//! Functions to decode nettext and helpers to map it to data structures

mod decode;

use std::collections::HashMap;

use crate::crypto;
pub use decode::*;

/// A parsed nettext term, with many helpers for destructuring
///
/// Lifetime 'a is the lifetime of the buffer containing the encoded data.
///
/// Lifetime 'b is the lifetime of another Term from which this one is borrowed, when it
/// is returned by one of the helper functions, or 'static when first returned from
/// `decode()`
#[derive(Eq, PartialEq, Debug)]
pub struct Term<'a, 'b>(AnyTerm<'a, 'b>);

#[derive(Eq, PartialEq, Clone)]
pub(crate) enum AnyTerm<'a, 'b> {
    Str(&'a [u8]),
    Dict(&'a [u8], HashMap<&'a [u8], AnyTerm<'a, 'b>>),
    DictRef(&'a [u8], &'b HashMap<&'a [u8], AnyTerm<'a, 'b>>),
    List(&'a [u8], Vec<NonListTerm<'a, 'b>>),
    ListRef(&'a [u8], &'b [NonListTerm<'a, 'b>]),
}

#[derive(Eq, PartialEq, Clone)]
pub(crate) enum NonListTerm<'a, 'b> {
    Str(&'a [u8]),
    Dict(&'a [u8], HashMap<&'a [u8], AnyTerm<'a, 'b>>),
    DictRef(&'a [u8], &'b HashMap<&'a [u8], AnyTerm<'a, 'b>>),
}

impl<'a, 'b> From<NonListTerm<'a, 'b>> for AnyTerm<'a, 'b> {
    fn from(x: NonListTerm<'a, 'b>) -> AnyTerm<'a, 'b> {
        match x {
            NonListTerm::Str(s) => AnyTerm::Str(s),
            NonListTerm::Dict(raw, d) => AnyTerm::Dict(raw, d),
            NonListTerm::DictRef(raw, d) => AnyTerm::DictRef(raw, d),
        }
    }
}

impl<'a, 'b> TryFrom<AnyTerm<'a, 'b>> for NonListTerm<'a, 'b> {
    type Error = ();
    fn try_from(x: AnyTerm<'a, 'b>) -> Result<NonListTerm<'a, 'b>, ()> {
        match x {
            AnyTerm::Str(s) => Ok(NonListTerm::Str(s)),
            AnyTerm::Dict(raw, d) => Ok(NonListTerm::Dict(raw, d)),
            AnyTerm::DictRef(raw, d) => Ok(NonListTerm::DictRef(raw, d)),
            _ => Err(()),
        }
    }
}

impl<'a> From<AnyTerm<'a, 'static>> for Term<'a, 'static> {
    fn from(x: AnyTerm<'a, 'static>) -> Term<'a, 'static> {
        Term(x)
    }
}

// ---- PUBLIC IMPLS ----

/// The type of errors returned by helper functions on `Term`
#[derive(Debug, Clone)]
pub enum TypeError {
    /// The term could not be decoded in the given type
    WrongType(&'static str),
    /// The term is not an array of the requested length
    WrongLength(usize, usize),
    /// The dictionnary is missing a key
    MissingKey(String),
    /// The dictionnary contains an invalid key
    UnexpectedKey(String),
    /// The underlying raw string contains garbage (should not happen in theory)
    Garbage,
}

impl From<std::str::Utf8Error> for TypeError {
    fn from(_x: std::str::Utf8Error) -> TypeError {
        TypeError::Garbage
    }
}

impl<'a, 'b> Term<'a, 'b> {
    // ---- STRUCTURAL MAPPINGS ----

    /// Get the term's raw representation
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term = decode(b"hello world").unwrap();
    /// assert_eq!(term.raw(), b"hello world");
    /// ```
    pub fn raw(&self) -> &'a [u8] {
        self.0.raw()
    }

    /// If the term is a single string, get that string
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term1 = decode(b"hello").unwrap();
    /// assert_eq!(term1.str().unwrap(), "hello");
    ///
    /// let term2 = decode(b"hello world").unwrap();
    /// assert!(term2.str().is_err());
    /// ```
    pub fn str(&self) -> Result<&'a str, TypeError> {
        match &self.0 {
            AnyTerm::Str(s) => Ok(std::str::from_utf8(s)?),
            _ => Err(TypeError::WrongType("STR")),
        }
    }

    /// If the term is a single string, or a list containing only strings,
    /// get its raw representation
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term1 = decode(b"hello world").unwrap();
    /// assert_eq!(term1.string().unwrap(), "hello world");
    ///
    /// let term2 = decode(b"hello { a= 5}").unwrap();
    /// assert!(term2.string().is_err());
    /// ```
    pub fn string(&self) -> Result<&'a str, TypeError> {
        match &self.0 {
            AnyTerm::Str(s) => Ok(std::str::from_utf8(s)?),
            AnyTerm::List(r, l) if l.iter().all(|x| matches!(x, NonListTerm::Str(_))) => {
                Ok(std::str::from_utf8(r)?)
            }
            _ => Err(TypeError::WrongType("STRING")),
        }
    }

    /// Return a list of terms made from this term.
    /// If it is a str or a dict, returns a list of a single term.
    /// If it is a list, that's the list of terms we return.
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term1 = decode(b"hello").unwrap();
    /// let list1 = term1.list();
    /// assert_eq!(list1.len(), 1);
    /// assert_eq!(list1[0].str().unwrap(), "hello");
    ///
    /// let term2 = decode(b"hello world").unwrap();
    /// let list2 = term2.list();
    /// assert_eq!(list2.len(), 2);
    /// assert_eq!(list2[0].str().unwrap(), "hello");
    /// assert_eq!(list2[1].str().unwrap(), "world");
    /// ```
    pub fn list(&self) -> Vec<Term<'a, '_>> {
        match self.0.mkref() {
            AnyTerm::ListRef(_r, l) => l.iter().map(|x| Term(x.mkref().into())).collect::<Vec<_>>(),
            x => vec![Term(x)],
        }
    }

    /// Same as `.list()`, but deconstructs it in a const length array,
    /// dynamically checking if there are the correct number of items.
    /// This allows to directly bind the resulting list into discrete variables.
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term1 = decode(b"hello").unwrap();
    /// let [s1] = term1.list_of().unwrap();
    /// assert_eq!(s1.str().unwrap(), "hello");
    ///
    /// let term2 = decode(b"hello world").unwrap();
    /// let [s2a, s2b] = term2.list_of().unwrap();
    /// assert_eq!(s2a.str().unwrap(), "hello");
    /// assert_eq!(s2b.str().unwrap(), "world");
    /// ```
    pub fn list_of<const N: usize>(&self) -> Result<[Term<'a, '_>; N], TypeError> {
        let list = self.list();
        let list_len = list.len();
        list.try_into()
            .map_err(|_| TypeError::WrongLength(list_len, N))
    }

    /// Same as `.list_of()`, but only binds the first N-1 terms.
    /// If there are exactly N terms, the last one is bound to the Nth return variable.
    /// If there are more then N terms, the remaining terms are bound to a new list term
    /// that is returned as the Nth return variable.
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term1 = decode(b"hello world").unwrap();
    /// let [s1a, s1b] = term1.list_of_first().unwrap();
    /// assert_eq!(s1a.str().unwrap(), "hello");
    /// assert_eq!(s1b.str().unwrap(), "world");
    ///
    /// let term2 = decode(b"hello mighty world").unwrap();
    /// let [s2a, s2b] = term2.list_of_first().unwrap();
    /// assert_eq!(s2a.str().unwrap(), "hello");
    /// assert_eq!(s2b.list().len(), 2);
    /// assert_eq!(s2b.raw(), b"mighty world");
    /// ```
    pub fn list_of_first<const N: usize>(&self) -> Result<[Term<'a, '_>; N], TypeError> {
        match self.0.mkref() {
            AnyTerm::ListRef(raw, list) => match list.len().cmp(&N) {
                std::cmp::Ordering::Less => Err(TypeError::WrongLength(list.len(), N)),
                std::cmp::Ordering::Equal => Ok(list
                    .iter()
                    .map(|x| Term(x.mkref().into()))
                    .collect::<Vec<_>>()
                    .try_into()
                    .unwrap()),
                std::cmp::Ordering::Greater => {
                    let mut ret = Vec::with_capacity(N);
                    for item in list[0..N - 1].iter() {
                        ret.push(Term(item.mkref().into()));
                    }

                    let remaining_begin = list[N - 1].raw().as_ptr() as usize;
                    let remaining_offset = remaining_begin - raw.as_ptr() as usize;
                    let remaining_raw = &raw[remaining_offset..];

                    ret.push(Term(AnyTerm::ListRef(remaining_raw, &list[N - 1..])));

                    Ok(ret.try_into().unwrap())
                }
            },
            x if N == 1 => Ok([Term(x)]
                .into_iter()
                .collect::<Vec<_>>()
                .try_into()
                .unwrap()),
            _ => Err(TypeError::WrongLength(1, N)),
        }
    }

    /// Checks term is a dictionnary and returns hashmap of inner terms.
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term = decode(b"{ k1 = v1, k2 = v2 }").unwrap();
    /// let dict = term.dict().unwrap();
    /// assert_eq!(dict.get("k1").unwrap().str().unwrap(), "v1");
    /// assert_eq!(dict.get("k2").unwrap().str().unwrap(), "v2");
    /// ```
    pub fn dict(&self) -> Result<HashMap<&'a str, Term<'a, '_>>, TypeError> {
        match self.0.mkref() {
            AnyTerm::DictRef(_, d) => {
                let mut res = HashMap::with_capacity(d.len());
                for (k, t) in d.iter() {
                    res.insert(std::str::from_utf8(k)?, Term(t.mkref()));
                }
                Ok(res)
            }
            _ => Err(TypeError::WrongType("DICT")),
        }
    }

    /// Checks term is a dictionnary whose keys are exactly those supplied,
    /// and returns the associated values as a list.
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term = decode(b"{ k1 = v1, k2 = v2, k3 = v3 }").unwrap();
    /// let [s1, s2] = term.dict_of(["k1", "k2"], true).unwrap();
    /// assert_eq!(s1.str().unwrap(), "v1");
    /// assert_eq!(s2.str().unwrap(), "v2");
    ///
    /// assert!(term.dict_of(["k1", "k2"], false).is_err());
    /// ```
    pub fn dict_of<const N: usize, T: AsRef<[u8]>>(
        &self,
        keys: [T; N],
        allow_extra_keys: bool,
    ) -> Result<[Term<'a, '_>; N], TypeError> {
        match self.0.mkref() {
            AnyTerm::DictRef(_, dict) => {
                // Check all required keys exist in dictionnary
                for k in keys.iter() {
                    if !dict.contains_key(k.as_ref()) {
                        return Err(TypeError::MissingKey(debug(k.as_ref()).to_string()));
                    }
                }
                if !allow_extra_keys {
                    // Check that dictionnary contains no extraneous keys
                    for k in dict.keys() {
                        if !keys.iter().any(|k2| k2.as_ref() == *k) {
                            return Err(TypeError::UnexpectedKey(debug(k).to_string()));
                        }
                    }
                }
                Ok(keys.map(|k| Term(dict.get(k.as_ref()).unwrap().mkref())))
            }
            _ => Err(TypeError::WrongType("DICT")),
        }
    }

    /// Checks term is a dictionnary whose keys are included in those supplied,
    /// and returns the associated values as a list of options.
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term = decode(b"{ k1 = v1, k2 = v2, k4 = v4 }").unwrap();
    /// let [s1, s2, s3] = term.dict_of_opt(["k1", "k2", "k3"], true).unwrap();
    /// assert_eq!(s1.unwrap().str().unwrap(), "v1");
    /// assert_eq!(s2.unwrap().str().unwrap(), "v2");
    /// assert!(s3.is_none());
    ///
    /// assert!(term.dict_of_opt(["k1", "k2", "k3"], false).is_err());
    /// ```
    pub fn dict_of_opt<const N: usize, T: AsRef<[u8]>>(
        &self,
        keys: [T; N],
        allow_extra_keys: bool,
    ) -> Result<[Option<Term<'a, '_>>; N], TypeError> {
        match self.0.mkref() {
            AnyTerm::DictRef(_, dict) => {
                if !allow_extra_keys {
                    // Check that dictionnary contains no extraneous keys
                    for k in dict.keys() {
                        if !keys.iter().any(|x| x.as_ref() == *k) {
                            return Err(TypeError::UnexpectedKey(debug(k).to_string()));
                        }
                    }
                }
                Ok(keys.map(|k| dict.get(k.as_ref()).map(|x| Term(x.mkref()))))
            }
            _ => Err(TypeError::WrongType("DICT")),
        }
    }

    // ---- TYPE CASTS ----

    /// Try to interpret this str as an i64
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term = decode(b"42").unwrap();
    /// assert_eq!(term.int().unwrap(), 42);
    /// ```
    pub fn int(&self) -> Result<i64, TypeError> {
        self.str()?
            .parse::<i64>()
            .map_err(|_| TypeError::WrongType("INT"))
    }

    /// Try to interpret this string as base64-encoded bytes (uses URL-safe, no-padding encoding)
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term = decode(b"aGVsbG8sIHdvcmxkIQ").unwrap();
    /// assert_eq!(term.bytes().unwrap(), b"hello, world!");
    /// ```
    pub fn bytes(&self) -> Result<Vec<u8>, TypeError> {
        let encoded = match &self.0 {
            AnyTerm::Str(s) => s,
            AnyTerm::List(r, l) if l.iter().all(|x| matches!(x, NonListTerm::Str(_))) => r,
            _ => return Err(TypeError::WrongType("BYTES")),
        };
        base64::decode_config(encoded, base64::URL_SAFE_NO_PAD)
            .map_err(|_| TypeError::WrongType("BYTES"))
    }

    /// Try to interpret this string as base64-encoded bytes,
    /// with an exact length.
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term = decode(b"aGVsbG8sIHdvcmxkIQ").unwrap();
    /// assert_eq!(&term.bytes_exact::<13>().unwrap(), b"hello, world!");
    /// ```
    pub fn bytes_exact<const N: usize>(&self) -> Result<[u8; N], TypeError> {
        let bytes = self.bytes()?;
        let bytes_len = bytes.len();
        bytes
            .try_into()
            .map_err(|_| TypeError::WrongLength(bytes_len, N))
    }
}

// ---- CRYPTO HELPERS ----

#[cfg(feature = "blake2")]
impl<'a, 'b> Term<'a, 'b> {
    /// Try to interpret this string as a Blake2b512 digest (32-bytes base64 encoded)
    ///
    /// Example:
    ///
    /// ```
    /// use nettext::dec::decode;
    ///
    /// let term = decode(b"{
    ///     message = hello,
    ///     hash = 5M-jmj03vjHFlgnoB5cHmcqmihm_qhUTXxZQheAdQaZboeGxRq62vQCStJ6sIUwQPM-jo2WVS7vlL3Sis2IMlA
    /// }").unwrap();
    /// let [msg, hash] = term.dict_of(["message", "hash"], false).unwrap();
    /// assert!(hash.b2sum().unwrap().verify(msg.raw()).is_ok());
    /// ```
    pub fn b2sum(&self) -> Result<crypto::Blake2Sum, TypeError> {
        Ok(crypto::Blake2Sum::from_bytes(self.bytes_exact()?))
    }
}

#[cfg(feature = "ed25519-dalek")]
impl<'a, 'b> Term<'a, 'b> {
    /// Try to interpret this string as an ed25519 keypair (64 bytes base64 encoded)
    pub fn keypair(&self) -> Result<crypto::Keypair, TypeError> {
        let bytes = self.bytes_exact::<64>()?;
        crypto::Keypair::from_bytes(&bytes).map_err(|_| TypeError::WrongType("KEYPAIR"))
    }

    /// Try to interpret this string as an ed25519 public key (32 bytes base64 encoded)
    pub fn public_key(&self) -> Result<crypto::PublicKey, TypeError> {
        let bytes = self.bytes_exact::<32>()?;
        crypto::PublicKey::from_bytes(&bytes).map_err(|_| TypeError::WrongType("PUBLICKEY"))
    }

    /// Try to interpret this string as an ed25519 secret key (32 bytes base64 encoded)
    pub fn secret_key(&self) -> Result<crypto::SecretKey, TypeError> {
        let bytes = self.bytes_exact::<32>()?;
        crypto::SecretKey::from_bytes(&bytes).map_err(|_| TypeError::WrongType("SECRETKEY"))
    }

    /// Try to interpret this string as an ed25519 signature (64 bytes base64 encoded)
    pub fn signature(&self) -> Result<crypto::Signature, TypeError> {
        let bytes = self.bytes_exact::<64>()?;
        crypto::Signature::from_bytes(&bytes).map_err(|_| TypeError::WrongType("SIGNATURE"))
    }
}

// ---- INTERNAL IMPLS ----

impl<'a, 'b> AnyTerm<'a, 'b> {
    fn raw(&self) -> &'a [u8] {
        match self {
            AnyTerm::Str(s) => s,
            AnyTerm::Dict(r, _)
            | AnyTerm::DictRef(r, _)
            | AnyTerm::List(r, _)
            | AnyTerm::ListRef(r, _) => r,
        }
    }

    fn mkref(&self) -> AnyTerm<'a, '_> {
        match &self {
            AnyTerm::Str(s) => AnyTerm::Str(s),
            AnyTerm::Dict(r, d) => AnyTerm::DictRef(r, d),
            AnyTerm::DictRef(r, d) => AnyTerm::DictRef(r, d),
            AnyTerm::List(r, l) => AnyTerm::ListRef(r, &l[..]),
            AnyTerm::ListRef(r, l) => AnyTerm::ListRef(r, l),
        }
    }
}

impl<'a, 'b> NonListTerm<'a, 'b> {
    fn raw(&self) -> &'a [u8] {
        match &self {
            NonListTerm::Str(s) => s,
            NonListTerm::Dict(r, _) | NonListTerm::DictRef(r, _) => r,
        }
    }

    fn mkref(&self) -> NonListTerm<'a, '_> {
        match &self {
            NonListTerm::Str(s) => NonListTerm::Str(s),
            NonListTerm::Dict(r, d) => NonListTerm::DictRef(r, d),
            NonListTerm::DictRef(r, d) => NonListTerm::DictRef(r, d),
        }
    }
}

// ---- DISPLAY REPR = Raw nettext representation ----

impl<'a, 'b> std::fmt::Display for AnyTerm<'a, 'b> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error> {
        write!(
            f,
            "{}",
            std::str::from_utf8(self.raw()).map_err(|_| Default::default())?
        )
    }
}

impl<'a, 'b> std::fmt::Display for Term<'a, 'b> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error> {
        write!(f, "{}", self.0)
    }
}

// ---- DEBUG REPR ----

pub(crate) fn debug(x: &[u8]) -> &str {
    std::str::from_utf8(x).unwrap_or("<invalid ascii>")
}

impl<'a, 'b> std::fmt::Debug for AnyTerm<'a, 'b> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error> {
        match self.mkref() {
            AnyTerm::Str(s) => write!(f, "Str(`{}`)", debug(s)),
            AnyTerm::DictRef(raw, d) => {
                write!(f, "Dict<`{}`", debug(raw))?;
                for (k, v) in d.iter() {
                    write!(f, "\n  `{}`={:?}", debug(k), v)?;
                }
                write!(f, ">")
            }
            AnyTerm::ListRef(raw, l) => {
                write!(f, "List[`{}`", debug(raw))?;
                for i in l.iter() {
                    write!(f, "\n  {:?}", i)?;
                }
                write!(f, "]")
            }
            _ => unreachable!(),
        }
    }
}

impl<'a, 'b> std::fmt::Debug for NonListTerm<'a, 'b> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error> {
        match self.mkref() {
            NonListTerm::Str(s) => write!(f, "Str(`{}`)", debug(s)),
            NonListTerm::DictRef(raw, d) => {
                write!(f, "Dict<`{}`", debug(raw))?;
                for (k, v) in d.iter() {
                    write!(f, "\n     `{}`={:?}", debug(k), v)?;
                }
                write!(f, ">")
            }
            _ => unreachable!(),
        }
    }
}