//! JavaScript semantics the TypeScript worker relies on: `\s` and `trim()`,
//! UTF-16 lengths, `parseInt`, `Date.parse` (for Usenet dates) and sha1 hex.

use sha1::{Digest, Sha1};

/// JS `\s` / `trim()` whitespace (WhiteSpace and LineTerminator).
pub fn is_space(c: char) -> bool {
    matches!(
        c,
        '\t' | '\n' | '\u{0B}' | '\u{0C}' | '\r' | ' ' | '\u{A0}' | '\u{1680}' | '\u{2000}'..='\u{200A}' | '\u{2028}' | '\u{2029}' | '\u{202F}' | '\u{205F}' | '\u{3000}' | '\u{FEFF}'
    )
}

pub fn trim(s: &str) -> &str {
    s.trim_matches(is_space)
}

/// `s.replace(/\s+/g, ' ')`.
pub fn collapse_spaces(s: &str) -> String {
    let mut out = String::with_capacity(s.len());
    let mut in_space = false;
    for c in s.chars() {
        if is_space(c) {
            if !in_space {
                out.push(' ');
                in_space = true;
            }
        } else {
            out.push(c);
            in_space = false;
        }
    }
    out
}

/// `s.split(/\s+/)`: like JS, a leading or trailing run gives an empty word.
pub fn split_spaces(s: &str) -> Vec<&str> {
    let mut out = Vec::new();
    let mut start = 0;
    let mut in_space = false;
    let mut run_start = 0;
    for (i, c) in s.char_indices() {
        if is_space(c) {
            if !in_space {
                run_start = i;
                in_space = true;
            }
        } else if in_space {
            out.push(&s[start..run_start]);
            start = i;
            in_space = false;
        }
    }
    if in_space {
        out.push(&s[start..run_start]);
        out.push("");
    } else {
        out.push(&s[start..]);
    }
    out
}

/// A string's `.length` in JavaScript (UTF-16 code units).
pub fn len16(s: &str) -> usize {
    if s.is_ascii() {
        s.len()
    } else {
        s.encode_utf16().count()
    }
}

/// `Number.parseInt(s, 10)`, None for NaN.
pub fn parse_int(s: &str) -> Option<i64> {
    let s = s.trim_start_matches(is_space);
    let (neg, digits) = match s.as_bytes().first() {
        Some(b'-') => (true, &s[1..]),
        Some(b'+') => (false, &s[1..]),
        _ => (false, s),
    };
    let mut n: i64 = 0;
    let mut any = false;
    for b in digits.bytes() {
        if !b.is_ascii_digit() {
            break;
        }
        n = n.wrapping_mul(10).wrapping_add((b - b'0') as i64);
        any = true;
    }
    if any {
        Some(if neg { -n } else { n })
    } else {
        None
    }
}

/// Days since 1970-01-01 of a proleptic Gregorian date (month 1..=12; a day past the month's end runs on, as in JS).
fn days_from_civil(y: i64, m: i64, d: i64) -> i64 {
    let y = if m <= 2 { y - 1 } else { y };
    let era = y.div_euclid(400);
    let yoe = y - era * 400;
    let mp = (m + 9) % 12;
    let doy = (153 * mp + 2) / 5 + d - 1;
    let doe = yoe * 365 + yoe / 4 - yoe / 100 + doy;
    era * 146_097 + doe - 719_468
}

/// The usual Date headers: [Day, ]D[D] Mon YY[YY] HH:MM:SS (GMT|UTC|UT|±hhmm). None for anything else.
fn fast_date(s: &[u8]) -> Option<i64> {
    let mut i = 0;
    if s.len() > 4 && s[3] == b',' && s[..3].iter().all(u8::is_ascii_alphabetic) {
        i = 4;
        while s.get(i) == Some(&b' ') {
            i += 1;
        }
    }
    let num = |i: &mut usize, min: usize, max: usize| -> Option<i64> {
        let start = *i;
        while *i < s.len() && s[*i].is_ascii_digit() && *i - start < max {
            *i += 1;
        }
        if *i - start < min || s.get(*i).is_some_and(u8::is_ascii_digit) {
            return None;
        }
        Some(std::str::from_utf8(&s[start..*i]).ok()?.parse().ok()?)
    };
    let expect = |i: &mut usize, c: u8| -> Option<()> {
        (s.get(*i) == Some(&c)).then(|| *i += 1)
    };
    let day = num(&mut i, 1, 2)?;
    expect(&mut i, b' ')?;
    const MONTHS: [&[u8]; 12] = [b"jan", b"feb", b"mar", b"apr", b"may", b"jun", b"jul", b"aug", b"sep", b"oct", b"nov", b"dec"];
    let mon = s.get(i..i + 3)?;
    let month = MONTHS.iter().position(|m| mon.iter().zip(m.iter()).all(|(a, b)| a.to_ascii_lowercase() == *b))? as i64 + 1;
    i += 3;
    expect(&mut i, b' ')?;
    let year_start = i;
    let mut year = num(&mut i, 2, 4)?;
    match i - year_start {
        2 => year += if year < 50 { 2000 } else { 1900 },
        4 => {}
        _ => return None,
    }
    expect(&mut i, b' ')?;
    let hour = num(&mut i, 2, 2)?;
    expect(&mut i, b':')?;
    let minute = num(&mut i, 2, 2)?;
    expect(&mut i, b':')?;
    let second = num(&mut i, 2, 2)?;
    expect(&mut i, b' ')?;
    if day < 1 || day > 31 || hour > 23 || minute > 59 || second > 59 {
        return None;
    }
    let offset_minutes = match &s[i..] {
        b"GMT" | b"UTC" | b"UT" => 0,
        [sign @ (b'+' | b'-'), h1, h2, m1, m2] if [h1, h2, m1, m2].iter().all(|c| c.is_ascii_digit()) => {
            let minutes = ((h1 - b'0') as i64 * 10 + (h2 - b'0') as i64) * 60 + (m1 - b'0') as i64 * 10 + (m2 - b'0') as i64;
            if *sign == b'+' { minutes } else { -minutes }
        }
        _ => return None,
    };
    let days = days_from_civil(year, month, day);
    Some((((days * 24 + hour) * 60 + minute - offset_minutes) * 60 + second) * 1000)
}

/// `Date.parse` for the Date header (RFC 5322 and the obsolete forms); None for NaN.
pub fn parse_date(s: &str) -> Option<i64> {
    let s = trim(s);
    if let Some(t) = fast_date(s.as_bytes()) {
        return Some(t);
    }
    parse_date_chrono(s)
}

fn parse_date_chrono(s: &str) -> Option<i64> {
    // "UTC" isn't an RFC 5322 zone (UT and GMT are), but Date.parse takes it (~a quarter of a.b.boneless).
    let owned;
    let s = match s.strip_suffix(" UTC") {
        Some(rest) => {
            owned = format!("{rest} GMT");
            owned.as_str()
        }
        None => s,
    };
    if let Ok(d) = chrono::DateTime::parse_from_rfc2822(s) {
        return Some(d.timestamp_millis());
    }
    // "Mon, 5 Oct 2026 10:00:00 +0000 (UTC)" and other trailing comments.
    if let Some(i) = s.find(" (") {
        if let Ok(d) = chrono::DateTime::parse_from_rfc2822(&s[..i]) {
            return Some(d.timestamp_millis());
        }
    }
    None
}

/// sha1 of the UTF-8 text, as lowercase hex (node's `hash('sha1', text)`).
pub fn sha1_hex(text: &str) -> String {
    let digest = Sha1::digest(text.as_bytes());
    let mut out = String::with_capacity(40);
    for b in digest {
        out.push(char::from_digit((b >> 4) as u32, 16).unwrap());
        out.push(char::from_digit((b & 15) as u32, 16).unwrap());
    }
    out
}

/// JSON.stringify of a string.
pub fn json_str(s: &str, out: &mut String) {
    out.push('"');
    for c in s.chars() {
        match c {
            '"' => out.push_str("\\\""),
            '\\' => out.push_str("\\\\"),
            '\u{08}' => out.push_str("\\b"),
            '\u{0C}' => out.push_str("\\f"),
            '\n' => out.push_str("\\n"),
            '\r' => out.push_str("\\r"),
            '\t' => out.push_str("\\t"),
            c if (c as u32) < 0x20 => out.push_str(&format!("\\u{:04x}", c as u32)),
            c => out.push(c),
        }
    }
    out.push('"');
}

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

    #[test]
    fn split_like_js() {
        assert_eq!(split_spaces("a  b"), vec!["a", "b"]);
        assert_eq!(split_spaces(" a b "), vec!["", "a", "b", ""]);
        assert_eq!(split_spaces(""), vec![""]);
    }

    #[test]
    fn parse_int_like_js() {
        assert_eq!(parse_int("123abc"), Some(123));
        assert_eq!(parse_int("  -5"), Some(-5));
        assert_eq!(parse_int("x"), None);
    }

    #[test]
    fn dates() {
        assert_eq!(parse_date("Mon, 05 Oct 2026 10:00:00 +0000"), Some(1_791_194_400_000));
        assert_eq!(parse_date("5 Oct 2026 10:00:00 GMT"), Some(1_791_194_400_000));
        assert_eq!(parse_date("Mon, 05 Oct 26 10:00:00 UTC"), Some(1_791_194_400_000));
        for d in [
            "Mon, 05 Oct 2026 10:00:00 +0000", "Mon, 5 Oct 2026 12:00:00 +0200", "05 Oct 2026 10:00:00 GMT", "Thu, 01 Jan 1970 00:00:00 GMT",
            "Sat, 29 Feb 2020 23:59:59 -0130", "Fri, 31 Dec 99 00:00:00 UTC", "Mon, 05 Oct 2026 10:00:00 UT",
        ] {
            assert_eq!(fast_date(d.as_bytes()), parse_date_chrono(d), "{d}");
        }
        assert_eq!(fast_date(b"Mon, 05 Oct 2026 10:00:00 EST"), None);
    }
}