// SPDX-License-Identifier: MPL-2.0

pub mod elf;
mod shebang;

use aster_rights::Full;

use self::{
    elf::{load_elf_to_vmar, ElfHeaders, ElfLoadInfo},
    shebang::parse_shebang_line,
};
use crate::{
    fs::{
        fs_resolver::{FsPath, FsResolver},
        path::Path,
        utils::{InodeType, Permission},
    },
    prelude::*,
    vm::vmar::Vmar,
};

/// Represents an executable file that is ready to be loaded into memory and executed.
///
/// This struct encapsulates the ELF file to be executed along with its header data,
/// the `argv` and the `envp` which is required for the program execution.
pub struct ProgramToLoad {
    elf_file: Path,
    file_first_page: Box<[u8; PAGE_SIZE]>,
    argv: Vec<CString>,
    envp: Vec<CString>,
}

impl ProgramToLoad {
    /// Constructs a new `ProgramToLoad` from a file, handling shebang interpretation if needed.
    ///
    /// About `recursion_limit`: recursion limit is used to limit th recursion depth of shebang executables.
    /// If the interpreter(the program behind #!) of shebang executable is also a shebang,
    /// then it will trigger recursion. We will try to setup VMAR for the interpreter.
    /// I guess for most cases, setting the `recursion_limit` as 1 should be enough.
    /// because the interpreter is usually an elf binary(e.g., /bin/bash)
    pub fn build_from_file(
        elf_file: Path,
        fs_resolver: &FsResolver,
        argv: Vec<CString>,
        envp: Vec<CString>,
        recursion_limit: usize,
    ) -> Result<Self> {
        let inode = elf_file.inode();
        let file_first_page = {
            // Read the first page of file header, which must contain the ELF header.
            let mut buffer = Box::new([0u8; PAGE_SIZE]);
            inode.read_bytes_at(0, &mut *buffer)?;
            buffer
        };
        if let Some(mut new_argv) = parse_shebang_line(&*file_first_page)? {
            if recursion_limit == 0 {
                return_errno_with_message!(Errno::ELOOP, "the recursieve limit is reached");
            }
            new_argv.extend_from_slice(&argv);
            let interpreter = {
                let filename = new_argv[0].to_str()?.to_string();
                let fs_path = FsPath::try_from(filename.as_str())?;
                fs_resolver.lookup(&fs_path)?
            };
            check_executable_file(&interpreter)?;
            return Self::build_from_file(
                interpreter,
                fs_resolver,
                new_argv,
                envp,
                recursion_limit - 1,
            );
        }

        Ok(Self {
            elf_file,
            file_first_page,
            argv,
            envp,
        })
    }

    /// Loads the executable into the specified virtual memory space.
    ///
    /// Returns a tuple containing:
    /// 1. The absolute path of the loaded executable.
    /// 2. Information about the ELF loading process.
    pub fn load_to_vmar(self, vmar: &Vmar<Full>, fs_resolver: &FsResolver) -> Result<ElfLoadInfo> {
        let elf_headers = ElfHeaders::parse_elf(&*self.file_first_page)?;
        let elf_load_info = load_elf_to_vmar(
            vmar,
            self.elf_file,
            fs_resolver,
            elf_headers,
            self.argv,
            self.envp,
        )?;

        Ok(elf_load_info)
    }
}

pub fn check_executable_file(path: &Path) -> Result<()> {
    if path.type_().is_directory() {
        return_errno_with_message!(Errno::EISDIR, "the file is a directory");
    }

    if path.type_() == InodeType::SymLink {
        return_errno_with_message!(Errno::ELOOP, "the file is a symbolic link");
    }

    if !path.type_().is_regular_file() {
        return_errno_with_message!(Errno::EACCES, "the path is not a regular file");
    }

    if path.inode().check_permission(Permission::MAY_EXEC).is_err() {
        return_errno_with_message!(Errno::EACCES, "the path is not executable");
    }

    Ok(())
}