use std::borrow::Cow;

use crate::{
    is_string_char, is_whitespace, DICT_ASSIGN, DICT_CLOSE, DICT_DELIM, DICT_OPEN, LIST_CLOSE,
    LIST_DELIM, LIST_OPEN,
};

pub type Pos = u32;

#[derive(Debug)]
pub enum ParseError {
    IncompleteInput,
    DuplicateKey(Pos),
    Garbage(Pos),
}

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

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

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

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

#[derive(Debug)]
enum TTerm {
    Str(IRaw),
    RawSeq(IRaw, ISeq),
    RawList(IRaw, ISeq),
    RawDict(IRaw, IDict),
}

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

pub fn decode(input: &[u8]) -> Result<(Buf<'_>, ITerm), ParseError> {
    let mut buf = Buf {
        bytes: input.into(),
        seqs: Vec::with_capacity(16),
        dicts: Vec::with_capacity(16),
        terms: Vec::with_capacity(16),
    };
    let all_buf = IRaw {
        start: 0,
        end: input.len() as Pos,
    };

    let mut stack = Vec::with_capacity(16);
    let (term, rest) = buf.decode(all_buf, &mut stack)?;
    assert!(stack.is_empty());

    let rest = buf.take_whitespace(rest);
    if rest.start < all_buf.end {
        return Err(ParseError::Garbage(rest.start));
    }

    Ok((buf, term))
}

enum StackItem {
    Term(ITerm),
    KeyValue(IRaw, ITerm),
}
type Stack = Vec<StackItem>;
impl StackItem {
    fn term(self) -> ITerm {
        match self {
            StackItem::Term(term) => term,
            _ => unreachable!(),
        }
    }
    fn kv(self) -> (IRaw, ITerm) {
        match self {
            StackItem::KeyValue(key, term) => (key, term),
            _ => unreachable!(),
        }
    }
}

impl<'a> Buf<'a> {
    // ============================================ PUBLIC ACCESS FUNCTIONS

    pub fn raw(&self, term: ITerm) -> Option<&[u8]> {
        match self.terms.get(term.0 as usize)? {
            TTerm::Str(r) | TTerm::RawSeq(r, _) | TTerm::RawList(r, _) | TTerm::RawDict(r, _) => {
                self.get_bytes(*r)
            }
        }
    }

    pub fn str(&self, term: ITerm) -> Option<&str> {
        match self.terms.get(term.0 as usize)? {
            TTerm::Str(r) => self
                .bytes
                .get(r.start as usize..r.end as usize)
                .map(|x| unsafe { std::str::from_utf8_unchecked(x) }),
            _ => None,
        }
    }

    pub fn seq<'x>(&'x self, term: &'x ITerm) -> Option<&'x [ITerm]> {
        match self.terms.get(term.0 as usize)? {
            TTerm::RawSeq(_, s) => self.seqs.get(s.seq_start as usize..s.seq_end as usize),
            _ => Some(std::slice::from_ref(term)),
        }
    }

    pub fn seq_of<const N: usize>(&self, term: ITerm) -> Option<[ITerm; N]> {
        match self.terms.get(term.0 as usize)? {
            TTerm::RawSeq(_, s) => {
                if (s.seq_end - s.seq_start) as usize == N {
                    let seq = self.seqs.get(s.seq_start as usize..s.seq_end as usize)?;
                    Some(seq.try_into().unwrap())
                } else {
                    None
                }
            }
            _ => None,
        }
    }

    pub fn list(&self, term: ITerm) -> Option<&[ITerm]> {
        match self.terms.get(term.0 as usize)? {
            TTerm::RawList(_, s) => self.seqs.get(s.seq_start as usize..s.seq_end as usize),
            _ => None,
        }
    }

    pub fn list_of<const N: usize>(&self, term: ITerm) -> Option<[ITerm; N]> {
        match self.terms.get(term.0 as usize)? {
            TTerm::RawList(_, s) if (s.seq_end - s.seq_start) as usize == N => {
                let seq = self.seqs.get(s.seq_start as usize..s.seq_end as usize)?;
                Some(seq.try_into().unwrap())
            }
            _ => None,
        }
    }

    pub fn dict_get(&self, term: ITerm, key: &str) -> Option<ITerm> {
        match self.terms.get(term.0 as usize)? {
            TTerm::RawDict(_, d) => {
                let dict = self.dicts.get(d.dict_start as usize..d.dict_end as usize)?;
                let pos = dict.binary_search_by(|(k, _)| self.get_bytes(*k).unwrap().cmp(key.as_bytes())).ok()?;
                Some(dict[pos].1)
            }
            _ => None,
        }
    }

    pub fn dict_of<const N: usize>(&self, term: ITerm, keys: [&str; N], allow_other: bool) -> Option<[ITerm; N]> {
        match self.terms.get(term.0 as usize)? {
            TTerm::RawDict(_, d) => {
                let dict = self.dicts.get(d.dict_start as usize..d.dict_end as usize)?;
                if dict.len() < N || (dict.len() > N && !allow_other) {
                    return None;
                }

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

                Some(ret)
            }
            _ => None,
        }
    }

    pub fn dict_iter(&self, term: ITerm) -> Option<impl Iterator<Item=(&str, ITerm)> + '_> {
        match self.terms.get(term.0 as usize)? {
            TTerm::RawDict(_, d) => {
                let dict = self.dicts.get(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).unwrap()) }, *v));
                Some(iter)
            }
            _ => None,
        }
    }

    // ============================================ NETTEXT PARSING

    fn decode(&mut self, raw: IRaw, stack: &mut Stack) -> Result<(ITerm, IRaw), ParseError> {
        let start = self.take_whitespace(raw);
        let stack_start = stack.len();

        let mut cur_end = start;
        let mut next_start = start;
        loop {
            match self.decode_nonseq_term(next_start, stack) {
                Err(_) => break,
                Ok((term, rest)) => {
                    stack.push(StackItem::Term(term));
                    cur_end = rest;
                    next_start = self.take_whitespace(rest);
                }
            }
        }

        if stack.len() == stack_start {
            Err(self.error_at(next_start))
        } else if stack.len() == stack_start + 1 {
            Ok((stack.pop().unwrap().term(), next_start))
        } else {
            let seq_raw = IRaw {
                start: start.start,
                end: cur_end.start,
            };
            let seq_start = self.seqs.len();
            self.seqs
                .extend(stack.drain(stack_start..).map(StackItem::term));
            let seq = TTerm::RawSeq(
                seq_raw,
                ISeq {
                    seq_start: seq_start as Pos,
                    seq_end: self.seqs.len() as Pos,
                },
            );
            Ok((self.push_term(seq), next_start))
        }
    }

    fn decode_nonseq_term(
        &mut self,
        raw: IRaw,
        stack: &mut Stack,
    ) -> Result<(ITerm, IRaw), ParseError> {
        if let Ok((term, rest)) = self.decode_string(raw) {
            Ok((term, rest))
        } else if let Ok((term, rest)) = self.decode_list(raw, stack) {
            Ok((term, rest))
        } else if let Ok((term, rest)) = self.decode_dict(raw, stack) {
            Ok((term, rest))
        } else {
            Err(self.error_at(raw))
        }
    }

    fn decode_list(&mut self, raw: IRaw, stack: &mut Stack) -> Result<(ITerm, IRaw), ParseError> {
        let stack_start = stack.len();

        let mut cur = self.take_whitespace(self.take_char(raw, LIST_OPEN)?);

        while let Ok((term, rest)) = self.decode(cur, stack) {
            stack.push(StackItem::Term(term));
            cur = self.take_whitespace(rest);
            if let Ok(rest) = self.take_char(rest, LIST_DELIM) {
                cur = self.take_whitespace(rest);
            } else {
                break;
            }
        }

        if let Ok(rest) = self.take_char(cur, LIST_CLOSE) {
            let seq_raw = IRaw {
                start: raw.start,
                end: rest.start,
            };
            let seq_start = self.seqs.len();
            self.seqs
                .extend(stack.drain(stack_start..).map(StackItem::term));
            let seq = TTerm::RawList(
                seq_raw,
                ISeq {
                    seq_start: seq_start as Pos,
                    seq_end: self.seqs.len() as Pos,
                },
            );
            Ok((self.push_term(seq), rest))
        } else {
            stack.truncate(stack_start);
            Err(self.error_at(cur))
        }
    }

    fn decode_dict(&mut self, raw: IRaw, stack: &mut Stack) -> Result<(ITerm, IRaw), ParseError> {
        let stack_start = stack.len();

        match self.decode_dict_inner(raw, stack) {
            Ok(rest) => {
                let dict_raw = IRaw {
                    start: raw.start,
                    end: rest.start,
                };
                let dict_start = self.dicts.len();
                self.dicts
                    .extend(stack.drain(stack_start..).map(StackItem::kv));
                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).unwrap() == self.get_bytes(*k2).unwrap() {
                        return Err(ParseError::DuplicateKey(k1.start));
                    }
                }

                let dict = TTerm::RawDict(
                    dict_raw,
                    IDict {
                        dict_start: dict_start as Pos,
                        dict_end: self.dicts.len() as Pos,
                    },
                );
                Ok((self.push_term(dict), rest))
            }
            Err(e) => {
                stack.truncate(stack_start);
                Err(e)
            }
        }
    }

    fn decode_dict_inner(&mut self, raw: IRaw, stack: &mut Stack) -> Result<IRaw, ParseError> {
        let mut cur = self.take_whitespace(self.take_char(raw, DICT_OPEN)?);

        while let Ok((key, rest)) = self.take_string(cur) {
            cur = self.take_whitespace(rest);

            cur = self.take_char(cur, DICT_ASSIGN)?;

            let (value, rest) = self.decode(cur, stack)?;
            cur = self.take_whitespace(rest);
            stack.push(StackItem::KeyValue(key, value));

            if let Ok(rest) = self.take_char(cur, DICT_DELIM) {
                cur = self.take_whitespace(rest);
            } else {
                break;
            }
        }

        let rest = self.take_char(cur, DICT_CLOSE)?;
        Ok(rest)
    }

    fn decode_string(&mut self, raw: IRaw) -> Result<(ITerm, IRaw), ParseError> {
        let (string_raw, rest) = self.take_string(raw)?;
        let string = self.push_term(TTerm::Str(string_raw));
        Ok((string, rest))
    }

    fn take_string(&mut self, raw: IRaw) -> Result<(IRaw, IRaw), ParseError> {
        let mut rest = raw;
        while rest.start < rest.end {
            if is_string_char(self.bytes[rest.start as usize]) {
                rest.start += 1;
            } else {
                break;
            }
        }

        if rest.start > raw.start {
            let string_raw = IRaw {
                start: raw.start,
                end: rest.start,
            };
            Ok((string_raw, rest))
        } else {
            Err(self.error_at(rest))
        }
    }

    #[inline]
    fn take_char(&self, raw: IRaw, c: u8) -> Result<IRaw, ParseError> {
        if raw.start >= raw.end {
            Err(ParseError::IncompleteInput)
        } else if self.bytes[raw.start as usize] != c {
            Err(ParseError::Garbage(raw.start))
        } else {
            Ok(IRaw {
                start: raw.start + 1,
                end: raw.end,
            })
        }
    }

    #[inline]
    fn take_whitespace(&self, mut raw: IRaw) -> IRaw {
        while raw.start < raw.end {
            if is_whitespace(self.bytes[raw.start as usize]) {
                raw.start += 1;
            } else {
                break;
            }
        }
        raw
    }

    #[inline]
    fn get_bytes(&self, raw: IRaw) -> Option<&[u8]> {
        self.bytes.get(raw.start as usize..raw.end as usize)
    }

    #[inline]
    fn error_at(&self, raw: IRaw) -> ParseError {
        if raw.start < raw.end {
            ParseError::Garbage(raw.start)
        } else {
            ParseError::IncompleteInput
        }
    }

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

    #[cfg(test)]
    fn debug(&self, i: ITerm) {
        use crate::debug as debug_str;

        let term = &self.terms[i.0 as usize];
        match term {
            TTerm::Str(r) => {
                eprintln!(
                    "{} -> {:?} = `{}`",
                    i.0,
                    term,
                    debug_str(&self.bytes[r.start as usize..r.end as usize])
                );
            }
            TTerm::RawSeq(r, s) => {
                eprintln!(
                    "{} -> {:?} = `{}` ((",
                    i.0,
                    term,
                    debug_str(&self.bytes[r.start as usize..r.end as usize])
                );
                for j in self.seqs[s.seq_start as usize..s.seq_end as usize].iter() {
                    self.debug(*j);
                }
                eprintln!("))");
            }
            TTerm::RawList(r, l) => {
                eprintln!(
                    "{} -> {:?} = `{}` [[",
                    i.0,
                    term,
                    debug_str(&self.bytes[r.start as usize..r.end as usize])
                );
                for j in self.seqs[l.seq_start as usize..l.seq_end as usize].iter() {
                    self.debug(*j);
                }
                eprintln!("]]");
            }
            TTerm::RawDict(r, d) => {
                eprintln!(
                    "{} -> {:?} = `{}` {{{{",
                    i.0,
                    term,
                    debug_str(&self.bytes[r.start as usize..r.end as usize])
                );
                for (k, v) in self.dicts[d.dict_start as usize..d.dict_end as usize].iter() {
                    eprint!(
                        "[`{}`] = ",
                        debug_str(&self.bytes[k.start as usize..k.end as usize])
                    );
                    self.debug(*v);
                }
                eprintln!("}}}}");
            }
        }
    }
}

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

    #[test]
    fn list_and_seq() {
        let string = "[ [ h1; h2; h3 ]; hello world [ acc bii; cooj   dlpa] ]";
        eprintln!("{}", string);
        let (buf, term) = decode(string.as_bytes()).unwrap();
        buf.debug(term);

        let [a, b] = buf.list_of(term).unwrap();

        assert_eq!(buf.raw(a).unwrap(), b"[ h1; h2; h3 ]");
        let l = buf.list(a).unwrap();
        assert_eq!(l.len(), 3);
        assert_eq!(buf.str(l[0]).unwrap(), "h1");
        assert_eq!(buf.str(l[1]).unwrap(), "h2");
        assert_eq!(buf.str(l[2]).unwrap(), "h3");

        assert_eq!(buf.raw(b).unwrap(), b"hello world [ acc bii; cooj   dlpa]");
        let [h, w, l] = buf.seq_of(b).unwrap();
        assert_eq!(buf.str(h).unwrap(), "hello");
        assert_eq!(buf.str(w).unwrap(), "world");

        assert_eq!(buf.raw(l).unwrap(), b"[ acc bii; cooj   dlpa]");
        let [l1, l2] = buf.list_of(l).unwrap();

        assert_eq!(buf.raw(l1).unwrap(), b"acc bii");
        let s = buf.seq(&l1).unwrap();
        assert_eq!(s.len(), 2);
        assert_eq!(buf.str(s[0]).unwrap(), "acc");
        assert_eq!(buf.str(s[1]).unwrap(), "bii");

        assert_eq!(buf.raw(l2).unwrap(), b"cooj   dlpa");
        let [s2a, s2b] = buf.seq_of(l2).unwrap();
        assert_eq!(buf.str(s2a).unwrap(), "cooj");
        assert_eq!(buf.str(s2b).unwrap(), "dlpa");
    }

    #[test]
    fn dict() {
        let string =
            "[ { a = plop; b = hello world }; ploplop { e=15; d=12 ;c = {key=val;key2=val2}} ]";
        eprintln!("{}", string);
        let (buf, term) = decode(string.as_bytes()).unwrap();
        buf.debug(term);

        let [a, b] = buf.list_of(term).unwrap();
        
        assert_eq!(buf.raw(a).unwrap(), b"{ a = plop; b = hello world }");
        let [aa, ab] = buf.dict_of(a, ["a", "b"], false).unwrap();
        assert_eq!(buf.raw(aa).unwrap(), b"plop");
        assert_eq!(buf.raw(ab).unwrap(), b"hello world");

        assert_eq!(buf.raw(b).unwrap(), b"ploplop { e=15; d=12 ;c = {key=val;key2=val2}}");
        let [ba, bb] = buf.seq_of(b).unwrap();
        assert_eq!(buf.str(ba).unwrap(), "ploplop");

        assert_eq!(buf.str(buf.dict_get(bb, "e").unwrap()).unwrap(), "15");
        let mut iter = buf.dict_iter(bb).unwrap();
        let (k1, v1) = iter.next().unwrap();
        assert_eq!(k1, "c");
        assert_eq!(buf.raw(v1).unwrap(), b"{key=val;key2=val2}");
        let (k2, v2) = iter.next().unwrap();
        assert_eq!(k2, "d");
        assert_eq!(buf.str(v2).unwrap(), "12");
        let (k3, v3) = iter.next().unwrap();
        assert_eq!(k3, "e");
        assert_eq!(buf.str(v3).unwrap(), "15");
        assert!(iter.next().is_none());
    }
}