//! Implementation of [Reader] for the text syntax.

use crate::error::io_syntax_error;
use crate::error::is_eof_io_error;
use crate::error::syntax_error;
use crate::error::Error;
use crate::error::ExpectedKind;
use crate::error::Received;

use crate::hex;

use crate::value::boundary as B;
use crate::value::reader::BinarySource;
use crate::value::reader::ReaderResult;
use crate::value::repr::Annotations;
use crate::value::CompoundClass;
use crate::value::DomainParse;
use crate::value::IOValue;
use crate::value::IOValueDomainCodec;
use crate::value::Map;
use crate::value::NestedValue;
use crate::value::Reader;
use crate::value::Record;
use crate::value::Set;
use crate::value::Token;
use crate::value::Value;
use crate::value::ViaCodec;

use lazy_static::lazy_static;

use num::bigint::BigInt;

use std::convert::TryInto;
use std::io;
use std::marker::PhantomData;

/// The text syntax Preserves reader.
pub struct TextReader<'de, 'src, N: NestedValue, Dec: DomainParse<N::Embedded>, S: BinarySource<'de>> {
    /// Underlying source of (utf8) bytes.
    pub source: &'src mut S,
    /// Decoder for producing Rust values embedded in the text.
    pub dec: Dec,
    /// Treatment of whitespace before a toplevel term.
    pub toplevel_whitespace_mode: ToplevelWhitespaceMode,
    phantom: PhantomData<&'de N>,
}

/// [TextReader] chooses `Document` mode to treat whitespace preceding end-of-file as a "no
/// more values" non-error situation, or `Value` mode to treat it as an "expected more input"
/// situation.
///
/// The Preserves syntax for `Value` treats any input at all, even whitespace, as an indicator
/// that a term is to follow. However, when using a TextReader to parse a *series* of `Value`s
/// in a `Document`, whitespace followed by EOF is to be treated as the permitted optional
/// whitespace at the end of a `Document.
pub enum ToplevelWhitespaceMode {
    Document,
    Value,
}

fn decode_utf8(bs: Vec<u8>) -> io::Result<String> {
    Ok(String::from_utf8(bs).map_err(|_| io_syntax_error("Invalid UTF-8"))?)
}

fn append_codepoint(bs: &mut Vec<u8>, n: u32) -> io::Result<()> {
    let c = char::from_u32(n).ok_or_else(|| io_syntax_error("Bad code point"))?;
    let mut buf = [0; 4];
    let _ = c.encode_utf8(&mut buf);
    bs.extend(&buf[0..c.len_utf8()]);
    Ok(())
}

impl<'de, 'src, N: NestedValue, Dec: DomainParse<N::Embedded>, S: BinarySource<'de>>
    TextReader<'de, 'src, N, Dec, S>
{
    /// Construct a new reader from a byte (utf8) source and embedded-value decoder.
    pub fn new(source: &'src mut S, dec: Dec) -> Self {
        TextReader {
            source,
            dec,
            toplevel_whitespace_mode: ToplevelWhitespaceMode::Document,
            phantom: PhantomData,
        }
    }

    pub fn toplevel_whitespace_mode(mut self, new_mode: ToplevelWhitespaceMode) -> Self {
        self.toplevel_whitespace_mode = new_mode;
        self
    }

    fn peek(&mut self) -> io::Result<u8> {
        self.source.peek()
    }

    fn skip(&mut self) -> io::Result<()> {
        self.source.skip()
    }

    fn next_byte(&mut self) -> io::Result<u8> {
        let b = self.source.peek()?;
        self.source.skip()?;
        Ok(b)
    }

    fn skip_whitespace(&mut self) {
        self.skip_whitespace_and_maybe_commas(false)
    }

    fn skip_whitespace_and_maybe_commas(&mut self, skip_commas: bool) {
        // Deliberately swallows errors.
        while let Ok(c) = self.peek() {
            match c {
                b' ' | b'\t' | b'\r' | b'\n' => {
                    let _ = self.skip();
                    ()
                }
                b',' if skip_commas => {
                    let _ = self.skip();
                    ()
                }
                _ => break,
            }
        }
    }

    // TODO: This is a duplicate of fn expected in PackedReader.
    fn expected(&mut self, k: ExpectedKind) -> Error {
        match Reader::<N>::demand_next(self, true) {
            Ok(v) => Error::Expected(k, Received::ReceivedOtherValue(format!("{:?}", v))),
            Err(e) => e.into(),
        }
    }

    fn gather_annotations(&mut self, vs: &mut Vec<N>) -> ReaderResult<()> {
        loop {
            self.skip_whitespace();
            match self.peek()? {
                b'#' => {
                    let m = self.source.mark()?;
                    self.skip()?;
                    match self.next_byte()? {
                        b' ' | b'\t' => vs.push(N::new(self.comment_line()?)),
                        b'\n' | b'\r' => vs.push(N::new("")),
                        _ => {
                            self.source.restore(&m)?;
                            return Ok(());
                        }
                    }
                }
                b'@' => {
                    self.skip()?;
                    vs.push(self.demand_next(true)?)
                }
                _ => return Ok(()),
            }
        }
    }

    fn prepend_annotations_to_next(&mut self, mut annotations: Vec<N>) -> ReaderResult<N> {
        let (existing_annotations, v) = Reader::<N>::demand_next(self, true)?.pieces();
        annotations.extend_from_slice(existing_annotations.slice());
        Ok(N::wrap(Annotations::new(Some(annotations)), v))
    }

    fn skip_annotations(&mut self) -> ReaderResult<()> {
        loop {
            self.skip_whitespace();
            match self.peek()? {
                b'#' => {
                    let m = self.source.mark()?;
                    self.skip()?;
                    match self.next_byte()? {
                        b' ' | b'\t' => { self.comment_line()?; () }
                        b'\n' | b'\r' => (),
                        _ => {
                            self.source.restore(&m)?;
                            return Ok(());
                        }
                    }
                }
                b'@' => {
                    self.skip()?;
                    self.skip_value()?;
                }
                _ => return Ok(()),
            }
        }
    }

    /// Retrieve the next [IOValue] in the input stream.
    pub fn next_iovalue(&mut self, read_annotations: bool) -> io::Result<IOValue> {
        let mut r = TextReader::new(self.source, ViaCodec::new(IOValueDomainCodec));
        let v = r.demand_next(read_annotations)?;
        Ok(v)
    }

    fn comment_line(&mut self) -> io::Result<String> {
        let mut bs = Vec::new();
        loop {
            let b = self.peek()?;
            self.skip()?;
            match b {
                b'\r' | b'\n' => return Ok(decode_utf8(bs)?),
                _ => bs.push(b),
            }
        }
    }

    fn read_hex_float(&mut self, bytecount: usize) -> io::Result<N> {
        if self.next_byte()? != b'"' {
            return Err(io_syntax_error(
                "Missing open-double-quote in hex-encoded floating-point number",
            ));
        }
        let bs = self.read_hex_binary()?;
        if bs.len() != bytecount {
            return Err(io_syntax_error(
                "Incorrect number of bytes in hex-encoded floating-point number",
            ));
        }
        match bytecount {
            4 => Ok(Value::from(f32::from_bits(u32::from_be_bytes(bs.try_into().unwrap()))).wrap()),
            8 => Ok(Value::from(f64::from_bits(u64::from_be_bytes(bs.try_into().unwrap()))).wrap()),
            _ => Err(io_syntax_error(
                "Unsupported byte count in hex-encoded floating-point number",
            )),
        }
    }

    fn read_stringlike<X, H, R>(
        &mut self,
        mut seed: R,
        xform_item: X,
        terminator: u8,
        hexescape: u8,
        hexescaper: H,
    ) -> io::Result<R>
    where
        X: Fn(&mut R, u8) -> io::Result<()>,
        H: Fn(&mut R, &mut Self) -> io::Result<()>,
    {
        loop {
            match self.next_byte()? {
                c if c == terminator => return Ok(seed),
                b'\\' => match self.next_byte()? {
                    c if c == hexescape => hexescaper(&mut seed, self)?,
                    c if c == terminator || c == b'\\' || c == b'/' => xform_item(&mut seed, c)?,
                    b'b' => xform_item(&mut seed, b'\x08')?,
                    b'f' => xform_item(&mut seed, b'\x0c')?,
                    b'n' => xform_item(&mut seed, b'\x0a')?,
                    b'r' => xform_item(&mut seed, b'\x0d')?,
                    b't' => xform_item(&mut seed, b'\x09')?,
                    _ => return Err(io_syntax_error("Invalid escape code")),
                },
                c => xform_item(&mut seed, c)?,
            }
        }
    }

    fn hexnum(&mut self, count: usize) -> io::Result<u32> {
        let mut v: u32 = 0;
        for _ in 0..count {
            let c = self.next_byte()?;
            match (c as char).to_digit(16) {
                Some(d) => v = v << 4 | d,
                None => return Err(io_syntax_error("Bad hex escape")),
            }
        }
        Ok(v)
    }

    fn read_string(&mut self, delimiter: u8) -> io::Result<String> {
        decode_utf8(self.read_stringlike(
            Vec::new(),
            |bs, c| Ok(bs.push(c)),
            delimiter,
            b'u',
            |bs, r| {
                let n1 = r.hexnum(4)?;
                if (0xd800..=0xdbff).contains(&n1) {
                    let mut ok = true;
                    ok = ok && r.next_byte()? == b'\\';
                    ok = ok && r.next_byte()? == b'u';
                    if !ok {
                        Err(io_syntax_error("Missing second half of surrogate pair"))
                    } else {
                        let n2 = r.hexnum(4)?;
                        if (0xdc00..=0xdfff).contains(&n2) {
                            let n = ((n1 - 0xd800) << 10) + (n2 - 0xdc00) + 0x10000;
                            append_codepoint(bs, n)
                        } else {
                            Err(io_syntax_error("Bad second half of surrogate pair"))
                        }
                    }
                } else {
                    append_codepoint(bs, n1)
                }
            },
        )?)
    }

    fn read_literal_binary(&mut self) -> io::Result<N> {
        Ok(N::new(
            &self.read_stringlike(
                Vec::new(),
                |bs, b| Ok(bs.push(b)),
                b'"',
                b'x',
                |bs, r| Ok(bs.push(r.hexnum(2)? as u8)),
            )?[..],
        ))
    }

    fn read_hex_binary(&mut self) -> io::Result<Vec<u8>> {
        let mut s = String::new();
        loop {
            self.skip_whitespace();
            let c1 = self.next_byte()? as char;
            if c1 == '"' {
                return Ok(hex::HexParser::Strict.decode(&s).unwrap());
            }
            let c2 = self.next_byte()? as char;
            if !(c1.is_digit(16) && c2.is_digit(16)) {
                return Err(io_syntax_error("Invalid hex binary"));
            }
            s.push(c1);
            s.push(c2);
        }
    }

    fn read_base64_binary(&mut self) -> io::Result<N> {
        let mut bs = Vec::new();
        loop {
            self.skip_whitespace();
            let mut c = self.next_byte()?;
            if c == b']' {
                let bs = base64::decode_config(&decode_utf8(bs)?, base64::STANDARD_NO_PAD)
                    .map_err(|_| io_syntax_error("Invalid base64 character"))?;
                return Ok(N::new(&bs[..]));
            }
            if c == b'-' {
                c = b'+';
            }
            if c == b'_' {
                c = b'/';
            }
            if c == b'=' {
                continue;
            }
            bs.push(c);
        }
    }

    fn upto(&mut self, delimiter: u8, read_annotations: bool, skip_commas: bool) -> io::Result<Vec<N>> {
        let mut vs = Vec::new();
        loop {
            self.skip_whitespace_and_maybe_commas(skip_commas);
            if self.peek()? == delimiter {
                self.skip()?;
                return Ok(vs);
            }
            vs.push(Reader::<N>::demand_next(self, read_annotations)?);
        }
    }

    fn read_set(&mut self, read_annotations: bool) -> io::Result<N> {
        let items = self.upto(b'}', read_annotations, true)?;
        let mut s = Set::<N>::new();
        for i in items {
            if s.contains(&i) {
                return Err(io_syntax_error("Duplicate set element"));
            }
            s.insert(i);
        }
        Ok(N::new(s))
    }

    fn read_dictionary(&mut self, read_annotations: bool) -> io::Result<N> {
        let mut d = Map::new();
        loop {
            self.skip_whitespace_and_maybe_commas(true);
            if self.peek()? == b'}' {
                self.skip()?;
                return Ok(N::new(d));
            }
            let k = Reader::<N>::demand_next(self, read_annotations)?;
            self.skip_whitespace();
            if self.next_byte()? != b':' {
                return Err(io_syntax_error("Missing expected key/value separator"));
            }
            if d.contains_key(&k) {
                return Err(io_syntax_error("Duplicate key"));
            }
            let v = Reader::<N>::demand_next(self, read_annotations)?;
            d.insert(k, v);
        }
    }

    fn require_delimiter(&mut self, msg: &'static str) -> io::Result<()> {
        if self.delimiter_follows()? {
            Ok(())
        } else {
            Err(io_syntax_error(msg))
        }
    }

    fn delimiter_follows(&mut self) -> io::Result<bool> {
        let c = match self.peek() {
            Err(e) if is_eof_io_error(&e) => return Ok(true),
            Err(e) => return Err(e)?,
            Ok(c) if (c as char).is_whitespace() => return Ok(true),
            Ok(c) => c,
        };
        Ok(match c {
            b'(' | b')' | b'{' | b'}' | b'[' | b']' | b'<' | b'>' | b'"' | b';' | b','
                | b'@' | b'#' | b':' | b'|' | b' ' => true,
            _ => false,
        })
    }

    fn read_raw_symbol_or_number(&mut self, mut bs: Vec<u8>) -> io::Result<N> {
        lazy_static! {
            static ref NUMBER_RE: regex::Regex =
                regex::Regex::new(r"^([-+]?\d+)(((\.\d+([eE][-+]?\d+)?)|([eE][-+]?\d+))([fF]?))?$")
                    .unwrap();
        }
        while !self.delimiter_follows()? {
            bs.push(self.next_byte()?);
        }
        let s = decode_utf8(bs)?;
        match NUMBER_RE.captures(&s) {
            None => Ok(N::symbol(&s)),
            Some(m) => match m.get(2) {
                None => Ok(N::new(s.parse::<BigInt>().map_err(|_| {
                    io_syntax_error(&format!("Invalid signed-integer number: {:?}", s))
                })?)),
                Some(_) => {
                    if let Some(maybe_f) = m.get(7) {
                        let s = m[1].to_owned() + &m[3];
                        if maybe_f.range().is_empty() {
                            Ok(N::new(s.parse::<f64>().map_err(|_| {
                                io_syntax_error(&format!(
                                    "Invalid double-precision number: {:?}",
                                    s
                                ))
                            })?))
                        } else {
                            Ok(N::new(s.parse::<f32>().map_err(|_| {
                                io_syntax_error(&format!(
                                    "Invalid single-precision number: {:?}",
                                    s
                                ))
                            })?))
                        }
                    } else {
                        panic!("Internal error: cannot analyze number {:?}", s)
                    }
                }
            },
        }
    }
}

impl<'de, 'src, N: NestedValue, Dec: DomainParse<N::Embedded>, S: BinarySource<'de>> Reader<'de, N>
    for TextReader<'de, 'src, N, Dec, S>
{
    fn next(&mut self, read_annotations: bool) -> io::Result<Option<N>> {
        'restart: loop {
            match self.toplevel_whitespace_mode {
                ToplevelWhitespaceMode::Document => self.skip_whitespace(),
                ToplevelWhitespaceMode::Value => (),
            }
            match self.peek() {
                Err(e) if is_eof_io_error(&e) => return Ok(None),
                _ => (),
            }
            match self.toplevel_whitespace_mode {
                ToplevelWhitespaceMode::Document => (),
                ToplevelWhitespaceMode::Value => self.skip_whitespace(),
            }
            return Ok(Some(match self.peek()? {
                b'"' => {
                    self.skip()?;
                    N::new(self.read_string(b'"')?)
                }
                b'|' => {
                    self.skip()?;
                    N::symbol(&self.read_string(b'|')?)
                }
                b';' => {
                    return Err(io_syntax_error(
                        "Semicolon is reserved syntax"
                    ));
                }
                b'@' => {
                    if read_annotations {
                        let mut annotations = Vec::new();
                        self.gather_annotations(&mut annotations)?;
                        self.prepend_annotations_to_next(annotations)?
                    } else {
                        self.skip_annotations()?;
                        self.demand_next(read_annotations)?
                    }
                }
                b':' => {
                    return Err(io_syntax_error(
                        "Unexpected key/value separator between items",
                    ));
                }
                b'#' => {
                    self.skip()?;
                    match self.next_byte()? {
                        b' ' | b'\t' => {
                            if read_annotations {
                                let mut annotations = vec![N::new(self.comment_line()?)];
                                self.gather_annotations(&mut annotations)?;
                                self.prepend_annotations_to_next(annotations)?
                            } else {
                                self.comment_line()?;
                                continue 'restart;
                            }
                        }
                        b'f' => { self.require_delimiter("Delimiter must follow #f")?; N::new(false) }
                        b't' => { self.require_delimiter("Delimiter must follow #t")?; N::new(true) }
                        b'{' => self.read_set(read_annotations)?,
                        b'"' => self.read_literal_binary()?,
                        b'x' => match self.next_byte()? {
                            b'"' => N::new(&self.read_hex_binary()?[..]),
                            b'f' => self.read_hex_float(4)?,
                            b'd' => self.read_hex_float(8)?,
                            _ => return Err(io_syntax_error("Invalid #x syntax")),
                        },
                        b'[' => self.read_base64_binary()?,
                        b'!' => {
                            let v = self.next_iovalue(read_annotations)?;
                            Value::Embedded(self.dec.parse_embedded(&v)?).wrap()
                        }
                        other => {
                            return Err(io_syntax_error(&format!("Invalid # syntax: {:?}", other)))
                        }
                    }
                }
                b'<' => {
                    self.skip()?;
                    let vs = self.upto(b'>', read_annotations, false)?;
                    if vs.is_empty() {
                        return Err(io_syntax_error("Missing record label"));
                    }
                    Value::Record(Record(vs)).wrap()
                }
                b'[' => {
                    self.skip()?;
                    N::new(self.upto(b']', read_annotations, true)?)
                }
                b'{' => {
                    self.skip()?;
                    self.read_dictionary(read_annotations)?
                }
                b'>' => return Err(io_syntax_error("Unexpected >")),
                b']' => return Err(io_syntax_error("Unexpected ]")),
                b'}' => return Err(io_syntax_error("Unexpected }")),
                b',' => return Err(io_syntax_error("Unexpected ,")),
                other => {
                    self.skip()?;
                    self.read_raw_symbol_or_number(vec![other])?
                }
            }))
        }
    }

    fn open_record(&mut self, arity: Option<usize>) -> ReaderResult<B::Type> {
        self.skip_annotations()?;
        if self.peek()? != b'<' {
            return Err(self.expected(ExpectedKind::Record(arity)));
        }
        self.skip()?;
        let mut b = B::Type::default();
        Reader::<N>::ensure_more_expected(self, &mut b, &B::Item::RecordLabel)?;
        Ok(b)
    }

    fn open_sequence_or_set(&mut self) -> ReaderResult<B::Item> {
        self.skip_annotations()?;
        let mark = Reader::<N>::mark(self)?;
        match self.next_byte()? {
            b'#' => match self.next_byte()? {
                b'{' => return Ok(B::Item::SetValue),
                _ => (),
            },
            b'[' => return Ok(B::Item::SequenceValue),
            _ => (),
        }
        Reader::<N>::restore(self, &mark)?;
        Err(self.expected(ExpectedKind::SequenceOrSet))
    }

    fn open_sequence(&mut self) -> ReaderResult<()> {
        self.skip_annotations()?;
        if self.peek()? != b'[' {
            return Err(self.expected(ExpectedKind::Sequence));
        }
        self.skip()?;
        Ok(())
    }

    fn open_set(&mut self) -> ReaderResult<()> {
        self.skip_annotations()?;
        let mark = Reader::<N>::mark(self)?;
        match self.next_byte()? {
            b'#' => match self.next_byte()? {
                b'{' => return Ok(()),
                _ => (),
            },
            _ => (),
        }
        Reader::<N>::restore(self, &mark)?;
        Err(self.expected(ExpectedKind::Set))
    }

    fn open_dictionary(&mut self) -> ReaderResult<()> {
        self.skip_annotations()?;
        if self.peek()? != b'{' {
            return Err(self.expected(ExpectedKind::Dictionary));
        }
        self.skip()?;
        Ok(())
    }

    #[inline]
    fn boundary(&mut self, b: &B::Type) -> ReaderResult<()> {
        match b {
            B::Type {
                closing: Some(B::Item::DictionaryKey),
                opening: Some(B::Item::DictionaryValue),
            } => {
                self.skip_whitespace();
                if self.next_byte()? != b':' {
                    return Err(syntax_error("Missing expected key/value separator"));
                }
            }
            B::Type {
                closing: Some(B::Item::DictionaryValue),
                opening: Some(B::Item::DictionaryKey),
            } => self.skip_whitespace_and_maybe_commas(true),
            B::Type {
                closing: Some(B::Item::SetValue),
                opening: Some(B::Item::SetValue),
            } => self.skip_whitespace_and_maybe_commas(true),
            B::Type {
                closing: Some(B::Item::SequenceValue),
                opening: Some(B::Item::SequenceValue),
            } => self.skip_whitespace_and_maybe_commas(true),
            _ => (),
        }
        Ok(())
    }

    fn close_compound(&mut self, b: &mut B::Type, i: &B::Item) -> ReaderResult<bool> {
        self.skip_whitespace();
        match self.peek()? {
            b'>' | b']' | b'}' => {
                self.skip()?;
                Ok(true)
            }
            _ => {
                b.shift(Some(i.clone()));
                Reader::<N>::boundary(self, b)?;
                Ok(false)
            }
        }
    }

    fn open_embedded(&mut self) -> ReaderResult<()> {
        self.skip_annotations()?;
        let mark = Reader::<N>::mark(self)?;
        match self.next_byte()? {
            b'#' => match self.next_byte()? {
                b'!' => return Ok(()),
                _ => (),
            },
            _ => (),
        }
        Reader::<N>::restore(self, &mark)?;
        Err(self.expected(ExpectedKind::Embedded))
    }

    fn close_embedded(&mut self) -> ReaderResult<()> {
        Ok(())
    }

    type Mark = S::Mark;

    fn mark(&mut self) -> io::Result<Self::Mark> {
        self.source.mark()
    }

    fn restore(&mut self, mark: &Self::Mark) -> io::Result<()> {
        self.source.restore(mark)
    }

    fn next_token(&mut self, read_embedded_annotations: bool) -> io::Result<Token<N>> {
        self.skip_annotations()?;
        let mark = Reader::<N>::mark(self)?;
        Ok(match self.next_byte()? {
            b'<' => Token::Compound(CompoundClass::Record),
            b'[' => Token::Compound(CompoundClass::Sequence),
            b'{' => Token::Compound(CompoundClass::Dictionary),
            b'>' => Token::End,
            b']' => Token::End,
            b'}' => Token::End,
            b'#' => match self.next_byte()? {
                b'!' => {
                    let v = self.next_iovalue(read_embedded_annotations)?;
                    Token::Embedded(self.dec.parse_embedded(&v)?)
                }
                b'{' => Token::Compound(CompoundClass::Set),
                _ => {
                    Reader::<N>::restore(self, &mark)?;
                    Token::Atom(self.demand_next(false)?)
                }
            },
            _ => {
                Reader::<N>::restore(self, &mark)?;
                Token::Atom(self.demand_next(false)?)
            }
        })
    }

    fn next_annotations_and_token(&mut self) -> io::Result<(Vec<N>, Token<N>)> {
        let mut annotations = Vec::new();
        self.gather_annotations(&mut annotations)?;
        Ok((annotations, self.next_token(true)?))
    }
}