Adding internal/config/builder.go

internal/config/builder.go

@@ -0,0 +1,102 @@
+package config
+
+import (
+	"errors"
+	"io"
+	"os"
+
+	"github.com/mitchellh/mapstructure"
+	"github.com/spf13/pflag"
+	"github.com/spf13/viper"
+)
+
+// This is a simple module that encapsulate the creation
+// of a config object and can override values from cli flags.
+
+type Builder struct {
+	in    io.Reader
+	flags *pflag.FlagSet
+	binds map[string]string
+}
+
+func NewBuilder() *Builder {
+	return &Builder{
+		binds: map[string]string{},
+	}
+}
+
+// Set the config file to read
+func (b *Builder) SetConfigFile(filename string) *Builder {
+	file, _ := os.Open(filename)
+	return b.SetSource(file)
+}
+
+// Set the source to read
+func (b *Builder) SetSource(in io.Reader) *Builder {
+	b.in = in
+	return b
+}
+
+// Set all flags that the builder should use.
+func (b *Builder) SetFlags(flags *pflag.FlagSet) *Builder {
+	b.flags = flags
+	return b
+}
+
+// Add a flag to the builder.
+func (b *Builder) AddFlag(flag *pflag.Flag) *Builder {
+	b.flags.AddFlag(flag)
+	return b
+}
+
+// Build the config object from file, cli-flags
+func (b *Builder) Build() (*Config, error) {
+	if b.in == nil {
+		return nil, errors.New("Config not set")
+	}
+
+	conf := New()
+
+	v := viper.New()
+	v.SetConfigType("yaml")
+
+	if b.flags != nil {
+		// bind flags in viper.
+		for key, flagname := range b.binds {
+			flag := b.flags.Lookup(flagname)
+			if flag == nil {
+				continue
+			}
+
+			if err := v.BindPFlag(key, flag); err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	// Read config and unmarshal
+	if err := v.ReadConfig(b.in); err != nil {
+		return nil, err
+	}
+
+	decoders := mapstructure.ComposeDecodeHookFunc(
+		mapstructure.TextUnmarshallerHookFunc(),
+		mapstructure.StringToTimeDurationHookFunc(),
+		mapstructure.StringToSliceHookFunc(","),
+		decodeShorthandShipConfig,
+	)
+
+	err := v.Unmarshal(&conf, viper.DecodeHook(decoders))
+	if err != nil {
+		return nil, err
+	}
+
+	// Call custom handler.
+	if b.flags != nil {
+		if err := conf.ReadCliFlags(b.flags); err != nil {
+			return nil, err
+		}
+	}
+
+	return &conf, nil
+}