use super::FileAttribute;
use crate::data_types::Align;
use crate::table::runtime::Time;
use crate::{unsafe_guid, CStr16, Char16, Identify};
use core::ffi::c_void;
use core::{mem, ptr};

/// Common trait for data structures that can be used with
/// `File::set_info()` or `File::get_info()`.
///
/// The long-winded name is needed because "FileInfo" is already taken by UEFI.
pub trait FileProtocolInfo: Align + Identify + FromUefi {}

/// Trait for going from an UEFI-originated pointer to a Rust reference
///
/// This is trivial for `Sized` types, but requires some work when operating on
/// dynamic-sized types like `NamedFileProtocolInfo`, as the second member of
/// the fat pointer must be reconstructed using hidden UEFI-provided metadata.
pub trait FromUefi {
    /// Turn an UEFI-provided pointer-to-base into a (possibly fat) Rust reference
    ///
    /// # Safety
    ///
    /// This function can lead to undefined behavior if the given pointer is not
    /// pointing to a valid object of the specified type.
    unsafe fn from_uefi<'ptr>(ptr: *mut c_void) -> &'ptr mut Self;
}

/// Internal trait for initializing one of the info types.
///
/// This is used with `FileInfo`, `FileSystemInfo`, and
/// `FileSystemVolumeLabel`, all of which are dynamically-sized structs
/// that have zero or more header fields followed by a variable-length
/// [Char16] name.
trait InfoInternal: Align + ptr::Pointee<Metadata = usize> {
    /// Offset in bytes of the start of the name slice at the end of
    /// the struct.
    fn name_offset() -> usize;

    /// Get a mutable pointer to the name slice at the end of the
    /// struct.
    unsafe fn name_ptr(ptr: *mut u8) -> *mut Char16 {
        let offset_of_str = Self::name_offset();
        ptr.add(offset_of_str) as *mut Char16
    }

    /// Create a new info type in user-provided storage.
    ///
    /// The structure will be created in-place within the provided
    /// `storage` buffer. The alignment and size of the buffer is
    /// checked, then the `init` function is called to fill in the
    /// struct header (everything except for the name slice). The name
    /// slice is then initialized, and at that point the struct is fully
    /// initialized so it's safe to create a reference.
    ///
    /// # Safety
    ///
    /// The `init` function must initialize the entire struct except for
    /// the name slice.
    unsafe fn new_impl<'buf, F>(
        storage: &'buf mut [u8],
        name: &CStr16,
        init: F,
    ) -> Result<&'buf mut Self, FileInfoCreationError>
    where
        F: FnOnce(*mut Self, u64),
    {
        // Calculate the final size of the struct.
        let name_length_ucs2 = name.as_slice_with_nul().len();
        let name_size = name_length_ucs2 * mem::size_of::<Char16>();
        let info_size = Self::name_offset() + name_size;
        let info_size = Self::round_up_to_alignment(info_size);

        // Make sure that the storage is properly aligned
        let storage = Self::align_buf(storage)
            .ok_or(FileInfoCreationError::InsufficientStorage(info_size))?;
        Self::assert_aligned(storage);

        // Make sure that the storage is large enough for our needs
        if storage.len() < info_size {
            return Err(FileInfoCreationError::InsufficientStorage(info_size));
        }

        // Create a raw fat pointer using the `storage` as a base.
        let info_ptr: *mut Self =
            ptr::from_raw_parts_mut(storage.as_mut_ptr() as *mut (), name_length_ucs2);

        // Initialize the struct header.
        init(info_ptr, info_size as u64);

        // Initialize the name slice.
        ptr::copy(
            name.as_ptr(),
            Self::name_ptr(storage.as_mut_ptr()),
            name_length_ucs2,
        );

        // The struct is now valid and safe to dereference.
        let info = &mut *info_ptr;
        Ok(info)
    }
}

impl<T> FromUefi for T
where
    T: InfoInternal + ?Sized,
{
    unsafe fn from_uefi<'ptr>(ptr: *mut c_void) -> &'ptr mut Self {
        let name_ptr = Self::name_ptr(ptr as *mut u8);
        let name = CStr16::from_ptr(name_ptr);
        let name_len = name.as_slice_with_nul().len();
        &mut *ptr::from_raw_parts_mut(ptr as *mut (), name_len)
    }
}

/// Errors that can occur when creating a `FileProtocolInfo`
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum FileInfoCreationError {
    /// The provided buffer was too small to hold the `FileInfo`. You need at
    /// least the indicated buffer size (in bytes). Please remember that using
    /// a misaligned buffer will cause a decrease of usable storage capacity.
    InsufficientStorage(usize),
}

/// Generic file information
///
/// The following rules apply when using this struct with `set_info()`:
///
/// - On directories, the file size is determined by the contents of the
///   directory and cannot be changed by setting `file_size`. This member is
///   ignored by `set_info()`.
/// - The `physical_size` is determined by the `file_size` and cannot be
///   changed. This member is ignored by `set_info()`.
/// - The `FileAttribute::DIRECTORY` bit cannot be changed. It must match the
///   file’s actual type.
/// - A value of zero in create_time, last_access, or modification_time causes
///   the fields to be ignored (and not updated).
/// - It is forbidden to change the name of a file to the name of another
///   existing file in the same directory.
/// - If a file is read-only, the only allowed change is to remove the read-only
///   attribute. Other changes must be carried out in a separate transaction.
#[derive(Debug)]
#[repr(C)]
#[unsafe_guid("09576e92-6d3f-11d2-8e39-00a0c969723b")]
pub struct FileInfo {
    size: u64,
    file_size: u64,
    physical_size: u64,
    create_time: Time,
    last_access_time: Time,
    modification_time: Time,
    attribute: FileAttribute,
    file_name: [Char16],
}

impl FileInfo {
    /// Create a `FileInfo` structure
    ///
    /// The structure will be created in-place within the provided storage
    /// buffer. The buffer must be large enough to hold the data structure,
    /// including a null-terminated UCS-2 `name` string.
    ///
    /// The buffer must be correctly aligned. You can query the required
    /// alignment using the `alignment()` method of the `Align` trait that this
    /// struct implements.
    #[allow(clippy::too_many_arguments)]
    pub fn new<'buf>(
        storage: &'buf mut [u8],
        file_size: u64,
        physical_size: u64,
        create_time: Time,
        last_access_time: Time,
        modification_time: Time,
        attribute: FileAttribute,
        file_name: &CStr16,
    ) -> core::result::Result<&'buf mut Self, FileInfoCreationError> {
        unsafe {
            Self::new_impl(storage, file_name, |ptr, size| {
                ptr::addr_of_mut!((*ptr).size).write(size);
                ptr::addr_of_mut!((*ptr).file_size).write(file_size);
                ptr::addr_of_mut!((*ptr).physical_size).write(physical_size);
                ptr::addr_of_mut!((*ptr).create_time).write(create_time);
                ptr::addr_of_mut!((*ptr).last_access_time).write(last_access_time);
                ptr::addr_of_mut!((*ptr).modification_time).write(modification_time);
                ptr::addr_of_mut!((*ptr).attribute).write(attribute);
            })
        }
    }

    /// File size (number of bytes stored in the file)
    pub fn file_size(&self) -> u64 {
        self.file_size
    }

    /// Physical space consumed by the file on the file system volume
    pub fn physical_size(&self) -> u64 {
        self.physical_size
    }

    /// Time when the file was created
    pub fn create_time(&self) -> &Time {
        &self.create_time
    }

    /// Time when the file was last accessed
    pub fn last_access_time(&self) -> &Time {
        &self.last_access_time
    }

    /// Time when the file's contents were last modified
    pub fn modification_time(&self) -> &Time {
        &self.modification_time
    }

    /// Attribute bits for the file
    pub fn attribute(&self) -> FileAttribute {
        self.attribute
    }

    /// Name of the file
    pub fn file_name(&self) -> &CStr16 {
        unsafe { CStr16::from_ptr(&self.file_name[0]) }
    }
}

impl Align for FileInfo {
    fn alignment() -> usize {
        8
    }
}

impl InfoInternal for FileInfo {
    fn name_offset() -> usize {
        80
    }
}

impl FileProtocolInfo for FileInfo {}

/// System volume information
///
/// May only be obtained on the root directory's file handle.
///
/// Please note that only the system volume's volume label may be set using
/// this information structure. Consider using `FileSystemVolumeLabel` instead.
#[derive(Debug)]
#[repr(C)]
#[unsafe_guid("09576e93-6d3f-11d2-8e39-00a0c969723b")]
pub struct FileSystemInfo {
    size: u64,
    read_only: bool,
    volume_size: u64,
    free_space: u64,
    block_size: u32,
    volume_label: [Char16],
}

impl FileSystemInfo {
    /// Create a `FileSystemInfo` structure
    ///
    /// The structure will be created in-place within the provided storage
    /// buffer. The buffer must be large enough to hold the data structure,
    /// including a null-terminated UCS-2 `name` string.
    ///
    /// The buffer must be correctly aligned. You can query the required
    /// alignment using the `alignment()` method of the `Align` trait that this
    /// struct implements.
    #[allow(clippy::too_many_arguments)]
    pub fn new<'buf>(
        storage: &'buf mut [u8],
        read_only: bool,
        volume_size: u64,
        free_space: u64,
        block_size: u32,
        volume_label: &CStr16,
    ) -> core::result::Result<&'buf mut Self, FileInfoCreationError> {
        unsafe {
            Self::new_impl(storage, volume_label, |ptr, size| {
                ptr::addr_of_mut!((*ptr).size).write(size);
                ptr::addr_of_mut!((*ptr).read_only).write(read_only);
                ptr::addr_of_mut!((*ptr).volume_size).write(volume_size);
                ptr::addr_of_mut!((*ptr).free_space).write(free_space);
                ptr::addr_of_mut!((*ptr).block_size).write(block_size);
            })
        }
    }

    /// Truth that the volume only supports read access
    pub fn read_only(&self) -> bool {
        self.read_only
    }

    /// Number of bytes managed by the file system
    pub fn volume_size(&self) -> u64 {
        self.volume_size
    }

    /// Number of available bytes for use by the file system
    pub fn free_space(&self) -> u64 {
        self.free_space
    }

    /// Nominal block size by which files are typically grown
    pub fn block_size(&self) -> u32 {
        self.block_size
    }

    /// Volume label
    pub fn volume_label(&self) -> &CStr16 {
        unsafe { CStr16::from_ptr(&self.volume_label[0]) }
    }
}

impl Align for FileSystemInfo {
    fn alignment() -> usize {
        8
    }
}

impl InfoInternal for FileSystemInfo {
    fn name_offset() -> usize {
        36
    }
}

impl FileProtocolInfo for FileSystemInfo {}

/// System volume label
///
/// May only be obtained on the root directory's file handle.
#[derive(Debug)]
#[repr(C)]
#[unsafe_guid("db47d7d3-fe81-11d3-9a35-0090273fc14d")]
pub struct FileSystemVolumeLabel {
    volume_label: [Char16],
}

impl FileSystemVolumeLabel {
    /// Create a `FileSystemVolumeLabel` structure
    ///
    /// The structure will be created in-place within the provided storage
    /// buffer. The buffer must be large enough to hold the data structure,
    /// including a null-terminated UCS-2 `name` string.
    ///
    /// The buffer must be correctly aligned. You can query the required
    /// alignment using the `alignment()` method of the `Align` trait that this
    /// struct implements.
    pub fn new<'buf>(
        storage: &'buf mut [u8],
        volume_label: &CStr16,
    ) -> core::result::Result<&'buf mut Self, FileInfoCreationError> {
        unsafe { Self::new_impl(storage, volume_label, |_ptr, _size| {}) }
    }

    /// Volume label
    pub fn volume_label(&self) -> &CStr16 {
        unsafe { CStr16::from_ptr(&self.volume_label[0]) }
    }
}

impl Align for FileSystemVolumeLabel {
    fn alignment() -> usize {
        2
    }
}

impl InfoInternal for FileSystemVolumeLabel {
    fn name_offset() -> usize {
        0
    }
}

impl FileProtocolInfo for FileSystemVolumeLabel {}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::alloc_api::vec;
    use crate::table::runtime::{Daylight, Time};
    use crate::CString16;

    fn validate_layout<T: InfoInternal + ?Sized>(info: &T, name: &[Char16]) {
        // Check the hardcoded struct alignment.
        assert_eq!(mem::align_of_val(info), T::alignment());
        // Check the hardcoded name slice offset.
        assert_eq!(
            unsafe { (name.as_ptr() as *const u8).offset_from(info as *const _ as *const u8) },
            T::name_offset() as isize
        );
    }

    #[test]
    fn test_file_info() {
        let mut storage = vec![0; 128];

        let file_size = 123;
        let physical_size = 456;
        let create_time = Time::new(1970, 1, 1, 0, 0, 0, 0, 0, Daylight::IN_DAYLIGHT);
        let last_access_time = Time::new(1971, 1, 1, 0, 0, 0, 0, 0, Daylight::IN_DAYLIGHT);
        let modification_time = Time::new(1972, 1, 1, 0, 0, 0, 0, 0, Daylight::IN_DAYLIGHT);
        let attribute = FileAttribute::READ_ONLY;
        let name = CString16::try_from("test_name").unwrap();
        let info = FileInfo::new(
            &mut storage,
            file_size,
            physical_size,
            create_time,
            last_access_time,
            modification_time,
            attribute,
            &name,
        )
        .unwrap();

        validate_layout(info, &info.file_name);

        //   Header size: 80 bytes
        // + Name size (including trailing null): 20 bytes
        // = 100
        // Round size up to match FileInfo alignment of 8: 104
        assert_eq!(info.size, 104);
        assert_eq!(info.size, mem::size_of_val(info) as u64);

        assert_eq!(info.file_size(), file_size);
        assert_eq!(info.physical_size(), physical_size);
        assert_eq!(info.create_time(), &create_time);
        assert_eq!(info.last_access_time(), &last_access_time);
        assert_eq!(info.modification_time(), &modification_time);
        assert_eq!(info.attribute(), attribute);
        assert_eq!(info.file_name(), name);
    }

    #[test]
    fn test_file_system_info() {
        let mut storage = vec![0; 128];

        let read_only = true;
        let volume_size = 123;
        let free_space = 456;
        let block_size = 789;
        let name = CString16::try_from("test_name2").unwrap();
        let info = FileSystemInfo::new(
            &mut storage,
            read_only,
            volume_size,
            free_space,
            block_size,
            &name,
        )
        .unwrap();

        validate_layout(info, &info.volume_label);

        //   Header size: 36 bytes
        // + Name size (including trailing null): 22 bytes
        // = 58
        // Round size up to match FileSystemInfo alignment of 8: 64
        assert_eq!(info.size, 64);
        assert_eq!(info.size, mem::size_of_val(info) as u64);

        assert_eq!(info.read_only, read_only);
        assert_eq!(info.volume_size, volume_size);
        assert_eq!(info.free_space, free_space);
        assert_eq!(info.block_size, block_size);
        assert_eq!(info.volume_label(), name);
    }

    #[test]
    fn test_file_system_volume_label() {
        let mut storage = vec![0; 128];

        let name = CString16::try_from("test_name").unwrap();
        let info = FileSystemVolumeLabel::new(&mut storage, &name).unwrap();

        validate_layout(info, &info.volume_label);

        assert_eq!(info.volume_label(), name);
    }
}