use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
use config::Config;
use index::keeper::AddTo;
use index::keeper::IndexSegmentKeeper;
use index::serialization::IndexSerialization;
use persy::{PRes, PersyError, PersyImpl, RecRef};
use snapshot::SnapshotId;
use std::collections::hash_map::Entry;
use std::collections::hash_map::HashMap;
use std::fmt::Display;
use std::io::{Cursor, Read, Write};
use std::str;
use std::sync::{Arc, Condvar, Mutex};
use transaction::Transaction;

/// Enum of all the possible Key or Value types for indexes
#[derive(Clone)]
pub enum IndexTypeId {
    U8,
    U16,
    U32,
    U64,
    I8,
    I16,
    I32,
    I64,
    STRING,
    PERSYID,
}

impl From<u8> for IndexTypeId {
    fn from(val: u8) -> IndexTypeId {
        match val {
            1 => IndexTypeId::U8,
            2 => IndexTypeId::U16,
            3 => IndexTypeId::U32,
            4 => IndexTypeId::U64,
            5 => IndexTypeId::I8,
            6 => IndexTypeId::I16,
            7 => IndexTypeId::I32,
            8 => IndexTypeId::I64,
            12 => IndexTypeId::STRING,
            13 => IndexTypeId::PERSYID,
            _ => panic!("type node defined for {}", val),
        }
    }
}

/// Trait implemented by all supported types in the index
pub trait IndexType: Display + Sized + Ord + Clone + AddTo + IndexSerialization {
    fn get_id() -> u8;
    fn get_type_id() -> IndexTypeId;
}

/// Define the behavior of the index in case a key value pair already exists
#[derive(Clone, Debug, PartialEq)]
pub enum ValueMode {
    /// An error will return if a key value pair already exists
    EXCLUSIVE,
    /// The value will be add to a list of values for the key, duplicate value will be collapsed to
    /// only one entry
    CLUSTER,
    /// The existing value will be replaced with the new value if a key value pair already exists
    REPLACE,
}

pub const INDEX_META_PREFIX: &str = "+_M";
pub const INDEX_DATA_PREFIX: &str = "+_D";

fn format_segment_name_meta(index_name: &str) -> String {
    format!("{}{}", INDEX_META_PREFIX, index_name)
}

fn format_segment_name_data(index_name: &str) -> String {
    format!("{}{}", INDEX_DATA_PREFIX, index_name)
}

impl From<u8> for ValueMode {
    fn from(value: u8) -> Self {
        match value {
            1 => ValueMode::EXCLUSIVE,
            2 => ValueMode::CLUSTER,
            3 => ValueMode::REPLACE,
            _ => unreachable!("is impossible to get a value mode from values not 1,2,3"),
        }
    }
}

impl ValueMode {
    fn to_u8(&self) -> u8 {
        match self {
            ValueMode::EXCLUSIVE => 1,
            ValueMode::CLUSTER => 2,
            ValueMode::REPLACE => 3,
        }
    }
}

struct IndexLock {
    write: bool,
    read_count: u32,
    cond: Arc<Condvar>,
}

impl IndexLock {
    fn new_write() -> IndexLock {
        IndexLock {
            write: true,
            read_count: 0,
            cond: Arc::new(Condvar::new()),
        }
    }

    fn new_read() -> IndexLock {
        IndexLock {
            write: false,
            read_count: 1,
            cond: Arc::new(Condvar::new()),
        }
    }

    fn inc_read(&mut self) {
        self.read_count += 1;
    }

    fn dec_read(&mut self) -> bool {
        self.read_count -= 1;
        self.read_count == 0
    }
}

pub struct Indexes {
    index_locks: Mutex<HashMap<String, IndexLock>>,
    config: Arc<Config>,
}

#[derive(Clone)]
pub struct IndexConfig {
    name: String,
    root: Option<RecRef>,
    pub key_type: u8,
    pub value_type: u8,
    page_min: usize,
    page_max: usize,
    pub value_mode: ValueMode,
}

impl IndexConfig {
    fn serialize(&self, w: &mut Write) -> PRes<()> {
        if let Some(ref root) = self.root {
            w.write_u64::<BigEndian>(root.page)?;
            w.write_u32::<BigEndian>(root.pos)?;
        } else {
            w.write_u64::<BigEndian>(0)?;
            w.write_u32::<BigEndian>(0)?;
        }
        w.write_u8(self.key_type)?;
        w.write_u8(self.value_type)?;
        w.write_u32::<BigEndian>(self.page_min as u32)?;
        w.write_u32::<BigEndian>(self.page_max as u32)?;
        w.write_u8(self.value_mode.to_u8())?;
        w.write_u16::<BigEndian>(self.name.len() as u16)?;
        w.write_all(self.name.as_bytes())?;
        Ok(())
    }
    fn deserialize(r: &mut Read) -> PRes<IndexConfig> {
        let index_root_page = r.read_u64::<BigEndian>()?;
        let index_root_pos = r.read_u32::<BigEndian>()?;
        let key_type = r.read_u8()?;
        let value_type = r.read_u8()?;
        let page_min = r.read_u32::<BigEndian>()? as usize;
        let page_max = r.read_u32::<BigEndian>()? as usize;
        let value_mode = ValueMode::from(r.read_u8()?);

        let name_size = r.read_u16::<BigEndian>()? as usize;
        let mut slice: Vec<u8> = vec![0; name_size];
        r.read_exact(&mut slice)?;
        let name: String = str::from_utf8(&slice[0..name_size])?.into();
        let root = if index_root_page != 0 && index_root_pos != 0 {
            Some(RecRef::new(index_root_page, index_root_pos))
        } else {
            None
        };
        Ok(IndexConfig {
            name,
            root,
            key_type,
            value_type,
            page_min,
            page_max,
            value_mode,
        })
    }
}

fn error_map(err: PersyError) -> PersyError {
    if let PersyError::SegmentNotFound = err {
        PersyError::IndexNotFound
    } else {
        err
    }
}

impl Indexes {
    pub fn new(config: &Arc<Config>) -> Indexes {
        Indexes {
            index_locks: Mutex::new(HashMap::new()),
            config: config.clone(),
        }
    }

    pub fn create_index<K, V>(
        p: &PersyImpl,
        tx: &mut Transaction,
        name: &str,
        min: usize,
        max: usize,
        value_mode: ValueMode,
    ) -> PRes<()>
    where
        K: Clone + Ord + IndexType,
        V: Clone + IndexType,
    {
        if min > max / 2 {
            return Err(PersyError::IndexMinElementsShouldBeAtLeastDoubleOfMax);
        }
        let segment_name_meta = format_segment_name_meta(name);
        p.create_segment(tx, &segment_name_meta)?;
        let segment_name_data = format_segment_name_data(name);
        p.create_segment(tx, &segment_name_data)?;
        let cfg = IndexConfig {
            name: name.to_string(),
            root: None,
            key_type: K::get_id(),
            value_type: V::get_id(),
            page_min: min,
            page_max: max,
            value_mode,
        };
        let mut scfg = Vec::new();
        cfg.serialize(&mut scfg)?;
        p.insert_record(tx, &segment_name_meta, &scfg)?;
        Ok(())
    }

    pub fn drop_index(p: &PersyImpl, tx: &mut Transaction, name: &str) -> PRes<()> {
        let segment_name_meta = format_segment_name_meta(name);
        p.drop_segment(tx, &segment_name_meta)?;
        let segment_name_data = format_segment_name_data(name);
        p.drop_segment(tx, &segment_name_data)?;
        Ok(())
    }

    pub fn update_index_root(p: &PersyImpl, tx: &mut Transaction, name: &str, root: Option<RecRef>) -> PRes<()> {
        let segment_name = format_segment_name_meta(name);
        let (id, mut config) = if let Some((rid, content)) = p.scan_tx(tx, &segment_name).map_err(error_map)?.next(p) {
            (rid, IndexConfig::deserialize(&mut Cursor::new(content))?)
        } else {
            return Err(PersyError::IndexNotFound);
        };

        if config.root != root {
            config.root = root;
            let mut scfg = Vec::new();
            config.serialize(&mut scfg)?;
            p.update_record(tx, &segment_name, &id.0, &scfg)?;
        }
        Ok(())
    }

    pub fn get_index(p: &PersyImpl, op_tx: Option<&Transaction>, name: &str) -> PRes<IndexConfig> {
        let segment_name_meta = format_segment_name_meta(name);
        let meta = if let Some(tx) = op_tx {
            p.scan_tx(tx, &segment_name_meta).map_err(error_map)?.next(p)
        } else {
            p.scan(&segment_name_meta).map_err(error_map)?.next(p)
        };

        if let Some((_, content)) = meta {
            Ok(IndexConfig::deserialize(&mut Cursor::new(content))?)
        } else {
            Err(PersyError::IndexNotFound)
        }
    }

    pub fn check_and_get_index<K: Clone + Ord + IndexType, V: Clone + IndexType>(
        p: &PersyImpl,
        op_tx: Option<&Transaction>,
        name: &str,
    ) -> PRes<IndexConfig> {
        let index = Indexes::get_index(p, op_tx, name)?;
        if index.key_type != K::get_id() {
            return Err(PersyError::IndexTypeMismatch(
                "given key type miss match to persistent key type".to_string(),
            ));
        }
        if index.value_type != V::get_id() {
            return Err(PersyError::IndexTypeMismatch(
                "given value type miss match to persistent key type".to_string(),
            ));
        }
        Ok(index)
    }

    pub fn check_and_get_index_keeper<'a, K: Clone + Ord + IndexType, V: Clone + IndexType>(
        p: &'a PersyImpl,
        tx: Option<&'a mut Transaction>,
        snapshot: Option<SnapshotId>,
        name: &str,
    ) -> PRes<IndexSegmentKeeper<'a>> {
        let (config, tx) = if let Some(t) = tx {
            (Indexes::check_and_get_index::<K, V>(p, Some(t), name)?, Some(t))
        } else {
            (Indexes::check_and_get_index::<K, V>(p, None, name)?, None)
        };
        Ok(IndexSegmentKeeper::new(
            name,
            &format_segment_name_data(name),
            config.root,
            p,
            tx,
            snapshot,
            config.value_mode,
        ))
    }

    pub fn write_lock(&self, indexes: &[String]) -> PRes<()> {
        for index in indexes {
            let seg_lock = IndexLock::new_write();
            loop {
                let mut lock_manager = self.index_locks.lock()?;
                let cond = match lock_manager.entry(index.clone()) {
                    Entry::Occupied(o) => o.get().cond.clone(),
                    Entry::Vacant(v) => {
                        v.insert(seg_lock);
                        break;
                    }
                };
                cond.wait_timeout(lock_manager, self.config.transaction_lock_timeout().clone())?;
            }
        }
        Ok(())
    }

    pub fn read_lock(&self, index: String) -> PRes<()> {
        loop {
            let mut lock_manager = self.index_locks.lock()?;
            let cond;
            match lock_manager.entry(index.clone()) {
                Entry::Occupied(mut o) => {
                    if o.get().write {
                        cond = o.get().cond.clone();
                    } else {
                        o.get_mut().inc_read();
                        break;
                    }
                }
                Entry::Vacant(v) => {
                    v.insert(IndexLock::new_read());
                    break;
                }
            };
            cond.wait_timeout(lock_manager, self.config.transaction_lock_timeout().clone())?;
        }
        Ok(())
    }

    pub fn read_unlock(&self, index: String) -> PRes<()> {
        let mut lock_manager = self.index_locks.lock()?;
        if let Entry::Occupied(mut lock) = lock_manager.entry(index) {
            if lock.get_mut().dec_read() {
                let cond = lock.get().cond.clone();
                lock.remove();
                cond.notify_one();
            }
        }
        Ok(())
    }

    pub fn write_unlock(&self, indexes: &[String]) -> PRes<()> {
        for index in indexes {
            let mut lock_manager = self.index_locks.lock()?;
            if let Some(lock) = lock_manager.remove(index) {
                lock.cond.notify_one();
            }
        }
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::{IndexConfig, ValueMode};
    use std::io::Cursor;

    #[test()]
    fn test_config_ser_des() {
        let cfg = IndexConfig {
            name: "abc".to_string(),
            root: None,
            key_type: 1,
            value_type: 1,
            page_min: 10,
            page_max: 30,
            value_mode: ValueMode::REPLACE,
        };

        let mut buff = Vec::new();
        cfg.serialize(&mut Cursor::new(&mut buff)).expect("serialization works");
        let read = IndexConfig::deserialize(&mut Cursor::new(&mut buff)).expect("deserialization works");
        assert_eq!(cfg.name, read.name);
        assert_eq!(cfg.root, read.root);
        assert_eq!(cfg.key_type, read.key_type);
        assert_eq!(cfg.value_type, read.value_type);
        assert_eq!(cfg.page_min, read.page_min);
        assert_eq!(cfg.page_max, read.page_max);
        assert_eq!(cfg.value_mode, read.value_mode);
    }
}