//! # http-range
//!
//! HTTP Range header parser.
//! Inspired by Go's net/http library.

static PREFIX: &'static str = "bytes=";
const PREFIX_LEN: usize = 6;

/// Range parsing error
#[derive(Debug)]
pub enum HttpRangeParseError {
    /// Returned if range is invalid.
    InvalidRange,
    /// Returned if first-byte-pos of all of the byte-range-spec
    /// values is greater than the content size.
    /// See https://github.com/golang/go/commit/aa9b3d7
    NoOverlap,
}

/// HTTP Range header representation.
#[derive(Debug, Clone, Copy)]
pub struct HttpRange {
    pub start: u64,
    pub length: u64,
}

impl HttpRange {
    /// Parses Range HTTP header string as per RFC 2616.
    ///
    /// `header` is HTTP Range header (e.g. `bytes=bytes=0-9`).
    /// `size` is full size of response (file).
    pub fn parse(header: &str, size: u64) -> Result<Vec<HttpRange>, HttpRangeParseError> {
        if header.is_empty() {
            return Ok(Vec::new());
        }

        if !header.starts_with(PREFIX) {
            return Err(HttpRangeParseError::InvalidRange);
        }

        let size_sig = size as i64;

        let mut no_overlap = false;

        let all_ranges: Vec<Option<HttpRange>> = try!(header[PREFIX_LEN..]
            .split(',')
            .map(|x| x.trim())
            .filter(|x| !x.is_empty())
            .map(|ra| {
                let mut start_end_iter = ra.split('-');

                let start_str =
                    try!(start_end_iter.next().ok_or(HttpRangeParseError::InvalidRange)).trim();
                let end_str = try!(start_end_iter.next().ok_or(HttpRangeParseError::InvalidRange))
                    .trim();

                if start_str.is_empty() {
                    // If no start is specified, end specifies the
                    // range start relative to the end of the file.
                    let mut length: i64 = try!(end_str.parse()
                        .map_err(|_| HttpRangeParseError::InvalidRange));

                    if length > size_sig {
                        length = size_sig;
                    }

                    Ok(Some(HttpRange {
                        start: (size_sig - length) as u64,
                        length: length as u64,
                    }))
                } else {
                    let start: i64 = try!(start_str.parse()
                        .map_err(|_| HttpRangeParseError::InvalidRange));

                    if start < 0 {
                        return Err(HttpRangeParseError::InvalidRange);
                    }
                    if start >= size_sig {
                        no_overlap = true;
                        return Ok(None);
                    }

                    let length = if end_str.is_empty() {
                        // If no end is specified, range extends to end of the file.
                        size_sig - start
                    } else {
                        let mut end: i64 = try!(end_str.parse()
                            .map_err(|_| HttpRangeParseError::InvalidRange));

                        if start > end {
                            return Err(HttpRangeParseError::InvalidRange);
                        }

                        if end >= size_sig {
                            end = size_sig - 1;
                        }

                        end - start + 1
                    };

                    Ok(Some(HttpRange {
                        start: start as u64,
                        length: length as u64,
                    }))
                }
            })
            .collect::<Result<_, _>>());

        let ranges: Vec<HttpRange> = all_ranges.into_iter().filter_map(|x| x).collect();

        if no_overlap && ranges.is_empty() {
            return Err(HttpRangeParseError::NoOverlap);
        }

        Ok(ranges)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    struct T(&'static str, u64, Vec<HttpRange>);

    #[test]
    fn test_parse() {
        let tests = vec![
            T("", 0, vec!()),
            T("", 1000, vec!()),
            T("foo", 0, vec!()),
            T("bytes=", 0, vec!()),
            T("bytes=7", 10, vec!()),
            T("bytes= 7 ", 10, vec!()),
            T("bytes=1-", 0, vec!()),
            T("bytes=5-4", 10, vec!()),
            T("bytes=0-2,5-4", 10, vec!()),
            T("bytes=2-5,4-3", 10, vec!()),
            T("bytes=--5,4--3", 10, vec!()),
            T("bytes=A-", 10, vec!()),
            T("bytes=A- ", 10, vec!()),
            T("bytes=A-Z", 10, vec!()),
            T("bytes= -Z", 10, vec!()),
            T("bytes=5-Z", 10, vec!()),
            T("bytes=Ran-dom, garbage", 10, vec!()),
            T("bytes=0x01-0x02", 10, vec!()),
            T("bytes=         ", 10, vec!()),
            T("bytes= , , ,   ", 10, vec!()),

            T("bytes=0-9", 10, vec!(
                HttpRange{start:0, length:10}
            )),
            T("bytes=0-", 10, vec!(
                HttpRange{start:0, length:10}
            )),
            T("bytes=5-", 10, vec!(
                HttpRange{start:5, length:5}
            )),
            T("bytes=0-20", 10, vec!(
                HttpRange{start:0, length:10}
            )),
            T("bytes=15-,0-5", 10, vec!(
                HttpRange{start:0, length:6}
            )),
            T("bytes=1-2,5-", 10, vec!(
                HttpRange{start:1, length:2},
                HttpRange{start:5, length:5}
            )),
            T("bytes=-2 , 7-", 11, vec!(
                HttpRange{start:9, length:2},
                HttpRange{start:7, length:4}
            )),
            T("bytes=0-0 ,2-2, 7-", 11, vec!(
                HttpRange{start:0, length:1},
                HttpRange{start:2, length:1},
                HttpRange{start:7, length:4}
            )),
            T("bytes=-5", 10, vec!(
                HttpRange{start:5, length:5}
            )),
            T("bytes=-15", 10, vec!(
                HttpRange{start:0, length:10}
            )),
            T("bytes=0-499", 10000, vec!(
                HttpRange{start:0, length:500}
            )),
            T("bytes=500-999", 10000, vec!(
                HttpRange{start:500, length:500}
            )),
            T("bytes=-500", 10000, vec!(
                HttpRange{start:9500, length:500}
            )),
            T("bytes=9500-", 10000, vec!(
                HttpRange{start:9500, length:500}
            )),
            T("bytes=0-0,-1", 10000, vec!(
                HttpRange{start:0, length:1},
                HttpRange{start:9999, length:1}
            )),
            T("bytes=500-600,601-999", 10000, vec!(
                HttpRange{start:500, length:101},
                HttpRange{start:601, length:399}
            )),
            T("bytes=500-700,601-999", 10000, vec!(
                HttpRange{start:500, length:201},
                HttpRange{start:601, length:399}
            )),

            // Match Apache laxity:
            T("bytes=   1 -2   ,  4- 5, 7 - 8 , ,,", 11, vec!(
                HttpRange{start:1, length:2},
                HttpRange{start:4, length:2},
                HttpRange{start:7, length:2}
            )),
        ];

        for t in tests {
            let header = t.0;
            let size = t.1;
            let expected = t.2;

            let res = HttpRange::parse(header, size);

            if res.is_err() {
                if expected.is_empty() {
                    continue;
                } else {
                    assert!(false,
                            "parse({}, {}) returned error {:?}",
                            header,
                            size,
                            res.unwrap_err());
                }
            }

            let got = res.unwrap();

            if got.len() != expected.len() {
                assert!(false,
                        "len(parseRange({}, {})) = {}, want {}",
                        header,
                        size,
                        got.len(),
                        expected.len());
                continue;
            }

            for i in 0..expected.len() {
                if got[i].start != expected[i].start {
                    assert!(false,
                            "parseRange({}, {})[{}].start = {}, want {}",
                            header,
                            size,
                            i,
                            got[i].start,
                            expected[i].start)
                }
                if got[i].length != expected[i].length {
                    assert!(false,
                            "parseRange({}, {})[{}].length = {}, want {}",
                            header,
                            size,
                            i,
                            got[i].length,
                            expected[i].length)
                }
            }
        }
    }
}