//! Look up accessible paths for items.
use hir::{
    AsAssocItem, AssocItem, AssocItemContainer, Crate, ItemInNs, MacroDef, ModPath, Module,
    ModuleDef, PathResolution, PrefixKind, ScopeDef, Semantics, Type,
};
use itertools::Itertools;
use rustc_hash::FxHashSet;
use syntax::{ast, utils::path_to_string_stripping_turbo_fish, AstNode, SyntaxNode};

use crate::{
    items_locator::{self, AssocItemSearch, DEFAULT_QUERY_SEARCH_LIMIT},
    RootDatabase,
};

use super::item_name;

/// A candidate for import, derived during various IDE activities:
/// * completion with imports on the fly proposals
/// * completion edit resolve requests
/// * assists
/// * etc.
#[derive(Debug)]
pub enum ImportCandidate {
    /// A path, qualified (`std::collections::HashMap`) or not (`HashMap`).
    Path(PathImportCandidate),
    /// A trait associated function (with no self parameter) or an associated constant.
    /// For 'test_mod::TestEnum::test_function', `ty` is the `test_mod::TestEnum` expression type
    /// and `name` is the `test_function`
    TraitAssocItem(TraitImportCandidate),
    /// A trait method with self parameter.
    /// For 'test_enum.test_method()', `ty` is the `test_enum` expression type
    /// and `name` is the `test_method`
    TraitMethod(TraitImportCandidate),
}

/// A trait import needed for a given associated item access.
/// For `some::path::SomeStruct::ASSOC_`, contains the
/// type of `some::path::SomeStruct` and `ASSOC_` as the item name.
#[derive(Debug)]
pub struct TraitImportCandidate {
    /// A type of the item that has the associated item accessed at.
    pub receiver_ty: Type,
    /// The associated item name that the trait to import should contain.
    pub assoc_item_name: NameToImport,
}

/// Path import for a given name, qualified or not.
#[derive(Debug)]
pub struct PathImportCandidate {
    /// Optional qualifier before name.
    pub qualifier: Option<FirstSegmentUnresolved>,
    /// The name the item (struct, trait, enum, etc.) should have.
    pub name: NameToImport,
}

/// A qualifier that has a first segment and it's unresolved.
#[derive(Debug)]
pub struct FirstSegmentUnresolved {
    fist_segment: ast::NameRef,
    full_qualifier: ast::Path,
}

/// A name that will be used during item lookups.
#[derive(Debug, Clone)]
pub enum NameToImport {
    /// Requires items with names that exactly match the given string, case-sensitive.
    Exact(String),
    /// Requires items with names that case-insensitively contain all letters from the string,
    /// in the same order, but not necessary adjacent.
    Fuzzy(String),
}

impl NameToImport {
    pub fn text(&self) -> &str {
        match self {
            NameToImport::Exact(text) => text.as_str(),
            NameToImport::Fuzzy(text) => text.as_str(),
        }
    }
}

/// A struct to find imports in the project, given a certain name (or its part) and the context.
#[derive(Debug)]
pub struct ImportAssets {
    import_candidate: ImportCandidate,
    candidate_node: SyntaxNode,
    module_with_candidate: Module,
}

impl ImportAssets {
    pub fn for_method_call(
        method_call: &ast::MethodCallExpr,
        sema: &Semantics<RootDatabase>,
    ) -> Option<Self> {
        let candidate_node = method_call.syntax().clone();
        Some(Self {
            import_candidate: ImportCandidate::for_method_call(sema, method_call)?,
            module_with_candidate: sema.scope(&candidate_node).module()?,
            candidate_node,
        })
    }

    pub fn for_exact_path(
        fully_qualified_path: &ast::Path,
        sema: &Semantics<RootDatabase>,
    ) -> Option<Self> {
        let candidate_node = fully_qualified_path.syntax().clone();
        if candidate_node.ancestors().find_map(ast::Use::cast).is_some() {
            return None;
        }
        Some(Self {
            import_candidate: ImportCandidate::for_regular_path(sema, fully_qualified_path)?,
            module_with_candidate: sema.scope(&candidate_node).module()?,
            candidate_node,
        })
    }

    pub fn for_fuzzy_path(
        module_with_candidate: Module,
        qualifier: Option<ast::Path>,
        fuzzy_name: String,
        sema: &Semantics<RootDatabase>,
        candidate_node: SyntaxNode,
    ) -> Option<Self> {
        Some(Self {
            import_candidate: ImportCandidate::for_fuzzy_path(qualifier, fuzzy_name, sema)?,
            module_with_candidate,
            candidate_node,
        })
    }

    pub fn for_fuzzy_method_call(
        module_with_method_call: Module,
        receiver_ty: Type,
        fuzzy_method_name: String,
        candidate_node: SyntaxNode,
    ) -> Option<Self> {
        Some(Self {
            import_candidate: ImportCandidate::TraitMethod(TraitImportCandidate {
                receiver_ty,
                assoc_item_name: NameToImport::Fuzzy(fuzzy_method_name),
            }),
            module_with_candidate: module_with_method_call,
            candidate_node,
        })
    }
}

/// An import (not necessary the only one) that corresponds a certain given [`PathImportCandidate`].
/// (the structure is not entirely correct, since there can be situations requiring two imports, see FIXME below for the details)
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct LocatedImport {
    /// The path to use in the `use` statement for a given candidate to be imported.
    pub import_path: ModPath,
    /// An item that will be imported with the import path given.
    pub item_to_import: ItemInNs,
    /// The path import candidate, resolved.
    ///
    /// Not necessary matches the import:
    /// For any associated constant from the trait, we try to access as `some::path::SomeStruct::ASSOC_`
    /// the original item is the associated constant, but the import has to be a trait that
    /// defines this constant.
    pub original_item: ItemInNs,
    /// A path of the original item.
    pub original_path: Option<ModPath>,
}

impl LocatedImport {
    pub fn new(
        import_path: ModPath,
        item_to_import: ItemInNs,
        original_item: ItemInNs,
        original_path: Option<ModPath>,
    ) -> Self {
        Self { import_path, item_to_import, original_item, original_path }
    }
}

impl ImportAssets {
    pub fn import_candidate(&self) -> &ImportCandidate {
        &self.import_candidate
    }

    pub fn search_for_imports(
        &self,
        sema: &Semantics<RootDatabase>,
        prefix_kind: PrefixKind,
    ) -> Vec<LocatedImport> {
        let _p = profile::span("import_assets::search_for_imports");
        self.search_for(sema, Some(prefix_kind))
    }

    /// This may return non-absolute paths if a part of the returned path is already imported into scope.
    pub fn search_for_relative_paths(&self, sema: &Semantics<RootDatabase>) -> Vec<LocatedImport> {
        let _p = profile::span("import_assets::search_for_relative_paths");
        self.search_for(sema, None)
    }

    fn search_for(
        &self,
        sema: &Semantics<RootDatabase>,
        prefixed: Option<PrefixKind>,
    ) -> Vec<LocatedImport> {
        let _p = profile::span("import_assets::search_for");

        let scope_definitions = self.scope_definitions(sema);
        let current_crate = self.module_with_candidate.krate();
        let mod_path = |item| {
            get_mod_path(
                sema.db,
                item_for_path_search(sema.db, item)?,
                &self.module_with_candidate,
                prefixed,
            )
        };

        match &self.import_candidate {
            ImportCandidate::Path(path_candidate) => {
                path_applicable_imports(sema, current_crate, path_candidate, mod_path)
            }
            ImportCandidate::TraitAssocItem(trait_candidate) => {
                trait_applicable_items(sema, current_crate, trait_candidate, true, mod_path)
            }
            ImportCandidate::TraitMethod(trait_candidate) => {
                trait_applicable_items(sema, current_crate, trait_candidate, false, mod_path)
            }
        }
        .into_iter()
        .filter(|import| import.import_path.len() > 1)
        .filter(|import| !scope_definitions.contains(&ScopeDef::from(import.item_to_import)))
        .sorted_by_key(|import| import.import_path.clone())
        .collect()
    }

    fn scope_definitions(&self, sema: &Semantics<RootDatabase>) -> FxHashSet<ScopeDef> {
        let _p = profile::span("import_assets::scope_definitions");
        let mut scope_definitions = FxHashSet::default();
        sema.scope(&self.candidate_node).process_all_names(&mut |_, scope_def| {
            scope_definitions.insert(scope_def);
        });
        scope_definitions
    }
}

fn path_applicable_imports(
    sema: &Semantics<RootDatabase>,
    current_crate: Crate,
    path_candidate: &PathImportCandidate,
    mod_path: impl Fn(ItemInNs) -> Option<ModPath> + Copy,
) -> FxHashSet<LocatedImport> {
    let _p = profile::span("import_assets::path_applicable_imports");

    match &path_candidate.qualifier {
        None => {
            items_locator::items_with_name(
                sema,
                current_crate,
                path_candidate.name.clone(),
                // FIXME: we could look up assoc items by the input and propose those in completion,
                // but that requries more preparation first:
                // * store non-trait assoc items in import_map to fully enable this lookup
                // * ensure that does not degrade the performance (bencmark it)
                // * write more logic to check for corresponding trait presence requirement (we're unable to flyimport multiple item right now)
                // * improve the associated completion item matching and/or scoring to ensure no noisy completions appear
                //
                // see also an ignored test under FIXME comment in the qualify_path.rs module
                AssocItemSearch::Exclude,
                Some(DEFAULT_QUERY_SEARCH_LIMIT),
            )
            .into_iter()
            .filter_map(|item| {
                let mod_path = mod_path(item)?;
                Some(LocatedImport::new(mod_path.clone(), item, item, Some(mod_path)))
            })
            .collect()
        }
        Some(first_segment_unresolved) => {
            let unresolved_qualifier =
                path_to_string_stripping_turbo_fish(&first_segment_unresolved.full_qualifier);
            let unresolved_first_segment = first_segment_unresolved.fist_segment.text();
            items_locator::items_with_name(
                sema,
                current_crate,
                path_candidate.name.clone(),
                AssocItemSearch::Include,
                Some(DEFAULT_QUERY_SEARCH_LIMIT),
            )
            .into_iter()
            .filter_map(|item| {
                import_for_item(
                    sema.db,
                    mod_path,
                    unresolved_first_segment,
                    &unresolved_qualifier,
                    item,
                )
            })
            .collect()
        }
    }
}

fn import_for_item(
    db: &RootDatabase,
    mod_path: impl Fn(ItemInNs) -> Option<ModPath>,
    unresolved_first_segment: &str,
    unresolved_qualifier: &str,
    original_item: ItemInNs,
) -> Option<LocatedImport> {
    let _p = profile::span("import_assets::import_for_item");

    let original_item_candidate = item_for_path_search(db, original_item)?;
    let import_path_candidate = mod_path(original_item_candidate)?;
    let import_path_string = import_path_candidate.to_string();

    let expected_import_end = if item_as_assoc(db, original_item).is_some() {
        unresolved_qualifier.to_string()
    } else {
        format!("{}::{}", unresolved_qualifier, item_name(db, original_item)?)
    };
    if !import_path_string.contains(unresolved_first_segment)
        || !import_path_string.ends_with(&expected_import_end)
    {
        return None;
    }

    let segment_import =
        find_import_for_segment(db, original_item_candidate, &unresolved_first_segment)?;
    let trait_item_to_import = item_as_assoc(db, original_item)
        .and_then(|assoc| assoc.containing_trait(db))
        .map(|trait_| ItemInNs::from(ModuleDef::from(trait_)));
    Some(match (segment_import == original_item_candidate, trait_item_to_import) {
        (true, Some(_)) => {
            // FIXME we should be able to import both the trait and the segment,
            // but it's unclear what to do with overlapping edits (merge imports?)
            // especially in case of lazy completion edit resolutions.
            return None;
        }
        (false, Some(trait_to_import)) => LocatedImport::new(
            mod_path(trait_to_import)?,
            trait_to_import,
            original_item,
            mod_path(original_item),
        ),
        (true, None) => LocatedImport::new(
            import_path_candidate,
            original_item_candidate,
            original_item,
            mod_path(original_item),
        ),
        (false, None) => LocatedImport::new(
            mod_path(segment_import)?,
            segment_import,
            original_item,
            mod_path(original_item),
        ),
    })
}

fn item_for_path_search(db: &RootDatabase, item: ItemInNs) -> Option<ItemInNs> {
    Some(match item {
        ItemInNs::Types(_) | ItemInNs::Values(_) => match item_as_assoc(db, item) {
            Some(assoc_item) => match assoc_item.container(db) {
                AssocItemContainer::Trait(trait_) => ItemInNs::from(ModuleDef::from(trait_)),
                AssocItemContainer::Impl(impl_) => {
                    ItemInNs::from(ModuleDef::from(impl_.target_ty(db).as_adt()?))
                }
            },
            None => item,
        },
        ItemInNs::Macros(_) => item,
    })
}

fn find_import_for_segment(
    db: &RootDatabase,
    original_item: ItemInNs,
    unresolved_first_segment: &str,
) -> Option<ItemInNs> {
    let segment_is_name = item_name(db, original_item)
        .map(|name| name.to_string() == unresolved_first_segment)
        .unwrap_or(false);

    Some(if segment_is_name {
        original_item
    } else {
        let matching_module =
            module_with_segment_name(db, &unresolved_first_segment, original_item)?;
        ItemInNs::from(ModuleDef::from(matching_module))
    })
}

fn module_with_segment_name(
    db: &RootDatabase,
    segment_name: &str,
    candidate: ItemInNs,
) -> Option<Module> {
    let mut current_module = match candidate {
        ItemInNs::Types(module_def_id) => ModuleDef::from(module_def_id).module(db),
        ItemInNs::Values(module_def_id) => ModuleDef::from(module_def_id).module(db),
        ItemInNs::Macros(macro_def_id) => MacroDef::from(macro_def_id).module(db),
    };
    while let Some(module) = current_module {
        if let Some(module_name) = module.name(db) {
            if module_name.to_string() == segment_name {
                return Some(module);
            }
        }
        current_module = module.parent(db);
    }
    None
}

fn trait_applicable_items(
    sema: &Semantics<RootDatabase>,
    current_crate: Crate,
    trait_candidate: &TraitImportCandidate,
    trait_assoc_item: bool,
    mod_path: impl Fn(ItemInNs) -> Option<ModPath>,
) -> FxHashSet<LocatedImport> {
    let _p = profile::span("import_assets::trait_applicable_items");

    let db = sema.db;

    let mut required_assoc_items = FxHashSet::default();
    let trait_candidates = items_locator::items_with_name(
        sema,
        current_crate,
        trait_candidate.assoc_item_name.clone(),
        AssocItemSearch::AssocItemsOnly,
        Some(DEFAULT_QUERY_SEARCH_LIMIT),
    )
    .into_iter()
    .filter_map(|input| item_as_assoc(db, input))
    .filter_map(|assoc| {
        let assoc_item_trait = assoc.containing_trait(db)?;
        required_assoc_items.insert(assoc);
        Some(assoc_item_trait.into())
    })
    .collect();

    let mut located_imports = FxHashSet::default();

    if trait_assoc_item {
        trait_candidate.receiver_ty.iterate_path_candidates(
            db,
            current_crate,
            &trait_candidates,
            None,
            |_, assoc| {
                if required_assoc_items.contains(&assoc) {
                    if let AssocItem::Function(f) = assoc {
                        if f.self_param(db).is_some() {
                            return None;
                        }
                    }

                    let item = ItemInNs::from(ModuleDef::from(assoc.containing_trait(db)?));
                    let original_item = assoc_to_item(assoc);
                    located_imports.insert(LocatedImport::new(
                        mod_path(item)?,
                        item,
                        original_item,
                        mod_path(original_item),
                    ));
                }
                None::<()>
            },
        )
    } else {
        trait_candidate.receiver_ty.iterate_method_candidates(
            db,
            current_crate,
            &trait_candidates,
            None,
            |_, function| {
                let assoc = function.as_assoc_item(db)?;
                if required_assoc_items.contains(&assoc) {
                    let item = ItemInNs::from(ModuleDef::from(assoc.containing_trait(db)?));
                    let original_item = assoc_to_item(assoc);
                    located_imports.insert(LocatedImport::new(
                        mod_path(item)?,
                        item,
                        original_item,
                        mod_path(original_item),
                    ));
                }
                None::<()>
            },
        )
    };

    located_imports
}

fn assoc_to_item(assoc: AssocItem) -> ItemInNs {
    match assoc {
        AssocItem::Function(f) => ItemInNs::from(ModuleDef::from(f)),
        AssocItem::Const(c) => ItemInNs::from(ModuleDef::from(c)),
        AssocItem::TypeAlias(t) => ItemInNs::from(ModuleDef::from(t)),
    }
}

fn get_mod_path(
    db: &RootDatabase,
    item_to_search: ItemInNs,
    module_with_candidate: &Module,
    prefixed: Option<PrefixKind>,
) -> Option<ModPath> {
    if let Some(prefix_kind) = prefixed {
        module_with_candidate.find_use_path_prefixed(db, item_to_search, prefix_kind)
    } else {
        module_with_candidate.find_use_path(db, item_to_search)
    }
}

impl ImportCandidate {
    fn for_method_call(
        sema: &Semantics<RootDatabase>,
        method_call: &ast::MethodCallExpr,
    ) -> Option<Self> {
        match sema.resolve_method_call(method_call) {
            Some(_) => None,
            None => Some(Self::TraitMethod(TraitImportCandidate {
                receiver_ty: sema.type_of_expr(&method_call.receiver()?)?,
                assoc_item_name: NameToImport::Exact(method_call.name_ref()?.to_string()),
            })),
        }
    }

    fn for_regular_path(sema: &Semantics<RootDatabase>, path: &ast::Path) -> Option<Self> {
        if sema.resolve_path(path).is_some() {
            return None;
        }
        path_import_candidate(
            sema,
            path.qualifier(),
            NameToImport::Exact(path.segment()?.name_ref()?.to_string()),
        )
    }

    fn for_fuzzy_path(
        qualifier: Option<ast::Path>,
        fuzzy_name: String,
        sema: &Semantics<RootDatabase>,
    ) -> Option<Self> {
        path_import_candidate(sema, qualifier, NameToImport::Fuzzy(fuzzy_name))
    }
}

fn path_import_candidate(
    sema: &Semantics<RootDatabase>,
    qualifier: Option<ast::Path>,
    name: NameToImport,
) -> Option<ImportCandidate> {
    Some(match qualifier {
        Some(qualifier) => match sema.resolve_path(&qualifier) {
            None => {
                let qualifier_start =
                    qualifier.syntax().descendants().find_map(ast::NameRef::cast)?;
                let qualifier_start_path =
                    qualifier_start.syntax().ancestors().find_map(ast::Path::cast)?;
                if sema.resolve_path(&qualifier_start_path).is_none() {
                    ImportCandidate::Path(PathImportCandidate {
                        qualifier: Some(FirstSegmentUnresolved {
                            fist_segment: qualifier_start,
                            full_qualifier: qualifier,
                        }),
                        name,
                    })
                } else {
                    return None;
                }
            }
            Some(PathResolution::Def(ModuleDef::Adt(assoc_item_path))) => {
                ImportCandidate::TraitAssocItem(TraitImportCandidate {
                    receiver_ty: assoc_item_path.ty(sema.db),
                    assoc_item_name: name,
                })
            }
            Some(_) => return None,
        },
        None => ImportCandidate::Path(PathImportCandidate { qualifier: None, name }),
    })
}

fn item_as_assoc(db: &RootDatabase, item: ItemInNs) -> Option<AssocItem> {
    item.as_module_def_id()
        .and_then(|module_def_id| ModuleDef::from(module_def_id).as_assoc_item(db))
}