use std::ffi::CStr;
use std::ffi::CString;
use std::ffi::OsString;
use std::fs::File;
use std::io::Read;
use std::os::fd::AsRawFd;
use std::os::raw::c_char;
use std::os::unix::fs::PermissionsExt;
use std::path::Path;
use std::path::PathBuf;
use std::sync::OnceLock;

use crate::bazel_bwrap;
use crate::exec_util::argv_to_cstrings;
use crate::exec_util::make_files_inheritable;
use codex_install_context::InstallContext;
use codex_utils_absolute_path::AbsolutePathBuf;
use sha2::Digest as _;
use sha2::Sha256;

const SHA256_HEX_LEN: usize = 64;
const NULL_SHA256_DIGEST: [u8; 32] = [0; 32];

#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) struct BundledBwrapLauncher {
    program: AbsolutePathBuf,
}

pub(crate) fn launcher() -> Option<BundledBwrapLauncher> {
    let current_exe = std::env::current_exe().ok()?;
    find_program(
        InstallContext::current(),
        &current_exe,
        Path::new("."),
        |key| std::env::var_os(key),
    )
    .map(|program| BundledBwrapLauncher { program })
}

/// Discover the bundled fallback for an explicit launcher and its environment.
pub fn find_bundled_bwrap_for_exe(
    exe: &Path,
    command_cwd: &Path,
    env: impl Fn(&str) -> Option<OsString>,
) -> Option<AbsolutePathBuf> {
    let exe = std::fs::canonicalize(exe).ok()?;
    let context = InstallContext::from_exe(
        /*is_macos*/ false,
        Some(&exe),
        /*method_override*/ None,
    );
    find_program(&context, &exe, command_cwd, env)
}

fn find_program(
    context: &InstallContext,
    exe: &Path,
    cwd: &Path,
    env: impl Fn(&str) -> Option<OsString>,
) -> Option<AbsolutePathBuf> {
    find_for_install_context(context)
        .or_else(|| find_legacy_for_exe(exe, bazel_bwrap::candidate(cwd, env)))
}

impl BundledBwrapLauncher {
    pub(crate) fn exec(&self, argv: Vec<String>, preserved_files: Vec<File>) -> ! {
        let bwrap_file = File::open(self.program.as_path()).unwrap_or_else(|err| {
            panic!(
                "failed to open bundled bubblewrap {}: {err}",
                self.program.as_path().display()
            )
        });
        if let Err(err) = verify_digest(&bwrap_file, expected_sha256(), self.program.as_path()) {
            eprintln!("{err}");
            std::process::exit(crate::BUNDLED_BWRAP_DIGEST_VERIFICATION_FAILURE_EXIT_CODE);
        }

        make_files_inheritable(&preserved_files);

        let fd_path = format!("/proc/self/fd/{}", bwrap_file.as_raw_fd());
        let program_cstring = CString::new(fd_path.as_str())
            .unwrap_or_else(|err| panic!("invalid bundled bubblewrap fd path: {err}"));
        let cstrings = argv_to_cstrings(&argv);
        let mut argv_ptrs: Vec<*const c_char> = cstrings
            .iter()
            .map(CString::as_c_str)
            .map(CStr::as_ptr)
            .collect();
        argv_ptrs.push(std::ptr::null());

        // SAFETY: `program_cstring` and every entry in `argv_ptrs` are valid C
        // strings for the duration of the call. On success `execv` does not return.
        unsafe {
            libc::execv(program_cstring.as_ptr(), argv_ptrs.as_ptr());
        }
        let err = std::io::Error::last_os_error();
        panic!(
            "failed to exec bundled bubblewrap {} via {fd_path}: {err}",
            self.program.as_path().display()
        );
    }
}

fn find_for_install_context(context: &InstallContext) -> Option<AbsolutePathBuf> {
    context
        .bundled_resource("bwrap")
        .filter(|path| is_executable_file(path))
}

fn find_legacy_for_exe(exe: &Path, bazel_candidate: Option<PathBuf>) -> Option<AbsolutePathBuf> {
    legacy_candidates_for_exe(exe, bazel_candidate)
        .into_iter()
        .find(|candidate| is_executable_file(candidate))
        .map(|path| {
            AbsolutePathBuf::from_absolute_path(&path).unwrap_or_else(|err| {
                panic!(
                    "failed to normalize bundled bubblewrap path {}: {err}",
                    path.display()
                )
            })
        })
}

fn legacy_candidates_for_exe(exe: &Path, bazel_candidate: Option<PathBuf>) -> Vec<PathBuf> {
    let Some(exe_dir) = exe.parent() else {
        return Vec::new();
    };

    let mut candidates = Vec::new();
    candidates.push(exe_dir.join("codex-resources").join("bwrap"));
    if let Some(package_target_dir) = exe_dir.parent() {
        candidates.push(package_target_dir.join("codex-resources").join("bwrap"));
    }
    candidates.push(exe_dir.join("bwrap"));
    if let Some(path) = bazel_candidate {
        candidates.push(path);
    }
    candidates
}

fn is_executable_file(path: &Path) -> bool {
    let Ok(metadata) = path.metadata() else {
        return false;
    };
    metadata.is_file() && metadata.permissions().mode() & 0o111 != 0
}

fn expected_sha256() -> Option<[u8; 32]> {
    static EXPECTED: OnceLock<Option<[u8; 32]>> = OnceLock::new();
    *EXPECTED.get_or_init(|| {
        let raw_digest = option_env!("CODEX_BWRAP_SHA256")?;
        let digest = parse_sha256_hex(raw_digest)
            .unwrap_or_else(|err| panic!("invalid CODEX_BWRAP_SHA256 value: {err}"));
        (digest != NULL_SHA256_DIGEST).then_some(digest)
    })
}

fn verify_digest(file: &File, expected: Option<[u8; 32]>, path: &Path) -> Result<(), String> {
    let Some(expected) = expected else {
        return Ok(());
    };

    let mut file = file
        .try_clone()
        .map_err(|err| format!("failed to clone bundled bubblewrap fd: {err}"))?;
    let mut hasher = Sha256::new();
    let mut buffer = [0_u8; 8192];
    loop {
        let read = file.read(&mut buffer).map_err(|err| {
            format!(
                "failed to read bundled bubblewrap {} for digest verification: {err}",
                path.display()
            )
        })?;
        if read == 0 {
            break;
        }
        hasher.update(&buffer[..read]);
    }

    let actual: [u8; 32] = hasher.finalize().into();
    if actual == expected {
        return Ok(());
    }

    Err(format!(
        "bundled bubblewrap digest mismatch for {}: expected sha256:{}, got sha256:{}",
        path.display(),
        bytes_to_hex(&expected),
        bytes_to_hex(&actual),
    ))
}

fn parse_sha256_hex(raw: &str) -> Result<[u8; 32], String> {
    if raw.len() != SHA256_HEX_LEN {
        return Err(format!(
            "expected {SHA256_HEX_LEN} hex characters, got {}",
            raw.len()
        ));
    }

    let mut digest = [0_u8; 32];
    for (index, byte) in digest.iter_mut().enumerate() {
        let start = index * 2;
        *byte = u8::from_str_radix(&raw[start..start + 2], 16)
            .map_err(|err| format!("invalid hex byte at offset {start}: {err}"))?;
    }
    Ok(digest)
}

fn bytes_to_hex(bytes: &[u8; 32]) -> String {
    const HEX: &[u8; 16] = b"0123456789abcdef";
    let mut hex = String::with_capacity(SHA256_HEX_LEN);
    for byte in bytes {
        hex.push(HEX[(byte >> 4) as usize] as char);
        hex.push(HEX[(byte & 0x0f) as usize] as char);
    }
    hex
}

#[cfg(test)]
#[path = "bundled_bwrap_tests.rs"]
mod tests;