pub mod decode;

use std::borrow::Cow;

use crate::is_string_char;

pub use decode::*;

pub const STR_INLINE_MAX: usize = 18;

pub type Pos = u32;

#[derive(Clone, Copy, Debug)]
pub struct ITerm(Pos);

#[derive(Clone, Copy, Debug)]
pub(crate) struct IRaw {
    start: Pos,
    end: Pos,
}

#[derive(Clone, Copy, Debug)]
pub(crate) struct ISeq {
    seq_start: Pos,
    seq_end: Pos,
}

#[derive(Clone, Copy, Debug)]
pub(crate) struct IDict {
    dict_start: Pos,
    dict_end: Pos,
}

#[derive(Debug)]
pub(crate) enum TTerm {
    Str(IRaw),
    StrInline(u8, [u8; STR_INLINE_MAX]),
    RawSeq(IRaw, ISeq),
    RawList(IRaw, ISeq),
    RawDict(IRaw, IDict),
    Seq(ISeq),
    List(ISeq),
    Dict(IDict),
}

#[derive(Debug)]
pub struct Buf<'a> {
    bytes: Cow<'a, [u8]>,
    seqs: Vec<ITerm>,
    dicts: Vec<(IRaw, ITerm)>,
    terms: Vec<TTerm>,
}

#[derive(Debug)]
pub enum TermError {
    InvalidIndex(ITerm),
    WrongType(&'static str, &'static str),
    WrongLength(usize, usize),
    WrongKeys,
    NoRawRepresentation,
}

#[derive(Debug)]
pub enum ValueError {
    InvalidIndex(ITerm),
    DuplicateKey,
    BadString,
    SeqInSeq,
}

impl<'a> Buf<'a> {
    pub fn new() -> Self {
        Self {
            bytes: Default::default(),
            seqs: Vec::with_capacity(16),
            dicts: Vec::with_capacity(16),
            terms: Vec::with_capacity(16),
        }
    }

    // ================ READING FUNCTIONS ==================

    pub fn raw(&self, term: ITerm) -> Result<&[u8], TermError> {
        match self.get_term(term)? {
            TTerm::StrInline(len, bytes) => Ok(&bytes[..*len as usize]),
            TTerm::Str(r) | TTerm::RawSeq(r, _) | TTerm::RawList(r, _) | TTerm::RawDict(r, _) => {
                Ok(self.get_bytes(*r))
            }
            _ => Err(TermError::NoRawRepresentation),
        }
    }

    pub fn str(&self, term: ITerm) -> Result<&str, TermError> {
        match self.get_term(term)? {
            TTerm::StrInline(len, bytes) => {
                let bytes = &bytes[..*len as usize];
                let s = unsafe { std::str::from_utf8_unchecked(bytes) };
                Ok(s)
            }
            TTerm::Str(r) => {
                let bytes = self.get_bytes(*r);
                let s = unsafe { std::str::from_utf8_unchecked(bytes) };
                Ok(s)
            }
            t => Err(TermError::WrongType("string", t.typename())),
        }
    }

    pub fn seq<'x>(&'x self, term: &'x ITerm) -> Result<&'x [ITerm], TermError> {
        match self.get_term(*term)? {
            TTerm::RawSeq(_, s) | TTerm::Seq(s) => {
                Ok(&self.seqs[s.seq_start as usize..s.seq_end as usize])
            }
            _ => Ok(std::slice::from_ref(term)),
        }
    }

    pub fn seq_of<const N: usize>(&self, term: ITerm) -> Result<[ITerm; N], TermError> {
        match self.get_term(term)? {
            TTerm::RawSeq(_, s) | TTerm::Seq(s) => {
                let seq_len = (s.seq_end - s.seq_start) as usize;
                if seq_len == N {
                    let seq = &self.seqs[s.seq_start as usize..s.seq_end as usize];
                    Ok(seq.try_into().unwrap())
                } else {
                    Err(TermError::WrongLength(N, seq_len))
                }
            }
            t => Err(TermError::WrongType("seq", t.typename())),
        }
    }

    pub fn list(&self, term: ITerm) -> Result<&[ITerm], TermError> {
        match self.get_term(term)? {
            TTerm::RawList(_, s) | TTerm::List(s) => {
                Ok(&self.seqs[s.seq_start as usize..s.seq_end as usize])
            }
            t => Err(TermError::WrongType("list", t.typename())),
        }
    }

    pub fn list_of<const N: usize>(&self, term: ITerm) -> Result<[ITerm; N], TermError> {
        match self.get_term(term)? {
            TTerm::RawList(_, s) | TTerm::List(s) => {
                let list_len = (s.seq_end - s.seq_start) as usize;
                if list_len == N {
                    let seq = &self.seqs[s.seq_start as usize..s.seq_end as usize];
                    Ok(seq.try_into().unwrap())
                } else {
                    Err(TermError::WrongLength(N, list_len))
                }
            }
            t => Err(TermError::WrongType("list", t.typename())),
        }
    }

    pub fn dict_get(&self, term: ITerm, key: &str) -> Result<Option<ITerm>, TermError> {
        match self.get_term(term)? {
            TTerm::RawDict(_, d) | TTerm::Dict(d) => {
                let dict = &self.dicts[d.dict_start as usize..d.dict_end as usize];
                let pos_opt = dict
                    .binary_search_by(|(k, _)| self.get_bytes(*k).cmp(key.as_bytes()))
                    .ok();
                Ok(pos_opt.map(|pos| dict[pos].1))
            }
            t => Err(TermError::WrongType("dict", t.typename())),
        }
    }

    pub fn dict_of<const N: usize>(
        &self,
        term: ITerm,
        keys: [&str; N],
        allow_other: bool,
    ) -> Result<[ITerm; N], TermError> {
        match self.get_term(term)? {
            TTerm::RawDict(_, d) | TTerm::Dict(d) => {
                let dict = &self.dicts[d.dict_start as usize..d.dict_end as usize];
                if dict.len() < N || (dict.len() > N && !allow_other) {
                    return Err(TermError::WrongKeys);
                }

                let mut ret = [ITerm(0); N];
                for i in 0..N {
                    let pos = dict
                        .binary_search_by(|(k, _)| self.get_bytes(*k).cmp(keys[i].as_bytes()))
                        .map_err(|_| TermError::WrongKeys)?;
                    ret[i] = dict[pos].1;
                }

                Ok(ret)
            }
            t => Err(TermError::WrongType("dict", t.typename())),
        }
    }

    pub fn dict_iter(
        &self,
        term: ITerm,
    ) -> Result<impl Iterator<Item = (&str, ITerm)> + '_, TermError> {
        match self.get_term(term)? {
            TTerm::RawDict(_, d) | TTerm::Dict(d) => {
                let dict = &self.dicts[d.dict_start as usize..d.dict_end as usize];
                let iter = dict.iter().map(|(k, v)| {
                    (
                        unsafe { std::str::from_utf8_unchecked(self.get_bytes(*k)) },
                        *v,
                    )
                });
                Ok(iter)
            }
            t => Err(TermError::WrongType("dict", t.typename())),
        }
    }

    // ================= WRITING FUNCTIONS ================

    pub fn push_str(&mut self, s: &str) -> Result<ITerm, ValueError> {
        let b = s.as_bytes();

        if !b.iter().copied().all(is_string_char) {
            return Err(ValueError::BadString);
        }

        let term = if b.len() <= STR_INLINE_MAX {
            let mut bytes = [0u8; STR_INLINE_MAX];
            bytes[..b.len()].copy_from_slice(b);
            TTerm::StrInline(b.len() as u8, bytes)
        } else {
            TTerm::Str(self.push_bytes(b))
        };

        Ok(self.push_term(term))
    }

    pub fn push_seq(&mut self, iterator: impl Iterator<Item = ITerm>) -> Result<ITerm, ValueError> {
        let seq_start = self.seqs.len();

        for term in iterator {
            match self.terms.get(term.0 as usize) {
                None => {
                    self.seqs.truncate(seq_start);
                    return Err(ValueError::InvalidIndex(term));
                }
                Some(TTerm::RawSeq(_, _)) => {
                    self.seqs.truncate(seq_start);
                    return Err(ValueError::SeqInSeq);
                }
                _ => {
                    self.seqs.push(term);
                }
            }
        }

        let seq = ISeq {
            seq_start: seq_start as Pos,
            seq_end: self.seqs.len() as Pos,
        };

        Ok(self.push_term(TTerm::Seq(seq)))
    }

    pub fn push_list(
        &mut self,
        iterator: impl Iterator<Item = ITerm>,
    ) -> Result<ITerm, ValueError> {
        let list_start = self.seqs.len();

        for term in iterator {
            match self.terms.get(term.0 as usize) {
                None => {
                    self.seqs.truncate(list_start);
                    return Err(ValueError::InvalidIndex(term));
                }
                _ => {
                    self.seqs.push(term);
                }
            }
        }

        let list = ISeq {
            seq_start: list_start as Pos,
            seq_end: self.seqs.len() as Pos,
        };

        Ok(self.push_term(TTerm::List(list)))
    }

    pub fn push_dict<'k>(
        &mut self,
        iterator: impl Iterator<Item = (&'k str, ITerm)>,
    ) -> Result<ITerm, ValueError> {
        let bytes_start = self.bytes.len();
        let dict_start = self.dicts.len();

        for (key, term) in iterator {
            if !key.as_bytes().iter().copied().all(is_string_char) {
                return Err(ValueError::BadString);
            }
            let key = self.push_bytes(key.as_bytes());

            match self.terms.get(term.0 as usize) {
                None => {
                    self.bytes.to_mut().truncate(bytes_start);
                    self.dicts.truncate(dict_start);
                    return Err(ValueError::InvalidIndex(term));
                }
                _ => {
                    self.dicts.push((key, term));
                }
            }
        }

        self.dicts[dict_start..]
            .sort_by_key(|(k, _)| (&self.bytes[k.start as usize..k.end as usize], k.start));

        for ((k1, _), (k2, _)) in self.dicts[dict_start..]
            .iter()
            .zip(self.dicts[dict_start + 1..].iter())
        {
            if self.get_bytes(*k1) == self.get_bytes(*k2) {
                self.bytes.to_mut().truncate(bytes_start);
                self.dicts.truncate(dict_start);
                return Err(ValueError::DuplicateKey);
            }
        }

        let dict = IDict {
            dict_start: dict_start as Pos,
            dict_end: self.dicts.len() as Pos,
        };

        Ok(self.push_term(TTerm::Dict(dict)))
    }

    pub fn push_raw(&mut self, raw: &[u8]) -> Result<ITerm, ParseError> {
        let bytes_len = self.bytes.len();
        let seqs_len = self.seqs.len();
        let dicts_len = self.dicts.len();
        let terms_len = self.terms.len();

        let raw = self.push_bytes(raw);
        let result = self.decode(raw);

        if result.is_err() {
            // reset to initial state
            self.bytes.to_mut().truncate(bytes_len);
            self.seqs.truncate(seqs_len);
            self.dicts.truncate(dicts_len);
            self.terms.truncate(terms_len);
        }

        result
    }

    // ==== Internal ====

    #[inline]
    fn get_term(&self, term: ITerm) -> Result<&TTerm, TermError> {
        self.terms
            .get(term.0 as usize)
            .ok_or(TermError::InvalidIndex(term))
    }

    #[inline]
    fn push_term(&mut self, term: TTerm) -> ITerm {
        let ret = ITerm(self.terms.len() as Pos);
        self.terms.push(term);
        ret
    }

    #[inline]
    fn push_bytes(&mut self, raw: &[u8]) -> IRaw {
        let bytes_start = self.bytes.len();
        self.bytes.to_mut().extend(raw);
        IRaw {
            start: bytes_start as Pos,
            end: self.bytes.len() as Pos,
        }
    }
}

impl TTerm {
    fn typename(&self) -> &'static str {
        match self {
            TTerm::Str(_) | TTerm::StrInline(_, _) => "string",
            TTerm::RawSeq(_, _) | TTerm::Seq(_) => "seq",
            TTerm::RawList(_, _) | TTerm::List(_) => "list",
            TTerm::RawDict(_, _) | TTerm::Dict(_) => "dict",
        }
    }
}

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

    #[test]
    fn test_sizeof() {
        assert_eq!(std::mem::size_of::<TTerm>(), 20);
    }
}