// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
use crate::error::generic_error;
use crate::fast_string::FastString;
use crate::module_specifier::ModuleSpecifier;
use crate::resolve_url;
use anyhow::Error;
use futures::future::FutureExt;
use futures::stream::FuturesUnordered;
use futures::stream::Stream;
use futures::stream::TryStreamExt;
use log::debug;
use serde::Deserialize;
use serde::Serialize;
use std::cell::RefCell;
use std::collections::HashMap;
use std::collections::HashSet;
use std::collections::VecDeque;
use std::future::Future;
use std::pin::Pin;
use std::rc::Rc;
use std::task::Context;
use std::task::Poll;

mod loaders;
mod map;

#[cfg(test)]
mod tests;

pub(crate) use loaders::ExtModuleLoader;
pub use loaders::ExtModuleLoaderCb;
pub use loaders::FsModuleLoader;
pub use loaders::ModuleLoader;
pub use loaders::NoopModuleLoader;
pub(crate) use map::ModuleMap;
#[cfg(test)]
pub(crate) use map::SymbolicModule;

pub type ModuleId = usize;
pub(crate) type ModuleLoadId = i32;
pub type ModuleCode = FastString;
pub type ModuleName = FastString;

const SUPPORTED_TYPE_ASSERTIONS: &[&str] = &["json"];

/// Throws V8 exception if assertions are invalid
pub(crate) fn validate_import_assertions(
  scope: &mut v8::HandleScope,
  assertions: &HashMap<String, String>,
) {
  for (key, value) in assertions {
    if key == "type" && !SUPPORTED_TYPE_ASSERTIONS.contains(&value.as_str()) {
      let message = v8::String::new(
        scope,
        &format!("\"{value}\" is not a valid module type."),
      )
      .unwrap();
      let exception = v8::Exception::type_error(scope, message);
      scope.throw_exception(exception);
      return;
    }
  }
}

#[derive(Debug)]
pub(crate) enum ImportAssertionsKind {
  StaticImport,
  DynamicImport,
}

pub(crate) fn parse_import_assertions(
  scope: &mut v8::HandleScope,
  import_assertions: v8::Local<v8::FixedArray>,
  kind: ImportAssertionsKind,
) -> HashMap<String, String> {
  let mut assertions: HashMap<String, String> = HashMap::default();

  let assertions_per_line = match kind {
    // For static imports, assertions are triples of (keyword, value and source offset)
    // Also used in `module_resolve_callback`.
    ImportAssertionsKind::StaticImport => 3,
    // For dynamic imports, assertions are tuples of (keyword, value)
    ImportAssertionsKind::DynamicImport => 2,
  };
  assert_eq!(import_assertions.length() % assertions_per_line, 0);
  let no_of_assertions = import_assertions.length() / assertions_per_line;

  for i in 0..no_of_assertions {
    let assert_key = import_assertions
      .get(scope, assertions_per_line * i)
      .unwrap();
    let assert_key_val = v8::Local::<v8::Value>::try_from(assert_key).unwrap();
    let assert_value = import_assertions
      .get(scope, (assertions_per_line * i) + 1)
      .unwrap();
    let assert_value_val =
      v8::Local::<v8::Value>::try_from(assert_value).unwrap();
    assertions.insert(
      assert_key_val.to_rust_string_lossy(scope),
      assert_value_val.to_rust_string_lossy(scope),
    );
  }

  assertions
}

pub(crate) fn get_asserted_module_type_from_assertions(
  assertions: &HashMap<String, String>,
) -> AssertedModuleType {
  assertions
    .get("type")
    .map(|ty| {
      if ty == "json" {
        AssertedModuleType::Json
      } else {
        AssertedModuleType::JavaScriptOrWasm
      }
    })
    .unwrap_or(AssertedModuleType::JavaScriptOrWasm)
}

/// A type of module to be executed.
///
/// For non-`JavaScript` modules, this value doesn't tell
/// how to interpret the module; it is only used to validate
/// the module against an import assertion (if one is present
/// in the import statement).
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, Serialize, Deserialize)]
#[repr(u32)]
pub enum ModuleType {
  JavaScript,
  Json,
}

impl std::fmt::Display for ModuleType {
  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
    match self {
      Self::JavaScript => write!(f, "JavaScript"),
      Self::Json => write!(f, "JSON"),
    }
  }
}

/// EsModule source code that will be loaded into V8.
///
/// Users can implement `Into<ModuleInfo>` for different file types that
/// can be transpiled to valid EsModule.
///
/// Found module URL might be different from specified URL
/// used for loading due to redirections (like HTTP 303).
/// Eg. Both "`https://example.com/a.ts`" and
/// "`https://example.com/b.ts`" may point to "`https://example.com/c.ts`"
/// By keeping track of specified and found URL we can alias modules and avoid
/// recompiling the same code 3 times.
// TODO(bartlomieju): I have a strong opinion we should store all redirects
// that happened; not only first and final target. It would simplify a lot
// of things throughout the codebase otherwise we may end up requesting
// intermediate redirects from file loader.
// NOTE: This should _not_ be made #[derive(Clone)] unless we take some precautions to avoid excessive string copying.
#[derive(Debug)]
pub struct ModuleSource {
  pub code: ModuleCode,
  pub module_type: ModuleType,
  module_url_specified: ModuleName,
  /// If the module was found somewhere other than the specified address, this will be [`Some`].
  module_url_found: Option<ModuleName>,
}

impl ModuleSource {
  /// Create a [`ModuleSource`] without a redirect.
  pub fn new(
    module_type: impl Into<ModuleType>,
    code: ModuleCode,
    specifier: &ModuleSpecifier,
  ) -> Self {
    let module_url_specified = specifier.as_ref().to_owned().into();
    Self {
      code,
      module_type: module_type.into(),
      module_url_specified,
      module_url_found: None,
    }
  }

  /// Create a [`ModuleSource`] with a potential redirect. If the `specifier_found` parameter is the same as the
  /// specifier, the code behaves the same was as `ModuleSource::new`.
  pub fn new_with_redirect(
    module_type: impl Into<ModuleType>,
    code: ModuleCode,
    specifier: &ModuleSpecifier,
    specifier_found: &ModuleSpecifier,
  ) -> Self {
    let module_url_found = if specifier == specifier_found {
      None
    } else {
      Some(specifier_found.as_ref().to_owned().into())
    };
    let module_url_specified = specifier.as_ref().to_owned().into();
    Self {
      code,
      module_type: module_type.into(),
      module_url_specified,
      module_url_found,
    }
  }

  #[cfg(test)]
  pub fn for_test(code: &'static str, file: impl AsRef<str>) -> Self {
    Self {
      code: ModuleCode::from_static(code),
      module_type: ModuleType::JavaScript,
      module_url_specified: file.as_ref().to_owned().into(),
      module_url_found: None,
    }
  }

  /// If the `found` parameter is the same as the `specified` parameter, the code behaves the same was as `ModuleSource::for_test`.
  #[cfg(test)]
  pub fn for_test_with_redirect(
    code: &'static str,
    specified: impl AsRef<str>,
    found: impl AsRef<str>,
  ) -> Self {
    let specified = specified.as_ref().to_string();
    let found = found.as_ref().to_string();
    let found = if found == specified {
      None
    } else {
      Some(found.into())
    };
    Self {
      code: ModuleCode::from_static(code),
      module_type: ModuleType::JavaScript,
      module_url_specified: specified.into(),
      module_url_found: found,
    }
  }
}

pub(crate) type PrepareLoadFuture =
  dyn Future<Output = (ModuleLoadId, Result<RecursiveModuleLoad, Error>)>;
pub type ModuleSourceFuture = dyn Future<Output = Result<ModuleSource, Error>>;

type ModuleLoadFuture =
  dyn Future<Output = Result<(ModuleRequest, ModuleSource), Error>>;

#[derive(Debug, PartialEq, Eq)]
pub enum ResolutionKind {
  /// This kind is used in only one situation: when a module is loaded via
  /// `JsRuntime::load_main_module` and is the top-level module, ie. the one
  /// passed as an argument to `JsRuntime::load_main_module`.
  MainModule,
  /// This kind is returned for all other modules during module load, that are
  /// static imports.
  Import,
  /// This kind is returned for all modules that are loaded as a result of a
  /// call to `import()` API (ie. top-level module as well as all its
  /// dependencies, and any other `import()` calls from that load).
  DynamicImport,
}

/// Describes the entrypoint of a recursive module load.
#[derive(Debug)]
enum LoadInit {
  /// Main module specifier.
  Main(String),
  /// Module specifier for side module.
  Side(String),
  /// Dynamic import specifier with referrer and expected
  /// module type (which is determined by import assertion).
  DynamicImport(String, String, AssertedModuleType),
}

#[derive(Debug, Eq, PartialEq)]
pub enum LoadState {
  Init,
  LoadingRoot,
  LoadingImports,
  Done,
}

/// This future is used to implement parallel async module loading.
pub(crate) struct RecursiveModuleLoad {
  pub id: ModuleLoadId,
  pub root_module_id: Option<ModuleId>,
  init: LoadInit,
  root_asserted_module_type: Option<AssertedModuleType>,
  root_module_type: Option<ModuleType>,
  state: LoadState,
  module_map_rc: Rc<RefCell<ModuleMap>>,
  pending: FuturesUnordered<Pin<Box<ModuleLoadFuture>>>,
  visited: HashSet<ModuleRequest>,
  // The loader is copied from `module_map_rc`, but its reference is cloned
  // ahead of time to avoid already-borrowed errors.
  loader: Rc<dyn ModuleLoader>,
}

impl RecursiveModuleLoad {
  /// Starts a new asynchronous load of the module graph for given specifier.
  ///
  /// The module corresponding for the given `specifier` will be marked as
  // "the main module" (`import.meta.main` will return `true` for this module).
  fn main(specifier: &str, module_map_rc: Rc<RefCell<ModuleMap>>) -> Self {
    Self::new(LoadInit::Main(specifier.to_string()), module_map_rc)
  }

  /// Starts a new asynchronous load of the module graph for given specifier.
  fn side(specifier: &str, module_map_rc: Rc<RefCell<ModuleMap>>) -> Self {
    Self::new(LoadInit::Side(specifier.to_string()), module_map_rc)
  }

  /// Starts a new asynchronous load of the module graph for given specifier
  /// that was imported using `import()`.
  fn dynamic_import(
    specifier: &str,
    referrer: &str,
    asserted_module_type: AssertedModuleType,
    module_map_rc: Rc<RefCell<ModuleMap>>,
  ) -> Self {
    Self::new(
      LoadInit::DynamicImport(
        specifier.to_string(),
        referrer.to_string(),
        asserted_module_type,
      ),
      module_map_rc,
    )
  }

  fn new(init: LoadInit, module_map_rc: Rc<RefCell<ModuleMap>>) -> Self {
    let id = {
      let mut module_map = module_map_rc.borrow_mut();
      let id = module_map.next_load_id;
      module_map.next_load_id += 1;
      id
    };
    let loader = module_map_rc.borrow().loader.clone();
    let asserted_module_type = match init {
      LoadInit::DynamicImport(_, _, module_type) => module_type,
      _ => AssertedModuleType::JavaScriptOrWasm,
    };
    let mut load = Self {
      id,
      root_module_id: None,
      root_asserted_module_type: None,
      root_module_type: None,
      init,
      state: LoadState::Init,
      module_map_rc: module_map_rc.clone(),
      loader,
      pending: FuturesUnordered::new(),
      visited: HashSet::new(),
    };
    // FIXME(bartlomieju): this seems fishy
    // Ignore the error here, let it be hit in `Stream::poll_next()`.
    if let Ok(root_specifier) = load.resolve_root() {
      if let Some(module_id) = module_map_rc
        .borrow()
        .get_id(root_specifier, asserted_module_type)
      {
        load.root_module_id = Some(module_id);
        load.root_asserted_module_type = Some(asserted_module_type);
        load.root_module_type = Some(
          module_map_rc
            .borrow()
            .get_info_by_id(module_id)
            .unwrap()
            .module_type,
        );
      }
    }
    load
  }

  fn resolve_root(&self) -> Result<ModuleSpecifier, Error> {
    match self.init {
      LoadInit::Main(ref specifier) => {
        self
          .loader
          .resolve(specifier, ".", ResolutionKind::MainModule)
      }
      LoadInit::Side(ref specifier) => {
        self.loader.resolve(specifier, ".", ResolutionKind::Import)
      }
      LoadInit::DynamicImport(ref specifier, ref referrer, _) => self
        .loader
        .resolve(specifier, referrer, ResolutionKind::DynamicImport),
    }
  }

  async fn prepare(&self) -> Result<(), Error> {
    let (module_specifier, maybe_referrer) = match self.init {
      LoadInit::Main(ref specifier) => {
        let spec =
          self
            .loader
            .resolve(specifier, ".", ResolutionKind::MainModule)?;
        (spec, None)
      }
      LoadInit::Side(ref specifier) => {
        let spec =
          self
            .loader
            .resolve(specifier, ".", ResolutionKind::Import)?;
        (spec, None)
      }
      LoadInit::DynamicImport(ref specifier, ref referrer, _) => {
        let spec = self.loader.resolve(
          specifier,
          referrer,
          ResolutionKind::DynamicImport,
        )?;
        (spec, Some(referrer.to_string()))
      }
    };

    self
      .loader
      .prepare_load(&module_specifier, maybe_referrer, self.is_dynamic_import())
      .await
  }

  fn is_currently_loading_main_module(&self) -> bool {
    !self.is_dynamic_import()
      && matches!(self.init, LoadInit::Main(..))
      && self.state == LoadState::LoadingRoot
  }

  fn is_dynamic_import(&self) -> bool {
    matches!(self.init, LoadInit::DynamicImport(..))
  }

  pub(crate) fn register_and_recurse(
    &mut self,
    scope: &mut v8::HandleScope,
    module_request: &ModuleRequest,
    module_source: ModuleSource,
  ) -> Result<(), ModuleError> {
    let expected_asserted_module_type = module_source.module_type.into();
    let module_url_found = module_source.module_url_found;
    let module_url_specified = module_source.module_url_specified;

    if module_request.asserted_module_type != expected_asserted_module_type {
      return Err(ModuleError::Other(generic_error(format!(
        "Expected a \"{}\" module but loaded a \"{}\" module.",
        module_request.asserted_module_type, module_source.module_type,
      ))));
    }

    // Register the module in the module map unless it's already there. If the
    // specified URL and the "true" URL are different, register the alias.
    let module_url_found = if let Some(module_url_found) = module_url_found {
      let (module_url_found1, module_url_found2) =
        module_url_found.into_cheap_copy();
      self.module_map_rc.borrow_mut().alias(
        module_url_specified,
        expected_asserted_module_type,
        module_url_found1,
      );
      module_url_found2
    } else {
      module_url_specified
    };

    let maybe_module_id = self
      .module_map_rc
      .borrow()
      .get_id(&module_url_found, expected_asserted_module_type);
    let module_id = match maybe_module_id {
      Some(id) => {
        debug!(
          "Already-registered module fetched again: {:?}",
          module_url_found
        );
        id
      }
      None => match module_source.module_type {
        ModuleType::JavaScript => {
          self.module_map_rc.borrow_mut().new_es_module(
            scope,
            self.is_currently_loading_main_module(),
            module_url_found,
            module_source.code,
            self.is_dynamic_import(),
          )?
        }
        ModuleType::Json => self.module_map_rc.borrow_mut().new_json_module(
          scope,
          module_url_found,
          module_source.code,
        )?,
      },
    };

    // Recurse the module's imports. There are two cases for each import:
    // 1. If the module is not in the module map, start a new load for it in
    //    `self.pending`. The result of that load should eventually be passed to
    //    this function for recursion.
    // 2. If the module is already in the module map, queue it up to be
    //    recursed synchronously here.
    // This robustly ensures that the whole graph is in the module map before
    // `LoadState::Done` is set.
    let mut already_registered = VecDeque::new();
    already_registered.push_back((module_id, module_request.clone()));
    self.visited.insert(module_request.clone());
    while let Some((module_id, module_request)) = already_registered.pop_front()
    {
      let referrer = ModuleSpecifier::parse(&module_request.specifier).unwrap();
      let imports = self
        .module_map_rc
        .borrow()
        .get_requested_modules(module_id)
        .unwrap()
        .clone();
      for module_request in imports {
        if !self.visited.contains(&module_request) {
          if let Some(module_id) = self.module_map_rc.borrow().get_id(
            module_request.specifier.as_str(),
            module_request.asserted_module_type,
          ) {
            already_registered.push_back((module_id, module_request.clone()));
          } else {
            let request = module_request.clone();
            let specifier =
              ModuleSpecifier::parse(&module_request.specifier).unwrap();
            let referrer = referrer.clone();
            let loader = self.loader.clone();
            let is_dynamic_import = self.is_dynamic_import();
            let fut = async move {
              let load_result = loader
                .load(&specifier, Some(&referrer), is_dynamic_import)
                .await;
              load_result.map(|s| (request, s))
            };
            self.pending.push(fut.boxed_local());
          }
          self.visited.insert(module_request);
        }
      }
    }

    // Update `self.state` however applicable.
    if self.state == LoadState::LoadingRoot {
      self.root_module_id = Some(module_id);
      self.root_asserted_module_type = Some(module_source.module_type.into());
      self.state = LoadState::LoadingImports;
    }
    if self.pending.is_empty() {
      self.state = LoadState::Done;
    }

    Ok(())
  }
}

impl Stream for RecursiveModuleLoad {
  type Item = Result<(ModuleRequest, ModuleSource), Error>;

  fn poll_next(
    self: Pin<&mut Self>,
    cx: &mut Context,
  ) -> Poll<Option<Self::Item>> {
    let inner = self.get_mut();
    // IMPORTANT: Do not borrow `inner.module_map_rc` here. It may not be
    // available.
    match inner.state {
      LoadState::Init => {
        let module_specifier = match inner.resolve_root() {
          Ok(url) => url,
          Err(error) => return Poll::Ready(Some(Err(error))),
        };
        let load_fut = if let Some(_module_id) = inner.root_module_id {
          // FIXME(bartlomieju): this is very bad
          // The root module is already in the module map.
          // TODO(nayeemrmn): In this case we would ideally skip to
          // `LoadState::LoadingImports` and synchronously recurse the imports
          // like the bottom of `RecursiveModuleLoad::register_and_recurse()`.
          // But the module map cannot be borrowed here. Instead fake a load
          // event so it gets passed to that function and recursed eventually.
          let asserted_module_type = inner.root_asserted_module_type.unwrap();
          let module_type = inner.root_module_type.unwrap();
          let module_request = ModuleRequest {
            specifier: module_specifier.to_string(),
            asserted_module_type,
          };
          // The code will be discarded, since this module is already in the
          // module map.
          let module_source = ModuleSource::new(
            module_type,
            Default::default(),
            &module_specifier,
          );
          futures::future::ok((module_request, module_source)).boxed()
        } else {
          let maybe_referrer = match inner.init {
            LoadInit::DynamicImport(_, ref referrer, _) => {
              resolve_url(referrer).ok()
            }
            _ => None,
          };
          let asserted_module_type = match inner.init {
            LoadInit::DynamicImport(_, _, module_type) => module_type,
            _ => AssertedModuleType::JavaScriptOrWasm,
          };
          let module_request = ModuleRequest {
            specifier: module_specifier.to_string(),
            asserted_module_type,
          };
          let loader = inner.loader.clone();
          let is_dynamic_import = inner.is_dynamic_import();
          async move {
            let result = loader
              .load(
                &module_specifier,
                maybe_referrer.as_ref(),
                is_dynamic_import,
              )
              .await;
            result.map(|s| (module_request, s))
          }
          .boxed_local()
        };
        inner.pending.push(load_fut);
        inner.state = LoadState::LoadingRoot;
        inner.try_poll_next_unpin(cx)
      }
      LoadState::LoadingRoot | LoadState::LoadingImports => {
        match inner.pending.try_poll_next_unpin(cx)? {
          Poll::Ready(None) => unreachable!(),
          Poll::Ready(Some(info)) => Poll::Ready(Some(Ok(info))),
          Poll::Pending => Poll::Pending,
        }
      }
      LoadState::Done => Poll::Ready(None),
    }
  }
}

#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, Serialize, Deserialize)]
#[repr(u32)]
pub(crate) enum AssertedModuleType {
  JavaScriptOrWasm,
  Json,
}

impl From<ModuleType> for AssertedModuleType {
  fn from(module_type: ModuleType) -> AssertedModuleType {
    match module_type {
      ModuleType::JavaScript => AssertedModuleType::JavaScriptOrWasm,
      ModuleType::Json => AssertedModuleType::Json,
    }
  }
}

impl std::fmt::Display for AssertedModuleType {
  fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
    match self {
      Self::JavaScriptOrWasm => write!(f, "JavaScriptOrWasm"),
      Self::Json => write!(f, "JSON"),
    }
  }
}

/// Describes a request for a module as parsed from the source code.
/// Usually executable (`JavaScriptOrWasm`) is used, except when an
/// import assertions explicitly constrains an import to JSON, in
/// which case this will have a `AssertedModuleType::Json`.
#[derive(Clone, Debug, Eq, Hash, PartialEq, Serialize, Deserialize)]
pub(crate) struct ModuleRequest {
  pub specifier: String,
  pub asserted_module_type: AssertedModuleType,
}

#[derive(Debug, PartialEq)]
pub(crate) struct ModuleInfo {
  #[allow(unused)]
  pub id: ModuleId,
  // Used in "bindings.rs" for "import.meta.main" property value.
  pub main: bool,
  pub name: ModuleName,
  pub requests: Vec<ModuleRequest>,
  pub module_type: ModuleType,
}

#[derive(Debug)]
pub(crate) enum ModuleError {
  Exception(v8::Global<v8::Value>),
  Other(Error),
}