Modularity: module builders generator (prebid#2491)

Makefile

@@ -1,8 +1,8 @@
 # Makefile
 
-all: deps test build
+all: deps test build-modules build
 
-.PHONY: deps test build image
+.PHONY: deps test build-modules build image
 
 # deps will clean out the vendor directory and use go mod for a fresh install
 deps:
@@ -18,6 +18,10 @@ else
 	go test github.com/prebid/prebid-server/adapters/$(adapter) -bench=.
 endif
 
+# build-modules generates modules/builder.go file which provides a list of all available modules
+build-modules:
+	go generate modules/modules.go
+
 # build will ensure all of our tests pass and then build the go binary
 build: test
 	go build -mod=vendor ./...

modules/generator/builder.tmpl

@@ -0,0 +1,21 @@
+package modules
+
+{{if .}}
+import (
+    {{- range .}}
+    {{.Vendor}}{{.Module | Title}} "github.com/prebid/prebid-server/modules/{{.Vendor}}/{{.Module}}"
+    {{- end}}
+)
+{{end}}
+
+// builders returns mapping between module name and its builder
+// vendor and module names are chosen based on the module directory name
+func builders() ModuleBuilders {
+    return ModuleBuilders{
+        {{- range .}}
+        "{{.Vendor}}": {
+            "{{.Module}}": {{.Vendor}}{{.Module | Title}}.Builder,
+        },
+        {{- end}}
+    }
+}

modules/generator/buildergen.go

@@ -0,0 +1,70 @@
+//go:build ignore
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"go/format"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"text/template"
+)
+
+var (
+	r        = regexp.MustCompile("^([^/]+)/([^/]+)/module.go$")
+	tmplName = "builder.tmpl"
+	outName  = "builder.go"
+)
+
+type Module struct {
+	Vendor string
+	Module string
+}
+
+func main() {
+	var modules []Module
+
+	filepath.WalkDir("./", func(path string, d fs.DirEntry, err error) error {
+		if !r.MatchString(path) {
+			return nil
+		}
+		match := r.FindStringSubmatch(path)
+		modules = append(modules, Module{
+			Vendor: match[1],
+			Module: match[2],
+		})
+		return nil
+	})
+
+	funcMap := template.FuncMap{"Title": strings.Title}
+	t, err := template.New(tmplName).Funcs(funcMap).ParseFiles(fmt.Sprintf("generator/%s", tmplName))
+	if err != nil {
+		panic(fmt.Sprintf("failed to parse builder template: %s", err))
+	}
+
+	f, err := os.Create(outName)
+	if err != nil {
+		panic(fmt.Sprintf("failed to create %s file: %s", outName, err))
+	}
+	defer f.Close()
+
+	var buf bytes.Buffer
+	if err = t.Execute(&buf, modules); err != nil {
+		panic(fmt.Sprintf("failed to generate %s file content: %s", outName, err))
+	}
+
+	content, err := format.Source(buf.Bytes())
+	if err != nil {
+		panic(fmt.Sprintf("failed to format generated code: %s", err))
+	}
+
+	if _, err = f.Write(content); err != nil {
+		panic(fmt.Sprintf("failed to write file content: %s", err))
+	}
+
+	fmt.Printf("%s file successfully generated\n", outName)
+}

modules/modules.go

@@ -9,6 +9,8 @@ import (
 	"github.com/prebid/prebid-server/hooks"
 )
 
+//go:generate go run ./generator/buildergen.go
+
 // NewBuilder returns a new module builder.
 func NewBuilder() Builder {
 	return &builder{builders()}