//! Logic for transforming the raw code given by the user into something actually
//! runnable, e.g. by adding a `main` function if it doesn't already exist.

use std::fmt::{self, Write as _};
use std::io;
use std::sync::Arc;

use rustc_ast::token::{Delimiter, TokenKind};
use rustc_ast::tokenstream::TokenTree;
use rustc_ast::{self as ast, AttrStyle, HasAttrs, StmtKind};
use rustc_errors::emitter::stderr_destination;
use rustc_errors::{ColorConfig, DiagCtxtHandle};
use rustc_parse::lexer::StripTokens;
use rustc_parse::new_parser_from_source_str;
use rustc_session::parse::ParseSess;
use rustc_span::edition::{DEFAULT_EDITION, Edition};
use rustc_span::source_map::SourceMap;
use rustc_span::symbol::sym;
use rustc_span::{DUMMY_SP, FileName, Span, kw};
use tracing::debug;

use super::GlobalTestOptions;
use crate::display::Joined as _;
use crate::html::markdown::LangString;

#[derive(Default)]
struct ParseSourceInfo {
    has_main_fn: bool,
    already_has_extern_crate: bool,
    supports_color: bool,
    has_global_allocator: bool,
    has_macro_def: bool,
    everything_else: String,
    crates: String,
    crate_attrs: String,
    maybe_crate_attrs: String,
}

/// Builder type for `DocTestBuilder`.
pub(crate) struct BuildDocTestBuilder<'a> {
    source: &'a str,
    crate_name: Option<&'a str>,
    edition: Edition,
    can_merge_doctests: bool,
    // If `test_id` is `None`, it means we're generating code for a code example "run" link.
    test_id: Option<String>,
    lang_str: Option<&'a LangString>,
    span: Span,
    global_crate_attrs: Vec<String>,
}

impl<'a> BuildDocTestBuilder<'a> {
    pub(crate) fn new(source: &'a str) -> Self {
        Self {
            source,
            crate_name: None,
            edition: DEFAULT_EDITION,
            can_merge_doctests: false,
            test_id: None,
            lang_str: None,
            span: DUMMY_SP,
            global_crate_attrs: Vec::new(),
        }
    }

    #[inline]
    pub(crate) fn crate_name(mut self, crate_name: &'a str) -> Self {
        self.crate_name = Some(crate_name);
        self
    }

    #[inline]
    pub(crate) fn can_merge_doctests(mut self, can_merge_doctests: bool) -> Self {
        self.can_merge_doctests = can_merge_doctests;
        self
    }

    #[inline]
    pub(crate) fn test_id(mut self, test_id: String) -> Self {
        self.test_id = Some(test_id);
        self
    }

    #[inline]
    pub(crate) fn lang_str(mut self, lang_str: &'a LangString) -> Self {
        self.lang_str = Some(lang_str);
        self
    }

    #[inline]
    pub(crate) fn span(mut self, span: Span) -> Self {
        self.span = span;
        self
    }

    #[inline]
    pub(crate) fn edition(mut self, edition: Edition) -> Self {
        self.edition = edition;
        self
    }

    #[inline]
    pub(crate) fn global_crate_attrs(mut self, global_crate_attrs: Vec<String>) -> Self {
        self.global_crate_attrs = global_crate_attrs;
        self
    }

    pub(crate) fn build(self, dcx: Option<DiagCtxtHandle<'_>>) -> DocTestBuilder {
        let BuildDocTestBuilder {
            source,
            crate_name,
            edition,
            can_merge_doctests,
            // If `test_id` is `None`, it means we're generating code for a code example "run" link.
            test_id,
            lang_str,
            span,
            global_crate_attrs,
        } = self;
        let can_merge_doctests = can_merge_doctests
            && lang_str.is_some_and(|lang_str| {
                !lang_str.compile_fail && !lang_str.test_harness && !lang_str.standalone_crate
            });

        let result = rustc_driver::catch_fatal_errors(|| {
            rustc_span::create_session_if_not_set_then(edition, |_| {
                parse_source(source, &crate_name, dcx, span)
            })
        });

        let Ok(Ok(ParseSourceInfo {
            has_main_fn,
            already_has_extern_crate,
            supports_color,
            has_global_allocator,
            has_macro_def,
            everything_else,
            crates,
            crate_attrs,
            maybe_crate_attrs,
        })) = result
        else {
            // If the AST returned an error, we don't want this doctest to be merged with the
            // others.
            return DocTestBuilder::invalid(
                Vec::new(),
                String::new(),
                String::new(),
                String::new(),
                source.to_string(),
                test_id,
            );
        };

        debug!("crate_attrs:\n{crate_attrs}{maybe_crate_attrs}");
        debug!("crates:\n{crates}");
        debug!("after:\n{everything_else}");

        // If it contains `#[feature]` or `#[no_std]`, we don't want it to be merged either.
        let can_be_merged = can_merge_doctests
            && !has_global_allocator
            && crate_attrs.is_empty()
            // If this is a merged doctest and a defined macro uses `$crate`, then the path will
            // not work, so better not put it into merged doctests.
            && !(has_macro_def && everything_else.contains("$crate"));
        DocTestBuilder {
            supports_color,
            has_main_fn,
            global_crate_attrs,
            crate_attrs,
            maybe_crate_attrs,
            crates,
            everything_else,
            already_has_extern_crate,
            test_id,
            invalid_ast: false,
            can_be_merged,
        }
    }
}

/// This struct contains information about the doctest itself which is then used to generate
/// doctest source code appropriately.
pub(crate) struct DocTestBuilder {
    pub(crate) supports_color: bool,
    pub(crate) already_has_extern_crate: bool,
    pub(crate) has_main_fn: bool,
    pub(crate) global_crate_attrs: Vec<String>,
    pub(crate) crate_attrs: String,
    /// If this is a merged doctest, it will be put into `everything_else`, otherwise it will
    /// put into `crate_attrs`.
    pub(crate) maybe_crate_attrs: String,
    pub(crate) crates: String,
    pub(crate) everything_else: String,
    pub(crate) test_id: Option<String>,
    pub(crate) invalid_ast: bool,
    pub(crate) can_be_merged: bool,
}

/// Contains needed information for doctest to be correctly generated with expected "wrapping".
pub(crate) struct WrapperInfo {
    pub(crate) before: String,
    pub(crate) after: String,
    pub(crate) returns_result: bool,
    insert_indent_space: bool,
}

impl WrapperInfo {
    fn len(&self) -> usize {
        self.before.len() + self.after.len()
    }
}

/// Contains a doctest information. Can be converted into code with the `to_string()` method.
pub(crate) enum DocTestWrapResult {
    Valid {
        crate_level_code: String,
        /// This field can be `None` if one of the following conditions is true:
        ///
        /// * The doctest's codeblock has the `test_harness` attribute.
        /// * The doctest has a `main` function.
        /// * The doctest has the `![no_std]` attribute.
        wrapper: Option<WrapperInfo>,
        /// Contains the doctest processed code without the wrappers (which are stored in the
        /// `wrapper` field).
        code: String,
    },
    /// Contains the original source code.
    SyntaxError(String),
}

impl std::string::ToString for DocTestWrapResult {
    fn to_string(&self) -> String {
        match self {
            Self::SyntaxError(s) => s.clone(),
            Self::Valid { crate_level_code, wrapper, code } => {
                let mut prog_len = code.len() + crate_level_code.len();
                if let Some(wrapper) = wrapper {
                    prog_len += wrapper.len();
                    if wrapper.insert_indent_space {
                        prog_len += code.lines().count() * 4;
                    }
                }
                let mut prog = String::with_capacity(prog_len);

                prog.push_str(crate_level_code);
                if let Some(wrapper) = wrapper {
                    prog.push_str(&wrapper.before);

                    // add extra 4 spaces for each line to offset the code block
                    if wrapper.insert_indent_space {
                        write!(
                            prog,
                            "{}",
                            fmt::from_fn(|f| code
                                .lines()
                                .map(|line| fmt::from_fn(move |f| write!(f, "    {line}")))
                                .joined("\n", f))
                        )
                        .unwrap();
                    } else {
                        prog.push_str(code);
                    }
                    prog.push_str(&wrapper.after);
                } else {
                    prog.push_str(code);
                }
                prog
            }
        }
    }
}

impl DocTestBuilder {
    fn invalid(
        global_crate_attrs: Vec<String>,
        crate_attrs: String,
        maybe_crate_attrs: String,
        crates: String,
        everything_else: String,
        test_id: Option<String>,
    ) -> Self {
        Self {
            supports_color: false,
            has_main_fn: false,
            global_crate_attrs,
            crate_attrs,
            maybe_crate_attrs,
            crates,
            everything_else,
            already_has_extern_crate: false,
            test_id,
            invalid_ast: true,
            can_be_merged: false,
        }
    }

    /// Transforms a test into code that can be compiled into a Rust binary, and returns the number of
    /// lines before the test code begins.
    pub(crate) fn generate_unique_doctest(
        &self,
        test_code: &str,
        dont_insert_main: bool,
        opts: &GlobalTestOptions,
        crate_name: Option<&str>,
    ) -> (DocTestWrapResult, usize) {
        if self.invalid_ast {
            // If the AST failed to compile, no need to go generate a complete doctest, the error
            // will be better this way.
            debug!("invalid AST:\n{test_code}");
            return (DocTestWrapResult::SyntaxError(test_code.to_string()), 0);
        }
        let mut line_offset = 0;
        let mut crate_level_code = String::new();
        let processed_code = self.everything_else.trim();
        if self.global_crate_attrs.is_empty() {
            // If there aren't any attributes supplied by #![doc(test(attr(...)))], then allow some
            // lints that are commonly triggered in doctests. The crate-level test attributes are
            // commonly used to make tests fail in case they trigger warnings, so having this there in
            // that case may cause some tests to pass when they shouldn't have.
            crate_level_code.push_str("#![allow(unused)]\n");
            line_offset += 1;
        }

        // Next, any attributes that came from #![doc(test(attr(...)))].
        for attr in &self.global_crate_attrs {
            crate_level_code.push_str(&format!("#![{attr}]\n"));
            line_offset += 1;
        }

        // Now push any outer attributes from the example, assuming they
        // are intended to be crate attributes.
        if !self.crate_attrs.is_empty() {
            crate_level_code.push_str(&self.crate_attrs);
            if !self.crate_attrs.ends_with('\n') {
                crate_level_code.push('\n');
            }
        }
        if !self.maybe_crate_attrs.is_empty() {
            crate_level_code.push_str(&self.maybe_crate_attrs);
            if !self.maybe_crate_attrs.ends_with('\n') {
                crate_level_code.push('\n');
            }
        }
        if !self.crates.is_empty() {
            crate_level_code.push_str(&self.crates);
            if !self.crates.ends_with('\n') {
                crate_level_code.push('\n');
            }
        }

        // Don't inject `extern crate std` because it's already injected by the
        // compiler.
        if !self.already_has_extern_crate &&
            !opts.no_crate_inject &&
            let Some(crate_name) = crate_name &&
            crate_name != "std" &&
            // Don't inject `extern crate` if the crate is never used.
            // NOTE: this is terribly inaccurate because it doesn't actually
            // parse the source, but only has false positives, not false
            // negatives.
            test_code.contains(crate_name)
        {
            // rustdoc implicitly inserts an `extern crate` item for the own crate
            // which may be unused, so we need to allow the lint.
            crate_level_code.push_str("#[allow(unused_extern_crates)]\n");

            crate_level_code.push_str(&format!("extern crate r#{crate_name};\n"));
            line_offset += 1;
        }

        // FIXME: This code cannot yet handle no_std test cases yet
        let wrapper = if dont_insert_main
            || self.has_main_fn
            || crate_level_code.contains("![no_std]")
        {
            None
        } else {
            let returns_result = processed_code.ends_with("(())");
            // Give each doctest main function a unique name.
            // This is for example needed for the tooling around `-C instrument-coverage`.
            let inner_fn_name = if let Some(ref test_id) = self.test_id {
                format!("_doctest_main_{test_id}")
            } else {
                "_inner".into()
            };
            let inner_attr = if self.test_id.is_some() { "#[allow(non_snake_case)] " } else { "" };
            let (main_pre, main_post) = if returns_result {
                (
                    format!(
                        "fn main() {{ {inner_attr}fn {inner_fn_name}() -> core::result::Result<(), impl core::fmt::Debug> {{\n",
                    ),
                    format!("\n}} {inner_fn_name}().unwrap() }}"),
                )
            } else if self.test_id.is_some() {
                (
                    format!("fn main() {{ {inner_attr}fn {inner_fn_name}() {{\n",),
                    format!("\n}} {inner_fn_name}() }}"),
                )
            } else {
                ("fn main() {\n".into(), "\n}".into())
            };
            // Note on newlines: We insert a line/newline *before*, and *after*
            // the doctest and adjust the `line_offset` accordingly.
            // In the case of `-C instrument-coverage`, this means that the generated
            // inner `main` function spans from the doctest opening codeblock to the
            // closing one. For example
            // /// ``` <- start of the inner main
            // /// <- code under doctest
            // /// ``` <- end of the inner main
            line_offset += 1;

            Some(WrapperInfo {
                before: main_pre,
                after: main_post,
                returns_result,
                insert_indent_space: opts.insert_indent_space,
            })
        };

        (
            DocTestWrapResult::Valid {
                code: processed_code.to_string(),
                wrapper,
                crate_level_code,
            },
            line_offset,
        )
    }
}

fn reset_error_count(psess: &ParseSess) {
    // Reset errors so that they won't be reported as compiler bugs when dropping the
    // dcx. Any errors in the tests will be reported when the test file is compiled,
    // Note that we still need to cancel the errors above otherwise `Diag` will panic on
    // drop.
    psess.dcx().reset_err_count();
}

const DOCTEST_CODE_WRAPPER: &str = "fn f(){";

fn parse_source(
    source: &str,
    crate_name: &Option<&str>,
    parent_dcx: Option<DiagCtxtHandle<'_>>,
    span: Span,
) -> Result<ParseSourceInfo, ()> {
    use rustc_errors::DiagCtxt;
    use rustc_errors::emitter::{Emitter, HumanEmitter};
    use rustc_span::source_map::FilePathMapping;

    let mut info =
        ParseSourceInfo { already_has_extern_crate: crate_name.is_none(), ..Default::default() };

    let wrapped_source = format!("{DOCTEST_CODE_WRAPPER}{source}\n}}");

    let filename = FileName::anon_source_code(&wrapped_source);

    let sm = Arc::new(SourceMap::new(FilePathMapping::empty()));
    let translator = rustc_driver::default_translator();
    info.supports_color =
        HumanEmitter::new(stderr_destination(ColorConfig::Auto), translator.clone())
            .supports_color();
    // Any errors in parsing should also appear when the doctest is compiled for real, so just
    // send all the errors that the parser emits directly into a `Sink` instead of stderr.
    let emitter = HumanEmitter::new(Box::new(io::sink()), translator);

    // FIXME(misdreavus): pass `-Z treat-err-as-bug` to the doctest parser
    let dcx = DiagCtxt::new(Box::new(emitter)).disable_warnings();
    let psess = ParseSess::with_dcx(dcx, sm);

    // Don't strip any tokens; it wouldn't matter anyway because the source is wrapped in a function.
    let mut parser =
        match new_parser_from_source_str(&psess, filename, wrapped_source, StripTokens::Nothing) {
            Ok(p) => p,
            Err(errs) => {
                errs.into_iter().for_each(|err| err.cancel());
                reset_error_count(&psess);
                return Err(());
            }
        };

    fn push_to_s(s: &mut String, source: &str, span: rustc_span::Span, prev_span_hi: &mut usize) {
        let extra_len = DOCTEST_CODE_WRAPPER.len();
        // We need to shift by the length of `DOCTEST_CODE_WRAPPER` because we
        // added it at the beginning of the source we provided to the parser.
        let mut hi = span.hi().0 as usize - extra_len;
        if hi > source.len() {
            hi = source.len();
        }
        s.push_str(&source[*prev_span_hi..hi]);
        *prev_span_hi = hi;
    }

    fn check_item(item: &ast::Item, info: &mut ParseSourceInfo, crate_name: &Option<&str>) -> bool {
        let mut is_extern_crate = false;
        if !info.has_global_allocator
            && item.attrs.iter().any(|attr| attr.has_name(sym::global_allocator))
        {
            info.has_global_allocator = true;
        }
        match item.kind {
            ast::ItemKind::Fn(ref fn_item) if !info.has_main_fn => {
                if fn_item.ident.name == sym::main {
                    info.has_main_fn = true;
                }
            }
            ast::ItemKind::ExternCrate(original, ident) => {
                is_extern_crate = true;
                if !info.already_has_extern_crate
                    && let Some(crate_name) = crate_name
                {
                    info.already_has_extern_crate = match original {
                        Some(name) => name.as_str() == *crate_name,
                        None => ident.as_str() == *crate_name,
                    };
                }
            }
            ast::ItemKind::MacroDef(..) => {
                info.has_macro_def = true;
            }
            _ => {}
        }
        is_extern_crate
    }

    let mut prev_span_hi = 0;
    let not_crate_attrs = &[sym::forbid, sym::allow, sym::warn, sym::deny, sym::expect];
    let parsed = parser.parse_item(rustc_parse::parser::ForceCollect::No);

    let result = match parsed {
        Ok(Some(ref item))
            if let ast::ItemKind::Fn(ref fn_item) = item.kind
                && let Some(ref body) = fn_item.body =>
        {
            for attr in &item.attrs {
                if attr.style == AttrStyle::Outer || attr.has_any_name(not_crate_attrs) {
                    // There is one exception to these attributes:
                    // `#![allow(internal_features)]`. If this attribute is used, we need to
                    // consider it only as a crate-level attribute.
                    if attr.has_name(sym::allow)
                        && let Some(list) = attr.meta_item_list()
                        && list.iter().any(|sub_attr| sub_attr.has_name(sym::internal_features))
                    {
                        push_to_s(&mut info.crate_attrs, source, attr.span, &mut prev_span_hi);
                    } else {
                        push_to_s(
                            &mut info.maybe_crate_attrs,
                            source,
                            attr.span,
                            &mut prev_span_hi,
                        );
                    }
                } else {
                    push_to_s(&mut info.crate_attrs, source, attr.span, &mut prev_span_hi);
                }
            }
            let mut has_non_items = false;
            for stmt in &body.stmts {
                let mut is_extern_crate = false;
                match stmt.kind {
                    StmtKind::Item(ref item) => {
                        is_extern_crate = check_item(item, &mut info, crate_name);
                    }
                    // We assume that the macro calls will expand to item(s) even though they could
                    // expand to statements and expressions.
                    StmtKind::MacCall(ref mac_call) => {
                        if !info.has_main_fn {
                            // For backward compatibility, we look for the token sequence `fn main(…)`
                            // in the macro input (!) to crudely detect main functions "masked by a
                            // wrapper macro". For the record, this is a horrible heuristic!
                            // See <https://github.com/rust-lang/rust/issues/56898>.
                            let mut iter = mac_call.mac.args.tokens.iter();
                            while let Some(token) = iter.next() {
                                if let TokenTree::Token(token, _) = token
                                    && let TokenKind::Ident(kw::Fn, _) = token.kind
                                    && let Some(TokenTree::Token(ident, _)) = iter.peek()
                                    && let TokenKind::Ident(sym::main, _) = ident.kind
                                    && let Some(TokenTree::Delimited(.., Delimiter::Parenthesis, _)) = {
                                        iter.next();
                                        iter.peek()
                                    }
                                {
                                    info.has_main_fn = true;
                                    break;
                                }
                            }
                        }
                    }
                    StmtKind::Expr(ref expr) => {
                        if matches!(expr.kind, ast::ExprKind::Err(_)) {
                            reset_error_count(&psess);
                            return Err(());
                        }
                        has_non_items = true;
                    }
                    StmtKind::Let(_) | StmtKind::Semi(_) | StmtKind::Empty => has_non_items = true,
                }

                // Weirdly enough, the `Stmt` span doesn't include its attributes, so we need to
                // tweak the span to include the attributes as well.
                let mut span = stmt.span;
                if let Some(attr) =
                    stmt.kind.attrs().iter().find(|attr| attr.style == AttrStyle::Outer)
                {
                    span = span.with_lo(attr.span.lo());
                }
                if info.everything_else.is_empty()
                    && (!info.maybe_crate_attrs.is_empty() || !info.crate_attrs.is_empty())
                {
                    // To keep the doctest code "as close as possible" to the original, we insert
                    // all the code located between this new span and the previous span which
                    // might contain code comments and backlines.
                    push_to_s(&mut info.crates, source, span.shrink_to_lo(), &mut prev_span_hi);
                }
                if !is_extern_crate {
                    push_to_s(&mut info.everything_else, source, span, &mut prev_span_hi);
                } else {
                    push_to_s(&mut info.crates, source, span, &mut prev_span_hi);
                }
            }
            if has_non_items {
                if info.has_main_fn
                    && let Some(dcx) = parent_dcx
                    && !span.is_dummy()
                {
                    dcx.span_warn(
                        span,
                        "the `main` function of this doctest won't be run as it contains \
                         expressions at the top level, meaning that the whole doctest code will be \
                         wrapped in a function",
                    );
                }
                info.has_main_fn = false;
            }
            Ok(info)
        }
        Err(e) => {
            e.cancel();
            Err(())
        }
        _ => Err(()),
    };

    reset_error_count(&psess);
    result
}