package chain

import (
	"errors"
	"fmt"
	"reflect"

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

type invoker struct {
	builtInCode map[cid.Cid]nativeCode
}

type invokeFunc func(act *Actor, vmctx *VMContext, params []byte) (InvokeRet, error)
type nativeCode []invokeFunc
type InvokeRet struct {
	result     []byte
	returnCode byte
}

func newInvoker() *invoker {
	inv := &invoker{
		builtInCode: make(map[cid.Cid]nativeCode),
	}
	// add builtInCode using: register(cid, singleton)
	return inv
}

func (inv *invoker) Invoke(act *Actor, vmctx *VMContext, method uint64, params []byte) (InvokeRet, error) {

	code, ok := inv.builtInCode[act.Code]
	if !ok {
		return InvokeRet{}, errors.New("no code for actor")
	}
	if method >= uint64(len(code)) || code[method] == nil {
		return InvokeRet{}, fmt.Errorf("no method %d on actor", method)
	}
	return code[method](act, vmctx, params)

}

func (inv *invoker) register(c cid.Cid, instance Invokee) {
	code, err := inv.transform(instance)
	if err != nil {
		panic(err)
	}
	inv.builtInCode[c] = code
}

type unmarshalCBOR interface {
	UnmarshalCBOR([]byte) (int, error)
}

type Invokee interface {
	Exports() []interface{}
}

var tUnmarhsalCBOR = reflect.TypeOf((*unmarshalCBOR)(nil)).Elem()
var tError = reflect.TypeOf((*error)(nil)).Elem()

func (*invoker) transform(instance Invokee) (nativeCode, error) {
	itype := reflect.TypeOf(instance)
	exports := instance.Exports()
	for i, m := range exports {
		i := i
		newErr := func(str string) error {
			return fmt.Errorf("transform(%s) export(%d): %s", itype.Name(), i, str)
		}
		if m == nil {
			continue
		}
		meth := reflect.ValueOf(m)
		t := meth.Type()
		if t.Kind() != reflect.Func {
			return nil, newErr("is not a function")
		}
		if t.NumIn() != 3 {
			return nil, newErr("wrong number of inputs should be: " +
				"*Actor, *VMContext, <type of parameter>")
		}
		if t.In(0) != reflect.TypeOf(&Actor{}) {
			return nil, newErr("first arguemnt should be *Actor")
		}
		if t.In(1) != reflect.TypeOf(&VMContext{}) {
			return nil, newErr("second argument should be *VMContext")
		}

		if !t.In(2).Implements(tUnmarhsalCBOR) {
			return nil, newErr("parameter doesn't implement UnmarshalCBOR")
		}

		if t.In(2).Kind() != reflect.Ptr {
			return nil, newErr("parameter has to be a pointer")
		}

		if t.NumOut() != 2 {
			return nil, newErr("wrong number of outputs should be: " +
				"(InvokeRet, error)")
		}
		if t.Out(0) != reflect.TypeOf(InvokeRet{}) {
			return nil, newErr("first output should be of type InvokeRet")
		}
		if !t.Out(1).Implements(tError) {
			return nil, newErr("second output should be error type")
		}

	}
	code := make(nativeCode, len(exports))
	for id, m := range exports {
		meth := reflect.ValueOf(m)
		code[id] = reflect.MakeFunc(reflect.TypeOf((invokeFunc)(nil)),
			func(in []reflect.Value) []reflect.Value {
				paramT := meth.Type().In(2).Elem()
				param := reflect.New(paramT)

				inBytes := in[2].Interface().([]byte)
				_, err := param.Interface().(unmarshalCBOR).UnmarshalCBOR(inBytes)
				if err != nil {
					return []reflect.Value{
						reflect.ValueOf(InvokeRet{}),
						reflect.ValueOf(err),
					}
				}
				return meth.Call([]reflect.Value{
					in[0], in[1], param,
				})
			}).Interface().(invokeFunc)

	}
	return code, nil
}