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use std::cmp;
use std::collections;
use std::ops;
use std::rc;

use grammar;

#[derive(Clone, Debug, Hash, PartialEq, Eq)]
pub struct RawNode {
    pub span: ops::Range<usize>,
    pub name: rc::Rc<str>,
    pub non_terminals: Vec<Node>,
}

impl RawNode {
    pub fn dump(&self, indent: usize) {
        println!(
            "{:indent$}{} @ {:?}",
            "",
            self.name,
            self.span,
            indent = indent
        );
        for each in self.non_terminals.iter() {
            each.dump(indent + 4);
        }
    }
}

impl PartialOrd for RawNode {
    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for RawNode {
    fn cmp(&self, other: &Self) -> cmp::Ordering {
        cmp::Ordering::Equal
            .then(self.span.start.cmp(&other.span.start))
            .then(self.span.end.cmp(&other.span.end))
            .then(self.name.cmp(&other.name))
            .then(self.non_terminals.cmp(&other.non_terminals))
    }
}

/// A reference-counted [`RawNode`]
///
/// [`RawNode`]: struct.RawNode.html
pub type Node = rc::Rc<RawNode>;

#[derive(Clone, Debug, Hash, PartialEq, Eq)]
struct PartialNode {
    /// We know the contents of this node within this span.
    known_span: ops::Range<usize>,
    /// The completed symbols of this node, in reverse order.
    reversed_non_terminals: Vec<Node>,
}

impl PartialNode {
    fn step_back(
        mut self,
        symbol: &grammar::Symbol,
        builder: &Builder,
    ) -> collections::BTreeSet<PartialNode> {
        let mut res = collections::BTreeSet::new();

        if self.known_span.start == 0 {
            // Stepping this back any further won't produce a sensible result.
            return res;
        }

        match symbol {
            grammar::Symbol::Terminal(_) => {
                self.known_span.start -= 1;
                res.insert(self);
            }

            grammar::Symbol::NonTerminal(name) => {
                for each in builder.get(..self.known_span.start, name.clone()) {
                    let mut new_partial = self.clone();
                    new_partial.known_span.start = each.span.start;
                    new_partial.reversed_non_terminals.push(each.clone());

                    res.insert(new_partial);
                }
            }
        }

        res
    }
}

impl PartialOrd for PartialNode {
    fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl Ord for PartialNode {
    fn cmp(&self, other: &Self) -> cmp::Ordering {
        cmp::Ordering::Equal
            .then(self.known_span.start.cmp(&other.known_span.start))
            .then(self.known_span.end.cmp(&other.known_span.end))
            .then(
                self.reversed_non_terminals
                    .cmp(&other.reversed_non_terminals),
            )
    }
}

#[derive(Clone, Debug, Default, Hash, PartialEq, Eq, PartialOrd, Ord)]
pub struct Builder(
    collections::BTreeMap<(usize, rc::Rc<str>), collections::BTreeSet<Node>>,
);

impl Builder {
    pub fn new() -> Builder {
        Default::default()
    }

    pub fn rule_completed<'a>(
        &mut self,
        span: ops::Range<usize>,
        name: rc::Rc<str>,
        symbols: &'a [grammar::Symbol],
    ) {
        let mut partials = collections::BTreeSet::new();
        partials.insert(PartialNode {
            known_span: span.end..span.end,
            reversed_non_terminals: vec![],
        });

        for symbol in symbols.iter().rev() {
            partials = partials
                .into_iter()
                .flat_map(|each| each.step_back(symbol, self))
                .collect();
        }

        let newly_completed_nodes = partials
            .into_iter()
            .filter(|each| each.known_span == span)
            .map(|each| {
                let mut non_terminals = each.reversed_non_terminals;
                non_terminals.reverse();

                rc::Rc::new(RawNode {
                    span: each.known_span,
                    name: name.clone(),
                    non_terminals: non_terminals,
                })
            }).collect::<Vec<_>>();

        // TODO: If newly_completed_nodes contains more than one item,
        // we should choose one to avoid an ambiguous parse tree.

        let node_set = self.0.entry((span.end, name)).or_default();
        for each in newly_completed_nodes {
            node_set.insert(each);
        }
    }

    pub fn get(
        &self,
        end_by: ops::RangeTo<usize>,
        named: rc::Rc<str>,
    ) -> collections::BTreeSet<Node> {
        self.0
            .get(&(end_by.end, named))
            .cloned()
            .unwrap_or_default()
    }
}