package config

import (
	"strings"

	"github.com/mitchellh/mapstructure"
	"github.com/spf13/cast"
	"github.com/spf13/viper"
)

// BindStructEnv binds struct using environment variables.
// Note: borrowed, see https://github.com/spf13/viper/pull/1429
func BindStructEnv(input interface{}) error {
	envKeysMap := map[string]interface{}{}
	if err := mapstructure.Decode(input, &envKeysMap); err != nil {
		return err
	}

	structKeys := flattenAndMergeMap(map[string]bool{}, envKeysMap, "")
	for key := range structKeys {
		if err := viper.BindEnv(key); err != nil {
			return err
		}
	}

	return nil
}

// FlattenAndMergeMap recursively flattens the given map into a map[string]bool
// of key paths (used as a set, easier to manipulate than a []string):
//   - each path is merged into a single key string, delimited with v.keyDelim
//   - if a path is shadowed by an earlier value in the initial shadow map,
//     it is skipped.
//
// The resulting set of paths is merged to the given shadow set at the same time.
// Note: borrowed, see https://github.com/spf13/viper/pull/1429
func flattenAndMergeMap(shadow map[string]bool, m map[string]any, prefix string) map[string]bool {
	if shadow != nil && prefix != "" && shadow[prefix] {
		// prefix is shadowed => nothing more to flatten
		return shadow
	}
	if shadow == nil {
		shadow = make(map[string]bool)
	}

	var m2 map[string]any
	if prefix != "" {
		prefix += "." // assuming that delimiter is a dot.
	}
	for k, val := range m {
		fullKey := prefix + k
		switch val := val.(type) {
		case map[string]any:
			m2 = val
		case map[any]any:
			m2 = cast.ToStringMap(val)
		default:
			// immediate value
			shadow[strings.ToLower(fullKey)] = true
			continue
		}
		// recursively merge to shadow map
		shadow = flattenAndMergeMap(shadow, m2, fullKey)
	}
	return shadow
}