package vm

import (
	"context"
	"fmt"
	"os"

	cid "github.com/ipfs/go-cid"

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

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

// stat counters
var (
	StatSends   uint64
	StatApplied uint64
)

type ExecutionLane int

const (
	// ExecutionLaneDefault signifies a default, non prioritized execution lane.
	ExecutionLaneDefault ExecutionLane = iota
	// ExecutionLanePriority signifies a prioritized execution lane with reserved resources.
	ExecutionLanePriority
)

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)
}

// Executor is the general vm execution interface, which is prioritized according to execution lanes.
// User must call Done when it is done with this executor to release resource holds by the execution
// environment
type Executor interface {
	Interface

	// Done must be called when done with the executor to release resource holds.
	// It is an error to invoke Interface methods after Done has been called.
	Done()
}

// WARNING: You will not affect your node's execution by misusing this feature, but you will confuse yourself thoroughly!
// An envvar that allows the user to specify debug actors bundles to be used by the FVM
// alongside regular execution. This is basically only to be used to print out specific logging information.
// Message failures, unexpected terminations,gas costs, etc. should all be ignored.
var useFvmDebug = os.Getenv("LOTUS_FVM_DEVELOPER_DEBUG") == "1"

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

	return NewLegacyVM(ctx, opts)
}

func NewVM(ctx context.Context, opts *VMOpts) (Executor, error) {
	switch opts.ExecutionLane {
	case ExecutionLaneDefault, ExecutionLanePriority:
	default:
		return nil, fmt.Errorf("invalid execution lane: %d", opts.ExecutionLane)
	}

	token := execution.getToken(opts.ExecutionLane)

	vmi, err := newVM(ctx, opts)
	if err != nil {
		token.Done()
		return nil, err
	}

	return newVMExecutor(vmi, token), nil
}