use alloc::{
    boxed::Box,
    collections::BTreeMap,
    string::ToString,
    sync::Arc,
    vec::Vec,
};
use core::str;
use core::sync::atomic::{AtomicUsize, Ordering};
use spin::{Mutex, RwLock};

use crate::context;
use crate::syscall::data::Stat;
use crate::syscall::error::*;
use crate::syscall::flag::{EventFlags, O_CREAT, MODE_FILE, MODE_DIR};
use crate::syscall::scheme::{calc_seek_offset_usize, Scheme};
use crate::scheme::{self, SchemeNamespace, SchemeId};
use crate::scheme::user::{UserInner, UserScheme};
use crate::syscall::usercopy::{UserSliceWo, UserSliceRo};

struct FolderInner {
    data: Box<[u8]>,
    pos: Mutex<usize>
}

impl FolderInner {
    fn read(&self, buf: UserSliceWo) -> Result<usize> {
        let mut pos_guard = self.pos.lock();

        let avail_buf = self.data.get(*pos_guard..).unwrap_or(&[]);
        let bytes_read = buf.copy_common_bytes_from_slice(avail_buf)?;
        *pos_guard += bytes_read;

        Ok(bytes_read)
    }

    fn seek(&self, pos: isize, whence: usize) -> Result<isize> {
        let mut seek = self.pos.lock();
        let new_offset = calc_seek_offset_usize(*seek, pos, whence, self.data.len())?;
        *seek = new_offset as usize;
        Ok(new_offset)
    }
}

#[derive(Clone)]
enum Handle {
    Scheme(Arc<UserInner>),
    File(Arc<Box<[u8]>>),
    Folder(Arc<FolderInner>)
}

pub struct RootScheme {
    scheme_ns: SchemeNamespace,
    scheme_id: SchemeId,
    next_id: AtomicUsize,
    handles: RwLock<BTreeMap<usize, Handle>>,
}

impl RootScheme {
    pub fn new(scheme_ns: SchemeNamespace, scheme_id: SchemeId) -> RootScheme {
        RootScheme {
            scheme_ns,
            scheme_id,
            next_id: AtomicUsize::new(0),
            handles: RwLock::new(BTreeMap::new()),
        }
    }
}

impl Scheme for RootScheme {
    fn open(&self, path: &str, flags: usize, uid: u32, _gid: u32) -> Result<usize> {
        let path = path.trim_matches('/');

        //TODO: Make this follow standards for flags and errors
        if flags & O_CREAT == O_CREAT {
            if uid == 0 {
                let context = {
                    let contexts = context::contexts();
                    let context = contexts.current().ok_or(Error::new(ESRCH))?;
                    Arc::downgrade(context)
                };

                let id = self.next_id.fetch_add(1, Ordering::SeqCst);

                let inner = {
                    let path_box = path.to_string().into_boxed_str();
                    let mut schemes = scheme::schemes_mut();
                    let inner = Arc::new(UserInner::new(self.scheme_id, id, path_box, flags, context));
                    schemes.insert(self.scheme_ns, path, |scheme_id| {
                        inner.scheme_id.store(scheme_id, Ordering::SeqCst);
                        Arc::new(UserScheme::new(Arc::downgrade(&inner)))
                    })?;
                    inner
                };

                self.handles.write().insert(id, Handle::Scheme(inner));

                Ok(id)
            } else {
                Err(Error::new(EACCES))
            }
        } else if path.is_empty() {
            let scheme_ns = {
                let contexts = context::contexts();
                let context_lock = contexts.current().ok_or(Error::new(ESRCH))?;
                let context = context_lock.read();
                context.ens
            };

            let mut data = Vec::new();
            {
                let schemes = scheme::schemes();
                for (name, _scheme_id) in schemes.iter_name(scheme_ns) {
                    data.extend_from_slice(name.as_bytes());
                    data.push(b'\n');
                }
            }

            let inner = Arc::new(FolderInner {
                data: data.into_boxed_slice(),
                pos: Mutex::new(0)
            });

            let id = self.next_id.fetch_add(1, Ordering::SeqCst);
            self.handles.write().insert(id, Handle::Folder(inner));
            Ok(id)
        } else {
            let inner = Arc::new(
                path.as_bytes().to_vec().into_boxed_slice()
            );

            let id = self.next_id.fetch_add(1, Ordering::SeqCst);
            self.handles.write().insert(id, Handle::File(inner));
            Ok(id)
        }
    }

    fn unlink(&self, path: &str, uid: u32, _gid: u32) -> Result<usize> {
        let path = path.trim_matches('/');

        if uid == 0 {
            let inner = {
                let handles = self.handles.read();
                handles.iter().find_map(|(_id, handle)| {
                    match handle {
                        Handle::Scheme(inner) => {
                            if path == inner.name.as_ref() {
                                return Some(inner.clone());
                            }
                        },
                        _ => (),
                    }
                    None
                }).ok_or(Error::new(ENOENT))?
            };

            inner.unmount()
        } else {
            Err(Error::new(EACCES))
        }
    }


    fn seek(&self, file: usize, pos: isize, whence: usize) -> Result<isize> {
        let handle = {
            let handles = self.handles.read();
            let handle = handles.get(&file).ok_or(Error::new(EBADF))?;
            handle.clone()
        };

        match handle {
            Handle::Scheme(_) => {
                Err(Error::new(EBADF))
            },
            Handle::File(_) => {
                Err(Error::new(EBADF))
            },
            Handle::Folder(inner) => {
                inner.seek(pos, whence)
            }
        }
    }

    fn fevent(&self, file: usize, flags: EventFlags) -> Result<EventFlags> {
        let handle = {
            let handles = self.handles.read();
            let handle = handles.get(&file).ok_or(Error::new(EBADF))?;
            handle.clone()
        };

        match handle {
            Handle::Scheme(inner) => {
                inner.fevent(flags)
            },
            Handle::File(_) => {
                Err(Error::new(EBADF))
            },
            Handle::Folder(_) => {
                Err(Error::new(EBADF))
            }
        }
    }

    fn fpath(&self, file: usize, buf: &mut [u8]) -> Result<usize> {
        let handle = {
            let handles = self.handles.read();
            let handle = handles.get(&file).ok_or(Error::new(EBADF))?;
            handle.clone()
        };

        let mut i = 0;
        let scheme_path = b":";
        while i < buf.len() && i < scheme_path.len() {
            buf[i] = scheme_path[i];
            i += 1;
        }

        match handle {
            Handle::Scheme(inner) => {
                let name = inner.name.as_bytes();
                let mut j = 0;
                while i < buf.len() && j < name.len() {
                    buf[i] = name[j];
                    i += 1;
                    j += 1;
                }
            },
            Handle::File(inner) => {
                let mut j = 0;
                while i < buf.len() && j < inner.len() {
                    buf[i] = inner[j];
                    i += 1;
                    j += 1;
                }
            },
            Handle::Folder(_) => ()
        }

        Ok(i)
    }

    fn fsync(&self, file: usize) -> Result<usize> {
        let handle = {
            let handles = self.handles.read();
            let handle = handles.get(&file).ok_or(Error::new(EBADF))?;
            handle.clone()
        };

        match handle {
            Handle::Scheme(inner) => {
                inner.fsync()
            },
            Handle::File(_) => {
                Err(Error::new(EBADF))
            },
            Handle::Folder(_) => {
                Err(Error::new(EBADF))
            }
        }
    }

    fn close(&self, file: usize) -> Result<usize> {
        let handle = self.handles.write().remove(&file).ok_or(Error::new(EBADF))?;
        match handle {
            Handle::Scheme(inner) => {
                let scheme_id = inner.scheme_id.load(Ordering::SeqCst);
                let mut schemes = scheme::schemes_mut();
                schemes.remove(scheme_id);
            },
            _ => ()
        }
        Ok(0)
    }
}
impl crate::scheme::KernelScheme for RootScheme {
    fn kread(&self, file: usize, buf: UserSliceWo) -> Result<usize> {
        let handle = {
            let handles = self.handles.read();
            let handle = handles.get(&file).ok_or(Error::new(EBADF))?;
            handle.clone()
        };

        match handle {
            Handle::Scheme(inner) => {
                inner.read(buf)
            },
            Handle::File(_) => {
                Err(Error::new(EBADF))
            },
            Handle::Folder(inner) => {
                inner.read(buf)
            }
        }
    }

    fn kwrite(&self, file: usize, buf: UserSliceRo) -> Result<usize> {
        let handle = {
            let handles = self.handles.read();
            let handle = handles.get(&file).ok_or(Error::new(EBADF))?;
            handle.clone()
        };

        match handle {
            Handle::Scheme(inner) => {
                inner.write(buf)
            },
            Handle::File(_) => {
                Err(Error::new(EBADF))
            },
            Handle::Folder(_) => {
                Err(Error::new(EBADF))
            }
        }
    }
    
    fn kfstat(&self, file: usize, buf: UserSliceWo) -> Result<usize> {
        let handle = {
            let handles = self.handles.read();
            let handle = handles.get(&file).ok_or(Error::new(EBADF))?;
            handle.clone()
        };

        buf.copy_exactly(&match handle {
            Handle::Scheme(_) => Stat {
                st_mode: MODE_FILE,
                st_uid: 0,
                st_gid: 0,
                st_size: 0,
                ..Default::default()
            },
            Handle::File(_) => Stat {
                st_mode: MODE_FILE,
                st_uid: 0,
                st_gid: 0,
                st_size: 0,
                ..Default::default()
            },
            Handle::Folder(inner) => Stat {
                st_mode: MODE_DIR,
                st_uid: 0,
                st_gid: 0,
                st_size: inner.data.len() as u64,
                ..Default::default()
            }
        })?;

        Ok(0)
    }

}