Login light
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/

// See page 311.

// Package storage is part of a hypothetical cloud storage server.
//!+main
package storage

import (
    "fmt"
    "log"
    "net/smtp"
)

var usage = make(map[string]int64)

func bytesInUse(username string) int64 { return usage[username] }

// Email sender configuration.
// NOTE: never put passwords in source code!
const sender = "notifications@example.com"
const password = "correcthorsebatterystaple"
const hostname = "smtp.example.com"

const template = `Warning: you are using %d bytes of storage,
%d%% of your quota.`

func CheckQuota(username string) {
    used := bytesInUse(username)
    const quota = 1000000000 // 1GB
    percent := 100 * used / quota
    if percent < 90 {
        return // OK
    }
    msg := fmt.Sprintf(template, used, percent)
    auth := smtp.PlainAuth("", sender, password, hostname)
    err := smtp.SendMail(hostname+":587", auth, sender,
        []string{username}, []byte(msg))
    if err != nil {
        log.Printf("smtp.SendMail(%s) failed: %s", username, err)
    }
}

//!-main