
		_ = os.Remove(tmpPath)
		return copyErr
	}
	if closeErr != nil {
		_ = os.Remove(tmpPath)
		return closeErr
	}
	_ = os.Remove(destPath)
	if err := os.Rename(tmpPath, destPath); err != nil {
		_ = os.Remove(tmpPath)
		return fmt.Errorf("geoip rename: %w", err)
	}
	return nil
}

func downloadGzippedMMDB(ctx context.Context, client *http.Client, url, destPath string) error {
	if client == nil {
		client = http.DefaultClient
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return err
	}
	resp, err := client.Do(req)
	if err != nil {
		return fmt.Errorf("geoip download: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("geoip download: http %s", resp.Status)
	}
	gzr, err := gzip.NewReader(resp.Body)
	if err != nil {
		return fmt.Errorf("geoip gzip: %w", err)
	}
	defer gzr.Close()

	dir := filepath.Dir(destPath)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return fmt.Errorf("geoip mkdir %q: %w (directory must exist or be creatable by the process)", dir, err)
	}
	tmp, err := os.CreateTemp(dir, "geolite-*.mmdb.part")
	if err != nil {
		return fmt.Errorf("geoip temp file in %q: %w", dir, err)
	}
	tmpPath := tmp.Name()
	_, copyErr := io.Copy(tmp, gzr)
	closeErr := tmp.Close()
	if copyErr != nil {
		_ = os.Remove(tmpPath)
		return copyErr
	}
	if closeErr != nil {
		_ = os.Remove(tmpPath)
		return closeErr
	}
	_ = os.Remove(destPath)
	if err := os.Rename(tmpPath, destPath); err != nil {
		_ = os.Remove(tmpPath)
		return fmt.Errorf("geoip rename: %w", err)
	}
	return nil
}