async fn get_settings(State(state): State<AppState>) -> Json<Value> {
    let settings = state.settings.read().await;
    Json(public_settings(&*settings))
}

async fn update_settings(State(state): State<AppState>, Json(mut input): Json<RuntimeSettings>) -> Result<Json<Value>, AppError> {
    let _configuration_guard = state.lock_configuration_operation().await;
    let _house_guard = state.lock_house_operation().await;
    let _cycle_guard = state.lock_zone_control_cycle().await;
    let old = state.settings.read().await.clone();
    if input.house_power_enabled != old.house_power_enabled || input.house_mode != old.house_mode {
        return Err(AppError::BadRequest(
            "house_power_enabled and house_mode must be changed through the House Control API".into(),
        ));
    }
    input.poll_interval_seconds = input.poll_interval_seconds.clamp(2, 3600);
    input.zone_interval_seconds = input.zone_interval_seconds.clamp(2, 3600);
    input.discovery_timeout_ms = input.discovery_timeout_ms.clamp(300, 30_000);
    if !matches!(input.house_mode.as_str(), "cool" | "heat" | "off") { return Err(AppError::BadRequest("house mode must be cool, heat or off".into())); }
    if input.control_strategy != "setpoint" { input.control_strategy = "setpoint".into(); }
    if !(input.discovery_broadcast.eq_ignore_ascii_case("auto")
        || input.discovery_broadcast.to_ascii_lowercase().starts_with("auto:")) {
        input.discovery_broadcast.parse::<std::net::SocketAddr>()
            .map_err(|_| AppError::BadRequest("invalid discovery broadcast address".into()))?;
    }
    if input.controller_id.trim().is_empty() { input.controller_id = old.controller_id; }
    if input.home_assistant.token.trim().is_empty() { input.home_assistant.token = old.home_assistant.token; }
    input.home_assistant.sensor_stale_after_seconds = input.home_assistant.sensor_stale_after_seconds.clamp(30, 86_400);
    if input.notifications.pushover_app_token.trim().is_empty() { input.notifications.pushover_app_token = old.notifications.pushover_app_token; }
    if input.notifications.pushover_user_key.trim().is_empty() { input.notifications.pushover_user_key = old.notifications.pushover_user_key; }
    if input.notifications.slack_webhook_url.trim().is_empty() { input.notifications.slack_webhook_url = old.notifications.slack_webhook_url; }
    if input.notifications.discord_webhook_url.trim().is_empty() { input.notifications.discord_webhook_url = old.notifications.discord_webhook_url; }
    input.notifications.cooldown_seconds = input.notifications.cooldown_seconds.clamp(30, 86_400);
    input.notifications.communication_failure_threshold = input.notifications.communication_failure_threshold.clamp(2, 100);
    input.notifications.target_timeout_minutes = input.notifications.target_timeout_minutes.clamp(5, 24 * 60);
    if !matches!(input.notifications.mode.as_str(), "problems" | "important") { return Err(AppError::BadRequest("notification mode must be problems or important".into())); }
    if !matches!(input.notifications.provider.as_str(), "pushover" | "slack" | "discord") { return Err(AppError::BadRequest("unsupported notification provider".into())); }
    input.history_retention_days = input.history_retention_days.clamp(1, 3650);
    input.event_log_retention_days = input.event_log_retention_days.clamp(1, 3650);
    normalize_sensor_aliases(&mut input);
    canonicalize_home_assistant_entities(&mut input);
    validate_night_mode(&mut input)?;
    input.influxdb.history_threshold_days = input.influxdb.history_threshold_days.clamp(1, 3650);
    if input.influxdb.token.trim().is_empty() { input.influxdb.token = old.influxdb.token; }
    if input.influxdb.password.trim().is_empty() { input.influxdb.password = old.influxdb.password; }
    influxdb::validate(&input.influxdb).map_err(|err| AppError::BadRequest(err.to_string()))?;
    if !input.home_assistant.url.trim().is_empty() {
        let parsed = url::Url::parse(&input.home_assistant.url).map_err(|_| AppError::BadRequest("invalid Home Assistant URL".into()))?;
        if !matches!(parsed.scheme(), "http" | "https") { return Err(AppError::BadRequest("Home Assistant URL must use http or https".into())); }
    }
    state.db.save_runtime_settings(&input)?;
    canonicalize_saved_zone_entities(&state, &input).await?;
    state.debug_gree_frames.store(input.debug.gree_frames, Ordering::Relaxed);
    *state.settings.write().await = input.clone();
    state.log("info", "settings.updated", "Settings updated", json!({}));
    state.broadcast("settings.updated", public_settings(&input));
    state.wake_zone_control();
    Ok(Json(public_settings(&input)))
}

fn normalize_sensor_aliases(settings: &mut RuntimeSettings) {
    settings.home_assistant.sensor_aliases = settings.home_assistant.sensor_aliases
        .iter()
        .filter_map(|(entity, alias)| {
            let entity = entity.trim();
            let alias = alias.trim();
            if entity.is_empty() || alias.is_empty() { return None; }
            Some((entity.chars().take(160).collect::<String>(), alias.chars().take(80).collect::<String>()))
        })
        .collect();
}

fn canonicalize_home_assistant_entities(settings: &mut RuntimeSettings) {
    let default_entity = settings.home_assistant.default_entity_id.clone();
    if let Some(entity_id) = home_assistant::resolve_entity_id(&settings.home_assistant, Some(&default_entity)) {
        settings.home_assistant.default_entity_id = entity_id;
    }
    let outdoor_entity = settings.home_assistant.outdoor_entity_id.clone();
    if !outdoor_entity.trim().is_empty() {
        if let Some(entity_id) = home_assistant::resolve_entity_id(&settings.home_assistant, Some(&outdoor_entity)) {
            settings.home_assistant.outdoor_entity_id = entity_id;
        }
    }
}

fn canonicalize_zone_ha_entity(zone: &mut Zone, settings: &RuntimeSettings) {
    let Some(configured) = zone.ha_entity_id.clone() else { return; };
    zone.ha_entity_id = home_assistant::resolve_entity_id(&settings.home_assistant, Some(&configured));
}

async fn canonicalize_saved_zone_entities(state: &AppState, settings: &RuntimeSettings) -> Result<(), AppError> {
    let mut zone_ids: Vec<String> = state.db.list_zones()?.into_iter().map(|zone| zone.id).collect();
    zone_ids.sort();
    zone_ids.dedup();
    for zone_id in zone_ids {
        let _zone_guard = state.lock_zone_operation(&zone_id).await;
        let Some(snapshot) = state.db.get_zone(&zone_id)? else { continue; };
        let _device_guard = state.lock_device_operation(&snapshot.device_id).await;
        let Some(mut zone) = state.db.get_zone(&zone_id)? else { continue; };
        let previous = zone.ha_entity_id.clone();
        canonicalize_zone_ha_entity(&mut zone, settings);
        if zone.ha_entity_id != previous {
            zone.updated_at = Utc::now();
            state.db.save_zone(&zone)?;
            state.broadcast("zone.updated", serde_json::to_value(&zone)?);
        }
    }
    Ok(())
}

fn validate_night_mode(settings: &mut RuntimeSettings) -> Result<(), AppError> {
    NaiveTime::parse_from_str(&settings.night_mode.start_time, "%H:%M")
        .map_err(|_| AppError::BadRequest("night mode start time must use HH:MM".into()))?;
    NaiveTime::parse_from_str(&settings.night_mode.end_time, "%H:%M")
        .map_err(|_| AppError::BadRequest("night mode end time must use HH:MM".into()))?;
    settings.night_mode.max_fan_speed = settings.night_mode.max_fan_speed.clamp(1, 5);
    Ok(())
}

async fn export_settings(State(state): State<AppState>) -> Result<Json<ConfigurationExport>, AppError> {
    let settings = state.settings.read().await.clone();
    let mut export = state.db.export_configuration(settings)?;
    // Backups are configuration snapshots, not a way to resurrect transient ownership,
    // timers or a stale physical device state after restore (K9).
    sanitize_configuration_runtime(&mut export);
    Ok(Json(export))
}

fn validate_configuration_export(export: &ConfigurationExport) -> Result<(), AppError> {
    if export.format_version != 1 { return Err(AppError::BadRequest("unsupported configuration export version".into())); }
    influxdb::validate(&export.settings.influxdb).map_err(|err| AppError::BadRequest(err.to_string()))?;
    if !matches!(export.settings.house_mode.as_str(), "cool" | "heat" | "off") {
        return Err(AppError::BadRequest("import contains an invalid house mode".into()));
    }

    let devices: std::collections::HashSet<&str> = export.devices.iter().map(|item| item.id.as_str()).collect();
    let zones: std::collections::HashSet<&str> = export.zones.iter().map(|item| item.id.as_str()).collect();
    let schedules: std::collections::HashSet<&str> = export.schedules.iter().map(|item| item.id.as_str()).collect();
    let automations: std::collections::HashSet<&str> = export.automations.iter().map(|item| item.id.as_str()).collect();
    if devices.len() != export.devices.len() || zones.len() != export.zones.len()
        || schedules.len() != export.schedules.len() || automations.len() != export.automations.len()
        || devices.contains("") || zones.contains("") || schedules.contains("") || automations.contains("")
    {
        return Err(AppError::BadRequest("import contains duplicate or empty resource IDs".into()));
    }
    let device_macs: std::collections::HashSet<&str> = export.devices.iter().map(|item| item.mac.as_str()).collect();
    if device_macs.len() != export.devices.len() {
        return Err(AppError::BadRequest("import contains duplicate device MAC addresses".into()));
    }
    if export.zones.iter().any(|item| !devices.contains(item.device_id.as_str())) {
        return Err(AppError::BadRequest("import contains a zone referencing a missing device".into()));
    }
    let mut zone_devices = std::collections::HashSet::new();
    for zone in &export.zones {
        if !zone_devices.insert(zone.device_id.as_str()) {
            return Err(AppError::BadRequest("import assigns one device to more than one thermostat zone".into()));
        }
        if !matches!(zone.mode.as_str(), "cool" | "heat") {
            return Err(AppError::BadRequest("import contains an invalid zone mode".into()));
        }
        if !matches!(zone.sensor_source.as_str(), "device" | "home_assistant" | "combined") {
            return Err(AppError::BadRequest("import contains an invalid zone sensor source".into()));
        }
    }

    if export.schedules.iter().any(|item| !zones.contains(item.zone_id.as_str())) {
        return Err(AppError::BadRequest("import contains a schedule referencing a missing zone".into()));
    }
    for item in &export.schedules {
        if item.weekdays.is_empty() || item.weekdays.iter().any(|day| !(1..=7).contains(day)) {
            return Err(AppError::BadRequest("import contains invalid schedule weekdays".into()));
        }
        NaiveTime::parse_from_str(&item.start_time, "%H:%M").map_err(|_| AppError::BadRequest("import contains an invalid schedule start time".into()))?;
        NaiveTime::parse_from_str(&item.end_time, "%H:%M").map_err(|_| AppError::BadRequest("import contains an invalid schedule end time".into()))?;
        if !matches!(item.preset.as_str(), "comfort" | "sleep" | "away" | "custom") {
            return Err(AppError::BadRequest("import contains an invalid schedule preset".into()));
        }
        if item.preset == "custom" && !(8.0..=30.0).contains(&item.setpoint) {
            return Err(AppError::BadRequest("import contains an invalid schedule setpoint".into()));
        }
    }
    validate_schedule_set(&export.schedules)?;

    if export.groups.iter().any(|group| {
        let members: std::collections::HashSet<&str> = group.zone_ids.iter().map(String::as_str).collect();
        group.id.trim().is_empty() || group.zone_ids.is_empty() || members.len() != group.zone_ids.len()
            || group.zone_ids.iter().any(|zone_id| !zones.contains(zone_id.as_str()))
    }) {
        return Err(AppError::BadRequest("import contains an invalid group, duplicate members or a missing zone reference".into()));
    }
    let groups: std::collections::HashSet<&str> = export.groups.iter().map(|item| item.id.as_str()).collect();
    if groups.len() != export.groups.len() {
        return Err(AppError::BadRequest("import contains duplicate group IDs".into()));
    }

    for item in &export.automations {
        match item.trigger_kind.as_str() {
            "temperature_above" | "temperature_below" => {
                let Some(trigger_id) = item.trigger_device_id.as_deref() else {
                    return Err(AppError::BadRequest("import contains a temperature automation without a trigger device".into()));
                };
                if !devices.contains(trigger_id) || item.threshold.is_none() {
                    return Err(AppError::BadRequest("import contains an invalid temperature automation trigger".into()));
                }
            }
            "time" => {
                let at = item.at_time.as_deref().ok_or_else(|| AppError::BadRequest("import contains a time automation without at_time".into()))?;
                NaiveTime::parse_from_str(at, "%H:%M").map_err(|_| AppError::BadRequest("import contains an invalid automation time".into()))?;
            }
            _ => return Err(AppError::BadRequest("import contains an unsupported automation trigger".into())),
        }

        if let Some(group_id) = item.action_group_id.as_deref().filter(|value| !value.is_empty()) {
            if !groups.contains(group_id) {
                return Err(AppError::BadRequest("import contains an automation referencing a missing group".into()));
            }
            if let Some(mode) = item.action.mode.as_deref() {
                if !matches!(mode, "auto" | "house" | "cool" | "heat") {
                    return Err(AppError::BadRequest("import contains an invalid group automation mode".into()));
                }
            }
            if let Some(preset) = item.action_preset.as_deref() {
                if !matches!(preset, "auto" | "comfort" | "sleep" | "away") {
                    return Err(AppError::BadRequest("import contains an invalid group automation preset".into()));
                }
            }
            if item.action.target_temperature.is_some() || item.action.fan_speed.is_some()
                || item.action.swing_vertical.is_some() || item.action.swing_horizontal.is_some()
                || item.action.quiet.is_some() || item.action.turbo.is_some() || item.action.light.is_some()
                || item.action.air.is_some() || item.action.xfan.is_some() || item.action.health.is_some() || item.action.sleep.is_some()
            {
                return Err(AppError::BadRequest("import contains unsupported fields in a group automation".into()));
            }
            if item.action.power.is_none() && item.action.mode.is_none() && item.action_preset.as_deref().filter(|v| !v.is_empty()).is_none() {
                return Err(AppError::BadRequest("import contains an empty group automation action".into()));
            }
        } else {
            if !devices.contains(item.action_device_id.as_str()) {
                return Err(AppError::BadRequest("import contains an automation referencing a missing device".into()));
            }
            engine::validate_command(&item.action)?;
            if item.action.is_empty() {
                return Err(AppError::BadRequest("import contains an empty automation action".into()));
            }
        }
    }
    Ok(())
}

fn sanitize_configuration_runtime(export: &mut ConfigurationExport) {
    let now = Utc::now();
    for device in &mut export.devices {
        device.power = false;
        device.mode = "cool".into();
        device.target_temperature = 23.0;
        device.fan_speed = 0;
        device.swing_vertical = false;
        device.swing_horizontal = false;
        device.quiet = false;
        device.turbo = false;
        device.light = false;
        device.air = false;
        device.xfan = false;
        device.health = false;
        device.sleep = false;
        device.current_temperature = None;
        device.outdoor_temperature = None;
        device.online = false;
        device.response_time_ms = None;
        device.last_seen = None;
        device.last_error = None;
        device.communication_failures = 0;
        device.updated_at = now;
    }
    for zone in &mut export.zones {
        zone.device_temperature = None;
        zone.external_temperature = None;
        zone.current_temperature = None;
        zone.control_temperature_source = "device".into();
        zone.active_preset = "comfort".into();
        zone.manual_preset = None;
        zone.manual_setpoint = None;
        zone.manual_override_until = None;
        zone.local_thermostat_power = None;
        zone.local_thermostat_resume_at = None;
        zone.local_thermostat_restore_zone_enabled = None;
        zone.temporary_quick_thermostat = None;
        zone.device_manual_override = false;
        zone.device_manual_override_since = None;
        zone.device_manual_override_until = None;
        zone.device_manual_override_fields.clear();
        zone.device_manual_override_baseline = None;
        zone.control_owner = "automation".into();
        zone.control_source = "automation".into();
        zone.control_since = None;
        zone.control_resume_at = None;
        zone.control_reason = "Imported configuration; runtime ownership reset".into();
        zone.last_power_change_at = None;
        zone.last_mode_change_at = None;
        zone.lockout_until = None;
        zone.lockout_reason = None;
        zone.effective_mode.clear();
        zone.effective_setpoint = None;
        zone.device_setpoint = None;
        zone.demand = false;
        zone.demand_since = None;
        zone.target_alerted_at = None;
        zone.last_action_at = None;
        zone.revision = 0;
        zone.updated_at = now;
    }
    for automation in &mut export.automations {
        automation.last_fired_at = None;
        automation.updated_at = now;
    }
}

async fn import_settings(State(state): State<AppState>, Json(mut export): Json<ConfigurationExport>) -> Result<Json<Value>, AppError> {
    validate_configuration_export(&export)?;
    export.settings.history_retention_days = export.settings.history_retention_days.clamp(1, 3650);
    export.settings.event_log_retention_days = export.settings.event_log_retention_days.clamp(1, 3650);
    normalize_sensor_aliases(&mut export.settings);
    canonicalize_home_assistant_entities(&mut export.settings);
    for zone in &mut export.zones { canonicalize_zone_ha_entity(zone, &export.settings); }
    validate_night_mode(&mut export.settings)?;
    export.settings.influxdb.history_threshold_days = export.settings.influxdb.history_threshold_days.clamp(1, 3650);

    // Configuration replacement is the broadest mutation in the application. Serialize it
    // against every structural editor and every live owner that can write zone/device state.
    // Global lock order: configuration -> automation -> house -> schedule -> zones -> devices.
    let _configuration_guard = state.lock_configuration_operation().await;
    let _automation_guard = state.lock_automation_operation().await;
    let _house_guard = state.lock_house_operation().await;
    let _schedule_guard = state.lock_schedule_operation().await;
    let _cycle_guard = state.lock_zone_control_cycle().await;

    let current_zones = state.db.list_zones()?;
    let current_devices = state.db.list_devices()?;
    let mut locked_zone_ids: Vec<String> = current_zones.iter().map(|zone| zone.id.clone())
        .chain(export.zones.iter().map(|zone| zone.id.clone()))
        .collect();
    locked_zone_ids.sort();
    locked_zone_ids.dedup();
    let mut _zone_guards = Vec::with_capacity(locked_zone_ids.len());
    for zone_id in &locked_zone_ids {
        _zone_guards.push(state.lock_zone_operation(zone_id).await);
    }

    let mut locked_device_ids: Vec<String> = current_devices.iter().map(|device| device.id.clone())
        .chain(export.devices.iter().map(|device| device.id.clone()))
        .collect();
    locked_device_ids.sort();
    locked_device_ids.dedup();
    let mut _device_guards = Vec::with_capacity(locked_device_ids.len());
    for device_id in &locked_device_ids {
        _device_guards.push(state.lock_device_operation(device_id).await);
    }

    // Before replacing ownership, safely stop every currently managed device whose zone is
    // removed or rewired by the imported configuration. Otherwise an orphaned physical unit
    // could keep running after its database owner disappears.
    let imported_zone_map: std::collections::HashMap<String, String> = export.zones.iter()
        .map(|zone| (zone.id.clone(), zone.device_id.clone()))
        .collect();
    let mut detach_devices = std::collections::HashSet::new();
    for current in &current_zones {
        if imported_zone_map.get(&current.id).map(String::as_str) != Some(current.device_id.as_str()) {
            detach_devices.insert(current.device_id.clone());
        }
    }
    for device_id in detach_devices {
        let Some(device) = state.db.get_device(&device_id)? else { continue; };
        if !device.enabled {
            return Err(AppError::BadRequest("cannot safely detach a technically disabled device; enable it so the controller can confirm it is powered off first".into()));
        }
        engine::force_power_off_device_locked(&state, &device_id).await?;
        state.log("info", "zone.detach_power_off", &format!("Powered off {} before detaching thermostat ownership", device.name), json!({
            "device_id": device.id, "source": "configuration.import"
        }));
    }

    // Configuration import never restores ephemeral owners/timers or cached physical state.
    // Imported devices are reconciled from a fresh poll and current house/zone gates.
    sanitize_configuration_runtime(&mut export);
    state.initial_device_sync_complete.store(false, Ordering::Release);
    state.db.replace_configuration(&export)?;
    state.debug_gree_frames.store(export.settings.debug.gree_frames, Ordering::Relaxed);
    *state.settings.write().await = export.settings.clone();

    let controllable_devices: std::collections::HashSet<String> = export.zones.iter()
        .filter(|zone| {
            let effective_mode = if zone.inherit_house_mode { export.settings.house_mode.as_str() } else { zone.mode.as_str() };
            export.settings.house_power_enabled
                && zone.enabled
                && effective_mode != "off"
        })
        .map(|zone| zone.device_id.clone())
        .collect();
    for device in export.devices.iter().filter(|device| device.enabled && !controllable_devices.contains(&device.id)) {
        if let Err(err) = engine::force_power_off_device_locked(&state, &device.id).await {
            state.log("error", "settings.import_reconcile_error", &err.to_string(), json!({"device_id": device.id}));
            return Err(err);
        }
    }
    // Rebuild live device snapshots before allowing the thermostat loop to make decisions.
    // Network failures are represented in device health by poll_one rather than reviving
    // imported cache values.
    engine::poll_all_locked(&state).await?;
    state.initial_device_sync_complete.store(true, Ordering::Release);
    state.wake_zone_control();
    state.log("info", "settings.imported", "Application configuration imported", json!({"format_version": export.format_version}));
    state.broadcast("configuration.imported", json!({"at": Utc::now()}));
    Ok(Json(json!({"ok": true})))
}