interfaces: refactor

interfaces/05-log-parser/refactor-notes/refactor-00/changes.md

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+## CHANGES
+
+### PROBLEM
++ adding new fields makes the code complex
++ needs to update: `result`, `parser`, `summarizer`
++ needs to add new fields to `parser`: `totalVisits` + `totalUniques`
++ in `parse()`: repeating line errors
+  + if we parsing out of it we'd need to have *parser — superfluous
+
+### SOLUTION
++ move all the result related logic to result.go
+
++ move `parser.go/result` -> `result.go`
+  + move `parser.go/parsing` logic -> `result.go`
+
++ add `addResult` -> `result.go`
+  + remove `parser struct`'s: `totalVisits`, `totalUniques`
+  + change `update()`'s last line: `p.sum[r.domain] = addResult`
+
++ remove `(line #d)` errors from `result.go`
+  + add: `return r, err` — named params are error prone
+  + always check for the error first
+    + `if r.visits < 0 || err != nil` -> `if err != nil || r.visits < 0`
+
++ `parser.go`: check the `parseFields()`:
+    ```golang
+    r, err := parseFields(line)
+    if err != nil {
+        p.lerr = fmt.Errorf("line %d: %v", p.lines, err)
+    }```
+
++ - `parser.go` and `summarize.go`
+  - remove `total int`
+  - let `summarize()` calculate the totals

interfaces/05-log-parser/refactor-notes/refactor-00/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 (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+	p := newParser()
+
+	in := bufio.NewScanner(os.Stdin)
+	for in.Scan() {
+		parsed := parse(p, in.Text())
+		update(p, parsed)
+	}
+
+	summarize(p)
+	dumpErrs([]error{in.Err(), err(p)})
+}
+
+// dumpErrs simplifies handling multiple errors
+func dumpErrs(errs []error) {
+	for _, err := range errs {
+		if err != nil {
+			fmt.Println("> Err:", err)
+		}
+	}
+}

interfaces/05-log-parser/refactor-notes/refactor-00/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
+
+import (
+	"fmt"
+)
+
+// parser keeps track of the parsing
+type parser struct {
+	sum     map[string]result // metrics per domain
+	domains []string          // unique domain names
+	lines   int               // number of parsed lines (for the error messages)
+	lerr    error             // the last error occurred
+
+	// totalVisits  int               // total visits for all domains
+	// totalUniques int               // total uniques for all domains
+}
+
+// newParser constructs, initializes and returns a new parser
+func newParser() *parser {
+	return &parser{sum: make(map[string]result)}
+}
+
+// parse a log line and return the result
+func parse(p *parser, line string) (r result) {
+	if p.lerr != nil {
+		return
+	}
+
+	p.lines++
+
+	r, err := parseResult(line)
+	if err != nil {
+		p.lerr = fmt.Errorf("line %d: %v", p.lines, err)
+	}
+
+	return r
+}
+
+// update the parsing results
+func update(p *parser, r result) {
+	if p.lerr != nil {
+		return
+	}
+
+	// Collect the unique domains
+	cur, ok := p.sum[r.domain]
+	if !ok {
+		p.domains = append(p.domains, r.domain)
+	}
+
+	// Keep track of total and per domain visits
+	// p.totalVisits += r.visits
+	// p.totalUniques += r.uniques
+
+	// create and assign a new copy of `visit`
+	// p.sum[r.domain] = result{
+	// 	domain:  r.domain,
+	// 	visits:  r.visits + cur.visits,
+	// 	uniques: r.uniques + cur.uniques,
+	// }
+	p.sum[r.domain] = addResult(r, cur)
+}
+
+// err returns the last error encountered
+func err(p *parser) error {
+	return p.lerr
+}

interfaces/05-log-parser/refactor-notes/refactor-00/result.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"
+	"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-00/summarize.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"
+	"sort"
+	"strings"
+)
+
+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)
+}