eure_document/parse/

record.rs

//! RecordParser for parsing record types from Eure documents.

use crate::parse::DocumentParser;
use crate::prelude_internal::*;

use super::{FromEure, ParseContext, ParseError, ParseErrorKind, ParserScope, UnionTagMode};

/// Helper for parsing record (map with string keys) from Eure documents.
///
/// Tracks accessed fields for unknown field checking.
///
/// # Flatten Context
///
/// When `flatten_ctx` is `Some`, this parser is part of a flattened chain:
/// - Field accesses are recorded in the shared `FlattenContext`
/// - `deny_unknown_fields()` is a no-op (root parser validates)
///
/// When `flatten_ctx` is `None`, this is a root parser:
/// - Field accesses are recorded in local `accessed` set
/// - `deny_unknown_fields()` actually validates
///
/// # Example
///
/// ```ignore
/// impl<'doc> FromEure<'doc> for User {
///     fn parse(ctx: &ParseContext<'doc>) -> Result<Self, ParseError> {
///         let mut rec = ctx.parse_record()?;
///         let name = rec.field::<String>("name")?;
///         let age = rec.field_optional::<u32>("age")?;
///         rec.deny_unknown_fields()?;
///         Ok(User { name, age })
///     }
/// }
/// ```
#[must_use]
pub struct RecordParser<'doc> {
    map: &'doc NodeMap,
    /// Union tag mode inherited from context.
    union_tag_mode: UnionTagMode,
    /// The parse context (holds doc, node_id, accessed, flatten_ctx).
    ctx: ParseContext<'doc>,
}

impl<'doc> RecordParser<'doc> {
    /// Create a new RecordParser for the given context.
    pub(crate) fn new(ctx: &ParseContext<'doc>) -> Result<Self, ParseError> {
        // Error if called in Extension scope - this is a user mistake
        // (using #[eure(flatten_ext)] with a record-parsing type)
        if let Some(fc) = ctx.flatten_ctx()
            && fc.scope() == ParserScope::Extension
        {
            return Err(ParseError {
                node_id: ctx.node_id(),
                kind: ParseErrorKind::RecordInExtensionScope,
            });
        }

        let node = ctx.node();
        match &node.content {
            NodeValue::Map(map) => Ok(Self {
                map,
                union_tag_mode: ctx.union_tag_mode(),
                ctx: ctx.clone(),
            }),
            NodeValue::Hole(_) => Err(ParseError {
                node_id: ctx.node_id(),
                kind: ParseErrorKind::UnexpectedHole,
            }),
            value => Err(ParseError {
                node_id: ctx.node_id(),
                kind: value
                    .value_kind()
                    .map(|actual| ParseErrorKind::TypeMismatch {
                        expected: crate::value::ValueKind::Map,
                        actual,
                    })
                    .unwrap_or(ParseErrorKind::UnexpectedHole),
            }),
        }
    }

    /// Create a new RecordParser from document and node ID directly.
    pub(crate) fn from_doc_and_node(
        doc: &'doc EureDocument,
        node_id: NodeId,
    ) -> Result<Self, ParseError> {
        let ctx = ParseContext::new(doc, node_id);
        Self::new(&ctx)
    }

    /// Mark a field as accessed.
    fn mark_accessed(&self, name: &str) {
        self.ctx.accessed().add_field(name);
    }

    /// Get the node ID being parsed.
    pub fn node_id(&self) -> NodeId {
        self.ctx.node_id()
    }

    /// Get a required field.
    ///
    /// Returns `ParseErrorKind::MissingField` if the field is not present or is excluded.
    pub fn parse_field<T>(&self, name: &str) -> Result<T, T::Error>
    where
        T: FromEure<'doc>,
        T::Error: From<ParseError>,
    {
        self.parse_field_with(name, T::parse)
    }

    pub fn parse_field_with<T>(&self, name: &str, mut parser: T) -> Result<T::Output, T::Error>
    where
        T: DocumentParser<'doc>,
        T::Error: From<ParseError>,
    {
        self.mark_accessed(name);
        let field_node_id = self
            .map
            .get(&ObjectKey::String(name.to_string()))
            .ok_or_else(|| ParseError {
                node_id: self.ctx.node_id(),
                kind: ParseErrorKind::MissingField(name.to_string()),
            })?;
        let ctx =
            ParseContext::with_union_tag_mode(self.ctx.doc(), *field_node_id, self.union_tag_mode);
        parser.parse(&ctx)
    }

    pub fn parse_field_optional<T>(&self, name: &str) -> Result<Option<T>, T::Error>
    where
        T: FromEure<'doc>,
        T::Error: From<ParseError>,
    {
        self.parse_field_optional_with(name, T::parse)
    }

    /// Get an optional field.
    ///
    /// Returns `Ok(None)` if the field is not present.
    pub fn parse_field_optional_with<T>(
        &self,
        name: &str,
        mut parser: T,
    ) -> Result<Option<T::Output>, T::Error>
    where
        T: DocumentParser<'doc>,
        T::Error: From<ParseError>,
    {
        self.mark_accessed(name);
        match self.map.get(&ObjectKey::String(name.to_string())) {
            Some(field_node_id) => {
                let ctx = ParseContext::with_union_tag_mode(
                    self.ctx.doc(),
                    *field_node_id,
                    self.union_tag_mode,
                );
                Ok(Some(parser.parse(&ctx)?))
            }
            None => Ok(None),
        }
    }

    /// Get the parse context for a field without parsing it.
    ///
    /// Use this when you need access to the field's NodeId or want to defer parsing.
    /// Returns `ParseErrorKind::MissingField` if the field is not present.
    pub fn field(&self, name: &str) -> Result<ParseContext<'doc>, ParseError> {
        self.mark_accessed(name);
        let field_node_id = self
            .map
            .get(&ObjectKey::String(name.to_string()))
            .ok_or_else(|| ParseError {
                node_id: self.ctx.node_id(),
                kind: ParseErrorKind::MissingField(name.to_string()),
            })?;
        Ok(ParseContext::with_union_tag_mode(
            self.ctx.doc(),
            *field_node_id,
            self.union_tag_mode,
        ))
    }

    /// Get the parse context for an optional field without parsing it.
    ///
    /// Use this when you need access to the field's NodeId or want to defer parsing.
    /// Returns `None` if the field is not present.
    pub fn field_optional(&self, name: &str) -> Option<ParseContext<'doc>> {
        self.mark_accessed(name);
        self.map
            .get(&ObjectKey::String(name.to_string()))
            .map(|node_id| {
                ParseContext::with_union_tag_mode(self.ctx.doc(), *node_id, self.union_tag_mode)
            })
    }

    /// Get a field as a nested record parser.
    ///
    /// Returns `ParseErrorKind::MissingField` if the field is not present.
    pub fn field_record(&self, name: &str) -> Result<RecordParser<'doc>, ParseError> {
        self.mark_accessed(name);
        let field_node_id = self
            .map
            .get(&ObjectKey::String(name.to_string()))
            .ok_or_else(|| ParseError {
                node_id: self.ctx.node_id(),
                kind: ParseErrorKind::MissingField(name.to_string()),
            })?;
        let ctx =
            ParseContext::with_union_tag_mode(self.ctx.doc(), *field_node_id, self.union_tag_mode);
        RecordParser::new(&ctx)
    }

    /// Get an optional field as a nested record parser.
    ///
    /// Returns `Ok(None)` if the field is not present.
    pub fn field_record_optional(
        &self,
        name: &str,
    ) -> Result<Option<RecordParser<'doc>>, ParseError> {
        self.mark_accessed(name);
        match self.map.get(&ObjectKey::String(name.to_string())) {
            Some(field_node_id) => {
                let ctx = ParseContext::with_union_tag_mode(
                    self.ctx.doc(),
                    *field_node_id,
                    self.union_tag_mode,
                );
                Ok(Some(RecordParser::new(&ctx)?))
            }
            None => Ok(None),
        }
    }

    /// Finish parsing with Deny policy (error if unknown fields exist).
    ///
    /// This also errors if the map contains non-string keys, as records
    /// should only have string-keyed fields.
    ///
    /// **Flatten behavior**: If this parser has a flatten_ctx (i.e., is a child
    /// in a flatten chain), this is a no-op. Only root parsers validate.
    pub fn deny_unknown_fields(self) -> Result<(), ParseError> {
        // If child (has flatten_ctx with Record scope), no-op - parent will validate
        if let Some(fc) = self.ctx.flatten_ctx()
            && fc.scope() == ParserScope::Record
        {
            return Ok(());
        }

        // Root parser - validate using accessed set
        let accessed = self.ctx.accessed();
        for (key, _) in self.map.iter() {
            match key {
                ObjectKey::String(name) => {
                    if !accessed.has_field(name.as_str()) {
                        return Err(ParseError {
                            node_id: self.ctx.node_id(),
                            kind: ParseErrorKind::UnknownField(name.clone()),
                        });
                    }
                }
                // Non-string keys are invalid in records
                other => {
                    return Err(ParseError {
                        node_id: self.ctx.node_id(),
                        kind: ParseErrorKind::InvalidKeyType(other.clone()),
                    });
                }
            }
        }
        Ok(())
    }

    /// Finish parsing with Allow policy (allow unknown string fields).
    ///
    /// This still errors if the map contains non-string keys, as records
    /// should only have string-keyed fields.
    pub fn allow_unknown_fields(self) -> Result<(), ParseError> {
        // Check for non-string keys (invalid in records)
        for (key, _) in self.map.iter() {
            if !matches!(key, ObjectKey::String(_)) {
                return Err(ParseError {
                    node_id: self.ctx.node_id(),
                    kind: ParseErrorKind::InvalidKeyType(key.clone()),
                });
            }
        }
        Ok(())
    }

    /// Get an iterator over unknown fields (for Schema policy or custom handling).
    ///
    /// Returns `Result` items:
    /// - `Ok((field_name, context))` for unaccessed string-keyed fields
    /// - `Err((invalid_key, context))` for non-string keys, allowing caller to handle directly
    ///
    /// Note: In flattened contexts, this still returns fields - use `deny_unknown_fields()`
    /// if you want the automatic no-op behavior for child parsers.
    pub fn unknown_fields(
        &self,
    ) -> impl Iterator<
        Item = Result<(&'doc str, ParseContext<'doc>), (&'doc ObjectKey, ParseContext<'doc>)>,
    > + '_ {
        let doc = self.ctx.doc();
        let mode = self.union_tag_mode;
        // Clone the accessed set for filtering - we need the current state
        let accessed = self.ctx.accessed().clone();
        self.map
            .iter()
            .filter_map(move |(key, &node_id)| match key {
                ObjectKey::String(name) => {
                    if !accessed.has_field(name.as_str()) {
                        Some(Ok((
                            name.as_str(),
                            ParseContext::with_union_tag_mode(doc, node_id, mode),
                        )))
                    } else {
                        None // Accessed, skip
                    }
                }
                other => Some(Err((
                    other,
                    ParseContext::with_union_tag_mode(doc, node_id, mode),
                ))),
            })
    }

    /// Get an iterator over all unknown entries including non-string keys.
    ///
    /// Returns (ObjectKey, context) pairs for:
    /// - String keys that haven't been accessed
    /// - All non-string keys (e.g., integer keys)
    ///
    /// This is useful for flatten map validation where both string and integer
    /// keys need to be validated against the map's key schema.
    pub fn unknown_entries(
        &self,
    ) -> impl Iterator<Item = (&'doc ObjectKey, ParseContext<'doc>)> + '_ {
        let doc = self.ctx.doc();
        let mode = self.union_tag_mode;
        // Clone the accessed set for filtering - we need the current state
        let accessed = self.ctx.accessed().clone();
        self.map.iter().filter_map(move |(key, &node_id)| {
            match key {
                ObjectKey::String(name) => {
                    // For string keys, only return if not accessed
                    if !accessed.has_field(name.as_str()) {
                        Some((key, ParseContext::with_union_tag_mode(doc, node_id, mode)))
                    } else {
                        None
                    }
                }
                // Non-string keys are always returned (they can't be "accessed" via field methods)
                _ => Some((key, ParseContext::with_union_tag_mode(doc, node_id, mode))),
            }
        })
    }

    /// Create a flatten context for child parsers in Record scope.
    ///
    /// This creates a FlattenContext initialized with the current accessed fields,
    /// and returns a ParseContext that children can use. Children created from this
    /// context will:
    /// - Add their accessed fields to the shared FlattenContext
    /// - Have deny_unknown_fields() be a no-op
    ///
    /// The root parser should call deny_unknown_fields() after all children are done.
    pub fn flatten(&self) -> ParseContext<'doc> {
        self.ctx.flatten()
    }
}

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

    fn create_test_doc() -> EureDocument {
        let mut doc = EureDocument::new();
        let root_id = doc.get_root_id();

        // Add fields: name = "Alice", age = 30
        let name_id = doc
            .add_map_child(ObjectKey::String("name".to_string()), root_id)
            .unwrap()
            .node_id;
        doc.node_mut(name_id).content = NodeValue::Primitive(PrimitiveValue::Text(
            crate::text::Text::plaintext("Alice".to_string()),
        ));

        let age_id = doc
            .add_map_child(ObjectKey::String("age".to_string()), root_id)
            .unwrap()
            .node_id;
        doc.node_mut(age_id).content = NodeValue::Primitive(PrimitiveValue::Integer(30.into()));

        doc
    }

    #[test]
    fn test_record_field() {
        let doc = create_test_doc();
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let name: String = rec.parse_field("name").unwrap();
        assert_eq!(name, "Alice");
    }

    #[test]
    fn test_record_field_missing() {
        let doc = create_test_doc();
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let result: Result<String, _> = rec.parse_field("nonexistent");
        assert!(matches!(
            result.unwrap_err().kind,
            ParseErrorKind::MissingField(_)
        ));
    }

    #[test]
    fn test_record_field_optional() {
        let doc = create_test_doc();
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let name: Option<String> = rec.parse_field_optional("name").unwrap();
        assert_eq!(name, Some("Alice".to_string()));

        let missing: Option<String> = rec.parse_field_optional("nonexistent").unwrap();
        assert_eq!(missing, None);
    }

    #[test]
    fn test_record_deny_unknown_fields() {
        let doc = create_test_doc();
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let _name: String = rec.parse_field("name").unwrap();
        // Didn't access "age", so deny should fail
        let result = rec.deny_unknown_fields();
        assert!(matches!(
            result.unwrap_err().kind,
            ParseErrorKind::UnknownField(_)
        ));
    }

    #[test]
    fn test_record_deny_unknown_fields_all_accessed() {
        let doc = create_test_doc();
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let _name: String = rec.parse_field("name").unwrap();
        let _age: num_bigint::BigInt = rec.parse_field("age").unwrap();
        // Accessed all fields, should succeed
        rec.deny_unknown_fields().unwrap();
    }

    #[test]
    fn test_record_allow_unknown_fields() {
        let doc = create_test_doc();
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let _name: String = rec.parse_field("name").unwrap();
        // Didn't access "age", but allow should succeed
        rec.allow_unknown_fields().unwrap();
    }

    #[test]
    fn test_record_unknown_fields_iterator() {
        let doc = create_test_doc();
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let _name: String = rec.parse_field("name").unwrap();
        // "age" should be in unknown fields
        let unknown: Vec<_> = rec.unknown_fields().collect::<Result<Vec<_>, _>>().unwrap();
        assert_eq!(unknown.len(), 1);
        assert_eq!(unknown[0].0, "age");
    }

    #[test]
    fn test_record_with_non_string_keys_deny_should_error() {
        // deny_unknown_fields() errors on non-string keys
        use crate::eure;

        let doc = eure!({ 0 = "value" });
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let result = rec.deny_unknown_fields();
        assert!(
            matches!(result.unwrap_err().kind, ParseErrorKind::InvalidKeyType(_)),
            "deny_unknown_fields() should error on non-string keys"
        );
    }

    #[test]
    fn test_record_with_non_string_keys_unknown_fields_iterator() {
        // unknown_fields() returns Err for non-string keys
        use crate::eure;

        let doc = eure!({ 0 = "value" });
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        // unknown_fields() should return an error for the non-string key
        let result: Result<Vec<_>, _> = rec.unknown_fields().collect();
        let (invalid_key, _ctx) = result.unwrap_err();
        assert!(
            matches!(invalid_key, ObjectKey::Number(_)),
            "unknown_fields() should return the invalid key directly"
        );
    }

    #[test]
    fn test_unknown_fields_err_contains_correct_context() {
        // Verify that the Err case contains a context pointing to the value node
        use crate::eure;

        let doc = eure!({ 42 = "test" });
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        let result: Result<Vec<_>, _> = rec.unknown_fields().collect();
        let (key, ctx) = result.unwrap_err();

        // Verify the key is the numeric key
        assert_eq!(key, &ObjectKey::Number(42.into()));
        // Verify the context can be used to parse the value
        let value: String = ctx.parse().unwrap();
        assert_eq!(value, "test");
    }

    #[test]
    fn test_unknown_fields_mixed_string_and_non_string_keys() {
        // Test that string keys return Ok, non-string keys return Err
        use crate::eure;

        let doc = eure!({
            name = "Alice"
            123 = "numeric"
        });
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        // Collect results to inspect both Ok and Err
        let mut ok_fields = Vec::new();
        let mut err_keys = Vec::new();
        for result in rec.unknown_fields() {
            match result {
                Ok((name, _ctx)) => ok_fields.push(name.to_string()),
                Err((key, _ctx)) => err_keys.push(key.clone()),
            }
        }

        // Should have one Ok (string key) and one Err (numeric key)
        assert_eq!(ok_fields, vec!["name"]);
        assert_eq!(err_keys, vec![ObjectKey::Number(123.into())]);
    }

    #[test]
    fn test_unknown_fields_accessed_fields_filtered_non_string_always_returned() {
        // Accessed string keys are filtered out, but non-string keys always return Err
        use crate::eure;

        let doc = eure!({
            name = "Alice"
            age = 30
            999 = "numeric"
        });
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        // Access the "name" field
        let _name: String = rec.parse_field("name").unwrap();

        // Check unknown_fields - "name" filtered, "age" is Ok, numeric is Err
        let mut ok_fields = Vec::new();
        let mut err_keys = Vec::new();
        for result in rec.unknown_fields() {
            match result {
                Ok((name, _ctx)) => ok_fields.push(name.to_string()),
                Err((key, _ctx)) => err_keys.push(key.clone()),
            }
        }

        assert_eq!(ok_fields, vec!["age"]);
        assert_eq!(err_keys, vec![ObjectKey::Number(999.into())]);
    }

    #[test]
    fn test_unknown_fields_multiple_non_string_keys() {
        // Test handling of multiple non-string keys
        use crate::eure;

        let doc = eure!({
            1 = "one"
            2 = "two"
        });
        let rec = doc.parse_record(doc.get_root_id()).unwrap();

        // Collect all errors
        let mut err_keys: Vec<ObjectKey> = Vec::new();
        for result in rec.unknown_fields() {
            if let Err((key, _ctx)) = result {
                err_keys.push(key.clone());
            }
        }

        // Should have both numeric keys as errors
        assert_eq!(err_keys.len(), 2);
        assert!(err_keys.contains(&ObjectKey::Number(1.into())));
        assert!(err_keys.contains(&ObjectKey::Number(2.into())));
    }

    #[test]
    fn test_parse_ext() {
        let mut doc = EureDocument::new();
        let root_id = doc.get_root_id();

        // Add extension: $ext-type.optional = true
        let ext_id = doc
            .add_extension("optional".parse().unwrap(), root_id)
            .unwrap()
            .node_id;
        doc.node_mut(ext_id).content = NodeValue::Primitive(PrimitiveValue::Bool(true));

        let ctx = doc.parse_extension_context(root_id);
        let optional: bool = ctx.parse_ext("optional").unwrap();
        assert!(optional);
    }

    #[test]
    fn test_parse_ext_optional_missing() {
        let doc = EureDocument::new();
        let root_id = doc.get_root_id();

        let ctx = doc.parse_extension_context(root_id);
        let optional: Option<bool> = ctx.parse_ext_optional("optional").unwrap();
        assert_eq!(optional, None);
    }

    /// Helper struct for testing three-level nested flatten pattern.
    /// Parses: { a, b, c, d, e } with three-level flatten.
    #[derive(Debug, PartialEq)]
    struct ThreeLevelFlatten {
        a: i32,
        b: i32,
        c: i32,
        d: i32,
        e: i32,
    }

    impl<'doc> FromEure<'doc> for ThreeLevelFlatten {
        type Error = ParseError;

        fn parse(ctx: &ParseContext<'doc>) -> Result<Self, Self::Error> {
            // Level 1
            let rec1 = ctx.parse_record()?;
            let a = rec1.parse_field("a")?;
            let ctx2 = rec1.flatten();

            // Level 2
            let rec2 = ctx2.parse_record()?;
            let b = rec2.parse_field("b")?;
            let c = rec2.parse_field("c")?;
            let ctx3 = rec2.flatten();

            // Level 3
            let rec3 = ctx3.parse_record()?;
            let d = rec3.parse_field("d")?;
            let e = rec3.parse_field("e")?;
            rec3.deny_unknown_fields()?;

            // Level 2 deny (no-op since child)
            rec2.deny_unknown_fields()?;

            // Level 1 deny (root - validates all)
            rec1.deny_unknown_fields()?;

            Ok(Self { a, b, c, d, e })
        }
    }

    #[test]
    fn test_nested_flatten_preserves_consumed_fields() {
        // Document: { a = 1, b = 2, c = 3, d = 4, e = 5 }
        //
        // Parsing structure:
        // Level 1: parse_record(), field(a), flatten() →
        //   Level 2: field(b), field(c), flatten() →
        //     Level 3: field(d), field(e), deny_unknown_fields()
        //   Level 2: deny_unknown_fields()
        // Level 1: deny_unknown_fields()
        //
        // Expected: All deny_unknown_fields() should succeed
        use crate::eure;

        let doc = eure!({ a = 1, b = 2, c = 3, d = 4, e = 5 });
        let result: ThreeLevelFlatten = doc.parse(doc.get_root_id()).unwrap();

        assert_eq!(
            result,
            ThreeLevelFlatten {
                a: 1,
                b: 2,
                c: 3,
                d: 4,
                e: 5
            }
        );
    }

    #[test]
    fn test_nested_flatten_catches_unaccessed_field() {
        // Document: { a = 1, b = 2, c = 3, d = 4, e = 5, f = 6 }
        //
        // Parsing structure (NOT accessing f):
        // Level 1: field(a), flatten() →
        //   Level 2: field(b), field(c), flatten() →
        //     Level 3: field(d), field(e), deny_unknown_fields()
        //   Level 2: deny_unknown_fields()
        // Level 1: deny_unknown_fields() <- Should FAIL because f is not accessed
        //
        // Expected: Level 1's deny_unknown_fields() should fail with UnknownField("f")
        use crate::eure;

        let doc = eure!({ a = 1, b = 2, c = 3, d = 4, e = 5, f = 6 });
        let result: Result<ThreeLevelFlatten, _> = doc.parse(doc.get_root_id());

        assert_eq!(
            result.unwrap_err().kind,
            ParseErrorKind::UnknownField("f".to_string())
        );
    }

    #[test]
    fn test_flatten_union_reverts_accessed_fields_on_failure() {
        use crate::eure;

        let doc = eure!({
            a = 1
            b = 2
            c = 3
            d = 4
        });

        // Define enum with two variants
        #[derive(Debug, PartialEq)]
        enum TestOption {
            A { a: i32, c: i32, e: i32 },
            B { a: i32, b: i32 },
        }

        impl<'doc> FromEure<'doc> for TestOption {
            type Error = ParseError;

            fn parse(ctx: &ParseContext<'doc>) -> Result<Self, Self::Error> {
                ctx.parse_union(VariantRepr::default())?
                    .variant("A", |ctx: &ParseContext<'_>| {
                        let rec = ctx.parse_record()?;
                        let a = rec.parse_field("a")?;
                        let c = rec.parse_field("c")?;
                        let e = rec.parse_field("e")?; // Will fail - field doesn't exist
                        rec.deny_unknown_fields()?;
                        Ok(TestOption::A { a, c, e })
                    })
                    .variant("B", |ctx: &ParseContext<'_>| {
                        let rec = ctx.parse_record()?;
                        let a = rec.parse_field("a")?;
                        let b = rec.parse_field("b")?;
                        rec.deny_unknown_fields()?;
                        Ok(TestOption::B { a, b })
                    })
                    .parse()
            }
        }

        // Parse with flatten
        let root_id = doc.get_root_id();
        let root_ctx = ParseContext::new(&doc, root_id);
        let record = root_ctx.parse_record().unwrap();

        // Parse union - should succeed with VariantB
        let option = record.flatten().parse::<TestOption>().unwrap();
        assert_eq!(option, TestOption::B { a: 1, b: 2 });

        // Access field d
        let d: i32 = record.parse_field("d").unwrap();
        assert_eq!(d, 4);

        // BUG: This should FAIL because field 'c' was never accessed by VariantB
        // (the successful variant), but it SUCCEEDS because VariantA tried 'c'
        // before failing
        let result = record.deny_unknown_fields();

        assert_eq!(
            result.unwrap_err(),
            ParseError {
                node_id: root_id,
                kind: ParseErrorKind::UnknownField("c".to_string()),
            }
        );
    }

    // =========================================================================
    // Tests for alternating flatten/flatten_ext scope changes
    // =========================================================================

    /// Tests alternating flatten -> flatten_ext -> flatten -> flatten_ext pattern
    #[derive(Debug, PartialEq)]
    struct AlternatingFlattenTest {
        normal1: i32,
        ext_normal2: i32,
        ext_normal3: i32,
        ext_content: String,
    }

    impl<'doc> FromEure<'doc> for AlternatingFlattenTest {
        type Error = ParseError;

        fn parse(ctx: &ParseContext<'doc>) -> Result<Self, Self::Error> {
            // Level 1: Record scope (flatten)
            let rec1 = ctx.parse_record()?;
            let normal1 = rec1.parse_field("normal")?;
            let ctx1 = rec1.flatten();

            // Level 2: Extension scope (flatten_ext)
            let ctx2 = ctx1.flatten_ext();
            assert_eq!(ctx2.parser_scope(), Some(ParserScope::Extension));
            let ext1_ctx = ctx2.ext("item")?;

            // Level 3: Record scope (flatten) - inside extension value
            let rec2 = ext1_ctx.parse_record()?;
            let ext_normal2 = rec2.parse_field("normal")?;
            let ctx3 = rec2.flatten();
            assert_eq!(ctx3.parser_scope(), Some(ParserScope::Record));

            // Level 4: Extension scope (flatten_ext)
            let ctx4 = ctx3.flatten_ext();
            assert_eq!(ctx4.parser_scope(), Some(ParserScope::Extension));
            let ext2_ctx = ctx4.ext("item")?;

            // Level 5: Record scope (flatten)
            let rec3 = ext2_ctx.parse_record()?;
            let ext_normal3 = rec3.parse_field("normal")?;
            let ctx5 = rec3.flatten();

            // Level 6: Extension scope (flatten_ext)
            let ctx6 = ctx5.flatten_ext();
            let ext3_ctx = ctx6.ext("item")?;

            // Innermost: Record
            let rec4 = ext3_ctx.parse_record()?;
            let ext_content = rec4.parse_field("content")?;

            // Deny at all levels
            rec4.deny_unknown_fields()?;
            ctx6.deny_unknown_extensions()?;
            rec3.deny_unknown_fields()?;
            ctx4.deny_unknown_extensions()?;
            rec2.deny_unknown_fields()?;
            ctx2.deny_unknown_extensions()?;
            rec1.deny_unknown_fields()?;
            ctx1.deny_unknown_extensions()?;

            Ok(Self {
                normal1,
                ext_normal2,
                ext_normal3,
                ext_content,
            })
        }
    }

    #[test]
    fn test_alternating_flatten_flatten_ext() {
        use crate::eure;

        let doc = eure!({
            normal = 1
            %item {
                normal = 2
                %item {
                    normal = 3
                    %item {
                        content = "Hello"
                    }
                }
            }
        });

        let result: AlternatingFlattenTest = doc.parse(doc.get_root_id()).unwrap();
        assert_eq!(
            result,
            AlternatingFlattenTest {
                normal1: 1,
                ext_normal2: 2,
                ext_normal3: 3,
                ext_content: "Hello".to_string(),
            }
        );
    }

    #[test]
    fn test_alternating_flatten_scope_changes() {
        use crate::eure;

        let doc = eure!({});
        let root_id = doc.get_root_id();
        let ctx = ParseContext::new(&doc, root_id);

        // flatten -> Record
        let ctx1 = ctx.flatten();
        assert_eq!(ctx1.parser_scope(), Some(ParserScope::Record));

        // flatten_ext -> Extension
        let ctx2 = ctx1.flatten_ext();
        assert_eq!(ctx2.parser_scope(), Some(ParserScope::Extension));

        // flatten -> Record (THIS IS THE BUG - currently stays Extension)
        let ctx3 = ctx2.flatten();
        assert_eq!(ctx3.parser_scope(), Some(ParserScope::Record));

        // flatten_ext -> Extension
        let ctx4 = ctx3.flatten_ext();
        assert_eq!(ctx4.parser_scope(), Some(ParserScope::Extension));
    }
}