From 562e6633b31ef3aaf75806322bfff45c1d7eebdc Mon Sep 17 00:00:00 2001
From: Konstantin Grachev <me@grachevko.ru>
Date: Thu, 15 Feb 2024 19:02:01 +0300
Subject: [PATCH] merge-channel: init

---
 merge-channel/Makefile     | 53 ++++++++++++++++++++++++++++++++++++++
 merge-channel/go.mod       | 11 ++++++++
 merge-channel/go.sum       | 10 +++++++
 merge-channel/main.go      | 38 +++++++++++++++++++++++++++
 merge-channel/main_test.go | 36 ++++++++++++++++++++++++++
 5 files changed, 148 insertions(+)
 create mode 100644 merge-channel/Makefile
 create mode 100644 merge-channel/go.mod
 create mode 100644 merge-channel/go.sum
 create mode 100644 merge-channel/main.go
 create mode 100644 merge-channel/main_test.go

diff --git a/merge-channel/Makefile b/merge-channel/Makefile
new file mode 100644
index 0000000..977c1c9
--- /dev/null
+++ b/merge-channel/Makefile
@@ -0,0 +1,53 @@
+.DEFAULT_GOAL := help
+
+# ==================================================================================== #
+# HELPERS
+# ==================================================================================== #
+
+## help: print this help message
+.PHONY: help
+help:
+	@echo 'Usage:'
+	@sed -n 's/^##//p' ${MAKEFILE_LIST} | column -t -s ':' |  sed -e 's/^/ /'
+
+## all: tidy + audit + test/cover
+all: generate tidy test lint test/cover
+
+
+# ==================================================================================== #
+# QUALITY CONTROL
+# ==================================================================================== #
+
+## tidy: format code and tidy modfile
+.PHONY: tidy
+tidy:
+	go fmt ./...
+	goimports -local=$(shell cat go.mod | grep module | awk '{print $$2}')/ -w .
+	go mod tidy -v
+
+## audit: run quality control checks
+.PHONY: lint
+lint:
+	go mod verify
+	go run github.com/golangci/golangci-lint/cmd/golangci-lint@latest run -v ./...
+
+
+# ==================================================================================== #
+# DEVELOPMENT
+# ==================================================================================== #
+
+## generate: run all generators
+.PHONY: generate
+generate:
+	go generate ./...
+
+## test: run all tests
+.PHONY: test
+test:
+	go test -race -buildvcs ./...
+
+## test/cover: run all tests and display coverage
+.PHONY: test/cover
+test/cover:
+	go test -race -buildvcs -coverprofile=/tmp/coverage.out ./...
+	go tool cover -html=/tmp/coverage.out
diff --git a/merge-channel/go.mod b/merge-channel/go.mod
new file mode 100644
index 0000000..3147e31
--- /dev/null
+++ b/merge-channel/go.mod
@@ -0,0 +1,11 @@
+module merge-channel
+
+go 1.21.6
+
+require github.com/stretchr/testify v1.8.4
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
diff --git a/merge-channel/go.sum b/merge-channel/go.sum
new file mode 100644
index 0000000..fa4b6e6
--- /dev/null
+++ b/merge-channel/go.sum
@@ -0,0 +1,10 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
+github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXlSw2iwfAo=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/merge-channel/main.go b/merge-channel/main.go
new file mode 100644
index 0000000..6a581c5
--- /dev/null
+++ b/merge-channel/main.go
@@ -0,0 +1,38 @@
+package main
+
+import (
+	"errors"
+	"sync"
+)
+
+var InsufficientChannelsErr = errors.New("channels count must be >2")
+
+func merge[T any](channels ...<-chan T) (<-chan T, error) {
+	out := make(chan T)
+
+	if len(channels) < 2 {
+		close(out)
+
+		return out, InsufficientChannelsErr
+	}
+
+	var wg sync.WaitGroup
+	wg.Add(len(channels))
+
+	for _, c := range channels {
+		go func(channel <-chan T) {
+			defer wg.Done()
+
+			for v := range channel {
+				out <- v
+			}
+		}(c)
+	}
+
+	go func() {
+		wg.Wait()
+		close(out)
+	}()
+
+	return out, nil
+}
diff --git a/merge-channel/main_test.go b/merge-channel/main_test.go
new file mode 100644
index 0000000..622c4c4
--- /dev/null
+++ b/merge-channel/main_test.go
@@ -0,0 +1,36 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMerge(t *testing.T) {
+	a := make(chan int, 5)
+	b := make(chan int, 5)
+
+	for i := 0; i < 5; i++ {
+		a <- i
+		b <- i
+	}
+
+	merged, err := merge(a, b)
+	assert.Nil(t, err)
+
+	close(a)
+	close(b)
+
+	sum := 0
+	for v := range merged {
+		sum += v
+	}
+	assert.Equal(t, sum, 20)
+}
+
+func TestInsufficient(t *testing.T) {
+	a := make(chan int)
+
+	_, err := merge(a)
+	assert.Equal(t, err, InsufficientChannelsErr)
+}