use std::collections::VecDeque;
use std::hash::{Hash, Hasher};

use anyhow::Result;

use crate::fst_traits::Fst;
use crate::semirings::Semiring;
use crate::{Label, StateId, Trs, EPS_LABEL};

/// Structure representing a path in a FST
/// (list of input labels, list of output labels and total weight).
#[derive(PartialEq, Debug, Clone, PartialOrd)]
pub struct FstPath<W: Semiring> {
    /// List of input labels.
    pub ilabels: Vec<Label>,
    /// List of output labels.
    pub olabels: Vec<Label>,
    /// Total weight of the path computed by multiplying the weight of each transition.
    pub weight: W,
}

impl<W: Semiring> FstPath<W> {
    /// Creates a new Path.
    pub fn new(ilabels: Vec<Label>, olabels: Vec<Label>, weight: W) -> Self {
        FstPath {
            ilabels,
            olabels,
            weight,
        }
    }

    /// Adds the content of an FST transition to the Path.
    /// Labels are added at the end of the corresponding vectors and the weight
    /// is multiplied by the total weight already stored in the Path.
    pub fn add_to_path(&mut self, ilabel: Label, olabel: Label, weight: &W) -> Result<()> {
        if ilabel != EPS_LABEL {
            self.ilabels.push(ilabel);
        }

        if olabel != EPS_LABEL {
            self.olabels.push(olabel);
        }

        self.weight.times_assign(weight)
    }

    /// Add a single weight to the Path by multiplying the weight by the total weight of the path.
    pub fn add_weight(&mut self, weight: &W) -> Result<()> {
        self.weight.times_assign(weight)
    }

    /// Append a Path to the current Path. Labels are appended and weights multiplied.
    pub fn concat(&mut self, other: FstPath<W>) -> Result<()> {
        self.ilabels.extend(other.ilabels);
        self.olabels.extend(other.olabels);
        self.weight.times_assign(other.weight)
    }

    pub fn is_empty(&self) -> bool {
        self.ilabels.is_empty() && self.olabels.is_empty() && self.weight.is_one()
    }
}

impl<W: Semiring> Default for FstPath<W> {
    /// Creates an empty path with a weight one.
    fn default() -> Self {
        FstPath {
            ilabels: vec![],
            olabels: vec![],
            weight: W::one(),
        }
    }
}

#[allow(clippy::derive_hash_xor_eq)]
impl<W: Semiring + Hash + Eq> Hash for FstPath<W> {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.ilabels.hash(state);
        self.olabels.hash(state);
        self.weight.hash(state);
    }
}

impl<W: Semiring + Hash + Eq> Eq for FstPath<W> {}

struct BfsState<W: Semiring> {
    state: StateId,
    weight_curr: W,
    next_ilabel_idx: StateId,
    next_olabel_idx: StateId,
}

/// Check if a FstPath can be generated by the given Fst.
///
/// Be careful with this function, it will loop forever if the path is not present
/// in the Fst and the Fst is cyclic.
pub fn check_path_in_fst<W: Semiring, F: Fst<W>>(fst: &F, fst_path: &FstPath<W>) -> bool {
    if let Some(start) = fst.start() {
        let mut queue = VecDeque::new();
        queue.push_back(BfsState {
            state: start,
            next_ilabel_idx: 0,
            next_olabel_idx: 0,
            weight_curr: W::one(),
        });

        while !queue.is_empty() {
            let lol = queue.pop_front().unwrap();
            let state = lol.state;
            let next_ilabel_idx = lol.next_ilabel_idx;
            let next_olabel_idx = lol.next_olabel_idx;
            let weight_curr = lol.weight_curr;

            if next_ilabel_idx >= fst_path.ilabels.len()
                && next_olabel_idx >= fst_path.olabels.len()
            {
                // No more labels left
                if let Some(final_weight) = unsafe { fst.final_weight_unchecked(state) } {
                    if weight_curr.times(final_weight).unwrap() == fst_path.weight {
                        return true;
                    }
                }
            }

            for tr in unsafe { fst.get_trs_unchecked(state) }.trs() {
                let match_ilabel = next_ilabel_idx < fst_path.ilabels.len()
                    && tr.ilabel == fst_path.ilabels[next_ilabel_idx];
                let match_olabel = next_olabel_idx < fst_path.olabels.len()
                    && tr.olabel == fst_path.olabels[next_ilabel_idx];
                let (new_next_ilabel_idx, new_next_olabel_idx) =
                    if tr.ilabel == EPS_LABEL && tr.olabel == EPS_LABEL {
                        (next_ilabel_idx, next_olabel_idx)
                    } else if tr.ilabel != EPS_LABEL && tr.olabel == EPS_LABEL {
                        if match_ilabel {
                            (next_ilabel_idx + 1, next_olabel_idx)
                        } else {
                            continue;
                        }
                    } else if tr.ilabel == EPS_LABEL && tr.olabel != EPS_LABEL {
                        if match_olabel {
                            (next_ilabel_idx, next_olabel_idx + 1)
                        } else {
                            continue;
                        }
                    } else {
                        if match_ilabel && match_olabel {
                            (next_ilabel_idx + 1, next_olabel_idx + 1)
                        } else {
                            continue;
                        }
                    };
                queue.push_back(BfsState {
                    state: tr.nextstate,
                    next_ilabel_idx: new_next_ilabel_idx,
                    next_olabel_idx: new_next_olabel_idx,
                    weight_curr: weight_curr.times(&tr.weight).unwrap(),
                })
            }
        }

        false
    } else {
        fst_path.is_empty()
    }
}

/// Creates a Path containing the arguments.
///
/// There are multiple forms to this macro :
///
/// - Create an unweighted acceptor path :
///
/// ```
/// # #[macro_use] extern crate rustfst; fn main() {
/// # use rustfst::semirings::{IntegerWeight, Semiring};
/// # use rustfst::FstPath;
/// let path : FstPath<IntegerWeight> = fst_path![1,2,3];
/// assert_eq!(path.ilabels, vec![1,2,3]);
/// assert_eq!(path.olabels, vec![1,2,3]);
/// assert_eq!(path.weight, IntegerWeight::one());
/// # }
/// ```
///
/// - Create an unweighted transducer path :
///
/// ```
/// # #[macro_use] extern crate rustfst; fn main() {
/// # use rustfst::semirings::{IntegerWeight, Semiring};
/// # use rustfst::FstPath;
/// let path : FstPath<IntegerWeight> = fst_path![1,2,3 => 1,2,4];
/// assert_eq!(path.ilabels, vec![1,2,3]);
/// assert_eq!(path.olabels, vec![1,2,4]);
/// assert_eq!(path.weight, IntegerWeight::one());
/// # }
/// ```
///
/// - Create a weighted acceptor path :
///
/// ```
/// # #[macro_use] extern crate rustfst; fn main() {
/// # use rustfst::semirings::{IntegerWeight, Semiring};
/// # use rustfst::FstPath;
/// let path : FstPath<IntegerWeight> = fst_path![1,2,3; 18];
/// assert_eq!(path.ilabels, vec![1,2,3]);
/// assert_eq!(path.olabels, vec![1,2,3]);
/// assert_eq!(path.weight, IntegerWeight::new(18));
/// # }
/// ```
///
/// - Create a weighted transducer path :
///
/// ```
/// # #[macro_use] extern crate rustfst; fn main() {
/// # use rustfst::semirings::{IntegerWeight, Semiring};
/// # use rustfst::FstPath;
/// let path : FstPath<IntegerWeight> = fst_path![1,2,3 => 1,2,4; 18];
/// assert_eq!(path.ilabels, vec![1,2,3]);
/// assert_eq!(path.olabels, vec![1,2,4]);
/// assert_eq!(path.weight, IntegerWeight::new(18));
/// # }
/// ```
///
#[macro_export]
macro_rules! fst_path {
    ( $( $x:expr ),*) => {
        {
            fn semiring_one<W: Semiring>() -> W {
                W::one()
            }
            FstPath::new(
                vec![$($x),*],
                vec![$($x),*],
                semiring_one()
            )
        }
    };
    ( $( $x:expr ),* => $( $y:expr ),* ) => {
        {
            fn semiring_one<W: Semiring>() -> W {
                W::one()
            }
            FstPath::new(
                vec![$($x),*],
                vec![$($y),*],
                semiring_one()
            )
        }
    };
    ( $( $x:expr ),* ; $weight:expr) => {
        {
            fn semiring_new<W: Semiring>(v: W::Type) -> W {
                W::new(v)
            }
            FstPath::new(
                vec![$($x),*],
                vec![$($x),*],
                semiring_new($weight)
            )
        }
    };
    ( $( $x:expr ),* => $( $y:expr ),* ; $weight:expr) => {
        {
            fn semiring_new<W: Semiring>(v: W::Type) -> W {
                W::new(v)
            }
            FstPath::new(
                vec![$($x),*],
                vec![$($y),*],
                semiring_new($weight)
            )
        }
    };
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::fst_impls::VectorFst;
    use crate::fst_traits::MutableFst;
    use crate::semirings::TropicalWeight;

    #[test]
    fn test_check_path_in_fst() -> Result<()> {
        let mut fst = VectorFst::<TropicalWeight>::new();
        fst.add_states(3);
        fst.set_start(0)?;
        fst.emplace_tr(0, 1, 2, 1.2, 1)?;
        fst.emplace_tr(0, 4, 6, 1.1, 1)?;
        fst.emplace_tr(1, 2, 3, 0.3, 2)?;
        fst.emplace_tr(1, 6, 7, 0.5, 2)?;
        fst.emplace_tr(0, 10, 12, 3.0, 2)?;
        fst.set_final(2, 3.2)?;

        assert!(!check_path_in_fst(
            &fst,
            &FstPath::new(vec![], vec![], TropicalWeight::one())
        ));
        assert!(!check_path_in_fst(
            &fst,
            &FstPath::new(vec![1], vec![2], TropicalWeight::new(1.2))
        ));
        assert!(!check_path_in_fst(
            &fst,
            &FstPath::new(vec![1, 2], vec![2, 3], TropicalWeight::new(1.5))
        ));
        assert!(check_path_in_fst(
            &fst,
            &FstPath::new(vec![1, 2], vec![2, 3], TropicalWeight::new(4.7))
        ));
        assert!(!check_path_in_fst(
            &fst,
            &FstPath::new(vec![10], vec![10], TropicalWeight::new(3.0))
        ));
        assert!(!check_path_in_fst(
            &fst,
            &FstPath::new(vec![12], vec![12], TropicalWeight::new(6.2))
        ));
        assert!(!check_path_in_fst(
            &fst,
            &FstPath::new(vec![10], vec![10], TropicalWeight::new(6.2))
        ));
        assert!(check_path_in_fst(
            &fst,
            &FstPath::new(vec![10], vec![12], TropicalWeight::new(6.2))
        ));

        Ok(())
    }
}