use std::collections::BTreeSet;
use std::sync::Arc;

use holzleitner_domain::AuditAction;

use crate::dto::{
    ApplyScansRequest, ApplyScansResponse, ScanEvent, ScanResult, ScanResultStatus,
};
use crate::error::ApplicationError;
use crate::ports::{ApplyScanOutcome, CarRepository, ScanRepository};

/// Wendet eine Liste von Scan-Events idempotent an.
///
/// Pro Event ein eigener Vorgang in der Persistence — ein einzelner
/// Reject blockiert die anderen nicht. Pflicht-Reasons (`Hold` /
/// `Remove`) werden hier vorab geprüft, ebenso die Ownership aller
/// in der Batch enthaltenen `actor_car_id`-Werte.
pub struct ApplyScansUseCase {
    repository: Arc<dyn ScanRepository>,
    cars: Arc<dyn CarRepository>,
}

impl ApplyScansUseCase {
    pub fn new(repository: Arc<dyn ScanRepository>, cars: Arc<dyn CarRepository>) -> Self {
        Self { repository, cars }
    }

    pub async fn execute(
        &self,
        request: ApplyScansRequest,
        actor_personalnummer: i64,
    ) -> Result<ApplyScansResponse, ApplicationError> {
        // Distinct car_ids auf einmal validieren — eine Query statt
        // pro-Event-Roundtrip.
        let distinct_cars: BTreeSet<uuid::Uuid> = request
            .scans
            .iter()
            .filter_map(|e| e.actor_car_id)
            .collect();
        if !distinct_cars.is_empty() {
            let ids: Vec<uuid::Uuid> = distinct_cars.into_iter().collect();
            self.cars
                .assert_owned_by_account(&ids, actor_personalnummer)
                .await?;
        }

        let mut results = Vec::with_capacity(request.scans.len());

        for event in &request.scans {
            if let Some(reason) = pre_validate(event) {
                results.push(ScanResult {
                    client_scan_id: event.client_scan_id,
                    status: ScanResultStatus::Rejected,
                    reason: Some(reason),
                    delivery_item_id: None,
                    new_scan_state: None,
                });
                continue;
            }

            let outcome = self
                .repository
                .apply_one(event, actor_personalnummer)
                .await?;

            results.push(match outcome {
                ApplyScanOutcome::Applied {
                    delivery_item_id,
                    new_state,
                } => ScanResult {
                    client_scan_id: event.client_scan_id,
                    status: ScanResultStatus::Applied,
                    reason: None,
                    delivery_item_id: Some(delivery_item_id),
                    new_scan_state: Some(new_state),
                },
                ApplyScanOutcome::Duplicate {
                    delivery_item_id,
                    current_state,
                } => ScanResult {
                    client_scan_id: event.client_scan_id,
                    status: ScanResultStatus::Duplicate,
                    reason: None,
                    delivery_item_id: Some(delivery_item_id),
                    new_scan_state: Some(current_state),
                },
                ApplyScanOutcome::Rejected { reason } => ScanResult {
                    client_scan_id: event.client_scan_id,
                    status: ScanResultStatus::Rejected,
                    reason: Some(reason),
                    delivery_item_id: None,
                    new_scan_state: None,
                },
            });
        }

        Ok(ApplyScansResponse { results })
    }
}

/// Validiert Pflichtfelder ohne DB-Aufruf. Liefert `Some(reason)`,
/// wenn das Event verworfen werden soll. Mengen- und Status-abhängige
/// Bounds (z. B. `credited + quantity <= required`, scannbar ⇒ done,
/// Lieferung aktiv) prüft erst das Repository mit dem gelockten Item.
fn pre_validate(event: &ScanEvent) -> Option<String> {
    // Eine gesetzte Menge muss positiv sein — und ist nur für die
    // Mengen-Gutschrift (Remove/Unremove) überhaupt sinnvoll.
    if let Some(q) = event.quantity {
        match event.action {
            AuditAction::Remove | AuditAction::Unremove if q <= 0 => {
                return Some("quantity must be > 0".into());
            }
            _ => {}
        }
    }

    match event.action {
        AuditAction::Hold | AuditAction::Remove => {
            let trimmed = event.reason.as_deref().map(str::trim).unwrap_or("");
            if trimmed.is_empty() {
                Some(format!(
                    "reason required for action {:?}",
                    event.action
                ))
            } else {
                None
            }
        }
        AuditAction::Scan
        | AuditAction::Unscan
        | AuditAction::Unhold
        | AuditAction::Unremove => None,
    }
}