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// Copyright 2024 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use super::edge::WeakEdgeRef;
use super::events::GraphObjectEventTracker;
use super::types::VertexMarker;
use super::{Edge, Metadata, VertexGraphMetadata, VertexId};
use fuchsia_inspect as inspect;
use std::collections::BTreeMap;
use std::sync::atomic::{AtomicU64, Ordering};

/// A vertex of the graph. When this is dropped, all the outgoing edges and metadata fields will
/// removed from Inspect.
#[derive(Debug)]
pub struct Vertex<I: VertexId> {
    _node: inspect::Node,
    metadata: VertexGraphMetadata<I>,
    incoming_edges: BTreeMap<u64, WeakEdgeRef>,
    outgoing_edges: BTreeMap<u64, WeakEdgeRef>,
    pub(crate) outgoing_edges_node: inspect::Node,
    internal_id: u64,
}

static NEXT_ID: AtomicU64 = AtomicU64::new(0);

impl<I> Vertex<I>
where
    I: VertexId,
{
    pub(crate) fn new<'a, M>(
        id: I,
        parent: &inspect::Node,
        initial_metadata: M,
        events_tracker: Option<GraphObjectEventTracker<VertexMarker<I>>>,
    ) -> Self
    where
        M: IntoIterator<Item = Metadata<'a>>,
    {
        let internal_id = NEXT_ID.fetch_add(1, Ordering::Relaxed);
        let metadata_iterator = initial_metadata.into_iter();
        parent.atomic_update(|parent| {
            let id_str = id.get_id();
            let node = parent.create_child(id_str.as_ref());
            let outgoing_edges_node = node.create_child("relationships");
            let metadata = VertexGraphMetadata::new(&node, id, metadata_iterator, events_tracker);
            Vertex {
                internal_id,
                _node: node,
                outgoing_edges_node,
                metadata,
                incoming_edges: BTreeMap::new(),
                outgoing_edges: BTreeMap::new(),
            }
        })
    }

    /// Add a new edge to the graph originating at this vertex and going to the vertex `to` with the
    /// given metadata.
    pub fn add_edge<'a, M>(&mut self, to: &mut Vertex<I>, initial_metadata: M) -> Edge
    where
        M: IntoIterator<Item = Metadata<'a>>,
    {
        let edge = Edge::new(
            self,
            to,
            initial_metadata,
            self.metadata.events_tracker().map(|e| e.for_edge()),
        );

        let weak_ref = edge.weak_ref();

        self.incoming_edges.retain(|_, n| n.is_valid());
        to.outgoing_edges.retain(|_, n| n.is_valid());

        to.incoming_edges.insert(self.internal_id, weak_ref.clone());
        self.outgoing_edges.insert(to.internal_id, weak_ref);
        edge
    }

    /// Get an exclusive reference to the metadata to modify it.
    pub fn meta(&mut self) -> &mut VertexGraphMetadata<I> {
        &mut self.metadata
    }

    pub(crate) fn id(&self) -> &I {
        self.metadata.id()
    }
}

impl<I> Drop for Vertex<I>
where
    I: VertexId,
{
    fn drop(&mut self) {
        self.outgoing_edges.iter().for_each(|(_, n)| n.mark_as_gone());
        self.incoming_edges.iter().for_each(|(_, n)| n.mark_as_gone());
        if let Some(events_tracker) = self.metadata.events_tracker() {
            events_tracker.record_removed(self.id().get_id().as_ref())
        }
    }
}