use std::{
    cmp,
    fmt::{self, Display, Write},
    str::FromStr,
};

use actix_http::{error::ParseError, header, HttpMessage};

use super::{Header, HeaderName, HeaderValue, InvalidHeaderValue, TryIntoHeaderValue, Writer};

/// `Range` header, defined
/// in [RFC 7233 §3.1](https://datatracker.ietf.org/doc/html/rfc7233#section-3.1)
///
/// The "Range" header field on a GET request modifies the method semantics to request transfer of
/// only one or more sub-ranges of the selected representation data, rather than the entire selected
/// representation data.
///
/// # ABNF
/// ```plain
/// Range = byte-ranges-specifier / other-ranges-specifier
/// other-ranges-specifier = other-range-unit "=" other-range-set
/// other-range-set = 1*VCHAR
///
/// bytes-unit = "bytes"
///
/// byte-ranges-specifier = bytes-unit "=" byte-range-set
/// byte-range-set = 1#(byte-range-spec / suffix-byte-range-spec)
/// byte-range-spec = first-byte-pos "-" [last-byte-pos]
/// suffix-byte-range-spec = "-" suffix-length
/// suffix-length = 1*DIGIT
/// first-byte-pos = 1*DIGIT
/// last-byte-pos = 1*DIGIT
/// ```
///
/// # Example Values
/// * `bytes=1000-`
/// * `bytes=-50`
/// * `bytes=0-1,30-40`
/// * `bytes=0-10,20-90,-100`
/// * `custom_unit=0-123`
/// * `custom_unit=xxx-yyy`
///
/// # Examples
/// ```
/// use actix_web::http::header::{Range, ByteRangeSpec};
/// use actix_web::HttpResponse;
///
/// let mut builder = HttpResponse::Ok();
/// builder.insert_header(Range::Bytes(
///     vec![ByteRangeSpec::FromTo(1, 100), ByteRangeSpec::From(200)]
/// ));
/// builder.insert_header(Range::Unregistered("letters".to_owned(), "a-f".to_owned()));
/// builder.insert_header(Range::bytes(1, 100));
/// builder.insert_header(Range::bytes_multi(vec![(1, 100), (200, 300)]));
/// ```
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Range {
    /// Byte range.
    Bytes(Vec<ByteRangeSpec>),

    /// Custom range, with unit not registered at IANA.
    ///
    /// (`other-range-unit`: String , `other-range-set`: String)
    Unregistered(String, String),
}

/// A range of bytes to fetch.
///
/// Each [`Range::Bytes`] header can contain one or more `ByteRangeSpec`s.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ByteRangeSpec {
    /// All bytes from `x` to `y`, inclusive.
    ///
    /// Serialized as `x-y`.
    ///
    /// Example: `bytes=500-999` would represent the second 500 bytes.
    FromTo(u64, u64),

    /// All bytes starting from `x`, inclusive.
    ///
    /// Serialized as `x-`.
    ///
    /// Example: For a file of 1000 bytes, `bytes=950-` would represent bytes 950-999, inclusive.
    From(u64),

    /// The last `y` bytes, inclusive.
    ///
    /// Using the spec terminology, this is `suffix-byte-range-spec`. Serialized as `-y`.
    ///
    /// Example: For a file of 1000 bytes, `bytes=-50` is equivalent to `bytes=950-`.
    Last(u64),
}

impl ByteRangeSpec {
    /// Given the full length of the entity, attempt to normalize the byte range into an satisfiable
    /// end-inclusive `(from, to)` range.
    ///
    /// The resulting range is guaranteed to be a satisfiable range within the bounds
    /// of `0 <= from <= to < full_length`.
    ///
    /// If the byte range is deemed unsatisfiable, `None` is returned. An unsatisfiable range is
    /// generally cause for a server to either reject the client request with a
    /// `416 Range Not Satisfiable` status code, or to simply ignore the range header and serve the
    /// full entity using a `200 OK` status code.
    ///
    /// This function closely follows [RFC 7233 §2.1]. As such, it considers ranges to be
    /// satisfiable if they meet the following conditions:
    ///
    /// > If a valid byte-range-set includes at least one byte-range-spec with a first-byte-pos that
    /// > is less than the current length of the representation, or at least one
    /// > suffix-byte-range-spec with a non-zero suffix-length, then the byte-range-set is
    /// > satisfiable. Otherwise, the byte-range-set is unsatisfiable.
    ///
    /// The function also computes remainder ranges based on the RFC:
    ///
    /// > If the last-byte-pos value is absent, or if the value is greater than or equal to the
    /// > current length of the representation data, the byte range is interpreted as the remainder
    /// > of the representation (i.e., the server replaces the value of last-byte-pos with a value
    /// > that is one less than the current length of the selected representation).
    ///
    /// [RFC 7233 §2.1]: https://datatracker.ietf.org/doc/html/rfc7233
    pub fn to_satisfiable_range(&self, full_length: u64) -> Option<(u64, u64)> {
        // If the full length is zero, there is no satisfiable end-inclusive range.
        if full_length == 0 {
            return None;
        }

        match *self {
            ByteRangeSpec::FromTo(from, to) => {
                if from < full_length && from <= to {
                    Some((from, cmp::min(to, full_length - 1)))
                } else {
                    None
                }
            }

            ByteRangeSpec::From(from) => {
                if from < full_length {
                    Some((from, full_length - 1))
                } else {
                    None
                }
            }

            ByteRangeSpec::Last(last) => {
                if last > 0 {
                    // From the RFC: If the selected representation is shorter than the specified
                    // suffix-length, the entire representation is used.
                    if last > full_length {
                        Some((0, full_length - 1))
                    } else {
                        Some((full_length - last, full_length - 1))
                    }
                } else {
                    None
                }
            }
        }
    }
}

impl Range {
    /// Constructs a common byte range header.
    ///
    /// Eg: `bytes=from-to`
    pub fn bytes(from: u64, to: u64) -> Range {
        Range::Bytes(vec![ByteRangeSpec::FromTo(from, to)])
    }

    /// Constructs a byte range header with multiple subranges.
    ///
    /// Eg: `bytes=from1-to1,from2-to2,fromX-toX`
    pub fn bytes_multi(ranges: Vec<(u64, u64)>) -> Range {
        Range::Bytes(
            ranges
                .into_iter()
                .map(|(from, to)| ByteRangeSpec::FromTo(from, to))
                .collect(),
        )
    }
}

impl fmt::Display for ByteRangeSpec {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            ByteRangeSpec::FromTo(from, to) => write!(f, "{}-{}", from, to),
            ByteRangeSpec::Last(pos) => write!(f, "-{}", pos),
            ByteRangeSpec::From(pos) => write!(f, "{}-", pos),
        }
    }
}

impl fmt::Display for Range {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Range::Bytes(ranges) => {
                write!(f, "bytes=")?;

                for (i, range) in ranges.iter().enumerate() {
                    if i != 0 {
                        f.write_str(",")?;
                    }

                    Display::fmt(range, f)?;
                }
                Ok(())
            }

            Range::Unregistered(unit, range_str) => {
                write!(f, "{}={}", unit, range_str)
            }
        }
    }
}

impl FromStr for Range {
    type Err = ParseError;

    fn from_str(s: &str) -> Result<Range, ParseError> {
        let (unit, val) = s.split_once('=').ok_or(ParseError::Header)?;

        match (unit, val) {
            ("bytes", ranges) => {
                let ranges = from_comma_delimited(ranges);

                if ranges.is_empty() {
                    return Err(ParseError::Header);
                }

                Ok(Range::Bytes(ranges))
            }

            (_, "") => Err(ParseError::Header),
            ("", _) => Err(ParseError::Header),

            (unit, range_str) => Ok(Range::Unregistered(unit.to_owned(), range_str.to_owned())),
        }
    }
}

impl FromStr for ByteRangeSpec {
    type Err = ParseError;

    fn from_str(s: &str) -> Result<ByteRangeSpec, ParseError> {
        let (start, end) = s.split_once('-').ok_or(ParseError::Header)?;

        match (start, end) {
            ("", end) => end
                .parse()
                .or(Err(ParseError::Header))
                .map(ByteRangeSpec::Last),

            (start, "") => start
                .parse()
                .or(Err(ParseError::Header))
                .map(ByteRangeSpec::From),

            (start, end) => match (start.parse(), end.parse()) {
                (Ok(start), Ok(end)) if start <= end => Ok(ByteRangeSpec::FromTo(start, end)),
                _ => Err(ParseError::Header),
            },
        }
    }
}

impl Header for Range {
    fn name() -> HeaderName {
        header::RANGE
    }

    #[inline]
    fn parse<T: HttpMessage>(msg: &T) -> Result<Self, ParseError> {
        header::from_one_raw_str(msg.headers().get(Self::name()))
    }
}

impl TryIntoHeaderValue for Range {
    type Error = InvalidHeaderValue;

    fn try_into_value(self) -> Result<HeaderValue, Self::Error> {
        let mut wrt = Writer::new();
        let _ = write!(wrt, "{}", self);
        HeaderValue::from_maybe_shared(wrt.take())
    }
}

/// Parses 0 or more items out of a comma delimited string, ignoring invalid items.
fn from_comma_delimited<T: FromStr>(s: &str) -> Vec<T> {
    s.split(',')
        .filter_map(|x| match x.trim() {
            "" => None,
            y => Some(y),
        })
        .filter_map(|x| x.parse().ok())
        .collect()
}

#[cfg(test)]
mod tests {
    use actix_http::{test::TestRequest, Request};

    use super::*;

    fn req(s: &str) -> Request {
        TestRequest::default()
            .insert_header((header::RANGE, s))
            .finish()
    }

    #[test]
    fn test_parse_bytes_range_valid() {
        let r: Range = Header::parse(&req("bytes=1-100")).unwrap();
        let r2: Range = Header::parse(&req("bytes=1-100,-")).unwrap();
        let r3 = Range::bytes(1, 100);
        assert_eq!(r, r2);
        assert_eq!(r2, r3);

        let r: Range = Header::parse(&req("bytes=1-100,200-")).unwrap();
        let r2: Range = Header::parse(&req("bytes= 1-100 , 101-xxx,  200- ")).unwrap();
        let r3 = Range::Bytes(vec![
            ByteRangeSpec::FromTo(1, 100),
            ByteRangeSpec::From(200),
        ]);
        assert_eq!(r, r2);
        assert_eq!(r2, r3);

        let r: Range = Header::parse(&req("bytes=1-100,-100")).unwrap();
        let r2: Range = Header::parse(&req("bytes=1-100, ,,-100")).unwrap();
        let r3 = Range::Bytes(vec![
            ByteRangeSpec::FromTo(1, 100),
            ByteRangeSpec::Last(100),
        ]);
        assert_eq!(r, r2);
        assert_eq!(r2, r3);

        let r: Range = Header::parse(&req("custom=1-100,-100")).unwrap();
        let r2 = Range::Unregistered("custom".to_owned(), "1-100,-100".to_owned());
        assert_eq!(r, r2);
    }

    #[test]
    fn test_parse_unregistered_range_valid() {
        let r: Range = Header::parse(&req("custom=1-100,-100")).unwrap();
        let r2 = Range::Unregistered("custom".to_owned(), "1-100,-100".to_owned());
        assert_eq!(r, r2);

        let r: Range = Header::parse(&req("custom=abcd")).unwrap();
        let r2 = Range::Unregistered("custom".to_owned(), "abcd".to_owned());
        assert_eq!(r, r2);

        let r: Range = Header::parse(&req("custom=xxx-yyy")).unwrap();
        let r2 = Range::Unregistered("custom".to_owned(), "xxx-yyy".to_owned());
        assert_eq!(r, r2);
    }

    #[test]
    fn test_parse_invalid() {
        let r: Result<Range, ParseError> = Header::parse(&req("bytes=1-a,-"));
        assert_eq!(r.ok(), None);

        let r: Result<Range, ParseError> = Header::parse(&req("bytes=1-2-3"));
        assert_eq!(r.ok(), None);

        let r: Result<Range, ParseError> = Header::parse(&req("abc"));
        assert_eq!(r.ok(), None);

        let r: Result<Range, ParseError> = Header::parse(&req("bytes=1-100="));
        assert_eq!(r.ok(), None);

        let r: Result<Range, ParseError> = Header::parse(&req("bytes="));
        assert_eq!(r.ok(), None);

        let r: Result<Range, ParseError> = Header::parse(&req("custom="));
        assert_eq!(r.ok(), None);

        let r: Result<Range, ParseError> = Header::parse(&req("=1-100"));
        assert_eq!(r.ok(), None);
    }

    #[test]
    fn test_fmt() {
        let range = Range::Bytes(vec![
            ByteRangeSpec::FromTo(0, 1000),
            ByteRangeSpec::From(2000),
        ]);
        assert_eq!(&range.to_string(), "bytes=0-1000,2000-");

        let range = Range::Bytes(vec![]);

        assert_eq!(&range.to_string(), "bytes=");

        let range = Range::Unregistered("custom".to_owned(), "1-xxx".to_owned());

        assert_eq!(&range.to_string(), "custom=1-xxx");
    }

    #[test]
    fn test_byte_range_spec_to_satisfiable_range() {
        assert_eq!(
            Some((0, 0)),
            ByteRangeSpec::FromTo(0, 0).to_satisfiable_range(3)
        );
        assert_eq!(
            Some((1, 2)),
            ByteRangeSpec::FromTo(1, 2).to_satisfiable_range(3)
        );
        assert_eq!(
            Some((1, 2)),
            ByteRangeSpec::FromTo(1, 5).to_satisfiable_range(3)
        );
        assert_eq!(None, ByteRangeSpec::FromTo(3, 3).to_satisfiable_range(3));
        assert_eq!(None, ByteRangeSpec::FromTo(2, 1).to_satisfiable_range(3));
        assert_eq!(None, ByteRangeSpec::FromTo(0, 0).to_satisfiable_range(0));

        assert_eq!(Some((0, 2)), ByteRangeSpec::From(0).to_satisfiable_range(3));
        assert_eq!(Some((2, 2)), ByteRangeSpec::From(2).to_satisfiable_range(3));
        assert_eq!(None, ByteRangeSpec::From(3).to_satisfiable_range(3));
        assert_eq!(None, ByteRangeSpec::From(5).to_satisfiable_range(3));
        assert_eq!(None, ByteRangeSpec::From(0).to_satisfiable_range(0));

        assert_eq!(Some((1, 2)), ByteRangeSpec::Last(2).to_satisfiable_range(3));
        assert_eq!(Some((2, 2)), ByteRangeSpec::Last(1).to_satisfiable_range(3));
        assert_eq!(Some((0, 2)), ByteRangeSpec::Last(5).to_satisfiable_range(3));
        assert_eq!(None, ByteRangeSpec::Last(0).to_satisfiable_range(3));
        assert_eq!(None, ByteRangeSpec::Last(2).to_satisfiable_range(0));
    }
}