use std::{borrow::Cow, env};

use crate::spec::{cvs, FramePointer, LldFlavor, SplitDebuginfo, TargetOptions};

pub fn opts(os: &'static str) -> TargetOptions {
    // ELF TLS is only available in macOS 10.7+. If you try to compile for 10.6
    // either the linker will complain if it is used or the binary will end up
    // segfaulting at runtime when run on 10.6. Rust by default supports macOS
    // 10.7+, but there is a standard environment variable,
    // MACOSX_DEPLOYMENT_TARGET, which is used to signal targeting older
    // versions of macOS. For example compiling on 10.10 with
    // MACOSX_DEPLOYMENT_TARGET set to 10.6 will cause the linker to generate
    // warnings about the usage of ELF TLS.
    //
    // Here we detect what version is being requested, defaulting to 10.7. ELF
    // TLS is flagged as enabled if it looks to be supported. The architecture
    // only matters for default deployment target which is 11.0 for ARM64 and
    // 10.7 for everything else.
    let has_thread_local = macos_deployment_target("x86_64") >= (10, 7);

    TargetOptions {
        os: os.into(),
        vendor: "apple".into(),
        // macOS has -dead_strip, which doesn't rely on function_sections
        function_sections: false,
        dynamic_linking: true,
        linker_is_gnu: false,
        executables: true,
        families: cvs!["unix"],
        is_like_osx: true,
        dwarf_version: Some(2),
        frame_pointer: FramePointer::Always,
        has_rpath: true,
        dll_suffix: ".dylib".into(),
        archive_format: "darwin".into(),
        has_thread_local,
        abi_return_struct_as_int: true,
        emit_debug_gdb_scripts: false,
        eh_frame_header: false,
        lld_flavor: LldFlavor::Ld64,

        // The historical default for macOS targets is to run `dsymutil` which
        // generates a packed version of debuginfo split from the main file.
        split_debuginfo: SplitDebuginfo::Packed,

        // This environment variable is pretty magical but is intended for
        // producing deterministic builds. This was first discovered to be used
        // by the `ar` tool as a way to control whether or not mtime entries in
        // the archive headers were set to zero or not. It appears that
        // eventually the linker got updated to do the same thing and now reads
        // this environment variable too in recent versions.
        //
        // For some more info see the commentary on #47086
        link_env: Cow::Borrowed(&[(Cow::Borrowed("ZERO_AR_DATE"), Cow::Borrowed("1"))]),

        ..Default::default()
    }
}

fn deployment_target(var_name: &str) -> Option<(u32, u32)> {
    let deployment_target = env::var(var_name).ok();
    deployment_target
        .as_ref()
        .and_then(|s| s.split_once('.'))
        .and_then(|(a, b)| a.parse::<u32>().and_then(|a| b.parse::<u32>().map(|b| (a, b))).ok())
}

fn macos_default_deployment_target(arch: &str) -> (u32, u32) {
    if arch == "arm64" { (11, 0) } else { (10, 7) }
}

fn macos_deployment_target(arch: &str) -> (u32, u32) {
    deployment_target("MACOSX_DEPLOYMENT_TARGET")
        .unwrap_or_else(|| macos_default_deployment_target(arch))
}

pub fn macos_llvm_target(arch: &str) -> String {
    let (major, minor) = macos_deployment_target(arch);
    format!("{}-apple-macosx{}.{}.0", arch, major, minor)
}

pub fn macos_link_env_remove() -> Vec<Cow<'static, str>> {
    let mut env_remove = Vec::with_capacity(2);
    // Remove the `SDKROOT` environment variable if it's clearly set for the wrong platform, which
    // may occur when we're linking a custom build script while targeting iOS for example.
    if let Ok(sdkroot) = env::var("SDKROOT") {
        if sdkroot.contains("iPhoneOS.platform") || sdkroot.contains("iPhoneSimulator.platform") {
            env_remove.push("SDKROOT".into())
        }
    }
    // Additionally, `IPHONEOS_DEPLOYMENT_TARGET` must not be set when using the Xcode linker at
    // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld",
    // although this is apparently ignored when using the linker at "/usr/bin/ld".
    env_remove.push("IPHONEOS_DEPLOYMENT_TARGET".into());
    env_remove
}

fn ios_deployment_target() -> (u32, u32) {
    deployment_target("IPHONEOS_DEPLOYMENT_TARGET").unwrap_or((7, 0))
}

pub fn ios_llvm_target(arch: &str) -> String {
    // Modern iOS tooling extracts information about deployment target
    // from LC_BUILD_VERSION. This load command will only be emitted when
    // we build with a version specific `llvm_target`, with the version
    // set high enough. Luckily one LC_BUILD_VERSION is enough, for Xcode
    // to pick it up (since std and core are still built with the fallback
    // of version 7.0 and hence emit the old LC_IPHONE_MIN_VERSION).
    let (major, minor) = ios_deployment_target();
    format!("{}-apple-ios{}.{}.0", arch, major, minor)
}

pub fn ios_sim_llvm_target(arch: &str) -> String {
    let (major, minor) = ios_deployment_target();
    format!("{}-apple-ios{}.{}.0-simulator", arch, major, minor)
}
