use crate::stdlib::{
    boxed::Box, collections::HashMap, io::Error as IoError, path::PathBuf, string::String,
};
use crate::{Engine, EvalAltResult, Module, ModuleResolver, Position, Shared};

/// Module resolution service that loads module script files from the file system.
///
/// Script files are cached so they are are not reloaded and recompiled in subsequent requests.
///
/// The [`new_with_path`][FileModuleResolver::new_with_path] and
/// [`new_with_path_and_extension`][FileModuleResolver::new_with_path_and_extension] constructor functions
/// allow specification of a base directory with module path used as a relative path offset
/// to the base directory. The script file is then forced to be in a specified extension
/// (default `.rhai`).
///
/// # Function Namespace
///
/// When a function within a script file module is loaded, all functions in the _global_ namespace
/// plus all those defined within the same module are _merged_ into a _unified_ namespace before
/// the call.  Therefore, functions in a module script can cross-call each other.
///
/// # Example
///
/// ```
/// use rhai::Engine;
/// use rhai::module_resolvers::FileModuleResolver;
///
/// // Create a new 'FileModuleResolver' loading scripts from the 'scripts' subdirectory
/// // with file extension '.x'.
/// let resolver = FileModuleResolver::new_with_path_and_extension("./scripts", "x");
///
/// let mut engine = Engine::new();
///
/// engine.set_module_resolver(Some(resolver));
/// ```
#[derive(Debug)]
pub struct FileModuleResolver {
    path: PathBuf,
    extension: String,

    #[cfg(not(feature = "sync"))]
    cache: crate::stdlib::cell::RefCell<HashMap<PathBuf, Shared<Module>>>,
    #[cfg(feature = "sync")]
    cache: crate::stdlib::sync::RwLock<HashMap<PathBuf, Shared<Module>>>,
}

impl Default for FileModuleResolver {
    #[inline(always)]
    fn default() -> Self {
        Self::new_with_path(PathBuf::default())
    }
}

impl FileModuleResolver {
    /// Create a new [`FileModuleResolver`] with a specific base path.
    ///
    /// # Example
    ///
    /// ```
    /// use rhai::Engine;
    /// use rhai::module_resolvers::FileModuleResolver;
    ///
    /// // Create a new 'FileModuleResolver' loading scripts from the 'scripts' subdirectory
    /// // with file extension '.rhai' (the default).
    /// let resolver = FileModuleResolver::new_with_path("./scripts");
    ///
    /// let mut engine = Engine::new();
    /// engine.set_module_resolver(Some(resolver));
    /// ```
    #[inline(always)]
    pub fn new_with_path<P: Into<PathBuf>>(path: P) -> Self {
        Self::new_with_path_and_extension(path, "rhai")
    }

    /// Create a new [`FileModuleResolver`] with a specific base path and file extension.
    ///
    /// The default extension is `.rhai`.
    ///
    /// # Example
    ///
    /// ```
    /// use rhai::Engine;
    /// use rhai::module_resolvers::FileModuleResolver;
    ///
    /// // Create a new 'FileModuleResolver' loading scripts from the 'scripts' subdirectory
    /// // with file extension '.x'.
    /// let resolver = FileModuleResolver::new_with_path_and_extension("./scripts", "x");
    ///
    /// let mut engine = Engine::new();
    /// engine.set_module_resolver(Some(resolver));
    /// ```
    #[inline(always)]
    pub fn new_with_path_and_extension<P: Into<PathBuf>, E: Into<String>>(
        path: P,
        extension: E,
    ) -> Self {
        Self {
            path: path.into(),
            extension: extension.into(),
            cache: Default::default(),
        }
    }

    /// Create a new [`FileModuleResolver`] with the current directory as base path.
    ///
    /// # Example
    ///
    /// ```
    /// use rhai::Engine;
    /// use rhai::module_resolvers::FileModuleResolver;
    ///
    /// // Create a new 'FileModuleResolver' loading scripts from the current directory
    /// // with file extension '.rhai' (the default).
    /// let resolver = FileModuleResolver::new();
    ///
    /// let mut engine = Engine::new();
    /// engine.set_module_resolver(Some(resolver));
    /// ```
    #[inline(always)]
    pub fn new() -> Self {
        Default::default()
    }
}

impl ModuleResolver for FileModuleResolver {
    fn resolve(
        &self,
        engine: &Engine,
        path: &str,
        pos: Position,
    ) -> Result<Shared<Module>, Box<EvalAltResult>> {
        // Construct the script file path
        let mut file_path = self.path.clone();
        file_path.push(path);
        file_path.set_extension(&self.extension); // Force extension

        let scope = Default::default();

        // See if it is cached
        let mut module: Option<Shared<Module>> = None;

        let mut module_ref = {
            #[cfg(not(feature = "sync"))]
            let c = self.cache.borrow();
            #[cfg(feature = "sync")]
            let c = self.cache.read().unwrap();

            if let Some(module) = c.get(&file_path) {
                Some(module.clone())
            } else {
                None
            }
        };

        if module_ref.is_none() {
            // Load the script file and compile it
            let ast = engine
                .compile_file(file_path.clone())
                .map_err(|err| match *err {
                    EvalAltResult::ErrorSystem(_, err) if err.is::<IoError>() => {
                        Box::new(EvalAltResult::ErrorModuleNotFound(path.to_string(), pos))
                    }
                    _ => Box::new(EvalAltResult::ErrorInModule(path.to_string(), err, pos)),
                })?;

            let m = Module::eval_ast_as_new(scope, &ast, engine).map_err(|err| {
                Box::new(EvalAltResult::ErrorInModule(path.to_string(), err, pos))
            })?;

            module = Some(m.into());
            module_ref = module.clone();
        };

        if let Some(module) = module {
            // Put it into the cache
            #[cfg(not(feature = "sync"))]
            self.cache.borrow_mut().insert(file_path, module);
            #[cfg(feature = "sync")]
            self.cache.write().unwrap().insert(file_path, module);
        }

        Ok(module_ref.unwrap())
    }
}