// Package synch ports the bank-sync deduplication helper from
// scripts/sync_fio_to_sheets.py.
package synch

import (
	"crypto/sha256"
	"encoding/hex"
	"math"
	"strconv"
	"strings"
)

// Transaction is the projection of a Fio transaction that participates
// in the Sync ID hash. Other fields (ks, ss, sender_account, …) are
// intentionally excluded — they are not part of the Python hash.
//
// Currency: leave "" to inherit the Python default of "CZK" (matches
// the HTML scraper path which omits the key entirely).
type Transaction struct {
	Date     string
	Amount   float64
	Currency string
	Sender   string
	VS       string
	Message  string
	BankID   string
}

// GenerateSyncID returns the lowercase SHA-256 hex digest of
// "date|amount|currency|sender|vs|message|bank_id" (lower-cased), used
// as the dedup key in column K of the payments sheet.
//
// Byte-stable with scripts/sync_fio_to_sheets.py generate_sync_id.
func GenerateSyncID(tx Transaction) string {
	currency := tx.Currency
	if currency == "" {
		currency = "CZK"
	}
	raw := strings.ToLower(strings.Join([]string{
		tx.Date,
		formatAmount(tx.Amount),
		currency,
		tx.Sender,
		tx.VS,
		tx.Message,
		tx.BankID,
	}, "|"))
	sum := sha256.Sum256([]byte(raw))
	return hex.EncodeToString(sum[:])
}

// formatAmount mimics Python's str(float) for Fio transaction amounts.
// Python uses decimal notation for abs(f) in [1e-4, 1e16) and scientific
// notation outside that range, always adding ".0" to whole-valued decimals.
func formatAmount(f float64) string {
	abs := math.Abs(f)
	if abs != 0 && (abs < 1e-4 || abs >= 1e16) {
		return strconv.FormatFloat(f, 'e', -1, 64)
	}
	s := strconv.FormatFloat(f, 'f', -1, 64)
	if !strings.ContainsRune(s, '.') {
		s += ".0"
	}
	return s
}