package vm

import (
	"context"
	"os"

	"github.com/ipfs/go-cid"

	"github.com/filecoin-project/go-state-types/network"

	"github.com/filecoin-project/lotus/chain/types"
)

type Interface interface {
	// Applies the given message onto the VM's current state, returning the result of the execution
	ApplyMessage(ctx context.Context, cmsg types.ChainMsg) (*ApplyRet, error)
	// Same as above but for system messages (the Cron invocation and block reward payments).
	// Must NEVER fail.
	ApplyImplicitMessage(ctx context.Context, msg *types.Message) (*ApplyRet, error)
	// Flush all buffered objects into the state store provided to the VM at construction.
	Flush(ctx context.Context) (cid.Cid, error)
}

var experimentalUseFvm = os.Getenv("LOTUS_USE_FVM_EXPERIMENTAL") == "1"

func NewVM(ctx context.Context, opts *VMOpts) (Interface, error) {
	if opts.NetworkVersion >= network.Version16 {
		return NewFVM(ctx, opts)
	}

	// Remove after v16 upgrade, this is only to support testing and validation of the FVM
	if experimentalUseFvm && opts.NetworkVersion >= network.Version15 {
		return NewFVM(ctx, opts)
	}

	return NewLegacyVM(ctx, opts)
}