use std::collections::HashMap;

use crate::syntax::map::{DupTreeMap, DupTreeSet};
use crate::syntax::visitor::{self, ExprKindMutVisitor, ExprKindVisitor};
use crate::syntax::*;

pub type Integer = isize;
pub type Natural = usize;
pub type Double = NaiveDouble;

/// Double with bitwise equality
#[derive(Debug, Copy, Clone)]
pub struct NaiveDouble(f64);

/// Constants for a pure type system
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum Const {
    Type,
    Kind,
    Sort,
}

/// Bound variable
///
/// The `Label` field is the variable's name (i.e. \"`x`\").
/// The `Int` field is a DeBruijn index.
/// See dhall-lang/standard/semantics.md for details
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct V<Label>(pub Label, pub usize);

// Definition order must match precedence order for
// pretty-printing to work correctly
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum BinOp {
    /// `x ? y`
    ImportAlt,
    /// `x || y`
    BoolOr,
    /// `x + y`
    NaturalPlus,
    /// `x ++ y`
    TextAppend,
    /// `x # y`
    ListAppend,
    /// `x && y`
    BoolAnd,
    /// `x ∧ y`
    RecursiveRecordMerge,
    /// `x ⫽ y`
    RightBiasedRecordMerge,
    /// `x ⩓ y`
    RecursiveRecordTypeMerge,
    /// `x * y`
    NaturalTimes,
    /// `x == y`
    BoolEQ,
    /// `x != y`
    BoolNE,
    /// x === y
    Equivalence,
}

/// Built-ins
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub enum Builtin {
    Bool,
    Natural,
    Integer,
    Double,
    Text,
    List,
    Optional,
    OptionalNone,
    NaturalBuild,
    NaturalFold,
    NaturalIsZero,
    NaturalEven,
    NaturalOdd,
    NaturalToInteger,
    NaturalShow,
    NaturalSubtract,
    IntegerToDouble,
    IntegerShow,
    IntegerNegate,
    IntegerClamp,
    DoubleShow,
    ListBuild,
    ListFold,
    ListLength,
    ListHead,
    ListLast,
    ListIndexed,
    ListReverse,
    OptionalFold,
    OptionalBuild,
    TextShow,
}

// Each node carries an annotation.
#[derive(Debug, Clone)]
pub struct Expr<Embed> {
    kind: Box<ExprKind<Expr<Embed>, Embed>>,
    span: Span,
}

pub type UnspannedExpr<Embed> = ExprKind<Expr<Embed>, Embed>;

/// Syntax tree for expressions
// Having the recursion out of the enum definition enables writing
// much more generic code and improves pattern-matching behind
// smart pointers.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum ExprKind<SubExpr, Embed> {
    Const(Const),
    ///  `x`
    ///  `x@n`
    Var(V<Label>),
    ///  `λ(x : A) -> b`
    Lam(Label, SubExpr, SubExpr),
    ///  `A -> B`
    ///  `∀(x : A) -> B`
    Pi(Label, SubExpr, SubExpr),
    ///  `f a`
    App(SubExpr, SubExpr),
    ///  `let x     = r in e`
    ///  `let x : t = r in e`
    Let(Label, Option<SubExpr>, SubExpr, SubExpr),
    ///  `x : t`
    Annot(SubExpr, SubExpr),
    ///  `assert : t`
    Assert(SubExpr),
    /// Built-in values
    Builtin(Builtin),
    // Binary operations
    BinOp(BinOp, SubExpr, SubExpr),
    ///  `True`
    BoolLit(bool),
    ///  `if x then y else z`
    BoolIf(SubExpr, SubExpr, SubExpr),
    ///  `1`
    NaturalLit(Natural),
    ///  `+2`
    IntegerLit(Integer),
    ///  `3.24`
    DoubleLit(Double),
    ///  `"Some ${interpolated} text"`
    TextLit(InterpolatedText<SubExpr>),
    ///  `[] : t`
    EmptyListLit(SubExpr),
    ///  `[x, y, z]`
    NEListLit(Vec<SubExpr>),
    ///  `Some e`
    SomeLit(SubExpr),
    ///  `{ k1 : t1, k2 : t1 }`
    RecordType(DupTreeMap<Label, SubExpr>),
    ///  `{ k1 = v1, k2 = v2 }`
    RecordLit(DupTreeMap<Label, SubExpr>),
    ///  `< k1 : t1, k2 >`
    UnionType(DupTreeMap<Label, Option<SubExpr>>),
    ///  `merge x y : t`
    Merge(SubExpr, SubExpr, Option<SubExpr>),
    ///  `toMap x : t`
    ToMap(SubExpr, Option<SubExpr>),
    ///  `e.x`
    Field(SubExpr, Label),
    ///  `e.{ x, y, z }`
    Projection(SubExpr, DupTreeSet<Label>),
    ///  `e.(t)`
    ProjectionByExpr(SubExpr, SubExpr),
    ///  `x::y`
    Completion(SubExpr, SubExpr),
    /// `./some/path`
    Import(Import<SubExpr>),
    /// Embeds the result of resolving an import
    Embed(Embed),
}

impl<Label> V<Label> {
    pub(crate) fn idx(&self) -> usize {
        self.1
    }
}

impl<SE, E> ExprKind<SE, E> {
    pub fn traverse_ref_with_special_handling_of_binders<'a, SE2, Err>(
        &'a self,
        visit_subexpr: impl FnMut(&'a SE) -> Result<SE2, Err>,
        visit_under_binder: impl FnOnce(&'a Label, &'a SE) -> Result<SE2, Err>,
    ) -> Result<ExprKind<SE2, E>, Err>
    where
        E: Clone,
    {
        visitor::TraverseRefWithBindersVisitor {
            visit_subexpr,
            visit_under_binder,
        }
        .visit(self)
    }

    pub(crate) fn traverse_ref<'a, SE2, Err>(
        &'a self,
        visit_subexpr: impl FnMut(&'a SE) -> Result<SE2, Err>,
    ) -> Result<ExprKind<SE2, E>, Err>
    where
        E: Clone,
    {
        visitor::TraverseRefVisitor { visit_subexpr }.visit(self)
    }

    fn traverse_mut<'a, Err>(
        &'a mut self,
        visit_subexpr: impl FnMut(&'a mut SE) -> Result<(), Err>,
    ) -> Result<(), Err> {
        visitor::TraverseMutVisitor { visit_subexpr }.visit(self)
    }

    pub fn map_ref_with_special_handling_of_binders<'a, SE2>(
        &'a self,
        mut map_subexpr: impl FnMut(&'a SE) -> SE2,
        mut map_under_binder: impl FnMut(&'a Label, &'a SE) -> SE2,
    ) -> ExprKind<SE2, E>
    where
        E: Clone,
    {
        trivial_result(self.traverse_ref_with_special_handling_of_binders(
            |x| Ok(map_subexpr(x)),
            |l, x| Ok(map_under_binder(l, x)),
        ))
    }

    pub fn map_ref<'a, SE2>(
        &'a self,
        mut map_subexpr: impl FnMut(&'a SE) -> SE2,
    ) -> ExprKind<SE2, E>
    where
        E: Clone,
    {
        trivial_result(self.traverse_ref(|x| Ok(map_subexpr(x))))
    }

    pub fn map_mut<'a>(&'a mut self, mut map_subexpr: impl FnMut(&'a mut SE)) {
        trivial_result(self.traverse_mut(|x| Ok(map_subexpr(x))))
    }
}

impl<E> Expr<E> {
    pub fn as_ref(&self) -> &UnspannedExpr<E> {
        &self.kind
    }
    pub fn span(&self) -> Span {
        self.span.clone()
    }

    pub fn new(kind: UnspannedExpr<E>, span: Span) -> Self {
        Expr {
            kind: Box::new(kind),
            span,
        }
    }

    pub fn rewrap<E2>(&self, kind: UnspannedExpr<E2>) -> Expr<E2> {
        Expr {
            kind: Box::new(kind),
            span: self.span.clone(),
        }
    }

    pub fn traverse_resolve_mut<Err, F1>(
        &mut self,
        f: &mut F1,
    ) -> Result<(), Err>
    where
        E: Clone,
        F1: FnMut(Import<Expr<E>>) -> Result<E, Err>,
    {
        match self.kind.as_mut() {
            ExprKind::BinOp(BinOp::ImportAlt, l, r) => {
                let garbage_expr = ExprKind::BoolLit(false);
                let new_self = if l.traverse_resolve_mut(f).is_ok() {
                    l
                } else {
                    r.traverse_resolve_mut(f)?;
                    r
                };
                *self.kind =
                    std::mem::replace(new_self.kind.as_mut(), garbage_expr);
            }
            _ => {
                self.kind.traverse_mut(|e| e.traverse_resolve_mut(f))?;
                if let ExprKind::Import(import) = self.kind.as_mut() {
                    let garbage_import = Import {
                        mode: ImportMode::Code,
                        location: ImportLocation::Missing,
                        hash: None,
                    };
                    // Move out of &mut import
                    let import = std::mem::replace(import, garbage_import);
                    *self.kind = ExprKind::Embed(f(import)?);
                }
            }
        }
        Ok(())
    }
}

impl<Label: PartialEq + Clone> V<Label> {
    pub(crate) fn shift(&self, delta: isize, var: &V<Label>) -> Option<Self> {
        let V(x, n) = var;
        let V(y, m) = self;
        Some(if x == y && n <= m {
            V(y.clone(), add_ui(*m, delta)?)
        } else {
            V(y.clone(), *m)
        })
    }

    pub(crate) fn over_binder(&self, x: &Label) -> Option<Self> {
        self.shift(-1, &V(x.clone(), 0))
    }
}

impl V<Label> {
    pub(crate) fn under_multiple_binders(
        &self,
        shift_map: &HashMap<Label, usize>,
    ) -> Self {
        let name = &self.0;
        let idx = self.1 + shift_map.get(name).unwrap_or(&0);
        V(name.clone(), idx)
    }
}

impl V<()> {
    pub(crate) fn under_multiple_binders(
        &self,
        shift_map: &HashMap<Label, usize>,
    ) -> Self {
        let mut idx = self.1;
        for (_, n) in shift_map {
            idx += n;
        }
        V((), idx)
    }
}

pub fn trivial_result<T>(x: Result<T, !>) -> T {
    match x {
        Ok(x) => x,
        Err(e) => e,
    }
}

/// Add an isize to an usize
/// Returns `None` on over/underflow
fn add_ui(u: usize, i: isize) -> Option<usize> {
    Some(if i < 0 {
        u.checked_sub(i.checked_neg()? as usize)?
    } else {
        u.checked_add(i as usize)?
    })
}

impl PartialEq for NaiveDouble {
    fn eq(&self, other: &Self) -> bool {
        self.0.to_bits() == other.0.to_bits()
    }
}

impl Eq for NaiveDouble {}

impl std::hash::Hash for NaiveDouble {
    fn hash<H>(&self, state: &mut H)
    where
        H: std::hash::Hasher,
    {
        self.0.to_bits().hash(state)
    }
}

impl From<f64> for NaiveDouble {
    fn from(x: f64) -> Self {
        NaiveDouble(x)
    }
}

impl From<NaiveDouble> for f64 {
    fn from(x: NaiveDouble) -> f64 {
        x.0
    }
}

impl<Label> From<Label> for V<Label> {
    fn from(x: Label) -> V<Label> {
        V(x, 0)
    }
}

impl<Embed: PartialEq> std::cmp::PartialEq for Expr<Embed> {
    fn eq(&self, other: &Self) -> bool {
        self.kind == other.kind
    }
}

impl<Embed: Eq> std::cmp::Eq for Expr<Embed> {}

impl<Embed: std::hash::Hash> std::hash::Hash for Expr<Embed> {
    fn hash<H>(&self, state: &mut H)
    where
        H: std::hash::Hasher,
    {
        self.kind.hash(state)
    }
}