use std::env;
use std::ffi::OsString;
use std::fmt::{Display, from_fn};
use std::num::ParseIntError;
use std::path::PathBuf;
use std::process::Command;

use itertools::Itertools;
use rustc_middle::middle::exported_symbols::SymbolExportKind;
use rustc_session::Session;
use rustc_target::spec::Target;
use tracing::debug;

use crate::errors::{AppleDeploymentTarget, XcrunError, XcrunSdkPathWarning};
use crate::fluent_generated as fluent;

#[cfg(test)]
mod tests;

/// The canonical name of the desired SDK for a given target.
pub(super) fn sdk_name(target: &Target) -> &'static str {
    match (&*target.os, &*target.abi) {
        ("macos", "") => "MacOSX",
        ("ios", "") => "iPhoneOS",
        ("ios", "sim") => "iPhoneSimulator",
        // Mac Catalyst uses the macOS SDK
        ("ios", "macabi") => "MacOSX",
        ("tvos", "") => "AppleTVOS",
        ("tvos", "sim") => "AppleTVSimulator",
        ("visionos", "") => "XROS",
        ("visionos", "sim") => "XRSimulator",
        ("watchos", "") => "WatchOS",
        ("watchos", "sim") => "WatchSimulator",
        (os, abi) => unreachable!("invalid os '{os}' / abi '{abi}' combination for Apple target"),
    }
}

pub(super) fn macho_platform(target: &Target) -> u32 {
    match (&*target.os, &*target.abi) {
        ("macos", _) => object::macho::PLATFORM_MACOS,
        ("ios", "macabi") => object::macho::PLATFORM_MACCATALYST,
        ("ios", "sim") => object::macho::PLATFORM_IOSSIMULATOR,
        ("ios", _) => object::macho::PLATFORM_IOS,
        ("watchos", "sim") => object::macho::PLATFORM_WATCHOSSIMULATOR,
        ("watchos", _) => object::macho::PLATFORM_WATCHOS,
        ("tvos", "sim") => object::macho::PLATFORM_TVOSSIMULATOR,
        ("tvos", _) => object::macho::PLATFORM_TVOS,
        ("visionos", "sim") => object::macho::PLATFORM_XROSSIMULATOR,
        ("visionos", _) => object::macho::PLATFORM_XROS,
        _ => unreachable!("tried to get Mach-O platform for non-Apple target"),
    }
}

/// Add relocation and section data needed for a symbol to be considered
/// undefined by ld64.
///
/// The relocation must be valid, and hence must point to a valid piece of
/// machine code, and hence this is unfortunately very architecture-specific.
///
///
/// # New architectures
///
/// The values here are basically the same as emitted by the following program:
///
/// ```c
/// // clang -c foo.c -target $CLANG_TARGET
/// void foo(void);
///
/// extern int bar;
///
/// void* foobar[2] = {
///     (void*)foo,
///     (void*)&bar,
///     // ...
/// };
/// ```
///
/// Can be inspected with:
/// ```console
/// objdump --macho --reloc foo.o
/// objdump --macho --full-contents foo.o
/// ```
pub(super) fn add_data_and_relocation(
    file: &mut object::write::Object<'_>,
    section: object::write::SectionId,
    symbol: object::write::SymbolId,
    target: &Target,
    kind: SymbolExportKind,
) -> object::write::Result<()> {
    let authenticated_pointer =
        kind == SymbolExportKind::Text && target.llvm_target.starts_with("arm64e");

    let data: &[u8] = match target.pointer_width {
        _ if authenticated_pointer => &[0, 0, 0, 0, 0, 0, 0, 0x80],
        32 => &[0; 4],
        64 => &[0; 8],
        pointer_width => unimplemented!("unsupported Apple pointer width {pointer_width:?}"),
    };

    if target.arch == "x86_64" {
        // Force alignment for the entire section to be 16 on x86_64.
        file.section_mut(section).append_data(&[], 16);
    } else {
        // Elsewhere, the section alignment is the same as the pointer width.
        file.section_mut(section).append_data(&[], target.pointer_width as u64);
    }

    let offset = file.section_mut(section).append_data(data, data.len() as u64);

    let flags = if authenticated_pointer {
        object::write::RelocationFlags::MachO {
            r_type: object::macho::ARM64_RELOC_AUTHENTICATED_POINTER,
            r_pcrel: false,
            r_length: 3,
        }
    } else if target.arch == "arm" {
        // FIXME(madsmtm): Remove once `object` supports 32-bit ARM relocations:
        // https://github.com/gimli-rs/object/pull/757
        object::write::RelocationFlags::MachO {
            r_type: object::macho::ARM_RELOC_VANILLA,
            r_pcrel: false,
            r_length: 2,
        }
    } else {
        object::write::RelocationFlags::Generic {
            kind: object::RelocationKind::Absolute,
            encoding: object::RelocationEncoding::Generic,
            size: target.pointer_width as u8,
        }
    };

    file.add_relocation(section, object::write::Relocation { offset, addend: 0, symbol, flags })?;

    Ok(())
}

/// Deployment target or SDK version.
///
/// The size of the numbers in here are limited by Mach-O's `LC_BUILD_VERSION`.
type OSVersion = (u16, u8, u8);

/// Parse an OS version triple (SDK version or deployment target).
fn parse_version(version: &str) -> Result<OSVersion, ParseIntError> {
    if let Some((major, minor)) = version.split_once('.') {
        let major = major.parse()?;
        if let Some((minor, patch)) = minor.split_once('.') {
            Ok((major, minor.parse()?, patch.parse()?))
        } else {
            Ok((major, minor.parse()?, 0))
        }
    } else {
        Ok((version.parse()?, 0, 0))
    }
}

pub fn pretty_version(version: OSVersion) -> impl Display {
    let (major, minor, patch) = version;
    from_fn(move |f| {
        write!(f, "{major}.{minor}")?;
        if patch != 0 {
            write!(f, ".{patch}")?;
        }
        Ok(())
    })
}

/// Minimum operating system versions currently supported by `rustc`.
fn os_minimum_deployment_target(os: &str) -> OSVersion {
    // When bumping a version in here, remember to update the platform-support docs too.
    //
    // NOTE: The defaults may change in future `rustc` versions, so if you are looking for the
    // default deployment target, prefer:
    // ```
    // $ rustc --print deployment-target
    // ```
    match os {
        "macos" => (10, 12, 0),
        "ios" => (10, 0, 0),
        "tvos" => (10, 0, 0),
        "watchos" => (5, 0, 0),
        "visionos" => (1, 0, 0),
        _ => unreachable!("tried to get deployment target for non-Apple platform"),
    }
}

/// The deployment target for the given target.
///
/// This is similar to `os_minimum_deployment_target`, except that on certain targets it makes sense
/// to raise the minimum OS version.
///
/// This matches what LLVM does, see in part:
/// <https://github.com/llvm/llvm-project/blob/llvmorg-18.1.8/llvm/lib/TargetParser/Triple.cpp#L1900-L1932>
fn minimum_deployment_target(target: &Target) -> OSVersion {
    match (&*target.os, &*target.arch, &*target.abi) {
        ("macos", "aarch64", _) => (11, 0, 0),
        ("ios", "aarch64", "macabi") => (14, 0, 0),
        ("ios", "aarch64", "sim") => (14, 0, 0),
        ("ios", _, _) if target.llvm_target.starts_with("arm64e") => (14, 0, 0),
        // Mac Catalyst defaults to 13.1 in Clang.
        ("ios", _, "macabi") => (13, 1, 0),
        ("tvos", "aarch64", "sim") => (14, 0, 0),
        ("watchos", "aarch64", "sim") => (7, 0, 0),
        (os, _, _) => os_minimum_deployment_target(os),
    }
}

/// Name of the environment variable used to fetch the deployment target on the given OS.
pub fn deployment_target_env_var(os: &str) -> &'static str {
    match os {
        "macos" => "MACOSX_DEPLOYMENT_TARGET",
        "ios" => "IPHONEOS_DEPLOYMENT_TARGET",
        "watchos" => "WATCHOS_DEPLOYMENT_TARGET",
        "tvos" => "TVOS_DEPLOYMENT_TARGET",
        "visionos" => "XROS_DEPLOYMENT_TARGET",
        _ => unreachable!("tried to get deployment target env var for non-Apple platform"),
    }
}

/// Get the deployment target based on the standard environment variables, or fall back to the
/// minimum version supported by `rustc`.
pub fn deployment_target(sess: &Session) -> OSVersion {
    let min = minimum_deployment_target(&sess.target);
    let env_var = deployment_target_env_var(&sess.target.os);

    if let Ok(deployment_target) = env::var(env_var) {
        match parse_version(&deployment_target) {
            Ok(version) => {
                let os_min = os_minimum_deployment_target(&sess.target.os);
                // It is common that the deployment target is set a bit too low, for example on
                // macOS Aarch64 to also target older x86_64. So we only want to warn when variable
                // is lower than the minimum OS supported by rustc, not when the variable is lower
                // than the minimum for a specific target.
                if version < os_min {
                    sess.dcx().emit_warn(AppleDeploymentTarget::TooLow {
                        env_var,
                        version: pretty_version(version).to_string(),
                        os_min: pretty_version(os_min).to_string(),
                    });
                }

                // Raise the deployment target to the minimum supported.
                version.max(min)
            }
            Err(error) => {
                sess.dcx().emit_err(AppleDeploymentTarget::Invalid { env_var, error });
                min
            }
        }
    } else {
        // If no deployment target variable is set, default to the minimum found above.
        min
    }
}

pub(super) fn add_version_to_llvm_target(
    llvm_target: &str,
    deployment_target: OSVersion,
) -> String {
    let mut components = llvm_target.split("-");
    let arch = components.next().expect("apple target should have arch");
    let vendor = components.next().expect("apple target should have vendor");
    let os = components.next().expect("apple target should have os");
    let environment = components.next();
    assert_eq!(components.next(), None, "too many LLVM triple components");

    let (major, minor, patch) = deployment_target;

    assert!(
        !os.contains(|c: char| c.is_ascii_digit()),
        "LLVM target must not already be versioned"
    );

    if let Some(env) = environment {
        // Insert version into OS, before environment
        format!("{arch}-{vendor}-{os}{major}.{minor}.{patch}-{env}")
    } else {
        format!("{arch}-{vendor}-{os}{major}.{minor}.{patch}")
    }
}

pub(super) fn get_sdk_root(sess: &Session) -> Option<PathBuf> {
    let sdk_name = sdk_name(&sess.target);

    match xcrun_show_sdk_path(sdk_name, sess.verbose_internals()) {
        Ok((path, stderr)) => {
            // Emit extra stderr, such as if `-verbose` was passed, or if `xcrun` emitted a warning.
            if !stderr.is_empty() {
                sess.dcx().emit_warn(XcrunSdkPathWarning { sdk_name, stderr });
            }
            Some(path)
        }
        Err(err) => {
            let mut diag = sess.dcx().create_err(err);

            // Recognize common error cases, and give more Rust-specific error messages for those.
            if let Some(developer_dir) = xcode_select_developer_dir() {
                diag.arg("developer_dir", &developer_dir);
                diag.note(fluent::codegen_ssa_xcrun_found_developer_dir);
                if developer_dir.as_os_str().to_string_lossy().contains("CommandLineTools") {
                    if sdk_name != "MacOSX" {
                        diag.help(fluent::codegen_ssa_xcrun_command_line_tools_insufficient);
                    }
                }
            } else {
                diag.help(fluent::codegen_ssa_xcrun_no_developer_dir);
            }

            diag.emit();
            None
        }
    }
}

/// Invoke `xcrun --sdk $sdk_name --show-sdk-path` to get the SDK path.
///
/// The exact logic that `xcrun` uses is unspecified (see `man xcrun` for a few details), and may
/// change between macOS and Xcode versions, but it roughly boils down to finding the active
/// developer directory, and then invoking `xcodebuild -sdk $sdk_name -version` to get the SDK
/// details.
///
/// Finding the developer directory is roughly done by looking at, in order:
/// - The `DEVELOPER_DIR` environment variable.
/// - The `/var/db/xcode_select_link` symlink (set by `xcode-select --switch`).
/// - `/Applications/Xcode.app` (hardcoded fallback path).
/// - `/Library/Developer/CommandLineTools` (hardcoded fallback path).
///
/// Note that `xcrun` caches its result, but with a cold cache this whole operation can be quite
/// slow, especially so the first time it's run after a reboot.
fn xcrun_show_sdk_path(
    sdk_name: &'static str,
    verbose: bool,
) -> Result<(PathBuf, String), XcrunError> {
    let mut cmd = Command::new("xcrun");
    if verbose {
        cmd.arg("--verbose");
    }
    // The `--sdk` parameter is the same as in xcodebuild, namely either an absolute path to an SDK,
    // or the (lowercase) canonical name of an SDK.
    cmd.arg("--sdk");
    cmd.arg(&sdk_name.to_lowercase());
    cmd.arg("--show-sdk-path");

    // We do not stream stdout/stderr lines directly to the user, since whether they are warnings or
    // errors depends on the status code at the end.
    let output = cmd.output().map_err(|error| XcrunError::FailedInvoking {
        sdk_name,
        command_formatted: format!("{cmd:?}"),
        error,
    })?;

    // It is fine to do lossy conversion here, non-UTF-8 paths are quite rare on macOS nowadays
    // (only possible with the HFS+ file system), and we only use it for error messages.
    let stderr = String::from_utf8_lossy_owned(output.stderr);
    if !stderr.is_empty() {
        debug!(stderr, "original xcrun stderr");
    }

    // Some versions of `xcodebuild` output beefy errors when invoked via `xcrun`,
    // but these are usually red herrings.
    let stderr = stderr
        .lines()
        .filter(|line| {
            !line.contains("Writing error result bundle")
                && !line.contains("Requested but did not find extension point with identifier")
        })
        .join("\n");

    if output.status.success() {
        Ok((stdout_to_path(output.stdout), stderr))
    } else {
        // Output both stdout and stderr, since shims of `xcrun` (such as the one provided by
        // nixpkgs), do not always use stderr for errors.
        let stdout = String::from_utf8_lossy_owned(output.stdout).trim().to_string();
        Err(XcrunError::Unsuccessful {
            sdk_name,
            command_formatted: format!("{cmd:?}"),
            stdout,
            stderr,
        })
    }
}

/// Invoke `xcode-select --print-path`, and return the current developer directory.
///
/// NOTE: We don't do any error handling here, this is only used as a canary in diagnostics (`xcrun`
/// will have already emitted the relevant error information).
fn xcode_select_developer_dir() -> Option<PathBuf> {
    let mut cmd = Command::new("xcode-select");
    cmd.arg("--print-path");
    let output = cmd.output().ok()?;
    if !output.status.success() {
        return None;
    }
    Some(stdout_to_path(output.stdout))
}

fn stdout_to_path(mut stdout: Vec<u8>) -> PathBuf {
    // Remove trailing newline.
    if let Some(b'\n') = stdout.last() {
        let _ = stdout.pop().unwrap();
    }
    #[cfg(unix)]
    let path = <OsString as std::os::unix::ffi::OsStringExt>::from_vec(stdout);
    #[cfg(not(unix))] // Unimportant, this is only used on macOS
    let path = OsString::from(String::from_utf8(stdout).unwrap());
    PathBuf::from(path)
}