impl and test src.ledger.Files.Amend(old, new Delta)

src/ledger/transaction.go

@@ -3,10 +3,12 @@ package ledger
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
 	"os"
 	"regexp"
+	"slices"
 	"strconv"
 	"unicode"
 )
@@ -112,19 +114,47 @@ func (files Files) _transactions(file string) ([]transaction, error) {
 
 func readTransaction(name string, r *bufio.Reader) (transaction, error) {
 	result, err := _readTransaction(name, r)
-	if err != nil {
+	if err != nil && !errors.Is(err, io.EOF) {
 		return result, err
 	}
 	if result.empty() {
-		return result, nil
-	}
-	if result.payee == "" && len(result.recipients) < 2 {
-		return result, fmt.Errorf("found a transaction with no payee and less than 2 recipeints: %+v", result)
+		return result, err
 	}
 	if result.payee != "" && len(result.recipients) < 1 {
 		return result, fmt.Errorf("found a transaction with payee but no recipeints: %+v", result)
 	}
-	return result, nil
+	if result.payee == "" {
+		if len(result.recipients) < 2 {
+			return result, fmt.Errorf("found a transaction with no payee and less than 2 recipeints: %+v", result)
+		}
+		func() {
+			sumPerRecipient := map[string]float64{}
+			recipients := []string{}
+			for _, recipient := range result.recipients {
+				recipients = append(recipients, recipient.name)
+				sumPerRecipient[recipient.name] += recipient.value
+			}
+			slices.Sort(recipients)
+			for _, k := range recipients {
+				v := sumPerRecipient[k]
+				everyoneElse := 0.0
+				for j := range sumPerRecipient {
+					if k != j {
+						everyoneElse += sumPerRecipient[j]
+					}
+				}
+				if -1.0*v == everyoneElse {
+					result.payee = k
+					result.recipients = slices.DeleteFunc(result.recipients, func(recipient transactionRecipient) bool {
+						return recipient.name == k
+					})
+					return
+				}
+			}
+			return
+		}()
+	}
+	return result, err
 }
 
 func _readTransaction(name string, r *bufio.Reader) (transaction, error) {