pub mod build;
pub mod cheapest_paths;
pub mod edge_docids_cache;
pub mod empty_paths_cache;
pub mod paths_map;
pub mod proximity;
pub mod resolve_paths;

use std::collections::{BTreeSet, HashMap, HashSet};
use std::ops::ControlFlow;

use heed::RoTxn;
use roaring::RoaringBitmap;

use super::db_cache::DatabaseCache;
use super::{NodeIndex, QueryGraph, QueryNode};
use crate::{Index, Result};

#[derive(Debug, Clone)]
pub enum EdgeDetails<E> {
    Unconditional,
    Data(E),
}

#[derive(Debug, Clone)]
pub struct Edge<E> {
    from_node: NodeIndex,
    to_node: NodeIndex,
    cost: u8,
    details: EdgeDetails<E>,
}

#[derive(Debug, Clone)]
pub struct EdgePointer<'graph, E> {
    pub index: EdgeIndex,
    pub edge: &'graph Edge<E>,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct EdgeIndex(pub usize);

pub trait RankingRuleGraphTrait {
    /// The details of an edge connecting two query nodes. These details
    /// should be sufficient to compute the edge's cost and associated document ids
    /// in [`compute_docids`](RankingRuleGraphTrait).
    type EdgeDetails: Sized;

    type BuildVisitedFromNode;

    /// Return the label of the given edge details, to be used when visualising
    /// the ranking rule graph using GraphViz.
    fn graphviz_edge_details_label(edge: &Self::EdgeDetails) -> String;

    /// Compute the document ids associated with the given edge.
    fn compute_docids<'transaction>(
        index: &Index,
        txn: &'transaction RoTxn,
        db_cache: &mut DatabaseCache<'transaction>,
        edge_details: &Self::EdgeDetails,
    ) -> Result<RoaringBitmap>;

    /// Prepare to build the edges outgoing from `from_node`.
    ///
    /// This call is followed by zero, one or more calls to [`build_visit_to_node`](RankingRuleGraphTrait::build_visit_to_node),
    /// which builds the actual edges.
    fn build_visit_from_node<'transaction>(
        index: &Index,
        txn: &'transaction RoTxn,
        db_cache: &mut DatabaseCache<'transaction>,
        from_node: &QueryNode,
    ) -> Result<Option<Self::BuildVisitedFromNode>>;

    /// Return the cost and details of the edges going from the previously visited node
    /// (with [`build_visit_from_node`](RankingRuleGraphTrait::build_visit_from_node)) to `to_node`.
    fn build_visit_to_node<'from_data, 'transaction: 'from_data>(
        index: &Index,
        txn: &'transaction RoTxn,
        db_cache: &mut DatabaseCache<'transaction>,
        to_node: &QueryNode,
        from_node_data: &'from_data Self::BuildVisitedFromNode,
    ) -> Result<Vec<(u8, EdgeDetails<Self::EdgeDetails>)>>;
}

pub struct RankingRuleGraph<G: RankingRuleGraphTrait> {
    pub query_graph: QueryGraph,
    // pub edges: Vec<HashMap<usize, Vec<Edge<G::EdgeDetails>>>>,
    pub all_edges: Vec<Option<Edge<G::EdgeDetails>>>,

    pub node_edges: Vec<RoaringBitmap>,

    pub successors: Vec<RoaringBitmap>,
    // to get the edges between two nodes:
    // 1. get node_outgoing_edges[from]
    // 2. get node_incoming_edges[to]
    // 3. take intersection betweem the two

    // TODO: node edges could be different I guess
    // something like:
    // pub node_edges: Vec<BitSet>
    // where each index is the result of:
    // the successor index in the top 16 bits, the edge index in the bottom 16 bits

    // TODO:
    // node_successors?

    // pub removed_edges: HashSet<EdgeIndex>,
    // pub tmp_removed_edges: HashSet<EdgeIndex>,
}
impl<G: RankingRuleGraphTrait> RankingRuleGraph<G> {
    pub fn get_edge(&self, edge_index: EdgeIndex) -> &Option<Edge<G::EdgeDetails>> {
        &self.all_edges[edge_index.0]
    }

    // Visit all edges between the two given nodes in order of increasing cost.
    pub fn visit_edges<'graph, O>(
        &'graph self,
        from: NodeIndex,
        to: NodeIndex,
        mut visit: impl FnMut(EdgeIndex, &'graph Edge<G::EdgeDetails>) -> ControlFlow<O>,
    ) -> Option<O> {
        let from_edges = &self.node_edges[from.0 as usize];
        for edge_idx in from_edges {
            let edge = self.all_edges[edge_idx as usize].as_ref().unwrap();
            if edge.to_node == to {
                let cf = visit(EdgeIndex(edge_idx as usize), edge);
                match cf {
                    ControlFlow::Continue(_) => continue,
                    ControlFlow::Break(o) => return Some(o),
                }
            }
        }

        None
    }

    fn remove_edge(&mut self, edge_index: EdgeIndex) {
        let edge_opt = &mut self.all_edges[edge_index.0];
        let Some(edge) = &edge_opt else { return };
        let (from_node, to_node) = (edge.from_node, edge.to_node);
        *edge_opt = None;

        let from_node_edges = &mut self.node_edges[from_node.0 as usize];
        from_node_edges.remove(edge_index.0 as u32);

        let mut new_successors_from_node = RoaringBitmap::new();
        for edge in from_node_edges.iter() {
            let Edge { to_node, .. } = &self.all_edges[edge as usize].as_ref().unwrap();
            new_successors_from_node.insert(to_node.0);
        }
        self.successors[from_node.0 as usize] = new_successors_from_node;
    }
    // pub fn remove_nodes(&mut self, nodes: &[usize]) {
    //     for &node in nodes {
    //         let edge_indices = &mut self.node_edges[node];
    //         for edge_index in edge_indices.iter() {
    //             self.all_edges[*edge_index] = None;
    //         }
    //         edge_indices.clear();

    //         let preds = &self.query_graph.edges[node].incoming;
    //         for pred in preds {
    //             let edge_indices = &mut self.node_edges[*pred];
    //             for edge_index in edge_indices.iter() {
    //                 let edge_opt = &mut self.all_edges[*edge_index];
    //                 let Some(edge) = edge_opt else { continue; };
    //                 if edge.to_node == node {
    //                     *edge_opt = None;
    //                 }
    //             }
    //             panic!("remove nodes is incorrect at the moment");
    //             edge_indices.clear();
    //         }
    //     }
    //     self.query_graph.remove_nodes(nodes);
    // }
    // pub fn simplify(&mut self) {
    //     loop {
    //         let mut nodes_to_remove = vec![];
    //         for (node_idx, node) in self.query_graph.nodes.iter().enumerate() {
    //             if !matches!(node, QueryNode::End | QueryNode::Deleted)
    //                 && self.node_edges[node_idx].is_empty()
    //             {
    //                 nodes_to_remove.push(node_idx);
    //             }
    //         }
    //         if nodes_to_remove.is_empty() {
    //             break;
    //         } else {
    //             self.remove_nodes(&nodes_to_remove);
    //         }
    //     }
    // }
    // fn is_removed_edge(&self, edge: EdgeIndex) -> bool {
    //     self.removed_edges.contains(&edge) || self.tmp_removed_edges.contains(&edge)
    // }

    pub fn graphviz(&self) -> String {
        let mut desc = String::new();
        desc.push_str("digraph G {\nrankdir = LR;\nnode [shape = \"record\"]\n");

        for (node_idx, node) in self.query_graph.nodes.iter().enumerate() {
            if matches!(node, QueryNode::Deleted) {
                continue;
            }
            desc.push_str(&format!("{node_idx} [label = {:?}]", node));
            if node_idx == self.query_graph.root_node.0 as usize {
                desc.push_str("[color = blue]");
            } else if node_idx == self.query_graph.end_node.0 as usize {
                desc.push_str("[color = red]");
            }
            desc.push_str(";\n");
        }
        for edge in self.all_edges.iter().flatten() {
            let Edge { from_node, to_node, cost, details } = edge;

            match &details {
                EdgeDetails::Unconditional => {
                    desc.push_str(&format!(
                        "{from_node} -> {to_node} [label = \"always cost {cost}\"];\n",
                        cost = edge.cost,
                    ));
                }
                EdgeDetails::Data(details) => {
                    desc.push_str(&format!(
                        "{from_node} -> {to_node} [label = \"cost {cost} {edge_label}\"];\n",
                        cost = edge.cost,
                        edge_label = G::graphviz_edge_details_label(details)
                    ));
                }
            }
        }

        desc.push('}');
        desc
    }
}