use anyhow::{Context, Error, Result, anyhow, bail};
use std::{
    cmp::Ordering,
    collections::HashSet,
    fs::{self, OpenOptions, read_dir},
    io::{self, Read, Write},
    path::{Path, PathBuf},
    process::{Command, Stdio},
    thread,
};

use crate::{
    CURRENT_FORMAT_VERSION,
    cargo_toml::{BINS_BUFFER_CAPACITY, append_bins, bins_start_end_ind},
    cmd::CmdRunner,
    exercise::{OUTPUT_CAPACITY, RunnableExercise},
    info_file::{ExerciseInfo, InfoFile},
    term::ProgressCounter,
};

const MAX_N_EXERCISES: usize = 999;
const MAX_EXERCISE_NAME_LEN: usize = 32;

// Find a char that isn't allowed in the exercise's `name` or `dir`.
fn forbidden_char(input: &str) -> Option<char> {
    input.chars().find(|c| !c.is_alphanumeric() && *c != '_')
}

// Check that the `Cargo.toml` file is up-to-date.
fn check_cargo_toml(
    exercise_infos: &[ExerciseInfo],
    cargo_toml_path: &str,
    exercise_path_prefix: &[u8],
) -> Result<()> {
    let current_cargo_toml = fs::read_to_string(cargo_toml_path)
        .with_context(|| format!("Failed to read the file `{cargo_toml_path}`"))?;

    let (bins_start_ind, bins_end_ind) = bins_start_end_ind(&current_cargo_toml)?;

    let old_bins = &current_cargo_toml.as_bytes()[bins_start_ind..bins_end_ind];
    let mut new_bins = Vec::with_capacity(BINS_BUFFER_CAPACITY);
    append_bins(&mut new_bins, exercise_infos, exercise_path_prefix);

    if old_bins != new_bins {
        if cfg!(debug_assertions) {
            bail!(
                "The file `dev/Cargo.toml` is outdated. Run `cargo dev update` to update it. Then run `cargo run -- dev check` again"
            );
        }

        bail!(
            "The file `Cargo.toml` is outdated. Run `rustlings dev update` to update it. Then run `rustlings dev check` again"
        );
    }

    Ok(())
}

// Check the info of all exercises and return their paths in a set.
fn check_info_file_exercises(info_file: &InfoFile) -> Result<HashSet<PathBuf>> {
    let mut names = HashSet::with_capacity(info_file.exercises.len());
    let mut paths = HashSet::with_capacity(info_file.exercises.len());

    let mut file_buf = String::with_capacity(1 << 14);
    for exercise_info in &info_file.exercises {
        let name = exercise_info.name.as_str();
        if name.is_empty() {
            bail!("Found an empty exercise name in `info.toml`");
        }
        if name.len() > MAX_EXERCISE_NAME_LEN {
            bail!(
                "The length of the exercise name `{name}` is bigger than the maximum {MAX_EXERCISE_NAME_LEN}"
            );
        }
        if let Some(c) = forbidden_char(name) {
            bail!("Char `{c}` in the exercise name `{name}` is not allowed");
        }

        if let Some(dir) = &exercise_info.dir {
            if dir.is_empty() {
                bail!("The exercise `{name}` has an empty dir name in `info.toml`");
            }
            if let Some(c) = forbidden_char(dir) {
                bail!("Char `{c}` in the exercise dir `{dir}` is not allowed");
            }
        }

        if exercise_info.hint.trim_ascii().is_empty() {
            bail!(
                "The exercise `{name}` has an empty hint. Please provide a hint or at least tell the user why a hint isn't needed for this exercise"
            );
        }

        if !names.insert(name) {
            bail!("The exercise name `{name}` is duplicated. Exercise names must all be unique");
        }

        let path = exercise_info.path();

        OpenOptions::new()
            .read(true)
            .open(&path)
            .with_context(|| format!("Failed to open the file {path}"))?
            .read_to_string(&mut file_buf)
            .with_context(|| format!("Failed to read the file {path}"))?;

        if !file_buf.contains("fn main()") {
            bail!(
                "The `main` function is missing in the file `{path}`.\n\
                 Create at least an empty `main` function to avoid language server errors"
            );
        }

        if !file_buf.contains("// TODO") {
            bail!(
                "Didn't find any `// TODO` comment in the file `{path}`.\n\
                 You need to have at least one such comment to guide the user."
            );
        }

        let contains_tests = file_buf.contains("#[test]\n");
        if exercise_info.test {
            if !contains_tests {
                bail!(
                    "The file `{path}` doesn't contain any tests. If you don't want to add tests to this exercise, set `test = false` for this exercise in the `info.toml` file"
                );
            }
        } else if contains_tests {
            bail!(
                "The file `{path}` contains tests annotated with `#[test]` but the exercise `{name}` has `test = false` in the `info.toml` file"
            );
        }

        file_buf.clear();

        paths.insert(PathBuf::from(path));
    }

    Ok(paths)
}

// Check `dir` for unexpected files.
// Only Rust files in `allowed_rust_files` and `README.md` files are allowed.
// Only one level of directory nesting is allowed.
fn check_unexpected_files(dir: &str, allowed_rust_files: &HashSet<PathBuf>) -> Result<()> {
    let unexpected_file = |path: &Path| {
        anyhow!(
            "Found the file `{}`. Only `README.md` and Rust files related to an exercise in `info.toml` are allowed in the `{dir}` directory",
            path.display()
        )
    };

    for entry in read_dir(dir).with_context(|| format!("Failed to open the `{dir}` directory"))? {
        let entry = entry.with_context(|| format!("Failed to read the `{dir}` directory"))?;

        if entry.file_type().unwrap().is_file() {
            let path = entry.path();
            let file_name = path.file_name().unwrap();
            if file_name == "README.md" {
                continue;
            }

            if !allowed_rust_files.contains(&path) {
                return Err(unexpected_file(&path));
            }

            continue;
        }

        let dir_path = entry.path();
        for entry in read_dir(&dir_path)
            .with_context(|| format!("Failed to open the directory {}", dir_path.display()))?
        {
            let entry = entry
                .with_context(|| format!("Failed to read the directory {}", dir_path.display()))?;
            let path = entry.path();

            if !entry.file_type().unwrap().is_file() {
                bail!(
                    "Found `{}` but expected only files. Only one level of exercise nesting is allowed",
                    path.display()
                );
            }

            let file_name = path.file_name().unwrap();
            if file_name == "README.md" {
                continue;
            }

            if !allowed_rust_files.contains(&path) {
                return Err(unexpected_file(&path));
            }
        }
    }

    Ok(())
}

fn check_exercises_unsolved(
    info_file: &'static InfoFile,
    cmd_runner: &'static CmdRunner,
) -> Result<()> {
    let mut stdout = io::stdout().lock();
    stdout.write_all(b"Running all exercises to check that they aren't already solved...\n")?;

    let handles = info_file
        .exercises
        .iter()
        .filter_map(|exercise_info| {
            if exercise_info.skip_check_unsolved {
                return None;
            }

            Some(
                thread::Builder::new()
                    .spawn(|| exercise_info.run_exercise(None, cmd_runner))
                    .map(|handle| (exercise_info.name.as_str(), handle)),
            )
        })
        .collect::<Result<Vec<_>, _>>()
        .context("Failed to spawn a thread to check if an exercise is already solved")?;

    let mut progress_counter = ProgressCounter::new(&mut stdout, handles.len())?;

    for (exercise_name, handle) in handles {
        let Ok(result) = handle.join() else {
            bail!("Panic while trying to run the exercise {exercise_name}");
        };

        match result {
            Ok(true) => {
                bail!(
                    "The exercise {exercise_name} is already solved.\n\
                     {SKIP_CHECK_UNSOLVED_HINT}",
                )
            }
            Ok(false) => (),
            Err(e) => return Err(e),
        }

        progress_counter.increment()?;
    }

    Ok(())
}

fn check_exercises(info_file: &'static InfoFile, cmd_runner: &'static CmdRunner) -> Result<()> {
    match info_file.format_version.cmp(&CURRENT_FORMAT_VERSION) {
        Ordering::Less => bail!(
            "`format_version` < {CURRENT_FORMAT_VERSION} (supported version)\n\
             Please migrate to the latest format version"
        ),
        Ordering::Greater => bail!(
            "`format_version` > {CURRENT_FORMAT_VERSION} (supported version)\n\
             Try updating the Rustlings program"
        ),
        Ordering::Equal => (),
    }

    let handle = thread::Builder::new()
        .spawn(move || check_exercises_unsolved(info_file, cmd_runner))
        .context("Failed to spawn a thread to check if any exercise is already solved")?;

    let info_file_paths = check_info_file_exercises(info_file)?;
    check_unexpected_files("exercises", &info_file_paths)?;

    handle.join().unwrap()
}

enum SolutionCheck {
    Success { sol_path: String },
    MissingOptional,
    RunFailure { output: Vec<u8> },
    Err(Error),
}

fn check_solutions(
    require_solutions: bool,
    info_file: &'static InfoFile,
    cmd_runner: &'static CmdRunner,
) -> Result<()> {
    let mut stdout = io::stdout().lock();
    stdout.write_all(b"Running all solutions...\n")?;

    let handles = info_file
        .exercises
        .iter()
        .map(|exercise_info| {
            thread::Builder::new().spawn(move || {
                let sol_path = exercise_info.sol_path();
                if !Path::new(&sol_path).exists() {
                    if require_solutions {
                        return SolutionCheck::Err(anyhow!(
                            "The solution of the exercise {} is missing",
                            exercise_info.name,
                        ));
                    }

                    return SolutionCheck::MissingOptional;
                }

                let mut output = Vec::with_capacity(OUTPUT_CAPACITY);
                match exercise_info.run_solution(Some(&mut output), cmd_runner) {
                    Ok(true) => SolutionCheck::Success { sol_path },
                    Ok(false) => SolutionCheck::RunFailure { output },
                    Err(e) => SolutionCheck::Err(e),
                }
            })
        })
        .collect::<Result<Vec<_>, _>>()
        .context("Failed to spawn a thread to check a solution")?;

    let mut sol_paths = HashSet::with_capacity(info_file.exercises.len());
    let mut fmt_cmd = Command::new("rustfmt");
    fmt_cmd
        .arg("--check")
        .arg("--edition")
        .arg("2024")
        .arg("--color")
        .arg("always")
        .stdin(Stdio::null());

    let mut progress_counter = ProgressCounter::new(&mut stdout, handles.len())?;

    for (exercise_info, handle) in info_file.exercises.iter().zip(handles) {
        let Ok(check_result) = handle.join() else {
            bail!(
                "Panic while trying to run the solution of the exercise {}",
                exercise_info.name,
            );
        };

        match check_result {
            SolutionCheck::Success { sol_path } => {
                fmt_cmd.arg(&sol_path);
                sol_paths.insert(PathBuf::from(sol_path));
            }
            SolutionCheck::MissingOptional => (),
            SolutionCheck::RunFailure { output } => {
                drop(progress_counter);
                stdout.write_all(&output)?;
                bail!(
                    "Running the solution of the exercise {} failed with the error above",
                    exercise_info.name,
                );
            }
            SolutionCheck::Err(e) => return Err(e),
        }

        progress_counter.increment()?;
    }

    let n_solutions = sol_paths.len();
    let handle = thread::Builder::new()
        .spawn(move || check_unexpected_files("solutions", &sol_paths))
        .context(
            "Failed to spawn a thread to check for unexpected files in the solutions directory",
        )?;

    if n_solutions > 0
        && !fmt_cmd
            .status()
            .context("Failed to run `rustfmt` on all solution files")?
            .success()
    {
        bail!("Some solutions aren't formatted. Run `rustfmt` on them");
    }

    handle.join().unwrap()
}

pub fn check(require_solutions: bool) -> Result<()> {
    let info_file = InfoFile::parse()?;

    if info_file.exercises.len() > MAX_N_EXERCISES {
        bail!("The maximum number of exercises is {MAX_N_EXERCISES}");
    }

    if cfg!(debug_assertions) {
        // A hack to make `cargo dev check` work when developing Rustlings.
        check_cargo_toml(&info_file.exercises, "dev/Cargo.toml", b"../")?;
    } else {
        check_cargo_toml(&info_file.exercises, "Cargo.toml", b"")?;
    }

    // Leaking is fine since they are used until the end of the program.
    let cmd_runner = Box::leak(Box::new(CmdRunner::build()?));
    let info_file = Box::leak(Box::new(info_file));

    check_exercises(info_file, cmd_runner)?;
    check_solutions(require_solutions, info_file, cmd_runner)?;

    println!("Everything looks fine!");

    Ok(())
}

const SKIP_CHECK_UNSOLVED_HINT: &str = "If this is an introduction exercise that is intended to be already solved, add `skip_check_unsolved = true` to the exercise's metadata in the `info.toml` file";
