//! HTTP Range
//!
//! Implemented according
//! - WIP [RFC9110](https://www.rfc-editor.org/rfc/rfc9110.html)
//! - WIP [RFC2616](https://www.ietf.org/rfc/rfc2616)
//!
//! Additional resources
//! - Obsolete [RFC7233](https://datatracker.ietf.org/doc/html/rfc7233)
//! - Obsolete [RFC7232](https://datatracker.ietf.org/doc/html/rfc7232)
//! - [Mozilla: HTTP range requests](https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests)
//! - [http.dev: HTTP Range Request](https://http.dev/range-request)

use std::ops::Range;
pub static RANGE_UNIT: &str = "bytes";

#[derive(Debug, PartialEq)]
/// Parsed values of the `CONTENT_RANGE` header
pub struct HttpRange {
    /// Ranges part of the `CONTENT_RANGE` header
    pub ranges: Vec<Range<u64>>,

    /// Complete length part of the `CONTENT_RANGE` header
    pub complete_length: Option<CompleteLength>,
}

#[derive(Debug, PartialEq)]
/// Complete length part of the range header
pub enum CompleteLength {
    /// Complete length of the selected representation is known by the sender and provided in the header
    Representation(u64),

    /// '*' - a complete length of the selected representation is unknown
    Unknown,
}

impl HttpRange {
    /// Returns a parsed value of `CONTENT_RANGE` header
    ///
    /// # Arguments
    ///
    /// * `content_range` - a `&str` input to parse, a value part of `CONTENT_RANGE` header
    /// * `content_length` - a `u64` length of existing content, in bytes
    pub fn from_header(content_range: &str, content_length: u64) -> Option<HttpRange> {
        if content_range.is_empty() {
            return None;
        }

        let parts = content_range
            .split("=")
            .map(|p| p.trim())
            .collect::<Vec<_>>();
        if parts.is_empty() {
            return None;
        }

        if parts[0] != RANGE_UNIT {
            return None;
        }

        if parts.len() != 2 {
            return None;
        }

        let params = parts[1].split("/").map(|p| p.trim()).collect::<Vec<_>>();
        if params.is_empty() {
            return None;
        }

        if params.len() > 2 {
            return None;
        }

        let range_params = params[0].split(",");
        let length_param = if params.len() == 2 { params[1] } else { "" };

        let mut ranges = Vec::<Range<u64>>::new();
        for range_param in range_params {
            let values = range_param.split("-").map(|v| v.trim()).collect::<Vec<_>>();
            if values.len() != 2 {
                return None;
            }
            let mut range = 0..content_length - 1;
            let start = values[0];
            let end = values[1];

            if !start.is_empty() && !end.is_empty() {
                range.start = start.parse::<u64>().unwrap();
                range.end = end.parse::<u64>().unwrap();
            }
            if start.is_empty() && !end.is_empty() {
                let count = end.parse::<u64>().unwrap();
                range.start = content_length - count;
            }

            if !start.is_empty() && end.is_empty() {
                range.start = start.parse::<u64>().unwrap();
            }

            ranges.push(range);
        }

        // processing for combined ranges
        // https://datatracker.ietf.org/doc/html/rfc7233#section-4.3
        ranges.sort_by(|a, b| a.start.cmp(&b.start));
        let ranges_count = ranges.len();
        if ranges_count > 1 {
            // merging continuous and overlapping ranges
            let mut retain = vec![true; ranges_count];
            let mut range_last = ranges[0].clone();
            for (index, range) in ranges.iter_mut().enumerate() {
                if index != 0 && (range_last.end + 1) >= range.start {
                    range.start = range_last.start;
                    retain[index - 1] = false;
                }
                range_last = range.clone();
            }

            // cleaning-up merged ranges
            let mut index = 0;
            ranges.retain(|_| {
                let keep = retain[index];
                index += 1;
                keep
            });
        }

        let complete_length = match length_param {
            "" => None,
            "*" => Some(CompleteLength::Unknown),
            _ => Some(CompleteLength::Representation(
                length_param.parse::<u64>().unwrap(),
            )),
        };

        let http_range = HttpRange {
            ranges,
            complete_length,
        };

        Some(http_range)
    }

    /// Returns a `CONTENT_RANGE` header value
    ///
    /// # Arguments
    ///
    /// * `http_range` - a reference to `HttpRange`
    pub fn to_header(&self) -> String {
        if self.ranges.is_empty() {
            return "".to_string();
        }

        let ranges = self
            .ranges
            .iter()
            .map(|r| format!("{}-{}", r.start, r.end))
            .collect::<Vec<_>>()
            .join(",");

        match &self.complete_length {
            Some(CompleteLength::Representation(content_length)) => {
                format!("{}={}/{}", RANGE_UNIT, ranges, content_length)
            }
            Some(CompleteLength::Unknown) => format!("{}={}/*", RANGE_UNIT, ranges),
            None => format!("{}={}", RANGE_UNIT, ranges),
        }
    }

    /// Returns a `bool` indicating if none of the ranges in `HttpRange` are satisfiable within `content_length`
    ///
    /// Reference: [416 Range Not Satisfiable](https://datatracker.ietf.org/doc/html/rfc7233#section-4.4)
    ///
    /// # Arguments
    ///
    /// * content_length - a `u64` length of existing content, in bytes
    pub fn none_satisfiable(&self, content_length: u64) -> bool {
        !self.any_satisfiable(content_length)
    }

    /// Returns a `bool` indicating if any of ranges in `HttpRange` are satisfiable within `content_length`
    ///
    /// Reference: [416 Range Not Satisfiable](https://datatracker.ietf.org/doc/html/rfc7233#section-4.4)
    ///
    /// # Arguments
    ///
    /// * `content_length` - a `u64` length of existing content, in bytes
    pub fn any_satisfiable(&self, content_length: u64) -> bool {
        // 416 Range Not Satisfiable
        // https://datatracker.ietf.org/doc/html/rfc7233#section-4.4
        for range in &self.ranges {
            if HttpRange::range_satisfiable(range, content_length) {
                return true;
            }
        }
        false
    }

    /// Returns a `bool` indicating if the given range is satisfiable within `content_length`
    ///
    /// Reference: [416 Range Not Satisfiable](https://datatracker.ietf.org/doc/html/rfc7233#section-4.4)
    ///
    /// # Arguments
    ///
    /// * `http_range` - a reference to `Range<u64>`
    /// * `content_length` - a `u64` length of existing content, in bytes
    pub fn range_satisfiable(range: &Range<u64>, content_length: u64) -> bool {
        range.start < content_length
    }
}

#[cfg(test)]
mod tests {

    use super::*;

    ///  Tests implemented according to:
    ///  https://datatracker.ietf.org/doc/html/rfc7233#section-4.2
    ///
    ///  Examples of byte-ranges-specifier values:
    ///    -  The first 500 bytes (byte offsets 0-499, inclusive):
    ///         bytes=0-499
    ///    -  The second 500 bytes (byte offsets 500-999, inclusive):
    ///         bytes=500-999
    ///
    ///  Additional examples, assuming a representation of length 10000:
    ///    The final 500 bytes (byte offsets 9500-9999, inclusive):
    ///         bytes=-500
    ///    Or:
    ///         bytes=9500-
    ///    -  The first and last bytes only (bytes 0 and 9999):
    ///         bytes=0-0,-1
    ///    -  Other valid (but not canonical) specifications of the second 500
    ///       bytes (byte offsets 500-999, inclusive):
    ///         bytes=500-600,601-999
    ///         bytes=500-700,601-999
    ///
    ///  Additional examples
    ///
    ///     - The first 500 bytes:
    ///         Content-Range: bytes 0-499/1234
    ///
    ///     - The second 500 bytes:
    ///         Content-Range: bytes 500-999/1234
    ///
    ///     - All except for the first 500 bytes:
    ///         Content-Range: bytes 500-1233/1234
    ///  
    ///     - The last 500 bytes:
    ///         Content-Range: bytes 734-1233/1234

    #[test]
    fn test1() {
        let http_range = HttpRange::from_header("bytes=0-499", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![0..499],
                complete_length: None
            }
        );
    }

    #[test]
    fn complete_length_unknown() {
        let http_range = HttpRange::from_header("bytes=0-499/*", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![0..499],
                complete_length: Some(CompleteLength::Unknown)
            }
        );
    }

    #[test]
    fn complete_length_test2() {
        let http_range = HttpRange::from_header("bytes=0-499/8000", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![0..499],
                complete_length: Some(CompleteLength::Representation(8000))
            }
        );
    }

    #[test]
    fn test2() {
        let http_range = HttpRange::from_header("bytes=500-999", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![500..999],
                complete_length: None
            }
        );
    }

    #[test]
    fn test3() {
        let http_range = HttpRange::from_header("bytes=-500", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![9500..9999],
                complete_length: None
            }
        );
    }

    #[test]
    fn test4() {
        let http_range = HttpRange::from_header("bytes=9500-", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![9500..9999],
                complete_length: None
            }
        );
    }

    #[test]
    fn test5() {
        let http_range = HttpRange::from_header("bytes=0-0,-1", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![0..0, 9999..9999],
                complete_length: None
            }
        );
    }
    #[test]
    fn test6() {
        // https://www.rfc-editor.org/rfc/rfc9110.html#section-14.1.2
        // the first, middle, and last 1000 bytes
        let http_range = HttpRange::from_header("bytes= 0-999, 4500-5499, -1000", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![0..999, 4500..5499, 9000..9999],
                complete_length: None
            }
        );
    }

    #[test]
    fn combined_merge_test6() {
        let http_range = HttpRange::from_header("bytes=500-600,601-999", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![500..999],
                complete_length: None
            }
        );
    }

    #[test]
    fn combined_merge_test7() {
        let http_range = HttpRange::from_header("bytes=601-999,500-600", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![500..999],
                complete_length: None
            }
        );
    }

    #[test]
    fn combined_merge_test8() {
        let http_range = HttpRange::from_header("bytes=500-700,601-999", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![500..999],
                complete_length: None
            }
        );
    }

    #[test]
    fn combined_merge_test9() {
        let http_range = HttpRange::from_header("bytes=601-999,500-700", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![500..999],
                complete_length: None
            }
        );
    }

    #[test]
    fn combined_merge_test10() {
        let http_range = HttpRange::from_header("bytes=300-400,400-700,601-999", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![300..999],
                complete_length: None
            }
        );
    }

    #[test]
    fn representation_test1() {
        let http_range = HttpRange::from_header("bytes=0-499/1234", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![0..499],
                complete_length: Some(CompleteLength::Representation(1234))
            }
        );
    }

    #[test]
    fn representation_test2() {
        let http_range = HttpRange::from_header("bytes=500-999/1234", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![500..999],
                complete_length: Some(CompleteLength::Representation(1234))
            }
        );
    }

    #[test]
    fn representation_test3() {
        let http_range = HttpRange::from_header("bytes=500-1233/1234", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![500..1233],
                complete_length: Some(CompleteLength::Representation(1234))
            }
        );
    }

    #[test]
    fn representation_test4() {
        let http_range = HttpRange::from_header("bytes=734-1233/1234", 10000).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![734..1233],
                complete_length: Some(CompleteLength::Representation(1234))
            }
        );
    }

    #[test]
    fn to_header_test1() {
        let http_range = HttpRange::from_header("bytes=734-1233/1234", 1234).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![734..1233],
                complete_length: Some(CompleteLength::Representation(1234))
            }
        );
        assert_eq!(http_range.to_header(), "bytes=734-1233/1234");
    }

    #[test]
    fn to_header_test2() {
        let http_range = HttpRange::from_header("bytes=734-1233/*", 1234).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![734..1233],
                complete_length: Some(CompleteLength::Unknown)
            }
        );
        assert_eq!(http_range.to_header(), "bytes=734-1233/*");
    }

    #[test]
    fn to_header_test3() {
        let http_range = HttpRange::from_header("bytes=734-1233", 1234).unwrap();
        assert_eq!(
            http_range,
            HttpRange {
                ranges: vec![734..1233],
                complete_length: None
            }
        );
        assert_eq!(http_range.to_header(), "bytes=734-1233");
    }

}