package invoice

import (
	"errors"
	"fmt"
	"strings"
)

// Quantity stores hundredths (e.g. 0.5 => 50).
func ParseQuantity(input string) (Quantity, error) {
	clean := strings.TrimSpace(input)
	if clean == "" {
		return 0, errors.New("empty quantity")
	}
	clean = strings.ReplaceAll(clean, " ", "")
	clean = strings.ReplaceAll(clean, ",", ".")
	if strings.HasPrefix(clean, ".") || strings.HasSuffix(clean, ".") {
		return 0, fmt.Errorf("invalid quantity: %q", input)
	}
	parts := strings.Split(clean, ".")
	if len(parts) > 2 {
		return 0, fmt.Errorf("invalid quantity: %q", input)
	}
	whole := parts[0]
	frac := ""
	if len(parts) == 2 {
		frac = parts[1]
	}
	if whole == "" {
		whole = "0"
	}
	for _, r := range whole {
		if r < '0' || r > '9' {
			return 0, fmt.Errorf("invalid quantity: %q", input)
		}
	}
	for _, r := range frac {
		if r < '0' || r > '9' {
			return 0, fmt.Errorf("invalid quantity: %q", input)
		}
	}
	if len(frac) > 2 {
		return 0, fmt.Errorf("invalid quantity: %q", input)
	}
	for len(frac) < 2 {
		frac += "0"
	}
	var wholeValue int64
	for _, r := range whole {
		wholeValue = wholeValue*10 + int64(r-'0')
	}
	var fracValue int64
	for _, r := range frac {
		fracValue = fracValue*10 + int64(r-'0')
	}
	return Quantity(wholeValue*100 + fracValue), nil
}

func FormatQuantity(q Quantity) string {
	value := int64(q)
	whole := value / 100
	frac := value % 100
	if frac == 0 {
		return fmt.Sprintf("%d", whole)
	}
	if frac%10 == 0 {
		return fmt.Sprintf("%d.%d", whole, frac/10)
	}
	return fmt.Sprintf("%d.%02d", whole, frac)
}