use std::borrow::Cow;
use std::debug_assert_matches;
use std::fmt::Formatter;
use std::str::FromStr;

use ruff_db::files::{File, directory_listing, system_path_to_file, vendored_path_to_file};
use ruff_db::system::SystemPath;
use ruff_db::vendored::VendoredPath;
use ruff_python_ast::PythonVersion;
use salsa::Database;
use salsa::plumbing::AsId;

use crate::module_name::ModuleName;
use crate::path::{SearchPath, SystemOrVendoredPathRef};
use crate::{Db, ResolverEnvironment};

/// Representation of a Python module.
#[derive(Clone, Copy, Eq, Hash, PartialEq, salsa::Supertype, salsa::SalsaValue)]
pub enum Module<'db> {
    File(FileModule<'db>),
    Namespace(NamespacePackage<'db>),
}

// The Salsa heap is tracked separately.
impl get_size2::GetSize for Module<'_> {}

#[salsa::tracked]
impl<'db> Module<'db> {
    pub(crate) fn file_module(
        db: &'db dyn Db,
        file: File,
        resolver_environment: ResolverEnvironment<'db>,
        name: Cow<'_, ModuleName>,
        kind: ModuleKind,
        search_path: SearchPath,
    ) -> Self {
        let known = KnownModule::try_from_search_path_and_name(&search_path, &name);

        Self::File(FileModule::new(
            db,
            name,
            kind,
            search_path,
            file,
            resolver_environment,
            known,
        ))
    }

    pub(crate) fn namespace_package(
        db: &'db dyn Db,
        resolver_environment: ResolverEnvironment<'db>,
        name: Cow<'_, ModuleName>,
    ) -> Self {
        Self::Namespace(NamespacePackage::new(db, resolver_environment, name))
    }

    /// The resolver environment used to resolve this module.
    fn resolver_environment(self, db: &'db dyn Database) -> ResolverEnvironment<'db> {
        match self {
            Module::File(module) => module.resolver_environment(db),
            Module::Namespace(module) => module.resolver_environment(db),
        }
    }

    /// The absolute name of the module (e.g. `foo.bar`)
    pub fn name(self, db: &'db dyn Database) -> &'db ModuleName {
        match self {
            Module::File(module) => module.name(db),
            Module::Namespace(ref package) => package.name(db),
        }
    }

    /// The file to the source code that defines this module
    ///
    /// This is `None` for namespace packages.
    pub fn file(self, db: &'db dyn Database) -> Option<File> {
        match self {
            Module::File(module) => Some(module.file(db)),
            Module::Namespace(_) => None,
        }
    }

    /// The Python version used to resolve this module.
    pub fn python_version(self, db: &'db dyn Database) -> PythonVersion {
        self.resolver_environment(db).python_version(db)
    }

    /// Is this a module that we special-case somehow? If so, which one?
    pub fn known(self, db: &'db dyn Database) -> Option<KnownModule> {
        match self {
            Module::File(module) => module.known(db),
            Module::Namespace(_) => None,
        }
    }

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

    /// The search path from which the module was resolved.
    ///
    /// It is guaranteed that if `None` is returned, then this is a namespace
    /// package. Otherwise, this is a regular package or file module.
    pub fn search_path(self, db: &'db dyn Database) -> Option<&'db SearchPath> {
        match self {
            Module::File(module) => Some(module.search_path(db)),
            Module::Namespace(_) => None,
        }
    }

    /// Returns whether this module resolves to a bundled typing-only stub.
    ///
    /// A project or installed module with the same name may still exist on a
    /// lower-priority search path and be available at runtime.
    pub fn is_type_check_only(self, db: &'db dyn Database) -> bool {
        self.search_path(db)
            .is_some_and(SearchPath::is_standard_library)
            && matches!(
                self.name(db).first_component(),
                "_typeshed" | "typing_extensions" | "ty_extensions"
            )
    }

    /// Determine whether this module is a single-file module or a package
    pub fn kind(self, db: &'db dyn Database) -> ModuleKind {
        match self {
            Module::File(module) => module.kind(db),
            Module::Namespace(_) => 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: &'db dyn Db) -> &'db [Module<'db>] {
        all_submodule_names_for_package(db, self).unwrap_or_default()
    }
}

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

#[salsa::tracked(returns(as_deref), heap_size=ruff_memory_usage::heap_size)]
fn all_submodule_names_for_package<'db>(
    db: &'db dyn Db,
    module: Module<'db>,
) -> Option<Box<[Module<'db>]>> {
    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")))
    }

    fn find_package_init_system(db: &dyn Db, dir: &SystemPath) -> Option<File> {
        let listing = directory_listing(db, dir).ok()?;
        if listing.entry_is_file(db, dir, "__init__.pyi") {
            system_path_to_file(db, dir.join("__init__.pyi")).ok()
        } else if listing.entry_is_file(db, dir, "__init__.py") {
            system_path_to_file(db, dir.join("__init__.py")).ok()
        } else {
            None
        }
    }

    fn find_package_init_vendored(db: &dyn Db, dir: &VendoredPath) -> Option<File> {
        vendored_path_to_file(db, dir.join("__init__.pyi"))
            .or_else(|_| vendored_path_to_file(db, dir.join("__init__.py")))
            .ok()
    }

    // 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 Module::File(module) = module else {
        return None;
    };
    if !matches!(module.kind(db), ModuleKind::Package) {
        return None;
    }

    let path = SystemOrVendoredPathRef::try_from_file(db, module.file(db))?;
    debug_assert_matches!(path.file_name(), Some("__init__.py" | "__init__.pyi"));

    let resolver_environment = module.resolver_environment(db);
    Some(match path.parent()? {
        SystemOrVendoredPathRef::System(parent_directory) => {
            directory_listing(db, parent_directory)
                .inspect_err(|error| {
                    tracing::debug!(
                        "Failed to read {parent_directory:?} when looking for \
                         its possible submodules: {error}"
                    );
                })
                .ok()?
                .iter()
                .filter(|(name, ty)| {
                    let path = SystemPath::new(name);
                    is_submodule(
                        ty.is_directory(),
                        ty.is_file(),
                        path.file_name(),
                        path.extension(),
                    )
                })
                .filter_map(|(entry_name, file_type)| {
                    let relative = SystemPath::new(entry_name);
                    let stem = relative.file_stem()?;
                    let path = parent_directory.join(relative);
                    let mut name = module.name(db).clone();
                    name.extend(&ModuleName::new(stem)?);

                    let (kind, file) = if file_type.is_directory() {
                        (ModuleKind::Package, find_package_init_system(db, &path)?)
                    } else {
                        let file = system_path_to_file(db, &path).ok()?;
                        (ModuleKind::Module, file)
                    };
                    Some(Module::file_module(
                        db,
                        file,
                        resolver_environment,
                        Cow::Owned(name),
                        kind,
                        module.search_path(db).clone(),
                    ))
                })
                .collect()
        }
        SystemOrVendoredPathRef::Vendored(parent_directory) => db
            .vendored()
            .read_directory(parent_directory)
            .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()?;
                let mut name = module.name(db).clone();
                name.extend(&ModuleName::new(stem)?);

                let (kind, file) = if entry.file_type().is_directory() {
                    (
                        ModuleKind::Package,
                        find_package_init_vendored(db, entry.path())?,
                    )
                } else {
                    let file = vendored_path_to_file(db, entry.path()).ok()?;
                    (ModuleKind::Module, file)
                };
                Some(Module::file_module(
                    db,
                    file,
                    resolver_environment,
                    Cow::Owned(name),
                    kind,
                    module.search_path(db).clone(),
                ))
            })
            .collect(),
    })
}

/// A module that resolves to a file (`lib.py` or `package/__init__.py`).
#[salsa::interned(debug, heap_size=ruff_memory_usage::heap_size)]
pub struct FileModule<'db> {
    #[returns(ref)]
    pub(super) name: ModuleName,
    #[returns(copy)]
    pub(super) kind: ModuleKind,
    #[returns(ref)]
    pub(super) search_path: SearchPath,
    #[returns(copy)]
    pub(super) file: File,
    #[returns(copy)]
    pub(super) resolver_environment: ResolverEnvironment<'db>,
    #[returns(copy)]
    pub(super) known: Option<KnownModule>,
}

/// A namespace package.
///
/// Namespace packages are special because there are
/// multiple possible paths and they have no corresponding code file.
#[salsa::interned(debug, heap_size=ruff_memory_usage::heap_size)]
pub struct NamespacePackage<'db> {
    #[returns(copy)]
    pub(super) resolver_environment: ResolverEnvironment<'db>,
    #[returns(ref)]
    pub(super) 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 modules in which types with dedicated semantic behavior 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,
    Os,
    Tempfile,
    Pathlib,
    Datetime,
    Decimal,
    Ipaddress,
    Re,
    Abc,
    Dataclasses,
    Functools,
    Collections,
    #[strum(serialize = "collections.abc")]
    CollectionsAbc,
    #[strum(serialize = "_collections_abc")]
    CollectionsAbcInternal,
    Inspect,
    #[strum(serialize = "string.templatelib")]
    Templatelib,
    #[strum(serialize = "_typeshed._type_checker_internals")]
    TypeCheckerInternals,
    TyExtensions,
    #[strum(serialize = "ty_extensions._internal")]
    TyExtensionsInternal,
    #[strum(serialize = "ty_extensions.pydantic")]
    TyExtensionsPydantic,
    #[strum(serialize = "importlib")]
    ImportLib,
    #[strum(serialize = "unittest.mock")]
    UnittestMock,
    Uuid,
    Warnings,
    Numbers,
    #[strum(serialize = "struct", serialize = "_struct")]
    Struct,
    // Third-party modules
    #[strum(serialize = "pydantic.config")]
    PydanticConfig,
    #[strum(serialize = "pydantic.fields")]
    PydanticFields,
    #[strum(serialize = "pydantic.functional_validators")]
    PydanticFunctionalValidators,
    #[strum(serialize = "pydantic.main")]
    PydanticMain,
    #[strum(serialize = "pydantic.root_model")]
    PydanticRootModel,
    #[strum(serialize = "pydantic_settings.main")]
    PydanticSettingsMain,
    #[strum(serialize = "pydantic.types")]
    PydanticTypes,
    Pytest,
    #[strum(serialize = "_pytest.config")]
    PytestConfig,
    #[strum(serialize = "_pytest.fixtures")]
    PytestFixtures,
    #[strum(serialize = "_pytest.mark.structures")]
    PytestMarkStructures,
}

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::Os => "os",
            Self::Tempfile => "tempfile",
            Self::Pathlib => "pathlib",
            Self::Datetime => "datetime",
            Self::Decimal => "decimal",
            Self::Ipaddress => "ipaddress",
            Self::Re => "re",
            Self::Abc => "abc",
            Self::Dataclasses => "dataclasses",
            Self::Functools => "functools",
            Self::Collections => "collections",
            Self::CollectionsAbc => "collections.abc",
            Self::CollectionsAbcInternal => "_collections_abc",
            Self::Inspect => "inspect",
            Self::TypeCheckerInternals => "_typeshed._type_checker_internals",
            Self::TyExtensions => "ty_extensions",
            Self::TyExtensionsInternal => "ty_extensions._internal",
            Self::TyExtensionsPydantic => "ty_extensions.pydantic",
            Self::ImportLib => "importlib",
            Self::Warnings => "warnings",
            Self::UnittestMock => "unittest.mock",
            Self::Uuid => "uuid",
            Self::Templatelib => "string.templatelib",
            Self::Numbers => "numbers",
            Self::Struct => "struct",
            Self::PydanticConfig => "pydantic.config",
            Self::PydanticFields => "pydantic.fields",
            Self::PydanticFunctionalValidators => "pydantic.functional_validators",
            Self::PydanticMain => "pydantic.main",
            Self::PydanticRootModel => "pydantic.root_model",
            Self::PydanticSettingsMain => "pydantic_settings.main",
            Self::PydanticTypes => "pydantic.types",
            Self::Pytest => "pytest",
            Self::PytestConfig => "_pytest.config",
            Self::PytestFixtures => "_pytest.fixtures",
            Self::PytestMarkStructures => "_pytest.mark.structures",
        }
    }

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

    fn try_from_search_path_and_name(search_path: &SearchPath, name: &ModuleName) -> Option<Self> {
        let known_module = Self::from_str(name.as_str()).ok()?;

        let is_expected_search_path = if known_module.is_third_party() {
            search_path.can_contain_third_party_code()
        } else {
            search_path.is_standard_library()
        };

        is_expected_search_path.then_some(known_module)
    }

    /// Return `true` if this module is provided by a supported third-party package.
    pub const fn is_third_party(self) -> bool {
        match self {
            Self::PydanticConfig
            | Self::PydanticFields
            | Self::PydanticFunctionalValidators
            | Self::PydanticMain
            | Self::PydanticRootModel
            | Self::PydanticSettingsMain
            | Self::PydanticTypes
            | Self::Pytest
            | Self::PytestConfig
            | Self::PytestFixtures
            | Self::PytestMarkStructures => true,
            Self::Builtins
            | Self::Enum
            | Self::Types
            | Self::Typeshed
            | Self::TypingExtensions
            | Self::Typing
            | Self::Sys
            | Self::Os
            | Self::Tempfile
            | Self::Pathlib
            | Self::Datetime
            | Self::Decimal
            | Self::Ipaddress
            | Self::Re
            | Self::Abc
            | Self::Dataclasses
            | Self::Functools
            | Self::Collections
            | Self::CollectionsAbc
            | Self::CollectionsAbcInternal
            | Self::Inspect
            | Self::Templatelib
            | Self::TypeCheckerInternals
            | Self::TyExtensions
            | Self::TyExtensionsInternal
            | Self::TyExtensionsPydantic
            | Self::ImportLib
            | Self::UnittestMock
            | Self::Uuid
            | Self::Warnings
            | Self::Numbers
            | Self::Struct => false,
        }
    }

    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_typing_extensions(self) -> bool {
        matches!(self, Self::TypingExtensions)
    }

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

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

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

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

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

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

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().filter(|module| !module.is_third_party()) {
            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}`"
            );
        }
    }
}
