feat: add viper provider for xload (#32)

* feat: add viper provider for xload

* introduce ValueMapper to give more control in public API

* add examples

xload/providers/viper/doc.go

@@ -0,0 +1,2 @@
+// Package viper provides a xload.Loader implementation that uses github.com/spf13/viper.
+package viper

xload/providers/viper/example_test.go

@@ -0,0 +1,91 @@
+package viper_test
+
+import (
+	"context"
+	"fmt"
+
+	vpr "github.com/spf13/viper"
+
+	"github.com/gojekfarm/xtools/xload"
+	"github.com/gojekfarm/xtools/xload/providers/viper"
+)
+
+type Config struct {
+	Log LogConfig `env:",prefix=LOG_"`
+}
+
+type LogConfig struct {
+	Level string `env:"LEVEL"`
+}
+
+func ExampleNew() {
+	v := vpr.New()
+	v.Set("LOG_LEVEL", "debug")
+
+	vl, err := viper.New(viper.From(v))
+	if err != nil {
+		panic(err)
+	}
+
+	cfg := &Config{}
+	if err := xload.Load(context.Background(), cfg, xload.WithLoader(vl)); err != nil {
+		panic(err)
+	}
+
+	fmt.Println(cfg.Log.Level)
+
+	// Output:
+	// debug
+}
+
+func ExampleFrom() {
+	_, err := viper.New(viper.From(vpr.New()))
+	if err != nil {
+		panic(err)
+	}
+}
+
+func ExampleLoader_ConfigFileUsed() {
+	_, err := viper.New(viper.ConfigFile("<path-to-config-file>.ext"))
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Println(vpr.ConfigFileUsed()) // <path-to-config-file>.ext
+}
+
+func ExampleNew_fileOptions() {
+	_, err := viper.New(
+		viper.ConfigName("config"),
+		viper.ConfigType("toml"),
+		viper.ConfigPaths([]string{"./", "/etc/<program/"}),
+	)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func ExampleAutoEnv_disable() {
+	_, err := viper.New(viper.AutoEnv(false))
+	if err != nil {
+		panic(err)
+	}
+}
+
+func ExampleValueMapper() {
+	_, err := viper.New(viper.ValueMapper(func(m map[string]any) map[string]string {
+		return xload.FlattenMap(m, "__")
+	}))
+	if err != nil {
+		panic(err)
+	}
+}
+
+func ExampleTransformer() {
+	_, err := viper.New(viper.Transformer(func(v *vpr.Viper, next xload.Loader) xload.Loader {
+		return xload.PrefixLoader("ENV_", next)
+	}))
+	if err != nil {
+		panic(err)
+	}
+}

xload/providers/viper/go.mod

@@ -0,0 +1,35 @@
+module github.com/gojekfarm/xtools/xload/providers/viper
+
+go 1.21.3
+
+replace github.com/gojekfarm/xtools/xload => ../..
+
+require (
+	github.com/gojekfarm/xtools/xload v0.5.0
+	github.com/spf13/viper v1.18.2
+	github.com/stretchr/testify v1.8.4
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
+	github.com/fsnotify/fsnotify v1.7.0 // indirect
+	github.com/hashicorp/hcl v1.0.0 // indirect
+	github.com/magiconair/properties v1.8.7 // indirect
+	github.com/mitchellh/mapstructure v1.5.0 // indirect
+	github.com/pelletier/go-toml/v2 v2.1.0 // indirect
+	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	github.com/sagikazarmark/locafero v0.4.0 // indirect
+	github.com/sagikazarmark/slog-shim v0.1.0 // indirect
+	github.com/sourcegraph/conc v0.3.0 // indirect
+	github.com/spf13/afero v1.11.0 // indirect
+	github.com/spf13/cast v1.6.0 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/subosito/gotenv v1.6.0 // indirect
+	go.uber.org/atomic v1.9.0 // indirect
+	go.uber.org/multierr v1.9.0 // indirect
+	golang.org/x/exp v0.0.0-20230905200255-921286631fa9 // indirect
+	golang.org/x/sys v0.15.0 // indirect
+	golang.org/x/text v0.14.0 // indirect
+	gopkg.in/ini.v1 v1.67.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)

xload/providers/viper/go.sum

@@ -0,0 +1,71 @@
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xload/providers/viper/options.go

@@ -0,0 +1,101 @@
+package viper
+
+import (
+	"context"
+	"strings"
+
+	"github.com/spf13/viper"
+
+	"github.com/gojekfarm/xtools/xload"
+)
+
+// Option allows configuring the Loader.
+type Option interface{ apply(*options) }
+
+type optionFunc func(*options)
+
+func (f optionFunc) apply(o *options) { f(o) }
+
+// From allows passing a pre-configured Viper instance.
+func From(v *viper.Viper) Option { return optionFunc(func(o *options) { o.viper = v }) }
+
+// ValueMapper allows specifying a custom value mapper function that will be used to flatten the config
+// for xload.Loader from Viper.
+type ValueMapper func(map[string]any) map[string]string
+
+func (m ValueMapper) apply(o *options) { o.mapValues = m }
+
+// ConfigFile allows specifying the config file to be used.
+type ConfigFile string
+
+func (p ConfigFile) apply(o *options) { o.file.absPath = string(p) }
+
+// ConfigName allows specifying the config file name.
+type ConfigName string
+
+func (n ConfigName) apply(o *options) { o.file.name = string(n) }
+
+// ConfigType allows specifying the config file type.
+type ConfigType string
+
+func (t ConfigType) apply(o *options) { o.file.ext = string(t) }
+
+// ConfigPaths allows specifying the config file search paths.
+type ConfigPaths []string
+
+// AutoEnv allows enabling/disabling automatic environment variable loading.
+type AutoEnv bool
+
+func (b AutoEnv) apply(o *options) { o.autoEnv = bool(b) }
+
+func (p ConfigPaths) apply(o *options) {
+	for _, path := range p {
+		o.file.paths = append(o.file.paths, path)
+	}
+}
+
+// Transformer allows specifying a custom transformer function.
+type Transformer func(v *viper.Viper, next xload.Loader) xload.Loader
+
+func (t Transformer) apply(o *options) { o.transform = t }
+
+type options struct {
+	viper     *viper.Viper
+	file      fileOpts
+	transform Transformer
+	mapValues ValueMapper
+	autoEnv   bool
+}
+
+type fileOpts struct {
+	absPath string
+	name    string
+	ext     string
+	paths   []string
+}
+
+func def() *options {
+	return &options{
+		viper: viper.New(),
+		file: fileOpts{
+			name:  "application",
+			ext:   "yaml",
+			paths: []string{"./", "../"},
+		},
+		autoEnv: true,
+		mapValues: func(in map[string]any) map[string]string {
+			out := make(map[string]string)
+
+			for key, value := range xload.FlattenMap(in, "_") {
+				out[key] = value
+			}
+
+			return out
+		},
+		transform: func(_ *viper.Viper, next xload.Loader) xload.Loader {
+			return xload.LoaderFunc(func(ctx context.Context, key string) (string, error) {
+				return next.Load(ctx, strings.ToLower(key))
+			})
+		},
+	}
+}

xload/providers/viper/options_test.go

@@ -0,0 +1,81 @@
+package viper
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/spf13/viper"
+	"github.com/stretchr/testify/assert"
+
+	"github.com/gojekfarm/xtools/xload"
+)
+
+func TestOptions(t *testing.T) {
+	testcases := []struct {
+		name string
+		opts []Option
+		want *options
+	}{
+		{
+			name: "ConfigFile",
+			opts: []Option{ConfigFile("/tmp/config.yaml")},
+			want: &options{file: fileOpts{absPath: "/tmp/config.yaml"}},
+		},
+		{
+			name: "ConfigName",
+			opts: []Option{ConfigName("config")},
+			want: &options{file: fileOpts{name: "config"}},
+		},
+		{
+			name: "ConfigType",
+			opts: []Option{ConfigType("json")},
+			want: &options{file: fileOpts{ext: "json"}},
+		},
+		{
+			name: "ConfigPaths",
+			opts: []Option{ConfigPaths{"/tmp", "/tmp/config"}},
+			want: &options{file: fileOpts{paths: []string{"/tmp", "/tmp/config"}}},
+		},
+		{
+			name: "AutoEnv",
+			opts: []Option{AutoEnv(true)},
+			want: &options{autoEnv: true},
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			opts := &options{}
+			for _, o := range tc.opts {
+				o.apply(opts)
+			}
+
+			assert.Equal(t, tc.want, opts)
+		})
+	}
+
+	t.Run("Transformer", func(t *testing.T) {
+		opts := &options{}
+		f := Transformer(func(_ *viper.Viper, _ xload.Loader) xload.Loader { return nil })
+		f.apply(opts)
+		assert.NotNil(t, opts.transform)
+		assert.True(t, fmt.Sprintf("%p", f) == fmt.Sprintf("%p", opts.transform))
+	})
+
+	t.Run("ValueMapper", func(t *testing.T) {
+		opts := &options{}
+		f := ValueMapper(func(_ map[string]any) map[string]string { return nil })
+		f.apply(opts)
+		assert.NotNil(t, opts.mapValues)
+		assert.True(t, fmt.Sprintf("%p", f) == fmt.Sprintf("%p", opts.mapValues))
+	})
+}
+
+func Test_def(t *testing.T) {
+	opts := def()
+
+	assert.Equal(t, fileOpts{name: "application", ext: "yaml", paths: []string{"./", "../"}}, opts.file)
+	assert.NotNil(t, opts.viper)
+	assert.NotNil(t, opts.mapValues)
+	assert.NotNil(t, opts.transform)
+}