//! Functions to generate nettext representations of data structures
//!
//! Example:
//!
//! ```
//! use nettext::enc::*;
//!
//! let nettext_encoding = seq([
//!     string("CALL").unwrap(),
//!     string("myfunction").unwrap(),
//!     dict([
//!         ("a", string("hello").unwrap()),
//!         ("b", string("world").unwrap()),
//!         ("c", raw(b"{ a = 12; b = 42 }").unwrap()),
//!         ("d", bytes_split(&((0..128u8).collect::<Vec<_>>()))),
//!     ]).unwrap(),
//! ]).unwrap().encode();
//! ```

mod error;

use std::borrow::{Borrow, Cow};
use std::collections::HashMap;

use crate::*;
use crate::dec::{self, decode};
use crate::{is_string_char, is_whitespace, BytesEncoding};

pub use error::Error;

/// A term meant to be encoded into a nettext representation
pub struct Term<'a>(T<'a>);

enum T<'a> {
    Str(&'a [u8]),
    OwnedStr(Vec<u8>),
    Dict(HashMap<Cow<'a, [u8]>, T<'a>>),
    List(Vec<T<'a>>),
    Seq(Vec<T<'a>>),
}

/// The result type for trying to encode something as nettext
pub type Result<'a> = std::result::Result<Term<'a>, Error>;

// ---- helpers to transform datatypes into encoder terms ----

/// Trait for anything that can be encoded as nettext
pub trait Encode {
    fn term(&self) -> Result<'_>;
}

impl<'a, 'b> Encode for dec::Term<'a, 'b> {
    fn term(&self) -> Result<'_> {
        Ok(Term(T::Str(self.raw())))
    }
}

// ---- helpers to build terms ----

/// Term corresponding to a string (that may contain whitespace)
///
/// ```
/// use nettext::enc::*;
///
/// assert_eq!(string("Hello world  .").unwrap().encode(), b"Hello world  .");
/// ```
pub fn string(s: &str) -> Result<'_> {
    for c in s.as_bytes().iter() {
        if !(is_string_char(*c) || is_whitespace(*c)) {
            return Err(Error::InvalidCharacter(*c));
        }
    }
    Ok(Term(T::Str(s.as_bytes())))
}

/// Same as `string` but takes an owned String
pub fn string_owned(s: String) -> Result<'static> {
    for c in s.as_bytes().iter() {
        if !(is_string_char(*c) || is_whitespace(*c)) {
            return Err(Error::InvalidCharacter(*c));
        }
    }
    Ok(Term(T::OwnedStr(s.into_bytes())))
}

/// Include a raw nettext value
///
/// ```
/// use nettext::enc::*;
///
/// assert_eq!(raw(b"Hello { a = b; c = d}  .").unwrap().encode(), b"Hello { a = b; c = d}  .");
/// ```
pub fn raw(bytes: &[u8]) -> Result<'_> {
    if decode(bytes).is_err() {
        return Err(Error::InvalidRaw);
    }
    Ok(Term(T::Str(bytes)))
}

/// Term corresponding to a byte slice,
/// encoding using base64 url-safe encoding without padding.
/// Since empty strings are not possible in nettext,
/// an empty byte string is encoded as an empty list (`[]`).
///
/// Example:
///
/// ```
/// use nettext::enc::*;
///
/// assert_eq!(bytes(b"hello, world!").encode(), b"aGVsbG8sIHdvcmxkIQ");
/// ```
pub fn bytes(bytes: &[u8]) -> Term<'static> {
    bytes_format(bytes, BytesEncoding::Base64 { split: false })
}

/// Same as `bytes()`, but splits the byte slice in 48-byte chunks
/// and encodes each chunk separately, putting them in a sequence of terms.
/// Usefull for long byte slices to have cleaner representations,
/// mainly usefull for dictionnary keys.
pub fn bytes_split(bytes: &[u8]) -> Term<'static> {
    bytes_format(bytes, BytesEncoding::Base64 { split: true })
}

pub fn bytes_format(bytes: &[u8], encoding: BytesEncoding) -> Term<'static> {
    match encoding {
        BytesEncoding::Base64 { .. } | BytesEncoding::Hex { .. } if bytes.is_empty() => {
            Term(T::List(vec![]))
        }
        BytesEncoding::Base64 { split: false } => Term(T::OwnedStr(
            base64::encode_config(bytes, base64::URL_SAFE_NO_PAD).into_bytes(),
        )),
        BytesEncoding::Base64 { split: true } => {
            let chunks = bytes
                .chunks(48)
                .map(|b| {
                    T::OwnedStr(base64::encode_config(b, base64::URL_SAFE_NO_PAD).into_bytes())
                })
                .collect::<Vec<_>>();
            if chunks.len() > 1 {
                Term(T::Seq(chunks))
            } else {
                Term(chunks.into_iter().next().unwrap())
            }
        }
        BytesEncoding::Hex { split: false } => Term(T::OwnedStr(hex::encode(bytes).into_bytes())),
        BytesEncoding::Hex { split: true } => {
            let chunks = bytes
                .chunks(32)
                .map(|b| T::OwnedStr(hex::encode(b).into_bytes()))
                .collect::<Vec<_>>();
            if chunks.len() > 1 {
                Term(T::Seq(chunks))
            } else {
                Term(chunks.into_iter().next().unwrap())
            }
        }
    }
}

// ---- composed terms -----

/// Term corresponding to a sequence of terms. Subsequences are banned and will raise an error.
///
/// ```
/// use nettext::enc::*;
///
/// assert_eq!(seq([
///     string("Hello").unwrap(),
///     string("world").unwrap()
/// ]).unwrap().encode(), b"Hello world");
/// ```
pub fn seq<'a, I: IntoIterator<Item = Term<'a>>>(terms: I) -> Result<'a> {
    let mut tmp = Vec::with_capacity(8);
    for t in terms {
        match t.0 {
            T::Seq(_) => return Err(Error::SeqInSeq),
            x => tmp.push(x),
        }
    }
    Ok(Term(T::Seq(tmp)))
}

/// Term corresponding to a sequence of terms. Sub-sequences are flattenned.
pub fn seq_flatten<'a, I: IntoIterator<Item = Term<'a>>>(terms: I) -> Term<'a> {
    let mut tmp = Vec::with_capacity(8);
    for t in terms {
        match t.0 {
            T::Seq(t) => tmp.extend(t),
            x => tmp.push(x),
        }
    }
    Term(T::Seq(tmp))
}

/// Term corresponding to a list of terms.
///
/// ```
/// use nettext::enc::*;
///
/// assert_eq!(list([
///     string("Hello").unwrap(),
///     string("world").unwrap()
/// ]).encode(), b"[\n  Hello;\n  world;\n]");
/// ```
pub fn list<'a, I: IntoIterator<Item = Term<'a>>>(terms: I) -> Term<'a> {
    let terms = terms.into_iter().map(|x| x.0).collect::<Vec<_>>();
    Term(T::List(terms))
}

/// Term corresponding to a dictionnary of items
///
/// ```
/// use nettext::enc::*;
///
/// assert_eq!(dict([
///     ("a", string("Hello").unwrap()),
///     ("b", string("world").unwrap())
/// ]).unwrap().encode(), b"{\n  a = Hello;\n  b = world;\n}");
/// ```
pub fn dict<'a, I: IntoIterator<Item = (&'a str, Term<'a>)>>(pairs: I) -> Result<'a> {
    let mut tmp = HashMap::new();
    for (k, v) in pairs {
        if tmp.insert(Cow::from(k.as_bytes()), v.0).is_some() {
            return Err(Error::DuplicateKey(k.to_string()));
        }
    }
    Ok(Term(T::Dict(tmp)))
}

impl<'a> Term<'a> {
    /// Append a term to an existing term.
    /// Transforms the initial term into a seq if necessary.
    #[must_use]
    pub fn append(self, t: Term<'a>) -> Term<'a> {
        match self.0 {
            T::Seq(mut v) => {
                v.push(t.0);
                Term(T::Seq(v))
            }
            x => Term(T::Seq(vec![x, t.0])),
        }
    }

    /// Inserts a key-value pair into a term that is a dictionnary.
    /// Fails if `self` is not a dictionnary.
    pub fn insert(self, k: &'a str, v: Term<'a>) -> Result<'a> {
        match self.0 {
            T::Dict(mut d) => {
                if d.insert(Cow::from(k.as_bytes()), v.0).is_some() {
                    return Err(Error::DuplicateKey(k.to_string()));
                }
                Ok(Term(T::Dict(d)))
            }
            _ => Err(Error::NotADictionnary),
        }
    }
}

// ---- additional internal functions for serde module ----

#[cfg(feature = "serde")]
pub(crate) fn dict_owned_u8<'a, I: IntoIterator<Item = (Vec<u8>, Term<'a>)>>(
    pairs: I,
) -> Result<'a> {
    let mut tmp = HashMap::new();
    for (k, v) in pairs {
        tmp.insert(Cow::from(k), v.0);
    }
    Ok(Term(T::Dict(tmp)))
}

#[cfg(feature = "serde")]
pub(crate) fn safe_raw(bytes: &[u8]) -> Term<'_> {
    Term(T::Str(bytes))
}

#[cfg(feature = "serde")]
pub(crate) fn safe_raw_owned(bytes: Vec<u8>) -> Term<'static> {
    Term(T::OwnedStr(bytes))
}

// ---- encoding function ----

impl<'a> Term<'a> {
    /// Generate the nettext representation of a term
    pub fn encode(self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(128);
        self.0.encode_aux(&mut buf, 0, true);
        buf
    }

    /// Generate the nettext representation of a term, as a String
    pub fn encode_string(self) -> String {
        unsafe { String::from_utf8_unchecked(self.encode()) }
    }

    /// Generate the concise nettext representation of a term
    pub fn encode_concise(self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(128);
        self.0.encode_concise_aux(&mut buf);
        buf
    }
}

impl<'a> T<'a> {
    fn encode_aux(self, buf: &mut Vec<u8>, indent: usize, is_toplevel: bool) {
        match self {
            T::Str(s) => buf.extend_from_slice(s),
            T::OwnedStr(s) => buf.extend_from_slice(&s),
            T::Dict(mut d) => {
                if d.is_empty() {
                    buf.extend_from_slice(&[DICT_OPEN, DICT_CLOSE]);
                } else if d.len() == 1 {
                    let (k, v) = d.into_iter().next().unwrap();
                    buf.extend_from_slice(&[DICT_OPEN, b' ']);
                    buf.extend_from_slice(k.borrow());
                    buf.extend_from_slice(&[b' ', DICT_ASSIGN, b' ']);
                    v.encode_aux(buf, indent + 2, false);
                    buf.extend_from_slice(&[b' ', DICT_CLOSE]);
                } else {
                    buf.extend_from_slice(&[DICT_OPEN, b'\n']);
                    let indent2 = indent + 2;
                    let mut keys = d.keys().cloned().collect::<Vec<_>>();
                    keys.sort();
                    for k in keys {
                        let v = d.remove(&k).unwrap();
                        for _ in 0..indent2 {
                            buf.push(b' ');
                        }
                        buf.extend_from_slice(k.borrow());
                        buf.extend_from_slice(&[b' ', DICT_ASSIGN, b' ']);
                        v.encode_aux(buf, indent2, false);
                        buf.extend_from_slice(&[DICT_DELIM, b'\n']);
                    }
                    for _ in 0..indent {
                        buf.push(b' ');
                    }
                    buf.push(DICT_CLOSE);
                }
            }
            T::List(l) => {
                if l.len() == 0 {
                    buf.extend_from_slice(&[LIST_OPEN, LIST_CLOSE]);
                } else if l.len() == 1 {
                    buf.extend_from_slice(&[LIST_OPEN, b' ']);
                    l.into_iter()
                        .next()
                        .unwrap()
                        .encode_aux(buf, indent + 2, false);
                    buf.extend_from_slice(&[b' ', LIST_CLOSE]);
                } else {
                    let indent2 = indent + 2;
                    buf.extend_from_slice(&[LIST_OPEN, b'\n']);
                    for item in l {
                        for _ in 0..indent2 {
                            buf.push(b' ');
                        }
                        item.encode_aux(buf, indent2, false);
                        buf.extend_from_slice(&[LIST_DELIM, b'\n']);
                    }
                    for _ in 0..indent {
                        buf.push(b' ');
                    }
                    buf.push(LIST_CLOSE);
                }
            }
            T::Seq(l) => {
                let indent2 = indent + 2;
                for (i, v) in l.into_iter().enumerate() {
                    if !is_toplevel && buf.iter().rev().take_while(|c| **c != b'\n').count() >= 70 {
                        buf.push(b'\n');
                        for _ in 0..indent2 {
                            buf.push(b' ');
                        }
                    } else if i > 0 {
                        buf.push(b' ');
                    }
                    v.encode_aux(buf, indent2, is_toplevel);
                }
            }
        }
    }

    fn encode_concise_aux(self, buf: &mut Vec<u8>) {
        match self {
            T::Str(s) => buf.extend_from_slice(s),
            T::OwnedStr(s) => buf.extend_from_slice(&s),
            T::Dict(mut d) => {
                buf.push(DICT_OPEN);
                let mut keys = d.keys().cloned().collect::<Vec<_>>();
                keys.sort();
                for (i, k) in keys.into_iter().enumerate() {
                    if i > 0 {
                        buf.push(DICT_DELIM);
                    }
                    let v = d.remove(&k).unwrap();
                    buf.extend_from_slice(k.borrow());
                    buf.push(DICT_ASSIGN);
                    v.encode_concise_aux(buf);
                }
                buf.push(DICT_CLOSE);
            }
            T::List(l) => {
                buf.push(LIST_OPEN);
                for (i, item) in l.into_iter().enumerate() {
                    if i > 0 {
                        buf.push(LIST_DELIM);
                    }
                    item.encode_concise_aux(buf);
                }
                buf.push(LIST_CLOSE);
            }
            T::Seq(l) => {
                for (i, v) in l.into_iter().enumerate() {
                    if i > 0 {
                        buf.push(b' ');
                    }
                    v.encode_concise_aux(buf);
                }
            }
        }
    }
}

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

    #[test]
    fn complex1() {
        let input = seq([
            string("HELLO").unwrap(),
            string("alexhelloworld").unwrap(),
            list([string("dude").unwrap(), string("why").unwrap()]),
            dict([
                ("from", string("jxx").unwrap()),
                ("subject", string("hello").unwrap()),
                ("data", raw(b"{ f1 = plop; f2 = kuko }").unwrap()),
            ])
            .unwrap(),
        ])
        .unwrap();

        let expected = "HELLO alexhelloworld [
    dude;
    why;
  ] {
    data = { f1 = plop; f2 = kuko };
    from = jxx;
    subject = hello;
  }";
        assert_eq!(debug(&input.encode()), expected);
    }

    #[test]
    fn complex1_concise() {
        let input = seq([
            string("HELLO").unwrap(),
            string("alexhelloworld").unwrap(),
            list([string("dude").unwrap(), string("why").unwrap()]),
            dict([
                ("from", string("jxx").unwrap()),
                ("subject", string("hello").unwrap()),
                ("data", raw(b"{ f1 = plop; f2 = kuko }").unwrap()),
            ])
            .unwrap(),
        ])
        .unwrap();
        let expected_concise = "HELLO alexhelloworld [dude;why] {data={ f1 = plop; f2 = kuko };from=jxx;subject=hello}";
        assert_eq!(debug(&input.encode_concise()), expected_concise);
    }
}