package main

import (
	"bufio"
	"bytes"
	_ "embed"
	"flag"
	"fmt"
	"os"
	"strconv"
	"strings"
)

//go:embed UnicodeData.txt
var unicodedata []byte

func die(msg string) {
	fmt.Fprintln(os.Stderr, msg)
	fmt.Fprintln(os.Stderr, "USAGE:", os.Args[0], "[-ranges RANGES]")
	flag.PrintDefaults()
	os.Exit(-1)
}

type rangeInterval struct {
	from int64
	to   int64
}

func (r *rangeInterval) contains(i int64) bool {
	return r.from <= i && i <= r.to
}

func parseHex(s string) (int64, error) {
	return strconv.ParseInt(s, 16, 32)
}

func parseRanges(ranges string) []rangeInterval {
	intervals := []rangeInterval{}
	if strings.TrimSpace(ranges) != "" {
		splitranges := strings.Split(ranges, " ")
		for _, r := range splitranges {
			fromto := strings.Split(r, "..")
			if len(fromto) != 2 {
				die("invalid ranges")
			}
			from, err := parseHex(fromto[0])
			if err != nil {
				die("invalid ranges")
			}
			to, err := parseHex(fromto[1])
			if err != nil {
				die("invalid ranges")
			}
			intervals = append(intervals, rangeInterval{from, to})
		}
	}
	return intervals
}

func printCodepoint(i int64, description string) {
	var ch rune = rune(i)
	var s string = string([]rune{ch})
	fmt.Println(s, description)
}

func main() {
	var ranges string
	flag.StringVar(&ranges, "ranges", "", "define multiple codepoint ranges with \"N1..N2 N3..N4\"")
	flag.Parse()
	rangeIntervals := parseRanges(ranges)

	scanner := bufio.NewScanner(bytes.NewReader(unicodedata))
	for scanner.Scan() {
		line := scanner.Text()
		splitline := strings.Split(line, ";")
		if len(splitline) < 2 || len(splitline[1]) == 0 {
			continue
		}
		codepoint, description := splitline[0], splitline[1]
		if (description[0] == '<' && description[len(description)-1] == '>') || strings.Contains(description, "MODIFIER") || strings.Contains(description, "VARIATION SELECTOR") {
			continue
		}

		i, err := parseHex(codepoint)
		if err != nil {
			continue
		}
		if len(rangeIntervals) == 0 {
			printCodepoint(i, description)
		}
		for _, r := range rangeIntervals {
			if r.contains(i) {
				printCodepoint(i, description)
				break
			}
		}
	}
}