// Package "engine" provides an extensible interface for users to interact with
// λ-calculus and other expression evaluation modes.
package engine

import (
	"git.maximhutz.com/max/lambda/internal/config"
	"git.maximhutz.com/max/lambda/pkg/emitter"
	"git.maximhutz.com/max/lambda/pkg/expr"
	"git.maximhutz.com/max/lambda/pkg/reducer"
)

// Engine is a process for reducing one expression.
type Engine struct {
	Config     *config.Config
	Expression expr.Expression
	Reducer    reducer.Reducer
	emitter.BaseEmitter[Event]
}

// New creates a new engine with the given expression and reducer.
func New(config *config.Config, expression expr.Expression, reducer reducer.Reducer) *Engine {
	return &Engine{
		Config:      config,
		Expression:  expression,
		Reducer:     reducer,
		BaseEmitter: *emitter.New[Event](),
	}
}

// Run begins the reduction process.
func (e *Engine) Run() {
	e.Emit(StartEvent)

	e.Expression = e.Reducer.Reduce(e.Expression, func(reduced expr.Expression) {
		e.Expression = reduced
		e.Emit(StepEvent)
	})

	e.Emit(StopEvent)
}