add: packaged log parser for methods

x-tba/2-methods/xxx-log-parser-methods/packaged/metrics/parser.go

@@ -0,0 +1,52 @@
+// 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 metrics
+
+import (
+	"fmt"
+)
+
+// Parser keep tracks of the parsing
+type Parser struct {
+	lines int   // number of parsed lines (for the error messages)
+	lerr  error // the last error occurred
+}
+
+// Parsed wraps a result for generating parser error
+type Parsed struct {
+	result       // use struct embedding
+	err    error // inject an error
+}
+
+// NewParser returns a new parser
+func NewParser() *Parser {
+	return new(Parser)
+}
+
+// Parse parses a log line and returns a result with an injected error
+func (l *Parser) Parse(line string) (parsed Parsed) {
+	// always set the error
+	defer func() { parsed.err = l.lerr }()
+
+	// if there was an error do not continue
+	if l.lerr != nil {
+		return
+	}
+
+	// chain the parser's error to the result's
+	res, err := parse(line)
+	if l.lines++; err != nil {
+		l.lerr = fmt.Errorf("%s: (line #%d)", err, l.lines)
+	}
+	return Parsed{result: res}
+}
+
+// Err returns the last error encountered
+func (l *Parser) Err() error {
+	return l.lerr
+}