//! The module contains the implementation of the `SETTINGS` frame and associated flags.

use http::StreamId;
use http::frame::{
    Flag,
    Frame,
    FrameHeader,
    RawFrame,
    pack_header,
};

/// An enum that lists all valid settings that can be sent in a SETTINGS
/// frame.
///
/// Each setting has a value that is a 32 bit unsigned integer (6.5.1.).
#[derive(Clone)]
#[derive(PartialEq)]
#[derive(Debug)]
#[derive(Copy)]
pub enum HttpSetting {
    HeaderTableSize(u32),
    EnablePush(u32),
    MaxConcurrentStreams(u32),
    InitialWindowSize(u32),
    MaxFrameSize(u32),
    MaxHeaderListSize(u32),
}

impl HttpSetting {
    /// Creates a new `HttpSetting` with the correct variant corresponding to
    /// the given setting id, based on the settings IDs defined in section
    /// 6.5.2.
    pub fn from_id(id: u16, val: u32) -> Option<HttpSetting> {
        match id {
            1 => Some(HttpSetting::HeaderTableSize(val)),
            2 => Some(HttpSetting::EnablePush(val)),
            3 => Some(HttpSetting::MaxConcurrentStreams(val)),
            4 => Some(HttpSetting::InitialWindowSize(val)),
            5 => Some(HttpSetting::MaxFrameSize(val)),
            6 => Some(HttpSetting::MaxHeaderListSize(val)),
            _ => None,
        }
    }

    /// Creates a new `HttpSetting` by parsing the given buffer of 6 bytes,
    /// which contains the raw byte representation of the setting, according
    /// to the "SETTINGS format" defined in section 6.5.1.
    ///
    /// The `raw_setting` parameter should have length at least 6 bytes, since
    /// the length of the raw setting is exactly 6 bytes.
    ///
    /// # Panics
    ///
    /// If given a buffer shorter than 6 bytes, the function will panic.
    fn parse_setting(raw_setting: &[u8]) -> Option<HttpSetting> {
        let id: u16 = ((raw_setting[0] as u16) << 8) | (raw_setting[1] as u16);
        let val: u32 = unpack_octets_4!(raw_setting, 2, u32);

        HttpSetting::from_id(id, val)
    }

    /// Returns the setting ID as an unsigned 16 bit integer, as defined in
    /// section 6.5.2.
    pub fn get_id(&self) -> u16 {
        match self {
            &HttpSetting::HeaderTableSize(_) => 1,
            &HttpSetting::EnablePush(_) => 2,
            &HttpSetting::MaxConcurrentStreams(_) => 3,
            &HttpSetting::InitialWindowSize(_) => 4,
            &HttpSetting::MaxFrameSize(_) => 5,
            &HttpSetting::MaxHeaderListSize(_) => 6,
        }
    }

    /// Gets the setting value by unpacking it from the wrapped `u32`.
    pub fn get_val(&self) -> u32 {
        match self {
            &HttpSetting::HeaderTableSize(ref val) => val.clone(),
            &HttpSetting::EnablePush(ref val) => val.clone(),
            &HttpSetting::MaxConcurrentStreams(ref val) => val.clone(),
            &HttpSetting::InitialWindowSize(ref val) => val.clone(),
            &HttpSetting::MaxFrameSize(ref val) => val.clone(),
            &HttpSetting::MaxHeaderListSize(ref val) => val.clone(),
        }
    }

    /// Serializes a setting into its "on-the-wire" representation of 6 octets,
    /// according to section 6.5.1.
    fn serialize(&self) -> [u8; 6] {
        let (id, val) = (self.get_id(), self.get_val());
        [
            ((id >> 8) & 0x00FF) as u8,
            ((id >> 0) & 0x00FF) as u8,
            (((val >> 24) & 0x000000FF) as u8),
            (((val >> 16) & 0x000000FF) as u8),
            (((val >>  8) & 0x000000FF) as u8),
            (((val >>  0) & 0x000000FF) as u8),
        ]
    }
}

/// An enum representing the flags that a `SettingsFrame` can have.
/// The integer representation associated to each variant is that flag's
/// bitmask.
///
/// HTTP/2 spec, section 6.5.
#[derive(Clone)]
#[derive(PartialEq)]
#[derive(Debug)]
#[derive(Copy)]
pub enum SettingsFlag {
    Ack = 0x1,
}

impl Flag for SettingsFlag {
    #[inline]
    fn bitmask(&self) -> u8 {
        *self as u8
    }
}

/// A struct representing the SETTINGS frames of HTTP/2, as defined in the
/// HTTP/2 spec, section 6.5.
///
/// The struct does not try to prevent the client from creating malformed
/// SETTINGS frames, such as ones that have the ACK flag set along with some
/// settings values. The users are responsible to follow the prescribed rules
/// before sending the frame to the peer.
///
/// On parsing received frames, it treats the following as errors:
///
/// - ACK flag and a number of settings both set
/// - Payload length not a multiple of 6
/// - Stream ID not zero (SETTINGS frames MUST be associated to stream 0)
///
/// What is *not* treated as an error (for now) are settings values out of
/// allowed bounds such as a EnablePush being set to something other than 0 or
/// 1.
#[derive(PartialEq)]
#[derive(Debug)]
#[derive(Clone)]
pub struct SettingsFrame {
    /// Contains all the settings that are currently set in the frame. It is
    /// safe to access this field (to read, add, or remove settings), even
    /// though a helper method `add_setting` exists.
    pub settings: Vec<HttpSetting>,
    /// Represents the flags currently set on the `SettingsFrame`, packed into
    /// a single byte.
    flags: u8,
}

impl SettingsFrame {
    /// Creates a new `SettingsFrame`
    pub fn new() -> SettingsFrame {
        SettingsFrame {
            settings: Vec::new(),
            // By default, no flags are set
            flags: 0,
        }
    }

    /// A convenience constructor that returns a `SettingsFrame` with the ACK
    /// flag already set and no settings.
    pub fn new_ack() -> SettingsFrame {
        SettingsFrame {
            settings: Vec::new(),
            flags: SettingsFlag::Ack.bitmask(),
        }
    }

    /// Adds the given setting to the frame.
    pub fn add_setting(&mut self, setting: HttpSetting) {
        self.settings.push(setting);
    }

    /// Sets the ACK flag for the frame. This method is just a convenience
    /// method for calling `frame.set_flag(SettingsFlag::Ack)`.
    pub fn set_ack(&mut self) {
        self.set_flag(SettingsFlag::Ack)
    }

    /// Checks whether the `SettingsFrame` has an ACK attached to it.
    pub fn is_ack(&self) -> bool {
        self.is_set(SettingsFlag::Ack)
    }

    /// Returns the total length of the payload in bytes.
    fn payload_len(&self) -> u32 {
        // Each setting is represented with 6 bytes =>
        6 * self.settings.len() as u32
    }

    /// Parses the given buffer, considering it a representation of a settings
    /// frame payload.
    ///
    /// # Returns
    ///
    /// A `Vec` of settings that are set by the given payload.
    ///
    /// Any unknown setting is ignored, as per the HTTP/2 spec requirement.
    ///
    /// If the frame is invalid (i.e. the length of the payload is not a
    /// multiple of 6) it returns `None`.
    fn parse_payload(payload: &[u8]) -> Option<Vec<HttpSetting>> {
        if payload.len() % 6 != 0 {
            return None;
        }

        // Iterates through chunks of the raw payload of size 6 bytes and
        // parses each of them into an `HttpSetting`
        Some(payload.chunks(6).filter_map(|chunk| {
            HttpSetting::parse_setting(chunk)
        }).collect())
    }
}

impl Frame for SettingsFrame {
    /// The type that represents the flags that the particular `Frame` can take.
    /// This makes sure that only valid `Flag`s are used with each `Frame`.
    type FlagType = SettingsFlag;

    /// Creates a new `SettingsFrame` with the given `RawFrame` (i.e. header and
    /// payload), if possible.
    ///
    /// # Returns
    ///
    /// `None` if a valid `SettingsFrame` cannot be constructed from the given
    /// `RawFrame`. The stream ID *must* be 0 in order for the frame to be
    /// valid. If the `ACK` flag is set, there MUST not be a payload. The
    /// total payload length must be multiple of 6.
    ///
    /// Otherwise, returns a newly constructed `SettingsFrame`.
    fn from_raw(raw_frame: RawFrame) -> Option<SettingsFrame> {
        // Unpack the header
        let (len, frame_type, flags, stream_id) = raw_frame.header();
        // Check that the frame type is correct for this frame implementation
        if frame_type != 0x4 {
            return None;
        }
        // Check that the length given in the header matches the payload
        // length; if not, something went wrong and we do not consider this a
        // valid frame.
        if (len as usize) != raw_frame.payload().len() {
            return None;
        }
        // Check that the SETTINGS frame is associated to stream 0
        if stream_id != 0 {
            return None;
        }
        if (flags & SettingsFlag::Ack.bitmask()) != 0 {
            if len != 0 {
                // The SETTINGS flag MUST not have a payload if Ack is set
                return None;
            } else {
                // Ack is set and there's no payload => just an Ack frame
                return Some(SettingsFrame {
                    settings: Vec::new(),
                    flags: flags,
                });
            }
        }

        match SettingsFrame::parse_payload(&raw_frame.payload()) {
            Some(settings) => {
                Some(SettingsFrame {
                    settings: settings,
                    flags: flags,
                })
            },
            None => None,
        }
    }

    /// Tests if the given flag is set for the frame.
    fn is_set(&self, flag: SettingsFlag) -> bool {
        (self.flags & flag.bitmask()) != 0
    }

    /// Returns the `StreamId` of the stream to which the frame is associated.
    ///
    /// A `SettingsFrame` always has to be associated to stream `0`.
    fn get_stream_id(&self) -> StreamId {
        0
    }

    /// Returns a `FrameHeader` based on the current state of the `Frame`.
    fn get_header(&self) -> FrameHeader {
        (self.payload_len(), 0x4, self.flags, 0)
    }

    /// Sets the given flag for the frame.
    fn set_flag(&mut self, flag: SettingsFlag) {
        self.flags |= flag.bitmask();
    }

    /// Returns a `Vec` with the serialized representation of the frame.
    fn serialize(&self) -> Vec<u8> {
        let mut buf = Vec::with_capacity(self.payload_len() as usize);
        // First the header...
        buf.extend(pack_header(&self.get_header()).to_vec().into_iter());
        // ...now the settings
        for setting in self.settings.iter() {
            buf.extend(setting.serialize().to_vec().into_iter());
        }

        buf
    }
}

#[cfg(test)]
mod tests {
    use super::{HttpSetting, SettingsFrame};
    use http::frame::tests::{build_test_frame};
    use http::frame::{pack_header, Frame, RawFrame};

    /// Tests that a `SettingsFrame` correctly handles a SETTINGS frame with
    /// no ACK flag and only a single setting.
    #[test]
    fn test_settings_frame_parse_no_ack_one_setting() {
        let payload = [0, 1, 0, 0, 0, 1];
        // A header with the flag indicating no padding
        let header = (payload.len() as u32, 4, 0, 0);

        let frame = build_test_frame::<SettingsFrame>(&header, &payload);

        // The frame correctly interprets the settings?
        assert_eq!(frame.settings, vec![HttpSetting::HeaderTableSize(1)]);
        // ...and the headers?
        assert_eq!(frame.get_header(), header);
    }

    /// Tests that a `SettingsFrame` correctly handles a SETTINGS frame with
    /// no ACK flag and multiple settings within the frame.
    #[test]
    fn test_settings_frame_parse_no_ack_multiple_settings() {
        let settings = vec![
            HttpSetting::HeaderTableSize(1),
            HttpSetting::MaxHeaderListSize(5),
            HttpSetting::EnablePush(0),
        ];
        let payload = {
            let mut res: Vec<u8> = Vec::new();
            for s in settings.iter().map(|s| s.serialize()) { res.extend(s.to_vec().into_iter()); }

            res
        };
        let header = (payload.len() as u32, 4, 0, 0);

        let frame = build_test_frame::<SettingsFrame>(&header, &payload);

        // The frame correctly interprets the settings?
        assert_eq!(frame.settings, settings);
        // ...and the headers?
        assert_eq!(frame.get_header(), header);
        assert!(!frame.is_ack());
    }

    /// Tests that a `SettingsFrame` correctly handles a SETTINGS frame with
    /// no ACK and multiple *duplicate* settings within the frame.
    #[test]
    fn test_settings_frame_parse_no_ack_duplicate_settings() {
        let settings = vec![
            HttpSetting::HeaderTableSize(1),
            HttpSetting::MaxHeaderListSize(5),
            HttpSetting::EnablePush(0),
            HttpSetting::HeaderTableSize(2),
        ];
        let payload = {
            let mut res: Vec<u8> = Vec::new();
            for s in settings.iter().map(|s| s.serialize()) { res.extend(s.to_vec().into_iter()); }

            res
        };
        let header = (payload.len() as u32, 4, 0, 0);

        let frame = build_test_frame::<SettingsFrame>(&header, &payload);

        // All the settings are returned, even the duplicates
        assert_eq!(frame.settings, settings);
        // ...and the headers?
        assert_eq!(frame.get_header(), header);
        assert!(!frame.is_ack());
    }

    /// Tests that a `SettingsFrame` correctly handles a SETTING frame with no
    /// ACK and an unknown setting within the frame. The unknown setting is
    /// simply ignored.
    #[test]
    fn test_settings_frame_parse_no_ack_unknown_setting() {
        let settings = vec![
            HttpSetting::HeaderTableSize(1),
            HttpSetting::MaxHeaderListSize(5),
        ];
        let payload = {
            let mut res: Vec<u8> = Vec::new();
            for s in settings.iter().map(|s| s.serialize()) { res.extend(s.to_vec().into_iter()); }
            res.extend(vec![0, 10, 0, 0, 0, 0].into_iter());
            for s in settings.iter().map(|s| s.serialize()) { res.extend(s.to_vec().into_iter()); }

            res
        };
        let header = (payload.len() as u32, 4, 0, 0);

        let frame = build_test_frame::<SettingsFrame>(&header, &payload);

        // All the settings are returned twice, but the unkown isn't found in
        // the returned Vec. For now, we ignore the unknown setting fully, not
        // exposing it in any way to any other higher-level clients.
        assert_eq!(frame.settings.len(), 4);
        assert_eq!(&frame.settings[0..2], &settings[..]);
        assert_eq!(&frame.settings[2..], &settings[..]);
        assert!(!frame.is_ack());
    }

    /// Tests that a `SettingsFrame` correctly handles a SETTINGS frame with an
    /// ACK flag and no settings.
    #[test]
    fn test_settings_frame_parse_ack_no_settings() {
        let payload = [];
        let header = (payload.len() as u32, 4, 1, 0);

        let frame = build_test_frame::<SettingsFrame>(&header, &payload);

        // No settings there?
        assert_eq!(frame.settings, vec![]);
        // ...and the headers?
        assert_eq!(frame.get_header(), header);
        // ...and the frame indicates it's an ACK
        assert!(frame.is_ack());
    }

    /// Tests that a `SettingsFrame` correctly handles a SETTINGS frame with an
    /// ACK flag, along with settings. In this case, the frame needs to be
    /// considered invalid.
    #[test]
    fn test_settings_frame_parse_ack_with_settings() {
        let settings = [
            HttpSetting::EnablePush(0),
        ];
        let payload = {
            let mut res: Vec<u8> = Vec::new();
            for s in settings.iter().map(|s| s.serialize()) { res.extend(s.to_vec().into_iter()); }

            res
        };
        let header = (payload.len() as u32, 4, 1, 0);

        let frame: Option<SettingsFrame> = Frame::from_raw(
            RawFrame::with_payload(header, payload));

        assert!(frame.is_none());
    }

    /// Tests that a `SettingsFrame` correctly handles a SETTINGS frame which
    /// was not associated to stream 0 by returning an error.
    #[test]
    fn test_settings_frame_parse_not_stream_zero() {
        let payload = vec![];
        // Header indicates that it is associated to stream 1
        let header = (payload.len() as u32, 4, 1, 1);

        let frame: Option<SettingsFrame> = Frame::from_raw(
            RawFrame::with_payload(header, payload));

        assert!(frame.is_none());
    }

    /// Tests that a `SettingsFrame` correctly handles a SETTINGS frame which
    /// does not have a payload with a number of bytes that's a multiple of 6.
    #[test]
    fn test_settings_frame_parse_not_multiple_of_six() {
        let payload = vec![1, 2, 3];

        let header = (payload.len() as u32, 4, 0, 0);

        let frame: Option<SettingsFrame> = Frame::from_raw(
            RawFrame::with_payload(header, payload));

        assert!(frame.is_none());
    }

    /// Tests that a `SettingsFrame` gets correctly serialized when it contains
    /// only settings and no ACK.
    #[test]
    fn test_settings_frame_serialize_no_ack_settings() {
        let mut frame = SettingsFrame::new();
        frame.add_setting(HttpSetting::EnablePush(0));
        let expected = {
            let mut res: Vec<u8> = Vec::new();
            res.extend(pack_header(&(6, 4, 0, 0)).to_vec().into_iter());
            res.extend(HttpSetting::EnablePush(0).serialize().to_vec().into_iter());

            res
        };

        let serialized = frame.serialize();

        assert_eq!(serialized, expected);
    }

    /// Tests that a `SettingsFrame` gets correctly serialized when it contains
    /// multiple settings and no ACK.
    #[test]
    fn test_settings_frame_serialize_no_ack_multiple_settings() {
        let mut frame = SettingsFrame::new();
        frame.add_setting(HttpSetting::EnablePush(0));
        frame.add_setting(HttpSetting::MaxHeaderListSize(0));
        let expected = {
            let mut res: Vec<u8> = Vec::new();
            res.extend(pack_header(&(6 * 2, 4, 0, 0)).to_vec().into_iter());
            res.extend(HttpSetting::EnablePush(0).serialize().to_vec().into_iter());
            res.extend(HttpSetting::MaxHeaderListSize(0).serialize().to_vec().into_iter());

            res
        };

        let serialized = frame.serialize();

        assert_eq!(serialized, expected);
    }

    /// Tests that a `SettingsFrame` gets correctly serialized when it contains
    /// multiple settings and no ACK.
    #[test]
    fn test_settings_frame_serialize_ack() {
        let frame = SettingsFrame::new_ack();
        let expected = pack_header(&(0, 4, 1, 0)).to_vec();

        let serialized = frame.serialize();

        assert_eq!(serialized, expected);
    }

    /// Tests that the `HttpSetting::parse_setting` method correctly creates
    /// settings from raw bytes.
    #[test]
    fn test_setting_deserialize() {
        {
            let buf = [0, 1, 0, 0, 1, 0];

            let setting = HttpSetting::parse_setting(&buf).unwrap();

            assert_eq!(setting, HttpSetting::HeaderTableSize(1 << 8));
        }
        {
            let buf = [0, 2, 0, 0, 0, 1];

            let setting = HttpSetting::parse_setting(&buf).unwrap();

            assert_eq!(setting, HttpSetting::EnablePush(1));
        }
        {
            let buf = [0, 3, 0, 0, 0, 0];

            let setting = HttpSetting::parse_setting(&buf).unwrap();

            assert_eq!(setting, HttpSetting::MaxConcurrentStreams(0));
        }
        {
            let buf = [0, 4, 0, 0, 0, 1];

            let setting = HttpSetting::parse_setting(&buf).unwrap();

            assert_eq!(setting, HttpSetting::InitialWindowSize(1));
        }
        {
            let buf = [0, 5, 0, 0, 0, 255];

            let setting = HttpSetting::parse_setting(&buf).unwrap();

            assert_eq!(setting, HttpSetting::MaxFrameSize((1 << 8) - 1));
        }
        {
            let buf = [0, 6, 0, 0, 0, 255];

            let setting = HttpSetting::parse_setting(&buf).unwrap();

            assert_eq!(setting, HttpSetting::MaxHeaderListSize((1 << 8) - 1));
        }
        {
            let buf = [0, 7, 0, 0, 0, 255];

            let setting = HttpSetting::parse_setting(&buf);

            assert!(setting.is_none());
        }
        {
            let buf = [0, 0, 0, 0, 0, 255];

            let setting = HttpSetting::parse_setting(&buf);

            assert!(setting.is_none());
        }
    }

    /// Tests that the `HttpSetting::serialize` method correctly creates
    /// a 6 byte buffer based on the given setting.
    #[test]
    fn test_setting_serialize() {
        {
            let buf = [0, 1, 0, 0, 1, 0];

            let setting = HttpSetting::HeaderTableSize(1 << 8);

            assert_eq!(buf, setting.serialize());
        }
        {
            let buf = [0, 2, 0, 0, 0, 1];

            let setting = HttpSetting::EnablePush(1);

            assert_eq!(buf, setting.serialize());
        }
        {
            let buf = [0, 3, 0, 0, 0, 0];

            let setting = HttpSetting::MaxConcurrentStreams(0);

            assert_eq!(buf, setting.serialize());
        }
        {
            let buf = [0, 4, 0, 0, 0, 1];

            let setting = HttpSetting::InitialWindowSize(1);

            assert_eq!(buf, setting.serialize());
        }
        {
            let buf = [0, 5, 0, 0, 0, 255];

            let setting = HttpSetting::MaxFrameSize((1 << 8) - 1);

            assert_eq!(buf, setting.serialize());
        }
        {
            let buf = [0, 6, 0, 0, 0, 255];

            let setting = HttpSetting::MaxHeaderListSize((1 << 8) - 1);

            assert_eq!(buf, setting.serialize());
        }
    }
}