use std::{
    collections::HashMap,
    sync::{Arc, Mutex},
};

use anyhow::Result;

use crate::{
    ExecState, ExecutorContext, KclError, ModuleId, SourceRange,
    errors::KclErrorDetails,
    execution::typed_path::TypedPath,
    modules::{ModulePath, ModuleRepr},
    parsing::ast::types::{ImportPath, ImportStatement, Node as AstNode},
    walk::{Node, Visitable},
};

/// Specific dependency between two modules. The 0th element of this info
/// is the "importing" module, the 1st is the "imported" module. The 0th
/// module *depends on* the 1st module.
type Dependency = (String, String);

type Graph = Vec<Dependency>;

pub(crate) type DependencyInfo = (AstNode<ImportStatement>, ModuleId, ModulePath, ModuleRepr);
pub(crate) type UniverseMap = HashMap<TypedPath, AstNode<ImportStatement>>;
pub(crate) type Universe = HashMap<String, DependencyInfo>;

/// Process a number of programs, returning the graph of dependencies.
///
/// This will (currently) return a list of lists of IDs that can be safely
/// run concurrently. Each "stage" is blocking in this model, which will
/// change in the future. Don't use this function widely, yet.
#[allow(clippy::iter_over_hash_type)]
pub(crate) fn import_graph(progs: &Universe, ctx: &ExecutorContext) -> Result<Vec<Vec<String>>, KclError> {
    let mut graph = Graph::new();

    for (name, (_, _, path, repr)) in progs.iter() {
        graph.extend(
            import_dependencies(path, repr, ctx)?
                .into_iter()
                .map(|(dependency, _, _)| (name.clone(), dependency))
                .collect::<Vec<_>>(),
        );
    }

    let all_modules: Vec<&str> = progs.keys().map(|v| v.as_str()).collect();
    topsort(&all_modules, graph)
}

#[allow(clippy::iter_over_hash_type)]
fn topsort(all_modules: &[&str], graph: Graph) -> Result<Vec<Vec<String>>, KclError> {
    if all_modules.is_empty() {
        return Ok(vec![]);
    }
    let mut dep_map = HashMap::<String, Vec<String>>::new();

    for (dependent, dependency) in graph.iter() {
        let mut dependencies = dep_map.remove(dependent).unwrap_or_default();
        dependencies.push(dependency.to_owned());
        dep_map.insert(dependent.to_owned(), dependencies);
    }

    // dep_map now contains reverse dependencies. For each module, it's a
    // list of what things are "waiting on it". A non-empty value for a key
    // means it's currently blocked.

    let mut waiting_modules = all_modules.to_owned();
    let mut order = vec![];

    loop {
        // Each pass through we need to find any modules which have nothing
        // "pointing at it" -- so-called reverse dependencies. This is an entry
        // that is either not in the dep_map OR an empty list.

        let mut stage_modules: Vec<String> = vec![];

        for module in &waiting_modules {
            let module = module.to_string();
            if dep_map.get(&module).map(|v| v.len()).unwrap_or(0) == 0 {
                // if it's None or empty, this is a node that we can process,
                // and remove from the graph.
                stage_modules.push(module.to_string());
            }
        }

        for stage_module in &stage_modules {
            // remove the ready-to-run module from the waiting list
            waiting_modules.retain(|v| *v != stage_module.as_str());

            // remove any dependencies for the next run
            for (_, waiting_for) in dep_map.iter_mut() {
                waiting_for.retain(|v| v != stage_module);
            }
        }

        if stage_modules.is_empty() {
            waiting_modules.sort();

            return Err(KclError::new_import_cycle(KclErrorDetails::new(
                format!("circular import of modules not allowed: {}", waiting_modules.join(", ")),
                // TODO: we can get the right import lines from the AST, but we don't
                vec![SourceRange::default()],
            )));
        }

        // not strictly needed here, but perhaps helpful to avoid thinking
        // there's any implied ordering as well as helping to make tests
        // easier.
        stage_modules.sort();

        order.push(stage_modules);

        if waiting_modules.is_empty() {
            break;
        }
    }

    Ok(order)
}

type ImportDependencies = Vec<(String, AstNode<ImportStatement>, ModulePath)>;

fn import_dependencies(
    path: &ModulePath,
    repr: &ModuleRepr,
    ctx: &ExecutorContext,
) -> Result<ImportDependencies, KclError> {
    let ModuleRepr::Kcl(prog, _) = repr else {
        // It has no dependencies, so return an empty list.
        return Ok(vec![]);
    };

    let ret = Arc::new(Mutex::new(vec![]));
    fn walk(
        ret: Arc<Mutex<ImportDependencies>>,
        node: Node<'_>,
        import_from: &ModulePath,
        ctx: &ExecutorContext,
    ) -> Result<(), KclError> {
        if let Node::ImportStatement(is) = node {
            // We only care about Kcl and Foreign imports for now.
            let resolved_path = ModulePath::from_import_path(&is.path, &ctx.settings.project_directory, import_from)?;
            match &is.path {
                ImportPath::Kcl { filename } => {
                    // We need to lock the mutex to push the dependency.
                    // This is a bit of a hack, but it works for now.
                    ret.lock()
                        .map_err(|err| {
                            KclError::new_internal(KclErrorDetails::new(
                                format!("Failed to lock mutex: {err}"),
                                Default::default(),
                            ))
                        })?
                        .push((filename.to_string(), is.clone(), resolved_path));
                }
                ImportPath::Foreign { path } => {
                    ret.lock()
                        .map_err(|err| {
                            KclError::new_internal(KclErrorDetails::new(
                                format!("Failed to lock mutex: {err}"),
                                Default::default(),
                            ))
                        })?
                        .push((path.to_string(), is.clone(), resolved_path));
                }
                ImportPath::Std { .. } => { // do nothing
                }
            }
        }

        for child in node.children().iter() {
            walk(ret.clone(), *child, import_from, ctx)?;
        }

        Ok(())
    }

    walk(ret.clone(), prog.into(), path, ctx)?;

    let ret = ret.lock().map_err(|err| {
        KclError::new_internal(KclErrorDetails::new(
            format!("Failed to lock mutex: {err}"),
            Default::default(),
        ))
    })?;

    Ok(ret.clone())
}

/// Mutates the `out` universe with the imported modules. Returns the imports of
/// only `repr`'s non-transitive imports.
pub(crate) async fn import_universe(
    ctx: &ExecutorContext,
    path: &ModulePath,
    repr: &ModuleRepr,
    out: &mut Universe,
    exec_state: &mut ExecState,
) -> Result<UniverseMap, KclError> {
    let modules = import_dependencies(path, repr, ctx)?;
    let mut module_imports = HashMap::new();
    for (filename, import_stmt, module_path) in modules {
        match &module_path {
            ModulePath::Main => {
                // We only care about what the root module imports.
            }
            ModulePath::Local { value, .. } => {
                module_imports.insert(value.clone(), import_stmt.clone());
            }
            ModulePath::Std { .. } => {
                // We don't care about std imports.
            }
        }

        if out.contains_key(&filename) {
            continue;
        }

        let source_range = SourceRange::from(&import_stmt);
        let attrs = &import_stmt.outer_attrs;
        let module_id = ctx
            .open_module(&import_stmt.path, attrs, &module_path, exec_state, source_range)
            .await?;

        let repr = {
            let Some(module_info) = exec_state.get_module(module_id) else {
                return Err(KclError::new_internal(KclErrorDetails::new(
                    format!("Module {module_id} not found"),
                    vec![import_stmt.into()],
                )));
            };
            module_info.repr.clone()
        };

        out.insert(filename, (import_stmt, module_id, module_path.clone(), repr.clone()));
        Box::pin(import_universe(ctx, &module_path, &repr, out, exec_state)).await?;
    }

    Ok(module_imports)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::parsing::ast::types::{ImportSelector, Program};

    macro_rules! kcl {
        ( $kcl:expr_2021 ) => {{ $crate::parsing::top_level_parse($kcl).unwrap() }};
    }

    fn into_module_info(program: AstNode<Program>) -> DependencyInfo {
        (
            AstNode::no_src(ImportStatement {
                selector: ImportSelector::None { alias: None },
                path: ImportPath::Kcl { filename: "".into() },
                visibility: Default::default(),
                digest: None,
            }),
            ModuleId::default(),
            ModulePath::Local { value: "".into() },
            ModuleRepr::Kcl(program, None),
        )
    }

    #[tokio::test]
    async fn order_imports() {
        let mut modules = HashMap::new();

        let a = kcl!("");
        modules.insert("a.kcl".to_owned(), into_module_info(a));

        let b = kcl!(
            "
import \"a.kcl\"
"
        );
        modules.insert("b.kcl".to_owned(), into_module_info(b));

        let ctx = ExecutorContext::new_mock(None).await;
        let order = import_graph(&modules, &ctx).unwrap();
        assert_eq!(vec![vec!["a.kcl".to_owned()], vec!["b.kcl".to_owned()]], order);
    }

    #[tokio::test]
    async fn order_imports_none() {
        let mut modules = HashMap::new();

        let a = kcl!(
            "
y = 2
"
        );
        modules.insert("a.kcl".to_owned(), into_module_info(a));

        let b = kcl!(
            "
x = 1
"
        );
        modules.insert("b.kcl".to_owned(), into_module_info(b));

        let ctx = ExecutorContext::new_mock(None).await;
        let order = import_graph(&modules, &ctx).unwrap();
        assert_eq!(vec![vec!["a.kcl".to_owned(), "b.kcl".to_owned()]], order);
    }

    #[tokio::test]
    async fn order_imports_2() {
        let mut modules = HashMap::new();

        let a = kcl!("");
        modules.insert("a.kcl".to_owned(), into_module_info(a));

        let b = kcl!(
            "
import \"a.kcl\"
"
        );
        modules.insert("b.kcl".to_owned(), into_module_info(b));

        let c = kcl!(
            "
import \"a.kcl\"
"
        );
        modules.insert("c.kcl".to_owned(), into_module_info(c));

        let ctx = ExecutorContext::new_mock(None).await;
        let order = import_graph(&modules, &ctx).unwrap();
        assert_eq!(
            vec![vec!["a.kcl".to_owned()], vec!["b.kcl".to_owned(), "c.kcl".to_owned()]],
            order
        );
    }

    #[tokio::test]
    async fn order_imports_cycle() {
        let mut modules = HashMap::new();

        let a = kcl!(
            "
import \"b.kcl\"
"
        );
        modules.insert("a.kcl".to_owned(), into_module_info(a));

        let b = kcl!(
            "
import \"a.kcl\"
"
        );
        modules.insert("b.kcl".to_owned(), into_module_info(b));

        let ctx = ExecutorContext::new_mock(None).await;
        import_graph(&modules, &ctx).unwrap_err();
    }
}