//! Information about users, perms, etc
use super::*;
use std::collections::HashMap;
use std::borrow::Cow;
use bitflags::bitflags;

/// The ID type used for backing user/group IDs
type GenericID = uuid::Uuid;

/// A user group ID
#[derive(Debug, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
pub struct GroupID(GenericID);

/// A unique user ID
#[derive(Debug, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
pub struct UserID(GenericID);

#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct User
{
    id: UserID,

    name: String,

    hidden: bool,

    desc: Option<String>,
    comment: Option<String>,
    
    /// Corresponds to a Unix `superuser`.
    ///
    /// All permissions checks are bypassed for a user with this set.
    is_god: bool,

    groups: Vec<GroupID>,
}

/// A group is a way of setting permissions for a whole set of users.
///
/// Users have groups, not the other way around.
/// A user can have multiple groups or none.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Group
{
    id: GroupID,

    hidden: bool,

    /// Corresponds to a Unix `superuser`.
    ///
    /// All permissions checks are bypassed for a user in a group with this set.
    is_god: bool,

    name: String,
    desc: Option<String>,
    comment: Option<String>,

    inherits: Option<Vec<GroupID>>,
}

impl Group
{
    /*
//TODO: Create bespoke iterator type for this, it's not possible here.
    pub fn inherits<'b, 'a>(&'b self, space: &'a Userspace) -> impl Iterator<Item = GroupID> +'a
	where 'b: 'a
    {
	match &self.inherits {
	    Some(inherits) => inherits.iter()
		.filter_map(|group| group.find_in_space(space).map(|parent| parent.inherits(space))).flatten(),
	    None => todo!()
	}
    }*/
}

pub trait AsEntityId
{
    fn entity_id(&self) -> Cow<'_, EntityID>;
}

impl AsEntityId for EntityID
{
    #[inline(always)] fn entity_id(&self) -> Cow<'_, EntityID> {
	Cow::Borrowed(self)
    }
}

impl AsEntityId for UserID
{
    fn entity_id(&self) -> Cow<'_, EntityID> {
	Cow::Owned(EntityID::User(self.clone()))
    }
}

impl AsEntityId for GroupID
{
    fn entity_id(&self) -> Cow<'_, EntityID> {
	Cow::Owned(EntityID::Group(self.clone()))
    }
}

impl<'a, T> AsEntityId for &'a T
where T: AsEntityId
{
    #[inline(always)] fn entity_id(&self) -> Cow<'_, EntityID> {
	T::entity_id(self)
    }
}

/// A trait for items that can have permissions bits set for them.
/// Users and groups implement this.
pub trait Entity
{    
    fn generic_id(&self) -> &GenericID;
    
    fn name(&self) -> &str;
    fn desc(&self) -> Option<&str>;
    fn comment(&self) -> Option<&str>;
    
    fn superuser(&self) -> bool;

    /// # Note
    /// This does not flatten inherited groups, that needs to be performed later
    fn groups(&self) -> &[GroupID];
}

impl Entity for User
{
    #[inline] fn generic_id(&self) -> &GenericID
    {
	&self.id.0
    }
    
    #[inline] fn name(&self) -> &str
    {
	&self.name[..]
    }
    #[inline] fn desc(&self) -> Option<&str>
    {
	self.desc.as_ref().map(String::as_str)
    }
    #[inline] fn comment(&self) -> Option<&str>
    {
	self.comment.as_ref().map(String::as_str)
    }
    
    #[inline] fn superuser(&self) -> bool
    {
	self.is_god
    }

    /// # Note
    /// This does not flatten inherited groups, that needs to be performed later
    #[inline] fn groups(&self) -> &[GroupID]
    {
	&self.groups[..]
    }
}

impl Entity for Group
{   
    #[inline] fn generic_id(&self) -> &GenericID
    {
	&self.id.0
    }
    
    #[inline] fn name(&self) -> &str
    {
	&self.name[..]
    }
    #[inline] fn desc(&self) -> Option<&str>
    {
	self.desc.as_ref().map(String::as_str)
    }
    #[inline] fn comment(&self) -> Option<&str>
    {
	self.comment.as_ref().map(String::as_str)
    }
    
    #[inline] fn superuser(&self) -> bool
    {
	self.is_god
    }

    /// # Note
    /// This does not flatten inherited groups, that needs to be performed later
    #[inline] fn groups(&self) -> &[GroupID]
    {
	self.inherits.as_ref().map(Vec::as_slice).unwrap_or(&[])
    }
}

/// Either a single user or a group of users
#[derive(Debug, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize)]
pub enum EntityID
{
    User(UserID),
    Group(GroupID),
}

impl UserID
{
    /// Attempt to find this user in this userspace
    pub fn find_in_space<'a>(&self, space: &'a Userspace) -> Option<&'a User>
    {
	space.users.get(self)
    }
    
    
    /// Attempt to find a mutable reference to this user in this userspace
    pub fn find_in_space_mut<'a>(&self, space: &'a mut Userspace) -> Option<&'a mut User>
    {
	space.users.get_mut(self)
    }
}

impl GroupID
{
    
    /// Attempt to find this group in this userspace
    pub fn find_in_space<'a>(&self, space: &'a Userspace) -> Option<&'a Group>
    {
	space.groups.get(self)
    }
    
    /// Attempt to find a mutable reference to this group in this userspace
    pub fn find_in_space_mut<'a>(&self, space: &'a mut Userspace) -> Option<&'a mut Group>
    {
	space.groups.get_mut(self)
    }
}

impl EntityID
{
    /// Attempt to find the entity that implements this ID in this space
    pub fn find_in_space<'a>(&self, space: &'a Userspace) -> Option<&'a (dyn Entity + 'static)>
    {
	match self {
	    Self::User(id) => space.users.get(id).map(|x| x as &dyn Entity),
	    Self::Group(id) => space.groups.get(id).map(|x| x as &dyn Entity),
	}
    }
}

bitflags! {
    /// A permission a user or group has for a data item.
    #[derive(Serialize, Deserialize)]
    struct Permission: u16 {
	/// Cannot read or write the item.
	///
	/// However they can see it, unless it is marked "hidden".
	const NONE = 0;
	/// Can read from the item but cannot write to it
	const READ = 1;
	/// Can write to the item
	///
	/// This does not imply `READ`.
	const WRITE = 2;

	/// Full access
	const FULL = Self::READ.bits | Self::WRITE.bits;
    }
}


/// A set of permissions informations for users and/or groups
#[derive(Debug, Serialize, Deserialize)]
pub struct Permissions
{
    blanket: Permission,
    
    spec: smallmap::Map<EntityID, Permission>,
}

/// Contains all users and groups
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct Userspace
{
    // use maps here for easier lookup, despite duplicating ID data
    users: HashMap<UserID, User>,
    groups: HashMap<GroupID, Group>,
}

impl Userspace
{
    /// Is this `User` or `Group` ID present in this space?
    pub fn contains_id(&self, ent: &impl AsEntityId) -> bool
    {
	ent.entity_id().find_in_space(self).is_some()
    }
}