// Copyright (c) 2016-2021 Fabian Schuiki

//! A name table that internalizes all names presented to it and allows for them
//! to be referred to by a lightweight tag. This structure is heavily inspired
//! by the interner used in the Rust compiler.

use std::borrow::Borrow;
use std::cell::RefCell;
use std::cmp::Ordering;
use std::collections::HashMap;
use std::fmt;
use std::hash::Hash;
use std::ops::Deref;
use std::rc::Rc;

/// A name is a lightweight 32 bit tag that refers to a string in a name table.
/// During parsing, encountered strings are inserted into the name table and
/// only the corresponding tag is kept in the token. Names which have their most
/// significant bit set represent case sensitive names, such as for extended
/// identifiers.
#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Name(pub u32);

impl Name {
    /// Check if the name is case sensitive.
    pub fn is_case_sensitive(&self) -> bool {
        self.0 & 1 == 1
    }

    /// Return the string representation of this name.
    pub fn as_str(self) -> RcStr {
        get_name_table().get(self)
    }
}

impl fmt::Debug for Name {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}({})", self, self.0)
    }
}

impl fmt::Display for Name {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        fmt::Display::fmt(&self.as_str(), f)
    }
}

// impl Encodable for Name {
//     fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
//         s.emit_bool(self.is_case_sensitive())?;
//         s.emit_str(self.as_str().borrow())?;
//         Ok(())
//     }
// }

// impl Decodable for Name {
//     fn decode<S: Decoder>(s: &mut S) -> Result<Name, S::Error> {
//         let case = s.read_bool()?;
//         let name = s.read_str()?;
//         Ok(get_name_table().intern(&name, case))
//     }
// }

impl Into<String> for Name {
    fn into(self) -> String {
        self.as_str().into()
    }
}

impl<'a> From<&'a str> for Name {
    fn from(s: &'a str) -> Name {
        get_name_table().intern(s, true)
    }
}

/// A reference-counted string that acts like a regular str slice, hiding the
/// fact that it is wrapped in Rc<>.
#[derive(Clone, PartialEq, Hash, PartialOrd)]
pub struct RcStr(Rc<String>);

impl RcStr {
    /// Create a new ref-counted string which is a copy of `value`.
    pub fn new(value: &str) -> RcStr {
        RcStr(Rc::new(value.to_string()))
    }

    /// Create a new ref-counted string that contains `value`, without
    /// allocating any new storage.
    pub fn from(value: String) -> RcStr {
        RcStr(Rc::new(value))
    }
}

impl Eq for RcStr {}

impl Ord for RcStr {
    fn cmp(&self, other: &RcStr) -> Ordering {
        self[..].cmp(&other[..])
    }
}

impl fmt::Debug for RcStr {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self[..].fmt(f)
    }
}

impl fmt::Display for RcStr {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self[..].fmt(f)
    }
}

impl Borrow<str> for RcStr {
    fn borrow(&self) -> &str {
        &self.0[..]
    }
}

impl Deref for RcStr {
    type Target = str;
    fn deref(&self) -> &str {
        &self.0[..]
    }
}

impl Into<String> for RcStr {
    fn into(self) -> String {
        (*self.0).clone()
    }
}

impl AsRef<str> for RcStr {
    fn as_ref(&self) -> &str {
        self.0.as_ref()
    }
}

/// A lookup table of names. Internalizes strings either in a case sensitive or
/// case insensitive way. Allows for bidirectional lookup, i.e. by string or by
/// assigned name.
pub struct NameTable {
    map: RefCell<HashMap<RcStr, Name>>,
    vect: RefCell<Vec<RcStr>>,
}

impl NameTable {
    /// Create a new empty name table.
    pub fn new() -> NameTable {
        NameTable {
            map: RefCell::new(HashMap::new()),
            vect: RefCell::new(Vec::new()),
        }
    }

    /// Obtain a name for a string. This either inserts the string into the
    /// table and returns the new name, or returns the existing name if the
    /// string already exists in the table.
    pub fn intern(&self, value: &str, case_sensitive: bool) -> Name {
        let mut map = self.map.borrow_mut();
        if let Some(&idx) = map.get(value) {
            return idx;
        }

        // Since the name is not present in the table yet, we allocate a new idx
        // for it. Also, if it is a case-insensitive name, we insert both its
        // original form as well as its lowercase form into the lookup table.
        let mut vect = self.vect.borrow_mut();
        if case_sensitive {
            let new_idx = Name((vect.len() as u32) << 1 | 1);
            let v = RcStr::new(value);
            map.insert(v.clone(), new_idx);
            vect.push(v);
            new_idx
        } else {
            let new_idx = Name((vect.len() as u32) << 1 | 0);
            let lower = value.to_lowercase();
            if let Some(&idx) = map.get(lower.as_str()) {
                return idx;
            }
            let v = RcStr::new(value);
            map.insert(RcStr::from(lower), new_idx);
            map.insert(v.clone(), new_idx);
            vect.push(v);
            new_idx
        }
    }

    /// Retrieve the string given a name tag.
    pub fn get(&self, idx: Name) -> RcStr {
        (*self.vect.borrow())[(idx.0 >> 1) as usize].clone()
    }

    /// Try to find a string.
    pub fn find<Q: ?Sized>(&self, value: &Q) -> Option<Name>
    where
        RcStr: Borrow<Q>,
        Q: Eq + Hash,
    {
        (*self.map.borrow()).get(value).map(|v| *v)
    }
}

/// Get this thread's current name table.
pub fn get_name_table() -> Rc<NameTable> {
    thread_local!(static TBL: Rc<NameTable> = {
        let nt = NameTable::new();
        // token::prefill_name_table(&mut nt);
        Rc::new(nt)
    });
    TBL.with(|x| x.clone())
}