use integers to calculate formulas for beancount amount formula

pkg/converters/beancount/beancount_amount_expression_evaluator.go

@@ -1,15 +1,20 @@
 package beancount
 
 import (
-	"fmt"
-	"strconv"
+	"math/big"
 	"strings"
 
 	"github.com/mayswind/ezbookkeeping/pkg/core"
 	"github.com/mayswind/ezbookkeeping/pkg/errs"
 	"github.com/mayswind/ezbookkeeping/pkg/log"
+	"github.com/mayswind/ezbookkeeping/pkg/utils"
 )
 
+const maxAllowedDecimalCount = 6
+const normalizeFactor = int64(1000000)
+const normalizedDecimalsMaxZeroString = "000000"
+const normalizedNumberToAmountFactor = int64(10000) // 1000000 / 100
+
 var operatorPriority = map[rune]int{
 	'+': 1,
 	'-': 1,
@@ -17,6 +22,44 @@ var operatorPriority = map[rune]int{
 	'/': 2,
 }
 
+func normalizeNumber(textualNumber string) (*big.Int, error) {
+	decimalSeparatorPos := strings.Index(textualNumber, ".")
+
+	if decimalSeparatorPos < 0 {
+		result := big.NewInt(0)
+		_, ok := result.SetString(textualNumber+normalizedDecimalsMaxZeroString, 10)
+
+		if !ok {
+			return nil, errs.ErrAmountInvalid
+		}
+
+		return result, nil
+	}
+
+	integer := utils.SubString(textualNumber, 0, decimalSeparatorPos)
+	decimals := utils.SubString(textualNumber, decimalSeparatorPos+1, len(textualNumber))
+
+	if len(decimals) > maxAllowedDecimalCount {
+		return nil, errs.ErrAmountInvalid
+	}
+
+	paddedDecimals := utils.SubString(decimals+normalizedDecimalsMaxZeroString, 0, maxAllowedDecimalCount)
+	result := big.NewInt(0)
+	_, ok := result.SetString(integer+paddedDecimals, 10)
+
+	if !ok {
+		return nil, errs.ErrAmountInvalid
+	}
+
+	return result, nil
+}
+
+func denormalizeNumberToTextualAmount(num *big.Int) string {
+	result := big.NewInt(0).Add(num, big.NewInt(0)) // make a copy of num
+	result = result.Div(result, big.NewInt(normalizedNumberToAmountFactor))
+	return utils.FormatAmount(result.Int64())
+}
+
 func toPostfixExprTokens(ctx core.Context, expr string) ([]string, error) {
 	finalTokens := make([]string, 0)
 	operatorStack := make([]rune, 0)
@@ -117,8 +160,8 @@ func toPostfixExprTokens(ctx core.Context, expr string) ([]string, error) {
 	return finalTokens, nil
 }
 
-func evaluatePostfixExpr(ctx core.Context, tokens []string) (float64, error) {
-	stack := make([]float64, 0)
+func evaluatePostfixExpr(ctx core.Context, tokens []string) (*big.Int, error) {
+	stack := make([]*big.Int, 0)
 
 	for i := 0; i < len(tokens); i++ {
 		token := tokens[i]
@@ -127,7 +170,7 @@ func evaluatePostfixExpr(ctx core.Context, tokens []string) (float64, error) {
 		case "+", "-", "*", "/": // operators
 			if len(stack) < 2 {
 				log.Warnf(ctx, "[beancount_amount_expression_evaluator.evaluatePostfixExpr] cannot evaluate expression \"%s\", because not enough operands", strings.Join(tokens, " "))
-				return 0, errs.ErrInvalidAmountExpression
+				return nil, errs.ErrInvalidAmountExpression
 			}
 
 			// pop the top two operands
@@ -138,39 +181,41 @@ func evaluatePostfixExpr(ctx core.Context, tokens []string) (float64, error) {
 			stack = stack[:len(stack)-1]
 
 			// evaluate the operation
-			var result float64
+			result := big.NewInt(0)
 			switch token {
 			case "+":
-				result = a + b
+				result.Add(a, b)
 			case "-":
-				result = a - b
+				result.Sub(a, b)
 			case "*":
-				result = a * b
+				result.Mul(a, b)
+				result.Div(result, big.NewInt(normalizeFactor))
 			case "/":
-				if b == 0 {
+				if b.Int64() == 0 {
 					log.Warnf(ctx, "[beancount_amount_expression_evaluator.evaluatePostfixExpr] cannot evaluate expression \"%s\", because division by zero", strings.Join(tokens, " "))
-					return 0, errs.ErrInvalidAmountExpression
+					return nil, errs.ErrInvalidAmountExpression
 				}
-				result = a / b
+				result.Mul(a, big.NewInt(normalizeFactor))
+				result.Div(result, b)
 			}
 
 			// push the result back to the stack
 			stack = append(stack, result)
 		default: // operands
-			num, err := strconv.ParseFloat(token, 64)
+			normalizedNum, err := normalizeNumber(token)
 
 			if err != nil {
 				log.Warnf(ctx, "[beancount_amount_expression_evaluator.evaluatePostfixExpr] cannot evaluate expression \"%s\", because containing invalid number", strings.Join(tokens, " "))
-				return 0, errs.ErrInvalidAmountExpression
+				return nil, errs.ErrInvalidAmountExpression
 			}
 
-			stack = append(stack, num)
+			stack = append(stack, normalizedNum)
 		}
 	}
 
 	if len(stack) != 1 {
 		log.Warnf(ctx, "[beancount_amount_expression_evaluator.evaluatePostfixExpr] cannot evaluate expression \"%s\", because missing operator", strings.Join(tokens, " "))
-		return 0, errs.ErrInvalidAmountExpression
+		return nil, errs.ErrInvalidAmountExpression
 	}
 
 	return stack[0], nil
@@ -193,5 +238,5 @@ func evaluateBeancountAmountExpression(ctx core.Context, expr string) (string, e
 		return "", err
 	}
 
-	return fmt.Sprintf("%.2f", result), nil
+	return denormalizeNumberToTextualAmount(result), nil
 }