use std::ascii::AsciiExt;
use std::io::prelude::*;
use std::io;
use std::io::{ErrorKind, SeekFrom};
use std::cmp;

use fs::{FileSystemRef, DiskSlice};
use file::File;
use dir_entry::*;

#[derive(Clone)]
pub(crate) enum DirRawStream<'a, 'b: 'a> {
    File(File<'a, 'b>),
    Root(DiskSlice<'a, 'b>),
}

impl <'a, 'b> DirRawStream<'a, 'b> {
    pub(crate) fn abs_pos(&self) -> Option<u64> {
        match self {
            &DirRawStream::File(ref file) => file.abs_pos(),
            &DirRawStream::Root(ref slice) => Some(slice.abs_pos()),
        }
    }

    pub(crate) fn first_cluster(&self) -> Option<u32> {
        match self {
            &DirRawStream::File(ref file) => file.first_cluster(),
            &DirRawStream::Root(_) => None,
        }
    }
}

impl <'a, 'b> Read for DirRawStream<'a, 'b> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        match self {
            &mut DirRawStream::File(ref mut file) => file.read(buf),
            &mut DirRawStream::Root(ref mut raw) => raw.read(buf),
        }
    }
}

impl <'a, 'b> Write for DirRawStream<'a, 'b> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        match self {
            &mut DirRawStream::File(ref mut file) => file.write(buf),
            &mut DirRawStream::Root(ref mut raw) => raw.write(buf),
        }
    }
    fn flush(&mut self) -> io::Result<()> {
        match self {
            &mut DirRawStream::File(ref mut file) => file.flush(),
            &mut DirRawStream::Root(ref mut raw) => raw.flush(),
        }
    }
}

impl <'a, 'b> Seek for DirRawStream<'a, 'b> {
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        match self {
            &mut DirRawStream::File(ref mut file) => file.seek(pos),
            &mut DirRawStream::Root(ref mut raw) => raw.seek(pos),
        }
    }
}

/// FAT directory
#[derive(Clone)]
pub struct Dir<'a, 'b: 'a> {
    stream: DirRawStream<'a, 'b>,
    fs: FileSystemRef<'a, 'b>,
}

impl <'a, 'b> Dir<'a, 'b> {

    pub(crate) fn new(stream: DirRawStream<'a, 'b>, fs: FileSystemRef<'a, 'b>) -> Dir<'a, 'b> {
        Dir { stream, fs }
    }

    /// Creates directory entries iterator
    pub fn iter(&self) -> DirIter<'a, 'b> {
        DirIter {
            stream: self.stream.clone(),
            fs: self.fs.clone(),
            err: false,
        }
    }

    fn split_path<'c>(path: &'c str) -> (&'c str, Option<&'c str>) {
        let mut path_split = path.trim_matches('/').splitn(2, "/");
        let comp = path_split.next().unwrap(); // safe unwrap - splitn always returns at least one element
        let rest_opt = path_split.next();
        (comp, rest_opt)
    }

    fn find_entry(&mut self, name: &str) -> io::Result<DirEntry<'a, 'b>> {
        for r in self.iter() {
            let e = r?;
            if e.file_name().eq_ignore_ascii_case(name) {
                return Ok(e);
            }
        }
        Err(io::Error::new(ErrorKind::NotFound, "file not found"))
    }

    /// Opens existing directory
    pub fn open_dir(&mut self, path: &str) -> io::Result<Dir<'a, 'b>> {
        let (name, rest_opt) = Self::split_path(path);
        let e = self.find_entry(name)?;
        match rest_opt {
            Some(rest) => e.to_dir().open_dir(rest),
            None => Ok(e.to_dir())
        }
    }

    /// Opens existing file.
    pub fn open_file(&mut self, path: &str) -> io::Result<File<'a, 'b>> {
        let (name, rest_opt) = Self::split_path(path);
        let e = self.find_entry(name)?;
        match rest_opt {
            Some(rest) => e.to_dir().open_file(rest),
            None => Ok(e.to_file())
        }
    }

    /// Creates new file or opens existing.
    pub fn create_file(&mut self, path: &str) -> io::Result<File<'a, 'b>> {
        let (name, rest_opt) = Self::split_path(path);
        let r = self.find_entry(name);
        match rest_opt {
            Some(rest) => r?.to_dir().create_file(rest),
            None => {
                match r {
                    Err(ref err) if err.kind() == ErrorKind::NotFound =>
                        Ok(self.create_entry(name, FileAttributes::from_bits_truncate(0), None)?.to_file()),
                    Err(err) => Err(err),
                    Ok(e) => Ok(e.to_file()),
                }
            }
        }
    }

    /// Creates new directory or opens existing.
    pub fn create_dir(&mut self, path: &str) -> io::Result<Dir<'a, 'b>> {
        let (name, rest_opt) = Self::split_path(path);
        let r = self.find_entry(name);
        match rest_opt {
            Some(rest) => r?.to_dir().create_dir(rest),
            None => {
                match r {
                    Err(ref err) if err.kind() == ErrorKind::NotFound => {
                        let cluster = self.fs.alloc_cluster(None)?;
                        let entry = self.create_entry(name, FileAttributes::DIRECTORY, Some(cluster))?;
                        let mut dir = entry.to_dir();
                        dir.create_entry(".", FileAttributes::DIRECTORY, entry.first_cluster())?;
                        dir.create_entry("..", FileAttributes::DIRECTORY, self.stream.first_cluster())?;
                        Ok(dir)
                    },
                    Err(err) => Err(err),
                    Ok(e) => Ok(e.to_dir()),
                }
            }
        }
    }

    fn is_empty(&mut self) -> io::Result<bool> {
        for r in self.iter() {
            let e = r?;
            let name = e.file_name();
            if name != "." && name != ".." {
                return Ok(false);
            }
        }
        Ok(true)
    }

    /// Removes existing file or directory.
    ///
    /// Make sure there is no reference to this file (no File instance) or filesystem corruption
    /// can happen.
    pub fn remove(&mut self, path: &str) -> io::Result<()> {
        let (name, rest_opt) = Self::split_path(path);
        let e = self.find_entry(name)?;
        match rest_opt {
            Some(rest) => e.to_dir().remove(rest),
            None => {
                trace!("removing {}", path);
                if e.is_dir() && !e.to_dir().is_empty()? {
                    return Err(io::Error::new(ErrorKind::NotFound, "removing non-empty directory is denied"));
                }
                match e.first_cluster() {
                    Some(n) => self.fs.cluster_iter(n).free()?,
                    _ => {},
                }
                let mut stream = self.stream.clone();
                stream.seek(SeekFrom::Start(e.offset_range.0 as u64))?;
                let num = (e.offset_range.1 - e.offset_range.0) as usize / DIR_ENTRY_SIZE as usize;
                for _ in 0..num {
                    let mut data = DirEntryData::deserialize(&mut stream)?;
                    trace!("removing dir entry {:?}", data);
                    data.set_free();
                    stream.seek(SeekFrom::Current(-(DIR_ENTRY_SIZE as i64)))?;
                    data.serialize(&mut stream)?;
                }
                Ok(())
            }
        }
    }

    fn find_free_entries(&mut self, num_entries: usize) -> io::Result<DirRawStream<'a, 'b>> {
        let mut stream = self.stream.clone();
        let mut first_free = 0;
        let mut num_free = 0;
        let mut i = 0;
        loop {
            let raw_entry = DirEntryData::deserialize(&mut stream)?;
            if raw_entry.is_end() {
                if num_free == 0 {
                    first_free = i;
                }
                stream.seek(io::SeekFrom::Start(first_free as u64 * DIR_ENTRY_SIZE))?;
                return Ok(stream);
            } else if raw_entry.is_free() {
                if num_free == 0 {
                    first_free = i;
                }
                num_free += 1;
                if num_free == num_entries {
                    stream.seek(io::SeekFrom::Start(first_free as u64 * DIR_ENTRY_SIZE))?;
                    return Ok(stream);
                }
            } else {
                num_free = 0;
            }
            i += 1;
        }
    }

    fn copy_short_name_part(dst: &mut [u8], src: &str) {
        let mut j = 0;
        for c in src.chars() {
            if j == dst.len() { break; }
            // replace characters allowed in long name but disallowed in short
            let c2 = match c {
                '.' | ' ' | '+' | ',' | ';' | '=' | '[' | ']' => '?',
                _ if c < '\u{80}' => c,
                _ => '?',
            };
            // short name is always uppercase
            let upper = c2.to_uppercase().next().unwrap(); // SAFE: uppercase must return at least one character
            let byte = upper as u8; // SAFE: upper is in range 0x20-0x7F
            dst[j] = byte;
            j += 1;
        }
    }

    fn gen_short_name(name: &str) -> [u8;11] {
        // padded by ' '
        let mut short_name = [0x20u8; 11];
        // find extension after last dot
        match name.rfind('.') {
            Some(index) => {
                // extension found - copy parts before and after dot
                Dir::copy_short_name_part(&mut short_name[0..8], &name[..index]);
                Dir::copy_short_name_part(&mut short_name[8..11], &name[index+1..]);
            },
            None => {
                // no extension - copy name and leave extension empty
                Dir::copy_short_name_part(&mut short_name[0..8], &name);
            }
        }
        // FIXME: make sure short name is unique...
        short_name
    }

    fn validate_name(name: &str) -> io::Result<()> {
        if name.len() == 0 {
            return Err(io::Error::new(ErrorKind::InvalidInput, "filename cannot be empty"));
        }
        if name.len() > 255 {
            return Err(io::Error::new(ErrorKind::InvalidInput, "filename is too long"));
        }
        for c in name.chars() {
            match c {
                'a'...'z' | 'A'...'Z' | '0'...'9' | '\u{80}'...'\u{FFFF}' |
                '$' | '%' | '\'' | '-' | '_' | '@' | '~' | '`' | '!' | '(' | ')' | '{' | '}' |
                '.' | ' ' | '+' | ',' | ';' | '=' | '[' | ']' => {},
                _ => return Err(io::Error::new(ErrorKind::InvalidInput, "invalid character in filename")),
            }
        }
        Ok(())
    }

    fn create_entry(&mut self, name: &str, attrs: FileAttributes, first_cluster: Option<u32>) -> io::Result<DirEntry<'a, 'b>> {
        trace!("create_entry {}", name);
        Self::validate_name(name)?;
        let num_lfn_entries = (name.len() + LFN_PART_LEN - 1) / LFN_PART_LEN;
        let num_entries = num_lfn_entries + 1; // multiple lfn entries + one file entry
        let mut stream = self.find_free_entries(num_entries)?;
        let start_pos = stream.seek(io::SeekFrom::Current(0))?;
        let short_name = Self::gen_short_name(name);
        let lfn_chsum = lfn_checksum(&short_name);
        let lfn_utf8 = name.encode_utf16().collect::<Vec<u16>>();
        for i in 0..num_lfn_entries {
            let lfn_index = num_lfn_entries - i;
            let mut order = lfn_index as u8;
            if i == 0 {
                order |= LFN_ENTRY_LAST_FLAG;
            }
            debug_assert!(order > 0);
            let lfn_pos = (lfn_index - 1) * LFN_PART_LEN;
            let mut lfn_part = [0xFFFFu16; LFN_PART_LEN];
            let lfn_part_len = cmp::min(name.len() - lfn_pos, LFN_PART_LEN);
            lfn_part[..lfn_part_len].copy_from_slice(&lfn_utf8[lfn_pos..lfn_pos+lfn_part_len]);
            if lfn_part_len < LFN_PART_LEN {
                lfn_part[lfn_part_len] = 0;
            }
            let mut lfn_entry = DirLfnEntryData::new(order, lfn_chsum);
            lfn_entry.copy_name_from_slice(&lfn_part);
            lfn_entry.serialize(&mut stream)?;
        }
        let mut raw_entry = DirFileEntryData::new(short_name, attrs);
        raw_entry.set_first_cluster(first_cluster, self.fs.fat_type);
        raw_entry.reset_created();
        raw_entry.reset_accessed();
        raw_entry.reset_modified();
        raw_entry.serialize(&mut stream)?;
        let end_pos = stream.seek(io::SeekFrom::Current(0))?;
        let abs_pos = stream.abs_pos().map(|p| p - DIR_ENTRY_SIZE);
        return Ok(DirEntry {
            data: raw_entry,
            lfn: Vec::new(),
            fs: self.fs,
            entry_pos: abs_pos.unwrap(), // safe
            offset_range: (start_pos, end_pos),
        });
    }
}

/// Directory entries iterator.
#[derive(Clone)]
pub struct DirIter<'a, 'b: 'a> {
    stream: DirRawStream<'a, 'b>,
    fs: FileSystemRef<'a, 'b>,
    err: bool,
}

impl <'a, 'b> DirIter<'a, 'b> {
    fn read_dir_entry(&mut self) -> io::Result<Option<DirEntry<'a, 'b>>> {
        let mut lfn_buf = LongNameBuilder::new();
        let mut offset = self.stream.seek(SeekFrom::Current(0))?;
        let mut begin_offset = offset;
        loop {
            let raw_entry = DirEntryData::deserialize(&mut self.stream)?;
            offset += DIR_ENTRY_SIZE;
            match raw_entry {
                DirEntryData::File(data) => {
                    // Check if this is end of dif
                    if data.is_end() {
                        return Ok(None);
                    }
                    // Check if this is deleted or volume ID entry
                    if data.is_free() || data.attrs.contains(FileAttributes::VOLUME_ID) {
                        lfn_buf.clear();
                        begin_offset = offset;
                        continue;
                    }
                    // Get entry position on volume
                    let entry_pos = self.stream.abs_pos().map(|p| p - DIR_ENTRY_SIZE);
                    // Check if LFN checksum is valid
                    lfn_buf.validate_chksum(&data.name);
                    return Ok(Some(DirEntry {
                        data,
                        lfn: lfn_buf.to_vec(),
                        fs: self.fs,
                        entry_pos: entry_pos.unwrap(), // safe
                        offset_range: (begin_offset, offset),
                    }));
                },
                DirEntryData::Lfn(data) => {
                    // Check if this is deleted entry
                    if data.is_free() {
                        lfn_buf.clear();
                        begin_offset = offset;
                        continue;
                    }
                    // Append to LFN buffer
                    lfn_buf.process(&data);
                }
            }
        }
    }
}

impl <'a, 'b> Iterator for DirIter<'a, 'b> {
    type Item = io::Result<DirEntry<'a, 'b>>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.err {
            return None;
        }
        let r = self.read_dir_entry();
        match r {
            Ok(Some(e)) => Some(Ok(e)),
            Ok(None) => None,
            Err(err) => {
                self.err = true;
                Some(Err(err))
            },
        }
    }
}

struct LongNameBuilder {
    buf: Vec<u16>,
    chksum: u8,
    index: u8,
}

fn lfn_checksum(short_name: &[u8]) -> u8 {
    let mut chksum = 0u8;
    for i in 0..11 {
        chksum = (((chksum & 1) << 7) as u16 + (chksum >> 1) as u16 + short_name[i] as u16) as u8;
    }
    chksum
}

impl LongNameBuilder {
    fn new() -> LongNameBuilder {
        LongNameBuilder {
            buf: Vec::<u16>::new(),
            chksum: 0,
            index: 0,
        }
    }

    fn clear(&mut self) {
        self.buf.clear();
        self.index = 0;
    }

    fn to_vec(mut self) -> Vec<u16> {
        if self.index == 1 {
            self.truncate();
            self.buf
        } else {
            warn!("unfinished LFN sequence {}", self.index);
            Vec::<u16>::new()
        }
    }

    fn truncate(&mut self) {
        // Truncate 0 and 0xFFFF characters from LFN buffer
        let mut lfn_len = self.buf.len();
        loop {
            if lfn_len == 0 {
                break;
            }
            match self.buf[lfn_len-1] {
                0xFFFF | 0 => lfn_len -= 1,
                _ => break,
            }
        }
        self.buf.truncate(lfn_len);
    }

    fn process(&mut self, data: &DirLfnEntryData) {
        let is_last = (data.order & LFN_ENTRY_LAST_FLAG) != 0;
        let index = data.order & 0x1F;
        if index == 0 {
            // Corrupted entry
            warn!("currupted lfn entry! {:x}", data.order);
            self.clear();
            return;
        }
        if is_last {
            // last entry is actually first entry in stream
            self.index = index;
            self.chksum = data.checksum;
            self.buf.resize(index as usize * LFN_PART_LEN, 0);
        } else if self.index == 0 || index != self.index - 1 || data.checksum != self.chksum {
            // Corrupted entry
            warn!("currupted lfn entry! {:x} {:x} {:x} {:x}", data.order, self.index, data.checksum, self.chksum);
            self.clear();
            return;
        } else {
            // Decrement LFN index only for non-last entries
            self.index -= 1;
        }
        let pos = LFN_PART_LEN * (index - 1) as usize;
        // copy name parts into LFN buffer
        data.copy_name_to_slice(&mut self.buf[pos..pos+13]);
    }

    fn validate_chksum(&mut self, short_name: &[u8]) {
        let chksum = lfn_checksum(short_name);
        if chksum != self.chksum {
            warn!("checksum mismatch {:x} {:x} {:?}", chksum, self.chksum, short_name);
            self.clear();
        }
    }
}