//! See `CompletionItem` structure.

use std::{fmt, mem};

use hir::Mutability;
use ide_db::{
    documentation::Documentation, imports::import_assets::LocatedImport, RootDatabase, SnippetCap,
    SymbolKind,
};
use itertools::Itertools;
use smallvec::SmallVec;
use stdx::{impl_from, never};
use syntax::{format_smolstr, SmolStr, TextRange, TextSize};
use text_edit::TextEdit;

use crate::{
    context::{CompletionContext, PathCompletionCtx},
    render::{render_path_resolution, RenderContext},
};

/// `CompletionItem` describes a single completion entity which expands to 1 or more entries in the
/// editor pop-up. It is basically a POD with various properties. To construct a
/// [`CompletionItem`], use [`Builder::new`] method and the [`Builder`] struct.
#[derive(Clone)]
#[non_exhaustive]
pub struct CompletionItem {
    /// Label in the completion pop up which identifies completion.
    pub label: SmolStr,
    /// Additional label details in the completion pop up that are
    /// displayed and aligned on the right side after the label.
    pub label_detail: Option<SmolStr>,

    /// Range of identifier that is being completed.
    ///
    /// It should be used primarily for UI, but we also use this to convert
    /// generic TextEdit into LSP's completion edit (see conv.rs).
    ///
    /// `source_range` must contain the completion offset. `text_edit` should
    /// start with what `source_range` points to, or VSCode will filter out the
    /// completion silently.
    pub source_range: TextRange,
    /// What happens when user selects this item.
    ///
    /// Typically, replaces `source_range` with new identifier.
    pub text_edit: TextEdit,
    pub is_snippet: bool,

    /// What item (struct, function, etc) are we completing.
    pub kind: CompletionItemKind,

    /// Lookup is used to check if completion item indeed can complete current
    /// ident.
    ///
    /// That is, in `foo.bar$0` lookup of `abracadabra` will be accepted (it
    /// contains `bar` sub sequence), and `quux` will rejected.
    pub lookup: SmolStr,

    /// Additional info to show in the UI pop up.
    pub detail: Option<String>,
    pub documentation: Option<Documentation>,

    /// Whether this item is marked as deprecated
    pub deprecated: bool,

    /// If completing a function call, ask the editor to show parameter popup
    /// after completion.
    pub trigger_call_info: bool,

    /// We use this to sort completion. Relevance records facts like "do the
    /// types align precisely?". We can't sort by relevances directly, they are
    /// only partially ordered.
    ///
    /// Note that Relevance ignores fuzzy match score. We compute Relevance for
    /// all possible items, and then separately build an ordered completion list
    /// based on relevance and fuzzy matching with the already typed identifier.
    pub relevance: CompletionRelevance,

    /// Indicates that a reference or mutable reference to this variable is a
    /// possible match.
    // FIXME: We shouldn't expose Mutability here (that is HIR types at all), its fine for now though
    // until we have more splitting completions in which case we should think about
    // generalizing this. See https://github.com/rust-lang/rust-analyzer/issues/12571
    pub ref_match: Option<(Mutability, TextSize)>,

    /// The import data to add to completion's edits.
    /// (ImportPath, LastSegment)
    pub import_to_add: SmallVec<[(String, String); 1]>,
}

// We use custom debug for CompletionItem to make snapshot tests more readable.
impl fmt::Debug for CompletionItem {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut s = f.debug_struct("CompletionItem");
        s.field("label", &self.label).field("source_range", &self.source_range);
        if self.text_edit.len() == 1 {
            let atom = self.text_edit.iter().next().unwrap();
            s.field("delete", &atom.delete);
            s.field("insert", &atom.insert);
        } else {
            s.field("text_edit", &self.text_edit);
        }
        s.field("kind", &self.kind);
        if self.lookup() != self.label {
            s.field("lookup", &self.lookup());
        }
        if let Some(detail) = &self.detail {
            s.field("detail", &detail);
        }
        if let Some(documentation) = &self.documentation {
            s.field("documentation", &documentation);
        }
        if self.deprecated {
            s.field("deprecated", &true);
        }

        if self.relevance != CompletionRelevance::default() {
            s.field("relevance", &self.relevance);
        }

        if let Some((mutability, offset)) = &self.ref_match {
            s.field("ref_match", &format!("&{}@{offset:?}", mutability.as_keyword_for_ref()));
        }
        if self.trigger_call_info {
            s.field("trigger_call_info", &true);
        }
        s.finish()
    }
}

#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
pub struct CompletionRelevance {
    /// This is set in cases like these:
    ///
    /// ```
    /// fn f(spam: String) {}
    /// fn main {
    ///     let spam = 92;
    ///     f($0) // name of local matches the name of param
    /// }
    /// ```
    pub exact_name_match: bool,
    /// See CompletionRelevanceTypeMatch doc comments for cases where this is set.
    pub type_match: Option<CompletionRelevanceTypeMatch>,
    /// This is set in cases like these:
    ///
    /// ```
    /// fn foo(a: u32) {
    ///     let b = 0;
    ///     $0 // `a` and `b` are local
    /// }
    /// ```
    pub is_local: bool,
    /// This is set when trait items are completed in an impl of that trait.
    pub is_item_from_trait: bool,
    /// This is set for when trait items are from traits with `#[doc(notable_trait)]`
    pub is_item_from_notable_trait: bool,
    /// This is set when an import is suggested whose name is already imported.
    pub is_name_already_imported: bool,
    /// This is set for completions that will insert a `use` item.
    pub requires_import: bool,
    /// Set for method completions of the `core::ops` and `core::cmp` family.
    pub is_op_method: bool,
    /// Set for item completions that are private but in the workspace.
    pub is_private_editable: bool,
    /// Set for postfix snippet item completions
    pub postfix_match: Option<CompletionRelevancePostfixMatch>,
    /// This is set for type inference results
    pub is_definite: bool,
    /// This is set for items that are function (associated or method)
    pub function: Option<CompletionRelevanceFn>,
}

#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub enum CompletionRelevanceTypeMatch {
    /// This is set in cases like these:
    ///
    /// ```
    /// enum Option<T> { Some(T), None }
    /// fn f(a: Option<u32>) {}
    /// fn main {
    ///     f(Option::N$0) // type `Option<T>` could unify with `Option<u32>`
    /// }
    /// ```
    CouldUnify,
    /// This is set in cases like these:
    ///
    /// ```
    /// fn f(spam: String) {}
    /// fn main {
    ///     let foo = String::new();
    ///     f($0) // type of local matches the type of param
    /// }
    /// ```
    Exact,
}

#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub enum CompletionRelevancePostfixMatch {
    /// Set in cases when item is postfix, but not exact
    NonExact,
    /// This is set in cases like these:
    ///
    /// ```
    /// (a > b).not$0
    /// ```
    ///
    /// Basically, we want to guarantee that postfix snippets always takes
    /// precedence over everything else.
    Exact,
}

#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub struct CompletionRelevanceFn {
    pub has_params: bool,
    pub has_self_param: bool,
    pub return_type: CompletionRelevanceReturnType,
}

#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub enum CompletionRelevanceReturnType {
    Other,
    /// Returns the Self type of the impl/trait
    DirectConstructor,
    /// Returns something that indirectly constructs the `Self` type of the impl/trait e.g. `Result<Self, ()>`, `Option<Self>`
    Constructor,
    /// Returns a possible builder for the type
    Builder,
}

impl CompletionRelevance {
    /// Provides a relevance score. Higher values are more relevant.
    ///
    /// The absolute value of the relevance score is not meaningful, for
    /// example a value of 0 doesn't mean "not relevant", rather
    /// it means "least relevant". The score value should only be used
    /// for relative ordering.
    ///
    /// See is_relevant if you need to make some judgement about score
    /// in an absolute sense.
    pub fn score(self) -> u32 {
        let mut score = 0;
        let CompletionRelevance {
            exact_name_match,
            type_match,
            is_local,
            is_item_from_trait,
            is_name_already_imported,
            requires_import,
            is_op_method,
            is_private_editable,
            postfix_match,
            is_definite,
            is_item_from_notable_trait,
            function,
        } = self;

        // lower rank private things
        if !is_private_editable {
            score += 1;
        }
        // lower rank trait op methods
        if !is_op_method {
            score += 10;
        }
        // lower rank for conflicting import names
        if !is_name_already_imported {
            score += 1;
        }
        // lower rank for items that don't need an import
        if !requires_import {
            score += 1;
        }
        if exact_name_match {
            score += 10;
        }
        score += match postfix_match {
            Some(CompletionRelevancePostfixMatch::Exact) => 100,
            Some(CompletionRelevancePostfixMatch::NonExact) => 0,
            None => 3,
        };
        score += match type_match {
            Some(CompletionRelevanceTypeMatch::Exact) => 8,
            Some(CompletionRelevanceTypeMatch::CouldUnify) => 3,
            None => 0,
        };
        // slightly prefer locals
        if is_local {
            score += 1;
        }
        if is_item_from_trait {
            score += 1;
        }
        if is_item_from_notable_trait {
            score += 1;
        }
        if is_definite {
            score += 10;
        }

        score += function
            .map(|asf| {
                let mut fn_score = match asf.return_type {
                    CompletionRelevanceReturnType::DirectConstructor => 15,
                    CompletionRelevanceReturnType::Builder => 10,
                    CompletionRelevanceReturnType::Constructor => 5,
                    CompletionRelevanceReturnType::Other => 0,
                };

                // When a fn is bumped due to return type:
                // Bump Constructor or Builder methods with no arguments,
                // over them than with self arguments
                if fn_score > 0 {
                    if !asf.has_params {
                        // bump associated functions
                        fn_score += 1;
                    } else if asf.has_self_param {
                        // downgrade methods (below Constructor)
                        fn_score = 1;
                    }
                }

                fn_score
            })
            .unwrap_or_default();

        score
    }

    /// Returns true when the score for this threshold is above
    /// some threshold such that we think it is especially likely
    /// to be relevant.
    pub fn is_relevant(&self) -> bool {
        self.score() > 0
    }
}

/// The type of the completion item.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum CompletionItemKind {
    SymbolKind(SymbolKind),
    Binding,
    BuiltinType,
    InferredType,
    Keyword,
    Snippet,
    UnresolvedReference,
    Expression,
}

impl_from!(SymbolKind for CompletionItemKind);

impl CompletionItemKind {
    #[cfg(test)]
    pub(crate) fn tag(self) -> &'static str {
        match self {
            CompletionItemKind::SymbolKind(kind) => match kind {
                SymbolKind::Attribute => "at",
                SymbolKind::BuiltinAttr => "ba",
                SymbolKind::Const => "ct",
                SymbolKind::ConstParam => "cp",
                SymbolKind::Derive => "de",
                SymbolKind::DeriveHelper => "dh",
                SymbolKind::Enum => "en",
                SymbolKind::Field => "fd",
                SymbolKind::Function => "fn",
                SymbolKind::Impl => "im",
                SymbolKind::Label => "lb",
                SymbolKind::LifetimeParam => "lt",
                SymbolKind::Local => "lc",
                SymbolKind::Macro => "ma",
                SymbolKind::Method => "me",
                SymbolKind::ProcMacro => "pm",
                SymbolKind::Module => "md",
                SymbolKind::SelfParam => "sp",
                SymbolKind::SelfType => "sy",
                SymbolKind::Static => "sc",
                SymbolKind::Struct => "st",
                SymbolKind::ToolModule => "tm",
                SymbolKind::Trait => "tt",
                SymbolKind::TraitAlias => "tr",
                SymbolKind::TypeAlias => "ta",
                SymbolKind::TypeParam => "tp",
                SymbolKind::Union => "un",
                SymbolKind::ValueParam => "vp",
                SymbolKind::Variant => "ev",
            },
            CompletionItemKind::Binding => "bn",
            CompletionItemKind::BuiltinType => "bt",
            CompletionItemKind::InferredType => "it",
            CompletionItemKind::Keyword => "kw",
            CompletionItemKind::Snippet => "sn",
            CompletionItemKind::UnresolvedReference => "??",
            CompletionItemKind::Expression => "ex",
        }
    }
}

impl CompletionItem {
    pub(crate) fn new(
        kind: impl Into<CompletionItemKind>,
        source_range: TextRange,
        label: impl Into<SmolStr>,
    ) -> Builder {
        let label = label.into();
        Builder {
            source_range,
            label,
            insert_text: None,
            is_snippet: false,
            trait_name: None,
            detail: None,
            documentation: None,
            lookup: None,
            kind: kind.into(),
            text_edit: None,
            deprecated: false,
            trigger_call_info: false,
            relevance: CompletionRelevance::default(),
            ref_match: None,
            imports_to_add: Default::default(),
            doc_aliases: vec![],
        }
    }

    /// What string is used for filtering.
    pub fn lookup(&self) -> &str {
        self.lookup.as_str()
    }

    pub fn ref_match(&self) -> Option<(String, text_edit::Indel, CompletionRelevance)> {
        // Relevance of the ref match should be the same as the original
        // match, but with exact type match set because self.ref_match
        // is only set if there is an exact type match.
        let mut relevance = self.relevance;
        relevance.type_match = Some(CompletionRelevanceTypeMatch::Exact);

        self.ref_match.map(|(mutability, offset)| {
            (
                format!("&{}{}", mutability.as_keyword_for_ref(), self.label),
                text_edit::Indel::insert(offset, format!("&{}", mutability.as_keyword_for_ref())),
                relevance,
            )
        })
    }
}

/// A helper to make `CompletionItem`s.
#[must_use]
#[derive(Clone)]
pub(crate) struct Builder {
    source_range: TextRange,
    imports_to_add: SmallVec<[LocatedImport; 1]>,
    trait_name: Option<SmolStr>,
    doc_aliases: Vec<SmolStr>,
    label: SmolStr,
    insert_text: Option<String>,
    is_snippet: bool,
    detail: Option<String>,
    documentation: Option<Documentation>,
    lookup: Option<SmolStr>,
    kind: CompletionItemKind,
    text_edit: Option<TextEdit>,
    deprecated: bool,
    trigger_call_info: bool,
    relevance: CompletionRelevance,
    ref_match: Option<(Mutability, TextSize)>,
}

impl Builder {
    pub(crate) fn from_resolution(
        ctx: &CompletionContext<'_>,
        path_ctx: &PathCompletionCtx,
        local_name: hir::Name,
        resolution: hir::ScopeDef,
    ) -> Self {
        let doc_aliases = ctx.doc_aliases_in_scope(resolution);
        render_path_resolution(
            RenderContext::new(ctx).doc_aliases(doc_aliases),
            path_ctx,
            local_name,
            resolution,
        )
    }

    pub(crate) fn build(self, db: &RootDatabase) -> CompletionItem {
        let _p = tracing::span!(tracing::Level::INFO, "item::Builder::build").entered();

        let label = self.label;
        let mut label_detail = None;
        let mut lookup = self.lookup.unwrap_or_else(|| label.clone());
        let insert_text = self.insert_text.unwrap_or_else(|| label.to_string());

        if !self.doc_aliases.is_empty() {
            let doc_aliases = self.doc_aliases.iter().join(", ");
            label_detail.replace(format_smolstr!(" (alias {doc_aliases})"));
            let lookup_doc_aliases = self
                .doc_aliases
                .iter()
                // Don't include aliases in `lookup` that aren't valid identifiers as including
                // them results in weird completion filtering behavior e.g. `Partial>` matching
                // `PartialOrd` because it has an alias of ">".
                .filter(|alias| {
                    let mut chars = alias.chars();
                    chars.next().is_some_and(char::is_alphabetic)
                        && chars.all(|c| c.is_alphanumeric() || c == '_')
                })
                // Deliberately concatenated without separators as adding separators e.g.
                // `alias1, alias2` results in LSP clients continuing to display the completion even
                // after typing a comma or space.
                .join("");
            if !lookup_doc_aliases.is_empty() {
                lookup = format_smolstr!("{lookup}{lookup_doc_aliases}");
            }
        }
        if let [import_edit] = &*self.imports_to_add {
            // snippets can have multiple imports, but normal completions only have up to one
            label_detail.replace(format_smolstr!(
                "{} (use {})",
                label_detail.as_deref().unwrap_or_default(),
                import_edit.import_path.display(db)
            ));
        } else if let Some(trait_name) = self.trait_name {
            label_detail.replace(format_smolstr!(
                "{} (as {trait_name})",
                label_detail.as_deref().unwrap_or_default(),
            ));
        }

        let text_edit = match self.text_edit {
            Some(it) => it,
            None => TextEdit::replace(self.source_range, insert_text),
        };

        let import_to_add = self
            .imports_to_add
            .into_iter()
            .filter_map(|import| {
                Some((
                    import.import_path.display(db).to_string(),
                    import.import_path.segments().last()?.display(db).to_string(),
                ))
            })
            .collect();

        CompletionItem {
            source_range: self.source_range,
            label,
            label_detail,
            text_edit,
            is_snippet: self.is_snippet,
            detail: self.detail,
            documentation: self.documentation,
            lookup,
            kind: self.kind,
            deprecated: self.deprecated,
            trigger_call_info: self.trigger_call_info,
            relevance: self.relevance,
            ref_match: self.ref_match,
            import_to_add,
        }
    }
    pub(crate) fn lookup_by(&mut self, lookup: impl Into<SmolStr>) -> &mut Builder {
        self.lookup = Some(lookup.into());
        self
    }
    pub(crate) fn label(&mut self, label: impl Into<SmolStr>) -> &mut Builder {
        self.label = label.into();
        self
    }
    pub(crate) fn trait_name(&mut self, trait_name: SmolStr) -> &mut Builder {
        self.trait_name = Some(trait_name);
        self
    }
    pub(crate) fn doc_aliases(&mut self, doc_aliases: Vec<SmolStr>) -> &mut Builder {
        self.doc_aliases = doc_aliases;
        self
    }
    pub(crate) fn insert_text(&mut self, insert_text: impl Into<String>) -> &mut Builder {
        self.insert_text = Some(insert_text.into());
        self
    }
    pub(crate) fn insert_snippet(
        &mut self,
        cap: SnippetCap,
        snippet: impl Into<String>,
    ) -> &mut Builder {
        let _ = cap;
        self.is_snippet = true;
        self.insert_text(snippet)
    }
    pub(crate) fn text_edit(&mut self, edit: TextEdit) -> &mut Builder {
        self.text_edit = Some(edit);
        self
    }
    pub(crate) fn snippet_edit(&mut self, _cap: SnippetCap, edit: TextEdit) -> &mut Builder {
        self.is_snippet = true;
        self.text_edit(edit)
    }
    pub(crate) fn detail(&mut self, detail: impl Into<String>) -> &mut Builder {
        self.set_detail(Some(detail))
    }
    pub(crate) fn set_detail(&mut self, detail: Option<impl Into<String>>) -> &mut Builder {
        self.detail = detail.map(Into::into);
        if let Some(detail) = &self.detail {
            if never!(detail.contains('\n'), "multiline detail:\n{}", detail) {
                self.detail = Some(detail.split('\n').next().unwrap().to_owned());
            }
        }
        self
    }
    #[allow(unused)]
    pub(crate) fn documentation(&mut self, docs: Documentation) -> &mut Builder {
        self.set_documentation(Some(docs))
    }
    pub(crate) fn set_documentation(&mut self, docs: Option<Documentation>) -> &mut Builder {
        self.documentation = docs.map(Into::into);
        self
    }
    pub(crate) fn set_deprecated(&mut self, deprecated: bool) -> &mut Builder {
        self.deprecated = deprecated;
        self
    }
    pub(crate) fn set_relevance(&mut self, relevance: CompletionRelevance) -> &mut Builder {
        self.relevance = relevance;
        self
    }
    pub(crate) fn with_relevance(
        &mut self,
        relevance: impl FnOnce(CompletionRelevance) -> CompletionRelevance,
    ) -> &mut Builder {
        self.relevance = relevance(mem::take(&mut self.relevance));
        self
    }
    pub(crate) fn trigger_call_info(&mut self) -> &mut Builder {
        self.trigger_call_info = true;
        self
    }
    pub(crate) fn add_import(&mut self, import_to_add: LocatedImport) -> &mut Builder {
        self.imports_to_add.push(import_to_add);
        self
    }
    pub(crate) fn ref_match(&mut self, mutability: Mutability, offset: TextSize) -> &mut Builder {
        self.ref_match = Some((mutability, offset));
        self
    }
}

#[cfg(test)]
mod tests {
    use itertools::Itertools;
    use test_utils::assert_eq_text;

    use super::{
        CompletionRelevance, CompletionRelevancePostfixMatch, CompletionRelevanceTypeMatch,
    };

    /// Check that these are CompletionRelevance are sorted in ascending order
    /// by their relevance score.
    ///
    /// We want to avoid making assertions about the absolute score of any
    /// item, but we do want to assert whether each is >, <, or == to the
    /// others.
    ///
    /// If provided vec![vec![a], vec![b, c], vec![d]], then this will assert:
    ///     a.score < b.score == c.score < d.score
    fn check_relevance_score_ordered(expected_relevance_order: Vec<Vec<CompletionRelevance>>) {
        let expected = format!("{:#?}", &expected_relevance_order);

        let actual_relevance_order = expected_relevance_order
            .into_iter()
            .flatten()
            .map(|r| (r.score(), r))
            .sorted_by_key(|(score, _r)| *score)
            .fold(
                (u32::MIN, vec![vec![]]),
                |(mut currently_collecting_score, mut out), (score, r)| {
                    if currently_collecting_score == score {
                        out.last_mut().unwrap().push(r);
                    } else {
                        currently_collecting_score = score;
                        out.push(vec![r]);
                    }
                    (currently_collecting_score, out)
                },
            )
            .1;

        let actual = format!("{:#?}", &actual_relevance_order);

        assert_eq_text!(&expected, &actual);
    }

    #[test]
    fn relevance_score() {
        use CompletionRelevance as Cr;
        let default = Cr::default();
        // This test asserts that the relevance score for these items is ascending, and
        // that any items in the same vec have the same score.
        let expected_relevance_order = vec![
            vec![],
            vec![Cr { is_op_method: true, is_private_editable: true, ..default }],
            vec![Cr { is_op_method: true, ..default }],
            vec![Cr { postfix_match: Some(CompletionRelevancePostfixMatch::NonExact), ..default }],
            vec![Cr { is_private_editable: true, ..default }],
            vec![default],
            vec![Cr { is_local: true, ..default }],
            vec![Cr { type_match: Some(CompletionRelevanceTypeMatch::CouldUnify), ..default }],
            vec![Cr { type_match: Some(CompletionRelevanceTypeMatch::Exact), ..default }],
            vec![Cr { exact_name_match: true, ..default }],
            vec![Cr { exact_name_match: true, is_local: true, ..default }],
            vec![Cr {
                exact_name_match: true,
                type_match: Some(CompletionRelevanceTypeMatch::Exact),
                ..default
            }],
            vec![Cr {
                exact_name_match: true,
                type_match: Some(CompletionRelevanceTypeMatch::Exact),
                is_local: true,
                ..default
            }],
            vec![Cr { postfix_match: Some(CompletionRelevancePostfixMatch::Exact), ..default }],
        ];

        check_relevance_score_ordered(expected_relevance_order);
    }
}