use std::str;

use super::pig::Pig;
use crate::task::{Task, TaskBuilder};
use failure::Fallible;

/// Rust implementation of part of utf8_codepoint from Taskwarrior's src/utf8.cpp
///
/// Note that the original function will return garbage for invalid hex sequences;
/// this panics instead.
fn hex_to_unicode(value: &[u8]) -> Fallible<String> {
    if value.len() < 4 {
        bail!("too short");
    }

    fn nyb(c: u8) -> Fallible<u16> {
        match c {
            b'0'..=b'9' => Ok((c - b'0') as u16),
            b'a'..=b'f' => Ok((c - b'a' + 10) as u16),
            b'A'..=b'F' => Ok((c - b'A' + 10) as u16),
            _ => bail!("invalid hex character"),
        }
    };

    let words = [nyb(value[0])? << 12 | nyb(value[1])? << 8 | nyb(value[2])? << 4 | nyb(value[3])?];
    Ok(String::from_utf16(&words[..])?)
}

/// Rust implementation of JSON::decode in Taskwarrior's src/JSON.cpp
///
/// Decode the given byte slice into a string using Taskwarrior JSON's escaping The slice is
/// assumed to be ASCII; unicode escapes within it will be expanded.
fn json_decode(value: &[u8]) -> Fallible<String> {
    let length = value.len();
    let mut rv = String::with_capacity(length);

    let mut pos = 0;
    while pos < length {
        let v = value[pos];
        if v == b'\\' {
            pos += 1;
            if pos == length {
                rv.push(v as char);
                break;
            }
            let v = value[pos];
            match v {
                b'"' | b'\\' | b'/' => rv.push(v as char),
                b'b' => rv.push(8 as char),
                b'f' => rv.push(12 as char),
                b'n' => rv.push('\n' as char),
                b'r' => rv.push('\r' as char),
                b't' => rv.push('\t' as char),
                b'u' => {
                    let unicode = hex_to_unicode(&value[pos + 1..pos + 5]).map_err(|_| {
                        let esc = &value[pos - 1..pos + 5];
                        match str::from_utf8(esc) {
                            Ok(s) => format_err!("invalid unicode escape `{}`", s),
                            Err(_) => format_err!("invalid unicode escape bytes {:?}", esc),
                        }
                    })?;
                    rv.push_str(&unicode);
                    pos += 4;
                }
                _ => {
                    rv.push(b'\\' as char);
                    rv.push(v as char);
                }
            }
        } else {
            rv.push(v as char)
        }
        pos += 1;
    }

    Ok(rv)
}

/// Rust implementation of Task::decode in Taskwarrior's src/Task.cpp
///
/// Note that the docstring for the C++ function does not match the
/// implementation!
fn decode(value: String) -> String {
    if let Some(_) = value.find('&') {
        return value.replace("&open;", "[").replace("&close;", "]");
    }
    value
}

/// Parse an "FF4" formatted task line.  From Task::parse in Taskwarrior's src/Task.cpp.
///
/// While Taskwarrior supports additional formats, this is the only format supported by
/// taskwarrior_rust.
pub(super) fn parse_ff4(line: &str) -> Fallible<Task> {
    let mut pig = Pig::new(line.as_bytes());
    let mut builder = TaskBuilder::new();

    pig.skip(b'[')?;
    let line = pig.get_until(b']')?;
    let mut subpig = Pig::new(line);
    while !subpig.depleted() {
        let name = subpig.get_until(b':')?;
        let name = str::from_utf8(name)?;
        subpig.skip(b':')?;
        let value = subpig.get_quoted(b'"')?;
        let value = json_decode(value)?;
        let value = decode(value);
        builder = builder.set(name, value);
        subpig.skip(b' ').ok(); // ignore if not found..
    }
    pig.skip(b']')?;
    if !pig.depleted() {
        bail!("trailing characters on line");
    }
    Ok(builder.finish())
}

#[cfg(test)]
mod test {
    use super::{decode, hex_to_unicode, json_decode, parse_ff4};
    use crate::task::Pending;

    #[test]
    fn test_hex_to_unicode_digits() {
        assert_eq!(hex_to_unicode(b"1234").unwrap(), "\u{1234}");
    }

    #[test]
    fn test_hex_to_unicode_lower() {
        assert_eq!(hex_to_unicode(b"abcd").unwrap(), "\u{abcd}");
    }

    #[test]
    fn test_hex_to_unicode_upper() {
        assert_eq!(hex_to_unicode(b"ABCD").unwrap(), "\u{abcd}");
    }

    #[test]
    fn test_hex_to_unicode_too_short() {
        assert!(hex_to_unicode(b"AB").is_err());
    }

    #[test]
    fn test_hex_to_unicode_invalid() {
        assert!(hex_to_unicode(b"defg").is_err());
    }

    #[test]
    fn test_json_decode_no_change() {
        assert_eq!(json_decode(b"abcd").unwrap(), "abcd");
    }

    #[test]
    fn test_json_decode_escape_quote() {
        assert_eq!(json_decode(b"ab\\\"cd").unwrap(), "ab\"cd");
    }

    #[test]
    fn test_json_decode_escape_backslash() {
        assert_eq!(json_decode(b"ab\\\\cd").unwrap(), "ab\\cd");
    }

    #[test]
    fn test_json_decode_escape_frontslash() {
        assert_eq!(json_decode(b"ab\\/cd").unwrap(), "ab/cd");
    }

    #[test]
    fn test_json_decode_escape_b() {
        assert_eq!(json_decode(b"ab\\bcd").unwrap(), "ab\x08cd");
    }

    #[test]
    fn test_json_decode_escape_f() {
        assert_eq!(json_decode(b"ab\\fcd").unwrap(), "ab\x0ccd");
    }

    #[test]
    fn test_json_decode_escape_n() {
        assert_eq!(json_decode(b"ab\\ncd").unwrap(), "ab\ncd");
    }

    #[test]
    fn test_json_decode_escape_r() {
        assert_eq!(json_decode(b"ab\\rcd").unwrap(), "ab\rcd");
    }

    #[test]
    fn test_json_decode_escape_t() {
        assert_eq!(json_decode(b"ab\\tcd").unwrap(), "ab\tcd");
    }

    #[test]
    fn test_json_decode_escape_other() {
        assert_eq!(json_decode(b"ab\\xcd").unwrap(), "ab\\xcd");
    }

    #[test]
    fn test_json_decode_escape_eos() {
        assert_eq!(json_decode(b"ab\\").unwrap(), "ab\\");
    }

    #[test]
    fn test_json_decode_escape_unicode() {
        assert_eq!(json_decode(b"ab\\u1234").unwrap(), "ab\u{1234}");
    }

    #[test]
    fn test_json_decode_escape_unicode_bad() {
        let rv = json_decode(b"ab\\uwxyz");
        assert_eq!(
            rv.unwrap_err().to_string(),
            "invalid unicode escape `\\uwxyz`"
        );
    }

    #[test]
    fn test_decode_no_change() {
        let s = "abcd &quot; efgh &".to_string();
        assert_eq!(decode(s.clone()), s);
    }

    #[test]
    fn test_decode_multi() {
        let s = "abcd &open; efgh &close; &open".to_string();
        assert_eq!(decode(s), "abcd [ efgh ] &open".to_string());
    }

    #[test]
    fn test_parse_ff4() {
        let s = "[description:\"desc\" entry:\"1437855511\" modified:\"1479480556\" \
                 priority:\"L\" project:\"lists\" status:\"pending\" tags:\"watch\" \
                 uuid:\"83ce989e-8634-4d62-841c-eb309383ff1f\"]";
        let task = parse_ff4(s).unwrap();
        assert_eq!(task.status, Pending);
        assert_eq!(task.description, "desc");
    }

    #[test]
    fn test_parse_ff4_fail() {
        assert!(parse_ff4("abc:10]").is_err());
        assert!(parse_ff4("[abc:10").is_err());
        assert!(parse_ff4("[abc:10  123:123]").is_err());
    }
}