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use std::marker::PhantomData;
use std::sync::Arc;

use anyhow::Result;

use crate::algorithms::compose::compose_filters::{ComposeFilter, ComposeFilterBuilder};
use crate::algorithms::compose::filter_states::{FilterState, IntegerFilterState};
use crate::algorithms::compose::lookahead_filters::lookahead_selector::Selector;
use crate::algorithms::compose::lookahead_filters::LookAheadComposeFilterTrait;
use crate::algorithms::compose::lookahead_matchers::{LookAheadMatcherData, LookaheadMatcher};
use crate::algorithms::compose::matchers::{MatchType, Matcher, MatcherFlags};
use crate::fst_properties::FstProperties;
use crate::fst_traits::CoreFst;
use crate::semirings::Semiring;
use crate::{StateId, Tr, EPS_LABEL, NO_LABEL, NO_STATE_ID};

#[derive(Clone, Debug)]
pub struct AltSequenceComposeFilter<W: Semiring, M1: Matcher<W>, M2: Matcher<W>> {
    matcher1: Arc<M1>,
    matcher2: Arc<M2>,
    /// Current fst1 state
    s1: StateId,
    /// Current fst2 state
    s2: StateId,
    /// Current filter state
    fs: IntegerFilterState,
    /// Only epsilons (and non-final) leaving s2 ?
    alleps2: bool,
    /// No epsilons leaving s2 ?
    noeps2: bool,
    w: PhantomData<W>,
}

#[derive(Debug, Clone)]
pub struct AltSequenceComposeFilterBuilder<W: Semiring, M1: Matcher<W>, M2: Matcher<W>> {
    matcher1: Arc<M1>,
    matcher2: Arc<M2>,
    w: PhantomData<W>,
}

impl<W: Semiring, M1: Matcher<W>, M2: Matcher<W>> ComposeFilterBuilder<W>
    for AltSequenceComposeFilterBuilder<W, M1, M2>
{
    type CF = AltSequenceComposeFilter<W, M1, M2>;
    type M1 = M1;
    type M2 = M2;

    fn new(
        fst1: Arc<M1::F>,
        fst2: Arc<M2::F>,
        matcher1: Option<M1>,
        matcher2: Option<M2>,
    ) -> Result<Self> {
        let matcher1 =
            matcher1.unwrap_or_else(|| M1::new(Arc::clone(&fst1), MatchType::MatchOutput).unwrap());
        let matcher2 =
            matcher2.unwrap_or_else(|| M2::new(Arc::clone(&fst2), MatchType::MatchInput).unwrap());
        Ok(Self {
            matcher1: Arc::new(matcher1),
            matcher2: Arc::new(matcher2),
            w: PhantomData,
        })
    }

    fn build(&self) -> Result<Self::CF> {
        Ok(AltSequenceComposeFilter::<W, M1, M2> {
            matcher1: Arc::clone(&self.matcher1),
            matcher2: Arc::clone(&self.matcher2),
            s1: NO_STATE_ID,
            s2: NO_STATE_ID,
            fs: <AltSequenceComposeFilter<W, M1, M2> as ComposeFilter<W>>::FS::new(NO_STATE_ID),
            alleps2: false,
            noeps2: false,
            w: PhantomData,
        })
    }
}

impl<W: Semiring, M1: Matcher<W>, M2: Matcher<W>> ComposeFilter<W>
    for AltSequenceComposeFilter<W, M1, M2>
{
    type M1 = M1;
    type M2 = M2;
    type FS = IntegerFilterState;

    fn start(&self) -> Self::FS {
        Self::FS::new(0)
    }

    fn set_state(&mut self, s1: usize, s2: usize, filter_state: &Self::FS) -> Result<()> {
        if !(self.s1 == s1 && self.s2 == s2 && &self.fs == filter_state) {
            self.s1 = s1;
            self.s2 = s2;
            self.fs = filter_state.clone();
            // TODO: Could probably use unchecked here as the state should exist.
            let fst2 = self.fst2();
            let na2 = fst2.num_trs(self.s2)?;
            let ne2 = fst2.num_input_epsilons(self.s2)?;
            let fin2 = fst2.is_final(self.s2)?;
            self.alleps2 = na2 == ne2 && !fin2;
            self.noeps2 = ne2 == 0;
        }
        Ok(())
    }

    fn filter_tr(&mut self, arc1: &mut Tr<W>, arc2: &mut Tr<W>) -> Result<Self::FS> {
        let res = if arc2.ilabel == NO_LABEL {
            if self.alleps2 {
                Self::FS::new_no_state()
            } else if self.noeps2 {
                Self::FS::new(0)
            } else {
                Self::FS::new(1)
            }
        } else if arc1.olabel == NO_LABEL {
            if self.fs == Self::FS::new(1) {
                Self::FS::new_no_state()
            } else {
                Self::FS::new(0)
            }
        } else {
            if arc1.olabel == EPS_LABEL {
                Self::FS::new_no_state()
            } else {
                Self::FS::new(0)
            }
        };
        Ok(res)
    }

    fn filter_final(&self, _w1: &mut W, _w2: &mut W) -> Result<()> {
        Ok(())
    }

    fn matcher1(&self) -> &Self::M1 {
        &self.matcher1
    }

    fn matcher2(&self) -> &Self::M2 {
        &self.matcher2
    }

    fn matcher1_shared(&self) -> &Arc<Self::M1> {
        &self.matcher1
    }

    fn matcher2_shared(&self) -> &Arc<Self::M2> {
        &self.matcher2
    }

    fn properties(&self, inprops: FstProperties) -> FstProperties {
        inprops
    }
}

impl<W: Semiring + 'static, M1: LookaheadMatcher<W>, M2: LookaheadMatcher<W>>
    LookAheadComposeFilterTrait<W> for AltSequenceComposeFilter<W, M1, M2>
{
    fn lookahead_flags(&self) -> MatcherFlags {
        unreachable!()
    }

    fn lookahead_tr(&self) -> bool {
        unreachable!()
    }

    fn lookahead_type(&self) -> MatchType {
        unreachable!()
    }

    fn lookahead_output(&self) -> bool {
        unreachable!()
    }

    fn selector(&self) -> &Selector {
        unreachable!()
    }

    fn lookahead_matcher_data(&self) -> Option<&LookAheadMatcherData<W>> {
        unreachable!()
    }
}