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use serde::de::DeserializeOwned;
use std::collections::hash_map;
use std::slice;

use crate::serialization::Serializer;

/// Iterator object for iterating over keys and values in PickleDB. Returned in [PickleDb::iter()](struct.PickleDb.html#method.iter)
pub struct PickleDbIterator<'a> {
    pub(crate) map_iter: hash_map::Iter<'a, String, Vec<u8>>,
    pub(crate) serializer: &'a Serializer,
}

impl<'a> Iterator for PickleDbIterator<'a> {
    type Item = PickleDbIteratorItem<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        match self.map_iter.next() {
            Some((key, value)) => Some(PickleDbIteratorItem {
                key,
                value,
                serializer: self.serializer,
            }),
            None => None,
        }
    }
}

/// The object returned in each iteration when iterating over keys and values in PickleDB
pub struct PickleDbIteratorItem<'a> {
    key: &'a str,
    value: &'a Vec<u8>,
    serializer: &'a Serializer,
}

impl<'a> PickleDbIteratorItem<'a> {
    /// Get the key
    pub fn get_key(&self) -> &str {
        self.key
    }

    /// Get the value of the key.
    ///
    /// The key is always a string but the value can be of any type. It's the user's
    /// responsibility to know the value type and give it while calling this method.
    /// If the key doesn't exist or if the type is wrong, `None` will be returned.
    /// Otherwise `Some(V)` will be returned.
    /// Since the values are stored in a serialized way the returned object is
    /// not a reference to the value stored in a DB but actually a new instance of it.
    /// The method returns `Some(V)` if deserialization succeeds or `None` otherwise.
    ///
    pub fn get_value<V>(&self) -> Option<V>
    where
        V: DeserializeOwned,
    {
        self.serializer.deserialize_data::<V>(self.value)
    }
}

/// Iterator object for iterating over items in a PickleDB list. Returned in [PickleDb::liter()](struct.PickleDb.html#method.liter)
pub struct PickleDbListIterator<'a> {
    pub(crate) list_iter: slice::Iter<'a, Vec<u8>>,
    pub(crate) serializer: &'a Serializer,
}

impl<'a> Iterator for PickleDbListIterator<'a> {
    type Item = PickleDbListIteratorItem<'a>;

    fn next(&mut self) -> Option<Self::Item> {
        match self.list_iter.next() {
            Some(value) => Some(PickleDbListIteratorItem {
                value,
                serializer: self.serializer,
            }),
            None => None,
        }
    }
}

/// The object returned in each iteration when iterating over a PickleDB list
pub struct PickleDbListIteratorItem<'a> {
    value: &'a Vec<u8>,
    serializer: &'a Serializer,
}

impl<'a> PickleDbListIteratorItem<'a> {
    /// Get the item in the current position.
    ///
    /// This method retrieves the item in the current position. It's the user's responsibility
    /// to know what is the correct type of the item and give it while calling this method.
    /// Since the item in the lists are stored in a serialized way the returned object
    /// is not a reference to the item stored in a DB but actually a new instance of it.
    /// The method returns `Some(V)` if deserialization succeeds or `None` otherwise.
    ///
    pub fn get_item<V>(&self) -> Option<V>
    where
        V: DeserializeOwned,
    {
        self.serializer.deserialize_data(self.value)
    }
}