use std::env;
use std::ffi::OsString;
use std::fs::{self, File};
use std::io::{self, BufRead, Write};
use std::ops::Not;
use std::path::{Path, PathBuf};
use std::process::Command;

use rustc_version::VersionMeta;

const XARGO_MIN_VERSION: (u32, u32, u32) = (0, 3, 22);

const CARGO_MIRI_HELP: &str = r#"Interprets bin crates and tests in Miri

Usage:
    cargo miri [subcommand] [<cargo options>...] [--] [<miri options>...] [--] [<program/test suite options>...]

Subcommands:
    run                      Run binaries (default)
    test                     Run tests
    setup                    Only perform automatic setup, but without asking questions (for getting a proper libstd)

Common options:
    -h, --help               Print this message
    --features               Features to compile for the package
    -V, --version            Print version info and exit

Other [options] are the same as `cargo check`.  Everything after the first "--" is
passed verbatim to Miri, which will pass everything after the second "--" verbatim
to the interpreted program.

Examples:
    cargo miri run -- -Zmiri-disable-stacked-borrows
    cargo miri test -- -- test-suite-filter
"#;

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
enum MiriCommand {
    Run,
    Test,
    Setup,
}

fn show_help() {
    println!("{}", CARGO_MIRI_HELP);
}

fn show_version() {
    println!(
        "miri {} ({} {})",
        env!("CARGO_PKG_VERSION"),
        env!("VERGEN_SHA_SHORT"),
        env!("VERGEN_COMMIT_DATE")
    );
}

fn show_error(msg: String) -> ! {
    eprintln!("fatal error: {}", msg);
    std::process::exit(1)
}

// Determines whether a `--flag` is present.
fn has_arg_flag(name: &str) -> bool {
    let mut args = std::env::args().take_while(|val| val != "--");
    args.any(|val| val == name)
}

/// Gets the value of a `--flag`.
fn get_arg_flag_value(name: &str) -> Option<String> {
    // Stop searching at `--`.
    let mut args = std::env::args().take_while(|val| val != "--");
    loop {
        let arg = match args.next() {
            Some(arg) => arg,
            None => return None,
        };
        if !arg.starts_with(name) {
            continue;
        }
        // Strip leading `name`.
        let suffix = &arg[name.len()..];
        if suffix.is_empty() {
            // This argument is exactly `name`; the next one is the value.
            return args.next();
        } else if suffix.starts_with('=') {
            // This argument is `name=value`; get the value.
            // Strip leading `=`.
            return Some(suffix[1..].to_owned());
        }
    }
}

/// Returns the path to the `miri` binary
fn find_miri() -> PathBuf {
    if let Some(path) = env::var_os("MIRI") {
        return path.into();
    }
    let mut path = std::env::current_exe().expect("current executable path invalid");
    path.set_file_name("miri");
    path
}

fn miri() -> Command {
    Command::new(find_miri())
}

fn version_info() -> VersionMeta {
    VersionMeta::for_command(miri()).expect("failed to determine underlying rustc version of Miri")
}

fn cargo() -> Command {
    Command::new(env::var_os("CARGO").unwrap_or_else(|| OsString::from("cargo")))
}

fn xargo_check() -> Command {
    Command::new(env::var_os("XARGO_CHECK").unwrap_or_else(|| OsString::from("xargo-check")))
}

fn xargo_version() -> Option<(u32, u32, u32)> {
    let out = xargo_check().arg("--version").output().ok()?;
    if !out.status.success() {
        return None;
    }
    // Parse output. The first line looks like "xargo 0.3.12 (b004f1c 2018-12-13)".
    let line = out
        .stderr
        .lines()
        .nth(0)
        .expect("malformed `xargo --version` output: not at least one line")
        .expect("malformed `xargo --version` output: error reading first line");
    let (name, version) = {
        let mut split = line.split(' ');
        (
            split.next().expect("malformed `xargo --version` output: empty"),
            split.next().expect("malformed `xargo --version` output: not at least two words"),
        )
    };
    if name != "xargo" {
        // This is some fork of xargo
        return None;
    }
    let mut version_pieces = version.split('.');
    let major = version_pieces
        .next()
        .expect("malformed `xargo --version` output: not a major version piece")
        .parse()
        .expect("malformed `xargo --version` output: major version is not an integer");
    let minor = version_pieces
        .next()
        .expect("malformed `xargo --version` output: not a minor version piece")
        .parse()
        .expect("malformed `xargo --version` output: minor version is not an integer");
    let patch = version_pieces
        .next()
        .expect("malformed `xargo --version` output: not a patch version piece")
        .parse()
        .expect("malformed `xargo --version` output: patch version is not an integer");
    if !version_pieces.next().is_none() {
        panic!("malformed `xargo --version` output: more than three pieces in version");
    }
    Some((major, minor, patch))
}

fn ask_to_run(mut cmd: Command, ask: bool, text: &str) {
    // Disable interactive prompts in CI (GitHub Actions, Travis, AppVeyor, etc).
    // Azure doesn't set `CI` though (nothing to see here, just Microsoft being Microsoft),
    // so we also check their `TF_BUILD`.
    let is_ci = env::var_os("CI").is_some() || env::var_os("TF_BUILD").is_some();
    if ask && !is_ci {
        let mut buf = String::new();
        print!("I will run `{:?}` to {}. Proceed? [Y/n] ", cmd, text);
        io::stdout().flush().unwrap();
        io::stdin().read_line(&mut buf).unwrap();
        match buf.trim().to_lowercase().as_ref() {
            // Proceed.
            "" | "y" | "yes" => {}
            "n" | "no" => show_error(format!("Aborting as per your request")),
            a => show_error(format!("I do not understand `{}`", a)),
        };
    } else {
        println!("Running `{:?}` to {}.", cmd, text);
    }

    if cmd.status().expect(&format!("failed to execute {:?}", cmd)).success().not() {
        show_error(format!("Failed to {}", text));
    }
}

/// Performs the setup required to make `cargo miri` work: Getting a custom-built libstd. Then sets
/// `MIRI_SYSROOT`. Skipped if `MIRI_SYSROOT` is already set, in which case we expect the user has
/// done all this already.
fn setup(subcommand: MiriCommand) {
    if std::env::var_os("MIRI_SYSROOT").is_some() {
        if subcommand == MiriCommand::Setup {
            println!("WARNING: MIRI_SYSROOT already set, not doing anything.")
        }
        return;
    }

    // Subcommands other than `setup` will do a setup if necessary, but
    // interactively confirm first.
    let ask_user = subcommand != MiriCommand::Setup;

    // First, we need xargo.
    if xargo_version().map_or(true, |v| v < XARGO_MIN_VERSION) {
        if std::env::var_os("XARGO_CHECK").is_some() {
            // The user manually gave us a xargo binary; don't do anything automatically.
            show_error(format!("Your xargo is too old; please upgrade to the latest version"))
        }
        let mut cmd = cargo();
        cmd.args(&["install", "xargo", "-f"]);
        ask_to_run(cmd, ask_user, "install a recent enough xargo");
    }

    // Determine where the rust sources are located.  `XARGO_RUST_SRC` env var trumps everything.
    let rust_src = match std::env::var_os("XARGO_RUST_SRC") {
        Some(path) => {
            let path = PathBuf::from(path);
            // Make path absolute if possible.
            path.canonicalize().unwrap_or(path)
        }
        None => {
            // Check for `rust-src` rustup component.
            let sysroot = miri()
                .args(&["--print", "sysroot"])
                .output()
                .expect("failed to determine sysroot")
                .stdout;
            let sysroot = std::str::from_utf8(&sysroot).unwrap();
            let sysroot = Path::new(sysroot.trim_end_matches('\n'));
            // Check for `$SYSROOT/lib/rustlib/src/rust/library`; test if that contains `std/Cargo.toml`.
            let rustup_src =
                sysroot.join("lib").join("rustlib").join("src").join("rust").join("library");
            if !rustup_src.join("std").join("Cargo.toml").exists() {
                // Ask the user to install the `rust-src` component, and use that.
                let mut cmd = Command::new("rustup");
                cmd.args(&["component", "add", "rust-src"]);
                ask_to_run(
                    cmd,
                    ask_user,
                    "install the `rust-src` component for the selected toolchain",
                );
            }
            rustup_src
        }
    };
    if !rust_src.exists() {
        show_error(format!("Given Rust source directory `{}` does not exist.", rust_src.display()));
    }

    // Next, we need our own libstd. Prepare a xargo project for that purpose.
    // We will do this work in whatever is a good cache dir for this platform.
    let dirs = directories::ProjectDirs::from("org", "rust-lang", "miri").unwrap();
    let dir = dirs.cache_dir();
    if !dir.exists() {
        fs::create_dir_all(&dir).unwrap();
    }
    // The interesting bit: Xargo.toml
    File::create(dir.join("Xargo.toml"))
        .unwrap()
        .write_all(
            br#"
[dependencies.std]
default_features = false
# We need the `panic_unwind` feature because we use the `unwind` panic strategy.
# Using `abort` works for libstd, but then libtest will not compile.
features = ["panic_unwind"]

[dependencies.test]
"#,
        )
        .unwrap();
    // The boring bits: a dummy project for xargo.
    // FIXME: With xargo-check, can we avoid doing this?
    File::create(dir.join("Cargo.toml"))
        .unwrap()
        .write_all(
            br#"
[package]
name = "miri-xargo"
description = "A dummy project for building libstd with xargo."
version = "0.0.0"

[lib]
path = "lib.rs"
"#,
        )
        .unwrap();
    File::create(dir.join("lib.rs")).unwrap();

    // Determine architectures.
    // We always need to set a target so rustc bootstrap can tell apart host from target crates.
    let host = version_info().host;
    let target = get_arg_flag_value("--target");
    let target = target.as_ref().unwrap_or(&host);
    // Now invoke xargo.
    let mut command = xargo_check();
    command.arg("check").arg("-q");
    command.arg("--target").arg(target);
    command.current_dir(&dir);
    command.env("XARGO_HOME", &dir);
    command.env("XARGO_RUST_SRC", &rust_src);
    // Use Miri as rustc to build a libstd compatible with us (and use the right flags).
    // However, when we are running in bootstrap, we cannot just overwrite `RUSTC`,
    // because we still need bootstrap to distinguish between host and target crates.
    // In that case we overwrite `RUSTC_REAL` instead which determines the rustc used
    // for target crates.
    if env::var_os("RUSTC_STAGE").is_some() {
        command.env("RUSTC_REAL", find_miri());
    } else {
        command.env("RUSTC", find_miri());
    }
    command.env("MIRI_BE_RUSTC", "1");
    // Make sure there are no other wrappers or flags getting in our way
    // (Cc https://github.com/rust-lang/miri/issues/1421).
    // This is consistent with normal `cargo build` that does not apply `RUSTFLAGS`
    // to the sysroot either.
    command.env_remove("RUSTC_WRAPPER");
    command.env_remove("RUSTFLAGS");
    // Finally run it!
    if command.status().expect("failed to run xargo").success().not() {
        show_error(format!("Failed to run xargo"));
    }

    // That should be it! But we need to figure out where xargo built stuff.
    // Unfortunately, it puts things into a different directory when the
    // architecture matches the host.
    let sysroot = if target == &host { dir.join("HOST") } else { PathBuf::from(dir) };
    std::env::set_var("MIRI_SYSROOT", &sysroot); // pass the env var to the processes we spawn, which will turn it into "--sysroot" flags
    // Figure out what to print.
    let print_sysroot = subcommand == MiriCommand::Setup && has_arg_flag("--print-sysroot"); // whether we just print the sysroot path
    if print_sysroot {
        // Print just the sysroot and nothing else; this way we do not need any escaping.
        println!("{}", sysroot.display());
    } else if subcommand == MiriCommand::Setup {
        println!("A libstd for Miri is now available in `{}`.", sysroot.display());
    }
}

fn phase_cargo_miri(mut args: env::Args) {
    // Require a subcommand before any flags.
    // We cannot know which of those flags take arguments and which do not,
    // so we cannot detect subcommands later.
    let subcommand = match args.next().as_deref() {
        Some("test") => MiriCommand::Test,
        Some("run") => MiriCommand::Run,
        Some("setup") => MiriCommand::Setup,
        // Invalid command.
        None => show_error(format!("`cargo miri` must be immediately followed by `test`, `run`, or `setup`.")),
        Some(s) => show_error(format!("unknown command `{}`", s)),
    };
    let verbose = has_arg_flag("-v");

    // We always setup.
    setup(subcommand);

    // Invoke actual cargo for the job, but with different flags.
    let miri_path = std::env::current_exe().expect("current executable path invalid");
    let cargo_cmd = match subcommand {
        MiriCommand::Test => "test",
        MiriCommand::Run => "run",
        MiriCommand::Setup => return, // `cargo miri setup` stops here.
    };
    let mut cmd = cargo();
    cmd.arg(cargo_cmd);

    // Make sure we know the build target, and cargo does, too.
    // This is needed to make the `CARGO_TARGET_*_RUNNER` env var do something,
    // and it later helps us detect which crates are proc-macro/build-script
    // (host crates) and which crates are needed for the program itself.
    let target = if let Some(target) = get_arg_flag_value("--target") {
        target
    } else {
        // No target given. Pick default and tell cargo about it.
        let host = version_info().host;
        cmd.arg("--target");
        cmd.arg(&host);
        host
    };

    // Forward all further arguments.
    cmd.args(args);

    // Set `RUSTC_WRAPPER` to ourselves.  Cargo will prepend that binary to its usual invocation,
    // i.e., the first argument is `rustc` -- which is what we use in `main` to distinguish
    // the two codepaths. (That extra argument is why we prefer this over setting `RUSTC`.)
    if env::var_os("RUSTC_WRAPPER").is_some() {
        println!("WARNING: Ignoring `RUSTC_WRAPPER` environment variable, Miri does not support wrapping.");
    }
    cmd.env("RUSTC_WRAPPER", &miri_path);
    if verbose {
        eprintln!("+ RUSTC_WRAPPER={:?}", miri_path);
    }

    // Set the runner for the current target to us as well, so we can interpret the binaries.
    let runner_env_name = format!("CARGO_TARGET_{}_RUNNER", target.to_uppercase().replace('-', "_"));
    cmd.env(runner_env_name, &miri_path);

    // Run cargo.
    if verbose {
        cmd.env("MIRI_VERBOSE", ""); // this makes `inside_cargo_rustc` verbose.
        eprintln!("+ {:?}", cmd);
    }
    let exit_status =
        cmd.spawn().expect("could not run cargo").wait().expect("failed to wait for cargo?");

    std::process::exit(exit_status.code().unwrap_or(-1))
}

fn phase_cargo_rustc(mut args: env::Args) {
    /// Determines if we are being invoked (as rustc) to build a crate for
    /// the "target" architecture, in contrast to the "host" architecture.
    /// Host crates are for build scripts and proc macros and still need to
    /// be built like normal; target crates need to be built for or interpreted
    /// by Miri.
    ///
    /// Currently, we detect this by checking for "--target=", which is
    /// never set for host crates. This matches what rustc bootstrap does,
    /// which hopefully makes it "reliable enough". This relies on us always
    /// invoking cargo itself with `--target`, which `in_cargo_miri` ensures.
    fn is_target_crate() -> bool {
        get_arg_flag_value("--target").is_some()
    }

    /// Returns whether or not Cargo invoked the wrapper (this binary) to compile
    /// the final, binary crate (either a test for 'cargo test', or a binary for 'cargo run')
    /// Cargo does not give us this information directly, so we need to check
    /// various command-line flags.
    fn is_runnable_crate() -> bool {
        let is_bin = get_arg_flag_value("--crate-type").as_deref() == Some("bin");
        let is_test = has_arg_flag("--test");
        let print = get_arg_flag_value("--print").is_some();
        (is_bin || is_test) && !print
    }

    let verbose = std::env::var_os("MIRI_VERBOSE").is_some();
    let target_crate = is_target_crate();

    if target_crate && is_runnable_crate() {
        // This is the binary or test crate that we want to interpret under Miri.
        // But we cannot run it here, as cargo invoked us as a compiler -- our stdin and stdout are not
        // like we want them.
        // Instead of compiling, we write JSON into the output file with all the relevant command-line flags
        // and environment variables; this is sued alter when cargo calls us again in the CARGO_TARGET_RUNNER phase.
        let filename = format!(
            "{}/{}{}",
            get_arg_flag_value("--out-dir").unwrap(),
            get_arg_flag_value("--crate-name").unwrap(),
            // This is technically a `-C` flag but the prefix seems unique enough...
            // (and cargo passes this before the filename so it should be unique)
            get_arg_flag_value("extra-filename").unwrap_or(String::new()),
        );
        eprintln!("Miri is supposed to run {}", filename);
        return;
    }

    let mut cmd = miri();
    // Forward arguments.
    cmd.args(args);
    // FIXME: Make the build check-only!

    // We make sure to only specify our custom Xargo sysroot for target crates - that is,
    // crates which are needed for interpretation by Miri. proc-macros and build scripts
    // should use the default sysroot.
    if target_crate {
        let sysroot =
            env::var_os("MIRI_SYSROOT").expect("The wrapper should have set MIRI_SYSROOT");
        cmd.arg("--sysroot");
        cmd.arg(sysroot);
    }

    // We want to compile, not interpret. We still use Miri to make sure the compiler version etc
    // are the exact same as what is used for interpretation.
    cmd.env("MIRI_BE_RUSTC", "1");

    // Run it.
    if verbose {
        eprintln!("+ {:?}", cmd);
    }
    match cmd.status() {
        Ok(exit) =>
            if !exit.success() {
                std::process::exit(exit.code().unwrap_or(42));
            },
        Err(e) => panic!("error running {:?}:\n{:?}", cmd, e),
    }
}

fn phase_cargo_runner(binary: &str, args: env::Args) {
    eprintln!("Asked to execute {}, args: {:?}", binary, args.collect::<Vec<_>>());
}

fn main() {
    // Check for version and help flags even when invoked as `cargo-miri`.
    if has_arg_flag("--help") || has_arg_flag("-h") {
        show_help();
        return;
    }
    if has_arg_flag("--version") || has_arg_flag("-V") {
        show_version();
        return;
    }

    let mut args = std::env::args();
    // Skip binary name.
    args.next().unwrap();

    // Dispatch to `cargo-miri` phase. There are three phases:
    // - When we are called via `cargo miri`, we run as the frontend and invoke the underlying
    //   cargo. We set RUSTC_WRAPPER and CARGO_TARGET_RUNNER to ourselves.
    // - When we are executed due to RUSTC_WRAPPER, we build crates or store the flags of
    //   binary crates for later interpretation.
    // - When we are executed due to CARGO_TARGET_RUNNER, we start interpretation based on the
    //   flags that were stored earlier.
    match &*args.next().unwrap() {
        "miri" => phase_cargo_miri(args),
        "rustc" => phase_cargo_rustc(args),
        binary => phase_cargo_runner(binary, args),
    }
}