use std::env;
use std::process::Command;
use std::str;

// List of cfgs this build script is allowed to set. The list is needed to support check-cfg, as we
// need to know all the possible cfgs that this script will set. If you need to set another cfg
// make sure to add it to this list as well.
const ALLOWED_CFGS: &'static [&'static str] = &[
    "freebsd10",
    "freebsd11",
    "freebsd12",
    "freebsd13",
    "freebsd14",
    "libc_align",
    "libc_cfg_target_vendor",
    "libc_const_extern_fn",
    "libc_const_extern_fn_unstable",
    "libc_const_size_of",
    "libc_core_cvoid",
    "libc_deny_warnings",
    "libc_int128",
    "libc_long_array",
    "libc_non_exhaustive",
    "libc_packedN",
    "libc_priv_mod_use",
    "libc_ptr_addr_of",
    "libc_thread_local",
    "libc_underscore_const_names",
    "libc_union",
];

// Extra values to allow for check-cfg.
const CHECK_CFG_EXTRA: &'static [(&'static str, &'static [&'static str])] = &[
    ("target_os", &["switch", "aix", "ohos"]),
    ("target_env", &["illumos", "wasi", "aix", "ohos"]),
    ("target_arch", &["loongarch64"]),
];

fn main() {
    // Avoid unnecessary re-building.
    println!("cargo:rerun-if-changed=build.rs");

    let (rustc_minor_ver, is_nightly) = rustc_minor_nightly();
    let rustc_dep_of_std = env::var("CARGO_FEATURE_RUSTC_DEP_OF_STD").is_ok();
    let align_cargo_feature = env::var("CARGO_FEATURE_ALIGN").is_ok();
    let const_extern_fn_cargo_feature = env::var("CARGO_FEATURE_CONST_EXTERN_FN").is_ok();
    let libc_ci = env::var("LIBC_CI").is_ok();
    let libc_check_cfg = env::var("LIBC_CHECK_CFG").is_ok();

    if env::var("CARGO_FEATURE_USE_STD").is_ok() {
        println!(
            "cargo:warning=\"libc's use_std cargo feature is deprecated since libc 0.2.55; \
             please consider using the `std` cargo feature instead\""
        );
    }

    // The ABI of libc used by libstd is backward compatible with FreeBSD 10.
    // The ABI of libc from crates.io is backward compatible with FreeBSD 11.
    //
    // On CI, we detect the actual FreeBSD version and match its ABI exactly,
    // running tests to ensure that the ABI is correct.
    match which_freebsd() {
        Some(10) if libc_ci || rustc_dep_of_std => set_cfg("freebsd10"),
        Some(11) if libc_ci => set_cfg("freebsd11"),
        Some(12) if libc_ci => set_cfg("freebsd12"),
        Some(13) if libc_ci => set_cfg("freebsd13"),
        Some(14) if libc_ci => set_cfg("freebsd14"),
        Some(_) | None => set_cfg("freebsd11"),
    }

    // On CI: deny all warnings
    if libc_ci {
        set_cfg("libc_deny_warnings");
    }

    // Rust >= 1.15 supports private module use:
    if rustc_minor_ver >= 15 || rustc_dep_of_std {
        set_cfg("libc_priv_mod_use");
    }

    // Rust >= 1.19 supports unions:
    if rustc_minor_ver >= 19 || rustc_dep_of_std {
        set_cfg("libc_union");
    }

    // Rust >= 1.24 supports const mem::size_of:
    if rustc_minor_ver >= 24 || rustc_dep_of_std {
        set_cfg("libc_const_size_of");
    }

    // Rust >= 1.25 supports repr(align):
    if rustc_minor_ver >= 25 || rustc_dep_of_std || align_cargo_feature {
        set_cfg("libc_align");
    }

    // Rust >= 1.26 supports i128 and u128:
    if rustc_minor_ver >= 26 || rustc_dep_of_std {
        set_cfg("libc_int128");
    }

    // Rust >= 1.30 supports `core::ffi::c_void`, so libc can just re-export it.
    // Otherwise, it defines an incompatible type to retaining
    // backwards-compatibility.
    if rustc_minor_ver >= 30 || rustc_dep_of_std {
        set_cfg("libc_core_cvoid");
    }

    // Rust >= 1.33 supports repr(packed(N)) and cfg(target_vendor).
    if rustc_minor_ver >= 33 || rustc_dep_of_std {
        set_cfg("libc_packedN");
        set_cfg("libc_cfg_target_vendor");
    }

    // Rust >= 1.40 supports #[non_exhaustive].
    if rustc_minor_ver >= 40 || rustc_dep_of_std {
        set_cfg("libc_non_exhaustive");
    }

    // Rust >= 1.47 supports long array:
    if rustc_minor_ver >= 47 || rustc_dep_of_std {
        set_cfg("libc_long_array");
    }

    if rustc_minor_ver >= 51 || rustc_dep_of_std {
        set_cfg("libc_ptr_addr_of");
    }

    // Rust >= 1.37.0 allows underscores as anonymous constant names.
    if rustc_minor_ver >= 37 || rustc_dep_of_std {
        set_cfg("libc_underscore_const_names");
    }

    // #[thread_local] is currently unstable
    if rustc_dep_of_std {
        set_cfg("libc_thread_local");
    }

    // Rust >= 1.62.0 allows to use `const_extern_fn` for "Rust" and "C".
    if rustc_minor_ver >= 62 {
        set_cfg("libc_const_extern_fn");
    } else {
        // Rust < 1.62.0 requires a crate feature and feature gate.
        if const_extern_fn_cargo_feature {
            if !is_nightly || rustc_minor_ver < 40 {
                panic!("const-extern-fn requires a nightly compiler >= 1.40");
            }
            set_cfg("libc_const_extern_fn_unstable");
            set_cfg("libc_const_extern_fn");
        }
    }

    // check-cfg is a nightly cargo/rustc feature to warn when unknown cfgs are used across the
    // codebase. libc can configure it if the appropriate environment variable is passed. Since
    // rust-lang/rust enforces it, this is useful when using a custom libc fork there.
    //
    // https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#check-cfg
    if libc_check_cfg {
        for cfg in ALLOWED_CFGS {
            println!("cargo:rustc-check-cfg=values({})", cfg);
        }
        for &(name, values) in CHECK_CFG_EXTRA {
            let values = values.join("\",\"");
            println!("cargo:rustc-check-cfg=values({},\"{}\")", name, values);
        }
    }
}

fn rustc_minor_nightly() -> (u32, bool) {
    macro_rules! otry {
        ($e:expr) => {
            match $e {
                Some(e) => e,
                None => panic!("Failed to get rustc version"),
            }
        };
    }

    let rustc = otry!(env::var_os("RUSTC"));
    let output = Command::new(rustc)
        .arg("--version")
        .output()
        .ok()
        .expect("Failed to get rustc version");
    let version = otry!(str::from_utf8(&output.stdout).ok());
    let mut pieces = version.split('.');

    if pieces.next() != Some("rustc 1") {
        panic!("Failed to get rustc version");
    }

    let minor = pieces.next();

    // If `rustc` was built from a tarball, its version string
    // will have neither a git hash nor a commit date
    // (e.g. "rustc 1.39.0"). Treat this case as non-nightly,
    // since a nightly build should either come from CI
    // or a git checkout
    let nightly_raw = otry!(pieces.next()).split('-').nth(1);
    let nightly = nightly_raw
        .map(|raw| raw.starts_with("dev") || raw.starts_with("nightly"))
        .unwrap_or(false);
    let minor = otry!(otry!(minor).parse().ok());

    (minor, nightly)
}

fn which_freebsd() -> Option<i32> {
    let output = std::process::Command::new("freebsd-version").output().ok();
    if output.is_none() {
        return None;
    }
    let output = output.unwrap();
    if !output.status.success() {
        return None;
    }

    let stdout = String::from_utf8(output.stdout).ok();
    if stdout.is_none() {
        return None;
    }
    let stdout = stdout.unwrap();

    match &stdout {
        s if s.starts_with("10") => Some(10),
        s if s.starts_with("11") => Some(11),
        s if s.starts_with("12") => Some(12),
        s if s.starts_with("13") => Some(13),
        s if s.starts_with("14") => Some(14),
        _ => None,
    }
}

fn set_cfg(cfg: &str) {
    if !ALLOWED_CFGS.contains(&cfg) {
        panic!("trying to set cfg {}, but it is not in ALLOWED_CFGS", cfg);
    }
    println!("cargo:rustc-cfg={}", cfg);
}