package main

import (
	"bufio"
	"context"
	"crypto/tls"
	"os"
	"sync"

	"github.com/jackc/pgx/v5/pgxpool"
	"go.lindenii.runxiyu.org/lindenii-common/scfg"
)

var config struct {
	Server_name string `scfg:"server_name"`
	TLS         struct {
		Cert string `scfg:"cert"`
		Key  string `scfg:"key"`
	} `scfg:"tls"`
	DB struct {
		Type string `scfg:"type"`
		Conn string `scfg:"conn"`
	} `scfg:"db"`
	MX struct {
		Net  string `scfg:"net"`
		Addr string `scfg:"addr"`
	} `scfg:"mx"`
	IMAP struct {
		Net  string `scfg:"net"`
		Addr string `scfg:"addr"`
	} `scfg:"imap"`
	_tls_config *tls.Config
}
var (
	config_mutex          sync.RWMutex // covers things like the database too
	config_context        context.Context
	config_context_cancel context.CancelFunc
	global_db             *pgxpool.Pool // only call Close() after replacing this global variable
)

// load_config loads the configuration file and sets up global things according
// to the configuration directives.
func load_config(path string) error {
	config_file, err := os.Open(path)
	if err != nil {
		return err
	}
	decoder := scfg.NewDecoder(bufio.NewReader(config_file))
	if func() error {
		config_mutex.Lock()
		defer config_mutex.Unlock()
		err = decoder.Decode(&config)
		if err != nil {
			return err
		}
		config_context, config_context_cancel = context.WithCancel(context.Background())

		// TLS key loading and TLS config creation
		cer, err := tls.LoadX509KeyPair(config.TLS.Cert, config.TLS.Key)
		if err != nil {
			return err
		}
		config._tls_config = &tls.Config{
			Certificates: []tls.Certificate{cer},
			MinVersion:   tls.VersionTLS13,
		}

		// Database setup
		if config.DB.Type != "postgres" {
			return err_unsupported_database_type
		}
		global_db, err = pgxpool.New(config_context, config.DB.Conn)
		// BUG: Context-related leak: cancel context when the config is invalidated
		if err != nil {
			return err
		}

		return nil
	}() != nil {
		return err
	}
	return nil
}

// config_fetch_one fetches one value from the configuration.
//
// Consecutive calls do not guarantee a consistent snapshot of the
// configuration. Use config_consistent_run in these cases.
func config_fetch_one[T any](x *T) T {
	config_mutex.RLock()
	defer config_mutex.RUnlock()
	return *x
}

// config_consistent_run runs the supplied function with a consistent snapshot
// of values covered by config_mutex.
func config_consistent_run(f func()) {
	config_mutex.RLock()
	defer config_mutex.RUnlock()
	f()
}