package main

import (
	"bufio"
	"fmt"
	"net"
	"net/http"
	"strings"
)

const ipverseBaseURL = "https://raw.githubusercontent.com/ipverse/country-ip-blocks/master/country"

// IPverseProvider fetches GeoIP data from the ipverse/country-ip-blocks GitHub repository.
// Data is sourced from Regional Internet Registries (RIRs) and aggregated by ipverse.
// Repository: https://github.com/ipverse/country-ip-blocks
type IPverseProvider struct{}

func (p *IPverseProvider) Name() string {
	return "ipverse"
}

// FetchCIDRs downloads IPv4 CIDR blocks for a country from ipverse.
// URL format: https://raw.githubusercontent.com/ipverse/country-ip-blocks/master/country/{cc}/ipv4-aggregated.txt
func (p *IPverseProvider) FetchCIDRs(countryCode string) ([]string, error) {
	url := fmt.Sprintf("%s/%s/ipv4-aggregated.txt", ipverseBaseURL, strings.ToLower(countryCode))
	return downloadAndParseCIDRs(url)
}

// downloadAndParseCIDRs is a shared helper that downloads a URL containing
// one CIDR per line and returns validated CIDR strings.
func downloadAndParseCIDRs(url string) ([]string, error) {
	resp, err := http.Get(url)
	if err != nil {
		return nil, fmt.Errorf("http get error on url %q: %v", url, err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("unexpected http status %d from %q", resp.StatusCode, url)
	}

	scanner := bufio.NewScanner(resp.Body)
	scanner.Split(bufio.ScanLines)

	var cidrs []string
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())

		// Skip empty lines and comments
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}

		_, ipnet, err := net.ParseCIDR(line)
		if err != nil {
			// Skip unparseable lines rather than failing the whole country
			continue
		}
		cidrs = append(cidrs, ipnet.String())
	}

	if err := scanner.Err(); err != nil {
		return nil, fmt.Errorf("error reading response body from %q: %v", url, err)
	}

	return cidrs, nil
}