interfaces: refactor

interfaces/05-log-parser/refactor-notes/refactor-03-deprecated/changes.md

@@ -0,0 +1,14 @@
+### PROBLEM
++ `parser.go/parse()` also does updating. back to square one.
+  + we need to extract the reusable behavior: scanning.
+
++ inflexible:
+  + adding a filter is hard. needs to change the `scan()` code.
+  + adding a grouper is also hard. domain grouping is hardcoded.
+
+## SOLUTION
++ 
+
+## IDEAS:
+
++ make domain filter accept variadic args

interfaces/05-log-parser/refactor-notes/refactor-03-deprecated/main.go

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+// 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"
+)
+
+/*
+p := pipeline{
+	read:     textReader(os.Stdin),
+	write:    textWriter(os.Stdout),
+	filterBy: notUsing(domainExtFilter("io")),
+	groupBy:  domainGrouper,
+}
+
+if err := start(p); err != nil {
+	fmt.Println("> Err:", err)
+}
+*/
+
+func main() {
+	p := newParser()
+
+	if err := parse(p); err != nil {
+		fmt.Println("> Err:", err)
+		return
+	}
+
+	summarize(p)
+}

interfaces/05-log-parser/refactor-notes/refactor-03-deprecated/parser.go

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+// 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
+
+// parser keeps track of the parsing
+type parser struct {
+	sum     map[string]result // metrics per domain
+	domains []string          // unique domain names
+}
+
+// newParser constructs, initializes and returns a new parser
+func newParser() *parser {
+	return &parser{sum: make(map[string]result)}
+}
+
+// parse all the log lines and update the results
+func parse(p *parser) error {
+	process := func(r result) {
+		update(p, r)
+	}
+
+	err := scan(process)
+
+	return err
+}
+
+func update(p *parser, r result) {
+	// Collect the unique domains
+	if _, ok := p.sum[r.domain]; !ok {
+		p.domains = append(p.domains, r.domain)
+	}
+
+	// create and assign a new copy of `visit`
+	p.sum[r.domain] = addResult(r, p.sum[r.domain])
+}

interfaces/05-log-parser/refactor-notes/refactor-03-deprecated/result.go

@@ -0,0 +1,53 @@
+// 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"
+	"strconv"
+	"strings"
+)
+
+const fieldsLength = 4
+
+// result stores the parsed result for a domain
+type result struct {
+	domain, page    string
+	visits, uniques int
+	// add more metrics if needed
+}
+
+// parseResult from a log line
+func parseResult(line string) (r result, err error) {
+	fields := strings.Fields(line)
+	if len(fields) != fieldsLength {
+		return r, fmt.Errorf("wrong input: %v", fields)
+	}
+
+	r.domain = fields[0]
+	r.page = fields[1]
+
+	r.visits, err = strconv.Atoi(fields[2])
+	if err != nil || r.visits < 0 {
+		return r, fmt.Errorf("wrong input: %q", fields[2])
+	}
+
+	r.uniques, err = strconv.Atoi(fields[3])
+	if err != nil || r.uniques < 0 {
+		return r, fmt.Errorf("wrong input: %q", fields[3])
+	}
+
+	return r, nil
+}
+
+// addResult to another one
+func addResult(r, other result) result {
+	r.visits += other.visits
+	r.uniques += other.uniques
+	return r
+}

interfaces/05-log-parser/refactor-notes/refactor-03-deprecated/scanner.go

@@ -0,0 +1,35 @@
+// 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 (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+type processFn func(r result)
+
+func scan(process processFn) error {
+	var (
+		l  = 1
+		in = bufio.NewScanner(os.Stdin)
+	)
+
+	for in.Scan() {
+		r, err := parseResult(in.Text())
+		if err != nil {
+			return fmt.Errorf("line %d: %v", l, err)
+		}
+
+		l++
+
+		process(r)
+	}
+	return in.Err()
+}

interfaces/05-log-parser/refactor-notes/refactor-03-deprecated/summarize.go

@@ -0,0 +1,48 @@
+// 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"
+	"strings"
+)
+
+// summarize summarizes and prints the parsing result
+// + violation: accesses the parsing internals: p.domains + p.sum + p.total
+// + give it the []result only.
+// + let it calculate the total.
+const (
+
+	//          DOMAINS PAGES VISITS UNIQUES
+	//             ^      ^     ^    ^
+	//             |      |     |    |
+	header     = "%-25s %-10s %10s %10s\n"
+	line       = "%-25s %-10s %10d %10d\n"
+	footer     = "\n%-36s %10d %10d\n" // -> "" VISITS UNIQUES
+	dash       = "-"
+	dashLength = 58
+)
+
+// summarize summarizes and prints the parsing result
+func summarize(p *parser) {
+	sort.Strings(p.domains)
+
+	fmt.Printf(header, "DOMAIN", "PAGES", "VISITS", "UNIQUES")
+	fmt.Println(strings.Repeat("-", dashLength))
+
+	var total result
+
+	for _, domain := range p.domains {
+		r := p.sum[domain]
+		total = addResult(total, r)
+
+		fmt.Printf(line, r.domain, r.page, r.visits, r.uniques)
+	}
+	fmt.Printf(footer, "TOTAL", total.visits, total.uniques)
+}