package rpc

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"reflect"
	"sync"

	"github.com/ethereum/go-ethereum/node"
	"github.com/status-im/status-go/geth/params"

	gethrpc "github.com/ethereum/go-ethereum/rpc"
)

// Handler defines handler for RPC methods.
type Handler func(context.Context, ...interface{}) (interface{}, error)

// Client represents RPC client with custom routing
// scheme. It automatically decides where RPC call
// goes - Upstream or Local node.
type Client struct {
	upstreamEnabled bool
	upstreamURL     string

	local    *gethrpc.Client
	upstream *gethrpc.Client

	router *router

	handlersMx sync.RWMutex       // mx guards handlers
	handlers   map[string]Handler // locally registered handlers
}

// NewClient initializes Client and tries to connect to both,
// upstream and local node.
//
// Client is safe for concurrent use and will automatically
// reconnect to the server if connection is lost.
func NewClient(node *node.Node, upstream params.UpstreamRPCConfig) (*Client, error) {
	c := &Client{
		handlers: make(map[string]Handler),
	}

	var err error
	c.local, err = node.Attach()
	if err != nil {
		return nil, fmt.Errorf("attach to local node: %s", err)
	}

	if upstream.Enabled {
		c.upstreamEnabled = upstream.Enabled
		c.upstreamURL = upstream.URL

		c.upstream, err = gethrpc.Dial(c.upstreamURL)
		if err != nil {
			return nil, fmt.Errorf("dial upstream server: %s", err)
		}
	}

	c.router = newRouter(c.upstreamEnabled)

	return c, nil
}

// Call performs a JSON-RPC call with the given arguments and unmarshals into
// result if no error occurred.
//
// The result must be a pointer so that package json can unmarshal into it. You
// can also pass nil, in which case the result is ignored.
//
// It uses custom routing scheme for calls.
func (c *Client) Call(result interface{}, method string, args ...interface{}) error {
	ctx := context.Background()
	return c.CallContext(ctx, result, method, args...)
}

// CallContext performs a JSON-RPC call with the given arguments. If the context is
// canceled before the call has successfully returned, CallContext returns immediately.
//
// The result must be a pointer so that package json can unmarshal into it. You
// can also pass nil, in which case the result is ignored.
//
// It uses custom routing scheme for calls.
func (c *Client) CallContext(ctx context.Context, result interface{}, method string, args ...interface{}) error {
	// check locally registered handlers first
	if handler, ok := c.handler(method); ok {
		return c.callMethod(ctx, result, handler, args...)
	}

	if c.router.routeRemote(method) {
		return c.upstream.CallContext(ctx, result, method, args...)
	}
	return c.local.CallContext(ctx, result, method, args...)
}

// RegisterHandler registers local handler for specific RPC method.
//
// If method is registered, it will be executed with given handler and
// never routed to the upstream or local servers.
func (c *Client) RegisterHandler(method string, handler Handler) {
	c.handlersMx.Lock()
	defer c.handlersMx.Unlock()

	c.handlers[method] = handler
}

// callMethod calls registered RPC handler with given args and pointer to result.
// It handles proper params and result converting
//
// TODO(divan): use cancellation via context here?
func (c *Client) callMethod(ctx context.Context, result interface{}, handler Handler, args ...interface{}) error {
	response, err := handler(ctx, args...)
	if err != nil {
		return err
	}

	// if result is nil, just ignore result -
	// the same way as gethrpc.CallContext() caller would expect
	if result == nil {
		return nil
	}

	if err := setResultFromRPCResponse(result, response); err != nil {
		return err
	}

	return nil
}

// handler is a concurrently safe method to get registered handler by name.
func (c *Client) handler(method string) (Handler, bool) {
	c.handlersMx.RLock()
	defer c.handlersMx.RUnlock()
	handler, ok := c.handlers[method]
	return handler, ok
}

// setResultFromRPCResponse tries to set result value from response using reflection
// as concrete types are unknown.
func setResultFromRPCResponse(result, response interface{}) (err error) {
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("invalid result type: %s", r)
		}
	}()

	responseValue := reflect.ValueOf(response)

	// If it is called via CallRaw, result has type json.RawMessage and
	// we should marshal the response before setting it.
	// Otherwise, it is called with CallContext and result is of concrete type,
	// thus we should try to set it as it is.
	// If response type and result type are incorrect, an error should be returned.
	// TODO(divan): add additional checks for result underlying value, if needed:
	// some example: https://golang.org/src/encoding/json/decode.go#L596
	switch reflect.ValueOf(result).Elem().Type() {
	case reflect.TypeOf(json.RawMessage{}), reflect.TypeOf([]byte{}):
		data, err := json.Marshal(response)
		if err != nil {
			return err
		}

		responseValue = reflect.ValueOf(data)
	}

	value := reflect.ValueOf(result).Elem()
	if !value.CanSet() {
		return errors.New("can't assign value to result")
	}
	value.Set(responseValue)

	return nil
}