wp-lang 0.3.0

use serde::{Deserialize, Deserializer, Serialize, Serializer};
use smol_str::SmolStr;

// ── Error formatting helpers ─────────────────────────────────────────

/// Build a user-friendly error message with a visual pointer to the problematic position.
///
/// Example output:
/// ```text
/// sep pattern error: at most one * allowed
///   {*a*}
///      ^
/// ```
fn fmt_err(raw: &str, pos: usize, msg: &str) -> String {
    let display = format!("{{{}}}", raw);
    // pos is relative to raw; in display string `{raw}`, offset by 1 for the leading `{`
    let pointer_offset = pos + 1;
    let pointer_line: String = " ".repeat(pointer_offset) + "^";
    format!(
        "sep pattern error: {}\n  {}\n  {}",
        msg, display, pointer_line
    )
}

/// Build an error message without position (for structural issues).
fn fmt_err_no_pos(raw: &str, msg: &str) -> String {
    format!("sep pattern error: {} in {{{}}}", msg, raw)
}

// ── Data structures ──────────────────────────────────────────────────

/// Result of a successful pattern match.
#[derive(Debug, Clone, PartialEq)]
pub struct SepMatch {
    /// Bytes consumed (not including preserve portion).
    pub consumed: usize,
    /// Total bytes matched (including preserve, for debugging).
    pub matched: usize,
}

/// A single segment inside a glob pattern.
#[derive(Debug, Clone, PartialEq)]
pub enum GlobSegment {
    /// Contiguous literal characters.
    Literal(SmolStr),
    /// `*` — zero or more arbitrary characters (non-greedy).
    Star,
    /// `?` — exactly one arbitrary character.
    Any,
    /// `\s` — one or more whitespace characters `[ \t\r\n]+`.
    Whitespace,
    /// `\S` — one or more non-whitespace characters `[^ \t\r\n]+`.
    NonWhitespace,
    /// `\h` — one or more horizontal whitespace `[ \t]+`.
    HorizontalWhitespace,
    /// `\H` — one or more non-horizontal-whitespace `[^ \t]+`.
    NonHorizontalWhitespace,
}

/// A compiled glob pattern with optional preserve tail.
#[derive(Debug, Clone, PartialEq)]
pub struct GlobPattern {
    pub segments: Vec<GlobSegment>,
    pub preserve: Option<Vec<GlobSegment>>,
}

/// Compiled matcher – either a plain literal or a glob.
#[derive(Debug, Clone, PartialEq)]
pub enum SepMatcher {
    /// Pure literal, use `str::find` (internally memchr / two-way).
    Literal(SmolStr),
    /// Contains wildcards / whitespace macros.
    Glob(GlobPattern),
}

/// A compiled separator pattern built from `{…}` syntax.
#[derive(Debug, Clone, PartialEq)]
pub struct SepPattern {
    pub(crate) raw: SmolStr,
    pub(crate) compiled: SepMatcher,
}

// ── build_pattern parser ─────────────────────────────────────────────

/// Build a `SepPattern` from the raw content inside `{…}`.
pub fn build_pattern(raw: &str) -> Result<SepPattern, String> {
    if raw.is_empty() {
        return Err("sep pattern error: pattern is empty, expected content inside {}".to_string());
    }

    // 1. Separate preserve portion: find un-escaped `(` … `)` at the very end.
    let (main_raw, preserve_raw) = split_preserve(raw)?;

    // 2. Parse main body segments.
    let main_offset = 0;
    let (segments, star_count) = parse_segments(raw, main_raw, main_offset)?;

    // 3. Parse preserve segments (if any).
    let preserve = if let Some(pr) = preserve_raw {
        let preserve_offset = main_raw.len() + 1; // +1 for '('
        let (psegs, _) = parse_segments(raw, pr, preserve_offset)?;
        Some(psegs)
    } else {
        None
    };

    // 4. Validate star count.
    if star_count > 1 {
        // Find position of the second `*` for the error pointer.
        let second_star_pos = find_nth_unescaped(raw, b'*', 2).unwrap_or(raw.len() - 1);
        return Err(fmt_err(raw, second_star_pos, "at most one * allowed"));
    }

    // 5. Ensure non-empty after parsing.
    if segments.is_empty() && preserve.as_ref().is_none_or(|p| p.is_empty()) {
        return Err(fmt_err_no_pos(
            raw,
            "pattern resolves to empty after parsing",
        ));
    }

    // 6. Choose matcher.
    let has_wildcard = segments.iter().any(|s| {
        matches!(
            s,
            GlobSegment::Star
                | GlobSegment::Any
                | GlobSegment::Whitespace
                | GlobSegment::NonWhitespace
                | GlobSegment::HorizontalWhitespace
                | GlobSegment::NonHorizontalWhitespace
        )
    });
    let compiled = if !has_wildcard && preserve.is_none() {
        // Pure literal – collapse all Literal segments into one string.
        let lit: String = segments
            .iter()
            .map(|s| match s {
                GlobSegment::Literal(l) => l.as_str(),
                _ => unreachable!(),
            })
            .collect();
        SepMatcher::Literal(SmolStr::from(lit))
    } else {
        SepMatcher::Glob(GlobPattern { segments, preserve })
    };

    Ok(SepPattern {
        raw: SmolStr::from(raw),
        compiled,
    })
}

/// Find the byte position of the n-th un-escaped occurrence of `target` in `s`.
fn find_nth_unescaped(s: &str, target: u8, n: usize) -> Option<usize> {
    let bytes = s.as_bytes();
    let mut count = 0;
    for i in 0..bytes.len() {
        if bytes[i] == target && !is_escaped(bytes, i) {
            count += 1;
            if count == n {
                return Some(i);
            }
        }
    }
    None
}

/// Split raw pattern into (main, Option<preserve>).
/// `(…)` must be at the very end of the string and un-escaped.
fn split_preserve(raw: &str) -> Result<(&str, Option<&str>), String> {
    let bytes = raw.as_bytes();
    let len = bytes.len();
    if len == 0 || bytes[len - 1] != b')' {
        return Ok((raw, None));
    }
    // Check the `)` is not escaped.
    if is_escaped(bytes, len - 1) {
        return Ok((raw, None));
    }
    // Walk backwards to find matching un-escaped `(`.
    let mut depth = 0i32;
    let mut open_pos = None;
    let mut i = len;
    while i > 0 {
        i -= 1;
        if bytes[i] == b')' && !is_escaped(bytes, i) {
            depth += 1;
        } else if bytes[i] == b'(' && !is_escaped(bytes, i) {
            depth -= 1;
            if depth == 0 {
                open_pos = Some(i);
                break;
            }
        }
    }
    let open = match open_pos {
        Some(p) => p,
        None => return Ok((raw, None)), // unbalanced – treat as literal
    };

    // Validate that `(` is at a valid position (nothing after `)` except end).
    // The `)` is already the last byte, so we only need to check that nothing
    // between the closing `)` position and end is unexpected. Since we matched
    // the *last* `)`, this is already guaranteed.

    // Also validate that there's no un-escaped `(` before `open` that also has
    // a `)` – this would mean `()` is not at the end. Actually, the simplest
    // check: there must be no un-escaped `(` in the main portion.
    let main_part = &raw[..open];
    {
        let mb = main_part.as_bytes();
        for j in 0..mb.len() {
            if mb[j] == b'(' && !is_escaped(mb, j) {
                return Err(fmt_err(
                    raw,
                    j,
                    "(...) must appear only at the end; found earlier '(' here",
                ));
            }
        }
    }

    let preserve_content = &raw[open + 1..len - 1];
    Ok((main_part, Some(preserve_content)))
}

/// Check if byte at `pos` is preceded by an odd number of backslashes.
fn is_escaped(bytes: &[u8], pos: usize) -> bool {
    let mut count = 0usize;
    let mut p = pos;
    while p > 0 {
        p -= 1;
        if bytes[p] == b'\\' {
            count += 1;
        } else {
            break;
        }
    }
    count % 2 == 1
}

/// Parse a segment string into `Vec<GlobSegment>` and count of `*`.
/// `raw` is the full original pattern (for error messages), `s` is the slice being parsed,
/// `base_offset` is the byte offset of `s` within `raw`.
fn parse_segments(
    raw: &str,
    s: &str,
    base_offset: usize,
) -> Result<(Vec<GlobSegment>, usize), String> {
    let mut segs = Vec::new();
    let mut lit_buf = String::new();
    let mut star_count = 0usize;
    let bytes = s.as_bytes();
    let len = bytes.len();
    let mut i = 0;

    while i < len {
        let b = bytes[i];
        if b == b'\\' && i + 1 < len {
            let next = bytes[i + 1];
            match next {
                b'\\' | b'*' | b'?' | b'{' | b'}' | b'(' | b')' => {
                    lit_buf.push(next as char);
                    i += 2;
                }
                b'0' => {
                    lit_buf.push('\0');
                    i += 2;
                }
                b'n' => {
                    lit_buf.push('\n');
                    i += 2;
                }
                b't' => {
                    lit_buf.push('\t');
                    i += 2;
                }
                b'r' => {
                    lit_buf.push('\r');
                    i += 2;
                }
                b's' => {
                    flush_literal(&mut lit_buf, &mut segs);
                    segs.push(GlobSegment::Whitespace);
                    i += 2;
                }
                b'S' => {
                    flush_literal(&mut lit_buf, &mut segs);
                    segs.push(GlobSegment::NonWhitespace);
                    i += 2;
                }
                b'h' => {
                    flush_literal(&mut lit_buf, &mut segs);
                    segs.push(GlobSegment::HorizontalWhitespace);
                    i += 2;
                }
                b'H' => {
                    flush_literal(&mut lit_buf, &mut segs);
                    segs.push(GlobSegment::NonHorizontalWhitespace);
                    i += 2;
                }
                _ => {
                    // Unknown escape: treat as literal character (e.g. \: → ':').
                    // This preserves backward compatibility with existing configs
                    // that use non-standard escapes like \:, \= etc.
                    lit_buf.push(next as char);
                    i += 2;
                }
            }
        } else if b == b'*' {
            flush_literal(&mut lit_buf, &mut segs);
            segs.push(GlobSegment::Star);
            star_count += 1;
            if star_count > 1 {
                return Err(fmt_err(
                    raw,
                    base_offset + i,
                    "at most one * allowed; use \\* to match a literal asterisk",
                ));
            }
            i += 1;
        } else if b == b'?' {
            flush_literal(&mut lit_buf, &mut segs);
            segs.push(GlobSegment::Any);
            i += 1;
        } else if b == b'(' || b == b')' {
            return Err(fmt_err(
                raw,
                base_offset + i,
                &format!(
                    "unexpected '{}'; (...) preserve must be at the end, use \\{} for literal",
                    b as char, b as char
                ),
            ));
        } else {
            // Regular character – but must handle UTF-8 properly.
            let ch = s[i..].chars().next().unwrap();
            lit_buf.push(ch);
            i += ch.len_utf8();
        }
    }
    flush_literal(&mut lit_buf, &mut segs);
    Ok((segs, star_count))
}

fn flush_literal(buf: &mut String, segs: &mut Vec<GlobSegment>) {
    if !buf.is_empty() {
        segs.push(GlobSegment::Literal(SmolStr::from(buf.as_str())));
        buf.clear();
    }
}

// ── Matching engine ──────────────────────────────────────────────────

impl SepPattern {
    /// Find the first match in `haystack`. Returns `(offset, SepMatch)` where
    /// `offset` is the byte position where the match starts (= field content length).
    pub fn find(&self, haystack: &str) -> Option<(usize, SepMatch)> {
        match &self.compiled {
            SepMatcher::Literal(lit) => {
                let pos = haystack.find(lit.as_str())?;
                Some((
                    pos,
                    SepMatch {
                        consumed: lit.len(),
                        matched: lit.len(),
                    },
                ))
            }
            SepMatcher::Glob(glob) => glob_find(glob, haystack),
        }
    }

    /// Match only at the start of `haystack` (for `consume_sep`).
    pub fn match_at_start(&self, haystack: &str) -> Option<SepMatch> {
        match &self.compiled {
            SepMatcher::Literal(lit) => {
                if haystack.starts_with(lit.as_str()) {
                    Some(SepMatch {
                        consumed: lit.len(),
                        matched: lit.len(),
                    })
                } else {
                    None
                }
            }
            SepMatcher::Glob(glob) => glob_match_at(glob, haystack, 0).map(|total| {
                let main_len = try_match_segments(&glob.segments, haystack).unwrap_or(0);
                let consumed = main_len;
                SepMatch {
                    consumed,
                    matched: total,
                }
            }),
        }
    }

    /// Return the raw pattern string.
    pub fn raw(&self) -> &str {
        self.raw.as_str()
    }
}

/// For a Star-at-start pattern, find how many bytes Star consumes (non-greedy)
/// and how many bytes the remaining main segments consume.
/// Returns `(star_bytes, rest_bytes)`.
fn try_match_star_split(segments: &[GlobSegment], s: &str) -> Option<(usize, usize)> {
    debug_assert!(matches!(segments.first(), Some(GlobSegment::Star)));
    let remaining = &segments[1..];
    // Non-greedy: try expanding Star from 0 chars upwards.
    if let Some(rest_len) = try_match_segments(remaining, s) {
        return Some((0, rest_len));
    }
    let mut char_iter = s.char_indices();
    while let Some((_, _)) = char_iter.next() {
        let byte_pos = char_iter.clone().next().map(|(p, _)| p).unwrap_or(s.len());
        let after = &s[byte_pos..];
        if let Some(rest_len) = try_match_segments(remaining, after) {
            return Some((byte_pos, rest_len));
        }
    }
    None
}

/// Find first occurrence of glob pattern in haystack.
fn glob_find(glob: &GlobPattern, haystack: &str) -> Option<(usize, SepMatch)> {
    let segs = &glob.segments;
    if segs.is_empty() {
        // Only preserve – scan haystack for the first position where preserve matches.
        // The offset is the field content length; consumed is 0 (preserve is not consumed).
        if let Some(preserve) = &glob.preserve {
            // Optimization: if first preserve segment is Literal, use str::find for fast skip.
            if let Some(GlobSegment::Literal(first_lit)) = preserve.first() {
                let lit = first_lit.as_str();
                let mut search_start = 0;
                while search_start <= haystack.len() {
                    if let Some(pos) = haystack[search_start..].find(lit) {
                        let abs_pos = search_start + pos;
                        if let Some(plen) = try_match_segments(preserve, &haystack[abs_pos..]) {
                            return Some((
                                abs_pos,
                                SepMatch {
                                    consumed: 0,
                                    matched: plen,
                                },
                            ));
                        }
                        let next_char_len = haystack[abs_pos..]
                            .chars()
                            .next()
                            .map(|c| c.len_utf8())
                            .unwrap_or(1);
                        search_start = abs_pos + next_char_len;
                    } else {
                        break;
                    }
                }
                return None;
            }
            // General case: scan char by char.
            for (pos, _) in haystack.char_indices() {
                if let Some(plen) = try_match_segments(preserve, &haystack[pos..]) {
                    return Some((
                        pos,
                        SepMatch {
                            consumed: 0,
                            matched: plen,
                        },
                    ));
                }
            }
            return None;
        }
        return None;
    }

    // Star-at-start: Star's consumed bytes = field content (offset),
    // remaining segments' consumed bytes = separator (consumed).
    if matches!(segs.first(), Some(GlobSegment::Star)) {
        let (star_bytes, rest_bytes) = try_match_star_split(segs, haystack)?;
        let preserve_bytes = if let Some(preserve) = &glob.preserve {
            let after_main = &haystack[star_bytes + rest_bytes..];
            try_match_segments(preserve, after_main)?
        } else {
            0
        };
        return Some((
            star_bytes,
            SepMatch {
                consumed: rest_bytes,
                matched: rest_bytes + preserve_bytes,
            },
        ));
    }

    // Optimization: if first segment is Literal, use str::find for fast skip.
    if let Some(GlobSegment::Literal(first_lit)) = segs.first() {
        let lit = first_lit.as_str();
        let mut search_start = 0;
        while search_start <= haystack.len() {
            if let Some(pos) = haystack[search_start..].find(lit) {
                let abs_pos = search_start + pos;
                if let Some(total) = glob_match_at(glob, haystack, abs_pos) {
                    let main_len = try_match_segments(segs, &haystack[abs_pos..]).unwrap_or(0);
                    return Some((
                        abs_pos,
                        SepMatch {
                            consumed: main_len,
                            matched: total,
                        },
                    ));
                }
                // Advance by one char (not lit.len()) to avoid skipping overlapping positions.
                let next_char_len = haystack[abs_pos..]
                    .chars()
                    .next()
                    .map(|c| c.len_utf8())
                    .unwrap_or(1);
                search_start = abs_pos + next_char_len;
            } else {
                break;
            }
        }
        return None;
    }

    // General case: scan char by char.
    for (pos, _) in haystack.char_indices() {
        if let Some(total) = glob_match_at(glob, haystack, pos) {
            let main_len = try_match_segments(segs, &haystack[pos..]).unwrap_or(0);
            return Some((
                pos,
                SepMatch {
                    consumed: main_len,
                    matched: total,
                },
            ));
        }
    }
    None
}

/// Attempt full match of glob pattern (main + preserve) starting at byte offset `start`.
/// Returns total matched length (main + preserve) or None.
fn glob_match_at(glob: &GlobPattern, haystack: &str, start: usize) -> Option<usize> {
    let s = &haystack[start..];
    let main_len = try_match_segments(&glob.segments, s)?;
    if let Some(preserve) = &glob.preserve {
        let rest = &s[main_len..];
        let plen = try_match_segments(preserve, rest)?;
        Some(main_len + plen)
    } else {
        Some(main_len)
    }
}

/// Try to match segments against the start of `s`. Returns consumed byte count.
fn try_match_segments(segments: &[GlobSegment], s: &str) -> Option<usize> {
    if segments.is_empty() {
        return Some(0);
    }
    match &segments[0] {
        GlobSegment::Literal(lit) => {
            if s.starts_with(lit.as_str()) {
                let rest = &s[lit.len()..];
                let tail = try_match_segments(&segments[1..], rest)?;
                Some(lit.len() + tail)
            } else {
                None
            }
        }
        GlobSegment::Any => {
            let ch = s.chars().next()?;
            let clen = ch.len_utf8();
            let rest = &s[clen..];
            let tail = try_match_segments(&segments[1..], rest)?;
            Some(clen + tail)
        }
        GlobSegment::Whitespace => {
            match_char_class_backtrack(consume_whitespace, s, &segments[1..])
        }
        GlobSegment::NonWhitespace => {
            match_char_class_backtrack(consume_non_whitespace, s, &segments[1..])
        }
        GlobSegment::HorizontalWhitespace => {
            match_char_class_backtrack(consume_horizontal_whitespace, s, &segments[1..])
        }
        GlobSegment::NonHorizontalWhitespace => {
            match_char_class_backtrack(consume_non_horizontal_whitespace, s, &segments[1..])
        }
        GlobSegment::Star => {
            // Non-greedy: try expanding from 0 chars upwards.
            let remaining = &segments[1..];
            let mut char_iter = s.char_indices();
            // Try matching 0 chars consumed by Star.
            if let Some(tail) = try_match_segments(remaining, s) {
                return Some(tail);
            }
            // Expand one char at a time.
            while let Some((_, ch)) = char_iter.next() {
                let byte_pos = char_iter.clone().next().map(|(p, _)| p).unwrap_or(s.len());
                // byte_pos points to start of next char (or end).
                // But we need to account for the current char's UTF-8 length:
                let after = &s[byte_pos..];
                if let Some(tail) = try_match_segments(remaining, after) {
                    return Some(byte_pos + tail);
                }
                // Don't expand past string.
                let _ = ch;
            }
            None
        }
    }
}

/// Match a character-class segment (like `\s`, `\S`, `\h`, `\H`) with greedy-then-backtrack.
///
/// `consume_fn` returns the maximum number of bytes that the character class matches at the
/// start of `s`. We try that maximum first (fast path); if the remaining segments don't match,
/// we backtrack one character at a time until we find a length that works (minimum 1 character).
fn match_char_class_backtrack(
    consume_fn: fn(&str) -> usize,
    s: &str,
    remaining: &[GlobSegment],
) -> Option<usize> {
    let max = consume_fn(s);
    if max == 0 {
        return None;
    }
    // Fast path: greedy consumption (covers most cases like \s followed by non-ws literal).
    let rest = &s[max..];
    if let Some(tail) = try_match_segments(remaining, rest) {
        return Some(max + tail);
    }
    // Slow path: backtrack from (max - 1 char) down to 1 char.
    // Walk backwards through char boundaries within consumed range.
    let consumed_slice = &s[..max];
    let mut pos = max;
    for (i, _) in consumed_slice.char_indices().rev() {
        // `i` is the start of the last char; skip it to try one less char.
        pos = i;
        if pos == 0 {
            break; // Must consume at least 1 char.
        }
        let rest = &s[pos..];
        if let Some(tail) = try_match_segments(remaining, rest) {
            return Some(pos + tail);
        }
    }
    let _ = pos;
    None
}

fn consume_whitespace(s: &str) -> usize {
    let mut n = 0;
    for ch in s.chars() {
        if ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n' {
            n += ch.len_utf8();
        } else {
            break;
        }
    }
    n
}

fn consume_non_whitespace(s: &str) -> usize {
    let mut n = 0;
    for ch in s.chars() {
        if ch != ' ' && ch != '\t' && ch != '\r' && ch != '\n' {
            n += ch.len_utf8();
        } else {
            break;
        }
    }
    n
}

fn consume_horizontal_whitespace(s: &str) -> usize {
    let mut n = 0;
    for ch in s.chars() {
        if ch == ' ' || ch == '\t' {
            n += ch.len_utf8();
        } else {
            break;
        }
    }
    n
}

fn consume_non_horizontal_whitespace(s: &str) -> usize {
    let mut n = 0;
    for ch in s.chars() {
        if ch != ' ' && ch != '\t' {
            n += ch.len_utf8();
        } else {
            break;
        }
    }
    n
}

// ── Serde ────────────────────────────────────────────────────────────

impl Serialize for SepPattern {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.serialize_str(self.raw.as_str())
    }
}

impl<'de> Deserialize<'de> for SepPattern {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let s = String::deserialize(deserializer)?;
        build_pattern(&s).map_err(serde::de::Error::custom)
    }
}

// ── Tests ────────────────────────────────────────────────────────────

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

    // ── build_pattern parsing ────────────────────────────────────────

    #[test]
    fn test_parse_literal() {
        let p = build_pattern("abc").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("abc".into()));
    }

    #[test]
    fn test_parse_literal_with_newline() {
        let p = build_pattern("ab\\n").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("ab\n".into()));
    }

    #[test]
    fn test_parse_literal_with_null() {
        let p = build_pattern("ab\\0").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("ab\0".into()));
    }

    #[test]
    fn test_parse_literal_with_tab() {
        let p = build_pattern("ab\\t").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("ab\t".into()));
    }

    #[test]
    fn test_parse_literal_with_cr() {
        let p = build_pattern("ab\\r").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("ab\r".into()));
    }

    #[test]
    fn test_parse_escaped_chars() {
        let p = build_pattern("a\\*b\\?c").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("a*b?c".into()));
    }

    #[test]
    fn test_parse_escaped_braces() {
        let p = build_pattern("a\\{b\\}c").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("a{b}c".into()));
    }

    #[test]
    fn test_parse_escaped_parens() {
        let p = build_pattern("a\\(b\\)").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("a(b)".into()));
    }

    #[test]
    fn test_parse_glob_star_eq() {
        let p = build_pattern("*=").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments.len(), 2);
                assert_eq!(g.segments[0], GlobSegment::Star);
                assert_eq!(g.segments[1], GlobSegment::Literal("=".into()));
                assert!(g.preserve.is_none());
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_parse_glob_key_star() {
        let p = build_pattern("key=*").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments.len(), 2);
                assert_eq!(g.segments[0], GlobSegment::Literal("key=".into()));
                assert_eq!(g.segments[1], GlobSegment::Star);
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_parse_glob_field_any() {
        let p = build_pattern("field?:").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments.len(), 3);
                assert_eq!(g.segments[0], GlobSegment::Literal("field".into()));
                assert_eq!(g.segments[1], GlobSegment::Any);
                assert_eq!(g.segments[2], GlobSegment::Literal(":".into()));
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_parse_whitespace() {
        let p = build_pattern("\\s=").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments.len(), 2);
                assert_eq!(g.segments[0], GlobSegment::Whitespace);
                assert_eq!(g.segments[1], GlobSegment::Literal("=".into()));
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_parse_horizontal_whitespace() {
        let p = build_pattern("\\h:\\h").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments.len(), 3);
                assert_eq!(g.segments[0], GlobSegment::HorizontalWhitespace);
                assert_eq!(g.segments[1], GlobSegment::Literal(":".into()));
                assert_eq!(g.segments[2], GlobSegment::HorizontalWhitespace);
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_parse_non_whitespace() {
        let p = build_pattern("\\s\\S=").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments.len(), 3);
                assert_eq!(g.segments[0], GlobSegment::Whitespace);
                assert_eq!(g.segments[1], GlobSegment::NonWhitespace);
                assert_eq!(g.segments[2], GlobSegment::Literal("=".into()));
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_parse_non_horizontal_whitespace() {
        let p = build_pattern("\\h\\H:\\H").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments.len(), 4);
                assert_eq!(g.segments[0], GlobSegment::HorizontalWhitespace);
                assert_eq!(g.segments[1], GlobSegment::NonHorizontalWhitespace);
                assert_eq!(g.segments[2], GlobSegment::Literal(":".into()));
                assert_eq!(g.segments[3], GlobSegment::NonHorizontalWhitespace);
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_parse_preserve() {
        let p = build_pattern("*(key=)").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments, vec![GlobSegment::Star]);
                let preserve = g.preserve.as_ref().unwrap();
                assert_eq!(preserve.len(), 1);
                assert_eq!(preserve[0], GlobSegment::Literal("key=".into()));
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_parse_preserve_with_whitespace() {
        let p = build_pattern("*\\s(next)").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments, vec![GlobSegment::Star, GlobSegment::Whitespace]);
                let preserve = g.preserve.as_ref().unwrap();
                assert_eq!(preserve.len(), 1);
                assert_eq!(preserve[0], GlobSegment::Literal("next".into()));
            }
            _ => panic!("expected Glob"),
        }
    }

    // ── Constraint violations ────────────────────────────────────────

    #[test]
    fn test_err_multi_star() {
        let e = build_pattern("*a*").unwrap_err();
        assert!(e.contains("at most one * allowed"), "got: {}", e);
        // Verify visual pointer is present
        assert!(
            e.contains("{*a*}"),
            "should show the full pattern, got: {}",
            e
        );
        assert!(e.contains("^"), "should have a pointer, got: {}", e);
    }

    #[test]
    fn test_err_preserve_not_end() {
        let e = build_pattern("(key)*=").unwrap_err();
        assert!(
            e.contains("(...)") || e.contains("preserve") || e.contains("unexpected '('"),
            "got: {}",
            e
        );
    }

    #[test]
    fn test_parse_star_in_preserve() {
        // `*(c*=)` — Star in main + anchored Star in preserve
        let p = build_pattern("*(c*=)").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert_eq!(g.segments, vec![GlobSegment::Star]);
                let preserve = g.preserve.as_ref().unwrap();
                assert_eq!(preserve.len(), 3);
                assert_eq!(preserve[0], GlobSegment::Literal("c".into()));
                assert_eq!(preserve[1], GlobSegment::Star);
                assert_eq!(preserve[2], GlobSegment::Literal("=".into()));
            }
            _ => panic!("expected Glob"),
        }
    }

    #[test]
    fn test_err_empty() {
        let e = build_pattern("").unwrap_err();
        assert!(e.contains("empty"), "got: {}", e);
    }

    #[test]
    fn test_unknown_escape_as_literal() {
        // Unknown escapes like \x, \z, \:, \= are treated as literal characters
        // for backward compatibility with existing configs.
        let p = build_pattern("ab\\x").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("abx".into()));

        let p = build_pattern("field\\:=").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("field:=".into()));

        let p = build_pattern("\\z").unwrap();
        assert_eq!(p.compiled, SepMatcher::Literal("z".into()));
    }

    #[test]
    fn test_err_visual_pointer_position() {
        // In `{*a*}`, the second `*` is at raw position 2 → display position 3
        let e = build_pattern("*a*").unwrap_err();
        let lines: Vec<&str> = e.lines().collect();
        assert!(lines.len() >= 3, "expected 3 lines, got: {}", e);
        // Line 2: `  {*a*}`
        assert!(lines[1].contains("{*a*}"), "got line1: {}", lines[1]);
        // Line 3: pointer `     ^` — the `^` should be under the second `*`
        let pointer_line = lines[2];
        let caret_pos = pointer_line.find('^').expect("no ^ found");
        // In `  {*a*}`, second `*` is at display col 4 (2 spaces + { + * + a + *)
        // base_offset=0 in main body, i=2 for second star → pointer_offset=2+1=3
        // with 2 leading spaces: col 5
        assert_eq!(
            caret_pos, 5,
            "caret at wrong position in: {:?}",
            pointer_line
        );
    }

    #[test]
    fn test_err_messages_display() {
        // This test prints all error messages for visual inspection.
        // Run with: cargo test -p wp-lang -- test_err_messages_display --nocapture
        let cases = vec![
            ("", "empty pattern"),
            ("*a*", "multiple stars"),
            ("(key)*=", "preserve not at end"),
            ("test(mid)abc", "paren not at end"),
        ];
        for (input, label) in cases {
            let err = build_pattern(input).unwrap_err();
            println!("--- {} ---\n{}\n", label, err);
        }
    }

    // ── Matching ─────────────────────────────────────────────────────

    #[test]
    fn test_match_literal() {
        let p = build_pattern("abc").unwrap();
        let (off, m) = p.find("xyzabcdef").unwrap();
        assert_eq!(off, 3);
        assert_eq!(m.consumed, 3);
        assert_eq!(m.matched, 3);
    }

    #[test]
    fn test_match_literal_no_match() {
        let p = build_pattern("abc").unwrap();
        assert!(p.find("xyzdef").is_none());
    }

    #[test]
    fn test_match_star_eq_non_greedy() {
        // `{*=}` on "a=b=c" → non-greedy: Star matches "a", "=" is separator
        // offset = 1 (Star consumed "a" = field content)
        // consumed = 1 ("=" = separator)
        let p = build_pattern("*=").unwrap();
        let (off, m) = p.find("a=b=c").unwrap();
        assert_eq!(off, 1);
        assert_eq!(m.consumed, 1);
        assert_eq!(m.matched, 1);
    }

    #[test]
    fn test_match_whitespace_eq() {
        // `{\s=}` on "key  =val" → offset=3, consumed=3 (" " " " "=")
        let p = build_pattern("\\s=").unwrap();
        let (off, m) = p.find("key  =val").unwrap();
        assert_eq!(off, 3);
        assert_eq!(m.consumed, 3);
        assert_eq!(m.matched, 3);
    }

    #[test]
    fn test_match_preserve() {
        // `{*\s(key=)}` on "hello  key=value"
        // Star matches "hello" (5 bytes = field content = offset)
        // \s matches "  " (2 bytes = separator consumed)
        // preserve "key=" (4 bytes, not consumed)
        let p = build_pattern("*\\s(key=)").unwrap();
        let (off, m) = p.find("hello  key=value").unwrap();
        assert_eq!(off, 5);
        assert_eq!(m.consumed, 2);
        assert_eq!(m.matched, 6); // 2 (\s) + 4 (preserve "key=")
    }

    #[test]
    fn test_match_field_any() {
        // `{field?:}` on "fieldA:value" → offset=0, consumed=7
        let p = build_pattern("field?:").unwrap();
        let (off, m) = p.find("fieldA:value").unwrap();
        assert_eq!(off, 0);
        assert_eq!(m.consumed, 7);
        assert_eq!(m.matched, 7);
    }

    #[test]
    fn test_match_horizontal_whitespace() {
        // `{\h:\h}` on "key\t:\tval" → offset=3, consumed=3
        let p = build_pattern("\\h:\\h").unwrap();
        let (off, m) = p.find("key\t:\tval").unwrap();
        assert_eq!(off, 3);
        assert_eq!(m.consumed, 3);
        assert_eq!(m.matched, 3);
    }

    #[test]
    fn test_match_non_whitespace() {
        // `{\s\S=}` on "msg=Test message externalId=0"
        // \s matches at first space (pos 8), but \S then consumes "message"
        // and "=" doesn't match " externalId..." → fail at pos 8.
        // At pos 16: \s matches " ", \S matches "externalId", "=" matches → success
        let p = build_pattern("\\s\\S=").unwrap();
        let (off, m) = p.find("msg=Test message externalId=0").unwrap();
        assert_eq!(off, 16); // split before " externalId="
        assert_eq!(m.consumed, 12); // " " + "externalId" + "="
        assert_eq!(m.matched, 12);
    }

    #[test]
    fn test_match_non_whitespace_preserve_kvarr() {
        // `{\s(\S=)}` — the kvarr separator pattern:
        // \s consumed (separator), \S= preserved (lookahead for next key=)
        let p = build_pattern("\\s(\\S=)").unwrap();
        let (off, m) = p.find("msg=Test message externalId=0").unwrap();
        assert_eq!(off, 16); // field content: "msg=Test message"
        assert_eq!(m.consumed, 1); // consumed: " " (space)
        assert_eq!(m.matched, 12); // matched: " " + "externalId" + "="
    }

    #[test]
    fn test_match_non_horizontal_whitespace() {
        // `{\h\H=}` on "key\t:\tval\texternalId=0"
        let p = build_pattern("\\H=").unwrap();
        let (off, m) = p.find("key\t:\tval\texternalId=0").unwrap();
        // \H matches "key" (stops at \t), then "=" doesn't match "\t:..." → fail
        // Scanning... \H at "externalId=0": matches "externalId", "=" matches → success
        assert_eq!(off, 10);
        assert_eq!(m.consumed, 11); // "externalId="
    }

    #[test]
    fn test_match_no_match() {
        let p = build_pattern("\\s=").unwrap();
        assert!(p.find("key=val").is_none());
    }

    #[test]
    fn test_match_at_start_literal() {
        let p = build_pattern("abc").unwrap();
        let m = p.match_at_start("abcdef").unwrap();
        assert_eq!(m.consumed, 3);
        assert!(p.match_at_start("xabc").is_none());
    }

    #[test]
    fn test_match_at_start_glob() {
        let p = build_pattern("\\s=").unwrap();
        let m = p.match_at_start("  =val").unwrap();
        assert_eq!(m.consumed, 3);
        assert!(p.match_at_start("val  =").is_none());
    }

    #[test]
    fn test_match_star_at_end() {
        // `{key=*}` on "key=value" → offset=0, consumed=9
        let p = build_pattern("key=*").unwrap();
        let (off, m) = p.find("key=value").unwrap();
        assert_eq!(off, 0);
        // Star matches "value" (all remaining since no following segment)
        // But non-greedy star with no remaining segments matches 0 chars
        // Actually, non-greedy star with no remaining segments: try 0 first → succeeds
        assert_eq!(m.consumed, 4); // "key=" + 0 chars from Star
        assert_eq!(m.matched, 4);
    }

    #[test]
    fn test_match_star_newline() {
        // `{\s=*\n}` on "  =hello\n"
        let p = build_pattern("\\s=*\\n").unwrap();
        let (off, m) = p.find("  =hello\n").unwrap();
        assert_eq!(off, 0);
        assert_eq!(m.consumed, 9);
    }

    #[test]
    fn test_match_preserve_only() {
        // Pattern with only preserve: `(abc)` applied to "abcdef"
        let p = build_pattern("(abc)").unwrap();
        match &p.compiled {
            SepMatcher::Glob(g) => {
                assert!(g.segments.is_empty());
                assert!(g.preserve.is_some());
            }
            _ => panic!("expected Glob"),
        }
        // Match at position 0
        let (off, m) = p.find("abcdef").unwrap();
        assert_eq!(off, 0);
        assert_eq!(m.consumed, 0);
        assert_eq!(m.matched, 3);

        // Match at non-zero offset: field content is "xyz", preserve "abc" found at pos 3
        let (off, m) = p.find("xyzabcdef").unwrap();
        assert_eq!(off, 3);
        assert_eq!(m.consumed, 0);
        assert_eq!(m.matched, 3);

        // No match
        assert!(p.find("xyzdef").is_none());
    }

    #[test]
    fn test_match_preserve_only_command() {
        // Real-world pattern: `{(command=)}` — find "command=" as lookahead separator
        let p = build_pattern("(command=)").unwrap();
        let (off, m) = p.find("hello command=value").unwrap();
        assert_eq!(off, 6); // "hello " is field content
        assert_eq!(m.consumed, 0); // separator is zero-width
        assert_eq!(m.matched, 8); // "command=".len()

        // Match at start
        let (off, m) = p.find("command=value").unwrap();
        assert_eq!(off, 0);
        assert_eq!(m.consumed, 0);
        assert_eq!(m.matched, 8);
    }

    #[test]
    fn test_match_preserve_with_star() {
        // `{(c*=)}` — preserve-only with anchored Star
        // On "hello cmd=value": find first position where c*= matches
        let p = build_pattern("(c*=)").unwrap();
        let (off, m) = p.find("hello cmd=value").unwrap();
        assert_eq!(off, 6); // "hello " is field content
        assert_eq!(m.consumed, 0);
        assert_eq!(m.matched, 4); // "cmd=" matched by c + Star("md") + =

        // Multiple candidates: picks first
        let (off, m) = p.find("hello cat=1 cmd=2").unwrap();
        assert_eq!(off, 6); // first "c" at position 6
        assert_eq!(m.consumed, 0);
        assert_eq!(m.matched, 4); // "cat="
    }

    // ── Serde round-trip ─────────────────────────────────────────────

    #[test]
    fn test_serde_roundtrip() {
        let p = build_pattern("*\\s(key=)").unwrap();
        let json = serde_json::to_string(&p).unwrap();
        // JSON escapes the backslash: raw `*\s(key=)` → JSON `"*\\s(key=)"`
        assert_eq!(json, r#""*\\s(key=)""#);
        let p2: SepPattern = serde_json::from_str(&json).unwrap();
        assert_eq!(p.raw, p2.raw);
        assert_eq!(p.compiled, p2.compiled);
    }

    #[test]
    fn test_serde_roundtrip_literal() {
        let p = build_pattern("abc").unwrap();
        let json = serde_json::to_string(&p).unwrap();
        let p2: SepPattern = serde_json::from_str(&json).unwrap();
        assert_eq!(p, p2);
    }
}