//! Module defining functions for evaluating an expression.

use super::{Caches, EvalContext, GlobalRuntimeState, Target};
use crate::ast::Expr;
use crate::packages::string_basic::{print_with_func, FUNC_TO_STRING};
use crate::types::dynamic::AccessMode;
use crate::{Dynamic, Engine, RhaiResult, RhaiResultOf, Scope, SmartString, ERR};
#[cfg(feature = "no_std")]
use std::prelude::v1::*;
use std::{fmt::Write, num::NonZeroUsize};

/// Search for a module within an imports stack.
#[cfg(not(feature = "no_module"))]
#[inline]
#[must_use]
pub fn search_imports(
    engine: &Engine,
    global: &GlobalRuntimeState,
    namespace: &crate::ast::Namespace,
) -> Option<crate::SharedModule> {
    debug_assert!(!namespace.is_empty());

    let root = namespace.root();

    // Qualified - check if the root module is directly indexed
    if !global.always_search_scope {
        if let Some(index) = namespace.index {
            let offset = global.num_imports() - index.get();

            if let m @ Some(_) = global.get_shared_import(offset) {
                return m;
            }
        }
    }

    // Do a text-match search if the index doesn't work
    global.find_import(root).map_or_else(
        || engine.global_sub_modules.get(root).cloned(),
        |offset| global.get_shared_import(offset),
    )
}

/// Search for a variable within the scope
///
/// # Panics
///
/// Panics if `expr` is not [`Expr::Variable`].
pub fn search_scope_only<'s>(
    engine: &Engine,
    global: &mut GlobalRuntimeState,
    caches: &mut Caches,
    scope: &'s mut Scope,
    this_ptr: Option<&'s mut Dynamic>,
    expr: &Expr,
) -> RhaiResultOf<Target<'s>> {
    // Make sure that the pointer indirection is taken only when absolutely necessary.

    let index = match expr {
        // Check if the variable is `this`
        Expr::ThisPtr(..) => unreachable!("Expr::ThisPtr should have been handled outside"),

        _ if global.always_search_scope => 0,

        Expr::Variable(_, Some(i), ..) => i.get() as usize,
        Expr::Variable(v, None, ..) => {
            // Scripted function with the same name
            #[cfg(not(feature = "no_function"))]
            if let Some(fn_def) = global
                .lib
                .iter()
                .flat_map(|m| m.iter_script_fn())
                .find_map(|(_, _, f, _, func)| if f == v.3 { Some(func) } else { None })
            {
                let val: Dynamic = crate::FnPtr {
                    name: v.3.clone(),
                    curry: <_>::default(),
                    environ: None,
                    fn_def: Some(fn_def.clone()),
                }
                .into();
                return Ok(val.into());
            }

            v.0.map_or(0, NonZeroUsize::get)
        }

        _ => unreachable!("Expr::Variable expected but gets {:?}", expr),
    };

    // Check the variable resolver, if any
    if let Some(ref resolve_var) = engine.resolve_var {
        let orig_scope_len = scope.len();

        let context = EvalContext::new(engine, global, caches, scope, this_ptr);
        let var_name = expr.get_variable_name(true).unwrap();
        let resolved_var = resolve_var(var_name, index, context);

        if orig_scope_len != scope.len() {
            // The scope is changed, always search from now on
            global.always_search_scope = true;
        }

        match resolved_var {
            Ok(Some(mut result)) => {
                result.set_access_mode(AccessMode::ReadOnly);
                return Ok(result.into());
            }
            Ok(None) => (),
            Err(err) => return Err(err.fill_position(expr.position())),
        }
    }

    let index = if index > 0 {
        scope.len() - index
    } else {
        // Find the variable in the scope
        let var_name = expr.get_variable_name(true).unwrap();

        match scope.search(var_name) {
            Some(index) => index,
            None => {
                return engine
                    .global_modules
                    .iter()
                    .find_map(|m| m.get_var(var_name))
                    .map_or_else(
                        || {
                            Err(
                                ERR::ErrorVariableNotFound(var_name.to_string(), expr.position())
                                    .into(),
                            )
                        },
                        |val| Ok(val.into()),
                    )
            }
        }
    };

    let val = scope.get_mut_by_index(index);

    Ok(val.into())
}

/// Search for a variable within the scope or within imports,
/// depending on whether the variable name is namespace-qualified.
pub fn search_namespace<'s>(
    engine: &Engine,
    global: &mut GlobalRuntimeState,
    caches: &mut Caches,
    scope: &'s mut Scope,
    this_ptr: Option<&'s mut Dynamic>,
    expr: &Expr,
) -> RhaiResultOf<Target<'s>> {
    match expr {
        Expr::Variable(_, Some(_), _) => {
            search_scope_only(engine, global, caches, scope, this_ptr, expr)
        }
        Expr::Variable(v, None, ..) => match &**v {
            // Normal variable access
            (_, ns, ..) if ns.is_empty() => {
                search_scope_only(engine, global, caches, scope, this_ptr, expr)
            }

            // Qualified variable access
            #[cfg(not(feature = "no_module"))]
            (_, ns, hash_var, var_name) => {
                // foo:bar::baz::VARIABLE
                if let Some(module) = search_imports(engine, global, ns) {
                    return module.get_qualified_var(*hash_var).map_or_else(
                        || {
                            let sep = crate::engine::NAMESPACE_SEPARATOR;

                            Err(ERR::ErrorVariableNotFound(
                                format!("{ns}{sep}{var_name}"),
                                ns.position(),
                            )
                            .into())
                        },
                        |mut target| {
                            // Module variables are constant
                            target.set_access_mode(AccessMode::ReadOnly);
                            Ok(target.into())
                        },
                    );
                }

                // global::VARIABLE
                #[cfg(not(feature = "no_function"))]
                if ns.path.len() == 1 && ns.root() == crate::engine::KEYWORD_GLOBAL {
                    if let Some(ref constants) = global.constants {
                        if let Some(value) =
                            crate::func::locked_write(constants).get_mut(var_name.as_str())
                        {
                            let mut target: Target = value.clone().into();
                            // Module variables are constant
                            target.as_mut().set_access_mode(AccessMode::ReadOnly);
                            return Ok(target);
                        }
                    }

                    let sep = crate::engine::NAMESPACE_SEPARATOR;

                    return Err(ERR::ErrorVariableNotFound(
                        format!("{ns}{sep}{var_name}"),
                        ns.position(),
                    )
                    .into());
                }

                Err(ERR::ErrorModuleNotFound(ns.to_string(), ns.position()).into())
            }

            #[cfg(feature = "no_module")]
            _ => unreachable!("Invalid expression {:?}", expr),
        },
        _ => unreachable!("Expr::Variable expected but gets {:?}", expr),
    }
}

impl Engine {
    /// Evaluate an expression.
    pub(crate) fn eval_expr(
        &self,
        global: &mut GlobalRuntimeState,
        caches: &mut Caches,
        scope: &mut Scope,
        mut this_ptr: Option<&mut Dynamic>,
        expr: &Expr,
    ) -> RhaiResult {
        self.track_operation(global, expr.position())?;

        #[cfg(feature = "debugging")]
        let reset =
            self.run_debugger_with_reset(global, caches, scope, this_ptr.as_deref_mut(), expr)?;
        #[cfg(feature = "debugging")]
        defer! { global if Some(reset) => move |g| g.debugger_mut().reset_status(reset) }

        match expr {
            // Constants
            Expr::IntegerConstant(x, ..) => Ok((*x).into()),
            Expr::StringConstant(x, ..) => Ok(x.clone().into()),
            Expr::BoolConstant(x, ..) => Ok((*x).into()),
            #[cfg(not(feature = "no_float"))]
            Expr::FloatConstant(x, ..) => Ok((*x).into()),
            Expr::CharConstant(x, ..) => Ok((*x).into()),
            Expr::Unit(..) => Ok(Dynamic::UNIT),
            Expr::DynamicConstant(x, ..) => Ok(x.as_ref().clone()),

            Expr::FnCall(x, pos) => {
                self.eval_fn_call_expr(global, caches, scope, this_ptr, x, *pos)
            }

            Expr::ThisPtr(var_pos) => this_ptr
                .ok_or_else(|| ERR::ErrorUnboundThis(*var_pos).into())
                .cloned(),

            Expr::Variable(..) => search_namespace(self, global, caches, scope, this_ptr, expr)
                .map(Target::take_or_clone),

            Expr::InterpolatedString(x, _) => {
                let mut concat = SmartString::new_const();

                for expr in &**x {
                    let item = &mut self
                        .eval_expr(global, caches, scope, this_ptr.as_deref_mut(), expr)?
                        .flatten();
                    let pos = expr.position();

                    if item.is_string() {
                        write!(concat, "{item}").unwrap();
                    } else {
                        let source = global.source();
                        let context = &(self, FUNC_TO_STRING, source, &*global, pos).into();
                        let display = print_with_func(FUNC_TO_STRING, context, item);
                        write!(concat, "{display}").unwrap();
                    }

                    #[cfg(not(feature = "unchecked"))]
                    self.throw_on_size((0, 0, concat.len()))
                        .map_err(|err| err.fill_position(pos))?;
                }

                Ok(self.get_interned_string(concat).into())
            }

            #[cfg(not(feature = "no_index"))]
            Expr::Array(x, ..) => {
                let mut array = crate::Array::with_capacity(x.len());

                #[cfg(not(feature = "unchecked"))]
                let mut total_data_sizes = (0, 0, 0);

                for item_expr in &**x {
                    let value = self
                        .eval_expr(global, caches, scope, this_ptr.as_deref_mut(), item_expr)?
                        .flatten();

                    #[cfg(not(feature = "unchecked"))]
                    if self.has_data_size_limit() {
                        let val_sizes = crate::eval::calc_data_sizes(&value, true);

                        total_data_sizes = (
                            total_data_sizes.0 + val_sizes.0 + 1,
                            total_data_sizes.1 + val_sizes.1,
                            total_data_sizes.2 + val_sizes.2,
                        );
                        self.throw_on_size(total_data_sizes)
                            .map_err(|err| err.fill_position(item_expr.position()))?;
                    }

                    array.push(value);
                }

                Ok(Dynamic::from_array(array))
            }

            #[cfg(not(feature = "no_object"))]
            #[cfg(not(feature = "indexmap"))]
            Expr::Map(x, ..) => {
                let mut map = x.1.clone();

                #[cfg(not(feature = "unchecked"))]
                let mut total_data_sizes = (0, 0, 0);

                for (key, value_expr) in &x.0 {
                    let value = self
                        .eval_expr(global, caches, scope, this_ptr.as_deref_mut(), value_expr)?
                        .flatten();

                    #[cfg(not(feature = "unchecked"))]
                    if self.has_data_size_limit() {
                        let delta = crate::eval::calc_data_sizes(&value, true);
                        total_data_sizes = (
                            total_data_sizes.0 + delta.0,
                            total_data_sizes.1 + delta.1 + 1,
                            total_data_sizes.2 + delta.2,
                        );
                        self.throw_on_size(total_data_sizes)
                            .map_err(|err| err.fill_position(value_expr.position()))?;
                    }

                    *map.get_mut(key.as_str()).unwrap() = value;
                }

                Ok(Dynamic::from_map(map))
            }

            #[cfg(not(feature = "no_object"))]
            #[cfg(feature = "indexmap")]
            Expr::Map(x, ..) => {
                let mut map = crate::Map::with_capacity(x.0.len());

                #[cfg(not(feature = "unchecked"))]
                let mut total_data_sizes = (0, 0, 0);

                for (key, value_expr) in &x.0 {
                    let value = self
                        .eval_expr(global, caches, scope, this_ptr.as_deref_mut(), value_expr)?
                        .flatten();

                    #[cfg(not(feature = "unchecked"))]
                    if self.has_data_size_limit() {
                        let delta = crate::eval::calc_data_sizes(&value, true);
                        total_data_sizes = (
                            total_data_sizes.0 + delta.0,
                            total_data_sizes.1 + delta.1 + 1,
                            total_data_sizes.2 + delta.2,
                        );
                        self.throw_on_size(total_data_sizes)
                            .map_err(|err| err.fill_position(value_expr.position()))?;
                    }

                    map.insert(key.as_str().into(), value);
                }

                Ok(Dynamic::from_map(map))
            }

            Expr::And(x, ..) => Ok((self
                .eval_expr(global, caches, scope, this_ptr.as_deref_mut(), &x.lhs)?
                .as_bool()
                .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, x.lhs.position()))?
                && self
                    .eval_expr(global, caches, scope, this_ptr, &x.rhs)?
                    .as_bool()
                    .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, x.rhs.position()))?)
            .into()),

            Expr::Or(x, ..) => Ok((self
                .eval_expr(global, caches, scope, this_ptr.as_deref_mut(), &x.lhs)?
                .as_bool()
                .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, x.lhs.position()))?
                || self
                    .eval_expr(global, caches, scope, this_ptr, &x.rhs)?
                    .as_bool()
                    .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, x.rhs.position()))?)
            .into()),

            Expr::Coalesce(x, ..) => {
                let value =
                    self.eval_expr(global, caches, scope, this_ptr.as_deref_mut(), &x.lhs)?;

                if value.is_unit() {
                    self.eval_expr(global, caches, scope, this_ptr, &x.rhs)
                } else {
                    Ok(value)
                }
            }

            #[cfg(not(feature = "no_custom_syntax"))]
            Expr::Custom(custom, pos) => {
                let expressions: crate::StaticVec<_> =
                    custom.inputs.iter().map(Into::into).collect();
                // The first token acts as the custom syntax's key
                let key_token = custom.tokens.first().unwrap();
                // The key should exist, unless the AST is compiled in a different Engine
                let custom_def = self.custom_syntax.get(key_token.as_str()).ok_or_else(|| {
                    Box::new(ERR::ErrorCustomSyntax(
                        format!("Invalid custom syntax prefix: {key_token}"),
                        custom.tokens.iter().map(<_>::to_string).collect(),
                        *pos,
                    ))
                })?;
                let mut context = EvalContext::new(self, global, caches, scope, this_ptr);

                (custom_def.func)(&mut context, &expressions, &custom.state)
                    .and_then(|r| self.check_data_size(r, expr.start_position()))
            }

            Expr::Stmt(x) => {
                self.eval_stmt_block(global, caches, scope, this_ptr, x.statements(), true)
            }

            #[cfg(not(feature = "no_index"))]
            Expr::Index(..) => {
                self.eval_dot_index_chain(global, caches, scope, this_ptr, expr, None)
            }

            #[cfg(not(feature = "no_object"))]
            Expr::Dot(..) => self.eval_dot_index_chain(global, caches, scope, this_ptr, expr, None),

            #[allow(unreachable_patterns)]
            _ => unreachable!("expression cannot be evaluated: {:?}", expr),
        }
    }
}