one_brackets/

node.rs

//! Object model of the bracket format.

use std::borrow::Cow;
use std::fmt;
use std::hash::{Hash, Hasher};
use std::ops::{Index, IndexMut};
use std::str::FromStr;

use crate::{AccessError, AccessErrorKind, Position, Text};

const BASE64: &str = "#base64:";

/// A node of a bracket file: a [`Value`] plus the position it was parsed from.
///
/// Quoted strings and atoms are kept distinct, so text written by the platform is written back
/// byte for byte. Whitespace between items is not kept: writing uses the platform layout.
/// Whitespace inside an atom, trailing whitespace included, is part of its text.
/// Equality and hashing ignore the position.
///
/// Like parsing and writing, cloning, comparison, hashing, `Debug` and dropping
/// are not recursive: a tree of any depth does not overflow the stack.
pub struct Node {
    value: Value,
    position: Option<Position>,
}

/// Content of a [`Node`].
#[derive(Clone, PartialEq, Eq, Hash)]
pub enum Value {
    /// A list `{a,b,c}`.
    List(Vec<Node>),
    /// A quoted string; doubled quotes and surrogate escapes `"\d83d` are already unescaped.
    Str(Text),
    /// An unquoted value: number, GUID, literal; may be empty (`{2,x,}`).
    ///
    /// It runs up to the next `,` or `}`: whitespace and line breaks before them are part of it.
    /// Binary data `{#base64:…}` is an atom too, line breaks included.
    Atom(Text),
}

impl Node {
    pub(crate) fn parsed(value: Value, position: Position) -> Self {
        Self {
            value,
            position: Some(position),
        }
    }

    /// A list of nodes.
    pub fn list(items: impl IntoIterator<Item = Node>) -> Self {
        Value::List(items.into_iter().collect()).into()
    }

    /// An unquoted atom (GUID, literal, number).
    pub fn atom(value: impl Into<Text>) -> Self {
        Value::Atom(value.into()).into()
    }

    /// A quoted string.
    ///
    /// There is no `From<&str>` for building: `Node::try_from(&str)` parses text.
    pub fn string(value: impl Into<Text>) -> Self {
        Value::Str(value.into()).into()
    }

    /// A counted list `{count,item1,item2,...}`, the common 1C shape.
    pub fn counted(items: impl IntoIterator<Item = Node>) -> Self {
        let items: Vec<Node> = items.into_iter().collect();
        Node::list(std::iter::once(Node::from(items.len())).chain(items))
    }

    pub fn value(&self) -> &Value {
        &self.value
    }

    pub fn into_value(mut self) -> Value {
        self.take_value()
    }

    /// Mutable access to the content; the position stays where the node was parsed.
    pub fn value_mut(&mut self) -> &mut Value {
        &mut self.value
    }

    /// Where the node starts in the input; `None` for nodes built in code.
    ///
    /// Edits do not change it: it always refers to the original text.
    pub fn position(&self) -> Option<Position> {
        self.position
    }

    pub fn is_list(&self) -> bool {
        matches!(self.value, Value::List(_))
    }

    pub fn is_str(&self) -> bool {
        matches!(self.value, Value::Str(_))
    }

    pub fn is_atom(&self) -> bool {
        matches!(self.value, Value::Atom(_))
    }

    /// An empty atom: no value between commas (`{1,,2}`).
    pub fn is_empty_atom(&self) -> bool {
        matches!(&self.value, Value::Atom(s) if s.is_empty())
    }

    pub fn as_list(&self) -> Option<&[Node]> {
        match &self.value {
            Value::List(items) => Some(items),
            _ => None,
        }
    }

    /// Text of a string or an atom, unpaired surrogates included.
    pub fn as_text(&self) -> Option<&Text> {
        match &self.value {
            Value::Str(s) | Value::Atom(s) => Some(s),
            Value::List(_) => None,
        }
    }

    /// Value of a string or an atom; `None` if it holds an unpaired surrogate.
    pub fn as_str(&self) -> Option<&str> {
        self.as_text()?.as_str()
    }

    /// Value of a string or an atom with unpaired surrogates replaced by U+FFFD.
    pub fn to_string_lossy(&self) -> Option<Cow<'_, str>> {
        Some(self.as_text()?.to_string_lossy())
    }

    /// Quoted string only.
    pub fn as_quoted(&self) -> Option<&str> {
        match &self.value {
            Value::Str(s) => s.as_str(),
            _ => None,
        }
    }

    /// Atom only, as written: trailing whitespace included.
    pub fn as_atom(&self) -> Option<&str> {
        match &self.value {
            Value::Atom(s) => s.as_str(),
            _ => None,
        }
    }

    /// Atom without leading and trailing whitespace: `{12\r\n}` gives `12`.
    ///
    /// The typed accessors (`as_i64`, `try_parse` and the like) read this text.
    pub fn as_atom_trimmed(&self) -> Option<&str> {
        self.as_atom().map(trim)
    }

    /// Atom parsed into any [`FromStr`] type: `node.as_parsed::<u32>()`.
    pub fn as_parsed<T: FromStr>(&self) -> Option<T> {
        self.as_atom_trimmed()?.parse().ok()
    }

    pub fn as_i64(&self) -> Option<i64> {
        self.as_parsed()
    }

    pub fn as_u64(&self) -> Option<u64> {
        self.as_parsed()
    }

    pub fn as_f64(&self) -> Option<f64> {
        self.as_parsed()
    }

    /// Atom `1` is `true`, `0` is `false`.
    pub fn as_bool(&self) -> Option<bool> {
        match self.as_atom_trimmed()? {
            "1" => Some(true),
            "0" => Some(false),
            _ => None,
        }
    }

    /// An atom shaped like a GUID `xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx`.
    pub fn as_guid(&self) -> Option<&str> {
        self.as_atom_trimmed().filter(|s| is_guid(s))
    }

    /// Payload of a `#base64:…` atom without the prefix and line breaks (not decoded).
    pub fn as_base64(&self) -> Option<String> {
        let data = self.as_atom()?.strip_prefix(BASE64)?;
        Some(data.chars().filter(|c| !c.is_ascii_whitespace()).collect())
    }

    /// List item by index.
    pub fn get(&self, idx: usize) -> Option<&Node> {
        self.as_list()?.get(idx)
    }

    /// Item by a path of indices from this node: `node.get_path(&[1, 0, 2])`.
    pub fn get_path(&self, path: &[usize]) -> Option<&Node> {
        path.iter().try_fold(self, |node, &idx| node.get(idx))
    }

    /// Number of list items; 0 for strings and atoms.
    pub fn len(&self) -> usize {
        self.as_list().map_or(0, <[Node]>::len)
    }

    /// List without items; strings and atoms are considered empty too.
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// List items; an empty iterator for strings and atoms.
    pub fn iter(&self) -> std::slice::Iter<'_, Node> {
        self.as_list().unwrap_or(&[]).iter()
    }

    pub fn into_list(mut self) -> Option<Vec<Node>> {
        match self.take_value() {
            Value::List(items) => Some(items),
            _ => None,
        }
    }

    /// Text of a string or an atom.
    pub fn into_text(mut self) -> Option<Text> {
        match self.take_value() {
            Value::Str(s) | Value::Atom(s) => Some(s),
            Value::List(_) => None,
        }
    }

    /// Value of a string or an atom; unpaired surrogates are replaced by U+FFFD.
    pub fn into_string(self) -> Option<String> {
        self.into_text()
            .map(|text| text.into_string().unwrap_or_else(|text| text.to_string()))
    }

    pub fn try_list(&self) -> Result<&[Node], AccessError> {
        self.as_list().ok_or_else(|| self.unexpected("list"))
    }

    pub fn try_text(&self) -> Result<&Text, AccessError> {
        self.as_text()
            .ok_or_else(|| self.unexpected("string or value"))
    }

    /// Fails for a list and for text with an unpaired surrogate.
    pub fn try_str(&self) -> Result<&str, AccessError> {
        self.unicode(self.try_text()?, "string or value")
    }

    pub fn try_quoted(&self) -> Result<&str, AccessError> {
        match &self.value {
            Value::Str(s) => self.unicode(s, "quoted string"),
            _ => Err(self.unexpected("quoted string")),
        }
    }

    /// Atom as written: trailing whitespace included.
    pub fn try_atom(&self) -> Result<&str, AccessError> {
        match &self.value {
            Value::Atom(s) => self.unicode(s, "value"),
            _ => Err(self.unexpected("value")),
        }
    }

    /// The text as `&str`, or an error about the unpaired surrogate in it.
    fn unicode<'a>(&self, text: &'a Text, expected: &'static str) -> Result<&'a str, AccessError> {
        text.as_str().ok_or_else(|| {
            AccessError::new(
                AccessErrorKind::InvalidValue {
                    expected: expected.into(),
                    found: self.describe(),
                    reason: "it holds an unpaired surrogate".to_owned(),
                },
                self.position,
            )
        })
    }

    /// Atom parsed into any [`FromStr`] type: `node.try_parse::<u32>()?`.
    ///
    /// The error names the target type and keeps the reason from [`FromStr::Err`].
    pub fn try_parse<T>(&self) -> Result<T, AccessError>
    where
        T: FromStr,
        T::Err: fmt::Display,
    {
        let expected = type_label::<T>();
        let atom = self
            .as_atom_trimmed()
            .ok_or_else(|| self.unexpected(expected.clone()))?;
        atom.parse().map_err(|e: T::Err| {
            AccessError::new(
                AccessErrorKind::InvalidValue {
                    expected,
                    found: self.describe(),
                    reason: e.to_string(),
                },
                self.position,
            )
        })
    }

    pub fn try_i64(&self) -> Result<i64, AccessError> {
        self.try_parse()
    }

    pub fn try_u64(&self) -> Result<u64, AccessError> {
        self.try_parse()
    }

    pub fn try_f64(&self) -> Result<f64, AccessError> {
        self.try_parse()
    }

    pub fn try_bool(&self) -> Result<bool, AccessError> {
        self.as_bool()
            .ok_or_else(|| self.unexpected("boolean (0 or 1)"))
    }

    pub fn try_guid(&self) -> Result<&str, AccessError> {
        self.as_guid().ok_or_else(|| self.unexpected("GUID"))
    }

    pub fn try_get(&self, idx: usize) -> Result<&Node, AccessError> {
        let items = self.try_list()?;
        items.get(idx).ok_or_else(|| {
            AccessError::new(
                AccessErrorKind::IndexOutOfBounds {
                    index: idx,
                    len: items.len(),
                },
                self.position,
            )
        })
    }

    /// Item by a path of indices: `node.try_get_path(&[0, 2, 0])?`.
    ///
    /// On failure the error carries the path to the node that could not be indexed.
    pub fn try_get_path(&self, path: &[usize]) -> Result<&Node, AccessError> {
        let mut node = self;
        for (depth, &idx) in path.iter().enumerate() {
            node = node.try_get(idx).map_err(|e| e.with_path(&path[..depth]))?;
        }
        Ok(node)
    }

    /// List items for editing: replace, push, insert or remove nodes.
    pub fn as_list_mut(&mut self) -> Option<&mut Vec<Node>> {
        match &mut self.value {
            Value::List(items) => Some(items),
            _ => None,
        }
    }

    pub fn get_mut(&mut self, idx: usize) -> Option<&mut Node> {
        self.as_list_mut()?.get_mut(idx)
    }

    pub fn get_path_mut(&mut self, path: &[usize]) -> Option<&mut Node> {
        path.iter().try_fold(self, |node, &idx| node.get_mut(idx))
    }

    /// List items; an empty iterator for strings and atoms.
    pub fn iter_mut(&mut self) -> std::slice::IterMut<'_, Node> {
        match &mut self.value {
            Value::List(items) => items.iter_mut(),
            _ => [].iter_mut(),
        }
    }

    pub fn try_list_mut(&mut self) -> Result<&mut Vec<Node>, AccessError> {
        if !self.is_list() {
            return Err(self.unexpected("list"));
        }
        Ok(self.as_list_mut().expect("checked above"))
    }

    pub fn try_get_mut(&mut self, idx: usize) -> Result<&mut Node, AccessError> {
        let position = self.position;
        let items = self.try_list_mut()?;
        let len = items.len();
        items.get_mut(idx).ok_or_else(|| {
            AccessError::new(
                AccessErrorKind::IndexOutOfBounds { index: idx, len },
                position,
            )
        })
    }

    /// Item by a path of indices for editing: `*node.try_get_path_mut(&[1, 0])? = Node::from(2)`.
    pub fn try_get_path_mut(&mut self, path: &[usize]) -> Result<&mut Node, AccessError> {
        let mut node = self;
        for (depth, &idx) in path.iter().enumerate() {
            node = node
                .try_get_mut(idx)
                .map_err(|e| e.with_path(&path[..depth]))?;
        }
        Ok(node)
    }

    /// Items of a counted list `{count,item1,item2,...}`: `{2,a,b}` gives `[a, b]`.
    ///
    /// Fails if the count is not a number or does not match the number of items.
    pub fn try_counted(&self) -> Result<&[Node], AccessError> {
        let declared: usize = self
            .try_get(0)?
            .try_parse()
            .map_err(|e| e.with_path(&[0]))?;
        let items = &self.try_list()?[1..];
        if items.len() != declared {
            return Err(AccessError::new(
                AccessErrorKind::CountMismatch {
                    declared,
                    actual: items.len(),
                },
                self.position,
            ));
        }
        Ok(items)
    }

    /// Pre-order depth-first traversal with the path from the root. Not recursive: forms can be deeply nested.
    pub fn walk<'a>(&'a self, mut visit: impl FnMut(&[usize], &'a Node)) {
        // (node, depth, index in parent)
        let mut stack = vec![(self, 0usize, 0usize)];
        let mut path = Vec::new();
        while let Some((node, depth, idx)) = stack.pop() {
            if depth > 0 {
                path.truncate(depth - 1);
                path.push(idx);
            }
            visit(&path, node);
            for (i, item) in node.iter().enumerate().rev() {
                stack.push((item, depth + 1, i));
            }
        }
    }

    /// Short description of the node for error messages.
    pub fn describe(&self) -> String {
        const MAX: usize = 40;
        let clip = |text: &Text| {
            let s = text.to_string_lossy();
            match s.char_indices().nth(MAX) {
                Some((end, _)) => format!("{}…", &s[..end]),
                None => s.into_owned(),
            }
        };
        match &self.value {
            Value::List(items) => match items.len() {
                0 => "empty list".to_owned(),
                1 => "list of 1 item".to_owned(),
                n => format!("list of {n} items"),
            },
            Value::Str(s) => format!("string {:?}", clip(s)),
            Value::Atom(s) if s.is_empty() => "empty value".to_owned(),
            Value::Atom(s) => format!("value `{}`", clip(s)),
        }
    }

    /// Moves the value out: fields of a `Drop` type cannot be moved directly.
    fn take_value(&mut self) -> Value {
        std::mem::replace(&mut self.value, Value::Atom(Text::new()))
    }

    pub(crate) fn unexpected(&self, expected: impl Into<Cow<'static, str>>) -> AccessError {
        AccessError::new(
            AccessErrorKind::UnexpectedType {
                expected: expected.into(),
                found: self.describe(),
            },
            self.position,
        )
    }
}

/// `u32` for primitives, `Foo` instead of `my_crate::model::Foo` for user types.
pub(crate) fn type_label<T>() -> Cow<'static, str> {
    let name = std::any::type_name::<T>();
    if name.contains('<') {
        Cow::Borrowed(name)
    } else {
        Cow::Borrowed(name.rsplit("::").next().unwrap_or(name))
    }
}

/// Trims whitespace as the platform skips it (see [`is_space`]).
fn trim(s: &str) -> &str {
    s.trim_matches(is_space)
}

/// Whitespace of the platform: ICU `u_isspace` as of Unicode 6.0 (ICU 4.6).
///
/// Categories Zs, Zl and Zp, `\t`..`\r`, `\x1c`..`\x1f` and U+0085: unlike
/// [`char::is_whitespace`], also U+00A0, U+2007, U+202F and U+180E.
pub(crate) fn is_space(c: char) -> bool {
    matches!(
        c,
        '\t'..='\r'
            | '\x1c'..='\x20'
            | '\u{85}'
            | '\u{a0}'
            | '\u{1680}'
            | '\u{180e}'
            | '\u{2000}'..='\u{200a}'
            | '\u{2028}'
            | '\u{2029}'
            | '\u{202f}'
            | '\u{205f}'
            | '\u{3000}'
    )
}

fn is_guid(s: &str) -> bool {
    let bytes = s.as_bytes();
    bytes.len() == 36
        && bytes.iter().enumerate().all(|(i, &b)| match i {
            8 | 13 | 18 | 23 => b == b'-',
            _ => b.is_ascii_hexdigit(),
        })
}

impl fmt::Debug for Node {
    /// Shows only the value: positions would drown the tree in noise.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.value.fmt(f)
    }
}

impl fmt::Debug for Value {
    /// The same text as a derived `Debug`, `{:#?}` included, but not recursive.
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fn indent(f: &mut fmt::Formatter<'_>, depth: usize) -> fmt::Result {
            (0..depth).try_for_each(|_| f.write_str("    "))
        }

        let pretty = f.alternate();
        // (items left, indentation depth of the list's `List(`)
        let mut stack: Vec<(std::slice::Iter<'_, Node>, usize)> = Vec::new();
        let mut next = Some((self, 0));
        loop {
            if let Some((value, depth)) = next.take() {
                let (name, text) = match value {
                    Value::List(items) if !items.is_empty() => {
                        if pretty {
                            f.write_str("List(\n")?;
                            indent(f, depth + 1)?;
                            f.write_str("[\n")?;
                            indent(f, depth + 2)?;
                        } else {
                            f.write_str("List([")?;
                        }
                        let mut items = items.iter();
                        next = items.next().map(|item| (&item.value, depth + 2));
                        stack.push((items, depth));
                        continue;
                    }
                    Value::List(_) => ("List", None),
                    Value::Str(s) => ("Str", Some(s)),
                    Value::Atom(s) => ("Atom", Some(s)),
                };
                f.write_str(name)?;
                f.write_str("(")?;
                if pretty {
                    f.write_str("\n")?;
                    indent(f, depth + 1)?;
                }
                match text {
                    Some(s) => write!(f, "{s:?}")?,
                    None => f.write_str("[]")?,
                }
                if pretty {
                    f.write_str(",\n")?;
                    indent(f, depth)?;
                }
                f.write_str(")")?;
            } else {
                // The innermost open list has no items left.
                let Some((_, depth)) = stack.pop() else {
                    return Ok(());
                };
                if pretty {
                    indent(f, depth + 1)?;
                    f.write_str("],\n")?;
                    indent(f, depth)?;
                    f.write_str(")")?;
                } else {
                    f.write_str("])")?;
                }
            }
            // A value is written: separate it from the next item of its list.
            let Some((items, depth)) = stack.last_mut() else {
                return Ok(());
            };
            if pretty {
                f.write_str(",\n")?;
            }
            if let Some(item) = items.next() {
                if pretty {
                    indent(f, *depth + 2)?;
                } else {
                    f.write_str(", ")?;
                }
                next = Some((&item.value, *depth + 2));
            }
        }
    }
}

impl Clone for Node {
    /// Not recursive: a deep tree does not overflow the stack.
    fn clone(&self) -> Self {
        let Value::List(items) = &self.value else {
            return Self {
                value: self.value.clone(),
                position: self.position,
            };
        };
        // (source items left, copied items, position of the list)
        let mut stack = vec![(items.iter(), Vec::with_capacity(items.len()), self.position)];
        loop {
            let (source, copied, _) = stack.last_mut().expect("clone stack is not empty");
            match source.next() {
                Some(item) => match &item.value {
                    Value::List(items) => {
                        stack.push((items.iter(), Vec::with_capacity(items.len()), item.position));
                    }
                    scalar => copied.push(Self {
                        value: scalar.clone(),
                        position: item.position,
                    }),
                },
                None => {
                    let (_, items, position) = stack.pop().expect("clone stack is not empty");
                    let done = Self {
                        value: Value::List(items),
                        position,
                    };
                    match stack.last_mut() {
                        Some((_, parent, _)) => parent.push(done),
                        None => return done,
                    }
                }
            }
        }
    }
}

impl Drop for Node {
    /// Not recursive: nested lists are moved onto a heap stack and dropped one by one.
    fn drop(&mut self) {
        let Value::List(items) = &mut self.value else {
            return;
        };
        // Items without nested items of their own drop without recursion anyway.
        if items.iter().all(Node::is_empty) {
            return;
        }
        let mut stack = std::mem::take(items);
        while let Some(mut node) = stack.pop() {
            if let Value::List(items) = &mut node.value {
                stack.append(items);
            }
        }
    }
}

impl PartialEq for Node {
    /// Ignores positions. Not recursive.
    fn eq(&self, other: &Self) -> bool {
        let mut stack = vec![(std::slice::from_ref(self), std::slice::from_ref(other))];
        while let Some((left, right)) = stack.pop() {
            if left.len() != right.len() {
                return false;
            }
            for (left, right) in left.iter().zip(right) {
                match (&left.value, &right.value) {
                    (Value::List(left), Value::List(right)) => stack.push((left, right)),
                    // Scalars, or a list against a scalar: compared without recursion.
                    (left, right) if left != right => return false,
                    _ => {}
                }
            }
        }
        true
    }
}

impl Eq for Node {}

impl Hash for Node {
    /// Ignores positions. Not recursive: pre-order with list lengths.
    fn hash<H: Hasher>(&self, state: &mut H) {
        let mut stack = vec![self];
        while let Some(node) = stack.pop() {
            std::mem::discriminant(&node.value).hash(state);
            match &node.value {
                Value::List(items) => {
                    items.len().hash(state);
                    stack.extend(items.iter().rev());
                }
                Value::Str(s) | Value::Atom(s) => s.hash(state),
            }
        }
    }
}

impl Index<usize> for Node {
    type Output = Node;

    fn index(&self, idx: usize) -> &Node {
        match self.try_get(idx) {
            Ok(node) => node,
            Err(e) => panic!("cannot index node: {e}"),
        }
    }
}

impl IndexMut<usize> for Node {
    fn index_mut(&mut self, idx: usize) -> &mut Node {
        match self.try_get_mut(idx) {
            Ok(node) => node,
            Err(e) => panic!("cannot index node: {e}"),
        }
    }
}

impl<'a> IntoIterator for &'a Node {
    type Item = &'a Node;
    type IntoIter = std::slice::Iter<'a, Node>;

    fn into_iter(self) -> Self::IntoIter {
        self.iter()
    }
}

impl<'a> IntoIterator for &'a mut Node {
    type Item = &'a mut Node;
    type IntoIter = std::slice::IterMut<'a, Node>;

    fn into_iter(self) -> Self::IntoIter {
        self.iter_mut()
    }
}

impl From<Value> for Node {
    fn from(value: Value) -> Self {
        Self {
            value,
            position: None,
        }
    }
}

impl From<bool> for Node {
    fn from(b: bool) -> Self {
        Node::atom(if b { "1" } else { "0" })
    }
}

macro_rules! from_number {
    ($($t:ty),*) => {$(
        impl From<$t> for Node {
            fn from(n: $t) -> Self {
                Node::atom(n.to_string())
            }
        }
    )*};
}

from_number!(i8, i16, i32, i64, u8, u16, u32, u64, usize, isize);

impl From<Vec<Node>> for Node {
    fn from(items: Vec<Node>) -> Self {
        Value::List(items).into()
    }
}

impl<T: Into<Node>> FromIterator<T> for Node {
    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
        Node::list(iter.into_iter().map(Into::into))
    }
}

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

    fn sample() -> Node {
        Node::from(vec![
            Node::atom("12"),
            Node::from(vec![
                Node::string("text"),
                Node::atom("c2f34349-b1e0-4060-8abf-3c59f38ac69f"),
                Node::from(true),
            ]),
            Node::atom("#base64:QUJD\r\r\nREVG\r\r\n"),
            Node::atom(""),
        ])
    }

    #[test]
    fn typed_accessors() {
        let node = sample();
        assert_eq!(node[0].as_i64(), Some(12));
        assert_eq!(node[0].as_f64(), Some(12.0));
        assert_eq!(node[0].as_parsed::<u8>(), Some(12));
        assert_eq!(
            node.get_path(&[1, 0]).and_then(Node::as_quoted),
            Some("text")
        );
        assert_eq!(node.get_path(&[1, 0]).and_then(Node::as_atom), None);
        assert!(node.get_path(&[1, 1]).and_then(Node::as_guid).is_some());
        assert_eq!(node.get_path(&[1, 2]).and_then(Node::as_bool), Some(true));
        assert_eq!(node[2].as_base64().as_deref(), Some("QUJDREVG"));
        assert!(node[3].is_empty_atom());
        assert_eq!(node.get_path(&[1, 5]), None);
        assert_eq!(node.len(), 4);
        assert_eq!(node[0].iter().count(), 0);
        assert_eq!(node[0].position(), None);
    }

    #[test]
    fn try_accessors_explain_mismatch() {
        let node = sample();
        insta::assert_snapshot!(node.try_get(7).unwrap_err(), @"index 7 is out of bounds for list of length 4");
        insta::assert_snapshot!(node[0].try_list().unwrap_err(), @"expected list, found value `12`");
        insta::assert_snapshot!(node[1].try_i64().unwrap_err(), @"expected i64, found list of 3 items");
        insta::assert_snapshot!(node[3].try_guid().unwrap_err(), @"expected GUID, found empty value");
        insta::assert_snapshot!(node[1][0].try_bool().unwrap_err(), @r#"expected boolean (0 or 1), found string "text""#);
        insta::assert_snapshot!(node[1][1].try_parse::<u32>().unwrap_err(), @"expected u32, found value `c2f34349-b1e0-4060-8abf-3c59f38ac69f`: invalid digit found in string");
        insta::assert_snapshot!(node.try_get_path(&[1, 0, 3]).unwrap_err(), @r#"expected list, found string "text" (path [1, 0])"#);
        insta::assert_snapshot!(node.try_get_path(&[1, 9]).unwrap_err(), @"index 9 is out of bounds for list of length 3 (path [1])");
    }

    #[test]
    fn parsed_nodes_report_positions() {
        let node: Node = "{1,\r\n{x,\"s\"}}".parse().unwrap();
        insta::assert_snapshot!(node.try_get_path(&[1, 0]).unwrap().try_parse::<u8>().unwrap_err(), @"expected u8, found value `x` at line 2, column 2: invalid digit found in string");
        insta::assert_snapshot!(node.try_get_path(&[1, 1, 0]).unwrap_err(), @r#"expected list, found string "s" at line 2, column 4 (path [1, 1])"#);
        insta::assert_snapshot!(node[1].try_get(5).unwrap_err(), @"index 5 is out of bounds for list of length 2 at line 2, column 1");
    }

    #[test]
    fn equality_ignores_positions() {
        let parsed: Node = "{1,\"a\"}".parse().unwrap();
        assert_eq!(parsed, Node::list([Node::from(1), Node::string("a")]));
    }

    #[test]
    fn walks_with_paths() {
        let mut visited = Vec::new();
        let node = Node::from(vec![
            Node::atom("12"),
            Node::from(vec![Node::string("a"), Node::from(vec![Node::from(true)])]),
            Node::atom(""),
        ]);
        node.walk(|path, node| visited.push(format!("{path:?} {}", node.describe())));
        insta::assert_snapshot!(visited.join("\n"), @r#"
        [] list of 3 items
        [0] value `12`
        [1] list of 2 items
        [1, 0] string "a"
        [1, 1] list of 1 item
        [1, 1, 0] value `1`
        [2] empty value
        "#);
    }

    #[test]
    #[should_panic(expected = "cannot index node: expected list, found value `12`")]
    fn index_panics_with_message() {
        let _ = &sample()[0][0];
    }

    #[test]
    fn type_labels_are_short() {
        struct Local;
        assert_eq!(type_label::<u32>(), "u32");
        assert_eq!(type_label::<Local>(), "Local");
        assert_eq!(type_label::<String>(), "String");
    }

    #[test]
    fn edits_in_place() {
        let mut node: Node = "{1,\r\n{a,\"b\"}}".parse().unwrap();
        node[0] = Node::from(2);
        *node.try_get_path_mut(&[1, 1]).unwrap().value_mut() = Value::Str("c".into());
        node.get_mut(1)
            .unwrap()
            .try_list_mut()
            .unwrap()
            .push(Node::atom("d"));
        for item in &mut node[1] {
            if item.as_atom() == Some("a") {
                *item = Node::atom("z");
            }
        }
        assert_eq!(node.to_string(), "{2,\r\n{z,\"c\",d}\r\n}");
        // The edited value keeps the position of the original node.
        assert_eq!(
            node.get_path(&[1, 1]).unwrap().position().unwrap().column,
            4
        );
        assert!(node.get_path_mut(&[0, 0]).is_none());
        assert_eq!(node[0].iter_mut().count(), 0);

        insta::assert_snapshot!(node.try_get_path_mut(&[1, 7]).unwrap_err(), @"index 7 is out of bounds for list of length 3 at line 2, column 1 (path [1])");
        insta::assert_snapshot!(node[0].try_list_mut().unwrap_err(), @"expected list, found value `2`");
    }

    #[test]
    #[should_panic(expected = "cannot index node: index 5 is out of bounds for list of length 2")]
    fn index_mut_panics_with_message() {
        let mut node = Node::list([Node::from(1), Node::from(2)]);
        node[5] = Node::from(3);
    }

    #[test]
    fn counted_lists() {
        let node: Node = "{2,a,\r\n{b}}".parse().unwrap();
        assert_eq!(
            node.try_counted().unwrap(),
            [Node::atom("a"), Node::list([Node::atom("b")])]
        );
        assert_eq!(Node::counted(node.try_counted().unwrap().to_vec()), node);
        assert_eq!(Node::counted([]).to_string(), "{0}");

        let bad: Node = "{\r\n{x},\r\n{3,a},\r\n{}}".parse().unwrap();
        insta::assert_snapshot!(bad[0].try_counted().unwrap_err(), @"expected usize, found value `x` at line 2, column 2 (path [0]): invalid digit found in string");
        insta::assert_snapshot!(bad[1].try_counted().unwrap_err(), @"list declares 3 items, but has 1 at line 3, column 1");
        insta::assert_snapshot!(bad[2].try_counted().unwrap_err(), @"index 0 is out of bounds for list of length 0 at line 4, column 1");
    }

    #[test]
    fn debug_matches_derived_layout() {
        let node = Node::list([
            Node::atom("1"),
            Node::list([]),
            Node::list([Node::string("a \"b\"")]),
        ]);
        assert_eq!(
            format!("{node:?}"),
            r#"List([Atom("1"), List([]), List([Str("a \"b\"")])])"#
        );
        insta::assert_snapshot!(format!("{node:#?}"), @r#"
        List(
            [
                Atom(
                    "1",
                ),
                List(
                    [],
                ),
                List(
                    [
                        Str(
                            "a \"b\"",
                        ),
                    ],
                ),
            ],
        )
        "#);
    }

    #[test]
    fn deep_trees_without_recursion() {
        let depth = 100_000;
        let deep = || {
            (0..depth).fold(Node::string("leaf"), |inner, _| {
                Node::list([Node::from(1), inner])
            })
        };
        let node = deep();
        let copy = node.clone();
        assert_eq!(copy, node);
        assert_ne!(copy, Node::list([]));

        let hash = |node: &Node| {
            let mut hasher = std::hash::DefaultHasher::new();
            node.hash(&mut hasher);
            hasher.finish()
        };
        assert_eq!(hash(&copy), hash(&deep()));

        let debug = format!("{node:?}");
        assert!(debug.starts_with("List([Atom(\"1\"), List(["));

        assert_eq!(node.into_list().map(|items| items.len()), Some(2));
        drop(copy);
    }

    #[test]
    fn typed_accessors_trim_atoms() {
        let node: Node = "{12\u{a0}\r\n,1 ,c2f34349-b1e0-4060-8abf-3c59f38ac69f\r\n}"
            .parse()
            .unwrap();
        assert_eq!(node[0].as_atom(), Some("12\u{a0}\r\n"));
        assert_eq!(node[0].as_atom_trimmed(), Some("12"));
        assert_eq!(node[0].try_parse::<u8>(), Ok(12));
        assert_eq!(node[1].as_bool(), Some(true));
        assert!(node[2].as_guid().is_some());
    }

    #[test]
    fn unpaired_surrogates() {
        let node = Node::string(Text::from_utf16(&[0x61, 0xD800]));
        assert_eq!(node.as_str(), None);
        assert_eq!(node.to_string_lossy().as_deref(), Some("a\u{fffd}"));
        insta::assert_snapshot!(node.try_str().unwrap_err(), @r#"expected string or value, found string "a�": it holds an unpaired surrogate"#);
        assert_eq!(node.clone().into_string().as_deref(), Some("a\u{fffd}"));
        assert_eq!(node.into_text(), Some(Text::from_utf16(&[0x61, 0xD800])));
    }

    #[test]
    fn detects_guid() {
        assert!(is_guid("c2f34349-b1e0-4060-8abf-3c59f38ac69f"));
        assert!(!is_guid("c2f34349-b1e0-4060-8abf-3c59f38ac69"));
    }
}