Initial Commit

2 files changed, 205 insertions, 0 deletions

diff --git a/backend/internal/utils/money.go b/backend/internal/utils/money.go
new file mode 100644
index 0000000..2dc2286
--- /dev/null
+++ b/backend/internal/utils/money.go
@@ -0,0 +1,99 @@
+package utils
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/Rhymond/go-money"
+)
+
+// supported currencies
+var currencies = money.Currencies{
+	"USD": money.GetCurrency(money.USD),
+	"EUR": money.GetCurrency(money.EUR),
+	"GBP": money.GetCurrency(money.GBP),
+	"JPY": money.GetCurrency(money.JPY),
+	"CNY": money.GetCurrency(money.CNY),
+}
+
+func ParseMoney(s string) (*money.Money, error) {
+	for _, c := range currencies {
+		numPart, ok := isCurrency(s, c)
+		if !ok {
+			continue
+		}
+
+		// Parse the number part
+		num, err := strconv.ParseUint(numPart, 10, 64)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse number: %w", err)
+		}
+
+		return money.New(int64(num), c.Code), nil
+	}
+	return nil, fmt.Errorf("matching currency not found")
+}
+
+func isCurrency(s string, c *money.Currency) (string, bool) {
+	var numPart string
+	for _, tp := range c.Template {
+		switch tp {
+		case '$':
+			// There should be a matching grapheme in the s at this position
+			remaining, ok := strings.CutPrefix(s, c.Grapheme)
+			if !ok {
+				return "", false
+			}
+			s = remaining
+		case '1':
+			// There should be a number, thousands, or decimal separator in the s at this position
+			// Number of expected decimal places
+			decimalFound := -1
+			// Read from string until a non-number, non-thousands, non-decimal, or EOF is found
+			for len(s) > 0 && (string(s[0]) == c.Thousand || string(s[0]) == c.Decimal || '0' <= s[0] && s[0] <= '9') {
+				// If the character is a number
+				if '0' <= s[0] && s[0] <= '9' {
+					// If we've hit decimal limit, break
+					if decimalFound == 0 {
+						break
+					}
+					// add the number to the numPart
+					numPart += string(s[0])
+					// Decrement the decimal count
+					// If the decimal has been found, `decimalFound` is positive
+					// If the decimal hasn't been found, `decimalFound` is negative, and decrementing it does nothing
+					decimalFound--
+				}
+				// If decimal has been found (>= 0) and the character is a thousand separator or decimal separator,
+				// then the number is invalid
+				if decimalFound >= 0 && (string(s[0]) == c.Thousand || string(s[0]) == c.Decimal) {
+					return "", false
+				}
+				// If the character is a decimal separator, set `decimalFound` to the number of
+				// expected decimal places for the currency
+				if string(s[0]) == c.Decimal {
+					decimalFound = c.Fraction
+				}
+				// Move to the next character
+				s = s[1:]
+			}
+			if decimalFound > 0 {
+				// If there should be more decimal places, add them
+				numPart += strings.Repeat("0", decimalFound)
+			} else if decimalFound < 0 {
+				// If no decimal was found, add the expected number of decimal places
+				numPart += strings.Repeat("0", c.Fraction)
+			}
+		case ' ':
+			// There should be a space in the s at this position
+			if len(s) == 0 || s[0] != ' ' {
+				return "", false
+			}
+			s = s[1:]
+		default:
+			panic(fmt.Sprintf("unsupported template character: %c", tp))
+		}
+	}
+	return numPart, true
+}
diff --git a/backend/internal/utils/money_test.go b/backend/internal/utils/money_test.go
new file mode 100644
index 0000000..27ace06
--- /dev/null
+++ b/backend/internal/utils/money_test.go
@@ -0,0 +1,106 @@
+package utils
+
+import (
+	"testing"
+
+	"github.com/Rhymond/go-money"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestParseMoney(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  *money.Money
+	}{
+		{
+			name:  "en-US int no comma",
+			input: "$123",
+			want:  money.New(12300, money.USD),
+		},
+		{
+			name:  "en-US int comma",
+			input: "$1,123",
+			want:  money.New(112300, money.USD),
+		},
+		{
+			name:  "en-US decimal comma",
+			input: "$1,123.45",
+			want:  money.New(112345, money.USD),
+		},
+		{
+			name:  "zh-CN decimal comma",
+			input: "1,234.56 \u5143",
+			want:  money.New(123456, money.CNY),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m, err := ParseMoney(tt.input)
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, m)
+		})
+	}
+}
+
+func Test_isCurrency(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		currency string
+		numPart  string
+		ok       bool
+	}{
+		{
+			name:     "en-US int no comma",
+			input:    "$123",
+			currency: money.USD,
+			numPart:  "12300",
+			ok:       true,
+		},
+		{
+			name:     "en-US int comma",
+			input:    "$1,123",
+			currency: money.USD,
+			numPart:  "112300",
+			ok:       true,
+		},
+		{
+			name:     "en-US decimal comma",
+			input:    "$1,123.45",
+			currency: money.USD,
+			numPart:  "112345",
+			ok:       true,
+		},
+		{
+			name:     "en-US 1 decimal comma",
+			input:    "$1,123.5",
+			currency: money.USD,
+			numPart:  "112350",
+			ok:       true,
+		},
+		{
+			name:     "en-US no grapheme",
+			input:    "1,234.56",
+			currency: money.USD,
+			numPart:  "",
+			ok:       false,
+		},
+		{
+			name:     "zh-CN decimal comma",
+			input:    "1,234.56 \u5143",
+			currency: money.CNY,
+			numPart:  "123456",
+			ok:       true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			c := money.GetCurrency(tt.currency)
+			numPart, ok := isCurrency(tt.input, c)
+			assert.Equal(t, tt.ok, ok)
+			assert.Equal(t, tt.numPart, numPart)
+		})
+	}
+}