/*
Copyright 2021 The Dapr Authors
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package config

import (
	"fmt"
	"reflect"
	"strconv"
	"time"

	"github.com/mitchellh/mapstructure"
)

var (
	typeDuration      = reflect.TypeOf(time.Duration(5))             //nolint: gochecknoglobals
	typeTime          = reflect.TypeOf(time.Time{})                  //nolint: gochecknoglobals
	typeStringDecoder = reflect.TypeOf((*StringDecoder)(nil)).Elem() //nolint: gochecknoglobals
)

// StringDecoder is used as a way for custom types (or alias types) to
// override the basic decoding function in the `decodeString`
// DecodeHook. `encoding.TextMashaller` was not used because it
// matches many Go types and would have potentially unexpected results.
// Specifying a custom decoding func should be very intentional.
type StringDecoder interface {
	DecodeString(value string) error
}

// Decode decodes generic map values from `input` to `output`, while providing helpful error information.
// `output` must be a pointer to a Go struct that contains `mapstructure` struct tags on fields that should
// be decoded. This function is useful when decoding values from configuration files parsed as
// `map[string]interface{}` or component metadata as `map[string]string`.
//
// Most of the heavy lifting is handled by the mapstructure library. A custom decoder is used to handle
// decoding string values to the supported primitives.
func Decode(input interface{}, output interface{}) error {
	decoder, err := mapstructure.NewDecoder(
		&mapstructure.DecoderConfig{ //nolint: exhaustruct
			Result:     output,
			DecodeHook: decodeString,
		})
	if err != nil {
		return err
	}

	return decoder.Decode(input)
}

//nolint:cyclop
func decodeString(f reflect.Type, t reflect.Type, data any) (any, error) {
	if t.Kind() == reflect.String && f.Kind() != reflect.String {
		return fmt.Sprintf("%v", data), nil
	}
	if f.Kind() == reflect.Ptr {
		f = f.Elem()
		data = reflect.ValueOf(data).Elem().Interface()
	}
	if f.Kind() != reflect.String {
		return data, nil
	}

	dataString, ok := data.(string)
	if !ok {
		return nil, fmt.Errorf("expected string: got %T", data)
	}

	var result any
	var decoder StringDecoder

	if t.Implements(typeStringDecoder) {
		result = reflect.New(t.Elem()).Interface()
		decoder = result.(StringDecoder)
	} else if reflect.PointerTo(t).Implements(typeStringDecoder) {
		result = reflect.New(t).Interface()
		decoder = result.(StringDecoder)
	}

	if decoder != nil {
		if err := decoder.DecodeString(dataString); err != nil {
			if t.Kind() == reflect.Ptr {
				t = t.Elem()
			}

			return nil, fmt.Errorf("invalid %s %q: %v", t.Name(), dataString, err)
		}

		return result, nil
	}

	switch t {
	case typeDuration:
		// Check for simple integer values and treat them
		// as milliseconds
		if val, err := strconv.Atoi(dataString); err == nil {
			return time.Duration(val) * time.Millisecond, nil
		}

		// Convert it by parsing
		d, err := time.ParseDuration(dataString)

		return d, invalidError(err, "duration", dataString)
	case typeTime:
		// Convert it by parsing
		t, err := time.Parse(time.RFC3339Nano, dataString)
		if err == nil {
			return t, nil
		}
		t, err = time.Parse(time.RFC3339, dataString)

		return t, invalidError(err, "time", dataString)
	}

	switch t.Kind() {
	case reflect.Uint:
		val, err := strconv.ParseUint(dataString, 10, 64)

		return uint(val), invalidError(err, "uint", dataString)
	case reflect.Uint64:
		val, err := strconv.ParseUint(dataString, 10, 64)

		return val, invalidError(err, "uint64", dataString)
	case reflect.Uint32:
		val, err := strconv.ParseUint(dataString, 10, 32)

		return uint32(val), invalidError(err, "uint32", dataString)
	case reflect.Uint16:
		val, err := strconv.ParseUint(dataString, 10, 16)

		return uint16(val), invalidError(err, "uint16", dataString)
	case reflect.Uint8:
		val, err := strconv.ParseUint(dataString, 10, 8)

		return uint8(val), invalidError(err, "uint8", dataString)

	case reflect.Int:
		val, err := strconv.ParseInt(dataString, 10, 64)

		return int(val), invalidError(err, "int", dataString)
	case reflect.Int64:
		val, err := strconv.ParseInt(dataString, 10, 64)

		return val, invalidError(err, "int64", dataString)
	case reflect.Int32:
		val, err := strconv.ParseInt(dataString, 10, 32)

		return int32(val), invalidError(err, "int32", dataString)
	case reflect.Int16:
		val, err := strconv.ParseInt(dataString, 10, 16)

		return int16(val), invalidError(err, "int16", dataString)
	case reflect.Int8:
		val, err := strconv.ParseInt(dataString, 10, 8)

		return int8(val), invalidError(err, "int8", dataString)

	case reflect.Float32:
		val, err := strconv.ParseFloat(dataString, 32)

		return float32(val), invalidError(err, "float32", dataString)
	case reflect.Float64:
		val, err := strconv.ParseFloat(dataString, 64)

		return val, invalidError(err, "float64", dataString)

	case reflect.Bool:
		val, err := strconv.ParseBool(dataString)

		return val, invalidError(err, "bool", dataString)

	default:
		return data, nil
	}
}

func invalidError(err error, msg, value string) error {
	if err == nil {
		return nil
	}

	return fmt.Errorf("invalid %s %q", msg, value)
}
