rh_codegen/generators/

struct_generator.rs

//! Struct generation functionality
//!
//! This module handles the generation of Rust structs from FHIR StructureDefinitions.

use std::collections::HashMap;

use crate::config::CodegenConfig;
use crate::fhir_types::StructureDefinition;
use crate::generators::{DocumentationGenerator, FieldGenerator, TypeUtilities};
use crate::rust_types::{RustField, RustStruct, RustType};
use crate::value_sets::ValueSetManager;
use crate::{CodegenError, CodegenResult};

/// Struct generator for FHIR StructureDefinitions
pub struct StructGenerator<'a> {
    config: &'a CodegenConfig,
    type_cache: &'a mut HashMap<String, RustStruct>,
    value_set_manager: &'a mut ValueSetManager,
}

impl<'a> StructGenerator<'a> {
    /// Create a new struct generator
    pub fn new(
        config: &'a CodegenConfig,
        type_cache: &'a mut HashMap<String, RustStruct>,
        value_set_manager: &'a mut ValueSetManager,
    ) -> Self {
        Self {
            config,
            type_cache,
            value_set_manager,
        }
    }

    /// Generate a Rust struct from a FHIR StructureDefinition
    pub fn generate_struct(
        &mut self,
        structure_def: &StructureDefinition,
    ) -> CodegenResult<RustStruct> {
        // Skip LogicalModels as they are conceptual models, not implementable types
        if structure_def.kind == "logical" {
            return Err(CodegenError::Generation {
                message: format!(
                    "Skipping LogicalModel '{}' - logical models are not generated as Rust types",
                    structure_def.name
                ),
            });
        }

        // Skip sample/example profiles such as `example-composition`, but do not skip
        // real FHIR types whose names contain "Example" (for example, ExampleScenario).
        if TypeUtilities::is_example_structure_definition(structure_def) {
            return Err(CodegenError::Generation {
                message: format!(
                    "Skipping example StructureDefinition '{}'",
                    structure_def.name
                ),
            });
        }

        // Skip files that begin with underscore (auto-generated/temporary files)
        if TypeUtilities::should_skip_underscore_prefixed(structure_def) {
            return Err(CodegenError::Generation {
                message: format!(
                    "Skipping underscore-prefixed StructureDefinition '{}' - underscore prefixed files are ignored",
                    structure_def.name
                ),
            });
        }

        // Generate struct name from URL or ID, not the name field
        let struct_name = crate::naming::Naming::struct_name(structure_def);

        // Check if we've already generated this type
        if let Some(cached_struct) = self.type_cache.get(&struct_name) {
            return Ok(cached_struct.clone());
        }

        // Create the struct with enhanced documentation
        let mut rust_struct = RustStruct::new(struct_name.clone());
        rust_struct.doc_comment =
            DocumentationGenerator::generate_struct_documentation(structure_def);

        // Use config to determine derives
        let mut derives = vec!["Debug".to_string(), "Clone".to_string()];
        if self.config.with_serde {
            derives.extend(vec!["Serialize".to_string(), "Deserialize".to_string()]);
        }

        // Add Default derive for profiles since they only have a base field that implements Default
        // Check using TypeRegistry to see if this is a profile
        let is_profile = crate::generators::type_registry::TypeRegistry::is_profile(structure_def);
        if is_profile {
            derives.push("Default".to_string());
        }

        rust_struct.derives = derives;

        // Set the base definition for inheritance if present
        if let Some(base_def) = &structure_def.base_definition {
            rust_struct.base_definition = Some(
                base_def
                    .split('/')
                    .next_back()
                    .unwrap_or(base_def)
                    .to_string(),
            );
        }

        // Handle primitive types specially
        if structure_def.kind == "primitive-type" {
            return self.generate_primitive_type_struct(structure_def, rust_struct);
        }

        // Extract element definitions from differential only (preferred FHIR approach)
        let elements = if let Some(differential) = &structure_def.differential {
            &differential.element
        } else if let Some(snapshot) = &structure_def.snapshot {
            &snapshot.element
        } else {
            return Ok(rust_struct); // No elements to process
        };

        // Process each element definition to create struct fields and nested structs
        let mut nested_structs_info = HashMap::new();
        let mut direct_fields = Vec::new();

        for element in elements {
            // Skip the root element
            if element.path == structure_def.name || element.path == structure_def.base_type {
                continue;
            }

            // Only process elements that belong to this struct
            let base_path = &structure_def.name;
            if !element.path.starts_with(&format!("{base_path}.")) {
                continue;
            }

            let field_path = element
                .path
                .strip_prefix(&format!("{base_path}."))
                .unwrap_or_else(|| {
                    panic!(
                        "codegen bug: element path '{}' does not start with '{base_path}.'",
                        element.path
                    )
                });

            if field_path.contains('.') {
                // This is a nested field - collect it for nested struct generation
                let nested_field_name = field_path.split('.').next().unwrap_or_else(|| {
                    panic!(
                        "codegen bug: field path '{}' contains '.' but has no prefix segment",
                        field_path
                    )
                });
                nested_structs_info
                    .entry(nested_field_name.to_string())
                    .or_insert_with(Vec::new)
                    .push(element.clone());
            } else {
                // This is a direct field of this struct
                direct_fields.push(element.clone());
            }
        }

        // First pass: Generate nested structs for BackboneElements
        let mut nested_structs: Vec<_> = nested_structs_info.iter().collect();
        nested_structs.sort_by_key(|(left_name, _)| *left_name);

        for (nested_field_name, nested_elements) in nested_structs {
            if let Some(nested_struct) = self.generate_nested_struct(
                &struct_name,
                nested_field_name,
                nested_elements,
                structure_def,
            )? {
                // Store the nested struct in cache for later use
                self.type_cache
                    .insert(nested_struct.name.clone(), nested_struct.clone());

                // Register the nested struct in TypeRegistry with proper classification
                crate::generators::type_registry::TypeRegistry::register_type_classification_only(
                    &nested_struct.name,
                    crate::generators::type_registry::TypeClassification::NestedStructure {
                        parent_resource: struct_name.clone(),
                    },
                );
            }
        }

        // Second pass: Process direct fields (now nested structs are available)
        for element in direct_fields {
            let fields = self.create_fields_from_element(&element)?;
            for mut field in fields {
                // Apply Box wrapper for circular dependencies
                field.field_type =
                    Self::apply_box_for_circular_dependencies(field.field_type, &rust_struct.name);
                rust_struct.add_field(field);
            }
        }

        // Cache the generated struct for future use
        self.type_cache.insert(struct_name, rust_struct.clone());

        Ok(rust_struct)
    }

    /// Generate a primitive type struct with special FHIR primitive type semantics
    pub fn generate_primitive_type_struct(
        &mut self,
        structure_def: &StructureDefinition,
        mut rust_struct: RustStruct,
    ) -> CodegenResult<RustStruct> {
        // For primitive types, don't inherit from Element
        rust_struct.base_definition = None;

        // Map FHIR primitive types to Rust types
        let rust_primitive_type = match structure_def.name.as_str() {
            "boolean" => RustType::Boolean,
            "integer" | "positiveInt" | "unsignedInt" => RustType::Integer,
            "decimal" => RustType::Float,
            "string" | "code" | "id" | "markdown" | "uri" | "url" | "canonical" | "oid"
            | "uuid" | "base64Binary" | "xhtml" => RustType::String,
            "date" | "dateTime" | "time" | "instant" => RustType::String, // Could use chrono types later
            _ => RustType::String, // Default to String for unknown primitive types
        };

        // The primitive type is just a type alias or newtype wrapper around the Rust primitive
        // For now, we'll create a struct with a single `value` field
        let value_field = RustField::new("value".to_string(), rust_primitive_type);
        rust_struct.add_field(value_field);

        // Cache the generated struct for future use
        let struct_name = rust_struct.name.clone();
        self.type_cache.insert(struct_name, rust_struct.clone());

        Ok(rust_struct)
    }

    /// Generate a nested struct for BackboneElements
    pub fn generate_nested_struct(
        &mut self,
        parent_struct_name: &str,
        nested_field_name: &str,
        nested_elements: &[crate::fhir_types::ElementDefinition],
        parent_structure_def: &StructureDefinition,
    ) -> CodegenResult<Option<RustStruct>> {
        // Generate the nested struct name (e.g., BundleEntry, BundleLink)
        let nested_struct_name = format!(
            "{}{}",
            parent_struct_name,
            crate::naming::Naming::to_pascal_case(nested_field_name)
        );

        // Check if we've already generated this nested struct
        if self.type_cache.contains_key(&nested_struct_name) {
            return Ok(None);
        }

        // Create the nested struct
        let mut nested_struct = RustStruct::new(nested_struct_name.clone());

        // Add documentation
        nested_struct.doc_comment = Some(
            DocumentationGenerator::generate_nested_struct_documentation(
                parent_struct_name,
                nested_field_name,
            ),
        );

        // Use config to determine derives
        let mut derives = vec!["Debug".to_string(), "Clone".to_string()];
        if self.config.with_serde {
            derives.extend(vec!["Serialize".to_string(), "Deserialize".to_string()]);
        }
        nested_struct.derives = derives;

        // Set base as BackboneElement since these are typically BackboneElements
        nested_struct.base_definition = Some("BackboneElement".to_string());

        // Process the nested elements
        let base_path = format!("{}.{}", parent_structure_def.name, nested_field_name);
        let mut sub_nested_structs = HashMap::new();
        let mut direct_fields = Vec::new();

        for element in nested_elements {
            if !element.path.starts_with(&base_path) {
                continue;
            }

            // Skip the BackboneElement definition itself (where path == base_path)
            if element.path == base_path {
                continue;
            }

            let field_path = element
                .path
                .strip_prefix(&format!("{base_path}."))
                .unwrap_or_else(|| {
                    panic!(
                        "codegen bug: element path '{}' does not start with '{base_path}.'",
                        element.path
                    )
                });

            if field_path.contains('.') {
                // This is a sub-nested field - collect it for recursive nested struct generation
                let sub_nested_field_name = field_path.split('.').next().unwrap_or_else(|| {
                    panic!(
                        "codegen bug: field path '{}' contains '.' but has no prefix segment",
                        field_path
                    )
                });
                sub_nested_structs
                    .entry(sub_nested_field_name.to_string())
                    .or_insert_with(Vec::new)
                    .push(element.clone());
            } else {
                // Check if this direct field is itself a BackboneElement that needs a nested struct
                let is_backbone_element = element
                    .element_type
                    .as_ref()
                    .and_then(|types| types.first())
                    .and_then(|t| t.code.as_ref())
                    .map(|code| code == "BackboneElement")
                    .unwrap_or(false);

                if is_backbone_element {
                    // Treat this as a sub-nested struct even though it appears as a direct field
                    sub_nested_structs
                        .entry(field_path.to_string())
                        .or_insert_with(Vec::new)
                        .push(element.clone());
                } else {
                    // This is a direct field of this nested struct
                    direct_fields.push(element.clone());
                }
            }
        }

        // First, generate any sub-nested structs
        let mut sorted_sub_nested_structs: Vec<_> = sub_nested_structs.iter().collect();
        sorted_sub_nested_structs.sort_by_key(|(left_name, _)| *left_name);

        for (sub_nested_field_name, sub_nested_elements) in sorted_sub_nested_structs {
            // For recursive calls, we need to create a modified context
            // The base path for sub-nested structs should be the current nested struct's path
            let sub_nested_struct_name = format!(
                "{}{}",
                nested_struct_name,
                crate::naming::Naming::to_pascal_case(sub_nested_field_name)
            );

            if !self.type_cache.contains_key(&sub_nested_struct_name) {
                let mut sub_nested_struct = RustStruct::new(sub_nested_struct_name.clone());

                sub_nested_struct.doc_comment = Some(
                    DocumentationGenerator::generate_sub_nested_struct_documentation(
                        &nested_struct_name,
                        sub_nested_field_name,
                    ),
                );

                // Use config to determine derives
                let mut derives = vec!["Debug".to_string(), "Clone".to_string()];
                if self.config.with_serde {
                    derives.extend(vec!["Serialize".to_string(), "Deserialize".to_string()]);
                }
                sub_nested_struct.derives = derives;
                sub_nested_struct.base_definition = Some("BackboneElement".to_string());

                // Process the sub-nested elements with full recursive support
                let sub_base_path = format!("{base_path}.{sub_nested_field_name}");

                // Separate sub-nested elements into direct fields and further sub-nested structures
                let mut sub_direct_fields = Vec::new();
                let mut sub_sub_nested_structs: HashMap<
                    String,
                    Vec<crate::fhir_types::ElementDefinition>,
                > = HashMap::new();

                for element in sub_nested_elements {
                    if !element.path.starts_with(&sub_base_path) {
                        continue;
                    }

                    // Skip the BackboneElement definition itself (where path == base_path)
                    if element.path == sub_base_path {
                        continue;
                    }

                    let sub_field_path = element
                        .path
                        .strip_prefix(&format!("{sub_base_path}."))
                        .unwrap_or_else(|| {
                            panic!("codegen bug: element path '{}' does not start with '{sub_base_path}.'", element.path)
                        });

                    if sub_field_path.contains('.') {
                        // This is a further sub-nested field - collect it for recursive generation
                        let sub_sub_nested_field_name = sub_field_path.split('.').next().unwrap_or_else(|| {
                            panic!("codegen bug: field path '{}' contains '.' but has no prefix segment", sub_field_path)
                        });
                        sub_sub_nested_structs
                            .entry(sub_sub_nested_field_name.to_string())
                            .or_default()
                            .push(element.clone());
                    } else {
                        // Check if this direct field is itself a BackboneElement that needs a nested struct
                        let is_backbone_element = element
                            .element_type
                            .as_ref()
                            .and_then(|types| types.first())
                            .and_then(|t| t.code.as_ref())
                            .map(|code| code == "BackboneElement")
                            .unwrap_or(false);

                        if is_backbone_element {
                            // Treat this as a further sub-nested struct even though it appears as a direct field
                            sub_sub_nested_structs
                                .entry(sub_field_path.to_string())
                                .or_default()
                                .push(element.clone());
                        } else {
                            // This is a direct field of this sub-nested struct
                            sub_direct_fields.push(element.clone());
                        }
                    }
                }

                // First, recursively generate any further sub-nested structs
                let mut sorted_sub_sub_nested_structs: Vec<_> =
                    sub_sub_nested_structs.iter().collect();
                sorted_sub_sub_nested_structs.sort_by_key(|(left_name, _)| *left_name);

                for (sub_sub_nested_field_name, sub_sub_nested_elements) in
                    sorted_sub_sub_nested_structs
                {
                    self.generate_deeply_nested_struct(
                        &sub_nested_struct_name,
                        sub_sub_nested_field_name,
                        sub_sub_nested_elements,
                        &sub_base_path,
                    )?;
                }

                // Then, process direct fields (now further sub-nested structs are available)
                for element in sub_direct_fields {
                    let fields = self.create_fields_from_element(&element)?;
                    for field in fields {
                        sub_nested_struct.add_field(field);
                    }
                }

                // Store the sub-nested struct in cache
                self.type_cache
                    .insert(sub_nested_struct_name.clone(), sub_nested_struct);

                // Register the sub-nested struct in TypeRegistry with proper classification
                // Use the parent struct name (first level nested struct's parent is the resource)
                crate::generators::type_registry::TypeRegistry::register_type_classification_only(
                    &sub_nested_struct_name,
                    crate::generators::type_registry::TypeClassification::NestedStructure {
                        parent_resource: parent_struct_name.to_string(),
                    },
                );
            }

            // Now create a field in the parent struct that references this sub-nested struct
            // Find the BackboneElement definition for this field
            let backbone_element_def = sub_nested_elements
                .iter()
                .find(|e| e.path == format!("{base_path}.{sub_nested_field_name}"));

            if let Some(element) = backbone_element_def {
                let fields = self.create_fields_from_element(element)?;
                for field in fields {
                    nested_struct.add_field(field);
                }
            }
        }

        // Then, process direct fields (now sub-nested structs are available)
        for element in direct_fields {
            let fields = self.create_fields_from_element(&element)?;
            for field in fields {
                nested_struct.add_field(field);
            }
        }

        Ok(Some(nested_struct))
    }

    /// Recursively generate deeply nested structs (for arbitrary nesting levels)
    fn generate_deeply_nested_struct(
        &mut self,
        parent_nested_struct_name: &str,
        field_name: &str,
        elements: &[crate::fhir_types::ElementDefinition],
        parent_base_path: &str,
    ) -> CodegenResult<()> {
        let nested_struct_name = format!(
            "{}{}",
            parent_nested_struct_name,
            crate::naming::Naming::to_pascal_case(field_name)
        );

        if !self.type_cache.contains_key(&nested_struct_name) {
            let mut nested_struct = RustStruct::new(nested_struct_name.clone());

            nested_struct.doc_comment = Some(
                DocumentationGenerator::generate_sub_nested_struct_documentation(
                    parent_nested_struct_name,
                    field_name,
                ),
            );

            // Use config to determine derives
            let mut derives = vec!["Debug".to_string(), "Clone".to_string()];
            if self.config.with_serde {
                derives.extend(vec!["Serialize".to_string(), "Deserialize".to_string()]);
            }
            nested_struct.derives = derives;
            nested_struct.base_definition = Some("BackboneElement".to_string());

            // Process the nested elements with full recursive support
            let base_path = format!("{parent_base_path}.{field_name}");

            // Separate nested elements into direct fields and further nested structures
            let mut direct_fields = Vec::new();
            let mut sub_nested_structs: HashMap<String, Vec<crate::fhir_types::ElementDefinition>> =
                HashMap::new();

            for element in elements {
                if !element.path.starts_with(&base_path) {
                    continue;
                }

                // Skip the BackboneElement definition itself (where path == base_path)
                if element.path == base_path {
                    continue;
                }

                let field_path = element
                    .path
                    .strip_prefix(&format!("{base_path}."))
                    .unwrap_or_else(|| {
                        panic!(
                            "codegen bug: element path '{}' does not start with '{base_path}.'",
                            element.path
                        )
                    });

                if field_path.contains('.') {
                    // This is a further nested field - collect it for recursive generation
                    let sub_nested_field_name = field_path.split('.').next().unwrap_or_else(|| {
                        panic!(
                            "codegen bug: field path '{}' contains '.' but has no prefix segment",
                            field_path
                        )
                    });
                    sub_nested_structs
                        .entry(sub_nested_field_name.to_string())
                        .or_default()
                        .push(element.clone());
                } else {
                    // Check if this direct field is itself a BackboneElement that needs a nested struct
                    let is_backbone_element = element
                        .element_type
                        .as_ref()
                        .and_then(|types| types.first())
                        .and_then(|t| t.code.as_ref())
                        .map(|code| code == "BackboneElement")
                        .unwrap_or(false);

                    if is_backbone_element {
                        // Treat this as a further nested struct even though it appears as a direct field
                        sub_nested_structs
                            .entry(field_path.to_string())
                            .or_default()
                            .push(element.clone());
                    } else {
                        // This is a direct field of this nested struct
                        direct_fields.push(element.clone());
                    }
                }
            }

            // First, recursively generate any further nested structs
            let mut sorted_sub_nested_structs: Vec<_> = sub_nested_structs.iter().collect();
            sorted_sub_nested_structs.sort_by_key(|(left_name, _)| *left_name);

            for (sub_nested_field_name, sub_nested_elements) in sorted_sub_nested_structs {
                self.generate_deeply_nested_struct(
                    &nested_struct_name,
                    sub_nested_field_name,
                    sub_nested_elements,
                    &base_path,
                )?;
            }

            // Then, process direct fields (now further nested structs are available)
            for element in direct_fields {
                let fields = self.create_fields_from_element(&element)?;
                for field in fields {
                    nested_struct.add_field(field);
                }
            }

            // Store the nested struct in cache
            self.type_cache
                .insert(nested_struct_name.clone(), nested_struct);

            // Register the deeply nested struct in TypeRegistry with proper classification
            // Extract the root parent resource name (e.g., "MedicationKnowledge" from "MedicationKnowledgeAdministrationguidelinesDosage")
            let root_parent_resource = Self::extract_root_parent_resource(&nested_struct_name);
            crate::generators::type_registry::TypeRegistry::register_type_classification_only(
                &nested_struct_name,
                crate::generators::type_registry::TypeClassification::NestedStructure {
                    parent_resource: root_parent_resource,
                },
            );
        }

        Ok(())
    }

    /// Extract the root parent resource name from a deeply nested struct name
    /// For example: "MedicationKnowledgeAdministrationguidelinesDosage" -> "MedicationKnowledge"
    fn extract_root_parent_resource(nested_struct_name: &str) -> String {
        // Use the TypeRegistry's method for consistency
        crate::generators::type_registry::TypeRegistry::extract_parent_from_name(nested_struct_name)
            .unwrap_or_else(|| nested_struct_name.to_string())
    }

    /// Check if a field should use a nested struct type instead of BackboneElement
    pub fn should_use_nested_struct_type(
        &self,
        element: &crate::fhir_types::ElementDefinition,
        element_types: &[crate::fhir_types::ElementType],
    ) -> bool {
        // Check if this element is a BackboneElement and we have nested elements for it
        if let Some(first_type) = element_types.first() {
            if let Some(code) = &first_type.code {
                if code == "BackboneElement" {
                    // Extract parent struct name and field name from the path
                    let path_parts: Vec<&str> = element.path.split('.').collect();
                    if path_parts.len() >= 2 {
                        let _parent_name = path_parts[0];
                        let _field_name = path_parts[1];
                        // We would check here if we have nested elements for this field
                        // For now, always return true for BackboneElements
                        return true;
                    }
                }
            }
        }
        false
    }

    /// Create a RustField from an ElementDefinition
    pub fn create_field_from_element(
        &mut self,
        element: &crate::fhir_types::ElementDefinition,
    ) -> CodegenResult<Option<RustField>> {
        let mut field_generator =
            FieldGenerator::new(self.config, self.type_cache, self.value_set_manager);
        field_generator.create_field_from_element(element)
    }

    /// Create RustField(s) from an ElementDefinition (supports choice types)
    pub fn create_fields_from_element(
        &mut self,
        element: &crate::fhir_types::ElementDefinition,
    ) -> CodegenResult<Vec<RustField>> {
        let mut field_generator =
            FieldGenerator::new(self.config, self.type_cache, self.value_set_manager);
        field_generator.create_fields_from_element(element)
    }

    /// Apply `Box` wrapper to field types that form circular dependencies.
    ///
    /// FHIR's `Identifier.assigner` is `Reference`, and `Reference.identifier` is `Identifier`,
    /// forming a direct cycle. Rust structs cannot contain themselves (even indirectly) without
    /// indirection, so we wrap these cross-references in `Box<T>` to break the cycle.
    ///
    /// Currently the only known cycle is `Identifier ↔ Reference`. If future FHIR versions
    /// introduce additional cycles, add them to the `circular_dependencies` table below.
    ///
    /// The recursive handling of `Option<T>` and `Vec<T>` ensures that `Option<Box<Reference>>`
    /// and `Vec<Box<Reference>>` are emitted correctly rather than `Box<Option<Reference>>`.
    fn apply_box_for_circular_dependencies(
        field_type: RustType,
        current_struct_name: &str,
    ) -> RustType {
        // Known circular dependency pairs that need Box wrapping
        let circular_dependencies = [("Identifier", "Reference"), ("Reference", "Identifier")];

        // Check if we need to wrap this type in Box
        match &field_type {
            RustType::Custom(type_name) => {
                for (struct_a, struct_b) in &circular_dependencies {
                    if (current_struct_name == *struct_a && type_name == *struct_b)
                        || (current_struct_name == *struct_b && type_name == *struct_a)
                    {
                        return RustType::Box(Box::new(field_type));
                    }
                }
                field_type
            }
            RustType::Option(inner) => {
                let boxed_inner = Self::apply_box_for_circular_dependencies(
                    (**inner).clone(),
                    current_struct_name,
                );
                if let RustType::Box(_) = boxed_inner {
                    RustType::Option(Box::new(boxed_inner))
                } else {
                    field_type
                }
            }
            RustType::Vec(inner) => {
                let boxed_inner = Self::apply_box_for_circular_dependencies(
                    (**inner).clone(),
                    current_struct_name,
                );
                if let RustType::Box(_) = boxed_inner {
                    RustType::Vec(Box::new(boxed_inner))
                } else {
                    field_type
                }
            }
            _ => field_type,
        }
    }
}

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

    #[test]
    fn test_underscore_prefixed_structure_skipping() {
        let config = CodegenConfig::default();
        let mut type_cache = HashMap::new();
        let mut value_set_manager = ValueSetManager::new();
        let mut generator = StructGenerator::new(&config, &mut type_cache, &mut value_set_manager);

        // Test structure with underscore prefixed name
        let underscore_structure = StructureDefinition {
            resource_type: "StructureDefinition".to_string(),
            id: "normal-id".to_string(),
            url: "http://hl7.org/fhir/StructureDefinition/_11179object_class".to_string(),
            name: "_11179object_class".to_string(),
            title: Some("Auto-generated class".to_string()),
            status: "active".to_string(),
            kind: "resource".to_string(),
            is_abstract: false,
            description: Some("An auto-generated resource".to_string()),
            purpose: None,
            base_type: "DomainResource".to_string(),
            base_definition: Some(
                "http://hl7.org/fhir/StructureDefinition/DomainResource".to_string(),
            ),
            version: None,
            differential: None,
            snapshot: None,
        };

        // Test that underscore-prefixed structures are rejected
        let result = generator.generate_struct(&underscore_structure);
        assert!(result.is_err());

        if let Err(CodegenError::Generation { message }) = result {
            assert!(message.contains("underscore prefixed files are ignored"));
            assert!(message.contains("_11179object_class"));
        } else {
            panic!("Expected CodegenError::Generation for underscore-prefixed structure");
        }
    }
}