package registry

import (
	"fmt"
	"reflect"

	"git.maximhutz.com/max/lambda/pkg/codec"
)

// A Codec is a type-erased codec that serializes and deserializes expressions
// as Expr values, regardless of the underlying representation type.
type Codec interface {
	codec.Codec[Expr]

	// InType returns the name of the representation this codec handles.
	InType() string
}

// A registeredCodec adapts a typed codec.Codec[T] into the type-erased Codec
// interface. It wraps decoded values into Expr on decode, and extracts the
// underlying T from an Expr on encode.
type registeredCodec[T any] struct {
	codec  codec.Codec[T]
	inType string
}

func (c registeredCodec[T]) Decode(s string) (Expr, error) {
	t, err := c.codec.Decode(s)
	if err != nil {
		return nil, err
	}

	return NewExpr(c.inType, t), nil
}

func (c registeredCodec[T]) Encode(r Expr) (string, error) {
	t, ok := r.Data().(T)
	if !ok {
		dataType := reflect.TypeOf(r.Data())
		allowedType := reflect.TypeFor[T]()
		return "", fmt.Errorf("Codec for '%s' cannot parse '%s'", allowedType, dataType)
	}

	return c.codec.Encode(t)
}

func (c registeredCodec[T]) InType() string { return c.inType }

// RegisterCodec registers a typed codec under the given representation name.
// Returns an error if a codec for that representation is already registered.
func RegisterCodec[T any](registry *Registry, m codec.Codec[T], inType string) error {
	if _, ok := registry.codecs[inType]; ok {
		return fmt.Errorf("Codec for '%s' already registered", inType)
	}

	registry.codecs[inType] = registeredCodec[T]{m, inType}
	return nil
}