use crate::fs::{Record, RecordType};
use crate::strprint::u32_hex;

#[repr(packed(1), C)]
pub struct BPB {
    pub bootjmp: [u8; 3],
    pub oem_name: [u8; 8],
    pub bytes_per_sector: u16,
    pub sectors_per_cluster: u8,
    pub reserved_sectors: u16,
    pub num_fats: u8,
    pub root_entry_count: u16,
    pub total_sectors_16: u16,
    pub media_type: u8,
    pub sectors_per_fat16: u16,
    pub sectors_per_track: u16,
    pub head_count: u16,
    pub hidden_sectors: u32,
    pub large_sector_count: u32,
    pub sectors_per_fat: u32,
    pub flags: u16,
    pub version: u16,
    pub root_cluster: u32,
    pub fsinfo_sector: u16,
    pub backup_boot_sector: u16,
    pub reserved0: [u8; 12],
    pub drive_number: u8,
    pub reserved1: u8,
    pub signature: u8,
    pub serial_number: u32,
    pub label: [u8; 11],
    pub identifier: [u8; 8],
}

#[repr(C)]
pub struct BPBUseful {
    pub oem_name: [u8; 8],
    pub reserved_sectors: u16,
    pub num_fats: u8,
    pub sectors_per_fat_16: u32,
    pub sectors_per_fat: u32,
    pub sectors_per_cluster: u8,
    pub root_cluster: u32,
    pub padding: [u8; 1],
}

impl BPBUseful {
    pub fn empty() -> Self {
        Self {
            oem_name: [0; 8],
            reserved_sectors: 0,
            num_fats: 0,
            sectors_per_fat_16: 0,
            sectors_per_fat: 0,
            sectors_per_cluster: 0,
            root_cluster: 0,
            padding: [0; 1],
        }
    }
    pub fn fat_size(&self) -> usize {
        self.sectors_per_fat as usize
    }
    pub fn first_data_sector(&self) -> usize {
        self.reserved_sectors as usize + (self.num_fats as usize * self.fat_size())
    }

    pub fn first_fat_sector(&self) -> usize {
        self.reserved_sectors as usize
    }
}

#[repr(packed(1), C)]
pub struct DirectoryEntry {
    pub name: [u8; 8],
    pub ext: [u8; 3],
    pub attributes: u8,
    pub reserved: u8,
    pub creation_time_tenth: u8,
    pub creation_time: u16,
    pub creation_date: u16,
    pub last_access_date: u16,
    pub first_cluster_high: u16,
    pub last_modified_time: u16,
    pub last_modified_date: u16,
    pub first_cluster_low: u16,
    pub file_size: u32,
}

/*
#[repr(packed(1), C)]
pub struct LongFileNameEntry {
    pub order: u8,
    pub first_five_two_byte_characters: [u16; 5], // [u8; 10]
    pub attributes: u8,                           // always 0x0F
    pub long_entry_type: u8,
    pub checksum: u8,
    pub next_six_two_byte_characters: [u16; 6], // [u8; 12]
    pub reserved: u16,
    pub final_two_two_byte_characters: [u16; 2], // [u8; 4]
    pub directory_entry: DirectoryEntry,
}
 */

#[repr(C)]
pub struct Fat32DirectoryReader {
    pub underlying: Fat32FileReader,
}

impl Fat32DirectoryReader {
    pub fn empty() -> Self {
        Self {
            underlying: Fat32FileReader::empty(),
        }
    }
}

#[repr(C)]
#[derive(Copy, Clone, Debug)]
pub struct Fat32FileReader {
    pub cluster: usize,
    pub sector: usize,
    pub cluster_idx: usize,
    pub sector_offset: usize,
    pub eof: u8,
    pub implementation: u32,
    pub padding: [u8; 32 - 24],
}

impl Fat32FileReader {
    pub fn empty() -> Self {
        Self {
            cluster: 0,
            sector: 0,
            cluster_idx: 0,
            sector_offset: 0,
            eof: 0,
            implementation: 0,
            padding: [0; 32 - 24],
        }
    }
}

pub enum Fat32Error {
    CouldNotReadBPB,
}

pub fn read_bpb() -> Result<BPBUseful, Fat32Error> {
    let bpb_addr = crate::syscalls::alloc_blocks(1);
    if crate::syscalls::read_hbd(0, bpb_addr, 1) != 0 {
        return Err(Fat32Error::CouldNotReadBPB);
    }
    let bpb = unsafe { (bpb_addr as *const BPB).read_volatile() };
    crate::syscalls::free_blocks(bpb_addr, 1);
    Ok(BPBUseful {
        oem_name: bpb.oem_name,
        reserved_sectors: bpb.reserved_sectors,
        num_fats: bpb.num_fats,
        sectors_per_fat_16: bpb.sectors_per_fat16 as u32,
        sectors_per_fat: bpb.sectors_per_fat,
        sectors_per_cluster: bpb.sectors_per_cluster,
        root_cluster: bpb.root_cluster,
        padding: [0; 1],
    })
}

pub fn reader_from_cluster(bpb: &BPBUseful, cluster: usize) -> Fat32FileReader {
    let first_sector_of_cluster =
        ((cluster - 2) * bpb.sectors_per_cluster as usize) + bpb.first_data_sector();
    Fat32FileReader {
        cluster,
        sector: first_sector_of_cluster,
        cluster_idx: 0,
        sector_offset: 0,
        eof: 0,
        implementation: 0,
        padding: [0; 32 - 24],
    }
}

pub fn root_target(bpb: &BPBUseful) -> u32 {
    bpb.root_cluster as u32
}

pub fn root_reader(bpb: &BPBUseful) -> Fat32DirectoryReader {
    let cluster = bpb.root_cluster as usize;
    Fat32DirectoryReader {
        underlying: reader_from_cluster(bpb, cluster),
    }
}

/// returns true if the record was read successfully, false if the end of the directory was reached
pub fn read_one_record(
    bpb: &BPBUseful,
    reader: &mut Fat32DirectoryReader,
    record: &mut Record,
) -> bool {
    let block_addr = crate::syscalls::alloc_blocks(1);
    let buf = unsafe { core::slice::from_raw_parts_mut(block_addr as *mut u8, 512) };
    // read without seeking
    let old_reader = reader.underlying;
    if !read_file(bpb, &mut reader.underlying, buf) {
        crate::syscalls::free_blocks(block_addr, 1);
        crate::syscalls::write_terminal(b"eof on dir");
        return false;
    }
    reader.underlying = old_reader;
    let mut done = false;
    while !done {
        let entry = unsafe {
            ((buf.as_ptr() as usize + reader.underlying.implementation as usize)
                as *const DirectoryEntry)
                .read_volatile()
        };
        if entry.name[0] == 0x00 {
            // end of directory
            crate::syscalls::free_blocks(block_addr, 1);
            return false;
        }
        #[allow(clippy::collapsible_if)]
        if entry.name[0] != 0xE5 {
            if entry.attributes != 0x0F {
                // for now we do not support long filenames
                let mut namelen = 0;
                let mut last_was_space = false;
                for i in 0..8 {
                    if last_was_space {
                        if entry.name[i] != b' ' {
                            last_was_space = false;
                        }
                    } else if entry.name[i] == b' ' {
                        namelen = i;
                        last_was_space = true;
                    }
                }
                if namelen == 0 {
                    namelen = 8;
                }
                record.name = [0; 12];
                record.name[..namelen].copy_from_slice(&entry.name[..namelen]);
                if entry.attributes & 0x10 != 0 {
                    record.record_type = RecordType::Directory as u8;
                } else {
                    record.record_type = RecordType::File as u8;
                    record.name[namelen] = b'.';
                    record.name[namelen + 1] = entry.ext[0];
                    record.name[namelen + 2] = entry.ext[1];
                    record.name[namelen + 3] = entry.ext[2];
                }
                record.target =
                    (entry.first_cluster_high as u32) << 16 | (entry.first_cluster_low as u32);
                record.total_size_bytes = entry.file_size;
                done = true;
            }
        }

        reader.underlying.implementation += 32;
        if reader.underlying.implementation >= 512 {
            reader.underlying.implementation = 0;
            seek_forward_one_sector(bpb, &mut reader.underlying);
            if !read_file(bpb, &mut reader.underlying, buf) {
                crate::syscalls::free_blocks(block_addr, 1);
                return false;
            }
        }
    }
    crate::syscalls::free_blocks(block_addr, 1);
    true
}

pub fn seek_forward_one_sector(bpb: &BPBUseful, reader: &mut Fat32FileReader) -> bool {
    if reader.eof != 0 {
        return false;
    }
    reader.sector += 1;
    reader.sector_offset = 0;
    reader.cluster_idx += 1;
    // if we reached the end of the cluster, let's consult the FAT to see where to go next
    if reader.cluster_idx >= bpb.sectors_per_cluster as usize {
        let fat_addr = crate::syscalls::alloc_blocks(1);
        let fat_ofs = reader.cluster * 4;
        let fat_sector = bpb.first_fat_sector() + (fat_ofs / 512);
        let ent_offset = fat_ofs % 512;
        if crate::syscalls::read_hbd(fat_sector, fat_addr, 1) != 0 {
            crate::syscalls::free_blocks(fat_addr, 1);
            crate::syscalls::write_terminal(b"fatfailure");
            return false;
        }
        let table_value =
            unsafe { ((fat_addr+(ent_offset)) as *const u32).read_volatile() } & 0x0FFFFFFF;
        crate::syscalls::free_blocks(fat_addr, 1);
        if table_value >= 0x0FFFFFF8 {
            // no more clusters, whole file has been read
            reader.eof = 1;
            return false;
        } else if table_value >= 0x00000002 {
            reader.cluster = table_value as usize;
            reader.cluster_idx = 0;
            reader.sector =
                ((reader.cluster - 2) * bpb.sectors_per_cluster as usize) + bpb.first_data_sector();
            reader.sector_offset = 0;
            if table_value == 0x00000000 || table_value == 0x00000001 {
                reader.eof = 1;
                return false;
            } else if table_value == 0x0FFFFFF7 {
                // bad cluster, stop reading
                crate::syscalls::write_terminal(b"badcluster");
                reader.eof = 1;
                return false;
            }
        } else {
            // cluster is free, keep going
            reader.eof = 1;
            return false;
        }
    }
    // continue reading
    true
}

pub fn read_file(bpb: &BPBUseful, reader: &mut Fat32FileReader, buffer: &mut [u8]) -> bool {
    if reader.eof != 0 {
        return false;
    }
    let mut buffer_idx = 0;
    let sector_addr = crate::syscalls::alloc_blocks(1);
    loop {
        if reader.eof != 0 {
            crate::syscalls::free_blocks(sector_addr, 1);
            return false;
        }
        // read current sector
        if crate::syscalls::read_hbd(reader.sector, sector_addr, 1) != 0 {
            crate::syscalls::free_blocks(sector_addr, 1);
            crate::syscalls::write_terminal(b"badhdb");
            return false;
        }
        let mut left_in_sector = 512 - reader.sector_offset;
        if left_in_sector == 0 {
            crate::syscalls::write_terminal(b"SECTORNULL?");
            crate::syscalls::free_blocks(sector_addr, 1);
            return false;
        }
        while buffer_idx < buffer.len() && left_in_sector > 0 {
            buffer[buffer_idx] = unsafe {
                (sector_addr as *const u8)
                    .add(reader.sector_offset)
                    .read_volatile()
            };
            buffer_idx += 1;
            left_in_sector -= 1;
            reader.sector_offset += 1;
        }

        // if sector is full, make sure next read will start at the correct position
        #[allow(clippy::collapsible_if)]
        if left_in_sector == 0 {
            // we don't care about the return value because if it fails, it'll be handled by the next iteration
            seek_forward_one_sector(bpb, reader);
        }

        // either buffer got filled, or we need to read the next sector
        if buffer_idx < buffer.len() {
            // we must've reached the end of the sector, let's read the next one
            continue;
        } else {
            // buffer got filled, we're done
            crate::syscalls::free_blocks(sector_addr, 1);
            return true;
        }
    }
}

/*
pub fn read_directory(bpb: &BPBUseful, cluster: usize) {
    let mut first_sector_of_cluster =
        ((cluster - 2) * bpb.sectors_per_cluster as usize) + bpb.first_data_sector();
    let mut fsoc_addr = crate::syscalls::alloc_blocks(1);
    if crate::syscalls::read_hbd(first_sector_of_cluster, fsoc_addr, 1) != 0 {
        crate::syscalls::free_blocks(fsoc_addr, 1);
        crate::syscalls::write_terminal(b"fsoc");
        return;
    }
    let mut traveled_in_sector = 0;
    loop {
        let entry = unsafe { (fsoc_addr as *const DirectoryEntry).read_volatile() };
        if entry.name[0] == 0x00 {
            break;
        }
        if entry.name[0] != 0xE5 {
            if entry.attributes == 0x0F {
                //crate::syscalls::write_terminal(b" unsupported utf16");
            } else {
                crate::syscalls::write_terminal(b"  - ");
                let namelen = entry.name.iter().position(|&x| x == 0).unwrap_or(8);
                crate::syscalls::write_terminal(&entry.name[..namelen]);
                if entry.attributes & 0x10 != 0 {
                    crate::syscalls::write_terminal(b" (dir)");
                } else {
                    let extlen = entry.ext.iter().position(|&x| x == 0).unwrap_or(3);
                    crate::syscalls::write_terminal(b".");
                    crate::syscalls::write_terminal(&entry.ext[..extlen]);
                }
                crate::syscalls::write_terminal(b"\n");
            }
        }

        fsoc_addr += 32;
        traveled_in_sector += 32;
        if traveled_in_sector >= 512 {
            fsoc_addr -= traveled_in_sector;
            traveled_in_sector = 0;
            first_sector_of_cluster += 1;
            if crate::syscalls::read_hbd(first_sector_of_cluster, fsoc_addr, 1) != 0 {
                crate::syscalls::free_blocks(fsoc_addr, 1);
                crate::syscalls::write_terminal(b"fsoc");
                return;
            }
        }
        continue;
    }
}
 */