use std::fmt::Formatter;
use std::str::FromStr;
use std::sync::Arc;

use ruff_db::files::File;
use ruff_python_ast::name::Name;
use ruff_python_stdlib::identifiers::is_identifier;

use super::path::SearchPath;
use crate::Db;
use crate::module_name::ModuleName;
use crate::module_resolver::path::SystemOrVendoredPathRef;

/// Representation of a Python module.
#[derive(Clone, PartialEq, Eq, Hash, get_size2::GetSize)]
pub struct Module {
    inner: Arc<ModuleInner>,
}

impl Module {
    pub(crate) fn file_module(
        name: ModuleName,
        kind: ModuleKind,
        search_path: SearchPath,
        file: File,
    ) -> Self {
        let known = KnownModule::try_from_search_path_and_name(&search_path, &name);

        Self {
            inner: Arc::new(ModuleInner::FileModule {
                name,
                kind,
                search_path,
                file,
                known,
            }),
        }
    }

    pub(crate) fn namespace_package(name: ModuleName) -> Self {
        Self {
            inner: Arc::new(ModuleInner::NamespacePackage { name }),
        }
    }

    /// The absolute name of the module (e.g. `foo.bar`)
    pub fn name(&self) -> &ModuleName {
        match &*self.inner {
            ModuleInner::FileModule { name, .. } => name,
            ModuleInner::NamespacePackage { name, .. } => name,
        }
    }

    /// The file to the source code that defines this module
    ///
    /// This is `None` for namespace packages.
    pub fn file(&self) -> Option<File> {
        match &*self.inner {
            ModuleInner::FileModule { file, .. } => Some(*file),
            ModuleInner::NamespacePackage { .. } => None,
        }
    }

    /// Is this a module that we special-case somehow? If so, which one?
    pub fn known(&self) -> Option<KnownModule> {
        match &*self.inner {
            ModuleInner::FileModule { known, .. } => *known,
            ModuleInner::NamespacePackage { .. } => None,
        }
    }

    /// Does this module represent the given known module?
    pub fn is_known(&self, known_module: KnownModule) -> bool {
        self.known() == Some(known_module)
    }

    /// The search path from which the module was resolved.
    pub(crate) fn search_path(&self) -> Option<&SearchPath> {
        match &*self.inner {
            ModuleInner::FileModule { search_path, .. } => Some(search_path),
            ModuleInner::NamespacePackage { .. } => None,
        }
    }

    /// Determine whether this module is a single-file module or a package
    pub fn kind(&self) -> ModuleKind {
        match &*self.inner {
            ModuleInner::FileModule { kind, .. } => *kind,
            ModuleInner::NamespacePackage { .. } => ModuleKind::Package,
        }
    }

    /// Return a list of all submodules of this module.
    ///
    /// Returns an empty list if the module is not a package, if it is an empty package,
    /// or if it is a namespace package (one without an `__init__.py` or `__init__.pyi` file).
    ///
    /// The names returned correspond to the "base" name of the module.
    /// That is, `{self.name}.{basename}` should give the full module name.
    pub fn all_submodules(&self, db: &dyn Db) -> Vec<Name> {
        self.all_submodules_inner(db).unwrap_or_default()
    }

    fn all_submodules_inner(&self, db: &dyn Db) -> Option<Vec<Name>> {
        fn is_submodule(
            is_dir: bool,
            is_file: bool,
            basename: Option<&str>,
            extension: Option<&str>,
        ) -> bool {
            is_dir
                || (is_file
                    && matches!(extension, Some("py" | "pyi"))
                    && !matches!(basename, Some("__init__.py" | "__init__.pyi")))
        }

        // It would be complex and expensive to compute all submodules for
        // namespace packages, since a namespace package doesn't correspond
        // to a single file; it can span multiple directories across multiple
        // search paths. For now, we only compute submodules for traditional
        // packages that exist in a single directory on a single search path.
        let ModuleInner::FileModule {
            kind: ModuleKind::Package,
            file,
            ..
        } = &*self.inner
        else {
            return None;
        };

        let path = SystemOrVendoredPathRef::try_from_file(db, *file)?;
        debug_assert!(
            matches!(path.file_name(), Some("__init__.py" | "__init__.pyi")),
            "expected package file `{:?}` to be `__init__.py` or `__init__.pyi`",
            path.file_name(),
        );

        Some(match path.parent()? {
            SystemOrVendoredPathRef::System(parent_directory) => db
                .system()
                .read_directory(parent_directory)
                .inspect_err(|err| {
                    tracing::debug!(
                        "Failed to read {parent_directory:?} when looking for \
                         its possible submodules: {err}"
                    );
                })
                .ok()?
                .flatten()
                .filter(|entry| {
                    let ty = entry.file_type();
                    let path = entry.path();
                    is_submodule(
                        ty.is_directory(),
                        ty.is_file(),
                        path.file_name(),
                        path.extension(),
                    )
                })
                .filter_map(|entry| {
                    let stem = entry.path().file_stem()?;
                    is_identifier(stem).then(|| Name::from(stem))
                })
                .collect(),
            SystemOrVendoredPathRef::Vendored(parent_directory) => db
                .vendored()
                .read_directory(parent_directory)
                .into_iter()
                .filter(|entry| {
                    let ty = entry.file_type();
                    let path = entry.path();
                    is_submodule(
                        ty.is_directory(),
                        ty.is_file(),
                        path.file_name(),
                        path.extension(),
                    )
                })
                .filter_map(|entry| {
                    let stem = entry.path().file_stem()?;
                    is_identifier(stem).then(|| Name::from(stem))
                })
                .collect(),
        })
    }
}

impl std::fmt::Debug for Module {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Module")
            .field("name", &self.name())
            .field("kind", &self.kind())
            .field("file", &self.file())
            .field("search_path", &self.search_path())
            .field("known", &self.known())
            .finish()
    }
}

#[derive(PartialEq, Eq, Hash, get_size2::GetSize)]
enum ModuleInner {
    /// A module that resolves to a file (`lib.py` or `package/__init__.py`)
    FileModule {
        name: ModuleName,
        kind: ModuleKind,
        search_path: SearchPath,
        file: File,
        known: Option<KnownModule>,
    },

    /// A namespace package. Namespace packages are special because
    /// there are multiple possible paths and they have no corresponding
    /// code file.
    NamespacePackage { name: ModuleName },
}

#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, get_size2::GetSize)]
pub enum ModuleKind {
    /// A single-file module (e.g. `foo.py` or `foo.pyi`)
    Module,

    /// A python package (`foo/__init__.py` or `foo/__init__.pyi`)
    Package,
}

impl ModuleKind {
    pub const fn is_package(self) -> bool {
        matches!(self, ModuleKind::Package)
    }
    pub const fn is_module(self) -> bool {
        matches!(self, ModuleKind::Module)
    }
}

/// Enumeration of various core stdlib modules in which important types are located
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, strum_macros::EnumString, get_size2::GetSize)]
#[cfg_attr(test, derive(strum_macros::EnumIter))]
#[strum(serialize_all = "snake_case")]
pub enum KnownModule {
    Builtins,
    Enum,
    Types,
    #[strum(serialize = "_typeshed")]
    Typeshed,
    TypingExtensions,
    Typing,
    Sys,
    Abc,
    Dataclasses,
    Collections,
    Inspect,
    #[strum(serialize = "_typeshed._type_checker_internals")]
    TypeCheckerInternals,
    TyExtensions,
    #[strum(serialize = "importlib")]
    ImportLib,
    #[cfg(test)]
    #[strum(serialize = "unittest.mock")]
    UnittestMock,
    #[cfg(test)]
    Uuid,
}

impl KnownModule {
    pub const fn as_str(self) -> &'static str {
        match self {
            Self::Builtins => "builtins",
            Self::Enum => "enum",
            Self::Types => "types",
            Self::Typing => "typing",
            Self::Typeshed => "_typeshed",
            Self::TypingExtensions => "typing_extensions",
            Self::Sys => "sys",
            Self::Abc => "abc",
            Self::Dataclasses => "dataclasses",
            Self::Collections => "collections",
            Self::Inspect => "inspect",
            Self::TypeCheckerInternals => "_typeshed._type_checker_internals",
            Self::TyExtensions => "ty_extensions",
            Self::ImportLib => "importlib",
            #[cfg(test)]
            Self::UnittestMock => "unittest.mock",
            #[cfg(test)]
            Self::Uuid => "uuid",
        }
    }

    pub fn name(self) -> ModuleName {
        ModuleName::new_static(self.as_str())
            .unwrap_or_else(|| panic!("{self} should be a valid module name!"))
    }

    pub(crate) fn try_from_search_path_and_name(
        search_path: &SearchPath,
        name: &ModuleName,
    ) -> Option<Self> {
        if search_path.is_standard_library() {
            Self::from_str(name.as_str()).ok()
        } else {
            None
        }
    }

    pub const fn is_builtins(self) -> bool {
        matches!(self, Self::Builtins)
    }

    pub const fn is_typing(self) -> bool {
        matches!(self, Self::Typing)
    }

    pub const fn is_ty_extensions(self) -> bool {
        matches!(self, Self::TyExtensions)
    }

    pub const fn is_inspect(self) -> bool {
        matches!(self, Self::Inspect)
    }

    pub const fn is_enum(self) -> bool {
        matches!(self, Self::Enum)
    }

    pub const fn is_importlib(self) -> bool {
        matches!(self, Self::ImportLib)
    }
}

impl std::fmt::Display for KnownModule {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        f.write_str(self.as_str())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use strum::IntoEnumIterator;

    #[test]
    fn known_module_roundtrip_from_str() {
        let stdlib_search_path = SearchPath::vendored_stdlib();

        for module in KnownModule::iter() {
            let module_name = module.name();

            assert_eq!(
                KnownModule::try_from_search_path_and_name(&stdlib_search_path, &module_name),
                Some(module),
                "The strum `EnumString` implementation appears to be incorrect for `{module_name}`"
            );
        }
    }
}