use std::env;
use std::ffi::OsString;
use std::hash::DefaultHasher;
use std::hash::Hash;
use std::hash::Hasher;
use std::path::Path;
use std::path::PathBuf;
use std::process::Command;
use std::process::ExitCode;

const TOOLCHAIN_CHANNEL: &str = "nightly-2025-09-18";
#[cfg(target_os = "linux")]
const TOOLCHAIN_TRIPLE: &str = "x86_64-unknown-linux-gnu";
#[cfg(all(target_os = "macos", target_arch = "aarch64"))]
const TOOLCHAIN_TRIPLE: &str = "aarch64-apple-darwin";
#[cfg(all(target_os = "macos", target_arch = "x86_64"))]
const TOOLCHAIN_TRIPLE: &str = "x86_64-apple-darwin";
#[cfg(target_os = "windows")]
const TOOLCHAIN_TRIPLE: &str = "x86_64-pc-windows-msvc";

fn main() -> ExitCode {
    match run() {
        Ok(code) => code,
        Err(err) => {
            eprintln!("{err}");
            ExitCode::from(1)
        }
    }
}

fn run() -> Result<ExitCode, String> {
    let manifest = env::var("ARGUMENT_COMMENT_LINT_MANIFEST")
        .map_err(|_| "ARGUMENT_COMMENT_LINT_MANIFEST must be set".to_string())?;
    let workspace_dir = env::current_dir().map_err(|err| format!("failed to get cwd: {err}"))?;
    let wrapper = find_repo_root(&workspace_dir)?
        .join("tools")
        .join("argument-comment-lint")
        .join("run-prebuilt-linter.py");

    let python = if cfg!(windows) { "python" } else { "python3" };
    let mut command = Command::new(python);
    command.arg(&wrapper);
    command.arg("--manifest-path");
    command.arg(&manifest);

    // Keep Linux on the narrower target set for now to match the current CI
    // rollout, while macOS and Windows continue to exercise all targets.
    if cfg!(target_os = "linux") {
        command.args(["--", "--lib", "--bins"]);
    }

    if env::var_os("CARGO_TARGET_DIR").is_none() {
        command.env("CARGO_TARGET_DIR", shared_target_dir(&workspace_dir));
    }

    command.env("RUSTUP_TOOLCHAIN", TOOLCHAIN_CHANNEL);
    command.env("RUSTUP_AUTO_INSTALL", "0");
    if env::var_os("RUSTUP_HOME").is_none()
        && let Some(rustup_home) = infer_rustup_home()
    {
        command.env("RUSTUP_HOME", rustup_home);
    }

    let status = command
        .status()
        .map_err(|err| format!("failed to execute {python}: {err}"))?;
    Ok(status
        .code()
        .and_then(|code| u8::try_from(code).ok())
        .map_or_else(|| ExitCode::from(1), ExitCode::from))
}

fn find_repo_root(cwd: &Path) -> Result<&Path, String> {
    if cwd
        .join("tools")
        .join("argument-comment-lint")
        .join("run-prebuilt-linter.py")
        .is_file()
    {
        return Ok(cwd);
    }

    let Some(parent) = cwd.parent() else {
        return Err(format!(
            "argument-comment wrapper not found relative to {}",
            cwd.display()
        ));
    };
    if parent
        .join("tools")
        .join("argument-comment-lint")
        .join("run-prebuilt-linter.py")
        .is_file()
    {
        return Ok(parent);
    }

    Err(format!(
        "argument-comment wrapper not found relative to {}",
        cwd.display()
    ))
}

fn shared_target_dir(workspace_dir: &Path) -> PathBuf {
    let namespace = if let Some(run_id) = env::var_os("GITHUB_RUN_ID") {
        let mut namespace = run_id;
        if let Some(run_attempt) = env::var_os("GITHUB_RUN_ATTEMPT") {
            namespace.push("-");
            namespace.push(run_attempt);
        }
        namespace
    } else {
        let mut hasher = DefaultHasher::new();
        workspace_dir.hash(&mut hasher);
        OsString::from(format!("{:016x}", hasher.finish()))
    };

    env::temp_dir()
        .join("argument-comment-lint")
        .join(namespace)
        .join(format!("{TOOLCHAIN_CHANNEL}-{TOOLCHAIN_TRIPLE}"))
}

fn infer_rustup_home() -> Option<OsString> {
    if let Some(rustup_home) = env::var_os("RUSTUP_HOME") {
        return Some(rustup_home);
    }

    if let Some(cargo_home) = env::var_os("CARGO_HOME")
        && let Some(home_dir) = Path::new(&cargo_home).parent()
    {
        let rustup_home = home_dir.join(".rustup");
        if rustup_home.is_dir() {
            return Some(rustup_home.into_os_string());
        }
    }

    for var in ["HOME", "USERPROFILE"] {
        if let Some(home) = env::var_os(var) {
            let rustup_home = Path::new(&home).join(".rustup");
            if rustup_home.is_dir() {
                return Some(rustup_home.into_os_string());
            }
        }
    }

    None
}