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// genson-core/src/schema/map_inference.rs
use crate::debug;
use crate::schema::core::SchemaInferenceConfig;
use serde_json::Value;
mod unification;
use unification::*;
/// Extract the non-null schema from a nullable schema, handling both old and new formats
fn extract_non_null_schema(schema: &Value) -> Value {
// Handle new format: {"type": ["null", "string"]}
if let Some(Value::Array(type_arr)) = schema.get("type") {
if type_arr.len() == 2 && type_arr.contains(&Value::String("null".into())) {
let non_null_type = type_arr
.iter()
.find(|t| *t != &Value::String("null".into()))
.unwrap();
// Create a new schema with the non-null type, preserving other properties
let mut non_null_schema = schema.clone();
non_null_schema
.as_object_mut()
.unwrap()
.insert("type".to_string(), non_null_type.clone());
return non_null_schema;
}
}
// Handle old legacy format: ["null", {"type": "string"}]
if let Value::Array(arr) = schema {
if arr.len() == 2 && arr.contains(&Value::String("null".to_string())) {
let non_null_schema = arr
.iter()
.find(|v| *v != &Value::String("null".to_string()))
.unwrap();
return non_null_schema.clone();
}
}
// Not a nullable schema, return as-is
schema.clone()
}
fn contains_anyof(value: &Value) -> bool {
match value {
Value::Object(obj) => {
if obj.contains_key("anyOf") {
return true;
}
obj.values().any(contains_anyof)
}
Value::Array(arr) => arr.iter().any(contains_anyof),
_ => false,
}
}
/// Post-process an inferred JSON Schema to rewrite certain object shapes as maps.
///
/// This mutates the schema in place, applying user overrides and heuristics.
///
/// # Rules
/// - If the current field name matches a `force_field_types` override, that wins
/// (`"map"` rewrites to `additionalProperties`, `"record"` leaves as-is).
/// - Otherwise, applies map inference heuristics based on:
/// - Total key cardinality (`map_threshold`)
/// - Required key cardinality (`map_max_required_keys`)
/// - Value homogeneity (all values must be homogeneous) OR
/// - Value unifiability (compatible record schemas when `unify_maps` enabled)
/// - Recurses into nested objects/arrays, carrying field names down so overrides apply.
pub(crate) fn rewrite_objects(
schema: &mut Value,
field_name: Option<&str>,
config: &SchemaInferenceConfig,
is_root: bool,
) {
if let Value::Object(obj) = schema {
// --- Forced overrides by field name ---
if let Some(name) = field_name {
if let Some(forced) = config.force_field_types.get(name) {
match forced.as_str() {
"map" => {
obj.remove("properties");
obj.remove("required");
obj.insert(
"additionalProperties".to_string(),
serde_json::json!({ "type": "string" }),
);
return; // no need to apply heuristics or recurse
}
"record" => {
if let Some(props) =
obj.get_mut("properties").and_then(|p| p.as_object_mut())
{
for (k, v) in props {
rewrite_objects(v, Some(k), config, false);
}
}
if let Some(items) = obj.get_mut("items") {
rewrite_objects(items, None, config, false);
}
return;
}
_ => {}
}
}
}
// --- Handle anyOf unions ---
if let Some(Value::Array(any_of_schemas)) = obj.get("anyOf") {
if config.unify_maps {
debug!(
config,
"Found anyOf union with {} schemas, attempting unification",
any_of_schemas.len()
);
if let Some(unified) =
unify_anyof_schemas(any_of_schemas, field_name.unwrap_or(""), config)
{
debug!(config, "Successfully unified anyOf schemas");
// Replace the entire schema with the unified result
*schema = unified;
// Recurse into the unified schema to apply further processing
rewrite_objects(schema, field_name, config, is_root);
return;
} else {
debug!(config, "Failed to unify anyOf schemas, leaving as-is");
}
}
// If unification disabled or failed, still recurse into each anyOf branch
if let Some(any_of_array) = obj.get_mut("anyOf").and_then(|a| a.as_array_mut()) {
for any_of_schema in any_of_array {
rewrite_objects(any_of_schema, field_name, config, false);
}
}
}
// --- Heuristic rewrite ---
if let Some(props) = obj.get("properties").and_then(|p| p.as_object()) {
let key_count = props.len(); // |UK| - total keys observed
let above_threshold = key_count >= config.map_threshold;
// Copy out child schema shapes
let child_schemas: Vec<Value> = props.values().cloned().collect();
// Detect map-of-records only if:
// - all children are identical
// - and that child is itself an object with "properties" (i.e. a proper record)
if above_threshold {
if let Some(first) = child_schemas.first() {
if first.get("type") == Some(&Value::String("object".into()))
&& first.get("properties").is_some()
&& child_schemas.len() > 1
{
let all_same = child_schemas.iter().all(|other| other == first);
if all_same {
obj.remove("properties");
obj.remove("required");
obj.insert("additionalProperties".to_string(), first.clone());
return;
}
}
}
}
// Calculate required key count |RK|
let required_key_count = obj
.get("required")
.and_then(|r| r.as_array())
.map(|r| r.len())
.unwrap_or(0);
// Check for unifiable schemas
let mut unified_schema: Option<Value> = None;
if let Some(first_schema) = props.values().next() {
// Normalise all schemas for comparison
let normalised_schemas: Vec<Value> =
props.values().map(extract_non_null_schema).collect();
let first_normalised = extract_non_null_schema(first_schema);
// Debug output to diagnose the issue
if config.debug {
debug!(
config,
"Checking homogeneity for field {:?} with {} schemas",
field_name.unwrap_or("root"),
normalised_schemas.len()
);
let mut unique_schemas = std::collections::BTreeSet::new();
for schema in &normalised_schemas {
unique_schemas.insert(serde_json::to_string(schema).unwrap_or_default());
}
if unique_schemas.len() <= 3 {
// Only show details for small sets
debug!(
config,
"Unique normalised schemas ({} total):",
unique_schemas.len()
);
for (i, schema_str) in unique_schemas.iter().enumerate() {
if schema_str.len() > 300 {
// Parse back to Value and pretty-print
if let Ok(schema_value) = serde_json::from_str::<Value>(schema_str)
{
let pretty_schema = serde_json::to_string_pretty(&schema_value)
.unwrap_or_default();
let lines: Vec<&str> = pretty_schema.lines().collect();
if lines.len() > 12 {
let first_6 = lines[..6].join("\n");
let last_6 = lines[lines.len() - 6..].join("\n");
debug!(
config,
" Schema {}:\n{}\n...({} lines omitted)...\n{}",
i,
first_6,
lines.len() - 12,
last_6
);
} else {
debug!(config, " Schema {}:\n{}", i, pretty_schema);
}
} else {
debug!(config, " Schema {}: [invalid JSON]", i);
}
} else {
debug!(config, " Schema {}: {}", i, schema_str);
}
}
} else {
debug!(
config,
"Found {} unique normalised schemas (too many to display)",
unique_schemas.len()
);
}
}
if normalised_schemas
.iter()
.all(|schema| schema == &first_normalised)
{
// All schemas are homogeneous after normalisation
debug!(config, "Schemas are homogeneous after normalisation");
unified_schema = Some(first_normalised);
} else if config.unify_maps {
debug!(config, "Schemas not homogeneous, attempting unification");
// Detect if these are all arrays of records
if child_schemas
.iter()
.all(|s| s.get("type") == Some(&Value::String("array".into())))
{
// Collect item schemas, short-circuit if any missing
let mut item_schemas = Vec::with_capacity(child_schemas.len());
let mut all_items_ok = true;
for s in &child_schemas {
if let Some(items) = s.get("items") {
item_schemas.push(items.clone());
} else {
all_items_ok = false;
break;
}
}
if all_items_ok {
if let Some(unified_items) = check_unifiable_schemas(
&item_schemas,
field_name.unwrap_or(""),
config,
) {
unified_schema = Some(serde_json::json!({
"type": "array",
"items": unified_items
}));
}
}
} else {
// NEW: Only try record unification if unify_maps is enabled and above threshold
// This ensures we only do expensive unification when it would result in map conversion
if above_threshold {
unified_schema = check_unifiable_schemas(
&child_schemas,
field_name.unwrap_or(""),
config,
);
}
}
}
}
// Apply map inference logic
let should_be_map = if above_threshold && unified_schema.is_some() {
debug!(
config,
"Checking if should convert to map: above_threshold=true, unified_schema=Some",
);
// Don't convert to map if the unified schema contains anyOf - let it be processed first
if unified_schema.as_ref().is_some_and(contains_anyof) {
debug!(config, "Not converting to map: unified schema contains anyOf that needs processing");
false
// Skip map inference if this is the root and no_root_map is enabled
} else if is_root && config.no_root_map {
debug!(
config,
"Skipping map conversion: is root and no_root_map=true"
);
false
} else if let Some(max_required) = config.map_max_required_keys {
let result = required_key_count <= max_required;
debug!(
config,
"Map conversion decision: required_keys={} <= max_required={} = {}",
required_key_count,
max_required,
result
);
result
} else {
debug!(
config,
"Map conversion: no max_required_keys limit, converting to map"
);
true
}
} else {
if !above_threshold {
debug!(
config,
"Not converting to map: below threshold ({} < {})",
key_count,
config.map_threshold
);
} else if unified_schema.is_none() {
debug!(config, "Not converting to map: no unified schema");
}
false
};
if should_be_map {
if let Some(schema) = unified_schema {
let pretty_schema = serde_json::to_string_pretty(&schema).unwrap_or_default();
let lines: Vec<&str> = pretty_schema.lines().collect();
if lines.len() > 12 {
let first_6 = lines[..6].join("\n");
let last_6 = lines[lines.len() - 6..].join("\n");
debug!(config, "Converting field {:?} to map with schema:\n{}\n...({} lines omitted)...\n{}",
field_name.unwrap_or("root"), first_6, lines.len() - 12, last_6);
} else {
debug!(
config,
"Converting field {:?} to map with schema:\n{}",
field_name.unwrap_or("root"),
pretty_schema
);
}
obj.remove("properties");
obj.remove("required");
obj.insert("type".to_string(), Value::String("object".to_string()));
// Process the schema being moved to additionalProperties for nested anyOf
let mut processed_schema = schema.clone();
rewrite_objects(&mut processed_schema, None, config, false);
obj.insert("additionalProperties".to_string(), processed_schema);
return;
}
}
}
// --- Recurse into nested values ---
if let Some(props) = obj.get_mut("properties").and_then(|p| p.as_object_mut()) {
for (k, v) in props {
rewrite_objects(v, Some(k), config, false);
}
}
if let Some(items) = obj.get_mut("items") {
rewrite_objects(items, None, config, false);
}
for v in obj.values_mut() {
rewrite_objects(v, None, config, false);
}
} else if let Value::Array(arr) = schema {
for v in arr {
rewrite_objects(v, None, config, false);
}
}
}