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use crate::{util, Cell, Ordering, Rc, Record, SaveOp, SortedFile, DB};

/// Storage of variable size values.
pub struct ByteStorage {
    pub file: Rc<SortedFile>,
    pub id_gen: Cell<u64>,
}

impl ByteStorage {
    pub fn new(root_page: u64) -> Self {
        let file = Rc::new(SortedFile::new(9 + BPF, 8, root_page));
        ByteStorage {
            file,
            id_gen: Cell::new(0),
        }
    }

    pub fn init(&self, db: &DB) {
        // Initialise id_gen to id of last record.
        let start = Fragment::new(u64::MAX);
        if let Some((pp, off)) = self.file.clone().dsc(db, Box::new(start)).next() {
            let p = pp.borrow();
            self.id_gen.set(1 + util::getu64(&p.data, off));
        }
    }

    pub fn save(&self, db: &DB, op: SaveOp) {
        self.file.save(db, op);
    }

    pub fn encode(&self, db: &DB, bytes: &[u8]) -> u64 {
        let result = self.id_gen.get();
        let mut r = Fragment::new(0);
        let n = bytes.len();
        let mut done = 0;
        let mut _frags = 0;
        loop {
            r.id = self.id_gen.get();
            self.id_gen.set(r.id + 1);
            let mut len = n - done;
            if len > BPF {
                r.len = (BPF << 1) as u8;
                len = BPF
            } else {
                r.len = 1 + ((len as u8) << 1);
            }
            // for i in 0..len { r.bytes[ i ] = bytes[ done + i ]; }
            r.bytes[..len].copy_from_slice(&bytes[done..(len + done)]);
            done += len;
            _frags += 1;
            self.file.insert(db, &r);
            if done == n {
                break;
            }
        }
        result
    }

    pub fn decode(&self, db: &DB, mut id: u64, inline: usize) -> Vec<u8> {
        let mut result = vec![0_u8; inline]; // inline bytes will be filled in from inline data.
        let start = Fragment::new(id);
        for (pp, off) in self.file.asc(db, Box::new(start)) {
            let p = pp.borrow();
            let xid = util::getu64(&p.data, off);
            debug_assert!(xid == id);
            id += 1;
            let len = p.data[off + 8] as usize;
            let off = off + 9;
            result.extend_from_slice(&p.data[off..off + (len >> 1)]);
            if len & 1 == 1 {
                break;
            }
        }
        result
    }

    pub fn delcode(&self, db: &DB, id: u64) {
        let start = Fragment::new(id);
        let mut n = 0;
        for (pp, off) in self.file.asc(db, Box::new(start)) {
            let p = pp.borrow();
            let xid = util::getu64(&p.data, off);
            debug_assert!(xid == id + n);
            n += 1;
            let len = &p.data[off + 8];
            if len & 1 == 1 {
                break;
            }
        }
        let mut r = Fragment::new(0);
        for xid in id..id + n {
            r.id = xid;
            self.file.remove(db, &r);
        }
    }
}

/// = 52. Number of bytes stored in each fragment.
///
/// Chosen so that node size is 64 bytes = 52 + 8 (id) + 1 (len) + 3 (node overhead).
const BPF: usize = 52;

/// Values are split into BPF size fragments.
struct Fragment {
    id: u64,
    /// Bit 0 encodes whether this is the last fragment.
    len: u8,
    bytes: [u8; BPF],
}

impl Fragment {
    pub fn new(id: u64) -> Self {
        Fragment {
            id,
            len: 0,
            bytes: [0; BPF],
        }
    }
}

impl Record for Fragment {
    fn compare(&self, _db: &DB, data: &[u8]) -> Ordering {
        let val = util::getu64(data, 0);
        self.id.cmp(&val)
    }

    fn save(&self, data: &mut [u8]) {
        util::setu64(data, self.id);
        data[8] = self.len;
        data[9..9 + BPF].copy_from_slice(&self.bytes[..BPF]);
    }
}