package config

import (
	"fmt"
	"strconv"
	"time"
)

// AppKey describes one application-configuration key: instance-global,
// stored (as an override) in the DB `config` table, read once at startup.
// Cold -- a changed value applies on the next backend restart.
type AppKey struct {
	Key         string
	Default     string
	Description string
	Validate    func(value string) error
}

// KeySessionDuration is the session cookie lifetime, in integer hours.
const (
	KeySessionDuration = "session.duration"
	// KeySessionIdleTimeout bounds an *onboarding Garmin session* (the
	// ephemeral, pre-account login attempt), not the login cookie --
	// session.duration is how long a signed-in user stays signed in
	// (hours); session.idle_timeout is how long an unfinished setup
	// attempt survives untouched before its subprocess is torn down
	// (minutes).
	KeySessionIdleTimeout = "session.idle_timeout"
)

var appRegistry = []AppKey{
	{
		Key:         KeySessionDuration,
		Default:     "720",
		Description: "Session cookie lifetime in hours",
		Validate:    validatePositiveInt,
	},
	{
		Key:         KeySessionIdleTimeout,
		Default:     "15",
		Description: "Idle timeout in minutes for an unfinished onboarding Garmin session",
		Validate:    validatePositiveInt,
	},
}

// AppRegistry returns every known application-configuration key, in
// display order.
func AppRegistry() []AppKey { return appRegistry }

func validatePositiveInt(v string) error {
	n, err := strconv.Atoi(v)
	if err != nil || n <= 0 {
		return fmt.Errorf("must be a positive integer, got %q", v)
	}
	return nil
}

// ValidateAppValue rejects unknown keys and invalid values -- every write
// path's guard, so the config table can never accumulate junk.
func ValidateAppValue(key, value string) error {
	for _, k := range appRegistry {
		if k.Key == key {
			if err := k.Validate(value); err != nil {
				return fmt.Errorf("%s: %w", key, err)
			}
			return nil
		}
	}
	return fmt.Errorf("unknown configuration key %q", key)
}

// AppConfig is the typed result of merging DB overrides over registry
// defaults.
type AppConfig struct {
	SessionDuration         time.Duration
	SetupSessionIdleTimeout time.Duration
}

// LoadApp merges overrides (store.ConfigValues' map) over defaults. Pure
// -- it takes the raw map instead of a *store.DB so this package needs no
// store dependency and the merge logic tests without a database. A bad
// stored value fails fast, same posture as LoadEnv() for env vars.
func LoadApp(overrides map[string]string) (AppConfig, error) {
	merged := map[string]string{}
	for _, k := range appRegistry {
		merged[k.Key] = k.Default
	}
	for key, value := range overrides {
		if err := ValidateAppValue(key, value); err != nil {
			return AppConfig{}, fmt.Errorf("app config: %w", err)
		}
		merged[key] = value
	}
	hours, _ := strconv.Atoi(merged[KeySessionDuration])
	idleMinutes, _ := strconv.Atoi(merged[KeySessionIdleTimeout])
	return AppConfig{
		SessionDuration:         time.Duration(hours) * time.Hour,
		SetupSessionIdleTimeout: time.Duration(idleMinutes) * time.Minute,
	}, nil
}