tether/engine.go

package tether

import (
	"encoding/json"
	"log/slog"
	"net/http"
	"sync"

	"github.com/cespare/xxhash"
	"github.com/wisplite/tether/reactivity"
	"gorm.io/gorm"
)

type Engine struct {
	db           *gorm.DB
	dbType       string // sqlite or postgres
	mutations    map[string]func(ctx *MutationCtx) interface{}
	queries      map[string]func(ctx *QueryCtx) interface{}
	dependencies map[string][]string
	hashMu       sync.RWMutex
	queryHashes  map[string]uint64
	tracker      *reactivity.Tracker
}

func NewEngine(db *gorm.DB, dbType string) *Engine {
	slog.SetLogLoggerLevel(slog.LevelDebug)
	tracker := reactivity.NewTracker()
	if dbType != "sqlite" && dbType != "postgres" {
		panic("Invalid database type")
	}
	e := &Engine{db: db, dbType: dbType, mutations: make(map[string]func(ctx *MutationCtx) interface{}), queries: make(map[string]func(ctx *QueryCtx) interface{}), dependencies: make(map[string][]string), queryHashes: make(map[string]uint64), tracker: tracker}
	db.Callback().Create().After("gorm:create").Register("tether:after_create", func(tx *gorm.DB) {
		if dbType == "postgres" {
			return
		}
		e.InvalidateTable(tx.Statement.Table)
	})
	return e
}

func (e *Engine) RegisterMutation(name string, mutation func(ctx *MutationCtx) interface{}) {
	e.mutations[name] = mutation // stores the mutation in the list of valid mutations
	slog.Debug("Registered mutation", "name", name)
}

func (e *Engine) RegisterQuery(name string, query func(ctx *QueryCtx) interface{}, dependencies []string) {
	e.queries[name] = query // stores the query in the list of valid queries
	for _, dependency := range dependencies {
		e.dependencies[dependency] = append(e.dependencies[dependency], name)
	}
	slog.Debug("Registered query", "name", name)
}

func (e *Engine) CreateTable(name string, schema interface{}) {
	e.db.AutoMigrate(schema)
	slog.Debug("Created table", "name", name)
}

func (e *Engine) Handle(w http.ResponseWriter, r *http.Request) {
	reactivity.Handle(w, r, e, e.tracker) // wraps the raw websocket connection with the engine handler
}

func (e *Engine) OnConnect(clientID string) error {
	slog.Debug("Connected to websocket", "client", clientID)
	// TODO: implement the logic to handle the connection
	return nil
}

func (e *Engine) OnDisconnect(clientID string) error {
	slog.Debug("Disconnected from websocket", "client", clientID)
	// TODO: implement the logic to handle the disconnection
	return nil
}

func (e *Engine) GetDependentQueries(tableName string) []string {
	return e.dependencies[tableName]
}

func (e *Engine) InvalidateTable(tableName string) {
	slog.Debug("Invalidating table", "table", tableName)
	dependentQueries := e.GetDependentQueries(tableName)
	for _, query := range dependentQueries {
		slog.Debug("Invalidating query", "query", query)
		subscriptions := e.tracker.GetQuerySubscriptions(query)
		slog.Debug("Subscriptions", "subscriptions", subscriptions)
		for _, subscription := range subscriptions {
			slog.Debug("Invalidating subscription", "subscription", subscription["clientID"])
			params := map[string]interface{}{}
			err := json.Unmarshal([]byte(subscription["params"]), &params)
			if err != nil {
				slog.Error("Failed to unmarshal params", "error", err)
				continue
			}
			_, err = e.ExecuteQuery(query, params, subscription["clientID"], false)
			if err != nil {
				slog.Error("Failed to execute query", "error", err)
				continue
			}
		}
	}
}

func (e *Engine) ExecuteQuery(query string, params map[string]interface{}, clientID string, forceSend bool) (interface{}, error) {
	/*
		TODO: implement the logic to execute the query
		Steps needed:
		1. Check which tables updated ✅
		2. Get the queries that rely on the tables ✅
		3. Get the subscriptions that need updating ✅
		4. Calculate hash for every query
		5. Send the updated queries if hash changed
	*/
	paramsJSON, err := json.Marshal(params)
	if err != nil {
		return nil, err
	}
	cacheKey := query + "?" + string(paramsJSON)
	e.hashMu.Lock()
	lastHash := e.queryHashes[cacheKey]
	e.hashMu.Unlock()
	slog.Debug("Executing query", "query", query, "params", params)
	result := e.queries[query](&QueryCtx{DB: e.db, AuthCtx: &AuthCtx{UserID: "", IsLoggedIn: true}, Params: params})
	responseJSON, err := json.Marshal(map[string]interface{}{"type": "query", "location": query, "data": result})
	if err != nil {
		return nil, err
	}
	queryHash := xxhash.Sum64(responseJSON)
	if lastHash == queryHash && !forceSend { // we want to force send on first subscription, regardless of if the query hasn't changed
		return result, nil
	}

	e.hashMu.Lock()
	e.queryHashes[cacheKey] = queryHash
	e.hashMu.Unlock()

	e.tracker.SendMessage(clientID, responseJSON)
	return result, nil
}

func (e *Engine) ExecuteMutation(mutation string, params map[string]interface{}, clientID string) (interface{}, error) {
	result := e.mutations[mutation](&MutationCtx{DB: e.db, AuthCtx: &AuthCtx{UserID: "", IsLoggedIn: true}, Params: params})
	return result, nil
}

func (e *Engine) OnReceiveMessage(clientID string, msg map[string]interface{}) error {
	slog.Debug("Received message", "from", clientID, "message", msg)
	switch msg["type"] {
	case "subscribe":
		paramsJSON, err := json.Marshal(msg["params"])
		if err != nil {
			return err
		}
		e.tracker.SubscribeToQuery(clientID, msg["location"].(string), string(paramsJSON))
		e.ExecuteQuery(msg["location"].(string), msg["params"].(map[string]interface{}), clientID, true)
	case "mutation":
		e.ExecuteMutation(msg["location"].(string), msg["params"].(map[string]interface{}), clientID)
	}
	return nil
}