package internal

import (
	"errors"
	"github.com/go-kratos/kratos/v2/log"
	"sync"

	// init encoding
	_ "github.com/go-kratos/kratos/v2/encoding/json"
	_ "github.com/go-kratos/kratos/v2/encoding/proto"
	_ "github.com/go-kratos/kratos/v2/encoding/xml"
	_ "github.com/go-kratos/kratos/v2/encoding/yaml"
)

var (
	// ErrNotFound is key not found.
	ErrNotFound = errors.New("key not found")
	// ErrTypeAssert is type assert error.
	ErrTypeAssert = errors.New("type assert error")

	_ Config = (*config)(nil)
)

// Observer is config observer.
type Observer func(string, Value)

// Config is a config interface.
type Config interface {
	Load() error
	Bytes() ([]byte, error)
	Value(key string) Value
}

type config struct {
	opts      options
	reader    Reader
	cached    sync.Map
	observers sync.Map
	log       *log.Helper
}

// New new a config with options.
func New(opts ...Option) Config {
	o := options{
		logger:   log.DefaultLogger,
		decoder:  defaultDecoder,
		resolver: defaultResolver,
	}
	for _, opt := range opts {
		opt(&o)
	}
	return &config{
		opts:   o,
		reader: newReader(o),
		log:    log.NewHelper(o.logger),
	}
}

func (c *config) Load() error {
	for _, src := range c.opts.sources {
		kvs, err := src.Load()
		if err != nil {
			return err
		}
		if err = c.reader.Merge(kvs...); err != nil {
			c.log.Errorf("failed to merge config source: %v", err)
			return err
		}
	}
	if err := c.reader.Resolve(); err != nil {
		c.log.Errorf("failed to resolve config source: %v", err)
		return err
	}
	return nil
}

func (c *config) Bytes() ([]byte, error) {
	return c.reader.Bytes()
}

func (c *config) Value(key string) Value {
	if v, ok := c.cached.Load(key); ok {
		return v.(Value)
	}
	if v, ok := c.reader.Value(key); ok {
		c.cached.Store(key, v)
		return v
	}
	return &errValue{err: ErrNotFound}
}