// Package config provides application configuration via environment and files.
package config

import (
	"errors"
	"fmt"
	"log/slog"
	"math"
	"os"
	"strconv"
	"time"

	"github.com/spf13/viper"
	"go.uber.org/fx"
	"sneak.berlin/go/neoirc/internal/globals"
	"sneak.berlin/go/neoirc/internal/logger"

	_ "github.com/joho/godotenv/autoload" // loads .env file
)

const defaultMOTD = ` _ __   ___  ___  (_)_ __ ___
| '_ \ / _ \/ _ \ | | '__/ __|
| | | |  __/ (_) || | | | (__
|_| |_|\___|\___/ |_|_|  \___|

Welcome to NeoIRC — IRC semantics over HTTP.
Type /help for available commands.`

// DefaultDBURL is the database URL used when DBURL is not set. Its
// _pragma parameters, which the SQLite driver runs on every connection
// it opens, set WAL mode and a 5000 ms busy timeout.
const DefaultDBURL = "file:///var/lib/neoirc/state.db" +
	"?_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)"

var errOutOfRange = errors.New("setting out of range")

// Params defines the dependencies for creating a Config.
type Params struct {
	fx.In

	Globals *globals.Globals
	Logger  *logger.Logger
}

// Config holds all application configuration values.
type Config struct {
	DBURL              string
	Debug              bool
	MaintenanceMode    bool
	MetricsPassword    string
	MetricsUsername    string
	Port               int
	SentryDSN          string
	MessageMaxAge      string
	MaxMessageSize     int
	QueueMaxAge        string
	MOTD               string
	ServerName         string
	FederationKey      string
	SessionIdleTimeout string
	HashcashBits       int
	OperName           string
	OperPassword       string
	LoginRateLimit     float64
	LoginRateBurst     int
	IRCListenAddr      string
	params             *Params
	log                *slog.Logger
}

// New creates a new Config by reading from files and environment variables.
// It returns an error when a number, true/false or duration setting does
// not parse or is out of range.
func New(
	_ fx.Lifecycle, params Params,
) (*Config, error) {
	log := params.Logger.Get()
	name := params.Globals.Appname

	viper.SetConfigName(name)
	viper.SetConfigType("yaml")
	viper.AddConfigPath("/etc/" + name)
	viper.AddConfigPath("$HOME/.config/" + name)
	viper.AutomaticEnv()

	viper.SetDefault("DEBUG", "false")
	viper.SetDefault("MAINTENANCE_MODE", "false")
	viper.SetDefault("PORT", "8080")
	viper.SetDefault("DBURL", DefaultDBURL)
	viper.SetDefault("SENTRY_DSN", "")
	viper.SetDefault("METRICS_USERNAME", "")
	viper.SetDefault("METRICS_PASSWORD", "")
	viper.SetDefault("MESSAGE_MAX_AGE", "720h")
	viper.SetDefault("MAX_MESSAGE_SIZE", "4096")
	viper.SetDefault("QUEUE_MAX_AGE", "720h")
	viper.SetDefault("MOTD", defaultMOTD)
	viper.SetDefault("SERVER_NAME", "")
	viper.SetDefault("FEDERATION_KEY", "")
	viper.SetDefault("SESSION_IDLE_TIMEOUT", "720h")
	viper.SetDefault("NEOIRC_HASHCASH_BITS", "20")
	viper.SetDefault("NEOIRC_OPER_NAME", "")
	viper.SetDefault("NEOIRC_OPER_PASSWORD", "")
	viper.SetDefault("LOGIN_RATE_LIMIT", "1")
	viper.SetDefault("LOGIN_RATE_BURST", "5")
	viper.SetDefault("IRC_LISTEN_ADDR", ":6667")

	err := viper.ReadInConfig()
	if err != nil {
		var notFound viper.ConfigFileNotFoundError
		if !errors.As(err, &notFound) {
			log.Error("config file malformed", "error", err)
			panic(err)
		}
	}

	cfg := &Config{
		DBURL:              viper.GetString("DBURL"),
		SentryDSN:          viper.GetString("SENTRY_DSN"),
		MetricsUsername:    viper.GetString("METRICS_USERNAME"),
		MetricsPassword:    viper.GetString("METRICS_PASSWORD"),
		MessageMaxAge:      viper.GetString("MESSAGE_MAX_AGE"),
		QueueMaxAge:        viper.GetString("QUEUE_MAX_AGE"),
		MOTD:               viper.GetString("MOTD"),
		ServerName:         viper.GetString("SERVER_NAME"),
		FederationKey:      viper.GetString("FEDERATION_KEY"),
		SessionIdleTimeout: viper.GetString("SESSION_IDLE_TIMEOUT"),
		OperName:           viper.GetString("NEOIRC_OPER_NAME"),
		OperPassword:       viper.GetString("NEOIRC_OPER_PASSWORD"),
		IRCListenAddr:      viper.GetString("IRC_LISTEN_ADDR"),
		log:                log,
		params:             &params,
	}

	err = parseSettings(cfg)
	if err != nil {
		return nil, err
	}

	// Viper counts an empty environment variable as unset, but an
	// empty IRC_LISTEN_ADDR must turn the IRC listener off.
	ircListenAddr, set := os.LookupEnv("IRC_LISTEN_ADDR")
	if set {
		cfg.IRCListenAddr = ircListenAddr
	}

	if cfg.Debug {
		params.Logger.EnableDebugLogging()
		cfg.log = params.Logger.Get()
	}

	return cfg, nil
}

// parseSettings reads the number and true/false settings into cfg and
// checks the duration settings. Each number and duration must be above
// zero. PORT and NEOIRC_HASHCASH_BITS may also be zero: port 0 lets the
// system pick a port, and 0 bits turns proof of work off. The error
// names each setting that does not parse or is out of range.
func parseSettings(cfg *Config) error {
	return errors.Join(
		parseInt("PORT", 0, &cfg.Port),
		parseInt("MAX_MESSAGE_SIZE", 1, &cfg.MaxMessageSize),
		parseInt("NEOIRC_HASHCASH_BITS", 0, &cfg.HashcashBits),
		parseInt("LOGIN_RATE_BURST", 1, &cfg.LoginRateBurst),
		parseFloat("LOGIN_RATE_LIMIT", &cfg.LoginRateLimit),
		parseBool("DEBUG", &cfg.Debug),
		parseBool("MAINTENANCE_MODE", &cfg.MaintenanceMode),
		checkDuration("MESSAGE_MAX_AGE", cfg.MessageMaxAge),
		checkDuration("QUEUE_MAX_AGE", cfg.QueueMaxAge),
		checkDuration("SESSION_IDLE_TIMEOUT", cfg.SessionIdleTimeout),
	)
}

// parseInt sets *value to the setting key read as a whole number. It
// returns an error when the value does not parse or is below minimum.
func parseInt(key string, minimum int, value *int) error {
	raw := viper.GetString(key)

	parsed, err := strconv.Atoi(raw)
	if err != nil {
		return fmt.Errorf("cannot parse %s: %w", key, err)
	}

	if parsed < minimum {
		return fmt.Errorf("%w: %s is %s, but must be at least %d",
			errOutOfRange, key, raw, minimum)
	}

	*value = parsed

	return nil
}

// parseFloat sets *value to the setting key read as a decimal number. It
// returns an error when the value does not parse or is not a finite
// number above zero.
func parseFloat(key string, value *float64) error {
	raw := viper.GetString(key)

	parsed, err := strconv.ParseFloat(raw, 64)
	if err != nil {
		return fmt.Errorf("cannot parse %s: %w", key, err)
	}

	if math.IsNaN(parsed) || math.IsInf(parsed, 0) || parsed <= 0 {
		return fmt.Errorf(
			"%w: %s is %s, but must be a finite number above zero",
			errOutOfRange, key, raw)
	}

	*value = parsed

	return nil
}

// parseBool sets *value to the setting key read as true or false.
func parseBool(key string, value *bool) error {
	parsed, err := strconv.ParseBool(viper.GetString(key))
	if err != nil {
		return fmt.Errorf("cannot parse %s: %w", key, err)
	}

	*value = parsed

	return nil
}

// checkDuration returns an error naming the setting key when value is
// not a Go duration above zero.
func checkDuration(key, value string) error {
	duration, err := time.ParseDuration(value)
	if err != nil {
		return fmt.Errorf("cannot parse %s: %w", key, err)
	}

	if duration <= 0 {
		return fmt.Errorf("%w: %s is %s, but must be above zero",
			errOutOfRange, key, value)
	}

	return nil
}