//! This module analyzes crates to find call sites that can serve as examples in the documentation.

use crate::clean;
use crate::config;
use crate::formats;
use crate::formats::renderer::FormatRenderer;
use crate::html::render::Context;

use rustc_data_structures::fx::FxHashMap;
use rustc_hir::{
    self as hir,
    intravisit::{self, Visitor},
    HirId,
};
use rustc_interface::interface;
use rustc_macros::{Decodable, Encodable};
use rustc_middle::hir::map::Map;
use rustc_middle::ty::{self, TyCtxt};
use rustc_serialize::{
    opaque::{Decoder, FileEncoder},
    Decodable, Encodable,
};
use rustc_session::getopts;
use rustc_span::{
    def_id::{CrateNum, DefPathHash, LOCAL_CRATE},
    edition::Edition,
    BytePos, FileName, SourceFile,
};

use std::fs;
use std::path::PathBuf;

#[derive(Debug, Clone)]
crate struct ScrapeExamplesOptions {
    output_path: PathBuf,
    target_crates: Vec<String>,
}

impl ScrapeExamplesOptions {
    crate fn new(
        matches: &getopts::Matches,
        diag: &rustc_errors::Handler,
    ) -> Result<Option<Self>, i32> {
        let output_path = matches.opt_str("scrape-examples-output-path");
        let target_crates = matches.opt_strs("scrape-examples-target-crate");
        match (output_path, !target_crates.is_empty()) {
            (Some(output_path), true) => Ok(Some(ScrapeExamplesOptions {
                output_path: PathBuf::from(output_path),
                target_crates,
            })),
            (Some(_), false) | (None, true) => {
                diag.err(&format!("must use --scrape-examples-output-path and --scrape-examples-target-crate together"));
                Err(1)
            }
            (None, false) => Ok(None),
        }
    }
}

#[derive(Encodable, Decodable, Debug, Clone)]
crate struct SyntaxRange {
    crate byte_span: (u32, u32),
    crate line_span: (usize, usize),
}

impl SyntaxRange {
    fn new(span: rustc_span::Span, file: &SourceFile) -> Self {
        let get_pos = |bytepos: BytePos| file.original_relative_byte_pos(bytepos).0;
        let get_line = |bytepos: BytePos| file.lookup_line(bytepos).unwrap();

        SyntaxRange {
            byte_span: (get_pos(span.lo()), get_pos(span.hi())),
            line_span: (get_line(span.lo()), get_line(span.hi())),
        }
    }
}

#[derive(Encodable, Decodable, Debug, Clone)]
crate struct CallLocation {
    crate call_expr: SyntaxRange,
    crate enclosing_item: SyntaxRange,
}

impl CallLocation {
    fn new(
        tcx: TyCtxt<'_>,
        expr_span: rustc_span::Span,
        expr_id: HirId,
        source_file: &SourceFile,
    ) -> Self {
        let enclosing_item_span =
            tcx.hir().span_with_body(tcx.hir().get_parent_item(expr_id)).source_callsite();
        assert!(enclosing_item_span.contains(expr_span));

        CallLocation {
            call_expr: SyntaxRange::new(expr_span, source_file),
            enclosing_item: SyntaxRange::new(enclosing_item_span, source_file),
        }
    }
}

#[derive(Encodable, Decodable, Debug, Clone)]
crate struct CallData {
    crate locations: Vec<CallLocation>,
    crate url: String,
    crate display_name: String,
    crate edition: Edition,
}

crate type FnCallLocations = FxHashMap<PathBuf, CallData>;
crate type AllCallLocations = FxHashMap<DefPathHash, FnCallLocations>;

/// Visitor for traversing a crate and finding instances of function calls.
struct FindCalls<'a, 'tcx> {
    tcx: TyCtxt<'tcx>,
    map: Map<'tcx>,
    cx: Context<'tcx>,
    target_crates: Vec<CrateNum>,
    calls: &'a mut AllCallLocations,
}

impl<'a, 'tcx> Visitor<'tcx> for FindCalls<'a, 'tcx>
where
    'tcx: 'a,
{
    type Map = Map<'tcx>;

    fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
        intravisit::NestedVisitorMap::OnlyBodies(self.map)
    }

    fn visit_expr(&mut self, ex: &'tcx hir::Expr<'tcx>) {
        intravisit::walk_expr(self, ex);

        let tcx = self.tcx;

        // If we visit an item that contains an expression outside a function body,
        // then we need to exit before calling typeck (which will panic). See
        // test/run-make/rustdoc-scrape-examples-invalid-expr for an example.
        let hir = tcx.hir();
        let owner = hir.local_def_id_to_hir_id(ex.hir_id.owner);
        if hir.maybe_body_owned_by(owner).is_none() {
            return;
        }

        // Get type of function if expression is a function call
        let (ty, span) = match ex.kind {
            hir::ExprKind::Call(f, _) => {
                let types = tcx.typeck(ex.hir_id.owner);

                match types.node_type_opt(f.hir_id) {
                    Some(ty) => (ty, ex.span),
                    None => {
                        return;
                    }
                }
            }
            hir::ExprKind::MethodCall(_, _, _, span) => {
                let types = tcx.typeck(ex.hir_id.owner);
                let def_id = types.type_dependent_def_id(ex.hir_id).unwrap();
                (tcx.type_of(def_id), span)
            }
            _ => {
                return;
            }
        };

        // If this span comes from a macro expansion, then the source code may not actually show
        // a use of the given item, so it would be a poor example. Hence, we skip all uses in macros.
        if span.from_expansion() {
            return;
        }

        // Save call site if the function resolves to a concrete definition
        if let ty::FnDef(def_id, _) = ty.kind() {
            // Ignore functions not from the crate being documented
            if self.target_crates.iter().all(|krate| *krate != def_id.krate) {
                return;
            }

            let file = tcx.sess.source_map().lookup_char_pos(span.lo()).file;
            let file_path = match file.name.clone() {
                FileName::Real(real_filename) => real_filename.into_local_path(),
                _ => None,
            };

            if let Some(file_path) = file_path {
                let abs_path = fs::canonicalize(file_path.clone()).unwrap();
                let cx = &self.cx;
                let mk_call_data = || {
                    let clean_span = crate::clean::types::Span::new(span);
                    let url = cx.href_from_span(clean_span, false).unwrap();
                    let display_name = file_path.display().to_string();
                    let edition = span.edition();
                    CallData { locations: Vec::new(), url, display_name, edition }
                };

                let fn_key = tcx.def_path_hash(*def_id);
                let fn_entries = self.calls.entry(fn_key).or_default();

                let location = CallLocation::new(tcx, span, ex.hir_id, &file);
                fn_entries.entry(abs_path).or_insert_with(mk_call_data).locations.push(location);
            }
        }
    }
}

crate fn run(
    krate: clean::Crate,
    renderopts: config::RenderOptions,
    cache: formats::cache::Cache,
    tcx: TyCtxt<'_>,
    options: ScrapeExamplesOptions,
) -> interface::Result<()> {
    let inner = move || -> Result<(), String> {
        // Generates source files for examples
        let (cx, _) = Context::init(krate, renderopts, cache, tcx).map_err(|e| e.to_string())?;

        // Collect CrateIds corresponding to provided target crates
        // If two different versions of the crate in the dependency tree, then examples will be collcted from both.
        let all_crates = tcx
            .crates(())
            .iter()
            .chain([&LOCAL_CRATE])
            .map(|crate_num| (crate_num, tcx.crate_name(*crate_num)))
            .collect::<Vec<_>>();
        let target_crates = options
            .target_crates
            .into_iter()
            .map(|target| all_crates.iter().filter(move |(_, name)| name.as_str() == target))
            .flatten()
            .map(|(crate_num, _)| **crate_num)
            .collect::<Vec<_>>();

        debug!("All crates in TyCtxt: {:?}", all_crates);
        debug!("Scrape examples target_crates: {:?}", target_crates);

        // Run call-finder on all items
        let mut calls = FxHashMap::default();
        let mut finder = FindCalls { calls: &mut calls, tcx, map: tcx.hir(), cx, target_crates };
        tcx.hir().visit_all_item_likes(&mut finder.as_deep_visitor());

        // Sort call locations within a given file in document order
        for fn_calls in calls.values_mut() {
            for file_calls in fn_calls.values_mut() {
                file_calls.locations.sort_by_key(|loc| loc.call_expr.byte_span.0);
            }
        }

        // Save output to provided path
        let mut encoder = FileEncoder::new(options.output_path).map_err(|e| e.to_string())?;
        calls.encode(&mut encoder).map_err(|e| e.to_string())?;
        encoder.flush().map_err(|e| e.to_string())?;

        Ok(())
    };

    if let Err(e) = inner() {
        tcx.sess.fatal(&e);
    }

    Ok(())
}

// Note: the Handler must be passed in explicitly because sess isn't available while parsing options
crate fn load_call_locations(
    with_examples: Vec<String>,
    diag: &rustc_errors::Handler,
) -> Result<AllCallLocations, i32> {
    let inner = || {
        let mut all_calls: AllCallLocations = FxHashMap::default();
        for path in with_examples {
            let bytes = fs::read(&path).map_err(|e| format!("{} (for path {})", e, path))?;
            let mut decoder = Decoder::new(&bytes, 0);
            let calls = AllCallLocations::decode(&mut decoder)?;

            for (function, fn_calls) in calls.into_iter() {
                all_calls.entry(function).or_default().extend(fn_calls.into_iter());
            }
        }

        Ok(all_calls)
    };

    inner().map_err(|e: String| {
        diag.err(&format!("failed to load examples: {}", e));
        1
    })
}