use std::collections::BTreeMap;
use serde::{Serialize, Deserialize};
use crate::FieldId;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct FieldsIdsMap {
    names_ids: BTreeMap<String, FieldId>,
    ids_names: BTreeMap<FieldId, String>,
    next_id: Option<FieldId>,
}

impl FieldsIdsMap {
    pub fn new() -> FieldsIdsMap {
        FieldsIdsMap {
            names_ids: BTreeMap::new(),
            ids_names: BTreeMap::new(),
            next_id: Some(0),
        }
    }

    /// Returns the number of fields ids in the map.
    pub fn len(&self) -> usize {
        self.names_ids.len()
    }

    /// Returns `true` if the map is empty.
    pub fn is_empty(&self) -> bool {
        self.names_ids.is_empty()
    }

    /// Returns the field id related to a field name, it will create a new field id if the
    /// name is not already known. Returns `None` if the maximum field id as been reached.
    pub fn insert(&mut self, name: &str) -> Option<FieldId> {
        match self.names_ids.get(name) {
            Some(id) => Some(*id),
            None => {
                let id = self.next_id?;
                self.next_id = id.checked_add(1);
                self.names_ids.insert(name.to_owned(), id);
                self.ids_names.insert(id, name.to_owned());
                Some(id)
            }
        }
    }

    /// Get the id of a field based on its name.
    pub fn id(&self, name: &str) -> Option<FieldId> {
        self.names_ids.get(name).copied()
    }

    /// Get the name of a field based on its id.
    pub fn name(&self, id: FieldId) -> Option<&str> {
        self.ids_names.get(&id).map(String::as_str)
    }

    /// Remove a field name and id based on its name.
    pub fn remove(&mut self, name: &str) -> Option<FieldId> {
        match self.names_ids.remove(name) {
            Some(id) => self.ids_names.remove_entry(&id).map(|(id, _)| id),
            None => None,
        }
    }

    /// Iterate over the ids and names in the ids order.
    pub fn iter(&self) -> impl Iterator<Item=(FieldId, &str)> {
        self.ids_names.iter().map(|(id, name)| (*id, name.as_str()))
    }

    /// Iterate over the ids in the order of the ids.
    pub fn ids<'a>(&'a self) -> impl Iterator<Item=FieldId> + 'a {
        self.ids_names.keys().copied()
    }

    /// Iterate over the names in the order of the ids.
    pub fn names(&self) -> impl Iterator<Item=&str> {
        self.ids_names.values().map(AsRef::as_ref)
    }
}

impl Default for FieldsIdsMap {
    fn default() -> FieldsIdsMap {
        FieldsIdsMap::new()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn fields_ids_map() {
        let mut map = FieldsIdsMap::new();

        assert_eq!(map.insert("id"), Some(0));
        assert_eq!(map.insert("title"), Some(1));
        assert_eq!(map.insert("description"), Some(2));
        assert_eq!(map.insert("id"), Some(0));
        assert_eq!(map.insert("title"), Some(1));
        assert_eq!(map.insert("description"), Some(2));

        assert_eq!(map.id("id"), Some(0));
        assert_eq!(map.id("title"), Some(1));
        assert_eq!(map.id("description"), Some(2));
        assert_eq!(map.id("date"), None);

        assert_eq!(map.len(), 3);

        assert_eq!(map.name(0), Some("id"));
        assert_eq!(map.name(1), Some("title"));
        assert_eq!(map.name(2), Some("description"));
        assert_eq!(map.name(4), None);

        assert_eq!(map.remove("title"), Some(1));

        assert_eq!(map.id("title"), None);
        assert_eq!(map.insert("title"), Some(3));
        assert_eq!(map.len(), 3);

        let mut iter = map.iter();
        assert_eq!(iter.next(), Some((0, "id")));
        assert_eq!(iter.next(), Some((2, "description")));
        assert_eq!(iter.next(), Some((3, "title")));
        assert_eq!(iter.next(), None);
    }
}