wip modernize code base

vendor/github.com/kelseyhightower/envconfig/usage.go

@@ -0,0 +1,164 @@
+// Copyright (c) 2016 Kelsey Hightower and others. All rights reserved.
+// Use of this source code is governed by the MIT License that can be found in
+// the LICENSE file.
+
+package envconfig
+
+import (
+	"encoding"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strconv"
+	"strings"
+	"text/tabwriter"
+	"text/template"
+)
+
+const (
+	// DefaultListFormat constant to use to display usage in a list format
+	DefaultListFormat = `This application is configured via the environment. The following environment
+variables can be used:
+{{range .}}
+{{usage_key .}}
+  [description] {{usage_description .}}
+  [type]        {{usage_type .}}
+  [default]     {{usage_default .}}
+  [required]    {{usage_required .}}{{end}}
+`
+	// DefaultTableFormat constant to use to display usage in a tabular format
+	DefaultTableFormat = `This application is configured via the environment. The following environment
+variables can be used:
+
+KEY	TYPE	DEFAULT	REQUIRED	DESCRIPTION
+{{range .}}{{usage_key .}}	{{usage_type .}}	{{usage_default .}}	{{usage_required .}}	{{usage_description .}}
+{{end}}`
+)
+
+var (
+	decoderType           = reflect.TypeOf((*Decoder)(nil)).Elem()
+	setterType            = reflect.TypeOf((*Setter)(nil)).Elem()
+	textUnmarshalerType   = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
+	binaryUnmarshalerType = reflect.TypeOf((*encoding.BinaryUnmarshaler)(nil)).Elem()
+)
+
+func implementsInterface(t reflect.Type) bool {
+	return t.Implements(decoderType) ||
+		reflect.PtrTo(t).Implements(decoderType) ||
+		t.Implements(setterType) ||
+		reflect.PtrTo(t).Implements(setterType) ||
+		t.Implements(textUnmarshalerType) ||
+		reflect.PtrTo(t).Implements(textUnmarshalerType) ||
+		t.Implements(binaryUnmarshalerType) ||
+		reflect.PtrTo(t).Implements(binaryUnmarshalerType)
+}
+
+// toTypeDescription converts Go types into a human readable description
+func toTypeDescription(t reflect.Type) string {
+	switch t.Kind() {
+	case reflect.Array, reflect.Slice:
+		if t.Elem().Kind() == reflect.Uint8 {
+			return "String"
+		}
+		return fmt.Sprintf("Comma-separated list of %s", toTypeDescription(t.Elem()))
+	case reflect.Map:
+		return fmt.Sprintf(
+			"Comma-separated list of %s:%s pairs",
+			toTypeDescription(t.Key()),
+			toTypeDescription(t.Elem()),
+		)
+	case reflect.Ptr:
+		return toTypeDescription(t.Elem())
+	case reflect.Struct:
+		if implementsInterface(t) && t.Name() != "" {
+			return t.Name()
+		}
+		return ""
+	case reflect.String:
+		name := t.Name()
+		if name != "" && name != "string" {
+			return name
+		}
+		return "String"
+	case reflect.Bool:
+		name := t.Name()
+		if name != "" && name != "bool" {
+			return name
+		}
+		return "True or False"
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		name := t.Name()
+		if name != "" && !strings.HasPrefix(name, "int") {
+			return name
+		}
+		return "Integer"
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		name := t.Name()
+		if name != "" && !strings.HasPrefix(name, "uint") {
+			return name
+		}
+		return "Unsigned Integer"
+	case reflect.Float32, reflect.Float64:
+		name := t.Name()
+		if name != "" && !strings.HasPrefix(name, "float") {
+			return name
+		}
+		return "Float"
+	}
+	return fmt.Sprintf("%+v", t)
+}
+
+// Usage writes usage information to stdout using the default header and table format
+func Usage(prefix string, spec interface{}) error {
+	// The default is to output the usage information as a table
+	// Create tabwriter instance to support table output
+	tabs := tabwriter.NewWriter(os.Stdout, 1, 0, 4, ' ', 0)
+
+	err := Usagef(prefix, spec, tabs, DefaultTableFormat)
+	tabs.Flush()
+	return err
+}
+
+// Usagef writes usage information to the specified io.Writer using the specifed template specification
+func Usagef(prefix string, spec interface{}, out io.Writer, format string) error {
+
+	// Specify the default usage template functions
+	functions := template.FuncMap{
+		"usage_key":         func(v varInfo) string { return v.Key },
+		"usage_description": func(v varInfo) string { return v.Tags.Get("desc") },
+		"usage_type":        func(v varInfo) string { return toTypeDescription(v.Field.Type()) },
+		"usage_default":     func(v varInfo) string { return v.Tags.Get("default") },
+		"usage_required": func(v varInfo) (string, error) {
+			req := v.Tags.Get("required")
+			if req != "" {
+				reqB, err := strconv.ParseBool(req)
+				if err != nil {
+					return "", err
+				}
+				if reqB {
+					req = "true"
+				}
+			}
+			return req, nil
+		},
+	}
+
+	tmpl, err := template.New("envconfig").Funcs(functions).Parse(format)
+	if err != nil {
+		return err
+	}
+
+	return Usaget(prefix, spec, out, tmpl)
+}
+
+// Usaget writes usage information to the specified io.Writer using the specified template
+func Usaget(prefix string, spec interface{}, out io.Writer, tmpl *template.Template) error {
+	// gather first
+	infos, err := gatherInfo(prefix, spec)
+	if err != nil {
+		return err
+	}
+
+	return tmpl.Execute(out, infos)
+}