Adding Custom Parsers

The subscription detector supports multiple bank export formats through a parser interface. You can add support for new formats by implementing a simple interface.

Built-in Parsers

Format	Description
handelsbanken-xlsx	Handelsbanken bank export (XLSX)
simple-json	Simple JSON format

Parser Interface

type Parser interface {
    Parse(filePath string) ([]Transaction, error)
}

type Transaction struct {
    Date   time.Time
    Text   string
    Amount float64
}

Adding a New Parser

1. Create Parser File

Create a new file internal/parser_mybank.go:

package internal

import (
    "encoding/csv"
    "os"
    "strconv"
    "time"
)

type MyBankParser struct{}

func (p *MyBankParser) Parse(filePath string) ([]Transaction, error) {
    file, err := os.Open(filePath)
    if err != nil {
        return nil, err
    }
    defer file.Close()

    reader := csv.NewReader(file)
    records, err := reader.ReadAll()
    if err != nil {
        return nil, err
    }

    var transactions []Transaction
    for i, record := range records {
        if i == 0 {
            continue // Skip header
        }

        date, _ := time.Parse("2006-01-02", record[0])
        amount, _ := strconv.ParseFloat(record[2], 64)

        transactions = append(transactions, Transaction{
            Date:   date,
            Text:   record[1],
            Amount: amount,
        })
    }

    return transactions, nil
}

2. Register the Parser

Add your parser to internal/parser.go:

var parsers = map[string]Parser{
    "handelsbanken-xlsx": &HandelsbankenParser{},
    "simple-json":        &SimpleJSONParser{},
    "mybank-csv":         &MyBankParser{},  // Add this line
}

3. Use Your Parser

./subscription-detector mybank-csv:export.csv

Simple JSON Format

The simple-json format is useful for testing or converting from other formats:

{
  "transactions": [
    {"date": "2025-01-15", "text": "Netflix", "amount": -99.00},
    {"date": "2025-02-15", "text": "Netflix", "amount": -99.00},
    {"date": "2025-03-15", "text": "Netflix", "amount": -99.00}
  ]
}

Handelsbanken Format

The Handelsbanken parser handles their XLSX export format with Swedish column names:

• Reskontradatum - Booking date
• Transaktionsdatum - Transaction date
• Text - Description/payee
• Belopp - Amount
• Saldo - Balance (optional, for credit cards)

Both regular account and credit card exports are supported.