move: log parser

interfaces/log-parser/01-methods/parser.go

@@ -0,0 +1,100 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+// result stores details about a log line
+type result struct {
+	domain string
+	visits int
+	// add more metrics when 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)
+	lerr    error             // the last error occurred
+}
+
+// newParser creates and returns a new parser
+func newParser() *parser {
+	return &parser{sum: make(map[string]result)}
+}
+
+// parse result from a log line
+func (p *parser) parse(line string) (r result) {
+	if p.lerr != nil {
+		return
+	}
+
+	p.lines++
+
+	fields := strings.Fields(line)
+	if len(fields) != 2 {
+		p.lerr = fmt.Errorf("wrong input: %v (line #%d)", fields, p.lines)
+		return
+	}
+
+	var err error
+
+	r.domain = fields[0]
+	r.visits, err = strconv.Atoi(fields[1])
+
+	if r.visits < 0 || err != nil {
+		p.lerr = fmt.Errorf("wrong input: %q (line #%d)", fields[1], p.lines)
+	}
+	return
+}
+
+// update the parsing results
+func (p *parser) update(r result) {
+	if p.lerr != nil {
+		return
+	}
+
+	// collect unique domains for easy access to sum map
+	if _, ok := p.sum[r.domain]; !ok {
+		p.domains = append(p.domains, r.domain)
+	}
+
+	// keep track of total visits
+	p.total += r.visits
+
+	// group the log lines by domain
+	p.sum[r.domain] = result{
+		domain: r.domain,
+		visits: r.visits + p.sum[r.domain].visits,
+	}
+}
+
+// summarize the parsing results
+func (p *parser) summarize() {
+	sort.Strings(p.domains)
+
+	fmt.Printf("%-30s %10s\n", "DOMAIN", "VISITS")
+	fmt.Println(strings.Repeat("-", 45))
+
+	for _, domain := range p.domains {
+		fmt.Printf("%-30s %10d\n", domain, p.sum[domain].visits)
+	}
+	fmt.Printf("\n%-30s %10d\n", "TOTAL", p.total)
+}
+
+// err returns the last error encountered
+func (p *parser) err() error {
+	return p.lerr
+}