// Accept a floating point number and display it comma-separated
// author: Alessio Treglia <quadrispro@ubuntu.com>
package main

import (
    "bytes"
    "fmt"
    "os"
    "path/filepath"
    "strconv"
    "strings"
)

func comma(s string) (string, error) {
    const places int = 3
    var buf bytes.Buffer
    var offset, startCur, endCur, sLength int

    sLength = len(s)
    endCur = sLength
    if endCur == 0 {
        return s, nil
    }
    if point := strings.Index(s, "."); point != -1 {
        endCur = point
    }
    if sign := s[0]; sign == '+' || sign == '-' {
        buf.WriteByte(sign)
        offset++
        startCur++
        endCur--
    }

    offset += endCur % places

    if offset > startCur {
        if _, err := buf.WriteString(s[startCur:offset]); err != nil {
            return s, err
        }
    }
    for ; offset < endCur; offset += places {
        if offset-startCur != 0 {
            buf.WriteRune(',')
        }
        buf.WriteString(s[offset : offset+places])
    }
    if sLength > endCur+1 {
        buf.WriteString(s[endCur+1 : sLength])
    }

    return buf.String(), nil
}

func main() {
    ProgName := filepath.Base(os.Args[0])
    for _, arg := range os.Args[1:] {
        if _, err := strconv.ParseFloat(arg, 64); err != nil {
            fmt.Fprintf(os.Stderr, "%s: error -- %v\n", ProgName, err)
        } else {
            if sWithCommas, err := comma(arg); err != nil {
                fmt.Fprintf(os.Stderr, "%s: error -- %v\n", ProgName, err)
            } else {
                fmt.Println(sWithCommas)
            }
        }
    }
}