package registry

import (
	"fmt"

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

// An Engine is a type-erased evaluation engine that can load an expression
// into a runnable Process.
type Engine interface {
	// Load prepares an expression for evaluation, returning a Process. Returns
	// an error if the expression's data does not match the engine's expected
	// representation type.
	Load(Expr) (Process, error)
	// Name returns the name of this engine.
	Name() string
	// InType returns the name of the representation this engine operates on.
	InType() string
}

// A registeredEngine adapts a typed engine.Engine[T] into the type-erased
// Engine interface. It extracts the underlying T from an Expr before passing it
// to the engine.
type registeredEngine[T any] struct {
	engine engine.Engine[T]
	name   string
	inType string
}

func (e registeredEngine[T]) InType() string { return e.inType }

func (e registeredEngine[T]) Name() string { return e.name }

func (e registeredEngine[T]) Load(expr Expr) (Process, error) {
	t, ok := expr.Data().(T)
	if !ok {
		return nil, fmt.Errorf("incorrect format '%s' for engine '%s'", expr.Repr(), e.inType)
	}

	process, err := e.engine(t)
	if err != nil {
		return nil, err
	}

	return registeredProcess[T]{process, e.inType}, nil
}

// RegisterEngine registers a typed engine under the given name. Returns an
// error if an engine with that name is already registered.
func RegisterEngine[T any](registry *Registry, e engine.Engine[T], name, inType string) error {
	if _, ok := registry.engines[name]; ok {
		return fmt.Errorf("engine '%s' already registered", name)
	}

	registry.engines[name] = &registeredEngine[T]{e, name, inType}
	return nil
}