//! Module defining script statements.

use super::{ASTNode, BinaryExpr, Expr, FnCallExpr, Ident, OptionFlags, AST_OPTION_FLAGS::*};
use crate::engine::KEYWORD_EVAL;
use crate::tokenizer::Token;
use crate::{calc_fn_hash, Position, StaticVec, INT};
#[cfg(feature = "no_std")]
use std::prelude::v1::*;
use std::{
    collections::BTreeMap,
    fmt,
    hash::Hash,
    mem,
    ops::{Deref, DerefMut},
};

/// _(internals)_ An op-assignment operator.
/// Exported under the `internals` feature only.
#[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
pub struct OpAssignment<'a> {
    /// Hash of the op-assignment call.
    pub hash_op_assign: u64,
    /// Hash of the underlying operator call (for fallback).
    pub hash_op: u64,
    /// Op-assignment operator.
    pub op_assign: &'a str,
    /// Underlying operator.
    pub op: &'a str,
}

impl OpAssignment<'_> {
    /// Create a new [`OpAssignment`].
    ///
    /// # Panics
    ///
    /// Panics if the name is not an op-assignment operator.
    #[must_use]
    #[inline(always)]
    pub fn new(name: &str) -> Self {
        Self::new_from_token(Token::lookup_from_syntax(name).expect("operator"))
    }
    /// Create a new [`OpAssignment`] from a [`Token`].
    ///
    /// # Panics
    ///
    /// Panics if the token is not an op-assignment operator.
    #[must_use]
    pub fn new_from_token(op: Token) -> Self {
        let op_raw = op
            .get_base_op_from_assignment()
            .expect("op-assignment operator")
            .literal_syntax();
        Self {
            hash_op_assign: calc_fn_hash(op.literal_syntax(), 2),
            hash_op: calc_fn_hash(op_raw, 2),
            op_assign: op.literal_syntax(),
            op: op_raw,
        }
    }
    /// Create a new [`OpAssignment`] from a base operator.
    ///
    /// # Panics
    ///
    /// Panics if the name is not an operator that can be converted into an op-operator.
    #[must_use]
    #[inline(always)]
    pub fn new_from_base(name: &str) -> Self {
        Self::new_from_base_token(Token::lookup_from_syntax(name).expect("operator"))
    }
    /// Convert a [`Token`] into a new [`OpAssignment`].
    ///
    /// # Panics
    ///
    /// Panics if the token is cannot be converted into an op-assignment operator.
    #[inline(always)]
    #[must_use]
    pub fn new_from_base_token(op: Token) -> Self {
        Self::new_from_token(op.convert_to_op_assignment().expect("operator"))
    }
}

/// A statements block with an optional condition.
#[derive(Debug, Clone, Hash)]
pub struct ConditionalStmtBlock {
    /// Optional condition.
    pub condition: Option<Expr>,
    /// Statements block.
    pub statements: StmtBlock,
}

impl<B: Into<StmtBlock>> From<(Option<Expr>, B)> for ConditionalStmtBlock {
    #[inline(always)]
    fn from(value: (Option<Expr>, B)) -> Self {
        Self {
            condition: value.0,
            statements: value.1.into(),
        }
    }
}

impl ConditionalStmtBlock {
    /// Does the condition exist?
    #[inline(always)]
    #[must_use]
    pub const fn has_condition(&self) -> bool {
        self.condition.is_some()
    }
}

/// _(internals)_ A type containing all cases for a `switch` statement.
/// Exported under the `internals` feature only.
#[derive(Debug, Clone, Hash)]
pub struct SwitchCases {
    /// Dictionary mapping value hashes to [`ConditionalStmtBlock`]'s.
    pub cases: BTreeMap<u64, Box<ConditionalStmtBlock>>,
    /// Statements block for the default case (there can be no condition for the default case).
    pub def_case: StmtBlock,
    /// List of range cases.
    pub ranges: StaticVec<(INT, INT, bool, ConditionalStmtBlock)>,
}

/// _(internals)_ A `try-catch` block.
/// Exported under the `internals` feature only.
#[derive(Debug, Clone, Hash)]
pub struct TryCatchBlock {
    /// `try` block.
    pub try_block: StmtBlock,
    /// `catch` variable, if any.
    pub catch_var: Option<Ident>,
    /// `catch` block.
    pub catch_block: StmtBlock,
}

/// _(internals)_ A scoped block of statements.
/// Exported under the `internals` feature only.
#[derive(Clone, Hash, Default)]
pub struct StmtBlock(StaticVec<Stmt>, (Position, Position));

impl StmtBlock {
    /// A [`StmtBlock`] that does not exist.
    pub const NONE: Self = Self::empty(Position::NONE);

    /// Create a new [`StmtBlock`].
    #[must_use]
    pub fn new(
        statements: impl IntoIterator<Item = Stmt>,
        start_pos: Position,
        end_pos: Position,
    ) -> Self {
        let mut statements: StaticVec<_> = statements.into_iter().collect();
        statements.shrink_to_fit();
        Self(statements, (start_pos, end_pos))
    }
    /// Create an empty [`StmtBlock`].
    #[inline(always)]
    #[must_use]
    pub const fn empty(pos: Position) -> Self {
        Self(StaticVec::new_const(), (pos, pos))
    }
    /// Is this statements block empty?
    #[inline(always)]
    #[must_use]
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }
    /// Number of statements in this statements block.
    #[inline(always)]
    #[must_use]
    pub fn len(&self) -> usize {
        self.0.len()
    }
    /// Get the statements of this statements block.
    #[inline(always)]
    #[must_use]
    pub fn statements(&self) -> &[Stmt] {
        &self.0
    }
    /// Extract the statements.
    #[inline(always)]
    #[must_use]
    pub(crate) fn take_statements(&mut self) -> StaticVec<Stmt> {
        mem::take(&mut self.0)
    }
    /// Get an iterator over the statements of this statements block.
    #[inline(always)]
    #[must_use]
    pub fn iter(&self) -> impl Iterator<Item = &Stmt> {
        self.0.iter()
    }
    /// Get the start position (location of the beginning `{`) of this statements block.
    #[inline(always)]
    #[must_use]
    pub const fn position(&self) -> Position {
        (self.1).0
    }
    /// Get the end position (location of the ending `}`) of this statements block.
    #[inline(always)]
    #[must_use]
    pub const fn end_position(&self) -> Position {
        (self.1).1
    }
    /// Get the positions (locations of the beginning `{` and ending `}`) of this statements block.
    #[inline(always)]
    #[must_use]
    pub const fn positions(&self) -> (Position, Position) {
        self.1
    }
    /// Get the positions (locations of the beginning `{` and ending `}`) of this statements block
    /// or a default.
    #[inline(always)]
    #[must_use]
    pub const fn positions_or_else(
        &self,
        def_start_pos: Position,
        def_end_pos: Position,
    ) -> (Position, Position) {
        (
            (self.1).0.or_else(def_start_pos),
            (self.1).1.or_else(def_end_pos),
        )
    }
    /// Set the positions of this statements block.
    #[inline(always)]
    pub fn set_position(&mut self, start_pos: Position, end_pos: Position) {
        self.1 = (start_pos, end_pos);
    }
}

impl Deref for StmtBlock {
    type Target = StaticVec<Stmt>;

    #[inline(always)]
    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl DerefMut for StmtBlock {
    #[inline(always)]
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl AsRef<[Stmt]> for StmtBlock {
    #[inline(always)]
    fn as_ref(&self) -> &[Stmt] {
        &self.0
    }
}

impl AsMut<[Stmt]> for StmtBlock {
    #[inline(always)]
    fn as_mut(&mut self) -> &mut [Stmt] {
        &mut self.0
    }
}

impl fmt::Debug for StmtBlock {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str("Block")?;
        fmt::Debug::fmt(&self.0, f)?;
        (self.1).0.debug_print(f)?;
        #[cfg(not(feature = "no_position"))]
        if !(self.1).1.is_none() {
            write!(f, "-{:?}", (self.1).1)?;
        }
        Ok(())
    }
}

impl From<Stmt> for StmtBlock {
    #[inline]
    fn from(stmt: Stmt) -> Self {
        match stmt {
            Stmt::Block(mut block, pos) => Self(block.iter_mut().map(mem::take).collect(), pos),
            Stmt::Noop(pos) => Self(StaticVec::new_const(), (pos, pos)),
            _ => {
                let pos = stmt.position();
                Self(vec![stmt].into(), (pos, Position::NONE))
            }
        }
    }
}

impl IntoIterator for StmtBlock {
    type Item = Stmt;
    type IntoIter = smallvec::IntoIter<[Stmt; 3]>;

    #[inline(always)]
    fn into_iter(self) -> Self::IntoIter {
        self.0.into_iter()
    }
}

impl Extend<Stmt> for StmtBlock {
    #[inline(always)]
    fn extend<T: IntoIterator<Item = Stmt>>(&mut self, iter: T) {
        self.0.extend(iter)
    }
}

/// _(internals)_ A statement.
/// Exported under the `internals` feature only.
#[derive(Debug, Clone, Hash)]
pub enum Stmt {
    /// No-op.
    Noop(Position),
    /// `if` expr `{` stmt `}` `else` `{` stmt `}`
    If(Expr, Box<(StmtBlock, StmtBlock)>, Position),
    /// `switch` expr `{` literal or range or _ `if` condition `=>` stmt `,` ... `}`
    ///
    /// ### Data Structure
    ///
    /// 0) Hash table for (condition, block)
    /// 1) Default block
    /// 2) List of ranges: (start, end, inclusive, condition, statement)
    Switch(Expr, Box<SwitchCases>, Position),
    /// `while` expr `{` stmt `}` | `loop` `{` stmt `}`
    ///
    /// If the guard expression is [`UNIT`][Expr::Unit], then it is a `loop` statement.
    While(Expr, Box<StmtBlock>, Position),
    /// `do` `{` stmt `}` `while`|`until` expr
    ///
    /// ### Option Flags
    ///
    /// * [`AST_OPTION_NONE`] = `while`
    /// * [`AST_OPTION_NEGATED`] = `until`
    Do(Box<StmtBlock>, Expr, OptionFlags, Position),
    /// `for` `(` id `,` counter `)` `in` expr `{` stmt `}`
    For(Expr, Box<(Ident, Option<Ident>, StmtBlock)>, Position),
    /// \[`export`\] `let`|`const` id `=` expr
    ///
    /// ### Option Flags
    ///
    /// * [`AST_OPTION_EXPORTED`] = `export`
    /// * [`AST_OPTION_CONSTANT`] = `const`
    Var(Expr, Box<Ident>, OptionFlags, Position),
    /// expr op`=` expr
    Assignment(Box<(Option<OpAssignment<'static>>, BinaryExpr)>, Position),
    /// func `(` expr `,` ... `)`
    ///
    /// Note - this is a duplicate of [`Expr::FnCall`] to cover the very common pattern of a single
    ///        function call forming one statement.
    FnCall(Box<FnCallExpr>, Position),
    /// `{` stmt`;` ... `}`
    Block(Box<[Stmt]>, (Position, Position)),
    /// `try` `{` stmt; ... `}` `catch` `(` var `)` `{` stmt; ... `}`
    TryCatch(Box<TryCatchBlock>, Position),
    /// [expression][Expr]
    Expr(Expr),
    /// `continue`/`break`
    ///
    /// ### Option Flags
    ///
    /// * [`AST_OPTION_NONE`] = `continue`
    /// * [`AST_OPTION_BREAK`] = `break`
    BreakLoop(OptionFlags, Position),
    /// `return`/`throw`
    ///
    /// ### Option Flags
    ///
    /// * [`AST_OPTION_NONE`] = `return`
    /// * [`AST_OPTION_BREAK`] = `throw`
    Return(OptionFlags, Option<Expr>, Position),
    /// `import` expr `as` var
    ///
    /// Not available under `no_module`.
    #[cfg(not(feature = "no_module"))]
    Import(Expr, Option<Box<Ident>>, Position),
    /// `export` var `as` var
    ///
    /// Not available under `no_module`.
    #[cfg(not(feature = "no_module"))]
    Export(Box<(Ident, Ident)>, Position),
    /// Convert a variable to shared.
    ///
    /// Not available under `no_closure`.
    ///
    /// # Notes
    ///
    /// This variant does not map to any language structure.  It is currently only used only to
    /// convert a normal variable into a shared variable when the variable is _captured_ by a closure.
    #[cfg(not(feature = "no_closure"))]
    Share(crate::Identifier),
}

impl Default for Stmt {
    #[inline(always)]
    fn default() -> Self {
        Self::Noop(Position::NONE)
    }
}

impl From<StmtBlock> for Stmt {
    #[inline(always)]
    fn from(block: StmtBlock) -> Self {
        Self::Block(block.0.into_boxed_slice(), block.1)
    }
}

impl Stmt {
    /// Is this statement [`Noop`][Stmt::Noop]?
    #[inline(always)]
    #[must_use]
    pub const fn is_noop(&self) -> bool {
        matches!(self, Self::Noop(..))
    }
    /// Get the [position][Position] of this statement.
    #[must_use]
    pub const fn position(&self) -> Position {
        match self {
            Self::Noop(pos)
            | Self::BreakLoop(.., pos)
            | Self::Block(.., (pos, ..))
            | Self::Assignment(.., pos)
            | Self::FnCall(.., pos)
            | Self::If(.., pos)
            | Self::Switch(.., pos)
            | Self::While(.., pos)
            | Self::Do(.., pos)
            | Self::For(.., pos)
            | Self::Return(.., pos)
            | Self::Var(.., pos)
            | Self::TryCatch(.., pos) => *pos,

            Self::Expr(x) => x.start_position(),

            #[cfg(not(feature = "no_module"))]
            Self::Import(.., pos) => *pos,
            #[cfg(not(feature = "no_module"))]
            Self::Export(.., pos) => *pos,

            #[cfg(not(feature = "no_closure"))]
            Self::Share(..) => Position::NONE,
        }
    }
    /// Override the [position][Position] of this statement.
    pub fn set_position(&mut self, new_pos: Position) -> &mut Self {
        match self {
            Self::Noop(pos)
            | Self::BreakLoop(.., pos)
            | Self::Block(.., (pos, ..))
            | Self::Assignment(.., pos)
            | Self::FnCall(.., pos)
            | Self::If(.., pos)
            | Self::Switch(.., pos)
            | Self::While(.., pos)
            | Self::Do(.., pos)
            | Self::For(.., pos)
            | Self::Return(.., pos)
            | Self::Var(.., pos)
            | Self::TryCatch(.., pos) => *pos = new_pos,

            Self::Expr(x) => {
                x.set_position(new_pos);
            }

            #[cfg(not(feature = "no_module"))]
            Self::Import(.., pos) => *pos = new_pos,
            #[cfg(not(feature = "no_module"))]
            Self::Export(.., pos) => *pos = new_pos,

            #[cfg(not(feature = "no_closure"))]
            Self::Share(..) => (),
        }

        self
    }
    /// Does this statement return a value?
    #[must_use]
    pub const fn returns_value(&self) -> bool {
        match self {
            Self::If(..)
            | Self::Switch(..)
            | Self::Block(..)
            | Self::Expr(..)
            | Self::FnCall(..) => true,

            Self::Noop(..) | Self::While(..) | Self::Do(..) | Self::For(..) | Self::TryCatch(..) => {
                false
            }

            Self::Var(..) | Self::Assignment(..) | Self::BreakLoop(..) | Self::Return(..) => false,

            #[cfg(not(feature = "no_module"))]
            Self::Import(..) | Self::Export(..) => false,

            #[cfg(not(feature = "no_closure"))]
            Self::Share(..) => false,
        }
    }
    /// Is this statement self-terminated (i.e. no need for a semicolon terminator)?
    #[must_use]
    pub const fn is_self_terminated(&self) -> bool {
        match self {
            Self::If(..)
            | Self::Switch(..)
            | Self::While(..)
            | Self::For(..)
            | Self::Block(..)
            | Self::TryCatch(..) => true,

            // A No-op requires a semicolon in order to know it is an empty statement!
            Self::Noop(..) => false,

            Self::Expr(Expr::Custom(x, ..)) if x.is_self_terminated() => true,

            Self::Var(..)
            | Self::Assignment(..)
            | Self::Expr(..)
            | Self::FnCall(..)
            | Self::Do(..)
            | Self::BreakLoop(..)
            | Self::Return(..) => false,

            #[cfg(not(feature = "no_module"))]
            Self::Import(..) | Self::Export(..) => false,

            #[cfg(not(feature = "no_closure"))]
            Self::Share(..) => false,
        }
    }
    /// Is this statement _pure_?
    ///
    /// A pure statement has no side effects.
    #[must_use]
    pub fn is_pure(&self) -> bool {
        match self {
            Self::Noop(..) => true,
            Self::Expr(expr) => expr.is_pure(),
            Self::If(condition, x, ..) => {
                condition.is_pure()
                    && x.0.iter().all(Stmt::is_pure)
                    && x.1.iter().all(Stmt::is_pure)
            }
            Self::Switch(expr, x, ..) => {
                expr.is_pure()
                    && x.cases.values().all(|block| {
                        block.condition.as_ref().map(Expr::is_pure).unwrap_or(true)
                            && block.statements.iter().all(Stmt::is_pure)
                    })
                    && x.ranges.iter().all(|(.., block)| {
                        block.condition.as_ref().map(Expr::is_pure).unwrap_or(true)
                            && block.statements.iter().all(Stmt::is_pure)
                    })
                    && x.def_case.iter().all(Stmt::is_pure)
            }

            // Loops that exit can be pure because it can never be infinite.
            Self::While(Expr::BoolConstant(false, ..), ..) => true,
            Self::Do(body, Expr::BoolConstant(x, ..), options, ..)
                if *x == options.contains(AST_OPTION_NEGATED) =>
            {
                body.iter().all(Stmt::is_pure)
            }

            // Loops are never pure since they can be infinite - and that's a side effect.
            Self::While(..) | Self::Do(..) => false,

            // For loops can be pure because if the iterable is pure, it is finite,
            // so infinite loops can never occur.
            Self::For(iterable, x, ..) => iterable.is_pure() && x.2.iter().all(Stmt::is_pure),

            Self::Var(..) | Self::Assignment(..) | Self::FnCall(..) => false,
            Self::Block(block, ..) => block.iter().all(|stmt| stmt.is_pure()),
            Self::BreakLoop(..) | Self::Return(..) => false,
            Self::TryCatch(x, ..) => {
                x.try_block.iter().all(Stmt::is_pure) && x.catch_block.iter().all(Stmt::is_pure)
            }

            #[cfg(not(feature = "no_module"))]
            Self::Import(..) => false,
            #[cfg(not(feature = "no_module"))]
            Self::Export(..) => false,

            #[cfg(not(feature = "no_closure"))]
            Self::Share(..) => false,
        }
    }
    /// Does this statement's behavior depend on its containing block?
    ///
    /// A statement that depends on its containing block behaves differently when promoted
    /// to an upper block.
    ///
    /// Currently only variable definitions (i.e. `let` and `const`), `import`/`export` statements,
    /// and `eval` calls (which may in turn call define variables) fall under this category.
    #[inline]
    #[must_use]
    pub fn is_block_dependent(&self) -> bool {
        match self {
            Self::Var(..) => true,

            Self::Expr(Expr::Stmt(s)) => s.iter().all(Stmt::is_block_dependent),

            Self::FnCall(x, ..) | Self::Expr(Expr::FnCall(x, ..)) => {
                !x.is_qualified() && x.name == KEYWORD_EVAL
            }

            #[cfg(not(feature = "no_module"))]
            Self::Import(..) | Self::Export(..) => true,

            _ => false,
        }
    }
    /// Is this statement _pure_ within the containing block?
    ///
    /// An internally pure statement only has side effects that disappear outside the block.
    ///
    /// Currently only variable definitions (i.e. `let` and `const`) and `import`/`export`
    /// statements are internally pure, other than pure expressions.
    #[inline]
    #[must_use]
    pub fn is_internally_pure(&self) -> bool {
        match self {
            Self::Var(expr, _, ..) => expr.is_pure(),

            Self::Expr(Expr::Stmt(s)) => s.iter().all(Stmt::is_internally_pure),

            #[cfg(not(feature = "no_module"))]
            Self::Import(expr, ..) => expr.is_pure(),
            #[cfg(not(feature = "no_module"))]
            Self::Export(..) => true,

            _ => self.is_pure(),
        }
    }
    /// Does this statement break the current control flow through the containing block?
    ///
    /// Currently this is only true for `return`, `throw`, `break` and `continue`.
    ///
    /// All statements following this statement will essentially be dead code.
    #[inline]
    #[must_use]
    pub const fn is_control_flow_break(&self) -> bool {
        match self {
            Self::Return(..) | Self::BreakLoop(..) => true,
            _ => false,
        }
    }
    /// Recursively walk this statement.
    /// Return `false` from the callback to terminate the walk.
    pub fn walk<'a>(
        &'a self,
        path: &mut Vec<ASTNode<'a>>,
        on_node: &mut impl FnMut(&[ASTNode]) -> bool,
    ) -> bool {
        // Push the current node onto the path
        path.push(self.into());

        if !on_node(path) {
            return false;
        }

        match self {
            Self::Var(e, _, ..) => {
                if !e.walk(path, on_node) {
                    return false;
                }
            }
            Self::If(e, x, ..) => {
                if !e.walk(path, on_node) {
                    return false;
                }
                for s in x.0.iter() {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
                for s in x.1.iter() {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
            }
            Self::Switch(e, x, ..) => {
                if !e.walk(path, on_node) {
                    return false;
                }
                for b in x.cases.values() {
                    if !b
                        .condition
                        .as_ref()
                        .map(|e| e.walk(path, on_node))
                        .unwrap_or(true)
                    {
                        return false;
                    }
                    for s in b.statements.iter() {
                        if !s.walk(path, on_node) {
                            return false;
                        }
                    }
                }
                for (.., b) in &x.ranges {
                    if !b
                        .condition
                        .as_ref()
                        .map(|e| e.walk(path, on_node))
                        .unwrap_or(true)
                    {
                        return false;
                    }
                    for s in b.statements.iter() {
                        if !s.walk(path, on_node) {
                            return false;
                        }
                    }
                }
                for s in x.def_case.iter() {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
            }
            Self::While(e, s, ..) | Self::Do(s, e, ..) => {
                if !e.walk(path, on_node) {
                    return false;
                }
                for s in &s.0 {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
            }
            Self::For(e, x, ..) => {
                if !e.walk(path, on_node) {
                    return false;
                }
                for s in x.2.iter() {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
            }
            Self::Assignment(x, ..) => {
                if !x.1.lhs.walk(path, on_node) {
                    return false;
                }
                if !x.1.rhs.walk(path, on_node) {
                    return false;
                }
            }
            Self::FnCall(x, ..) => {
                for s in &x.args {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
            }
            Self::Block(x, ..) => {
                for s in x.iter() {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
            }
            Self::TryCatch(x, ..) => {
                for s in x.try_block.iter() {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
                for s in x.catch_block.iter() {
                    if !s.walk(path, on_node) {
                        return false;
                    }
                }
            }
            Self::Expr(e) | Self::Return(_, Some(e), _) => {
                if !e.walk(path, on_node) {
                    return false;
                }
            }
            #[cfg(not(feature = "no_module"))]
            Self::Import(e, ..) => {
                if !e.walk(path, on_node) {
                    return false;
                }
            }
            _ => (),
        }

        path.pop().unwrap();

        true
    }
}