move: funcs and ptrs to root

26-functions-and-pointers/04-pass-by-value-semantics/parser.go

@@ -0,0 +1,59 @@
+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]int // visits per unique domain
+	domains []domain       // unique domain names
+	total   int            // total visits to all domains
+	lines   int            // number of parsed lines (for the error messages)
+}
+
+// newParser creates and returns a new parser.
+func newParser() parser {
+	return parser{sum: make(map[string]int)}
+}
+
+// parse parses the given text and returns a domain struct
+func parse(p parser, line string) (dom domain, err error) {
+	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) parser {
+	if _, ok := p.sum[d.name]; !ok {
+		p.domains = append(p.domains, d)
+	}
+
+	p.sum[d.name] += d.visits
+	p.total += d.visits
+
+	return p
+}