anyxml 0.12.1

//! Provide SAX parsers and auxiliary data structures.
//!
//! To receive events from the parser, the application must configure a SAX handler.  \
//! The handler must implement [`SAXHandler`], [`EntityResolver`], and [`ErrorHandler`].
//!
//! The default implementation for each trait except for [`EntityResolver::resolve_entity`]
//! does nothing. The default implementation for [`EntityResolver::resolve_entity`] simply
//! searches local files.  \
//! If the application only handles trusted data, redirecting to the [`DefaultSAXHandler`]
//! implementation should suffice.
//! However, when handling untrusted resources, it may be advisable to perform some sanitization
//! in [`EntityResolver::resolve_entity`] or [`EntityResolver::get_external_subset`].
//!
//! Parsers can be generated via [`XMLReaderBuilder`].  \
//! If a custom handler is required, execute [`XMLReaderBuilder::set_handler`].  \
//! Since the handler type is statically determined, it is impossible to reassign
//! a different type of handler to an already generated parser.
//!
//! ## Example
//! ```rust
//! use std::fmt::Write as _;
//!
//! use anyxml::sax::{Attributes, EntityResolver, ErrorHandler, SAXHandler, XMLReader};
//!
//! #[derive(Default)]
//! struct ExampleHandler {
//!     buffer: String,
//! }
//! impl EntityResolver for ExampleHandler {}
//! impl ErrorHandler for ExampleHandler {}
//! impl SAXHandler for ExampleHandler {
//!     fn start_document(&mut self) {
//!         writeln!(self.buffer, "start document").ok();
//!     }
//!     fn end_document(&mut self) {
//!         writeln!(self.buffer, "end document").ok();
//!     }
//!
//!     fn start_element(
//!         &mut self,
//!         _namespace_name: Option<&str>,
//!         _local_name: Option<&str>,
//!         qname: &str,
//!         _atts: &Attributes,
//!     ) {
//!         writeln!(self.buffer, "start element {qname}").ok();
//!     }
//!     fn end_element(
//!         &mut self,
//!         _namespace_name: Option<&str>,
//!         _local_name: Option<&str>,
//!         qname: &str
//!     ) {
//!         writeln!(self.buffer, "end element {qname}").ok();
//!     }
//!
//!     fn characters(&mut self, data: &str) {
//!         writeln!(self.buffer, "characters '{data}'").ok();
//!     }
//! }
//!
//! let mut reader = XMLReader::builder()
//!     .set_handler(ExampleHandler::default())
//!     .build();
//! reader.parse_str(r#"<?xml version="1.0"?><greeting>Hello!!</greeting>"#, None).ok();
//!
//! let handler = reader.handler;
//! assert_eq!(r#"start document
//! start element greeting
//! characters 'Hello!!'
//! end element greeting
//! end document
//! "#, handler.buffer);
//! ```
//!
//! # Progressive Parser
//! A normal SAX Parser appears to retrieve all document resources at once, but using a
//! Progressive Parser allows the application to feed document resources to the parser
//! sequentially.
//!
//! For example, when parsing chunked document resources, the application can feed resources
//! to the parser sequentially as they are acquired, rather than collecting all resources and
//! feeding them as a single batch.
//!
//! When parsing XML documents that retrieve external resources, note that the application
//! must set the appropriate base URI for the parser before starting parsing.  \
//! By default, the current directory is set as the base URI.
//!
//! ## Example
//! ```rust
//! use anyxml::sax::{Attributes, DebugHandler, XMLReader};
//!
//! let mut reader = XMLReader::builder()
//!     .set_handler(DebugHandler::default())
//!     .progressive_parser()
//!     .build();
//! let source = br#"<greeting>Hello!!</greeting>"#;
//!
//! for chunk in source.chunks(5) {
//!     reader.parse_chunk(chunk, false).ok();
//! }
//! // Note that the last chunk must set `finish` to `true`.
//! // As shown below, it's okay for an empty chunk.
//! reader.parse_chunk([], true).ok();
//!
//! let handler = reader.handler;
//! assert_eq!(r#"setDocumentLocator()
//! startDocument()
//! startElement(None, greeting, greeting)
//! characters(Hello!!)
//! endElement(None, greeting, greeting)
//! endDocument()
//! "#, handler.buffer);
//! ```
//!
//! # Parser embeded DTD validation feature
//! Applications can enable DTD validation through parser options.  \
//! Note that when enabling the DTD validation option, all external entity loading options
//! are automatically enabled, as some XML documents require loading external DTD subsets
//! for validation.
//!
//! Furthermore, this option does not control whether the DTD is parsed.  \
//! For example, even if the DTD validation option is disabled, parsing the internal DTD
//! subset always occurs to perform attribute value normalization, add default attributes,
//! and resolve internal entity references.
//!
//! ## Example
//! ```rust
//! use anyxml::sax::{
//!     error::SAXParseError,
//!     EntityResolver, ErrorHandler, ParserOption, SAXHandler, XMLReader,
//! };
//!
//! #[derive(Default)]
//! struct ExampleHandler {
//!     buffer: String,
//! }
//! impl EntityResolver for ExampleHandler {}
//! impl ErrorHandler for ExampleHandler {
//!     fn error(&mut self, error: SAXParseError) {
//!         self.buffer.push_str(&format!("\n{error}"));
//!     }
//! }
//! impl SAXHandler for ExampleHandler {}
//!
//! const DOCUMENT: &str = r#"<?xml version="1.0"?>
//! <!DOCTYPE root [
//!     <!ELEMENT root EMPTY>
//!     <!ATTLIST root attr1 CDATA #IMPLIED>
//!     <!ATTLIST root attr2 CDATA #REQUIRED>
//! ]>
//! <root attr1="attr1">non empty string</root>
//! "#;
//!
//! const EXPECT: &str = r#"
//! document.xml[line:7,column:20][dtd-valid][error] #REQUIRED attribute 'attr2' of the element 'root' is not specified.
//! document.xml[line:7,column:44][dtd-valid][error] The content of element 'root' does not match to its content model."#;
//!
//! let mut reader = XMLReader::builder()
//!     .set_handler(ExampleHandler::default())
//!     .enable_option(ParserOption::Validation)
//!     .build();
//! reader.parse_str(DOCUMENT, None).unwrap();
//! assert_eq!(reader.handler.buffer, EXPECT);
//! ```

mod attributes;
mod contentspec;
pub mod error;
mod handler;
mod parser;
mod source;

use std::{
    collections::{BTreeMap, HashMap, HashSet},
    sync::{
        Arc, LazyLock, RwLock,
        atomic::{AtomicUsize, Ordering},
    },
};

use crate::{
    XML_XML_NAMESPACE,
    error::XMLError,
    uri::{URIStr, URIString},
};

pub use attributes::{Attribute, Attributes};
pub use contentspec::ContentSpec;
pub(crate) use contentspec::{ElementContent, ElementContentStateID};
pub use handler::{DebugHandler, DefaultSAXHandler, EntityResolver, ErrorHandler, SAXHandler};
pub use parser::{
    DefaultParserSpec, ParserConfig, ParserOption, ParserSpec, ProgressiveParserSpec,
    ProgressiveParserSpecificContext, XMLProgressiveReaderBuilder, XMLReader, XMLReaderBuilder,
};
pub(crate) use parser::{ParserState, ParserSubState};
pub(crate) use source::INPUT_CHUNK;
pub use source::InputSource;

/// Pseudo entity name for document entities.
pub const DOCUMENT_ENTITY_NAME: &str = "[document]";
/// Pseudo entity name for external DTD subsets.
pub const EXTERNAL_DTD_SUBSET_ENTITY_NAME: &str = "[dtd]";

/// Attribute type of attlist declarations.
///
/// # Reference
/// - [3.3.1 Attribute Types](https://www.w3.org/TR/xml/#sec-attribute-types)
#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub enum AttributeType {
    /// CDATA type (`'CDATA'`)
    #[default]
    CDATA,
    /// ID type (`'ID'`)
    ID,
    /// IDREF type (`'IDREF'`)
    IDREF,
    /// IDREFS type (`'IDREFS'`)
    IDREFS,
    /// Entity Name type (`'ENTITY'`)
    ENTITY,
    /// Entity Names type (`'ENTITIES'`)
    ENTITIES,
    /// Name token type (`'NMTOKEN'`)
    NMTOKEN,
    /// Name tokens type (`'NMTOKENS'`)
    NMTOKENS,
    /// Notation type (`'NOTATION'`)
    NOTATION(HashSet<Box<str>>),
    /// Enumeration type
    Enumeration(HashSet<Box<str>>),
}

impl std::fmt::Display for AttributeType {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::CDATA => write!(f, "CDATA"),
            Self::ID => write!(f, "ID"),
            Self::IDREF => write!(f, "IDREF"),
            Self::IDREFS => write!(f, "IDREFS"),
            Self::ENTITY => write!(f, "ENTITY"),
            Self::ENTITIES => write!(f, "ENTITIES"),
            Self::NMTOKEN => write!(f, "NMTOKEN"),
            Self::NMTOKENS => write!(f, "NMTOKENS"),
            ty @ (Self::NOTATION(set) | Self::Enumeration(set)) => {
                if matches!(ty, Self::NOTATION(_)) {
                    write!(f, "NOTATION ")?;
                }
                write!(f, "(")?;
                let mut set = set.iter().collect::<Vec<_>>();
                set.sort_unstable();
                let mut iter = set.iter();
                if let Some(name) = iter.next() {
                    write!(f, "{name}")?;
                }
                for name in iter {
                    write!(f, "|{name}")?;
                }
                write!(f, ")")
            }
        }
    }
}

/// Default declaration of attlist declarations.
///
/// # Reference
/// - [3.3.2 Attribute Defaults](https://www.w3.org/TR/xml/#sec-attr-defaults)
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum DefaultDecl {
    /// `'#REQUIRED'`
    REQUIRED,
    /// `'#IMPLIED'`
    IMPLIED,
    /// default attribute value with `'#FIXED'`
    FIXED(Box<str>),
    /// default attribute value without `'#FIXED'`
    None(Box<str>),
}

impl std::fmt::Display for DefaultDecl {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::REQUIRED => write!(f, "#REQUIRED"),
            Self::IMPLIED => write!(f, "#IMPLIED"),
            Self::FIXED(def) => write!(f, "#FIXED \"{def}\""),
            Self::None(def) => write!(f, "\"{def}\""),
        }
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub(crate) struct AttlistDeclMap(
    // (attribute type, default value declaration, is external markup declaration)
    HashMap<Box<str>, HashMap<Box<str>, (AttributeType, DefaultDecl, bool)>>,
);
// declaration for `xml:id`.
// since the `get` method must return a reference, it is provided as a static variable.
static XML_ID_ATTRIBUTE_DECL: (AttributeType, DefaultDecl, bool) =
    (AttributeType::ID, DefaultDecl::IMPLIED, false);

impl AttlistDeclMap {
    /// Returns `true` if newly inserted, and `false` if an element or attribute with
    /// the same name is already registered.
    pub(crate) fn insert(
        &mut self,
        elem_name: impl Into<Box<str>>,
        attr_name: impl Into<Box<str>>,
        att_type: AttributeType,
        default_decl: DefaultDecl,
        is_external_markup: bool,
    ) -> bool {
        use std::collections::hash_map::Entry::*;
        let elem_name: Box<str> = elem_name.into();
        let attr_name: Box<str> = attr_name.into();
        match self.0.entry(elem_name) {
            Vacant(entry) => {
                entry.insert(HashMap::from([(
                    attr_name,
                    (att_type, default_decl, is_external_markup),
                )]));
            }
            Occupied(mut entry) => {
                let map = entry.get_mut();
                match map.entry(attr_name) {
                    Vacant(entry) => {
                        entry.insert((att_type, default_decl, is_external_markup));
                    }
                    Occupied(_) => return false,
                }
            }
        }
        true
    }

    pub(crate) fn get(
        &self,
        elem_name: &str,
        attr_name: &str,
    ) -> Option<&(AttributeType, DefaultDecl, bool)> {
        if let Some(ret) = self.0.get(elem_name).and_then(|map| map.get(attr_name)) {
            return Some(ret);
        }

        if attr_name == "xml:id" {
            // 'xml:id' attribute is considered to be defined as an ID type.
            return Some(&XML_ID_ATTRIBUTE_DECL);
        }

        None
    }

    // pub fn contains(&self, elem_name: &str, attr_name: &str) -> bool {
    //     self.get(elem_name, attr_name).is_some()
    // }

    pub(crate) fn clear(&mut self) {
        self.0.clear();
    }

    pub(crate) fn attlist(
        &self,
        elem_name: &str,
    ) -> Option<impl Iterator<Item = (&str, &(AttributeType, DefaultDecl, bool))>> {
        self.0
            .get(elem_name)
            .map(|map| map.iter().map(|(attr, value)| (attr.as_ref(), value)))
    }

    pub(crate) fn iter_all(
        &self,
    ) -> impl Iterator<Item = (&str, &str, &(AttributeType, DefaultDecl, bool))> {
        self.0.iter().flat_map(|(elem, map)| {
            map.iter()
                .map(move |(attr, value)| (elem.as_ref(), attr.as_ref(), value))
        })
    }
}

#[derive(Debug, Clone, Default)]
pub(crate) struct ElementDeclMap(HashMap<Box<str>, ContentSpec>);

impl ElementDeclMap {
    pub(crate) fn insert(
        &mut self,
        name: impl Into<Box<str>>,
        contentspec: ContentSpec,
    ) -> Result<(), XMLError> {
        use std::collections::hash_map::Entry::*;
        let name: Box<str> = name.into();
        match self.0.entry(name) {
            Occupied(_) => Err(XMLError::ParserDuplicateElementDecl),
            Vacant(entry) => {
                entry.insert(contentspec);
                Ok(())
            }
        }
    }

    pub(crate) fn get(&self, name: &str) -> Option<&ContentSpec> {
        self.0.get(name)
    }

    pub(crate) fn get_mut(&mut self, name: &str) -> Option<&mut ContentSpec> {
        self.0.get_mut(name)
    }

    // pub fn contains(&self, name: &str) -> bool {
    //     self.0.contains_key(name)
    // }

    pub(crate) fn clear(&mut self) {
        self.0.clear();
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub(crate) enum EntityDecl {
    InternalGeneralEntity {
        base_uri: Arc<URIStr>,
        replacement_text: Box<str>,
        in_external_markup: bool,
    },
    InternalParameterEntity {
        base_uri: Arc<URIStr>,
        replacement_text: Box<str>,
    },
    ExternalGeneralParsedEntity {
        base_uri: Arc<URIStr>,
        system_id: Box<URIStr>,
        public_id: Option<Box<str>>,
        in_external_markup: bool,
    },
    ExternalGeneralUnparsedEntity {
        base_uri: Arc<URIStr>,
        system_id: Box<URIStr>,
        public_id: Option<Box<str>>,
        notation_name: Box<str>,
    },
    ExternalParameterEntity {
        base_uri: Arc<URIStr>,
        system_id: Box<URIStr>,
        public_id: Option<Box<str>>,
    },
}

static PREDEFINED_ENTITY_LT: LazyLock<EntityDecl> =
    LazyLock::new(|| EntityDecl::InternalGeneralEntity {
        base_uri: URIString::parse("?predefined").unwrap().into(),
        replacement_text: "&#60;".into(), // '<', 0x3C
        in_external_markup: false,
    });
static PREDEFINED_ENTITY_GT: LazyLock<EntityDecl> =
    LazyLock::new(|| EntityDecl::InternalGeneralEntity {
        base_uri: URIString::parse("?predefined").unwrap().into(),
        replacement_text: "&#62;".into(), // '>', 0x3E
        in_external_markup: false,
    });
static PREDEFINED_ENTITY_AMP: LazyLock<EntityDecl> =
    LazyLock::new(|| EntityDecl::InternalGeneralEntity {
        base_uri: URIString::parse("?predefined").unwrap().into(),
        replacement_text: "&#38;".into(), // '&', 0x26
        in_external_markup: false,
    });
static PREDEFINED_ENTITY_APOS: LazyLock<EntityDecl> =
    LazyLock::new(|| EntityDecl::InternalGeneralEntity {
        base_uri: URIString::parse("?predefined").unwrap().into(),
        replacement_text: "&#39;".into(), // ''', 0x27
        in_external_markup: false,
    });
static PREDEFINED_ENTITY_QUOT: LazyLock<EntityDecl> =
    LazyLock::new(|| EntityDecl::InternalGeneralEntity {
        base_uri: URIString::parse("?predefined").unwrap().into(),
        replacement_text: "&#34;".into(), // '"', 0x22
        in_external_markup: false,
    });

#[derive(Debug, Clone, PartialEq, Eq, Default)]
pub(crate) struct EntityMap(HashMap<Box<str>, EntityDecl>);

impl EntityMap {
    pub(crate) fn insert(
        &mut self,
        name: impl Into<Box<str>>,
        decl: EntityDecl,
    ) -> Result<(), XMLError> {
        use std::collections::hash_map::Entry::*;
        let name: Box<str> = name.into();

        // Report an error for entity value literals of predefined entities with incorrect formats.
        //
        // # Reference
        // [4.6 Predefined Entities](https://www.w3.org/TR/xml/#sec-predefined-ent)
        if matches!(name.as_ref(), "lt" | "gt" | "amp" | "apos" | "quot") {
            let EntityDecl::InternalGeneralEntity {
                replacement_text, ..
            } = &decl
            else {
                return Err(XMLError::ParserIncorrectPredefinedEntityDecl);
            };

            let c = if let Some(code) = replacement_text
                .strip_prefix("&#x")
                .and_then(|t| t.strip_suffix(";"))
            {
                u32::from_str_radix(code, 16)
                    .ok()
                    .and_then(char::from_u32)
                    .ok_or(XMLError::ParserIncorrectPredefinedEntityDecl)?
            } else if let Some(code) = replacement_text
                .strip_prefix("&#")
                .and_then(|t| t.strip_suffix(";"))
            {
                code.parse::<u32>()
                    .ok()
                    .and_then(char::from_u32)
                    .ok_or(XMLError::ParserIncorrectPredefinedEntityDecl)?
            } else {
                if replacement_text.len() != 1 || matches!(name.as_ref(), "lt" | "amp") {
                    return Err(XMLError::ParserIncorrectPredefinedEntityDecl);
                }
                replacement_text.chars().next().unwrap()
            };

            let ret = match name.as_ref() {
                "lt" => c == '<',
                "gt" => c == '>',
                "amp" => c == '&',
                "apos" => c == '\'',
                "quot" => c == '"',
                _ => unreachable!(),
            };

            if !ret {
                return Err(XMLError::ParserIncorrectPredefinedEntityDecl);
            }
        }

        match self.0.entry(name) {
            Occupied(_) => Err(XMLError::ParserDuplicateEntityDecl),
            Vacant(entry) => {
                entry.insert(decl);
                Ok(())
            }
        }
    }

    pub(crate) fn get(&self, name: &str) -> Option<&EntityDecl> {
        match name {
            "lt" => Some(&PREDEFINED_ENTITY_LT),
            "gt" => Some(&PREDEFINED_ENTITY_GT),
            "amp" => Some(&PREDEFINED_ENTITY_AMP),
            "apos" => Some(&PREDEFINED_ENTITY_APOS),
            "quot" => Some(&PREDEFINED_ENTITY_QUOT),
            _ => self.0.get(name),
        }
    }

    pub(crate) fn clear(&mut self) {
        self.0.clear();
    }

    pub(crate) fn iter(&self) -> impl Iterator<Item = (&str, &EntityDecl)> {
        self.0.iter().map(|(name, decl)| (name.as_ref(), decl))
    }
}

static ARC_XML_XML_NAMESPACE_PREFIX: LazyLock<Arc<str>> = LazyLock::new(|| "xml".into());
static ARC_XML_XML_NAMESPACE: LazyLock<Arc<str>> = LazyLock::new(|| XML_XML_NAMESPACE.into());

/// Namespace mapping.
#[derive(Debug, Clone)]
pub struct Namespace {
    /// Namespace prefix. If no prefix is bound, set `""`.
    pub prefix: Arc<str>,
    /// Namespace name.
    pub namespace_name: Arc<str>,
}

/// Namespace declaration stack.
pub struct NamespaceStack {
    // (namespace, before overwrite)
    // Namespaces declared closer to the document element appear earlier in the list.
    // The second `usize` is the position of the namespace that bound the same prefix until
    // the namespace declaration appeared. If there is no such namespace, it is `usize::MAX`.
    namespaces: Vec<(Namespace, usize)>,
    // (prefix, position in `namespaces`)
    prefix_map: BTreeMap<Arc<str>, usize>,
}

impl NamespaceStack {
    /// Check if `prefix` is declared in this stack.
    pub fn is_declared(&self, prefix: &str) -> bool {
        self.prefix_map.contains_key(prefix)
    }

    /// The depth of this stack.
    pub fn len(&self) -> usize {
        self.namespaces.len()
    }

    /// Check if no namespaces are declared.
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// If `prefix` is declared, return declared namespace,
    /// otherwise return [`None`].
    pub fn get(&self, prefix: &str) -> Option<Namespace> {
        let &index = self.prefix_map.get(prefix)?;
        Some(self.namespaces[index].0.clone())
    }

    pub(crate) fn push(&mut self, prefix: &str, namespace_name: &str) {
        if let Some(index) = self.prefix_map.get_mut(prefix) {
            let previous = *index;
            *index = self.namespaces.len();
            self.namespaces.push((
                Namespace {
                    prefix: self.namespaces[previous].0.prefix.clone(),
                    namespace_name: namespace_name.into(),
                },
                previous,
            ));
        } else {
            let namespace = Namespace {
                prefix: prefix.into(),
                namespace_name: namespace_name.into(),
            };
            self.prefix_map
                .insert(namespace.prefix.clone(), self.namespaces.len());
            self.namespaces.push((namespace, usize::MAX));
        }
    }

    pub(crate) fn pop(&mut self) -> Option<Namespace> {
        if self.len() == 1 {
            return None;
        }
        let (namespace, previous) = self.namespaces.pop().unwrap();
        if previous < usize::MAX {
            *self.prefix_map.get_mut(&namespace.prefix).unwrap() = previous;
        } else {
            self.prefix_map.remove(&namespace.prefix);
        }
        Some(namespace)
    }

    pub(crate) fn truncate(&mut self, depth: usize) {
        while self.namespaces.len() > depth {
            self.pop();
        }
    }

    pub(crate) fn clear(&mut self) {
        self.truncate(1);
    }

    /// Generate a namespace iterator.
    pub fn iter(&self) -> NsIter<'_> {
        self.into_iter()
    }
}

impl Default for NamespaceStack {
    fn default() -> Self {
        Self {
            namespaces: vec![(
                Namespace {
                    prefix: ARC_XML_XML_NAMESPACE_PREFIX.clone(),
                    namespace_name: ARC_XML_XML_NAMESPACE.clone(),
                },
                usize::MAX,
            )],
            prefix_map: BTreeMap::from([(ARC_XML_XML_NAMESPACE_PREFIX.clone(), 0)]),
        }
    }
}

/// Namespace iterator.
pub struct NsIter<'a> {
    iter: std::collections::btree_map::Iter<'a, Arc<str>, usize>,
    stack: &'a NamespaceStack,
}

impl<'a> Iterator for NsIter<'a> {
    type Item = &'a Namespace;

    fn next(&mut self) -> Option<Self::Item> {
        let (_, index) = self.iter.next()?;
        Some(&self.stack.namespaces[*index].0)
    }
}

impl<'a> IntoIterator for &'a NamespaceStack {
    type IntoIter = NsIter<'a>;
    type Item = &'a Namespace;

    fn into_iter(self) -> Self::IntoIter {
        NsIter {
            iter: self.prefix_map.iter(),
            stack: self,
        }
    }
}

/// Notation.
#[derive(Debug, Clone, PartialEq, Eq, Default, Hash)]
pub struct Notation {
    /// Notation name.
    pub name: Box<str>,
    /// System identifier of this notation.
    pub system_id: Option<Box<str>>,
    /// Public identifier of this notation.
    pub public_id: Option<Box<str>>,
}

/// A locator indicating the parser's current position within the document.
///
/// Basically, this object has no meaning except during document parsing.
pub struct Locator {
    system_id: RwLock<Arc<URIStr>>,
    public_id: RwLock<Option<Arc<str>>>,
    line: AtomicUsize,
    column: AtomicUsize,
}

impl Locator {
    pub(crate) fn new(
        system_id: Arc<URIStr>,
        public_id: Option<Arc<str>>,
        line: usize,
        column: usize,
    ) -> Self {
        Self {
            system_id: RwLock::new(system_id),
            public_id: RwLock::new(public_id),
            line: line.into(),
            column: column.into(),
        }
    }

    /// The system identifier for the current document.
    pub fn system_id(&self) -> Arc<URIStr> {
        self.system_id.read().unwrap().clone()
    }

    /// The public identifier for the current document.
    pub fn public_id(&self) -> Option<Arc<str>> {
        self.public_id.read().unwrap().clone()
    }

    /// Line number in the parsing process.
    pub fn line(&self) -> usize {
        self.line.load(Ordering::Acquire)
    }

    /// Offset from the first character within the line at the position being processed.
    pub fn column(&self) -> usize {
        self.column.load(Ordering::Acquire)
    }

    pub(crate) fn set_system_id(&self, system_id: Arc<URIStr>) {
        *self.system_id.write().unwrap() = system_id;
    }

    pub(crate) fn set_public_id(&self, public_id: Option<Arc<str>>) {
        *self.public_id.write().unwrap() = public_id;
    }

    pub(crate) fn set_line(&self, line: usize) {
        self.line.store(line, Ordering::Release);
    }

    pub(crate) fn set_column(&self, column: usize) {
        self.column.store(column, Ordering::Release);
    }

    pub(crate) fn update_line(&self, f: impl Fn(usize) -> usize) {
        while self
            .line
            .fetch_update(Ordering::Release, Ordering::Acquire, |line| Some(f(line)))
            .is_err()
        {}
    }

    pub(crate) fn update_column(&self, f: impl Fn(usize) -> usize) {
        while self
            .column
            .fetch_update(Ordering::Release, Ordering::Acquire, |column| {
                Some(f(column))
            })
            .is_err()
        {}
    }
}

impl Default for Locator {
    fn default() -> Self {
        let system_id = std::env::current_dir().unwrap_or_default();
        let system_id = URIString::parse_file_path(system_id)
            .unwrap_or_else(|_| URIString::parse("").unwrap())
            .into();
        Self::new(system_id, None, 1, 1)
    }
}