//! This is a CoAP server application that exposes SAUL entries.
//!
//! For discovery, this exposes all entries as
//! rt="tag:chrysn@fsfe.org,2020-10-02:saul";saul=ACT_LED_RGB or similar.
//!
//! For GETs, the supported formats are:
//! * text/plain;encoding=utf-8 -- renders through the phydat's Display implementation, or uses the
//!   command-line listing on the index
//! * application/cbor (individuals only) -- renders CBOR equivalent to RIOT's phydat_to_json
//!   output
//!
//!   The implementation of the CBOR serialization doubles as a playground for comparing individual
//!   embedded CBOR libraries (serde_cbor, minicbor, ciborium-ll); all are implemented, but all but
//!   minicbor are commented out in the renderer.
//! * application/link-format (index only) -- gives the index as produced by the `saul.rs` command
//!   line output
//!
//! For actor PUTs, the supported formats are:
//! * text/plain;charset=utf-8 -- only single integer values and no units are supported.
//! * application/cbor -- like in GETs (but with limited units support). Numerics are accepted as
//!   integers or decimal fractions; unlike fractions are processed to the GCD.
//! * 65362 (experimental) -- RGB hex color codes in '#rrggbb' format as used with CSS (but
//!   without the named colors or alternative forms); those are fed in without units.

use coap_message_utils::{option_value::Block2RequestData, OptionsExt};
use coap_handler_implementations::{wkc, helpers::block2_write};
use coap_message::{Code, MessageOption, MinimalWritableMessage, MutableWritableMessage, ReadableMessage, error::RenderableOnMinimal};
use coap_numbers::{code, option};
use core::fmt::Write;
use riot_wrappers::error::NumericError;
use riot_wrappers::saul::{Phydat, RegistryEntry, Unit};

/// An extended phydat that almost behaves like phydat_to_json but with CBOR
///
/// It produces a map containing a "u" entry with the text form of the unit, and a "d" entry with
/// either a single numeric of a vector of 2 or 3 numeric entries. Numeric entries are integers or
/// decimal fractions (thus easily expressing the phydat's scale value without actually
/// calculating)
///
/// It can be serialized using serde, minicbor or ciborium_ll. (ciborium would use serde, but is
/// not an option here as it uses alloc).
struct JsonStylePhydat(Phydat);

impl serde::Serialize for JsonStylePhydat {
    fn serialize<S: serde::Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
        use serde::ser::{Error, SerializeStruct};

        if self.0.scale() != 0 {
            // The simple workaround of expressing it as a tag-unwrapped(?) array would be
            // ambiguous against the possibly elided outer array
            return Err(S::Error::custom("has scale"));
        }

        let unit = self.0.unit().and_then(|u| u.name_verbose());
        let length = 1 + unit.is_some() as usize;

        // dont-serialize: For the desired CBOR outcome the struct's name won't be serialized
        // anyway (it also has none)
        let mut map = s.serialize_struct("dont-serialize", length)?;
        if let Some(u) = unit {
            map.serialize_field("u", u)?;
        }
        match self.0.value() {
            // Single values are mapped without an outer array
            &[v] => map.serialize_field("d", &v)?,
            v => map.serialize_field("d", v)?,
        };
        map.end()
    }
}

impl<C> minicbor::Encode<C> for JsonStylePhydat {
    fn encode<W: minicbor::encode::Write>(
        &self,
        e: &mut minicbor::Encoder<W>,
        _ctx: &mut C,
    ) -> Result<(), minicbor::encode::Error<W::Error>> {
        let unit = self.0.unit().and_then(|u| u.name_verbose());
        let length = 1 + unit.is_some() as usize;

        let mut map = e.map(length as _)?;
        if let Some(u) = unit {
            map.encode("u")?;
            map.encode(u)?;
        }
        map.encode("d");
        // minicbor is incredibly lax when it comes to what items are actually written to, but then
        // again, that makes work very easy in this case
        let item_encoder = match self.0.value().len() {
            1 => map,
            n => map.array(n as _)?,
        };
        for v in self.0.value() {
            if self.0.scale() != 0 {
                let tagged = item_encoder.tag(minicbor::data::Tag::Decimal)?;
                let list = tagged.array(2)?;
                list.encode(self.0.scale())?;
                list.encode(v)?;
            } else {
                item_encoder.encode(v)?;
            }
        }

        Ok(())
    }
}

impl<'a, C> minicbor::Decode<'a, C> for JsonStylePhydat {
    /// Decode a JsonStylePhydat item from CBOR
    ///
    /// This decoder is generally strict, it currently accepts one oddity: It lets unrecognized
    /// units slip silently; consequently it also doesn't complain if the unit is given multiple
    /// times if it's nonsensical.
    // Yikes, that's a lot of code for "matching that CDDL, give me..."
    fn decode(d: &mut minicbor::Decoder<'_>, _ctx: &mut C) -> Result<Self, minicbor::decode::Error> {
        #[derive(Default)]
        struct NumericState {
            values: heapless::Vec<i16, 3>,
            minscale: Option<i8>,
        }

        impl NumericState {
            fn push(&mut self, val: ScaledI16) -> Result<(), minicbor::decode::Error> {
                let ScaledI16(mut value, mut scale) = val;
                if self.values.len() == 0 {
                    self.values.push(value);
                    self.minscale = Some(scale);
                    return Ok(());
                }

                while scale > self.minscale.unwrap() {
                    scale -= 1;
                    value = value
                        .checked_mul(10)
                        .ok_or(minicbor::decode::Error::message(
                            "Phydat can't express that range",
                        ))?;
                }
                while scale < self.minscale.unwrap() {
                    self.minscale = Some(self.minscale.unwrap() - 1);
                    for v in self.values.iter_mut() {
                        *v = v.checked_mul(10).ok_or(minicbor::decode::Error::message(
                            "Phydat can't express that range",
                        ))?;
                    }
                }
                self.values.push(value);
                Ok(())
            }
        }

        struct ScaledI16(i16, i8);

        impl<'b, C> minicbor::Decode<'b, C> for ScaledI16 {
            fn decode(d: &mut minicbor::Decoder<'_>, _ctx: &mut C) -> Result<Self, minicbor::decode::Error> {
                if d.probe().tag().is_err() {
                    return Ok(ScaledI16(d.decode()?, 0));
                }
                if d.tag()? != minicbor::data::Tag::Decimal {
                    return Err(minicbor::decode::Error::message("Unsupported tag"));
                }
                if !matches!(d.array(), Ok(Some(2))) {
                    return Err(minicbor::decode::Error::message("Unsupported array length"));
                }
                let scale = d.decode()?;
                let value = d.decode()?;
                Ok(ScaledI16(value, scale))
            }
        }

        let mut unit = None;
        let mut state: NumericState = Default::default();
        let mut d_seen = false;

        let mut items_remaining = d.map()?;
        while match items_remaining {
            Some(0) => false,
            Some(n) => {
                items_remaining = Some(n - 1);
                true
            }
            None => matches!(d.probe().simple(), Ok(0x1f)),
        } {
            match d.str()? {
                "u" => {
                    if unit.is_some() {
                        return Err(minicbor::decode::Error::message("Duplicate unit"));
                    }
                    unit = match d.str()? {
                        "%" => Some(Unit::Percent),
                        "none" => Some(Unit::None),
                        // FIXME: List is incomplete, should use utility function, maybe even in
                        // RIOT -- as it's incomplete, failing silently
                        _ => None,
                    };
                }
                "d" => {
                    if d_seen {
                        return Err(minicbor::decode::Error::message("Duplicate data"));
                    }
                    d_seen = true;
                    if d.probe().array().is_ok() {
                        for val in d.array_iter()? {
                            state.push(val?)?;
                        }
                    } else {
                        let val = d.decode()?;
                        state.push(val)?;
                    }
                }
                _ => {
                    return Err(minicbor::decode::Error::message("Unknown key"));
                }
            }
        }
        if items_remaining.is_none() {
            // To allow the wrapper to do the assertion on being at EOF
            let _ = d.simple();
        }

        Ok(Self(Phydat::new(
            &state.values,
            unit,
            state.minscale.unwrap_or(0),
        )))
    }
}

impl JsonStylePhydat {
    fn push_to_ciborium<W: ciborium_io::Write>(
        &self,
        e: &mut ciborium_ll::Encoder<W>,
    ) -> Result<(), W::Error> {
        use ciborium_ll::Header;

        fn numeric(n: impl Into<i64>) -> Header {
            let n = n.into();
            if n > 0 {
                Header::Positive(n as u64)
            } else {
                Header::Negative((!n) as u64)
            }
        }

        let unit = self.0.unit().and_then(|u| u.name_verbose());
        let length = 1 + unit.is_some() as usize;

        let mut map = e.push(Header::Map(Some(length as _)))?;
        if let Some(u) = unit {
            e.text("u", None)?;
            e.text(u, None)?;
        }
        e.text("d", None)?;

        match self.0.value().len() {
            1 => {}
            n => {
                e.push(Header::Array(Some(n)))?;
            }
        };
        for v in self.0.value() {
            if self.0.scale() != 0 {
                e.push(Header::Tag(4))?;
                e.push(Header::Array(Some(2)))?;
                e.push(numeric(self.0.scale()))?;
                e.push(numeric(*v))?;
            } else {
                e.push(numeric(*v))?;
            }
        }

        Ok(())
    }
}

#[derive(Copy, Clone, Debug)]
pub enum ContentFormat {
    TextPlain,
    LinkFormat,
    Cbor, // a CBOR-JSON convertible mapping of the Json format
    RGB,  // An ad-hoc '#RRGGBB' hex format used with code point 65362
}

impl ContentFormat {
    fn from_option(opt: &impl MessageOption) -> Result<Self, ()> {
        Ok(match opt.value_uint().ok_or(())? {
            0u16 => ContentFormat::TextPlain,
            40 => ContentFormat::LinkFormat,
            60 => ContentFormat::Cbor,
            65362 => ContentFormat::RGB,
            _ => Err(())?,
        })
    }

    fn as_number(self) -> u16 {
        match self {
            ContentFormat::TextPlain => 0,
            ContentFormat::LinkFormat => 40,
            ContentFormat::Cbor => 60,
            ContentFormat::RGB => 65362,
        }
    }
}

pub enum SaulRequest {
    GetIndex {
        accept: ContentFormat,
        block2: Block2RequestData,
    },
    Get {
        entry: RegistryEntry,
        accept: ContentFormat,
        block2: Block2RequestData,
    },
    // No details at all -- the request was already acted on in the extraction part
    Put,
}

use SaulRequest::*;

#[derive(Debug)]
pub enum Error {
    // some on which we may provide extra text
    ReadError(NumericError),
    WriteError(NumericError),
    UnsupportedContentFormat,
    FormatError(ContentFormat),
    NotAcceptableForIndex,
    NotAcceptableForItem,
    UnknownContentFormat,
    MethodNotAllowedRoot,
    MethodNotAllowedItem,
    // some are just "the weird stack can't express simple things"
    MissingCoAPStackSupport,
    // ... and some straightforward general ones
    BadOption,
    NotFound,
}

use Error::*;

impl Error {
    fn code(&self) -> u8 {
        match self {
            // maybe say something smarter on unreadable devices?
            ReadError(_) => code::INTERNAL_SERVER_ERROR,
            WriteError(_) => code::INTERNAL_SERVER_ERROR,

            UnsupportedContentFormat => code::UNSUPPORTED_CONTENT_FORMAT,
            FormatError(ContentFormat) => code::BAD_REQUEST,
            NotAcceptableForIndex => code::NOT_ACCEPTABLE,
            NotAcceptableForItem => code::NOT_ACCEPTABLE,
            UnknownContentFormat => code::UNSUPPORTED_CONTENT_FORMAT,
            MethodNotAllowedRoot => code::METHOD_NOT_ALLOWED,
            MethodNotAllowedItem => code::METHOD_NOT_ALLOWED,
            BadOption => code::BAD_OPTION,
            NotFound => code::NOT_FOUND,

            MissingCoAPStackSupport => code::INTERNAL_SERVER_ERROR,
        }
    }

    fn message(&self) -> &'static str {
        match self {
            // maybe say something smarter on unreadable devices?
            ReadError(_) => "Read error or unsupported",
            WriteError(_) => "Write error or unsupported",

            UnsupportedContentFormat => "Try text/plain, CBOR or 65362",

            FormatError(ContentFormat::RGB) => "Format is hex #RRGGBB",
            FormatError(ContentFormat::TextPlain) => "Only single ASCII int supported",
            FormatError(ContentFormat::Cbor) => r#"like {"u":"%","d":[0,0,100]}"#,
            FormatError(ContentFormat::LinkFormat) => "", // inapplicable, won't happen

            NotAcceptableForIndex => "Try text/plain or link-format",
            NotAcceptableForItem => "Try text/plain or CBOR",
            UnknownContentFormat => "",
            MethodNotAllowedRoot => "",
            MethodNotAllowedItem => "",
            BadOption => "",
            NotFound => "",

            // and likely it won't be able to send that either, but let's try.
            MissingCoAPStackSupport => "CoAP stack can not send message",
        }
    }
}

impl RenderableOnMinimal for Error {
    type Error<IE: RenderableOnMinimal + core::fmt::Debug> = IE;
    fn render<M: MinimalWritableMessage>(self, msg: &mut M) -> Result<(), M::UnionError> {
        msg.set_code(Code::new(self.code())?);
        let _ = msg.set_payload(self.message().as_bytes());
        Ok(())
    }
}

/// A handler for SAUL requests, using SAUL_MATCH_SUBTREE to manage its resources.
///
/// The path this is registered at must be passed in as the prefix, as link-format responses
/// necessitate knowing one's own path, and the prefix needs to be stripped off when processing the
/// Uri-Path options.
///
/// As the link-format handler is bad, the name must be simple.
pub struct SaulHandler {
    prefix: &'static [&'static str],
}

impl SaulHandler {
    /// Create a SaulHandler
    ///
    /// The prefix needs to be passed in in order to produce proper link-format responses which can
    /// not be path-relative, and should thus be equal to the prefix assigned in the tree.
    pub fn new(prefix: &'static [&'static str]) -> Self {
        Self { prefix }
    }

    fn put_value(
        &self,
        entry: RegistryEntry,
        content_format: ContentFormat,
        body: &[u8],
    ) -> Result<(), Error> {
        let phydat = match content_format {
            ContentFormat::TextPlain => {
                let val: i16 = core::str::from_utf8(body)
                    .ok()
                    .and_then(|s| s.parse().ok())
                    .ok_or_else(|| FormatError(ContentFormat::TextPlain))?;
                Phydat::new(&[val], None, 0)
            }
            ContentFormat::Cbor => {
                let mut decoder = minicbor::Decoder::new(body);
                let jsp: JsonStylePhydat = decoder
                    .decode()
                    .map_err(|e| FormatError(ContentFormat::Cbor))?;

                if decoder.datatype().map_err(|e| e.is_end_of_input()) != Err(true) {
                    return Err(FormatError(ContentFormat::Cbor));
                }
                jsp.0
            }
            ContentFormat::RGB => {
                if body.len() != 7 || body[0] != b'#' {
                    return Err(FormatError(ContentFormat::RGB));
                }
                let mut bytes = [0u8; 3];
                hex::decode_to_slice(&body[1..], bytes.as_mut())
                    .map_err(|_| FormatError(ContentFormat::RGB))?;

                Phydat::new(
                    &[bytes[0].into(), bytes[1].into(), bytes[2].into()],
                    None,
                    0,
                )
            }
            _ => Err(UnsupportedContentFormat)?,
        };
        entry
            .write(phydat)
            // in the rough anticipation that maybe one day this won't return a NumericError but
            // something more wrapped that would then still implement Into<NumericError> for
            // exactly this kind of compatibility
            .map_err(|e| WriteError(e.into()))
    }
}

impl coap_handler::Handler for SaulHandler {
    type RequestData = SaulRequest;

    type ExtractRequestError = Error;
    type BuildResponseError<M: MinimalWritableMessage> = Error;

    fn extract_request_data<M: ReadableMessage>(
        &mut self,
        request: &M,
    ) -> Result<SaulRequest, Error> {
        #[derive(PartialEq, Copy, Clone)]
        enum Path {
            Initial,
            Root,
            Index(usize),
            NotFound,
        }

        impl Path {
            fn crank(&mut self, optval: &str) {
                *self = match (*self, optval) {
                    (Path::Initial, "") => Path::Root,
                    (Path::Initial, x) => {
                        if let Ok(i) = x.parse() {
                            Path::Index(i)
                        } else {
                            Path::NotFound
                        }
                    }
                    (_, _) => Path::NotFound,
                };
            }
        }

        let mut path = Path::Initial;
        let mut block2 = None;
        let mut accept = None;
        let mut content_format = None;

        for opt in request
            .options()
            .take_uri_path(|p| path.crank(p))
            .take_block2(&mut block2)
        {
            match opt.number() {
                option::ACCEPT => {
                    // Not converting the error here...
                    accept = Some(ContentFormat::from_option(&opt));
                }
                option::CONTENT_FORMAT => {
                    content_format =
                        Some(ContentFormat::from_option(&opt).map_err(|_| UnknownContentFormat)?);
                }
                x => match option::get_criticality(x) {
                    option::Criticality::Critical => return Err(BadOption),
                    _ => {}
                },
            }
        }

        let block2 = block2.unwrap_or_default();
        let content_format = content_format.unwrap_or(ContentFormat::TextPlain);
        let accept = accept
            .unwrap_or(Ok(ContentFormat::TextPlain))
            // ... but delaying error conversion until here when we know (well we did before but
            // Rust can't know that) the path
            .map_err(|_| match path {
                Path::Root => NotAcceptableForIndex,
                _ => NotAcceptableForItem,
            })?;

        match path {
            Path::Root => {
                if request.code().into() == code::GET {
                    Ok(GetIndex { accept, block2 })
                } else {
                    Err(MethodNotAllowedRoot)
                }
            }
            Path::Index(index) => {
                let entry = RegistryEntry::nth(index).ok_or(NotFound)?;
                match request.code().into() {
                    code::GET => Ok(Get {
                        entry,
                        accept,
                        block2,
                    }),
                    code::PUT => {
                        self.put_value(entry, content_format, request.payload())?;
                        Ok(Put)
                    }
                    _ => Err(MethodNotAllowedItem),
                }
            }
            _ => Err(NotFound),
        }
    }
    fn estimate_length(&mut self, _: &<Self as coap_handler::Handler>::RequestData) -> usize {
        // Still enough to get a reasonable block in there if it comes to Block2 through countless
        // sensors or a read-all
        200
    }
    fn build_response<M: MutableWritableMessage>(
        &mut self,
        response: &mut M,
        request: Self::RequestData,
    ) -> Result<(), Self::BuildResponseError<M>> {
        let code = match request {
            GetIndex { accept, block2 } => block2_write(block2, response, |w| {
                match accept {
                    ContentFormat::TextPlain => {
                        riot_shell_commands::saul(w, ["saul"].iter().map(|x| *x));
                    }
                    ContentFormat::LinkFormat => {
                        coap_handler_implementations::wkc::write_link_format(w, self, self.prefix)
                            .unwrap();
                    }
                    _ => Err(NotAcceptableForItem)?,
                };
                Ok(code::CONTENT)
            })?,
            Get {
                entry,
                accept,
                block2,
            } => {
                // FIXME: Not sending the content format because it goes between ETag and Block2
                // and the block2_writer won't let us put data inbetween there
                block2_write(block2, response, |w| {
                    // FIXME: In the error case, block and content-format are still there :-(
                    // Worse yet, serde errors are not caught.
                    let phydat = entry.read().map_err(|e| ReadError(e.into()))?;
                    match accept {
                        ContentFormat::TextPlain => writeln!(w, "{}", phydat).unwrap(),
                        ContentFormat::Cbor => {
                            use serde::Serialize;
                            let phydat = JsonStylePhydat(phydat);

                            // Enable this to use serde_cbor
                            // phydat.serialize(&mut serde_cbor::ser::Serializer::new(w));

                            // Usually, this is serialized using minicbor
                            minicbor::encode(&phydat, w);

                            // Enable this to try out ciborium
                            // let mut encoder = ciborium_ll::Encoder::from(w);
                            // phydat.push_to_ciborium(&mut encoder).unwrap();
                            // use ciborium_io::Write;
                            // encoder.flush().unwrap();
                        }
                        _ => Err(NotAcceptableForItem)?,
                    };

                    Ok(code::CONTENT)
                })?
            }
            Put => code::CHANGED,
        };

        response.set_code(Code::new(code).map_err(|_| Error::MissingCoAPStackSupport)?);
        Ok(())
    }
}

pub enum Record {
    Root,
    Entry(usize, RegistryEntry),
}

impl coap_handler::Record for Record {
    type PathElement = heapless::String<4>;
    // FIXME: Once TAIT is stable, replace with the simpler forms below
    type PathElements = core::iter::Once<heapless::String<4>>;
    type Attributes = core::iter::Cloned<core::slice::Iter<'static, coap_handler::Attribute>>;
    // type PathElements = impl Iterator<Item = Self::PathElement>;
    // type Attributes = impl Iterator<Item = coap_handler::Attribute>;

    fn path(&self) -> Self::PathElements {
        let mut buf = heapless::String::new();
        if let Record::Entry(i, _e) = self {
            // Error for i > 9999 checked elsewhere, so this shouldn't happened (but we'll let it
            // slide)
            let _ = write!(buf, "{}", i);
        } // else, Root is just rendered as "" which is already in there
        core::iter::once(buf)
    }
    fn rel(&self) -> core::option::Option<&str> {
        None
    }
    fn attributes(&self) -> Self::Attributes {
        match self {
            Record::Root => [coap_handler::Attribute::Title("SAUL index")].iter().cloned(),
            // FIXME: produce rt="tag:chrysn@fsfe.org,2020-10-02:saul";saul=ACT_LED_RGB
            Record::Entry(_i, e) => [
                coap_handler::Attribute::ResourceType("tag:chrysn@fsfe.org,2020-10-02:saul"),
                // Title would be nice but requires more elaborate structure than [] even though
                // it's a &'static string because the array itself will need to be passed; might
                // work with a heapless::Vec
                // coap_handler::Attribute::Title(e.name().unwrap_or("unnamed")),
                // ... but still, where do we transport the custom saul attribute?
            ]
            .iter()
            .cloned(),
        }
    }
}

// To be removed with TAIT, see below
fn first_arg_fits_in_4_bytes(data: &(usize, RegistryEntry)) -> bool {
    data.0 <= 9999
}

// To be removed with TAIT, see below
fn make_record(data: (usize, RegistryEntry)) -> Record {
    Record::Entry(data.0, data.1)
}

/// A SaulHandler lists all its SAUL devices in /.well-known/core. This is especially useful when
/// registering at a Resource Directory using simple registration and lookup clients try to
/// discover sensors.
impl coap_handler::Reporting for SaulHandler {
    type Record<'res> = Record;
    // FIXME: Once TAIT is stable, this all can become its simple form again, and the filter/map
    // workhorses can become (empty) closures.
    type Reporter<'res> = core::iter::Chain<
        core::iter::Once<Record>,
        core::iter::Map<
            core::iter::Filter<
                core::iter::Enumerate<riot_wrappers::saul::AllRegistryEntries>,
                fn(&(usize, RegistryEntry)) -> bool,
            >,
            fn((usize, RegistryEntry)) -> Record,
        >,
    >;
    // or type Reporter<'res> = impl Iterator<Item=Record>;
    fn report(&self) -> Self::Reporter<'_> {
        core::iter::once(Record::Root).chain(
            RegistryEntry::all()
                .enumerate()
                // for the String<4>, but whoever has so many sensors will have a hard time
                // listing them all in .wk/c anyway
                .filter(first_arg_fits_in_4_bytes as _)
                // or .filter(|(i, _r)| *i <= 9999)
                .map(make_record as _),
                // or .map(|(i, r)| Record::Entry(i, r))
        )
    }
}