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

use arc_swap::ArcSwapOption;
use get_size2::GetSize;
use ruff_python_ast::{AnyRootNodeRef, ModModule, NodeIndex};
use ruff_python_parser::{ParseOptions, Parsed, parse_unchecked};

use crate::Db;
use crate::files::File;
use crate::source::source_text;

/// Returns the parsed AST of `file`, including its token stream.
///
/// The query uses Ruff's error-resilient parser. That means that the parser always succeeds to produce an
/// AST even if the file contains syntax errors. The parse errors
/// are then accessible through [`Parsed::errors`].
///
/// The query is only cached when the [`source_text()`] hasn't changed. This is because
/// comparing two ASTs is a non-trivial operation and every offset change is directly
/// reflected in the changed AST offsets.
/// The other reason is that Ruff's AST doesn't implement `Eq` which Salsa requires
/// for determining if a query result is unchanged.
///
/// The LRU capacity of 200 was picked without any empirical evidence that it's optimal,
/// instead it's a wild guess that it should be unlikely that incremental changes involve
/// more than 200 modules. Parsed ASTs within the same revision are never evicted by Salsa.
#[salsa::tracked(returns(ref), no_eq, heap_size=ruff_memory_usage::heap_size, lru=200)]
pub fn parsed_module(db: &dyn Db, file: File) -> ParsedModule {
    let _span = tracing::trace_span!("parsed_module", ?file).entered();

    let parsed = parsed_module_impl(db, file);

    ParsedModule::new(file, parsed)
}

pub fn parsed_module_impl(db: &dyn Db, file: File) -> Parsed<ModModule> {
    let source = source_text(db, file);
    let ty = file.source_type(db);

    let target_version = db.python_version();
    let options = ParseOptions::from(ty).with_target_version(target_version);
    parse_unchecked(&source, options)
        .try_into_module()
        .expect("PySourceType always parses into a module")
}

/// A wrapper around a parsed module.
///
/// This type manages instances of the module AST. A particular instance of the AST
/// is represented with the [`ParsedModuleRef`] type.
#[derive(Clone, get_size2::GetSize)]
pub struct ParsedModule {
    file: File,
    #[get_size(size_fn = arc_swap_size)]
    inner: Arc<ArcSwapOption<indexed::IndexedModule>>,
}

impl ParsedModule {
    pub fn new(file: File, parsed: Parsed<ModModule>) -> Self {
        Self {
            file,
            inner: Arc::new(ArcSwapOption::new(Some(indexed::IndexedModule::new(
                parsed,
            )))),
        }
    }
    /// Loads a reference to the parsed module.
    ///
    /// Note that holding on to the reference will prevent garbage collection
    /// of the AST. This method will reparse the module if it has been collected.
    pub fn load(&self, db: &dyn Db) -> ParsedModuleRef {
        let parsed = match self.inner.load_full() {
            Some(parsed) => parsed,
            None => {
                // Re-parse the file.
                let parsed = indexed::IndexedModule::new(parsed_module_impl(db, self.file));
                tracing::debug!(
                    "File `{}` was reparsed after being collected in the current Salsa revision",
                    self.file.path(db)
                );

                self.inner.store(Some(parsed.clone()));
                parsed
            }
        };

        ParsedModuleRef {
            module: self.clone(),
            indexed: parsed,
        }
    }

    /// Clear the parsed module, dropping the AST once all references to it are dropped.
    pub fn clear(&self) {
        self.inner.store(None);
    }

    /// Returns the file to which this module belongs.
    pub fn file(&self) -> File {
        self.file
    }
}

impl std::fmt::Debug for ParsedModule {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        f.debug_tuple("ParsedModule").field(&self.inner).finish()
    }
}

impl PartialEq for ParsedModule {
    fn eq(&self, other: &Self) -> bool {
        Arc::ptr_eq(&self.inner, &other.inner)
    }
}

impl Eq for ParsedModule {}

/// Cheap cloneable wrapper around an instance of a module AST.
#[derive(Clone)]
pub struct ParsedModuleRef {
    module: ParsedModule,
    indexed: Arc<indexed::IndexedModule>,
}

impl ParsedModuleRef {
    /// Returns a reference to the [`ParsedModule`] that this instance was loaded from.
    pub fn module(&self) -> &ParsedModule {
        &self.module
    }

    /// Returns a reference to the AST node at the given index.
    pub fn get_by_index<'ast>(&'ast self, index: NodeIndex) -> AnyRootNodeRef<'ast> {
        self.indexed.get_by_index(index)
    }
}

impl std::ops::Deref for ParsedModuleRef {
    type Target = Parsed<ModModule>;

    fn deref(&self) -> &Self::Target {
        &self.indexed.parsed
    }
}

/// Returns the heap-size of the currently stored `T` in the `ArcSwap`.
fn arc_swap_size<T>(arc_swap: &Arc<ArcSwapOption<T>>) -> usize
where
    T: GetSize,
{
    if let Some(value) = &*arc_swap.load() {
        T::get_heap_size(value)
    } else {
        0
    }
}

mod indexed {
    use std::sync::Arc;

    use ruff_python_ast::visitor::source_order::*;
    use ruff_python_ast::*;
    use ruff_python_parser::Parsed;

    /// A wrapper around the AST that allows access to AST nodes by index.
    #[derive(Debug, get_size2::GetSize)]
    pub struct IndexedModule {
        index: Box<[AnyRootNodeRef<'static>]>,
        pub parsed: Parsed<ModModule>,
    }

    impl IndexedModule {
        /// Create a new [`IndexedModule`] from the given AST.
        #[allow(clippy::unnecessary_cast)]
        pub fn new(parsed: Parsed<ModModule>) -> Arc<Self> {
            let mut visitor = Visitor {
                nodes: Vec::new(),
                index: 0,
            };

            let mut inner = Arc::new(IndexedModule {
                parsed,
                index: Box::new([]),
            });

            AnyNodeRef::from(inner.parsed.syntax()).visit_source_order(&mut visitor);

            let index: Box<[AnyRootNodeRef<'_>]> = visitor.nodes.into_boxed_slice();

            // SAFETY: We cast from `Box<[AnyRootNodeRef<'_>]>` to `Box<[AnyRootNodeRef<'static>]>`,
            // faking the 'static lifetime to create the self-referential struct. The node references
            // are into the `Arc<Parsed<ModModule>>`, so are valid for as long as the `IndexedModule`
            // is alive. We make sure to restore the correct lifetime in `get_by_index`.
            //
            // Note that we can never move the data within the `Arc` after this point.
            Arc::get_mut(&mut inner).unwrap().index =
                unsafe { Box::from_raw(Box::into_raw(index) as *mut [AnyRootNodeRef<'static>]) };

            inner
        }

        /// Returns the node at the given index.
        pub fn get_by_index<'ast>(&'ast self, index: NodeIndex) -> AnyRootNodeRef<'ast> {
            let index = index
                .as_u32()
                .expect("attempted to access uninitialized `NodeIndex`");

            // Note that this method restores the correct lifetime: the nodes are valid for as
            // long as the reference to `IndexedModule` is alive.
            self.index[index as usize]
        }
    }

    /// A visitor that collects nodes in source order.
    pub struct Visitor<'a> {
        pub index: u32,
        pub nodes: Vec<AnyRootNodeRef<'a>>,
    }

    impl<'a> Visitor<'a> {
        fn visit_node<T>(&mut self, node: &'a T)
        where
            T: HasNodeIndex + std::fmt::Debug,
            AnyRootNodeRef<'a>: From<&'a T>,
        {
            node.node_index().set(NodeIndex::from(self.index));
            self.nodes.push(AnyRootNodeRef::from(node));
            self.index += 1;
        }
    }

    impl<'a> SourceOrderVisitor<'a> for Visitor<'a> {
        #[inline]
        fn visit_mod(&mut self, module: &'a Mod) {
            self.visit_node(module);
            walk_module(self, module);
        }

        #[inline]
        fn visit_stmt(&mut self, stmt: &'a Stmt) {
            self.visit_node(stmt);
            walk_stmt(self, stmt);
        }

        #[inline]
        fn visit_annotation(&mut self, expr: &'a Expr) {
            self.visit_node(expr);
            walk_annotation(self, expr);
        }

        #[inline]
        fn visit_expr(&mut self, expr: &'a Expr) {
            self.visit_node(expr);
            walk_expr(self, expr);
        }

        #[inline]
        fn visit_decorator(&mut self, decorator: &'a Decorator) {
            self.visit_node(decorator);
            walk_decorator(self, decorator);
        }

        #[inline]
        fn visit_comprehension(&mut self, comprehension: &'a Comprehension) {
            self.visit_node(comprehension);
            walk_comprehension(self, comprehension);
        }

        #[inline]
        fn visit_except_handler(&mut self, except_handler: &'a ExceptHandler) {
            self.visit_node(except_handler);
            walk_except_handler(self, except_handler);
        }

        #[inline]
        fn visit_arguments(&mut self, arguments: &'a Arguments) {
            self.visit_node(arguments);
            walk_arguments(self, arguments);
        }

        #[inline]
        fn visit_parameters(&mut self, parameters: &'a Parameters) {
            self.visit_node(parameters);
            walk_parameters(self, parameters);
        }

        #[inline]
        fn visit_parameter(&mut self, arg: &'a Parameter) {
            self.visit_node(arg);
            walk_parameter(self, arg);
        }

        fn visit_parameter_with_default(
            &mut self,
            parameter_with_default: &'a ParameterWithDefault,
        ) {
            self.visit_node(parameter_with_default);
            walk_parameter_with_default(self, parameter_with_default);
        }

        #[inline]
        fn visit_keyword(&mut self, keyword: &'a Keyword) {
            self.visit_node(keyword);
            walk_keyword(self, keyword);
        }

        #[inline]
        fn visit_alias(&mut self, alias: &'a Alias) {
            self.visit_node(alias);
            walk_alias(self, alias);
        }

        #[inline]
        fn visit_with_item(&mut self, with_item: &'a WithItem) {
            self.visit_node(with_item);
            walk_with_item(self, with_item);
        }

        #[inline]
        fn visit_type_params(&mut self, type_params: &'a TypeParams) {
            self.visit_node(type_params);
            walk_type_params(self, type_params);
        }

        #[inline]
        fn visit_type_param(&mut self, type_param: &'a TypeParam) {
            self.visit_node(type_param);
            walk_type_param(self, type_param);
        }

        #[inline]
        fn visit_match_case(&mut self, match_case: &'a MatchCase) {
            self.visit_node(match_case);
            walk_match_case(self, match_case);
        }

        #[inline]
        fn visit_pattern(&mut self, pattern: &'a Pattern) {
            self.visit_node(pattern);
            walk_pattern(self, pattern);
        }

        #[inline]
        fn visit_pattern_arguments(&mut self, pattern_arguments: &'a PatternArguments) {
            self.visit_node(pattern_arguments);
            walk_pattern_arguments(self, pattern_arguments);
        }

        #[inline]
        fn visit_pattern_keyword(&mut self, pattern_keyword: &'a PatternKeyword) {
            self.visit_node(pattern_keyword);
            walk_pattern_keyword(self, pattern_keyword);
        }

        #[inline]
        fn visit_elif_else_clause(&mut self, elif_else_clause: &'a ElifElseClause) {
            self.visit_node(elif_else_clause);
            walk_elif_else_clause(self, elif_else_clause);
        }

        #[inline]
        fn visit_f_string(&mut self, f_string: &'a FString) {
            self.visit_node(f_string);
            walk_f_string(self, f_string);
        }

        #[inline]
        fn visit_interpolated_string_element(
            &mut self,
            interpolated_string_element: &'a InterpolatedStringElement,
        ) {
            self.visit_node(interpolated_string_element);
            walk_interpolated_string_element(self, interpolated_string_element);
        }

        #[inline]
        fn visit_t_string(&mut self, t_string: &'a TString) {
            self.visit_node(t_string);
            walk_t_string(self, t_string);
        }

        #[inline]
        fn visit_string_literal(&mut self, string_literal: &'a StringLiteral) {
            self.visit_node(string_literal);
            walk_string_literal(self, string_literal);
        }

        #[inline]
        fn visit_bytes_literal(&mut self, bytes_literal: &'a BytesLiteral) {
            self.visit_node(bytes_literal);
            walk_bytes_literal(self, bytes_literal);
        }

        #[inline]
        fn visit_identifier(&mut self, identifier: &'a Identifier) {
            self.visit_node(identifier);
            walk_identifier(self, identifier);
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::Db;
    use crate::files::{system_path_to_file, vendored_path_to_file};
    use crate::parsed::parsed_module;
    use crate::system::{
        DbWithTestSystem, DbWithWritableSystem as _, SystemPath, SystemVirtualPath,
    };
    use crate::tests::TestDb;
    use crate::vendored::{VendoredFileSystemBuilder, VendoredPath};
    use zip::CompressionMethod;

    #[test]
    fn python_file() -> crate::system::Result<()> {
        let mut db = TestDb::new();
        let path = "test.py";

        db.write_file(path, "x = 10")?;

        let file = system_path_to_file(&db, path).unwrap();

        let parsed = parsed_module(&db, file).load(&db);

        assert!(parsed.has_valid_syntax());

        Ok(())
    }

    #[test]
    fn python_ipynb_file() -> crate::system::Result<()> {
        let mut db = TestDb::new();
        let path = SystemPath::new("test.ipynb");

        db.write_file(path, "%timeit a = b")?;

        let file = system_path_to_file(&db, path).unwrap();

        let parsed = parsed_module(&db, file).load(&db);

        assert!(parsed.has_valid_syntax());

        Ok(())
    }

    #[test]
    fn virtual_python_file() -> crate::system::Result<()> {
        let mut db = TestDb::new();
        let path = SystemVirtualPath::new("untitled:Untitled-1");

        db.write_virtual_file(path, "x = 10");

        let virtual_file = db.files().virtual_file(&db, path);

        let parsed = parsed_module(&db, virtual_file.file()).load(&db);

        assert!(parsed.has_valid_syntax());

        Ok(())
    }

    #[test]
    fn virtual_ipynb_file() -> crate::system::Result<()> {
        let mut db = TestDb::new();
        let path = SystemVirtualPath::new("untitled:Untitled-1.ipynb");

        db.write_virtual_file(path, "%timeit a = b");

        let virtual_file = db.files().virtual_file(&db, path);

        let parsed = parsed_module(&db, virtual_file.file()).load(&db);

        assert!(parsed.has_valid_syntax());

        Ok(())
    }

    #[test]
    fn vendored_file() {
        let mut db = TestDb::new();

        let mut vendored_builder = VendoredFileSystemBuilder::new(CompressionMethod::Stored);
        vendored_builder
            .add_file(
                "path.pyi",
                r#"
import sys

if sys.platform == "win32":
    from ntpath import *
    from ntpath import __all__ as __all__
else:
    from posixpath import *
    from posixpath import __all__ as __all__"#,
            )
            .unwrap();
        let vendored = vendored_builder.finish().unwrap();
        db.with_vendored(vendored);

        let file = vendored_path_to_file(&db, VendoredPath::new("path.pyi")).unwrap();

        let parsed = parsed_module(&db, file).load(&db);

        assert!(parsed.has_valid_syntax());
    }
}