//! Implementations of CriRef (and Cri) based on heap allocated data that closely resembles the
//! CBOR serialization

use minicbor::data::Type;

use crate::characterclasses::{PATH_UE, QUERY_UE, FRAGMENT_UE, HOST_UE, AsciiSet, contains_byte};

#[derive(Debug, Clone)]
enum FirstComponent {
    Discard(Discard),
    Nothing,
    JustAuthority(AuthorityIsh),
    SchemeAuthority(Scheme, AuthorityIsh),
}

#[derive(Debug, Clone)]
pub enum Scheme {
    SchemeName(String),
    SchemeId(i8),
}

#[derive(Debug, Clone)]
struct UserInfo(Pet<HOST_UE>);

#[derive(Debug, Clone)]
enum AuthorityIsh {
    HostPort(Option<UserInfo>, Host, Option<Port>),
    NoAuthority, // true
    LeadingSlash, // null
}

#[derive(Debug, Clone)]
pub struct Host(HostImpl);

#[derive(Debug, Clone)]
enum HostImpl {
    HostName(PetSequence<'.', HOST_UE>),
    HostIp4(no_std_net::Ipv4Addr),
    HostIp6(no_std_net::Ipv6Addr, Option<String>),
}

impl<'a> crate::traits::Host for &'a Host {
    type HostItem<'b> = &'b Pet<HOST_UE> where Self: 'b;
    type HostIter<'b> = &'b [Pet<HOST_UE>] where Self: 'b;

    fn as_ref(&self) -> crate::traits::HostRef<'_, Self::HostItem<'_>, Self::HostIter<'_>> {
        match &self.0 {
            HostImpl::HostName(seq) => crate::traits::HostRef::Hostname(&seq.0[..]),
            HostImpl::HostIp4(a) => crate::traits::HostRef::IPv4(a),
            HostImpl::HostIp6(address, zone) => crate::traits::HostRef::IPv6 { address, zone: zone.as_ref().map(|a| a.as_str()) },
        }
    }
}

/// Text or percent-encoded text.
///
/// The separator is encoded in the type. Instances should not contain that character in PET
/// fields, but users should not (at least unsafely) rely on that.
#[derive(Debug, Clone)]
pub enum Pet<const UNESCAPED: AsciiSet> {
    JustText(String),
    Alternating(Vec<(String, Box<[u8]>)>),
}

impl<const UNESCAPED: AsciiSet> Pet<UNESCAPED> {
    /// Take a single item from the decoder, and succeed if there is a text-or-pet as the next
    /// item.
    ///
    /// This may (but currently doesn't) fail if the separator (or any other characters for which
    /// it doesn't make sense) shows up in the PET parts, as that is unnecessary.
    fn load(decoder: &mut minicbor::Decoder) -> Result<Self, LoadError> {
        match decoder.datatype()? {
            Type::String => Ok(Pet::JustText(decoder.str()?.to_string())),
            Type::Array => {
                let mut items = decoder.array()?
                    .ok_or(LoadError(LoadErrorImpl::ParsingError /* indefininte length array */))?;
                // FIXME: guard against resource exhaustion attack by bounding this to decoder's
                // remaining length
                let mut vec = Vec::with_capacity(((items + 1) / 2) as _);
                loop {
                    let text = if vec.len() != 0 || decoder.datatype()? == Type::String {
                        items -= 1;
                        decoder.str()?.to_string()
                    } else {
                        // FIXME: This is a hot-fix for "it starts with pet" cases as the original
                        // code here was written to start always with text; some refactoring (maybe
                        // even on the storage type) is due.
                        String::new()
                    };
                    let pet = if items > 0 {
                        items -= 1;
                        Box::from(decoder.bytes()?)
                    } else {
                        Box::from([])
                    };
                    vec.push((text, pet));

                    if items == 0 {
                        break;
                    }
                }

                Ok(Pet::Alternating(vec))
            }
            _ => return Err(LoadError(LoadErrorImpl::UnexpectedType))
        }
    }

    fn load_if_present(decoder: &mut minicbor::Decoder) -> Result<Option<Self>, LoadError> {
        match decoder.datatype() {
            Err(e) if e.is_end_of_input() => Ok(None),
            _ => Ok(Some(Self::load(decoder)?)),
        }
    }

    fn format_str_to_uri(w: &mut core::fmt::Formatter<'_>, part: &str) -> Result<(), core::fmt::Error>{
        for b in part.as_bytes() {
            if contains_byte(UNESCAPED, *b) {
                write!(w, "{}", core::str::from_utf8(&[*b]).expect("All bytes <128 are valid UTF-8"))?
            } else {
                Self::format_pet_to_uri(w, &[*b])?;
            }
        }
        Ok(())
    }

    fn format_pet_to_uri(w: &mut core::fmt::Formatter<'_>, pet: &[u8]) -> Result<(), core::fmt::Error>{
        for c in pet {
            write!(w, "%{:2X}", c)?;
        }
        Ok(())
    }
}

impl<'a, const UNESCAPED: AsciiSet> crate::traits::TextOrPet<UNESCAPED> for &'a Pet<UNESCAPED> {
    type UriEncoded<'b> = &'b Self where Self: 'b;

    fn to_uri_component(&self) -> Self::UriEncoded<'_> {
        &self
    }
}

// The URI encoding display -- saving us another type
impl<const UNESCAPED: AsciiSet> core::fmt::Display for Pet<UNESCAPED> {
    fn fmt(&self, w: &mut core::fmt::Formatter<'_>) -> Result<(), core::fmt::Error> {
        match self {
            Pet::Alternating(v) => {
                for (text, bytes) in v {
                    Self::format_str_to_uri(w, text)?;
                    Self::format_pet_to_uri(w, bytes)?;
                };
            },
            Pet::JustText(s) => {
                Self::format_str_to_uri(w, s)?;
            }
        };
        Ok(())
    }
}

type Port = u16;

#[allow(non_camel_case_types)]
type u7 = u8;

#[derive(Debug, Clone)]
enum Discard {
    DiscardAll,
    Numeric(u7),
}

#[derive(Debug, Clone)]
struct PetSequence<const SEP: char, const UNESCAPED: AsciiSet>(Vec<Pet<UNESCAPED>>);

type Path = Option<PetSequence<'/', PATH_UE>>;
type Query = Option<PetSequence<'?', QUERY_UE>>;
type Fragment = Option<Pet<FRAGMENT_UE>>;

impl<const SEP: char, const UNESCAPED: AsciiSet> PetSequence<SEP, UNESCAPED> {
    fn load_optional(decoder: &mut minicbor::Decoder) -> Result<Option<Self>, LoadError> {
        Ok(match decoder.datatype() {
            Ok(Type::Array) => {
                let number = decoder.array()?
                    .ok_or(LoadError(LoadErrorImpl::ParsingError /* indefininte length array */))?
                    as usize;
                let mut pathstrings = Vec::with_capacity(number);
                for _ in 0..number {
                    pathstrings.push(Pet::load(decoder)?)
                }
                Some(PetSequence(pathstrings))
            }
            Ok(Type::Null) => {
                decoder.null().expect("A null was already found");
                None
            }
            Ok(_) => return Err(LoadError(LoadErrorImpl::UnexpectedType)),
            Err(e) if e.is_end_of_input() => None,
            Err(e) => return Err(e.into()),
        })
    }
}


/// A CRI reference whose implementation is as close as possible to the CDDL specification, backed
/// by heap memory.
///
/// (Not that this'd be ideal for use, but it's what one would get from naïve CBOR implementations).
#[derive(Debug, Clone)]
pub struct NativeCBORCriRef {
    scheme_authority_discard: FirstComponent,
    path: Path,
    query: Query,
    fragment: Fragment,
}

/// A CRI reference that is known to be also a full CRI
#[derive(Clone, Debug)]
pub struct NativeCBORCri(NativeCBORCriRef);

#[derive(Debug)]
pub struct LoadError(LoadErrorImpl);

#[derive(Debug)]
enum LoadErrorImpl {
    /// A failure indicating non-wellformedness of the CBOR happened.
    ///
    /// (Or the CBOR library doesn't even understand what is going on).
    ParsingError,
    /// The CBOR item appears to be incomplete.
    PrematureEnd,
    /// A type was encountered that was not expected. This can indicate that an extension to CRIs
    /// is used that is not understood.
    UnexpectedType,
}

trait ErrorExt<T> {
    fn eof_as_none(self) -> Result<Option<T>, LoadError>;
}

impl<T> ErrorExt<T> for Result<T, minicbor::decode::Error> {
    fn eof_as_none(self) -> Result<Option<T>, LoadError> {
        match self {
            Ok(s) => Ok(Some(s)),
            Err(e) if e.is_end_of_input() => Ok(None),
            Err(e) => Err(e.into()),
        }
    }
}

// Only go through directly if all errors are sure syntax errors (eg. when you discovered something
// is Type::String and then .str() fails)
impl From<minicbor::decode::Error> for LoadError {
    fn from(e: minicbor::decode::Error) -> Self {
        if e.is_type_mismatch() {
            LoadError(LoadErrorImpl::UnexpectedType)
        } else if e.is_end_of_input() {
            LoadError(LoadErrorImpl::PrematureEnd)
        } else {
            LoadError(LoadErrorImpl::ParsingError)
        }
    }
}

impl<'a> TryFrom<&'a [u8]> for NativeCBORCriRef {
    type Error = LoadError;
    fn try_from(s: &'a [u8]) -> Result<Self, LoadError> {
        let mut decoder = minicbor::Decoder::new(s);
        let length = decoder.array().unwrap(); // FIXME: See https://github.com/core-wg/href/issues/18
        load_cri_ref(&mut decoder)
    }
}

impl crate::traits::Scheme for &Scheme {
    fn to_cri_id(&self) -> Option<i16> {
        match self {
            Scheme::SchemeName(_) => None,
            Scheme::SchemeId(n) => Some((*n).into()),
        }
    }

    fn to_text_scheme(&self) -> &str {
        match self {
            Scheme::SchemeName(s) => s,
            Scheme::SchemeId(-1) => "coap",
            Scheme::SchemeId(-2) => "coaps",
            Scheme::SchemeId(-3) => "http",
            Scheme::SchemeId(-4) => "https",
            Scheme::SchemeId(_) => todo!("Check validity earlier"),
        }
    }
}

impl super::accessor::CriBase for NativeCBORCriRef {
    type Scheme<'a> = &'a Scheme where Self: 'a;
    type Host<'a> = &'a Host where Self: 'a;

    type PathItem<'a> = &'a Pet<PATH_UE> where Self: 'a;
    type PathIter<'a> = impl Iterator<Item=Self::PathItem<'a>> + ExactSizeIterator where Self: 'a;
    type QueryItem<'a> = &'a Pet<QUERY_UE> where Self: 'a;
    type QueryIter<'a> = impl Iterator<Item=Self::QueryItem<'a>> where Self: 'a;
    type FragmentItem<'a> = &'a Pet<FRAGMENT_UE> where Self: 'a;
    type UserInfoItem<'a> = &'a Pet<HOST_UE> where Self: 'a;

    fn path(&self) -> Self::PathIter<'_> {
        use super::accessor::CriRef;
        match &self.path {
            Some(p) => &p.0[..],
            None => &[],
        }.iter()
    }
    fn query(&self) -> Self::QueryIter<'_> {
        match &self.query {
            Some(q) => &q.0[..],
            None => &[],
        }.iter()
    }
    fn fragment(&self) -> Option<Self::FragmentItem<'_>> {
        match &self.fragment {
            Some(s) => Some(&s),
            None => None,
        }
    }

    fn userinfo(&self) -> Option<Self::UserInfoItem<'_>> {
        match &self.scheme_authority_discard {
            FirstComponent::SchemeAuthority(_, AuthorityIsh::HostPort(Some(UserInfo(a)), _, _)) => Some(a),
            FirstComponent::JustAuthority(AuthorityIsh::HostPort(Some(UserInfo(a)), _, _)) => Some(a),

            FirstComponent::SchemeAuthority(_, AuthorityIsh::HostPort(None, _, _)) => None,
            FirstComponent::JustAuthority(AuthorityIsh::HostPort(None, _, _)) => None,

            _ => panic!("Used wrong"),
        }
    }

    fn host(&self) -> Self::Host<'_> {
        match &self.scheme_authority_discard {
            FirstComponent::SchemeAuthority(_, AuthorityIsh::HostPort(_, h, _)) => h.into(),
            FirstComponent::JustAuthority(AuthorityIsh::HostPort(_, h, _)) => h.into(),
            _ => panic!("Used wrong"),
        }
    }

    fn port(&self) -> Option<u16> {
        match self.scheme_authority_discard {
            FirstComponent::SchemeAuthority(_, AuthorityIsh::HostPort(_, _, p)) => p,
            FirstComponent::JustAuthority(AuthorityIsh::HostPort(_, _, p)) => p,
            _ => panic!("Used wrong"),
        }
    }
}

impl super::accessor::CriRef for NativeCBORCriRef {
    fn discard(&self) -> crate::accessor::Discard {
        match self.scheme_authority_discard {
            // FIXME do we really need a separate type here?
            FirstComponent::Discard(Discard::DiscardAll) => crate::accessor::Discard::All,
            FirstComponent::Discard(Discard::Numeric(n)) => crate::accessor::Discard::Some(n.into()),
            FirstComponent::Nothing => crate::accessor::Discard::Some(0), // FIXME is that correct?
            _ => crate::accessor::Discard::All,
        }
    }
    fn scheme(&self) -> Option<Self::Scheme<'_>> {
        match &self.scheme_authority_discard {
            // FIXME do we really need a separate type here?
            FirstComponent::SchemeAuthority(s, _) => Some(s),
            _ => None,
        }
    }
    fn authority(&self) -> Option<crate::traits::Authority> {
        match self.scheme_authority_discard {
            FirstComponent::Discard(_) => None,
            FirstComponent::JustAuthority(AuthorityIsh::HostPort(_, _, _)) |
                FirstComponent::SchemeAuthority(_, AuthorityIsh::HostPort(_, _,_)) => Some(crate::traits::Authority::HostPort),
            FirstComponent::JustAuthority(AuthorityIsh::NoAuthority) |
                FirstComponent::SchemeAuthority(_, AuthorityIsh::NoAuthority) => Some(crate::traits::Authority::NoAuthoritySlashless),
            FirstComponent::JustAuthority(AuthorityIsh::LeadingSlash) |
                FirstComponent::SchemeAuthority(_, AuthorityIsh::LeadingSlash) => Some(crate::traits::Authority::NoAuthoritySlashStart),
            FirstComponent::Nothing => None, // FIXME is this right?
        }
    }
}

/// Error type of conversions from a CRI reference to a CRI
#[derive(Debug)]
pub struct RefIsRelative;

impl<'a> TryFrom<NativeCBORCriRef> for NativeCBORCri {
    type Error = RefIsRelative;
    fn try_from(s: NativeCBORCriRef) -> Result<Self, RefIsRelative> {
        use super::accessor::CriRef;
        if s.scheme().is_some() {
            Ok(NativeCBORCri(s))
        } else {
            Err(RefIsRelative)
        }
    }
}

impl super::accessor::CriBase for NativeCBORCri {
    type Scheme<'a> = &'a Scheme where Self: 'a;
    type Host<'a> = &'a Host where Self: 'a;

    type PathItem<'a> = &'a Pet<PATH_UE> where Self: 'a;
    type PathIter<'a> = impl Iterator<Item=Self::PathItem<'a>> + ExactSizeIterator where Self: 'a;
    type QueryItem<'a> = &'a Pet<QUERY_UE> where Self: 'a;
    type QueryIter<'a> = impl Iterator<Item=Self::QueryItem<'a>> where Self: 'a;
    type FragmentItem<'a> = &'a Pet<FRAGMENT_UE> where Self: 'a;
    type UserInfoItem<'a> = &'a Pet<HOST_UE> where Self: 'a;

    fn path(&self) -> Self::PathIter<'_> {
        self.0.path()
    }
    fn query(&self) -> Self::QueryIter<'_> {
        self.0.query()
    }
    fn fragment(&self) -> Option<Self::FragmentItem<'_>> {
        self.0.fragment()
    }

    // All these have panics they can reach internally; some of them are still legitimate "bad use"
    // panics (eg. asking any of them on a URN style CRI) while others are not (a Discard can't be
    // reached because self was checked at construction not to have that)
    fn userinfo(&self) -> Option<Self::UserInfoItem<'_>> {
        self.0.userinfo()
    }
    fn host(&self) -> Self::Host<'_> {
        self.0.host()
    }
    fn port(&self) -> Option<u16> {
        self.0.port()
    }
}

impl super::accessor::Cri for NativeCBORCri {
    fn scheme(&self) -> Self::Scheme<'_> {
        use super::accessor::CriRef;
        self.0.scheme()
            .expect("This was checked at construction time to be present")
    }
    fn authority(&self) -> crate::traits::Authority {
        use super::accessor::CriRef;
        self.0.authority()
            .expect("This was checked at construction time to be present")
    }
}


fn load_host_port(decoder: &mut minicbor::Decoder) -> Result<(Option<UserInfo>, Host, Option<Port>), LoadError> {
    // FIXME error handling (indefinite arrays or stopping CRI should not panic)
    let mut elements = decoder.array().expect("I was promised an array, must be badly encoded").expect("No indefinite arrays please");
    let mut first_datatype = decoder.datatype().expect("Odd place to stop a CRI");
    let mut userinfo = None;
    if first_datatype == Type::Bool {
        let boolean = decoder.bool().expect("Type was just checked");
        if boolean != false {
            return Err(LoadError(LoadErrorImpl::UnexpectedType));
        }

        userinfo = Some(UserInfo(Pet::load(decoder)?));

        first_datatype = decoder.datatype().expect("Odd place to stop a CRI (userinfo but no remaining authority)");

        elements -= 2;
    }
    let host = match first_datatype {
        Type::Bytes => {
            elements -= 1;
            let bytes = decoder.bytes()?;
            Host(match bytes.len() {
                4 => HostImpl::HostIp4(<[u8; 4]>::try_from(bytes).expect("Length was just checked").into()),
                16 => {
                    let zone = match decoder.datatype()? {
                        Type::String => {
                            elements -= 1;
                            Some(decoder.str()?)
                        }
                        _ => None,
                    };
                    HostImpl::HostIp6(<[u8; 16]>::try_from(bytes).expect("Length was just checked").into(), zone.map(|s| s.to_string()))
                }
                _ => return Err(LoadError(LoadErrorImpl::UnexpectedType))
            })
        }
        Type::String | Type::Array => {
            // not PetSequence::load_optional as it can contain a terminal
            let mut hoststrings = Vec::with_capacity(elements as _); // May be 1 too many
            while elements > 0 && match decoder.datatype()? {
                Type::String => true,
                Type::Array => true,
                _ => false,
            } {
                elements -= 1;
                let string = Pet::load(decoder)?;
                hoststrings.push(string);
            }
            Host(HostImpl::HostName(PetSequence(hoststrings)))
        }
        _ => return Err(LoadError(LoadErrorImpl::UnexpectedType))
    };
    let mut port = None;
    match elements {
        1 => {
            port = Some(decoder.u16()?);
        }
        0 => (),
        // Really it's unexpected that the String series before terminated early, or there's more
        // after an IP byte string.
        _ => return Err(LoadError(LoadErrorImpl::UnexpectedType))
    }

    Ok((userinfo, host, port))
}

fn load_authorityish(decoder: &mut minicbor::Decoder) -> Result<AuthorityIsh, LoadError> {
    Ok(match decoder.datatype()
        .eof_as_none()?
       {
        None => {
            AuthorityIsh::LeadingSlash
        }
        Some(Type::Null) => {
            decoder.null().expect("A null was already found");
            AuthorityIsh::LeadingSlash
        }
        Some(Type::Bool) => {
            let boolean = decoder.bool().expect("Type was just checked");
            if boolean == false {
                return Err(LoadError(LoadErrorImpl::UnexpectedType));
            }
            AuthorityIsh::NoAuthority
        }
        Some(Type::Array) => {
            let (authority, host, port) = load_host_port(decoder)?;
            AuthorityIsh::HostPort(authority, host, port)
        }
        _ => return Err(LoadError(LoadErrorImpl::UnexpectedType))
    })
}

fn load_first_component(decoder: &mut minicbor::Decoder) -> Result<FirstComponent, LoadError> {
    Ok(match decoder.datatype() {
        Err(e) if e.is_end_of_input() => {
            // empty CRI
            FirstComponent::Nothing
        }
        Ok(Type::U8) => {
            let discard = decoder.u8()?;
            FirstComponent::Discard(Discard::Numeric(discard))
        }
        Ok(Type::Bool) => {
            let discard = decoder.bool().expect("Type was just checked");
            if discard == false {
                return Err(LoadError(LoadErrorImpl::UnexpectedType));
            }
            FirstComponent::Discard(Discard::DiscardAll)
        }
        Ok(Type::I8) => {
            let scheme = Scheme::SchemeId(decoder.i8()?);
            FirstComponent::SchemeAuthority(scheme, load_authorityish(decoder)?)
        }
        Ok(Type::String) => {
            let scheme = Scheme::SchemeName(decoder.str()?.to_string());
            FirstComponent::SchemeAuthority(scheme, load_authorityish(decoder)?)
        }
        Ok(Type::Null) => {
            // still gotta consume it
            decoder.null().expect("A null was already found");
            FirstComponent::JustAuthority(load_authorityish(decoder)?)
        }
        Ok(Type::Array) => {
            FirstComponent::JustAuthority(AuthorityIsh::LeadingSlash)
        }
        Ok(_) => return Err(LoadError(LoadErrorImpl::UnexpectedType)),
        Err(e) => return Err(e.into()),
    })
}


fn load_cri_ref(decoder: &mut minicbor::Decoder) -> Result<NativeCBORCriRef, LoadError> {
    let first = load_first_component(decoder)?;
    let path = PetSequence::load_optional(decoder)?;
    let query = PetSequence::load_optional(decoder)?;
    let fragment = Pet::load_if_present(decoder)?;

    // FIXME assert that this is the end of the reader

    Ok(NativeCBORCriRef {
        scheme_authority_discard: first,
        path,
        query,
        fragment,
    })
}


/// This is also covered by the larger tests in `vector`; unlike that module, this module should be
/// usable even in embedded situations (and doubles as minimal example).
#[test]
fn load() {
    // Base CRI from vectors
    let data = hex::decode("85218263666f6f19126782627061627468816571756572796466726167").unwrap();
    
    let _: NativeCBORCriRef = data[..].try_into().expect("Basic example could not be parsed");
}