// SPDX-License-Identifier: Apache-2.0 OR MIT
//
// Modifications Copyright Kani Contributors
// See GitHub history for details.
//! Markdown formatting for rustdoc.
//!

use rustc_span::edition::Edition;

use std::default::Default;
use std::str;
use std::{borrow::Cow, marker::PhantomData};

use crate::doctest;

use pulldown_cmark::{CodeBlockKind, Event, Parser, Tag};

#[derive(Copy, Clone, Eq, PartialEq, Debug)]
pub /* via find_testable_code */ enum ErrorCodes {
    Yes,
    No,
}

impl ErrorCodes {
    pub(crate) fn as_bool(self) -> bool {
        match self {
            ErrorCodes::Yes => true,
            ErrorCodes::No => false,
        }
    }
}

/// Controls whether a line will be hidden or shown in HTML output.
///
/// All lines are used in documentation tests.
enum Line<'a> {
    Hidden(&'a str),
    Shown(Cow<'a, str>),
}

impl<'a> Line<'a> {
    fn for_code(self) -> Cow<'a, str> {
        match self {
            Line::Shown(l) => l,
            Line::Hidden(l) => Cow::Borrowed(l),
        }
    }
}

// FIXME: There is a minor inconsistency here. For lines that start with ##, we
// have no easy way of removing a potential single space after the hashes, which
// is done in the single # case. This inconsistency seems okay, if non-ideal. In
// order to fix it we'd have to iterate to find the first non-# character, and
// then reallocate to remove it; which would make us return a String.
fn map_line(s: &str) -> Line<'_> {
    let trimmed = s.trim();
    if trimmed.starts_with("##") {
        Line::Shown(Cow::Owned(s.replacen("##", "#", 1)))
    } else if let Some(stripped) = trimmed.strip_prefix("# ") {
        // # text
        Line::Hidden(stripped)
    } else if trimmed == "#" {
        // We cannot handle '#text' because it could be #[attr].
        Line::Hidden("")
    } else {
        Line::Shown(Cow::Borrowed(s))
    }
}

pub fn find_testable_code<T: doctest::Tester>(
    doc: &str,
    tests: &mut T,
    error_codes: ErrorCodes,
    enable_per_target_ignores: bool,
    extra_info: Option<&ExtraInfo<'_>>,
) {
    let mut parser = Parser::new(doc).into_offset_iter();
    let mut prev_offset = 0;
    let mut nb_lines = 0;
    let mut register_header = None;
    while let Some((event, offset)) = parser.next() {
        match event {
            Event::Start(Tag::CodeBlock(kind)) => {
                let block_info = match kind {
                    CodeBlockKind::Fenced(ref lang) => {
                        if lang.is_empty() {
                            Default::default()
                        } else {
                            LangString::parse(
                                lang,
                                error_codes,
                                enable_per_target_ignores,
                                extra_info,
                            )
                        }
                    }
                    CodeBlockKind::Indented => Default::default(),
                };
                if !block_info.rust {
                    continue;
                }

                let mut test_s = String::new();

                while let Some((Event::Text(s), _)) = parser.next() {
                    test_s.push_str(&s);
                }
                let text = test_s
                    .lines()
                    .map(|l| map_line(l).for_code())
                    .collect::<Vec<Cow<'_, str>>>()
                    .join("\n");

                nb_lines += doc[prev_offset..offset.start].lines().count();
                // If there are characters between the preceding line ending and
                // this code block, `str::lines` will return an additional line,
                // which we subtract here.
                if nb_lines != 0 && !&doc[prev_offset..offset.start].ends_with('\n') {
                    nb_lines -= 1;
                }
                let line = tests.get_line() + nb_lines + 1;
                tests.add_test(text, block_info, line);
                prev_offset = offset.start;
            }
            Event::Start(Tag::Heading(level, _, _)) => {
                register_header = Some(level as u32);
            }
            Event::Text(ref s) if register_header.is_some() => {
                let level = register_header.unwrap();
                if s.is_empty() {
                    tests.register_header("", level);
                } else {
                    tests.register_header(s, level);
                }
                register_header = None;
            }
            _ => {}
        }
    }
}

// We never pass an actual ExtraInfo, only None for Option<ExtraInfo>
pub struct ExtraInfo<'tcx> {
    _unused: PhantomData<&'tcx ()>,
}

impl<'tcx> ExtraInfo<'tcx> {
    fn error_invalid_codeblock_attr(&self, msg: &str, _help: &str) {
        unreachable!("{}", msg);
    }
}

#[derive(Eq, PartialEq, Clone, Debug)]
pub struct LangString {
    original: String,
    pub should_panic: bool,
    pub(crate) no_run: bool,
    pub ignore: Ignore,
    pub(crate) rust: bool,
    pub(crate) test_harness: bool,
    pub compile_fail: bool,
    pub(crate) error_codes: Vec<String>,
    pub(crate) allow_fail: bool,
    pub edition: Option<Edition>,
}

#[derive(Eq, PartialEq, Clone, Debug)]
pub enum Ignore {
    All,
    None,
    Some(Vec<String>),
}

impl Default for LangString {
    fn default() -> Self {
        Self {
            original: String::new(),
            should_panic: false,
            no_run: false,
            ignore: Ignore::None,
            rust: true,
            test_harness: false,
            compile_fail: false,
            error_codes: Vec::new(),
            allow_fail: false,
            edition: None,
        }
    }
}

impl LangString {
    fn tokens(string: &str) -> impl Iterator<Item = &str> {
        // Pandoc, which Rust once used for generating documentation,
        // expects lang strings to be surrounded by `{}` and for each token
        // to be proceeded by a `.`. Since some of these lang strings are still
        // loose in the wild, we strip a pair of surrounding `{}` from the lang
        // string and a leading `.` from each token.

        let string = string.trim();

        let first = string.chars().next();
        let last = string.chars().last();

        let string = if first == Some('{') && last == Some('}') {
            &string[1..string.len() - 1]
        } else {
            string
        };

        string
            .split(|c| c == ',' || c == ' ' || c == '\t')
            .map(str::trim)
            .map(|token| token.strip_prefix('.').unwrap_or(token))
            .filter(|token| !token.is_empty())
    }

    fn parse(
        string: &str,
        allow_error_code_check: ErrorCodes,
        enable_per_target_ignores: bool,
        extra: Option<&ExtraInfo<'_>>,
    ) -> LangString {
        let allow_error_code_check = allow_error_code_check.as_bool();
        let mut seen_rust_tags = false;
        let mut seen_other_tags = false;
        let mut data = LangString::default();
        let mut ignores = vec![];

        data.original = string.to_owned();

        for token in Self::tokens(string) {
            match token {
                "should_panic" => {
                    data.should_panic = true;
                    seen_rust_tags = !seen_other_tags;
                }
                "no_run" => {
                    data.no_run = true;
                    seen_rust_tags = !seen_other_tags;
                }
                "ignore" => {
                    data.ignore = Ignore::All;
                    seen_rust_tags = !seen_other_tags;
                }
                x if x.starts_with("ignore-") => {
                    if enable_per_target_ignores {
                        ignores.push(x.trim_start_matches("ignore-").to_owned());
                        seen_rust_tags = !seen_other_tags;
                    }
                }
                "allow_fail" => {
                    data.allow_fail = true;
                    seen_rust_tags = !seen_other_tags;
                }
                "rust" => {
                    data.rust = true;
                    seen_rust_tags = true;
                }
                "test_harness" => {
                    data.test_harness = true;
                    seen_rust_tags = !seen_other_tags || seen_rust_tags;
                }
                "compile_fail" => {
                    data.compile_fail = true;
                    seen_rust_tags = !seen_other_tags || seen_rust_tags;
                    data.no_run = true;
                }
                x if x.starts_with("edition") => {
                    data.edition = x[7..].parse::<Edition>().ok();
                }
                x if allow_error_code_check && x.starts_with('E') && x.len() == 5 => {
                    if x[1..].parse::<u32>().is_ok() {
                        data.error_codes.push(x.to_owned());
                        seen_rust_tags = !seen_other_tags || seen_rust_tags;
                    } else {
                        seen_other_tags = true;
                    }
                }
                x if extra.is_some() => {
                    let s = x.to_lowercase();
                    if let Some((flag, help)) = if s == "compile-fail"
                        || s == "compile_fail"
                        || s == "compilefail"
                    {
                        Some((
                            "compile_fail",
                            "the code block will either not be tested if not marked as a rust one \
                             or won't fail if it compiles successfully",
                        ))
                    } else if s == "should-panic" || s == "should_panic" || s == "shouldpanic" {
                        Some((
                            "should_panic",
                            "the code block will either not be tested if not marked as a rust one \
                             or won't fail if it doesn't panic when running",
                        ))
                    } else if s == "no-run" || s == "no_run" || s == "norun" {
                        Some((
                            "no_run",
                            "the code block will either not be tested if not marked as a rust one \
                             or will be run (which you might not want)",
                        ))
                    } else if s == "allow-fail" || s == "allow_fail" || s == "allowfail" {
                        Some((
                            "allow_fail",
                            "the code block will either not be tested if not marked as a rust one \
                             or will be run (which you might not want)",
                        ))
                    } else if s == "test-harness" || s == "test_harness" || s == "testharness" {
                        Some((
                            "test_harness",
                            "the code block will either not be tested if not marked as a rust one \
                             or the code will be wrapped inside a main function",
                        ))
                    } else {
                        None
                    } {
                        if let Some(extra) = extra {
                            extra.error_invalid_codeblock_attr(
                                &format!("unknown attribute `{x}`. Did you mean `{flag}`?"),
                                help,
                            );
                        }
                    }
                    seen_other_tags = true;
                }
                _ => seen_other_tags = true,
            }
        }

        // ignore-foo overrides ignore
        if !ignores.is_empty() {
            data.ignore = Ignore::Some(ignores);
        }

        data.rust &= !seen_other_tags || seen_rust_tags;

        data
    }
}