learngo/25-functions/exercises/rewrite-log-parser-using-funcs/main.go

// Copyright © 2018 Inanc Gumus
// Learn Go Programming Course
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
//
// For more tutorials  : https://learngoprogramming.com
// In-person training  : https://www.linkedin.com/in/inancgumus/
// Follow me on twitter: https://twitter.com/inancgumus

package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
	"strings"
)

// result stores the parsed result for a domain
type result struct {
	domain string
	visits int
	// add more metrics if needed
}

// parser keep tracks of the parsing
type parser struct {
	sum     map[string]result // metrics per domain
	domains []string          // unique domain names
	total   int               // total visits for all domains
	lines   int               // number of parsed lines (for the error messages)
}

func main() {
	p := parser{sum: make(map[string]result)}

	// Scan the standard-in line by line
	in := bufio.NewScanner(os.Stdin)
	for in.Scan() {
		p.lines++

		// Parse the fields
		fields := strings.Fields(in.Text())
		if len(fields) != 2 {
			fmt.Printf("wrong input: %v (line #%d)\n", fields, p.lines)
			return
		}

		domain := fields[0]

		// Sum the total visits per domain
		visits, err := strconv.Atoi(fields[1])
		if visits < 0 || err != nil {
			fmt.Printf("wrong input: %q (line #%d)\n", fields[1], p.lines)
			return
		}

		// Collect the unique domains
		if _, ok := p.sum[domain]; !ok {
			p.domains = append(p.domains, domain)
		}

		// Keep track of total and per domain visits
		p.total += visits

		// You cannot assign to composite values
		// p.sum[domain].visits += visits

		// create and assign a new copy of `visit`
		p.sum[domain] = result{
			domain: domain,
			visits: visits + p.sum[domain].visits,
		}
	}

	// Print the visits per domain
	sort.Strings(p.domains)

	fmt.Printf("%-30s %10s\n", "DOMAIN", "VISITS")
	fmt.Println(strings.Repeat("-", 45))

	for _, domain := range p.domains {
		parsed := p.sum[domain]
		fmt.Printf("%-30s %10d\n", domain, parsed.visits)
	}

	// Print the total visits for all domains
	fmt.Printf("\n%-30s %10d\n", "TOTAL", p.total)

	// Let's handle the error
	if err := in.Err(); err != nil {
		fmt.Println("> Err:", err)
	}
}