use std::fmt::Write;

use ecow::{EcoString, eco_format};
use typst::engine::Sink;
use typst::foundations::{
    AsOutput, Capturer, CastInfo, Func, ParamInfo, Repr, Value, repr,
};
use typst::layout::Length;
use typst::syntax::ast::AstNode;
use typst::syntax::{LinkedNode, Side, Source, SyntaxKind, ast};
use typst::utils::{Numeric, round_with_precision};
use typst_eval::CapturesVisitor;

use crate::analyze::analyze_expr_with_fallback;
use crate::docs::{find_param_docs, find_value_docs};
use crate::utils::summarize_font_family;
use crate::{IdeWorld, analyze_expr, analyze_import, analyze_labels};

/// Describe the item under the cursor.
///
/// Passing a `document` (from a previous compilation) is optional, but enhances
/// the tooltips. Label tooltips, for instance, are only generated when the
/// document is available.
pub fn tooltip(
    world: &dyn IdeWorld,
    output: Option<impl AsOutput>,
    source: &Source,
    cursor: usize,
    side: Side,
) -> Option<Tooltip> {
    let leaf = LinkedNode::new(source.root()).leaf_at(cursor, side)?;
    if leaf.kind().is_trivia() {
        return None;
    }

    named_param_tooltip(world, &leaf)
        .or_else(|| font_tooltip(world, &leaf))
        .or_else(|| output.and_then(|output| label_tooltip(output, &leaf)))
        .or_else(|| import_tooltip(world, &leaf))
        .or_else(|| expr_tooltip(world, &leaf))
        .or_else(|| closure_tooltip(&leaf))
}

/// A hover tooltip.
#[derive(Debug, Clone, PartialEq)]
pub enum Tooltip {
    /// A string of text.
    Text(EcoString),
    /// A string of Typst code.
    Code(EcoString),
}

/// Tooltip for a hovered expression.
fn expr_tooltip(world: &dyn IdeWorld, leaf: &LinkedNode) -> Option<Tooltip> {
    let mut ancestor = leaf;
    while !ancestor.is::<ast::Expr>() {
        ancestor = ancestor.parent()?;
    }

    let expr = ancestor.cast::<ast::Expr>()?;
    // We only analyze embeddable code expressions or math expressions that
    // access variables.
    let analyze = expr.hash()
        || matches!(
            expr,
            ast::Expr::MathIdent(_)
                | ast::Expr::MathFieldAccess(_)
                | ast::Expr::MathCall(_)
        );
    if !analyze {
        return None;
    }

    let values = analyze_expr(world, ancestor);

    if let [(value, _), rest @ ..] = values.as_slice()
        && rest.iter().all(|(v, _)| value == v)
    {
        if let Some(docs) = find_value_docs(world, value) {
            return Some(Tooltip::Text(docs.summary()));
        }

        if let &Value::Length(length) = value
            && let Some(tooltip) = length_tooltip(length)
        {
            return Some(tooltip);
        }
    }

    if expr.is_literal() {
        return None;
    }

    let mut last = None;
    let mut pieces: Vec<EcoString> = vec![];
    let mut iter = values.iter();
    for (value, _) in (&mut iter).take(Sink::MAX_VALUES - 1) {
        if let Some((prev, count)) = &mut last {
            if *prev == value {
                *count += 1;
                continue;
            } else if *count > 1 {
                write!(pieces.last_mut().unwrap(), " (×{count})").unwrap();
            }
        }
        pieces.push(value.repr());
        last = Some((value, 1));
    }

    if let Some((_, count)) = last
        && count > 1
    {
        write!(pieces.last_mut().unwrap(), " (×{count})").unwrap();
    }

    if iter.next().is_some() {
        pieces.push("...".into());
    }

    let tooltip = repr::pretty_comma_list(&pieces, false);
    (!tooltip.is_empty()).then(|| Tooltip::Code(tooltip.into()))
}

/// Tooltips for imports.
fn import_tooltip(world: &dyn IdeWorld, leaf: &LinkedNode) -> Option<Tooltip> {
    if leaf.kind() == SyntaxKind::Star
        && let Some(parent) = leaf.parent()
        && let Some(import) = parent.cast::<ast::ModuleImport>()
        && let Some(node) = parent.find(import.source().span())
        && let Some(value) = analyze_import(world, &node)
        && let Some(scope) = value.scope()
    {
        let names: Vec<_> =
            scope.iter().map(|(name, ..)| eco_format!("`{name}`")).collect();
        let list = repr::separated_list(&names, "and");
        return Some(Tooltip::Text(eco_format!("This star imports {list}")));
    }

    None
}

/// Tooltip for a hovered closure.
fn closure_tooltip(leaf: &LinkedNode) -> Option<Tooltip> {
    // Only show this tooltip when hovering over the equals sign or arrow of
    // the closure. Showing it across the whole subtree is too noisy.
    if !matches!(leaf.kind(), SyntaxKind::Eq | SyntaxKind::Arrow) {
        return None;
    }

    // Find the closure to analyze.
    let parent = leaf.parent()?;
    if parent.kind() != SyntaxKind::Closure {
        return None;
    }

    // Analyze the closure's captures.
    let mut visitor = CapturesVisitor::new(None, Capturer::Function);
    visitor.visit(parent);

    let captures = visitor.finish();
    let mut names: Vec<_> =
        captures.iter().map(|(name, ..)| eco_format!("`{name}`")).collect();
    if names.is_empty() {
        return None;
    }

    names.sort();

    let tooltip = repr::separated_list(&names, "and");
    Some(Tooltip::Text(eco_format!("This closure captures {tooltip}")))
}

/// Tooltip text for a hovered length.
fn length_tooltip(length: Length) -> Option<Tooltip> {
    length.em.is_zero().then(|| {
        Tooltip::Code(eco_format!(
            "{}pt = {}mm = {}cm = {}in",
            round_with_precision(length.abs.to_pt(), 2),
            round_with_precision(length.abs.to_mm(), 2),
            round_with_precision(length.abs.to_cm(), 2),
            round_with_precision(length.abs.to_inches(), 2),
        ))
    })
}

/// Tooltip for a hovered reference or label.
fn label_tooltip(output: impl AsOutput, leaf: &LinkedNode) -> Option<Tooltip> {
    let target = match leaf.kind() {
        SyntaxKind::RefMarker => leaf.text().trim_start_matches('@'),
        SyntaxKind::Label => leaf.text().trim_start_matches('<').trim_end_matches('>'),
        _ => return None,
    };

    for (label, detail) in analyze_labels(output).0 {
        if label.resolve().as_str() == target {
            return Some(Tooltip::Text(detail?));
        }
    }

    None
}

/// Tooltips for components of a named parameter.
fn named_param_tooltip(world: &dyn IdeWorld, leaf: &LinkedNode) -> Option<Tooltip> {
    let (func, named) =
        // Ensure that we are in a named pair in the arguments to a function
        // call or set rule.
        if let Some(parent) = leaf.parent()
        && let Some(named) = parent.cast::<ast::Named>()
        && let Some(grand) = parent.parent()
        && matches!(grand.kind(), SyntaxKind::Args | SyntaxKind::MathArgs)
        && let Some(grand_grand) = grand.parent()
        && let Some(expr) = grand_grand.cast::<ast::Expr>()
        && let Some(callee_span) = match expr {
            ast::Expr::FuncCall(call) => Some(call.callee().span()),
            ast::Expr::MathCall(call) => Some(call.callee().span()),
            ast::Expr::SetRule(set) => Some(set.target().span()),
            _ => None,
        }
        && let Some(callee) = grand_grand.find(callee_span)

        // Find metadata about the function.
        && let Some(value) = analyze_expr_with_fallback(world, &callee)
        && let Ok(func) = value.cast::<Func>()
         { (func, named) }
        else { return None; };

    // Hovering over the parameter name.
    if leaf.index() == 0
        && let Some(ident) = leaf.cast::<ast::Ident>()
        && let Some(param) = func.param(&ident)
        && let Some(docs) = find_param_docs(world, &param)
    {
        return Some(Tooltip::Text(docs.summary()));
    }

    // Hovering over a string parameter value.
    if let Some(string) = leaf.cast::<ast::Str>()
        && let Some(param) = func.param(&named.name())
        && let ParamInfo::Native(param) = param
        && let Some(docs) = find_string_doc(&param.input, &string.get())
    {
        return Some(Tooltip::Text(docs.into()));
    }

    None
}

/// Find documentation for a castable string.
fn find_string_doc(info: &CastInfo, string: &str) -> Option<&'static str> {
    match info {
        CastInfo::Value(Value::Str(s), docs) if s.as_str() == string => Some(docs),
        CastInfo::Union(options) => {
            options.iter().find_map(|option| find_string_doc(option, string))
        }
        _ => None,
    }
}

/// Tooltip for font.
fn font_tooltip(world: &dyn IdeWorld, leaf: &LinkedNode) -> Option<Tooltip> {
    // Ensure that we are on top of a string.
    if let Some(string) = leaf.cast::<ast::Str>()
        && let lower = string.get().to_lowercase()

        // Ensure that we are in the arguments to the text function.
        && let Some(parent) = leaf.parent()
        && let Some(named) = parent.cast::<ast::Named>()
        && named.name().as_str() == "font"

        // Find the font family.
        && let book = world.book()
        && let Some((_, iter)) = book
            .families()
            .find(|&(family, _)| family.to_lowercase().as_str() == lower.as_str())
    {
        let detail = summarize_font_family(iter.filter_map(|id| book.info(id)).collect());
        return Some(Tooltip::Text(detail));
    }

    None
}

#[cfg(test)]
mod tests {
    use std::borrow::Borrow;

    use typst::syntax::Side;
    use typst_layout::PagedDocument;

    use super::{Tooltip, tooltip};
    use crate::tests::{FilePos, TestWorld, WorldLike};

    type Response = Option<Tooltip>;

    trait ResponseExt {
        /// Assert that there is no tooltip.
        fn must_be_none(&self) -> &Self;
        /// Assert that the tooltip equals the given message.
        fn must_be_text(&self, text: &str) -> &Self;
        /// Assert that the tooltip equals the given code.
        fn must_be_code(&self, code: &str) -> &Self;
    }

    impl ResponseExt for Response {
        #[track_caller]
        fn must_be_none(&self) -> &Self {
            assert_eq!(*self, None);
            self
        }

        #[track_caller]
        fn must_be_text(&self, text: &str) -> &Self {
            assert_eq!(*self, Some(Tooltip::Text(text.into())));
            self
        }

        #[track_caller]
        fn must_be_code(&self, code: &str) -> &Self {
            assert_eq!(*self, Some(Tooltip::Code(code.into())));
            self
        }
    }

    #[track_caller]
    fn test(world: impl WorldLike, pos: impl FilePos, side: Side) -> Response {
        let world = world.acquire();
        let world = world.borrow();
        let (source, cursor) = pos.resolve(world);
        let doc = typst::compile::<PagedDocument>(world).output.ok();
        tooltip(world, doc.as_ref(), &source, cursor, side)
    }

    #[test]
    fn test_tooltip() {
        test("#let x = 1 + 2", -1, Side::After).must_be_none();
        test("#let x = 1 + 2", 5, Side::After).must_be_code("3");
        test("#let x = 1 + 2", 6, Side::Before).must_be_code("3");
    }

    /// Literal values don't get a tooltip, just idenfitifers.
    #[test]
    fn test_tooltip_math_literals() {
        let world = "$x'^2 &!= \\u{3C0} \"is\" pi #true$";
        test(world, 0 /*  $  */, Side::After).must_be_none();
        test(world, 1 /*  x  */, Side::After).must_be_none();
        test(world, 2 /*  '  */, Side::After).must_be_none();
        test(world, 3 /*  ^  */, Side::After).must_be_none();
        test(world, 4 /*  2  */, Side::After).must_be_none();
        test(world, 5 /*     */, Side::After).must_be_none();
        test(world, 6 /*  &  */, Side::After).must_be_none();
        test(world, 7 /*  != */, Side::After).must_be_none();
        test(world, 10 /* \\ */, Side::After).must_be_none();
        test(world, 11 /* u  */, Side::After).must_be_none();
        test(world, 12 /* {  */, Side::After).must_be_none();
        test(world, 13 /* 3  */, Side::After).must_be_none();
        test(world, 19 /* \" */, Side::After).must_be_none();
        test(world, 20 /* is */, Side::After).must_be_none();
        test(world, 24 /* pi */, Side::After)
            .must_be_code("symbol(\"π\", (\"alt\", \"ϖ\"))");
        test(world, 27 /* \# */, Side::After).must_be_none();
        test(world, 28 /*true*/, Side::After).must_be_none();
    }

    #[test]
    fn test_tooltip_math_field_access() {
        test("$pi.alt$", 1, Side::After).must_be_code("symbol(\"π\", (\"alt\", \"ϖ\"))");
        test("$pi.alt$", 3, Side::After).must_be_code("symbol(\"ϖ\")");
        test("$pi.alt$", 4, Side::After).must_be_code("symbol(\"ϖ\")");
    }

    #[test]
    fn test_tooltip_set() {
        let box_desc = "An inline-level container that sizes content.";
        let fill_desc = "The box's background color.";
        let red = "rgb(\"#ff4136\")";
        test("#set box(fill: red,)", 0 /*#*/, Side::After).must_be_none();
        test("#set box(fill: red,)", 1 /*s*/, Side::After).must_be_none();
        test("#set box(fill: red,)", 5 /*b*/, Side::After).must_be_text(box_desc);
        test("#set box(fill: red,)", 8 /*(*/, Side::After).must_be_none();
        test("#set box(fill: red,)", 9 /*f*/, Side::After).must_be_text(fill_desc);
        test("#set box(fill: red,)", 13 /*:*/, Side::After).must_be_none();
        test("#set box(fill: red,)", 15 /*r*/, Side::After).must_be_code(red);
        test("#set box(fill: red,)", 18 /*,*/, Side::After).must_be_none();
        test("#set box(fill: red,)", 19 /*)*/, Side::After).must_be_none();
    }

    #[test]
    fn test_tooltip_function_call() {
        let box_desc = "An inline-level container that sizes content.";
        // Function value
        test("#box", 0 /*#*/, Side::After).must_be_none();
        test("#box", 1 /*b*/, Side::After).must_be_text(box_desc);
        test("#(box)", 0 /*#*/, Side::After).must_be_none();
        test("#(box)", 1 /*(*/, Side::After).must_be_text(box_desc);
        test("#(box)", 2 /*b*/, Side::After).must_be_text(box_desc);
        test("#(box)", 5 /*)*/, Side::After).must_be_text(box_desc);
        // Basic call
        test("#box()", 1 /*b*/, Side::After).must_be_text(box_desc);
        test("#box()", 4 /*(*/, Side::After).must_be_code("box()");
        test("#box()", 5 /*)*/, Side::After).must_be_code("box()");
        // Field access call
        test("#std.box()", 1 /*s*/, Side::After).must_be_code("<module global>");
        test("#std.box()", 4 /*.*/, Side::After).must_be_text(box_desc);
        test("#std.box()", 5 /*b*/, Side::After).must_be_text(box_desc);
        test("#std.box()", 8 /*(*/, Side::After).must_be_code("box()");
        // Positional args and trailing comma
        test("#box([],)", 4 /*(*/, Side::After).must_be_code("box(body: [])");
        test("#box([],)", 5 /*[*/, Side::After).must_be_code("[]");
        test("#box([],)", 6 /*]*/, Side::After).must_be_code("[]");
        test("#box([],)", 7 /*,*/, Side::After).must_be_code("box(body: [])");
        test("#box([],)", 8 /*)*/, Side::After).must_be_code("box(body: [])");
        // Content args
        test("#box[]", 4 /*[*/, Side::After).must_be_code("[]");
        test("#box[]", 5 /*]*/, Side::After).must_be_code("[]");
        // Named args
        let fill_desc = "The box's background color.";
        let red_box = "box(fill: rgb(\"#ff4136\"))";
        test("#box(fill:red,)", 5 /*f*/, Side::After).must_be_text(fill_desc);
        test("#box(fill:red,)", 9 /*:*/, Side::After).must_be_code(red_box);
        test("#box(fill:red,)", 10 /*r*/, Side::After).must_be_code("rgb(\"#ff4136\")");
        test("#box(fill:red,)", 13 /*,*/, Side::After).must_be_code(red_box);
        // Spread args
        test("#box(..none,)", 5 /*.*/, Side::After).must_be_code("box()");
        test("#box(..none,)", 7 /*(*/, Side::After).must_be_none();
        test("#box(..none,)", 11 /*,*/, Side::After).must_be_code("box()");
        test("#box(..([],))", 5 /*.*/, Side::After).must_be_code("box(body: [])");
        test("#box(..([],))", 7 /*(*/, Side::After).must_be_code("([],)");
    }

    #[test]
    fn test_tooltip_math_function_call() {
        // Content plus parens
        test("$f(x)$", 1 /*f*/, Side::After).must_be_none();
        test("$f(x)$", 2 /*(*/, Side::After).must_be_none();
        test("$f(x)$", 3 /*x*/, Side::After).must_be_none();
        test("$sin()$", 1 /*s*/, Side::After)
            .must_be_code("op(text: [sin], limits: false)");
        // Actual function call + empty arg + trailing comma
        let vec_z = "vec(children: ([ℤ], []))";
        test("$vec(ZZ, ,)$", 1 /*v*/, Side::After).must_be_text("A column vector.");
        test("$vec(ZZ, ,)$", 4 /*(*/, Side::After).must_be_code(vec_z);
        test("$vec(ZZ, ,)$", 5 /*Z*/, Side::After).must_be_code("symbol(\"ℤ\")");
        test("$vec(ZZ, ,)$", 7 /*,*/, Side::After).must_be_code(vec_z);
        test("$vec(ZZ, ,)$", 8 /* */, Side::After).must_be_none();
        test("$vec(ZZ, ,)$", 9 /*,*/, Side::After).must_be_code(vec_z);
        test("$vec(ZZ, ,)$", 10 /*)*/, Side::After).must_be_code(vec_z);
        // Named args
        let vec_gap = "vec(gap: 0% + 1em, children: ())";
        test("$vec(gap:#1em)$", 5 /*g*/, Side::After)
            .must_be_text("The gap between elements.");
        test("$vec(gap:#1em)$", 8 /*:*/, Side::After).must_be_code(vec_gap);
        test("$vec(gap:#1em)$", 10 /*1*/, Side::After).must_be_none();
        // 2d args and spread args
        let mat = "mat(rows: (([1],), ([2],)))";
        test("$mat(1; ..#([2],))$", 1 /*m*/, Side::After).must_be_text("A matrix.");
        test("$mat(1; ..#([2],))$", 5 /*1*/, Side::After).must_be_none();
        test("$mat(1; ..#([2],))$", 6 /*;*/, Side::After).must_be_code(mat);
        test("$mat(1; ..#([2],))$", 8 /*.*/, Side::After).must_be_code(mat);
        test("$mat(1; ..#([2],))$", 10 /*#*/, Side::After).must_be_code(mat);
        test("$mat(1; ..#([2],))$", 11 /*(*/, Side::After).must_be_code("([2],)");
        // Symbol function and named arg
        test("$hat(i,size:#1em)$", 1, Side::After).must_be_code("symbol(\"^\")");
        test("$hat(i,size:#1em)$", 7, Side::After)
            .must_be_text("The size of the accent, relative to the width of the base.");
        // Field access call
        let box_desc = "An inline-level container that sizes content.";
        test("$std.box()$", 1 /*s*/, Side::After).must_be_code("<module global>");
        test("$std.box()$", 4 /*.*/, Side::After).must_be_text(box_desc);
        test("$std.box()$", 5 /*b*/, Side::After).must_be_text(box_desc);
        test("$std.box()$", 8 /*(*/, Side::After).must_be_code("box()");
    }

    #[test]
    fn test_tooltip_empty_contextual() {
        test("#{context}", -1, Side::Before).must_be_code("context()");
    }

    #[test]
    fn test_tooltip_closure() {
        test("#let f(x) = x + y", 11, Side::Before)
            .must_be_text("This closure captures `y`");
        // Same tooltip if `y` is defined first.
        test("#let y = 10; #let f(x) = x + y", 24, Side::Before)
            .must_be_text("This closure captures `y`");
        // Names are sorted.
        test("#let f(x) = x + y + z + a", 11, Side::Before)
            .must_be_text("This closure captures `a`, `y`, and `z`");
        // Names are de-duplicated.
        test("#let f(x) = x + y + z + y", 11, Side::Before)
            .must_be_text("This closure captures `y` and `z`");
        // With arrow syntax.
        test("#let f = (x) => x + y", 15, Side::Before)
            .must_be_text("This closure captures `y`");
        // No recursion with arrow syntax.
        test("#let f = (x) => x + y + f", 13, Side::After)
            .must_be_text("This closure captures `f` and `y`");
    }

    #[test]
    fn test_tooltip_import() {
        let world = TestWorld::new("#import \"other.typ\": a, b")
            .with_source("other.typ", "#let (a, b, c) = (1, 2, 3)");
        test(&world, -5, Side::After).must_be_code("1");
    }

    #[test]
    fn test_tooltip_star_import() {
        let world = TestWorld::new("#import \"other.typ\": *")
            .with_source("other.typ", "#let (a, b, c) = (1, 2, 3)");
        test(&world, -2, Side::Before).must_be_none();
        test(&world, -2, Side::After).must_be_text("This star imports `a`, `b`, and `c`");
    }

    #[test]
    fn test_tooltip_field_call() {
        let world = TestWorld::new("#import \"other.typ\"\n#other.f()")
            .with_source("other.typ", "#let f = (x) => 1");
        test(&world, -4, Side::After).must_be_code("(..) => ..");
    }

    #[test]
    fn test_tooltip_reference() {
        test("#figure(caption: [Hi])[]<f> @f", -1, Side::Before).must_be_text("Hi");
    }

    #[test]
    fn test_tooltip_user_function() {
        let world = TestWorld::new("#import \"lib.typ\"\n#lib.foo(none, tree: 2)")
            .with_source("lib.typ", crate::tests::EXAMPLE_CLOSURE);
        // Function itself.
        test(&world, -17, Side::After).must_be_text("A useful function.");
        // Named parameter.
        test(&world, -7, Side::After).must_be_text("Tree with three slashes.");
    }

    #[test]
    fn test_tooltip_user_function_in_math() {
        let world = TestWorld::new("#import \"lib.typ\"\n$lib.foo(none, tree: 2)$")
            .with_source("lib.typ", crate::tests::EXAMPLE_CLOSURE);
        // Function itself.
        test(&world, -18, Side::After).must_be_text("A useful function.");
        // Named parameter.
        test(&world, -8, Side::After).must_be_text("Tree with three slashes.");
    }
}
