// Package config loads application configuration from environment variables.
package config

import (
	"errors"
	"fmt"
	"log/slog"
	"net/netip"
	"os"
	"strconv"
	"strings"
	"time"

	"go.uber.org/fx"
	"sneak.berlin/go/webhooker/internal/globals"
	"sneak.berlin/go/webhooker/internal/logger"

	// Populates the environment from a ./.env file automatically for
	// development configuration. Kept in one place only (here).
	_ "github.com/joho/godotenv/autoload"
)

const (
	// EnvironmentDev represents development environment.
	EnvironmentDev = "dev"
	// EnvironmentProd represents production environment.
	EnvironmentProd = "prod"

	// defaultPort is the default HTTP listen port.
	defaultPort = 8080

	// defaultRetentionSweepInterval is how often the retention
	// reaper deletes events older than each webhook's RetentionDays.
	defaultRetentionSweepInterval = time.Hour

	// defaultSessionIdleTimeout is how long a session may go without
	// authenticated activity before it expires.
	defaultSessionIdleTimeout = 24 * time.Hour

	// defaultReceiverRateLimit is the default number of requests
	// per minute each client IP may send to a single webhook
	// receiver entrypoint. Generous for legitimate webhook
	// senders while bounding abuse of the one unauthenticated,
	// internet-exposed endpoint.
	defaultReceiverRateLimit = 120

	// maxPort is the highest valid TCP port number. The lower
	// bound (at least 1) is enforced by envPositiveInt.
	maxPort = 65535
)

// ErrInvalidEnvironment is returned when WEBHOOKER_ENVIRONMENT
// contains an unrecognised value.
var ErrInvalidEnvironment = errors.New("invalid environment")

// ErrNonPositiveValue is returned when an environment variable that
// requires a positive integer is set to zero or a negative number.
var ErrNonPositiveValue = errors.New("value must be positive")

// ErrInvalidPort is returned when an environment variable holding a
// TCP port number is set above the valid port range.
var ErrInvalidPort = errors.New("invalid port")

// ErrInvalidCIDR is returned when an environment variable holding a
// list of CIDR blocks contains an entry that is neither a CIDR block
// nor a bare IP address.
var ErrInvalidCIDR = errors.New("invalid CIDR")

//nolint:revive // ConfigParams is a standard fx naming convention.
type ConfigParams struct {
	fx.In

	Globals *globals.Globals
	Logger  *logger.Logger
}

// Config holds all application configuration loaded from
// environment variables.
type Config struct {
	DataDir         string
	Debug           bool
	MaintenanceMode bool
	Environment     string
	MetricsPassword string
	MetricsUsername string
	Port            int
	SentryDSN       string

	// RetentionSweepInterval is how often the retention reaper runs.
	RetentionSweepInterval time.Duration

	// SessionIdleTimeout is the sliding inactivity window after
	// which a session expires. Non-positive disables idle expiry.
	SessionIdleTimeout time.Duration

	// ReceiverRateLimit is the number of requests per minute each
	// client IP may send to a single webhook receiver entrypoint.
	ReceiverRateLimit int

	// TrustedProxies is the set of networks whose members are
	// allowed to speak for the client with forwarded headers
	// (X-Forwarded-For, X-Real-IP, True-Client-IP). It is empty
	// unless TRUSTED_PROXIES is set, and empty means no peer is
	// trusted: forwarded headers are then ignored entirely and
	// clients are identified by the connection's own address.
	TrustedProxies []netip.Prefix

	params *ConfigParams
	log    *slog.Logger
}

// IsDev returns true if running in development environment.
func (c *Config) IsDev() bool {
	return c.Environment == EnvironmentDev
}

// IsProd returns true if running in production environment.
func (c *Config) IsProd() bool {
	return c.Environment == EnvironmentProd
}

// envString returns the value of the named environment variable,
// or an empty string if not set.
func envString(key string) string {
	return os.Getenv(key)
}

// envBool returns the value of the named environment variable
// parsed as a boolean. Returns defaultValue if not set. If the
// variable is set but cannot be parsed, it returns a wrapped error
// naming the key and the bad value, so startup fails loudly rather
// than silently falling back to the default.
//
// Parsing is strconv.ParseBool, which accepts 1, t, T, TRUE, true,
// True, 0, f, F, FALSE, false and False. Anything else — "yes",
// "on", or a typo like "ture" — is an error rather than a silent
// false.
func envBool(key string, defaultValue bool) (bool, error) {
	v := os.Getenv(key)
	if v == "" {
		return defaultValue, nil
	}

	b, err := strconv.ParseBool(v)
	if err != nil {
		return false, fmt.Errorf(
			"invalid boolean for %s: %q: %w", key, v, err,
		)
	}

	return b, nil
}

// envPositiveInt returns the value of the named environment variable
// parsed as a positive integer. Returns defaultValue if not set. If
// the variable is set but cannot be parsed, or parses to less than
// one, it returns a wrapped error naming the key and the bad value,
// so startup fails loudly rather than silently falling back to the
// default.
func envPositiveInt(
	key string,
	defaultValue int,
) (int, error) {
	v := os.Getenv(key)
	if v == "" {
		return defaultValue, nil
	}

	i, err := strconv.Atoi(v)
	if err != nil {
		return 0, fmt.Errorf(
			"invalid integer for %s: %q: %w", key, v, err,
		)
	}

	if i < 1 {
		return 0, fmt.Errorf(
			"%w: %s must be at least 1, got %q",
			ErrNonPositiveValue, key, v,
		)
	}

	return i, nil
}

// envPort returns the value of the named environment variable parsed
// as a TCP port number. Returns defaultValue if not set. A set value
// that is unparseable, below 1, or above maxPort is a hard error
// naming the key and the bad value.
func envPort(key string, defaultValue int) (int, error) {
	port, err := envPositiveInt(key, defaultValue)
	if err != nil {
		return 0, err
	}

	if port > maxPort {
		return 0, fmt.Errorf(
			"%w: %s must be at most %d, got %d",
			ErrInvalidPort, key, maxPort, port,
		)
	}

	return port, nil
}

// envDuration returns the value of the named environment variable
// parsed as a Go duration (e.g. "1h", "30m"). Returns defaultValue if
// not set. If the variable is set but cannot be parsed, it returns a
// wrapped error naming the key and the bad value, so startup fails
// loudly rather than silently falling back to the default.
func envDuration(
	key string,
	defaultValue time.Duration,
) (time.Duration, error) {
	v := os.Getenv(key)
	if v == "" {
		return defaultValue, nil
	}

	d, err := time.ParseDuration(v)
	if err != nil {
		return 0, fmt.Errorf(
			"invalid duration for %s: %q: %w", key, v, err,
		)
	}

	return d, nil
}

// parseCIDR parses one trusted-proxy list entry, which may be a
// CIDR block ("10.0.0.0/8") or a bare address ("10.0.0.1", treated
// as a single-host block).
func parseCIDR(entry string) (netip.Prefix, error) {
	if strings.Contains(entry, "/") {
		prefix, err := netip.ParsePrefix(entry)
		if err != nil {
			return netip.Prefix{}, err //nolint:wrapcheck // wrapped by caller
		}

		return prefix.Masked(), nil
	}

	addr, err := netip.ParseAddr(entry)
	if err != nil {
		return netip.Prefix{}, err //nolint:wrapcheck // wrapped by caller
	}

	return netip.PrefixFrom(addr.Unmap(), addr.Unmap().BitLen()), nil
}

// envPrefixList returns the value of the named environment variable
// parsed as a comma-separated list of CIDR blocks (bare addresses
// allowed). An unset, empty, or blank value yields an empty list. A
// set value containing an unparseable entry is a hard error naming
// the key and the bad entry, so startup fails loudly rather than
// silently running with a list the operator did not intend.
func envPrefixList(key string) ([]netip.Prefix, error) {
	v := strings.TrimSpace(os.Getenv(key))
	if v == "" {
		return nil, nil
	}

	var prefixes []netip.Prefix

	for entry := range strings.SplitSeq(v, ",") {
		entry = strings.TrimSpace(entry)
		if entry == "" {
			continue
		}

		prefix, err := parseCIDR(entry)
		if err != nil {
			return nil, fmt.Errorf(
				"%w: %s: %q: %w", ErrInvalidCIDR, key, entry, err,
			)
		}

		prefixes = append(prefixes, prefix)
	}

	return prefixes, nil
}

// resolveEnvironment reads WEBHOOKER_ENVIRONMENT, defaulting to
// dev, and rejects unrecognised values.
func resolveEnvironment() (string, error) {
	environment := os.Getenv("WEBHOOKER_ENVIRONMENT")
	if environment == "" {
		environment = EnvironmentDev
	}

	if environment != EnvironmentDev &&
		environment != EnvironmentProd {
		return "", fmt.Errorf(
			"%w: WEBHOOKER_ENVIRONMENT must be '%s' or '%s', got '%s'",
			ErrInvalidEnvironment,
			EnvironmentDev, EnvironmentProd, environment,
		)
	}

	return environment, nil
}

// loadFromEnv builds a Config from the environment. Every value that
// needs parsing fails loudly when it is set but unparseable: the
// documented defaults apply only to variables that are unset (or
// empty), never as a substitute for a value the operator actually
// provided.
func loadFromEnv() (*Config, error) {
	environment, err := resolveEnvironment()
	if err != nil {
		return nil, err
	}

	port, err := envPort("PORT", defaultPort)
	if err != nil {
		return nil, err
	}

	debug, err := envBool("DEBUG", false)
	if err != nil {
		return nil, err
	}

	maintenanceMode, err := envBool("MAINTENANCE_MODE", false)
	if err != nil {
		return nil, err
	}

	retentionSweepInterval, err := envDuration(
		"RETENTION_SWEEP_INTERVAL",
		defaultRetentionSweepInterval,
	)
	if err != nil {
		return nil, err
	}

	sessionIdleTimeout, err := envDuration(
		"SESSION_IDLE_TIMEOUT",
		defaultSessionIdleTimeout,
	)
	if err != nil {
		return nil, err
	}

	receiverRateLimit, err := envPositiveInt(
		"RECEIVER_RATE_LIMIT",
		defaultReceiverRateLimit,
	)
	if err != nil {
		return nil, err
	}

	trustedProxies, err := envPrefixList("TRUSTED_PROXIES")
	if err != nil {
		return nil, err
	}

	return &Config{
		DataDir:                envString("DATA_DIR"),
		Debug:                  debug,
		MaintenanceMode:        maintenanceMode,
		Environment:            environment,
		MetricsUsername:        envString("METRICS_USERNAME"),
		MetricsPassword:        envString("METRICS_PASSWORD"),
		Port:                   port,
		SentryDSN:              envString("SENTRY_DSN"),
		RetentionSweepInterval: retentionSweepInterval,
		SessionIdleTimeout:     sessionIdleTimeout,
		ReceiverRateLimit:      receiverRateLimit,
		TrustedProxies:         trustedProxies,
	}, nil
}

// New creates a Config by reading environment variables.
//
//nolint:revive // lc parameter is required by fx even if unused.
func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
	log := params.Logger.Get()

	// A set-but-unparseable value anywhere in the environment is a
	// hard error, so fx aborts startup rather than running with a
	// silently substituted default.
	s, err := loadFromEnv()
	if err != nil {
		return nil, err
	}

	s.log = log
	s.params = &params

	// Set default DataDir. All SQLite databases (main application
	// DB and per-webhook event DBs) live here. The same default is
	// used regardless of environment; override with DATA_DIR if
	// needed.
	if s.DataDir == "" {
		s.DataDir = "/var/lib/webhooker"
	}

	if s.Debug {
		params.Logger.EnableDebugLogging()
	}

	// Log configuration summary (without secrets)
	log.Info("Configuration loaded",
		"environment", s.Environment,
		"port", s.Port,
		"debug", s.Debug,
		"maintenanceMode", s.MaintenanceMode,
		"dataDir", s.DataDir,
		"retentionSweepInterval", s.RetentionSweepInterval.String(),
		"receiverRateLimit", s.ReceiverRateLimit,
		"trustedProxies", len(s.TrustedProxies),
		"hasSentryDSN", s.SentryDSN != "",
		"hasMetricsAuth",
		s.MetricsUsername != "" && s.MetricsPassword != "",
	)

	return s, nil
}