// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package rpc

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"math/big"
	"reflect"
	"unicode"
	"unicode/utf8"

	"fmt"

	"golang.org/x/net/context"
)

// Is this an exported - upper case - name?
func isExported(name string) bool {
	rune, _ := utf8.DecodeRuneInString(name)
	return unicode.IsUpper(rune)
}

// Is this type exported or a builtin?
func isExportedOrBuiltinType(t reflect.Type) bool {
	for t.Kind() == reflect.Ptr {
		t = t.Elem()
	}
	// PkgPath will be non-empty even for an exported type,
	// so we need to check the type name as well.
	return isExported(t.Name()) || t.PkgPath() == ""
}

var errorType = reflect.TypeOf((*error)(nil)).Elem()

// Implements this type the error interface
func isErrorType(t reflect.Type) bool {
	for t.Kind() == reflect.Ptr {
		t = t.Elem()
	}
	return t.Implements(errorType)
}

var subscriptionType = reflect.TypeOf((*Subscription)(nil)).Elem()

func isSubscriptionType(t reflect.Type) bool {
	for t.Kind() == reflect.Ptr {
		t = t.Elem()
	}
	return t == subscriptionType
}

// isPubSub tests whether the given method return the pair (v2.Subscription, error)
func isPubSub(methodType reflect.Type) bool {
	if methodType.NumOut() != 2 {
		return false
	}
	return isSubscriptionType(methodType.Out(0)) && isErrorType(methodType.Out(1))
}

// formatName will convert to first character to lower case
func formatName(name string) string {
	ret := []rune(name)
	if len(ret) > 0 {
		ret[0] = unicode.ToLower(ret[0])
	}
	return string(ret)
}

var bigIntType = reflect.TypeOf((*big.Int)(nil)).Elem()

// Indication if this type should be serialized in hex
func isHexNum(t reflect.Type) bool {
	if t == nil {
		return false
	}
	for t.Kind() == reflect.Ptr {
		t = t.Elem()
	}

	return t == bigIntType
}

var blockNumberType = reflect.TypeOf((*BlockNumber)(nil)).Elem()

// Indication if the given block is a BlockNumber
func isBlockNumber(t reflect.Type) bool {
	if t == nil {
		return false
	}

	for t.Kind() == reflect.Ptr {
		t = t.Elem()
	}

	return t == blockNumberType
}

var contextType = reflect.TypeOf(new(context.Context)).Elem()

// suitableCallbacks iterates over the methods of the given type. It will determine if a method satisfies the criteria
// for a RPC callback or a subscription callback and adds it to the collection of callbacks or subscriptions. See server
// documentation for a summary of these criteria.
func suitableCallbacks(rcvr reflect.Value, typ reflect.Type) (callbacks, subscriptions) {
	callbacks := make(callbacks)
	subscriptions := make(subscriptions)

METHODS:
	for m := 0; m < typ.NumMethod(); m++ {
		method := typ.Method(m)
		mtype := method.Type
		mname := formatName(method.Name)
		if method.PkgPath != "" { // method must be exported
			continue
		}

		var h callback
		h.isSubscribe = isPubSub(mtype)
		h.rcvr = rcvr
		h.method = method
		h.errPos = -1

		firstArg := 1
		numIn := mtype.NumIn()
		if numIn >= 2 && mtype.In(1) == contextType {
			h.hasCtx = true
			firstArg = 2
		}

		if h.isSubscribe {
			h.argTypes = make([]reflect.Type, numIn-firstArg) // skip rcvr type
			for i := firstArg; i < numIn; i++ {
				argType := mtype.In(i)
				if isExportedOrBuiltinType(argType) {
					h.argTypes[i-firstArg] = argType
				} else {
					continue METHODS
				}
			}

			subscriptions[mname] = &h
			continue METHODS
		}

		// determine method arguments, ignore first arg since it's the receiver type
		// Arguments must be exported or builtin types
		h.argTypes = make([]reflect.Type, numIn-firstArg)
		for i := firstArg; i < numIn; i++ {
			argType := mtype.In(i)
			if !isExportedOrBuiltinType(argType) {
				continue METHODS
			}
			h.argTypes[i-firstArg] = argType
		}

		// check that all returned values are exported or builtin types
		for i := 0; i < mtype.NumOut(); i++ {
			if !isExportedOrBuiltinType(mtype.Out(i)) {
				continue METHODS
			}
		}

		// when a method returns an error it must be the last returned value
		h.errPos = -1
		for i := 0; i < mtype.NumOut(); i++ {
			if isErrorType(mtype.Out(i)) {
				h.errPos = i
				break
			}
		}

		if h.errPos >= 0 && h.errPos != mtype.NumOut()-1 {
			continue METHODS
		}

		switch mtype.NumOut() {
		case 0, 1:
			break
		case 2:
			if h.errPos == -1 { // method must one return value and 1 error
				continue METHODS
			}
			break
		default:
			continue METHODS
		}

		callbacks[mname] = &h
	}

	return callbacks, subscriptions
}

func newSubscriptionId() (string, error) {
	var subid [16]byte
	n, _ := rand.Read(subid[:])
	if n != 16 {
		return "", errors.New("Unable to generate subscription id")
	}
	return "0x" + hex.EncodeToString(subid[:]), nil
}

// SupportedModules returns the collection of API's that the RPC server offers
// on which the given client connects.
func SupportedModules(client Client) (map[string]string, error) {
	req := JSONRequest{
		Id:      new(int64),
		Version: "2.0",
		Method:  "rpc_modules",
	}
	if err := client.Send(req); err != nil {
		return nil, err
	}

	var response JSONSuccessResponse
	if err := client.Recv(&response); err != nil {
		return nil, err
	}
	if response.Result != nil {
		mods := make(map[string]string)
		if modules, ok := response.Result.(map[string]interface{}); ok {
			for m, v := range modules {
				mods[m] = fmt.Sprintf("%s", v)
			}
			return mods, nil
		}
	}
	return nil, fmt.Errorf("unable to retrieve modules")
}