package main

import (
	"fmt"
	"regexp"
	"strconv"
	"strings"
	"time"

	"git.gensokyo.cafe/kkyy/mycurrencynet"
	"github.com/dustin/go-humanize"
	"github.com/go-errors/errors"
	"github.com/samber/lo"
	tele "gopkg.in/telebot.v3"
)

var exchangeRates = mycurrencynet.New()

func initExchangeRates() {
	if err := exchangeRates.Update(); err != nil {
		logger.Panicw("Failed to update exchange rates", "err", err)
	}
	logger.Info("Exchange rates updated")

	go exchangeRates.UpdateEvery(
		time.Hour,
		func(err error) {
			logger.Errorw("Failed to update exchange rates", "err", err)
		},
		func() {
			logger.Info("Exchange rates updated")
		},
	)
}

func handleExchangeRateCmd(c tele.Context) error {
	msg := c.Message()
	if msg == nil {
		return nil
	}

	if msg.Payload == "" {
		return c.Reply("Usage: `/xr <currency> [<currency> ...] [to] <currency>`",
			&tele.SendOptions{ParseMode: tele.ModeMarkdown},
			tele.Silent,
		)
	}

	from, to, err := parseXrRequest(msg.Payload)
	if err != nil {
		return c.Reply(err.Error(), tele.Silent)
	}
	codes := append([]string{to.Code}, lo.Map(from, func(i xrCurrency, _ int) string { return i.Code })...)
	currencies, err := exchangeRates.Get(codes...)
	if err != nil {
		return c.Reply(err.Error(), tele.Silent)
	}
	toCur := currencies[0]

	// format reply
	var replyLines []string
	for i, fromItem := range from {
		fromCur := currencies[i+1]
		replyLines = append(replyLines, fmtXrPair(fromCur, toCur, fromItem.Amount))
	}

	return c.Reply(strings.Join(replyLines, "\n"), &tele.SendOptions{ParseMode: tele.ModeMarkdown}, tele.Silent)
}

type xrCurrency struct {
	Code   string
	Amount float64
}

func parseXrRequest(input string) (from []xrCurrency, to xrCurrency, err error) {
	args := strings.Fields(input)

	var tmpTo *xrCurrency = nil
	fillFrom := true

	c := xrCurrency{Amount: -1}
	for _, arg := range args {
		arg = strings.ToUpper(arg)

		switch {
		case arg == "TO":
			fillFrom = false
			continue

		case fillFrom:
			num, sym, tErr := parseXrToken(arg)
			if tErr != nil {
				err = tErr
				return
			}
			if num != -1 {
				if c.Amount != -1 {
					err = errors.New("invalid input")
					return
				}
				c.Amount = num
			}
			if c.Amount == -1 {
				c.Amount = 1
			}

			if sym != "" {
				c.Code = sym
				from = append(from, c)
				c = xrCurrency{Amount: -1}
			}

		case !fillFrom:
			if tmpTo != nil {
				err = errors.New("invalid input")
				return
			}
			tmpTo = &xrCurrency{Code: arg}

		default:
			err = errors.New("invalid input")
			return
		}
	}

	if len(from) < 1 || len(from) > 10 {
		err = errors.New("invalid input")
		return
	}

	if fillFrom {
		if len(from) < 2 {
			err = errors.New("invalid input")
			return
		}
		tmpTo = &from[len(from)-1]
		from = from[:len(from)-1]
	}

	if tmpTo == nil {
		err = errors.New("invalid input")
		return
	}
	to = *tmpTo

	return
}

var xrTokenRe = regexp.MustCompile(`^([0-9.]+)?([A-Z]{3,})?$`)

func parseXrToken(token string) (num float64, sym string, err error) {
	num = -1
	matches := xrTokenRe.FindStringSubmatch(token)
	if len(matches) != 3 {
		err = errors.New("invalid input")
		return
	}

	if matches[1] != "" {
		num, err = strconv.ParseFloat(matches[1], 64)
		if err != nil {
			return
		}
		if num <= 0 {
			err = errors.New("invalid input: amount must be positive")
			return
		}
	}

	sym = matches[2]
	if num == 0 && sym == "" {
		err = errors.New("invalid input")
	}
	return
}

func fmtXrPair(from, to *mycurrencynet.Currency, amount float64) string {
	rate := from.To(to) * amount
	fromInfo := fmt.Sprintf("%s (%s)", from.Name, from.Code)
	toInfo := fmt.Sprintf("%s (%s)", to.Name, to.Code)

	return fmt.Sprintf("*%s* %s\n= *%s* %s\n", fmtXrFloat(amount), fromInfo, fmtXrFloat(rate), toInfo)
}

func fmtXrFloat(num float64) string {
	if num < 100 {
		return fmt.Sprintf("%.4g", num)
	}
	return humanize.CommafWithDigits(num, 2)
}