hsa-app/internal/receipt/receipt.go

// Package receipt holds the receipt domain model and pure validation logic.
package receipt

import (
	"fmt"
	"strings"
	"time"
)

// Receipt is a stored receipt record. Category and Who are referenced by id into
// the categories/people lookup tables (PersonID is nil when "Who" is unset).
type Receipt struct {
	ID               string
	UploadedBy       string
	UploadedAt       time.Time
	ReceiptDate      time.Time
	AmountCents      int64
	CategoryID       int64
	PersonID         *int64
	FilePath         string
	ImageData        []byte
	FileSizeBytes    int64
	OriginalFilename string
	MimeType         string
	DeletedAt        *time.Time
}

// ParseAmountCents parses a positive dollar amount into integer cents without
// using floating point. Accepts an optional leading "$", surrounding spaces, and
// thousands separators. Rejects empty, non-numeric, more than two decimal places,
// zero, and negative values.
func ParseAmountCents(s string) (int64, error) {
	s = strings.TrimSpace(s)
	s = strings.TrimPrefix(s, "$")
	s = strings.ReplaceAll(s, ",", "")
	s = strings.TrimSpace(s)
	if s == "" {
		return 0, fmt.Errorf("empty amount")
	}
	if strings.HasPrefix(s, "-") {
		return 0, fmt.Errorf("amount must be positive")
	}

	whole, frac, hasDot := strings.Cut(s, ".")
	if hasDot && strings.Contains(frac, ".") {
		return 0, fmt.Errorf("invalid amount %q", s)
	}
	if whole == "" && frac == "" {
		return 0, fmt.Errorf("invalid amount %q", s)
	}

	// Normalise the fractional part to exactly two digits.
	switch len(frac) {
	case 0:
		frac = "00"
	case 1:
		frac = frac + "0"
	case 2:
		// ok
	default:
		return 0, fmt.Errorf("amount has more than two decimal places: %q", s)
	}

	var cents int64
	for _, r := range whole + frac {
		if r < '0' || r > '9' {
			return 0, fmt.Errorf("invalid amount %q", s)
		}
		cents = cents*10 + int64(r-'0')
	}
	if cents <= 0 {
		return 0, fmt.Errorf("amount must be greater than zero")
	}
	return cents, nil
}