use std::{
    env,
    fs::{copy, create_dir_all, read_dir, write},
    io, mem,
    path::{Path, PathBuf},
    process::Command,
};
use which::which;

/// Unwraps a Result and panics in a way that prints a nicer error message to the user.
macro_rules! panic_err {
    ($value:expr)                => {{ $value.unwrap_or_else(|err| panic!("{err}")) }};
    ($value:expr, $($arg:expr)+) => {{ $value.unwrap_or_else(|err| panic!("{}: {err}", format_args!($($arg),+))) }};
}

/// Formats arguments in a way that is intended to address environment variables.
macro_rules! env_name {
    ($($arg:expr),+) => {{ format!($($arg),+).replace("-", "_").to_uppercase() }};
}

/// Expands to the value of an environment variable.
macro_rules! env {
    ($($arg:expr),+) => { panic_err!(env::var(env_name!($($arg),+))) };
}

/// Expands to the value of a cargo configuration environment variable.
macro_rules! cfg {
    ($($arg:expr),+) => { env!("CARGO_CFG_{}", format_args!($($arg),+)) };
}

/// Whether a cargo feature is enabled.
macro_rules! feature {
    ($($arg:expr),+) => { env::var_os(env_name!("CARGO_FEATURE_{}", format_args!($($arg),+))).is_some() };
}

fn main() {
    let src_path = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("src");
    let out_path = PathBuf::from(env!("OUT_DIR"));

    panic_err!(
        copy_recursive(&src_path, &out_path),
        "failed to copy luajit source (is the Git submodule initialised?)"
    );

    panic_err!(write(out_path.join(".relver"), get_relver()));
    println!("cargo::rerun-if-changed={}", src_path.display()); // rerun if luajit source changed

    // NOTE: we cannot build bindings without building luajit first (luajit generates some headers)
    build_runtime(&out_path.join("src"));
    build_bindings(&out_path.join("src"));
}

fn get_relver() -> String {
    let out = panic_err!(
        Command::new("git")
            .args(["show", "-s", "--format=%ct"])
            .output(),
        "failed to obtain luajit release version (is the Git command available?)"
    );

    String::from_utf8_lossy(&out.stdout).into()
}

fn copy_recursive(src: impl AsRef<Path>, dst: impl AsRef<Path>) -> io::Result<()> {
    create_dir_all(dst.as_ref())?;

    for entry in read_dir(src)? {
        let entry = entry?;
        if entry.file_name().to_str() == Some(".git") {
            continue;
        }

        let path = dst.as_ref().join(entry.file_name());
        if entry.file_type()?.is_dir() {
            copy_recursive(entry.path(), path)?;
        } else {
            copy(entry.path(), path)?;
        }
    }

    Ok(())
}

fn find_make() -> Command {
    // always use gnu make on bsds
    let name = match parse_target(&env!("HOST")) {
        (_, _, "freebsd" | "openbsd" | "netbsd" | "dragonfly", _) => "gmake",
        _ => "make",
    };

    Command::new(panic_err!(which(name), "failed to find make"))
}

fn find_cc(target: impl AsRef<str>) -> PathBuf {
    let cc = cc::Build::new().target(target.as_ref()).get_compiler();
    let path = panic_err!(which(cc.path()), "failed to find cc");
    path.to_str().unwrap().into()
}

fn parse_target(target: &str) -> (&str, &str, &str, Option<&str>) {
    let mut i = target.splitn(4, "-");
    let arch = i.next().unwrap();
    let vendor = i.next().unwrap();
    let os = i.next().unwrap();
    let env = i.next();
    (arch, vendor, os, env)
}

fn build_runtime(src_path: &Path) {
    let host = env!("HOST"); // host triplet
    let host_cc = find_cc(&host).to_str().unwrap().to_owned();
    let host_ptr_width = 8 * mem::size_of::<usize>();

    let target = env!("TARGET"); // target triplet
    let target_cc = find_cc(&target).to_str().unwrap().to_owned();
    // let target_features: HashSet<&str> = HashSet::from_iter(cfg!("target_feature").split(","));
    let target_ptr_width: usize = cfg!("target_pointer_width").parse().unwrap();

    let mut make = find_make();

    make.current_dir(src_path)
        .env_clear()
        .arg("-e")
        .env("PATH", env!("PATH"))
        .env("MAKEFLAGS", env!("CARGO_MAKEFLAGS"))
        .env("BUILDMODE", "static");

    let ccopt = vec![format!("-O{} -fomit-frame-pointer", env!("OPT_LEVEL"))]; // propagate opt_level
    let mut ccdebug = vec![];
    let mut xcflags = vec![];

    if env!("OPT_LEVEL") == "0" {
        ccdebug.push("-g"); // generate debug information
        xcflags.push("-DLUAJIT_USE_GDBJIT"); // gdb support
        xcflags.push("-DLUA_USE_APICHECK -DLUA_USE_ASSERT"); // enable assertions
    }

    xcflags.push(if feature!("unwind") {
        "-DLUAJIT_UNWIND_EXTERNAL -funwind-tables" // external frame unwinding (C++ exceptions)
    } else {
        "-DLUAJIT_UNWIND_INTERNAL" // internal frame unwinding (setjmp/longjmp)
    });

    if !feature!("jit") {
        xcflags.push("-DLUAJIT_DISABLE_JIT");
    }

    if !feature!("ffi") {
        xcflags.push("-DLUAJIT_DISABLE_FFI");
    }

    if !feature!("bundled-alloc") {
        xcflags.push("-DLUAJIT_USE_SYSMALLOC"); // using system malloc disables the bundled allocator
    }

    if feature!("lua52") {
        xcflags.push("-DLUAJIT_ENABLE_LUA52COMPAT");
    }

    // host toolchain config
    match (host_ptr_width, target_ptr_width) {
        (64, 64) | (32, 32) => make.env("HOST_CC", &host_cc),
        (64, 32) => make.env("HOST_CC", format!("{host_cc} -m32")),
        (n, m) if n != m => panic!("cannot cross-compile on {n}-bit host for {m}-bit target"),
        (n, _) => panic!("unsupported {n}-bit architecture"),
    };

    // target system config
    match cfg!("target_os").as_str() {
        "linux" | "android" => make.env("TARGET_SYS", "Linux"),
        "windows" => make.env("TARGET_SYS", "Windows"),
        "macos" => make.env("TARGET_SYS", "Darwin").env(
            "MACOSX_DEPLOYMENT_TARGET",
            env::var("MACOSX_DEPLOYMENT_TARGET").as_deref().unwrap_or(
                match cfg!("target_arch").as_str() {
                    "x86_64" | "x86_64h" => "10.12",
                    "aarch64" | "arm64" | "arm64e" => "11.0",
                    arch => panic!("unsupported MacOS target architecture '{arch}'"),
                },
            ),
        ),
        "ios" => make.env("TARGET_SYS", "iOS"),
        "solaris" => make.env("TARGET_SYS", "SunOS"),
        _ => make.env("TARGET_SYS", "Other"),
    };

    // target toolchain config
    if let Some(cross) = target_cc.strip_suffix("gcc") {
        make.env("CC", "gcc").env("CROSS", cross);
    } else if let Some(cross) = target_cc.strip_suffix("clang") {
        make.env("CC", "clang").env("CROSS", cross);
    } else {
        let path = Path::new(&target_cc);
        make.env("CC", path.file_name().unwrap())
            .env("CROSS", format!("{}/", path.parent().unwrap().display()));
    }

    // propagate linker config
    if let Ok(path) = env::var("RUSTC_LINKER") {
        make.env("TARGET_LD", panic_err!(which(path), "failed to find ld"));
    }

    make.env("CCOPT", ccopt.join(" "))
        .env("CCDEBUG", ccdebug.join(" "))
        .env("XCFLAGS", xcflags.join(" "));

    if target == host {
        println!("--- begin compile for {target}:");
    } else {
        println!("--- begin cross-compile on {host} for {target}:");
    }

    println!("{make:?}");
    let status = panic_err!(make.status(), "failed to execute make");
    (!status.success()).then(|| panic!("failed to compile luajit: {status}: {make:?}"));

    println!(
        "cargo::rustc-env=LUAJIT_SYS_JITLIB={}",
        src_path.join("jit").display(),
    );

    if feature!("runtime") {
        println!("cargo::rustc-link-search=native={}", src_path.display());
        println!("cargo::rustc-link-lib=static=luajit");
    }
}

fn build_bindings(src_path: &Path) {
    let mut clang_args = vec![format!("--target={}", env!("TARGET"))];
    let abi = if feature!("unwind") {
        clang_args.push("-fexceptions".into());
        bindgen::Abi::CUnwind
    } else {
        clang_args.push("-fno-exceptions".into());
        bindgen::Abi::C
    };

    let mut bindgen = bindgen::builder()
        .clang_args(clang_args)
        .allowlist_item(r"^(lua|LUA).*_.+$")
        .formatter(bindgen::Formatter::None)
        .default_macro_constant_type(bindgen::MacroTypeVariation::Signed)
        .generate_cstr(true)
        .override_abi(abi, ".*");

    for header in ["lua.h", "lualib.h", "lauxlib.h", "luaconf.h", "luajit.h"] {
        bindgen = bindgen.header(src_path.join(header).to_str().unwrap());
    }

    let path = src_path.join("bindgen.rs");
    panic_err!(panic_err!(bindgen.generate(), "failed to generate bindings").write_to_file(&path));
    println!("cargo::rustc-env=LUAJIT_SYS_BINDGEN={}", path.display());
}