// Package bootstrap
// Path: /internal/platform/bootstrap
// File: loader.go
//
// Purpose
//   Centralized application initializer (the “application kernel”).
//   Constructs and wires the core runtime graph used by the system:
//   configuration, database, schema bootstrap, session manager (SCS), router (Gin),
//   CSRF wrapper (nosurf), and the HTTP server.
//
// Responsibilities (as implemented here)
//   1) Load strongly-typed configuration from disk (config.Load).
//   2) Open MySQL with pool tuning and DSN options (parseTime, utf8mb4, UTC).
//   3) Ensure initial schema on an empty DB (databasePlatform.EnsureInitialSchema).
//   4) Register gob types needed by sessions (map[string]string, []string, time.Time).
//   5) Create an SCS session manager via platform/session.New.
//   6) Build a Gin engine, attach global middleware, static mounts, and error handlers.
//   7) Inject *App into Gin context (c.Set("app", app)) for handler access.
//   8) Wrap Gin with SCS LoadAndSave, then wrap that with CSRF (nosurf).
//   9) Construct http.Server with Handler and ReadHeaderTimeout.
//
// HTTP stack order (matches code)
//   Gin Router  →  SCS LoadAndSave  →  CSRF Wrapper  →  http.Server
//
// Design guarantees
//   - Single source of truth via the App struct (Config, DB, SessionManager, Router, Handler, Server).
//   - Stable middleware order: SCS wraps Gin before CSRF.
//   - Gin handlers can access *App via c.MustGet("app").
//   - Error surfaces are unified via custom NoRoute/NoMethod/Recovery handlers.
//   - Extensible: add infra (cache/mailer/metrics) here.
//
// Operational details observed in this file
//   - MySQL DSN uses: parseTime=true, charset=utf8mb4, loc=UTC.
//   - Pool sizing and conn lifetime are read from config if set.
//   - Schema application is idempotent and runs on startup.
//   - Static files are served at /static and /favicon.ico.
//   - Logging uses gin.Logger(). Recovery uses gin.CustomRecovery with weberr.Recovery.
//   - ReadHeaderTimeout is set to 10s (currently hard-coded).
//
// Notes & TODOs (code-accurate)
//   - There’s a second DB ping: openMySQL() pings, and Load() pings again.
//     This is harmless but redundant; consider deleting one for clarity.
//   - gin.Recovery() is commented out; we use CustomRecovery instead (intentional).
//   - Consider moving ReadHeaderTimeout to config to match the rest of server tuning.
//
// Change log
//   [2025-10-28] Document EnsureInitialSchema bootstrap, explicit gob registrations,
//                clarified middleware/handler order, and server timeout behavior.
//   [2025-10-24] Migrated to SCS-first wrapping and explicit App wiring.

package bootstrap

import (
	"context"
	"database/sql"
	"encoding/gob"
	"fmt"
	"net/http"
	"time"

	weberr "synlotto-website/internal/http/error"
	databasePlatform "synlotto-website/internal/platform/database"

	"synlotto-website/internal/platform/config"
	"synlotto-website/internal/platform/csrf"
	"synlotto-website/internal/platform/session"

	"github.com/alexedwards/scs/v2"
	"github.com/gin-gonic/gin"

	_ "github.com/go-sql-driver/mysql"
)

type App struct {
	Config         config.Config
	DB             *sql.DB
	SessionManager *scs.SessionManager
	Router         *gin.Engine
	Handler        http.Handler
	Server         *http.Server
}

func Load(configPath string) (*App, error) {
	// Load configuration
	cfg, err := config.Load(configPath)
	if err != nil {
		return nil, fmt.Errorf("load config: %w", err)
	}

	// Open DB
	db, err := openMySQL(cfg)
	if err != nil {
		return nil, err
	}
	// Ensure initial schema (idempotent; safe on restarts)
	if err := databasePlatform.EnsureInitialSchema(db); err != nil {
		return nil, fmt.Errorf("ensure schema: %w", err)
	}

	// Register gob types used in session values
	gob.Register(map[string]string{})
	gob.Register([]string{})
	gob.Register(time.Time{})

	// Create SCS session manager
	sessions := session.New(cfg)

	// Build Gin router and global middleware
	router := gin.New()
	router.Use(gin.Logger())
	router.Static("/static", "./web/static")
	router.StaticFile("/favicon.ico", "./web/static/favicon.ico")

	// Assemble App prior to injecting into context
	app := &App{
		Config:         cfg,
		DB:             db,
		SessionManager: sessions,
		Router:         router,
	}

	// Inject *App into Gin context for handler access
	router.Use(func(c *gin.Context) {
		c.Set("app", app)
		c.Next()
	})

	// Error handling surfaces
	router.NoRoute(weberr.NoRoute(app.SessionManager))
	router.NoMethod(weberr.NoMethod(app.SessionManager))
	router.Use(gin.CustomRecovery(weberr.Recovery(app.SessionManager)))

	// Wrap: Gin → SCS → CSRF (nosurf)
	handler := sessions.LoadAndSave(router)
	handler = csrf.Wrap(handler, cfg)

	// 9) Build HTTP server
	addr := fmt.Sprintf("%s:%d", cfg.HttpServer.Address, cfg.HttpServer.Port)
	srv := &http.Server{
		Addr:              addr,
		Handler:           handler,
		ReadHeaderTimeout: 10 * time.Second, // ToDo: consider moving to config
	}

	app.Handler = handler
	app.Server = srv

	return app, nil
}

func openMySQL(cfg config.Config) (*sql.DB, error) {
	dbCfg := cfg.Database

	// Credentials are used as-is; escaping handled by DSN rules for mysql driver.
	escapedUser := dbCfg.Username
	escapedPass := dbCfg.Password

	// DSN opts: parseTime=true, utf8mb4, UTC location
	dsn := fmt.Sprintf("%s:%s@tcp(%s:%d)/%s?parseTime=true&charset=utf8mb4,utf8&loc=UTC",
		escapedUser,
		escapedPass,
		dbCfg.Server,
		dbCfg.Port,
		dbCfg.DatabaseNamed,
	)

	db, err := sql.Open("mysql", dsn)
	if err != nil {
		return nil, fmt.Errorf("mysql open: %w", err)
	}

	// Pool tuning from config (optional)
	if dbCfg.MaxOpenConnections > 0 {
		db.SetMaxOpenConns(dbCfg.MaxOpenConnections)
	}
	if dbCfg.MaxIdleConnections > 0 {
		db.SetMaxIdleConns(dbCfg.MaxIdleConnections)
	}
	if dbCfg.ConnectionMaxLifetime != "" {
		if d, err := time.ParseDuration(dbCfg.ConnectionMaxLifetime); err == nil {
			db.SetConnMaxLifetime(d)
		}
	}

	// Connectivity check with timeout
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()
	if err := db.PingContext(ctx); err != nil {
		_ = db.Close()
		return nil, fmt.Errorf("mysql ping: %w", err)
	}

	return db, nil
}