//! Module that defines the public evaluation API of [`Engine`].

use crate::eval::{Caches, GlobalRuntimeState};
use crate::parser::ParseState;
use crate::types::dynamic::Variant;
use crate::{
    Dynamic, Engine, OptimizationLevel, Position, RhaiResult, RhaiResultOf, Scope, AST, ERR,
};
use std::any::type_name;
#[cfg(feature = "no_std")]
use std::prelude::v1::*;

impl Engine {
    /// Evaluate a string as a script, returning the result value or an error.
    ///
    /// # Example
    ///
    /// ```
    /// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
    /// use rhai::Engine;
    ///
    /// let engine = Engine::new();
    ///
    /// assert_eq!(engine.eval::<i64>("40 + 2")?, 42);
    /// # Ok(())
    /// # }
    /// ```
    #[inline(always)]
    pub fn eval<T: Variant + Clone>(&self, script: &str) -> RhaiResultOf<T> {
        self.eval_with_scope(&mut Scope::new(), script)
    }
    /// Evaluate a string as a script with own scope, returning the result value or an error.
    ///
    /// ## Constants Propagation
    ///
    /// If not [`OptimizationLevel::None`][crate::OptimizationLevel::None], constants defined within
    /// the scope are propagated throughout the script _including_ functions.
    ///
    /// This allows functions to be optimized based on dynamic global constants.
    ///
    /// # Example
    ///
    /// ```
    /// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
    /// use rhai::{Engine, Scope};
    ///
    /// let engine = Engine::new();
    ///
    /// // Create initialized scope
    /// let mut scope = Scope::new();
    /// scope.push("x", 40_i64);
    ///
    /// assert_eq!(engine.eval_with_scope::<i64>(&mut scope, "x += 2; x")?, 42);
    /// assert_eq!(engine.eval_with_scope::<i64>(&mut scope, "x += 2; x")?, 44);
    ///
    /// // The variable in the scope is modified
    /// assert_eq!(scope.get_value::<i64>("x").expect("variable x should exist"), 44);
    /// # Ok(())
    /// # }
    /// ```
    #[inline]
    pub fn eval_with_scope<T: Variant + Clone>(
        &self,
        scope: &mut Scope,
        script: &str,
    ) -> RhaiResultOf<T> {
        let ast = self.compile_with_scope_and_optimization_level(
            scope,
            &[script],
            self.optimization_level,
        )?;
        self.eval_ast_with_scope(scope, &ast)
    }
    /// Evaluate a string containing an expression, returning the result value or an error.
    ///
    /// # Example
    ///
    /// ```
    /// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
    /// use rhai::Engine;
    ///
    /// let engine = Engine::new();
    ///
    /// assert_eq!(engine.eval_expression::<i64>("40 + 2")?, 42);
    /// # Ok(())
    /// # }
    /// ```
    #[inline(always)]
    pub fn eval_expression<T: Variant + Clone>(&self, script: &str) -> RhaiResultOf<T> {
        self.eval_expression_with_scope(&mut Scope::new(), script)
    }
    /// Evaluate a string containing an expression with own scope, returning the result value or an error.
    ///
    /// # Example
    ///
    /// ```
    /// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
    /// use rhai::{Engine, Scope};
    ///
    /// let engine = Engine::new();
    ///
    /// // Create initialized scope
    /// let mut scope = Scope::new();
    /// scope.push("x", 40_i64);
    ///
    /// assert_eq!(engine.eval_expression_with_scope::<i64>(&mut scope, "x + 2")?, 42);
    /// # Ok(())
    /// # }
    /// ```
    #[inline]
    pub fn eval_expression_with_scope<T: Variant + Clone>(
        &self,
        scope: &mut Scope,
        script: &str,
    ) -> RhaiResultOf<T> {
        let scripts = [script];
        let (stream, tokenizer_control) =
            self.lex_raw(&scripts, self.token_mapper.as_ref().map(<_>::as_ref));
        let mut state = ParseState::new(self, scope, Default::default(), tokenizer_control);

        // No need to optimize a lone expression
        let ast = self.parse_global_expr(
            &mut stream.peekable(),
            &mut state,
            |_| {},
            #[cfg(not(feature = "no_optimize"))]
            OptimizationLevel::None,
            #[cfg(feature = "no_optimize")]
            OptimizationLevel::default(),
        )?;

        self.eval_ast_with_scope(scope, &ast)
    }
    /// Evaluate an [`AST`], returning the result value or an error.
    ///
    /// # Example
    ///
    /// ```
    /// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
    /// use rhai::Engine;
    ///
    /// let engine = Engine::new();
    ///
    /// // Compile a script to an AST and store it for later evaluation
    /// let ast = engine.compile("40 + 2")?;
    ///
    /// // Evaluate it
    /// assert_eq!(engine.eval_ast::<i64>(&ast)?, 42);
    /// # Ok(())
    /// # }
    /// ```
    #[inline(always)]
    pub fn eval_ast<T: Variant + Clone>(&self, ast: &AST) -> RhaiResultOf<T> {
        self.eval_ast_with_scope(&mut Scope::new(), ast)
    }
    /// Evaluate an [`AST`] with own scope, returning the result value or an error.
    ///
    /// # Example
    ///
    /// ```
    /// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
    /// use rhai::{Engine, Scope};
    ///
    /// let engine = Engine::new();
    ///
    /// // Create initialized scope
    /// let mut scope = Scope::new();
    /// scope.push("x", 40_i64);
    ///
    /// // Compile a script to an AST and store it for later evaluation
    /// let ast = engine.compile("x += 2; x")?;
    ///
    /// // Evaluate it
    /// assert_eq!(engine.eval_ast_with_scope::<i64>(&mut scope, &ast)?, 42);
    /// assert_eq!(engine.eval_ast_with_scope::<i64>(&mut scope, &ast)?, 44);
    ///
    /// // The variable in the scope is modified
    /// assert_eq!(scope.get_value::<i64>("x").expect("variable x should exist"), 44);
    /// # Ok(())
    /// # }
    /// ```
    #[inline]
    pub fn eval_ast_with_scope<T: Variant + Clone>(
        &self,
        scope: &mut Scope,
        ast: &AST,
    ) -> RhaiResultOf<T> {
        let global = &mut GlobalRuntimeState::new(self);

        let result = self.eval_ast_with_scope_raw(scope, global, ast, 0)?;

        #[cfg(feature = "debugging")]
        if self.debugger.is_some() {
            global.debugger.status = crate::eval::DebuggerStatus::Terminate;
            let lib = &[
                #[cfg(not(feature = "no_function"))]
                ast.as_ref(),
            ];
            let node = &crate::ast::Stmt::Noop(Position::NONE);
            self.run_debugger(scope, global, lib, &mut None, node, 0)?;
        }

        let typ = self.map_type_name(result.type_name());

        result.try_cast::<T>().ok_or_else(|| {
            let t = self.map_type_name(type_name::<T>()).into();
            ERR::ErrorMismatchOutputType(t, typ.into(), Position::NONE).into()
        })
    }
    /// Evaluate an [`AST`] with own scope, returning the result value or an error.
    #[inline]
    pub(crate) fn eval_ast_with_scope_raw<'a>(
        &self,
        scope: &mut Scope,
        global: &mut GlobalRuntimeState,
        ast: &'a AST,
        level: usize,
    ) -> RhaiResult {
        let mut caches = Caches::new();
        global.source = ast.source_raw().cloned();

        #[cfg(not(feature = "no_module"))]
        let orig_embedded_module_resolver = std::mem::replace(
            &mut global.embedded_module_resolver,
            ast.resolver().cloned(),
        );

        let statements = ast.statements();

        if statements.is_empty() {
            return Ok(Dynamic::UNIT);
        }

        let mut _lib = &[
            #[cfg(not(feature = "no_function"))]
            ast.as_ref(),
        ][..];
        #[cfg(not(feature = "no_function"))]
        if !ast.has_functions() {
            _lib = &[];
        }

        let result =
            self.eval_global_statements(scope, global, &mut caches, statements, _lib, level);

        #[cfg(not(feature = "no_module"))]
        {
            global.embedded_module_resolver = orig_embedded_module_resolver;
        }

        result
    }
    /// _(internals)_ Evaluate a list of statements with no `this` pointer.
    /// Exported under the `internals` feature only.
    ///
    /// This is commonly used to evaluate a list of statements in an [`AST`] or a script function body.
    ///
    /// # WARNING - Low Level API
    ///
    /// This function is very low level.
    #[cfg(feature = "internals")]
    #[inline(always)]
    pub fn eval_statements_raw(
        &self,
        scope: &mut Scope,
        global: &mut GlobalRuntimeState,
        caches: &mut Caches,
        statements: &[crate::ast::Stmt],
        lib: &[&crate::Module],
        level: usize,
    ) -> RhaiResult {
        self.eval_global_statements(scope, global, caches, statements, lib, level)
    }
}

/// Evaluate a string as a script, returning the result value or an error.
///
/// # Example
///
/// ```
/// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
/// let result: i64 = rhai::eval("40 + 2")?;
///
/// assert_eq!(result, 42);
/// # Ok(())
/// # }
/// ```
#[inline(always)]
pub fn eval<T: Variant + Clone>(script: &str) -> RhaiResultOf<T> {
    Engine::new().eval(script)
}
