package main

import (
	"context"
	"fmt"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/creativenoz/aurganize-v62/backend/internal/config"
	"github.com/creativenoz/aurganize-v62/backend/pkg/logger"
	"github.com/labstack/echo/v4"
	"github.com/labstack/echo/v4/middleware"
	"github.com/rs/zerolog/log"
)

func main() {
	// =========================================================================
	// Loading Configuration
	// =========================================================================
	cfg, err := config.Load()
	if err != nil {
		// we are not using logger here, since we need config information to set the log level
		fmt.Fprintf(os.Stderr, "Failed to load configurations : %v\n", err)
		// hence when config load fails we exit application, cause have not point in continuing further
		os.Exit(1)
	}
	// =========================================================================
	// Initializing Logger
	// =========================================================================
	logger.Init(cfg.Server.Environment)
	log.Info().
		Str("Version", "0.6.2").
		Str("environment", cfg.Server.Environment).
		Msg("Starting Aurganize v6.2 API server")

	// =========================================================================
	// Create Echo Instance
	// =========================================================================
	e := echo.New()
	e.HideBanner = true
	e.HidePort = true

	e.HTTPErrorHandler = customHTTPErrorHandler // we are using a custom error handler

	e.Server.ReadTimeout = cfg.Server.ReadTimeout
	e.Server.WriteTimeout = cfg.Server.WriteTimeout

	log.Info().Msg("Echo server instance created")
	// =========================================================================
	// Middleware Pipeline
	// =========================================================================

	// Setting safe recover middleware
	e.Use(middleware.Recover())
	// Middleware catches panic
	// Returns 500 Internal Server Error
	// Server keeps running
	// -------------------------------------------------------------------------
	// Setting request ID middleware
	e.Use(middleware.RequestID())
	// Trace request through entire system
	// Link frontend error to backend logs
	// This adds a header : X-Request-ID: abc-123-def-456
	// ------------------------------------------------------------------------
	// Setting Logger format
	e.Use(middleware.LoggerWithConfig(middleware.LoggerConfig{
		Format: `{"time":"${time_rfc3339}","method":"${method}","uri":"${uri}",` +
			`"status":${status},"latency_ms":${latency_ms},"error":"${error}"}` + "\n",
		Output: log.Logger,
	}))
	// We are setting a custom log format, which is consisten with our logger format
	// 	{
	//   "time": "2025-11-26T10:30:45Z",
	//   "method": "POST",
	//   "uri": "/api/v1/login",
	//   "status": 200,
	//   "latency_ms": 45,
	//   "error": ""
	// }
	// -----------------------------------------------------------------------
	// Setting CORS (Cross-Origin Resource Sharing) middleware
	e.Use(middleware.CORSWithConfig(middleware.CORSConfig{
		AllowOrigins: []string{
			"http://localhost:5173",     // (Development) Svelte dev server : this is the port suggested to be used with front-end
			"http://localhost:3000",     // (Developement) Alternative dev port : this is an alternative port kept aside
			"https://app.aurganize.com", // (Production) Production frontend : we can use this subdomain itself for front-end
		},
		AllowMethods: []string{
			http.MethodGet,
			http.MethodPost,
			http.MethodPut,
			http.MethodDelete,
			http.MethodPatch,
			http.MethodOptions,
		},
		AllowHeaders: []string{
			"Origin",
			"Content-Type",
			"Accept",
			"Authorization",
			"X-Request-ID",
		},

		AllowCredentials: true, // Not sure about why are using this option

		MaxAge: 3600, // 1 hour in seconds
	}))
	// Prevents malicious sites from calling your API
	// ----------------------------------------------------------------------
	// Setting Security Headers middleware
	e.Use(middleware.SecureWithConfig(middleware.SecureConfig{
		XSSProtection:         "1; mode=block",
		ContentTypeNosniff:    "nosniff",
		XFrameOptions:         "SAMEORIGIN",
		HSTSMaxAge:            31536000,
		HSTSExcludeSubdomains: false,
		ContentSecurityPolicy: "default-src 'self'",
	}))
	// X-XSS-Protection:
	// - Blocks cross-site scripting attacks
	// - Browser detects XSS and blocks page

	// X-Content-Type-Options: nosniff:
	// - Prevents MIME-type sniffing
	// - Browser trusts Content-Type header
	// - Prevents executing scripts as HTML

	// X-Frame-Options: SAMEORIGIN:
	// - Prevents clickjacking
	// - Page can't be embedded in iframe (except same origin)
	// - Protects against UI redress attacks

	// Strict-Transport-Security (HSTS):
	// - Forces HTTPS for 1 year
	// - Prevents downgrade attacks
	// - Can't be disabled by user

	// Content-Security-Policy:
	// - Only load resources from same origin
	// - Prevents loading malicious scripts
	// - Additional layer of XSS protection
	// -------------------------------------------------------------------
	// Setting Gzip compression middleware
	e.Use(middleware.Gzip())

	// TODO : Rate Limiting middleware (planning to use redis for custom rate limiter)

	log.Info().Msg("Middleware configured")

	// =========================================================================
	// Middleware Pipeline
	// =========================================================================

	e.GET("/health", healthCheckHandler(cfg)) // (Public - health check)
	api := e.Group("/api/v6.2")

	api.GET("/ping", func(c echo.Context) error { // (Public - connectivity test)
		return c.JSON(http.StatusOK, map[string]string{
			"message":   "pika pikaaa",
			"timestamp": time.Now().UTC().Format(time.RFC3339),
			"version":   "0.6.2",
		})
	})

	log.Info().Msg("Routes configured")
	// =========================================================================
	// Start Server in a new thread
	// =========================================================================

	serverAddr := fmt.Sprintf(":%s", cfg.Server.Port)

	go func() {
		log.Info().
			Str("address", serverAddr).
			Str("environment", cfg.Server.Environment).
			Msg("Server starting")

		if err := e.Start(serverAddr); err != nil && err != http.ErrServerClosed {
			log.Fatal().
				Err(err).
				Msg("Failed to start server")
		}
	}()
	// =========================================================================
	// Shutdown Logic
	// =========================================================================

	quit := make(chan os.Signal, 1)
	// Creates a channel named quit that can carry values of type os.Signal.
	// The 1 means it’s a buffered channel with capacity 1 → it can hold one signal without blocking.
	// This channel will be used to receive OS signals like Ctrl+C or kill.

	signal.Notify(quit, os.Interrupt, syscall.SIGTERM)
	// Whenever the process receives any of these signals, send them into the quit channel.”
	// os.Interrupt → typically the signal sent when you press Ctrl+C in the terminal.
	// syscall.SIGTERM → the “please terminate” signal, used by process managers / Docker / Kubernetes,

	<-quit // Blocks until we get a signal in this channel
	// This is a receive operation on the channel.
	// The code blocks here and does nothing until:
	// the OS sends os.Interrupt or SIGTERM,
	// which signal.Notify pushes into quit.
	// When a signal arrives, <-quit unblocks and the program continues.

	log.Info().Msg("Shutting down server gracefully..")

	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	// Creates a context with timeout of 10 seconds.
	// This context is passed to e.Shutdown(ctx)
	// Echo will have at most 10 seconds to shut down gracefully.
	// After 10 seconds, the context is cancelled, and shutdown will be forced.

	if err := e.Shutdown(ctx); err != nil {
		log.Error().
			Err(err).
			Msg("Server forced to shutdown, graceful shutdown failed")
	}
	// Calls Echo’s Shutdown method with your timeout context.
	// e.Shutdown(ctx):
	// -- stops accepting new requests,
	// -- waits for in-flight requests to finish,
	// -- closes the server gracefully (within the timeout).
	// If something goes wrong (e.g., it can’t shut down in time), err is non-nil:
	// -- logs an error saying graceful shutdown failed and it had to force close.

	log.Info().Msg("API Server exited")

}

// HealthCheck Handler function
// This endpoint is to be used by:
//   - Load balancers to determine if instance is healthy
//   - Kubernetes for liveness and readiness probes
//   - Monitoring systems for uptime checks
func healthCheckHandler(c *config.Config) echo.HandlerFunc {
	return func(e echo.Context) error {
		// TODO : we need to add health check for
		// - Database connection
		// - Redis connection if we are using it
		// - NATS connection

		// For now we are just returning OK, since most of the service dependecies are not implemented yet.
		response := map[string]interface{}{
			"status":      "healthy",
			"version":     "0.6.2",
			"environment": c.Server.Environment,
			"timestamp":   time.Now().UTC(),
			"checks": map[string]string{
				"server":   "ok",
				"database": "not setup",
				"redis":    "not setup",
				"nats":     "not setup",
			},
			"uptime": 999999999999, // logic yet to be implemented
		}
		return e.JSON(http.StatusOK, response)
	}
}

// CustomHTTPErrorHandler
// Used to provide consistent error response
// Converts Echo erros to JSON format, that can be parsed at frontend
func customHTTPErrorHandler(err error, c echo.Context) {

	// Setting default values
	code := http.StatusInternalServerError
	message := "internal server error"

	// Checking if the error is and Echo error
	// We do this through a type assertion err.(*echo.HTTPError) [ basetype.(type to assert to)]
	if he, ok := err.(*echo.HTTPError); ok {
		code = he.Code
		// Then we again check with a type assertion
		if msg, ok := he.Message.(string); ok {
			message = msg
		}
	}

	log.Debug().
		Err(err).
		Int("status", code).
		Str("method", c.Request().Method).
		Str("path", c.Request().URL.Path).
		Msg("HTTP error")

	if code >= 500 {
		log.Error().
			Err(err).
			Int("status", code).
			Str("method", c.Request().Method).
			Str("path", c.Request().URL.Path).
			Msg("HTTP error")
	}

	// If the response is not already written
	// Then we don't have to again log
	if !c.Response().Committed {
		c.JSON(code, map[string]interface{}{
			"error": map[string]interface{}{
				"code":       code,
				"message":    message,
				"timestamp":  time.Now().UTC(),
				"path":       c.Request().URL.Path,
				"request_id": c.Response().Header().Get(echo.HeaderXRequestID),
			},
		})
	}

}