//! Module that defines the extern API of `Engine`.

use crate::any::{Any, AnyExt, Dynamic};
use crate::call::FuncArgs;
use crate::engine::{Engine, FnAny, FnSpec};
use crate::error::ParseError;
use crate::fn_register::RegisterFn;
use crate::parser::{lex, parse, FnDef, Position, AST};
use crate::result::EvalAltResult;
use crate::scope::Scope;
use std::{
    any::{type_name, TypeId},
    fs::File,
    io::prelude::*,
    path::PathBuf,
    sync::Arc,
};

impl<'e> Engine<'e> {
    pub(crate) fn register_fn_raw(
        &mut self,
        fn_name: &str,
        args: Option<Vec<TypeId>>,
        f: Box<FnAny>,
    ) {
        debug_println!(
            "Register function: {} with {}",
            fn_name,
            if let Some(a) = &args {
                format!(
                    "{} parameter{}",
                    a.len(),
                    if a.len() > 1 { "s" } else { "" }
                )
            } else {
                "no parameter".to_string()
            }
        );

        let spec = FnSpec {
            name: fn_name.to_string().into(),
            args,
        };

        self.ext_functions.insert(spec, f);
    }

    /// Register a custom type for use with the `Engine`.
    /// The type must be `Clone`.
    pub fn register_type<T: Any + Clone>(&mut self) {
        self.register_type_with_name::<T>(type_name::<T>());
    }

    /// Register a custom type for use with the `Engine` with a name for the `type_of` function.
    /// The type must be `Clone`.
    pub fn register_type_with_name<T: Any + Clone>(&mut self, name: &str) {
        // Add the pretty-print type name into the map
        self.type_names
            .insert(type_name::<T>().to_string(), name.to_string());
    }

    /// Register an iterator adapter for a type with the `Engine`.
    pub fn register_iterator<T: Any, F>(&mut self, f: F)
    where
        F: Fn(&Dynamic) -> Box<dyn Iterator<Item = Dynamic>> + 'static,
    {
        self.type_iterators.insert(TypeId::of::<T>(), Box::new(f));
    }

    /// Register a getter function for a member of a registered type with the `Engine`.
    pub fn register_get<T: Any + Clone, U: Any + Clone>(
        &mut self,
        name: &str,
        callback: impl Fn(&mut T) -> U + 'static,
    ) {
        let get_name = "get$".to_string() + name;
        self.register_fn(&get_name, callback);
    }

    /// Register a setter function for a member of a registered type with the `Engine`.
    pub fn register_set<T: Any + Clone, U: Any + Clone>(
        &mut self,
        name: &str,
        callback: impl Fn(&mut T, U) -> () + 'static,
    ) {
        let set_name = "set$".to_string() + name;
        self.register_fn(&set_name, callback);
    }

    /// Shorthand for registering both getter and setter functions
    /// of a registered type with the `Engine`.
    pub fn register_get_set<T: Any + Clone, U: Any + Clone>(
        &mut self,
        name: &str,
        get_fn: impl Fn(&mut T) -> U + 'static,
        set_fn: impl Fn(&mut T, U) -> () + 'static,
    ) {
        self.register_get(name, get_fn);
        self.register_set(name, set_fn);
    }

    /// Compile a string into an AST.
    pub fn compile(&self, input: &str) -> Result<AST, ParseError> {
        let tokens_stream = lex(input);
        parse(&mut tokens_stream.peekable(), self.optimize)
    }

    fn read_file(path: PathBuf) -> Result<String, EvalAltResult> {
        let mut f = File::open(path.clone())
            .map_err(|err| EvalAltResult::ErrorReadingScriptFile(path.clone(), err))?;

        let mut contents = String::new();

        f.read_to_string(&mut contents)
            .map_err(|err| EvalAltResult::ErrorReadingScriptFile(path.clone(), err))
            .map(|_| contents)
    }

    /// Compile a file into an AST.
    pub fn compile_file(&self, path: PathBuf) -> Result<AST, EvalAltResult> {
        Self::read_file(path)
            .and_then(|contents| self.compile(&contents).map_err(|err| err.into()))
    }

    /// Evaluate a file.
    pub fn eval_file<T: Any + Clone>(&mut self, path: PathBuf) -> Result<T, EvalAltResult> {
        Self::read_file(path).and_then(|contents| self.eval::<T>(&contents))
    }

    /// Evaluate a string.
    pub fn eval<T: Any + Clone>(&mut self, input: &str) -> Result<T, EvalAltResult> {
        let mut scope = Scope::new();
        self.eval_with_scope(&mut scope, input)
    }

    /// Evaluate a string with own scope.
    pub fn eval_with_scope<T: Any + Clone>(
        &mut self,
        scope: &mut Scope,
        input: &str,
    ) -> Result<T, EvalAltResult> {
        let ast = self.compile(input).map_err(EvalAltResult::ErrorParsing)?;
        self.eval_ast_with_scope(scope, &ast)
    }

    /// Evaluate an AST.
    pub fn eval_ast<T: Any + Clone>(&mut self, ast: &AST) -> Result<T, EvalAltResult> {
        let mut scope = Scope::new();
        self.eval_ast_with_scope(&mut scope, ast)
    }

    /// Evaluate an AST with own scope.
    pub fn eval_ast_with_scope<T: Any + Clone>(
        &mut self,
        scope: &mut Scope,
        ast: &AST,
    ) -> Result<T, EvalAltResult> {
        fn eval_ast_internal(
            engine: &mut Engine,
            scope: &mut Scope,
            ast: &AST,
        ) -> Result<Dynamic, EvalAltResult> {
            engine.clear_functions();

            #[cfg(feature = "no_function")]
            let AST(statements) = ast;

            #[cfg(not(feature = "no_function"))]
            let statements = {
                let AST(statements, functions) = ast;
                engine.load_script_functions(functions);
                statements
            };

            let result = statements
                .iter()
                .try_fold(().into_dynamic(), |_, stmt| engine.eval_stmt(scope, stmt));

            engine.clear_functions();

            result
        }

        match eval_ast_internal(self, scope, ast) {
            Err(EvalAltResult::Return(out, pos)) => out.downcast::<T>().map(|v| *v).map_err(|a| {
                EvalAltResult::ErrorMismatchOutputType(
                    self.map_type_name((*a).type_name()).to_string(),
                    pos,
                )
            }),

            Ok(out) => out.downcast::<T>().map(|v| *v).map_err(|a| {
                EvalAltResult::ErrorMismatchOutputType(
                    self.map_type_name((*a).type_name()).to_string(),
                    Position::eof(),
                )
            }),

            Err(err) => Err(err),
        }
    }

    /// Evaluate a file, but throw away the result and only return error (if any).
    /// Useful for when you don't need the result, but still need to keep track of possible errors.
    ///
    /// Note - if `retain_functions` is set to `true`, functions defined by previous scripts are _retained_
    ///        and not cleared from run to run.
    pub fn consume_file(
        &mut self,
        path: PathBuf,
        retain_functions: bool,
    ) -> Result<(), EvalAltResult> {
        Self::read_file(path).and_then(|contents| self.consume(&contents, retain_functions))
    }

    /// Evaluate a string, but throw away the result and only return error (if any).
    /// Useful for when you don't need the result, but still need to keep track of possible errors.
    ///
    /// Note - if `retain_functions` is set to `true`, functions defined by previous scripts are _retained_
    ///        and not cleared from run to run.
    pub fn consume(&mut self, input: &str, retain_functions: bool) -> Result<(), EvalAltResult> {
        self.consume_with_scope(&mut Scope::new(), retain_functions, input)
    }

    /// Evaluate a string, but throw away the result and only return error (if any).
    /// Useful for when you don't need the result, but still need to keep track of possible errors.
    ///
    /// Note - if `retain_functions` is set to `true`, functions defined by previous scripts are _retained_
    ///        and not cleared from run to run.
    pub fn consume_with_scope(
        &mut self,
        scope: &mut Scope,
        retain_functions: bool,
        input: &str,
    ) -> Result<(), EvalAltResult> {
        let tokens_stream = lex(input);

        let ast = parse(&mut tokens_stream.peekable(), self.optimize)
            .map_err(EvalAltResult::ErrorParsing)?;

        self.consume_ast_with_scope(scope, retain_functions, &ast)
    }

    /// Evaluate an AST, but throw away the result and only return error (if any).
    /// Useful for when you don't need the result, but still need to keep track of possible errors.
    ///
    /// Note - if `retain_functions` is set to `true`, functions defined by previous scripts are _retained_
    ///        and not cleared from run to run.
    pub fn consume_ast_with_scope(
        &mut self,
        scope: &mut Scope,
        retain_functions: bool,
        ast: &AST,
    ) -> Result<(), EvalAltResult> {
        if !retain_functions {
            self.clear_functions();
        }

        #[cfg(feature = "no_function")]
        let AST(statements) = ast;

        #[cfg(not(feature = "no_function"))]
        let statements = {
            let AST(ref statements, ref functions) = ast;
            self.load_script_functions(functions);
            statements
        };

        let result = statements
            .iter()
            .try_fold(().into_dynamic(), |_, o| self.eval_stmt(scope, o))
            .map(|_| ());

        if !retain_functions {
            self.clear_functions();
        }

        result
    }

    /// Load a list of functions into the Engine.
    pub(crate) fn load_script_functions<'a>(
        &mut self,
        functions: impl IntoIterator<Item = &'a Arc<FnDef>>,
    ) {
        for f in functions.into_iter() {
            match self
                .script_functions
                .binary_search_by(|fn_def| fn_def.compare(&f.name, f.params.len()))
            {
                Ok(n) => self.script_functions[n] = f.clone(),
                Err(n) => self.script_functions.insert(n, f.clone()),
            }
        }
    }

    /// Call a script function retained inside the Engine.
    ///
    /// # Example
    ///
    /// ```rust
    /// # fn main() -> Result<(), rhai::EvalAltResult> {
    /// # #[cfg(not(feature = "no_stdlib"))]
    /// # #[cfg(not(feature = "no_function"))]
    /// # {
    /// use rhai::Engine;
    ///
    /// let mut engine = Engine::new();
    ///
    /// engine.consume("fn add(x, y) { x.len() + y }", true)?;
    ///
    /// let result: i64 = engine.call_fn("add", (String::from("abc"), 123_i64))?;
    ///
    /// assert_eq!(result, 126);
    /// # }
    /// # Ok(())
    /// # }
    /// ```
    #[cfg(not(feature = "no_function"))]
    pub fn call_fn<A: FuncArgs, T: Any + Clone>(
        &mut self,
        name: &str,
        args: A,
    ) -> Result<T, EvalAltResult> {
        // Split out non-generic portion to avoid exploding code size
        fn call_fn_internal(
            engine: &mut Engine,
            name: &str,
            mut values: Vec<Dynamic>,
        ) -> Result<Dynamic, EvalAltResult> {
            let values: Vec<_> = values.iter_mut().map(Dynamic::as_mut).collect();

            let result = engine.call_fn_raw(name, values, None, Position::none());

            result
        }

        call_fn_internal(self, name, args.into_vec()).and_then(|b| {
            b.downcast().map(|b| *b).map_err(|a| {
                EvalAltResult::ErrorMismatchOutputType(
                    self.map_type_name((*a).type_name()).into(),
                    Position::none(),
                )
            })
        })
    }

    /// Override default action of `print` (print to stdout using `println!`)
    ///
    /// # Example
    ///
    /// ```rust
    /// # fn main() -> Result<(), rhai::EvalAltResult> {
    /// use rhai::Engine;
    ///
    /// let mut result = String::from("");
    /// {
    ///     let mut engine = Engine::new();
    ///
    ///     // Override action of 'print' function
    ///     engine.on_print(|s| result.push_str(s));
    ///     engine.consume("print(40 + 2);", false)?;
    /// }
    /// assert_eq!(result, "42");
    /// # Ok(())
    /// # }
    /// ```
    pub fn on_print(&mut self, callback: impl FnMut(&str) + 'e) {
        self.on_print = Box::new(callback);
    }

    /// Override default action of `debug` (print to stdout using `println!`)
    ///
    /// # Example
    ///
    /// ```rust
    /// # fn main() -> Result<(), rhai::EvalAltResult> {
    /// use rhai::Engine;
    ///
    /// let mut result = String::from("");
    /// {
    ///     let mut engine = Engine::new();
    ///
    ///     // Override action of 'debug' function
    ///     engine.on_debug(|s| result.push_str(s));
    ///     engine.consume(r#"debug("hello");"#, false)?;
    /// }
    /// assert_eq!(result, "\"hello\"");
    /// # Ok(())
    /// # }
    /// ```
    pub fn on_debug(&mut self, callback: impl FnMut(&str) + 'e) {
        self.on_debug = Box::new(callback);
    }
}