//go:build ignore

// Parses Wireshark's packet-e212.c and generates utils/mccmnc_data.go.
// Run: go generate ./utils/...
package main

import (
	"fmt"
	"go/format"
	"io"
	"log"
	"net/http"
	"os"
	"regexp"
	"sort"
	"strconv"
	"strings"
)

const wiresharkURL = "https://raw.githubusercontent.com/wireshark/wireshark/master/epan/dissectors/packet-e212.c"

// matches entries like { 123, "Some Name" } in C value_string arrays
var entryRe = regexp.MustCompile(`\{\s*(\d+),\s*"([^"]+)"\s*\}`)

func main() {
	log.SetFlags(0)

	src := fetchSource()

	countries := parseTable(src, "E212_codes[]", func(code int) string {
		return fmt.Sprintf("%03d", code)
	})
	networks := parseTable(src, "mcc_mnc_2digits_codes[]", func(code int) string {
		return fmt.Sprintf("%03d-%02d", code/100, code%100)
	})
	// 3-digit MNC: only add if no 2-digit entry exists for the same key
	for k, v := range parseTable(src, "mcc_mnc_3digits_codes[]", func(code int) string {
		return fmt.Sprintf("%03d-%03d", code/1000, code%1000)
	}) {
		if _, ok := networks[k]; !ok {
			networks[k] = v
		}
	}

	var buf strings.Builder
	buf.WriteString("// Code generated by gen_mccmnc from Wireshark's packet-e212.c; DO NOT EDIT.\n\npackage utils\n\n")
	writeMap(&buf, "mccCountry", "MCC to country name (ITU-T E.212)", countries)
	writeMap(&buf, "mccmncNetwork", "MCC-MNC to network/operator name (ITU-T E.212)", networks)

	formatted, err := format.Source([]byte(buf.String()))
	if err != nil {
		log.Fatalf("gofmt: %v", err)
	}
	if err := os.WriteFile("mccmnc_data.go", formatted, 0644); err != nil {
		log.Fatal(err)
	}
	fmt.Printf("generated mccmnc_data.go: %d countries, %d networks\n", len(countries), len(networks))
}

func fetchSource() string {
	resp, err := http.Get(wiresharkURL)
	if err != nil {
		log.Fatal(err)
	}
	defer resp.Body.Close()
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		log.Fatal(err)
	}
	return string(body)
}

func parseTable(src, name string, formatKey func(int) string) map[string]string {
	block := extractBlock(src, name)
	if block == "" {
		log.Fatalf("table %s not found", name)
	}
	result := make(map[string]string)
	for _, m := range entryRe.FindAllStringSubmatch(block, -1) {
		if m[2] == "Unassigned" || m[2] == "Unset" {
			continue
		}
		code, _ := strconv.Atoi(m[1])
		result[formatKey(code)] = m[2]
	}
	return result
}

// extractBlock returns the body of a C value_string array, up to its { 0, NULL } terminator.
func extractBlock(src, name string) string {
	marker := "value_string " + name + " = {"
	start := strings.Index(src, marker)
	if start < 0 {
		return ""
	}
	end := strings.Index(src[start:], "{ 0, NULL }")
	if end < 0 {
		return ""
	}
	return src[start : start+end]
}

func writeMap(buf *strings.Builder, varName, comment string, m map[string]string) {
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	fmt.Fprintf(buf, "// %s maps %s.\nvar %s = map[string]string{\n", varName, comment, varName)
	for _, k := range keys {
		fmt.Fprintf(buf, "\t%q: %q,\n", k, m[k])
	}
	buf.WriteString("}\n\n")
}