interfaces: refactor

interfaces/05-log-parser/functional/pipeline.go

@@ -0,0 +1,78 @@
+// 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 "os"
+
+type (
+	processFn func(r result)
+	inputFn   func(processFn) error
+	outputFn  func([]result) error
+	filterFn  func(result) (include bool)
+	groupFn   func(result) (key string)
+)
+
+type pipeline struct {
+	read   inputFn
+	write  outputFn
+	filter filterFn
+	group  groupFn
+}
+
+func (p *pipeline) filterBy(f filterFn) *pipeline { p.filter = f; return p }
+func (p *pipeline) groupBy(f groupFn) *pipeline   { p.group = f; return p }
+func (p *pipeline) from(f inputFn) *pipeline      { p.read = f; return p }
+func (p *pipeline) to(f outputFn) *pipeline       { p.write = f; return p }
+
+func (p *pipeline) defaults() {
+	if p.filter == nil {
+		p.filter = noopFilter
+	}
+
+	if p.group == nil {
+		p.group = domainGrouper
+	}
+
+	if p.read == nil {
+		p.read = textReader(os.Stdin)
+	}
+
+	if p.write == nil {
+		p.write = textWriter(os.Stdout)
+	}
+}
+
+func (p *pipeline) start() error {
+	p.defaults()
+
+	// retrieve and process the lines
+	sum := make(map[string]result)
+
+	process := func(r result) {
+		if !p.filter(r) {
+			return
+		}
+
+		k := p.group(r)
+		sum[k] = r.add(sum[k])
+	}
+
+	// return err from input reader
+	if err := p.read(process); err != nil {
+		return err
+	}
+
+	// prepare the results for outputting
+	var out []result
+	for _, res := range sum {
+		out = append(out, res)
+	}
+
+	// return err from output reader
+	return p.write(out)
+}