// backend\setup\main.go

package main

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"flag"
	"fmt"
	"log"
	"net/url"
	"os"
	"strings"
	"time"

	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
	"github.com/joho/godotenv"
	"golang.org/x/crypto/bcrypt"
)

func main() {
	reset := flag.Bool("reset", false, "Datenbank komplett löschen und neu anlegen")
	flag.Parse()

	if err := godotenv.Load(".env", "backend/.env"); err != nil {
		log.Println("Keine .env Datei gefunden, nutze System-Environment oder Fallbacks")
	}

	databaseURL := env("DATABASE_URL", "postgres://postgres:postgres@localhost:5432/teg?sslmode=disable")

	parsedURL, err := url.Parse(databaseURL)
	if err != nil {
		log.Fatal(err)
	}

	databaseName := strings.TrimPrefix(parsedURL.Path, "/")
	if databaseName == "" {
		log.Fatal("DATABASE_URL enthält keinen Datenbanknamen")
	}

	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	if *reset {
		if err := dropDatabaseIfExists(ctx, parsedURL, databaseName); err != nil {
			log.Fatal(err)
		}
	}

	if err := createDatabaseIfNotExists(ctx, parsedURL, databaseName); err != nil {
		log.Fatal(err)
	}

	db, err := pgxpool.New(ctx, databaseURL)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	if err := db.Ping(ctx); err != nil {
		log.Fatal(err)
	}

	if err := createSchema(ctx, db); err != nil {
		log.Fatal(err)
	}

	password, created, err := createAdminIfNotExists(ctx, db)
	if err != nil {
		log.Fatal(err)
	}

	printAdminResult(password, created)
}

func dropDatabaseIfExists(ctx context.Context, parsedURL *url.URL, databaseName string) error {
	if databaseName == "postgres" || databaseName == "template0" || databaseName == "template1" {
		return fmt.Errorf("datenbank %q darf nicht per -reset gelöscht werden", databaseName)
	}

	maintenanceURL := *parsedURL
	maintenanceURL.Path = "/postgres"

	db, err := pgxpool.New(ctx, maintenanceURL.String())
	if err != nil {
		return err
	}
	defer db.Close()

	var exists bool

	err = db.QueryRow(
		ctx,
		`SELECT EXISTS(SELECT 1 FROM pg_database WHERE datname = $1)`,
		databaseName,
	).Scan(&exists)

	if err != nil {
		return err
	}

	if !exists {
		fmt.Printf("Datenbank %q existiert nicht, Reset übersprungen\n", databaseName)
		return nil
	}

	fmt.Printf("Datenbank %q wird zurückgesetzt...\n", databaseName)

	_, err = db.Exec(
		ctx,
		`
		SELECT pg_terminate_backend(pid)
		FROM pg_stat_activity
		WHERE datname = $1
		  AND pid <> pg_backend_pid()
		`,
		databaseName,
	)

	if err != nil {
		return err
	}

	_, err = db.Exec(ctx, `DROP DATABASE IF EXISTS `+quoteIdentifier(databaseName))
	if err != nil {
		return err
	}

	fmt.Printf("Datenbank %q wurde gelöscht\n", databaseName)

	return nil
}

func createDatabaseIfNotExists(ctx context.Context, parsedURL *url.URL, databaseName string) error {
	maintenanceURL := *parsedURL
	maintenanceURL.Path = "/postgres"

	db, err := pgxpool.New(ctx, maintenanceURL.String())
	if err != nil {
		return err
	}
	defer db.Close()

	var exists bool

	err = db.QueryRow(
		ctx,
		`SELECT EXISTS(SELECT 1 FROM pg_database WHERE datname = $1)`,
		databaseName,
	).Scan(&exists)

	if err != nil {
		return err
	}

	if exists {
		fmt.Printf("Datenbank %q existiert bereits\n", databaseName)
		return nil
	}

	_, err = db.Exec(ctx, `CREATE DATABASE `+quoteIdentifier(databaseName))
	if err != nil {
		return err
	}

	fmt.Printf("Datenbank %q wurde erstellt\n", databaseName)

	return nil
}

func createSchema(ctx context.Context, db *pgxpool.Pool) error {
	queries := []string{
		`CREATE EXTENSION IF NOT EXISTS pgcrypto`,

		`
		CREATE TABLE IF NOT EXISTS users (
			id UUID PRIMARY KEY DEFAULT gen_random_uuid(),

			username TEXT UNIQUE,
			display_name TEXT,

			email TEXT NOT NULL UNIQUE,
			password_hash TEXT NOT NULL,

			avatar TEXT,
			unit TEXT,
			user_group TEXT,
			rights TEXT[] NOT NULL DEFAULT '{}'::TEXT[],

			created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
			updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
		)
		`,

		`
		CREATE TABLE IF NOT EXISTS teams (
			id UUID PRIMARY KEY DEFAULT gen_random_uuid(),

			name TEXT NOT NULL UNIQUE,
			initial TEXT NOT NULL,
			href TEXT NOT NULL DEFAULT '#',

			created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
			updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
		)
		`,

		`
		CREATE TABLE IF NOT EXISTS user_teams (
			user_id UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
			team_id UUID NOT NULL REFERENCES teams(id) ON DELETE CASCADE,

			created_at TIMESTAMPTZ NOT NULL DEFAULT now(),

			PRIMARY KEY (user_id, team_id)
		)
		`,

		`
		CREATE TABLE IF NOT EXISTS devices (
			id UUID PRIMARY KEY DEFAULT gen_random_uuid(),

			inventory_number TEXT NOT NULL,
			manufacturer TEXT NOT NULL DEFAULT '',
			model TEXT NOT NULL DEFAULT '',
			serial_number TEXT NOT NULL DEFAULT '',
			mac_address TEXT NOT NULL DEFAULT '',
			location TEXT NOT NULL DEFAULT '',
			loan_status TEXT NOT NULL DEFAULT 'Verfügbar',
			comment TEXT NOT NULL DEFAULT '',

			created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
			updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
		)
		`,

		`
		CREATE TABLE IF NOT EXISTS device_relations (
			device_id UUID NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
			related_device_id UUID NOT NULL REFERENCES devices(id) ON DELETE CASCADE,

			created_at TIMESTAMPTZ NOT NULL DEFAULT now(),

			PRIMARY KEY (device_id, related_device_id),
			CONSTRAINT device_relations_no_self_reference CHECK (device_id <> related_device_id)
		)
		`,

		`
		CREATE TABLE IF NOT EXISTS device_history (
			id UUID PRIMARY KEY DEFAULT gen_random_uuid(),

			device_id UUID NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
			user_id UUID REFERENCES users(id) ON DELETE SET NULL,

			action TEXT NOT NULL,
			changes JSONB NOT NULL DEFAULT '[]'::JSONB,

			created_at TIMESTAMPTZ NOT NULL DEFAULT now()
		)
		`,

		`CREATE INDEX IF NOT EXISTS idx_users_email ON users(email)`,
		`CREATE INDEX IF NOT EXISTS idx_users_username ON users(username)`,

		`CREATE INDEX IF NOT EXISTS idx_teams_name ON teams(name)`,
		`CREATE INDEX IF NOT EXISTS idx_user_teams_user_id ON user_teams(user_id)`,
		`CREATE INDEX IF NOT EXISTS idx_user_teams_team_id ON user_teams(team_id)`,

		`CREATE UNIQUE INDEX IF NOT EXISTS idx_devices_inventory_number_unique ON devices(lower(inventory_number))`,
		`CREATE UNIQUE INDEX IF NOT EXISTS idx_devices_serial_number_unique ON devices(lower(serial_number)) WHERE serial_number <> ''`,
		`CREATE UNIQUE INDEX IF NOT EXISTS idx_devices_mac_address_unique ON devices(lower(mac_address)) WHERE mac_address <> ''`,

		`CREATE INDEX IF NOT EXISTS idx_devices_manufacturer ON devices(manufacturer)`,
		`CREATE INDEX IF NOT EXISTS idx_devices_model ON devices(model)`,
		`CREATE INDEX IF NOT EXISTS idx_devices_location ON devices(location)`,
		`CREATE INDEX IF NOT EXISTS idx_devices_loan_status ON devices(loan_status)`,

		`CREATE INDEX IF NOT EXISTS idx_device_relations_device_id ON device_relations(device_id)`,
		`CREATE INDEX IF NOT EXISTS idx_device_relations_related_device_id ON device_relations(related_device_id)`,

		`CREATE INDEX IF NOT EXISTS idx_device_history_device_id ON device_history(device_id)`,
		`CREATE INDEX IF NOT EXISTS idx_device_history_user_id ON device_history(user_id)`,
		`CREATE INDEX IF NOT EXISTS idx_device_history_created_at ON device_history(created_at)`,
	}

	for _, query := range queries {
		if _, err := db.Exec(ctx, query); err != nil {
			return err
		}
	}

	fmt.Println("Tabellen und Indizes wurden erstellt oder existieren bereits")

	return nil
}

func createAdminIfNotExists(ctx context.Context, db *pgxpool.Pool) (string, bool, error) {
	adminUsername := env("ADMIN_USERNAME", "admin")
	adminDisplayName := env("ADMIN_DISPLAY_NAME", "Administrator")
	adminEmail := env("ADMIN_EMAIL", "admin@example.com")
	adminAvatar := env("ADMIN_AVATAR", "")
	adminUnit := env("ADMIN_UNIT", "Administration")
	adminGroup := env("ADMIN_GROUP", "admin")
	adminRights := splitCSV(env("ADMIN_RIGHTS", "admin,users:read,users:write,teams:read,teams:write,devices:read,devices:write"))

	adminTeamName := env("ADMIN_TEAM_NAME", "Administration")
	adminTeamInitial := env("ADMIN_TEAM_INITIAL", "A")
	adminTeamHref := env("ADMIN_TEAM_HREF", "#")

	teamID, err := ensureTeam(ctx, db, adminTeamName, adminTeamInitial, adminTeamHref)
	if err != nil {
		return "", false, err
	}

	var existingUserID string

	err = db.QueryRow(
		ctx,
		`
		SELECT id
		FROM users
		WHERE username = $1 OR email = $2
		LIMIT 1
		`,
		adminUsername,
		adminEmail,
	).Scan(&existingUserID)

	if err == nil {
		if err := assignUserToTeam(ctx, db, existingUserID, teamID); err != nil {
			return "", false, err
		}

		return "", false, nil
	}

	if !errors.Is(err, pgx.ErrNoRows) {
		return "", false, err
	}

	password, err := generatePassword(24)
	if err != nil {
		return "", false, err
	}

	passwordHash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
	if err != nil {
		return "", false, err
	}

	var userID string

	err = db.QueryRow(
		ctx,
		`
		INSERT INTO users (
			username,
			display_name,
			email,
			password_hash,
			avatar,
			unit,
			user_group,
			rights
		)
		VALUES ($1, $2, $3, $4, $5, $6, $7, $8::TEXT[])
		RETURNING id
		`,
		adminUsername,
		adminDisplayName,
		adminEmail,
		string(passwordHash),
		adminAvatar,
		adminUnit,
		adminGroup,
		toPostgresTextArray(adminRights),
	).Scan(&userID)

	if err != nil {
		return "", false, err
	}

	if err := assignUserToTeam(ctx, db, userID, teamID); err != nil {
		return "", false, err
	}

	return password, true, nil
}

func ensureTeam(ctx context.Context, db *pgxpool.Pool, name string, initial string, href string) (string, error) {
	name = strings.TrimSpace(name)
	initial = strings.TrimSpace(initial)
	href = strings.TrimSpace(href)

	if name == "" {
		name = "Administration"
	}

	if initial == "" {
		initial = strings.ToUpper(string([]rune(name)[0]))
	}

	if href == "" {
		href = "#"
	}

	var teamID string

	err := db.QueryRow(
		ctx,
		`
		INSERT INTO teams (name, initial, href)
		VALUES ($1, $2, $3)
		ON CONFLICT (name)
		DO UPDATE SET
			initial = EXCLUDED.initial,
			href = EXCLUDED.href,
			updated_at = now()
		RETURNING id
		`,
		name,
		initial,
		href,
	).Scan(&teamID)

	return teamID, err
}

func assignUserToTeam(ctx context.Context, db *pgxpool.Pool, userID string, teamID string) error {
	_, err := db.Exec(
		ctx,
		`
		INSERT INTO user_teams (user_id, team_id)
		VALUES ($1, $2)
		ON CONFLICT (user_id, team_id) DO NOTHING
		`,
		userID,
		teamID,
	)

	return err
}

func generatePassword(length int) (string, error) {
	randomBytes := make([]byte, length)

	if _, err := rand.Read(randomBytes); err != nil {
		return "", err
	}

	password := base64.RawURLEncoding.EncodeToString(randomBytes)

	if len(password) > length {
		password = password[:length]
	}

	return password, nil
}

func printAdminResult(password string, created bool) {
	adminUsername := env("ADMIN_USERNAME", "admin")
	adminEmail := env("ADMIN_EMAIL", "admin@example.com")
	adminTeamName := env("ADMIN_TEAM_NAME", "Administration")

	fmt.Println("")

	if created {
		fmt.Println("=================================================")
		fmt.Println("Admin-User wurde erstellt")
		fmt.Println("=================================================")
		fmt.Printf("Benutzername: %s\n", adminUsername)
		fmt.Printf("E-Mail:       %s\n", adminEmail)
		fmt.Printf("Team:         %s\n", adminTeamName)
		fmt.Printf("Passwort:     %s\n", password)
		fmt.Println("=================================================")
		fmt.Println("Bitte Passwort sicher speichern. Es wird nicht erneut angezeigt.")
		fmt.Println("")
		return
	}

	fmt.Println("=================================================")
	fmt.Println("Admin-User existiert bereits")
	fmt.Println("=================================================")
	fmt.Printf("Benutzername: %s\n", adminUsername)
	fmt.Printf("E-Mail:       %s\n", adminEmail)
	fmt.Printf("Team:         %s\n", adminTeamName)
	fmt.Println("Passwort:     wird nicht angezeigt, da nur der Hash gespeichert wird")
	fmt.Println("=================================================")
	fmt.Println("")
}

func toPostgresTextArray(values []string) string {
	if len(values) == 0 {
		return "{}"
	}

	escaped := make([]string, 0, len(values))

	for _, value := range values {
		value = strings.TrimSpace(value)

		if value == "" {
			continue
		}

		value = strings.ReplaceAll(value, `\`, `\\`)
		value = strings.ReplaceAll(value, `"`, `\"`)

		escaped = append(escaped, `"`+value+`"`)
	}

	if len(escaped) == 0 {
		return "{}"
	}

	return "{" + strings.Join(escaped, ",") + "}"
}

func splitCSV(value string) []string {
	parts := strings.Split(value, ",")
	result := make([]string, 0, len(parts))

	for _, part := range parts {
		part = strings.TrimSpace(part)

		if part != "" {
			result = append(result, part)
		}
	}

	return result
}

func quoteIdentifier(value string) string {
	return `"` + strings.ReplaceAll(value, `"`, `""`) + `"`
}

func env(key string, fallback string) string {
	value := os.Getenv(key)

	if value == "" {
		return fallback
	}

	return value
}