massive: move a lot of things

25-functions-and-pointers/08x-log-parser-pointers/log.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org 4
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions-and-pointers/08x-log-parser-pointers/log_err_missing.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions-and-pointers/08x-log-parser-pointers/log_err_negative.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org -100
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions-and-pointers/08x-log-parser-pointers/log_err_str.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org FOUR
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions-and-pointers/08x-log-parser-pointers/main.go

@@ -0,0 +1,57 @@
+// 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() {
+	in := bufio.NewScanner(os.Stdin)
+
+	p := newParser()
+	for in.Scan() {
+		// dom, err := parse(p, in.Text())
+		// if err != nil {
+		// 	fmt.Println(err)
+		// 	return
+		// }
+
+		// p = push(p, dom)
+
+		add(p, in.Text())
+	}
+
+	summarize(p)
+	dumpErrs(in.Err(), err(p))
+}
+
+// funcs not always need to be reused.
+// here, it tells about what it does: it summarizes the parsing result.
+func summarize(p *parser) {
+	// multiple iterators can be created. each one remembers the last
+	// read domain record.
+
+	next, cur := iterator(p)
+	for next() {
+		dom := cur()
+		fmt.Printf("%-25s -> %d\n", dom.name, dom.visits)
+	}
+	fmt.Printf("\n%-25s -> %d\n", "TOTAL", p.total)
+}
+
+// this variadic func simplifies the multiple error handling
+func dumpErrs(errs ...error) {
+	for _, err := range errs {
+		if err != nil {
+			fmt.Printf("> Err: %s\n", err)
+		}
+	}
+}

25-functions-and-pointers/08x-log-parser-pointers/parser.go

@@ -0,0 +1,110 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// domain represents a domain log record
+type domain struct {
+	name   string
+	visits int
+}
+
+// parser parses a log file and provides an iterator to iterate upon the domains
+//
+// the parser struct is carefully crafted to be usable using its zero values except the map field
+type parser struct {
+	sum     map[string]domain // visits per unique domain
+	domains []string          // unique domain names
+	total   int               // total visits to all domains
+	lines   int               // number of parsed lines (for the error messages)
+	lerr    error             // saves the last error occurred
+}
+
+// newParser creates and returns a new parser.
+func newParser() *parser {
+	return &parser{sum: make(map[string]domain)}
+}
+
+// add parses the given line and saves the result to the internal list of
+// domains. it doesn't add the record when the parsing fails.
+func add(p *parser, line string) {
+	// if there was a previous error do not add
+	if p.lerr != nil {
+		return
+	}
+
+	dom, err := parse(p, line)
+
+	// store only the last error
+	if err != nil {
+		p.lerr = err
+		return
+	}
+
+	push(p, dom)
+}
+
+// iterator returns two functions for iterating over domains.
+// next = returns true when there are more domains to iterate on.
+// cur  = returns the current domain
+func iterator(p *parser) (next func() bool, cur func() domain) {
+	// remember the last received line
+	var last int
+
+	next = func() bool {
+		defer func() { last++ }()
+		return len(p.domains) > last
+	}
+
+	cur = func() domain {
+		// return a copy so the caller cannot change it
+		name := p.domains[last-1]
+		return p.sum[name]
+	}
+
+	return
+}
+
+// error returns the last error occurred
+func err(p *parser) error {
+	return p.lerr
+}
+
+// parse parses the given text and returns a domain struct
+func parse(p *parser, line string) (dom domain, err error) {
+	p.lines++ // increase the parsed line counter (only write is here)
+
+	fields := strings.Fields(line)
+	if len(fields) != 2 {
+		err = fmt.Errorf("wrong input: %v (line #%d)", fields, p.lines)
+		return
+	}
+
+	name, visits := fields[0], fields[1]
+
+	n, err := strconv.Atoi(visits)
+	if n < 0 || err != nil {
+		err = fmt.Errorf("wrong input: %q (line #%d)", visits, p.lines)
+		return
+	}
+
+	return domain{name: name, visits: n}, nil
+}
+
+// push pushes the given domain to the internal list of domains.
+// it also increases the total visits for all the domains.
+func push(p *parser, d domain) {
+	name := d.name
+
+	// collect the unique domains
+	if _, ok := p.sum[name]; !ok {
+		p.domains = append(p.domains, name)
+	}
+
+	p.total += d.visits
+	d.visits += p.sum[name].visits
+	p.sum[name] = d
+}