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

use ruff_python_ast::{ModModule, PySourceType};
use ruff_python_parser::{parse_unchecked_source, Parsed};

use crate::files::{File, FilePath};
use crate::source::source_text;
use crate::Db;

/// 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 Sala requires
/// for determining if a query result is unchanged.
#[salsa::tracked(no_eq, return_ref)]
pub fn parsed_module(db: &dyn Db, file: File) -> ParsedModule {
    let _span = tracing::trace_span!("parse_module", file = ?file.path(db)).entered();

    let source = source_text(db, file);
    let path = file.path(db);

    let ty = match path {
        FilePath::System(path) => path
            .extension()
            .map_or(PySourceType::Python, PySourceType::from_extension),
        FilePath::Vendored(_) => PySourceType::Stub,
        FilePath::SystemVirtual(path) => path
            .extension()
            .map_or(PySourceType::Python, PySourceType::from_extension),
    };

    ParsedModule::parse(&source, ty)
}

/// Cheap cloneable wrapper around the parsed module.
#[derive(Clone)]
pub struct ParsedModule {
    inner: Arc<ParsedInner>,
}

struct ParsedInner {
    parsed: Parsed<ModModule<'static>>,

    // It's important that allocator comes **after** parsed
    // so that it gets dropped **after** parsed.
    allocator: Box<std::sync::Mutex<ruff_allocator::Allocator>>,
}

impl ParsedModule {
    pub fn parse(source: &str, ty: PySourceType) -> Self {
        let allocator = Box::new(std::sync::Mutex::new(ruff_allocator::Allocator::new()));

        let parsed: Parsed<ModModule<'static>> = {
            let allocator = allocator.lock().unwrap();
            let parsed = parse_unchecked_source(&source, ty, &allocator);
            unsafe { std::mem::transmute(parsed) }
        };

        Self {
            inner: Arc::new(ParsedInner { parsed, allocator }),
        }
    }

    pub fn parsed<'a>(&'a self) -> &'a Parsed<ModModule<'a>> {
        unsafe { std::mem::transmute(&self.inner.parsed) }
    }
}

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

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

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

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

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

        let parsed = parsed_module(&db, file);

        assert!(parsed.is_valid());

        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".to_string())?;

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

        let parsed = parsed_module(&db, file);

        assert!(parsed.is_valid());

        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 file = db.files().add_virtual_file(&db, path).unwrap();

        let parsed = parsed_module(&db, file);

        assert!(parsed.is_valid());

        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 file = db.files().add_virtual_file(&db, path).unwrap();

        let parsed = parsed_module(&db, file);

        assert!(parsed.is_valid());

        Ok(())
    }

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

        let mut vendored_builder = VendoredFileSystemBuilder::new();
        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);

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