import type * as core from "../core/index.js";
import type * as JSONSchema from "./json-schema.js";
import { type $ZodRegistry, globalRegistry } from "./registries.js";
import type * as schemas from "./schemas.js";
import type { StandardJSONSchemaV1, StandardSchemaWithJSONProps } from "./standard-schema.js";
import { assignProp } from "./util.js";

function assignProps<T extends object>(target: T, ...sources: object[]): T {
  for (const source of sources) {
    for (const key of Reflect.ownKeys(source)) {
      if (Object.prototype.propertyIsEnumerable.call(source, key)) {
        assignProp(target, key, (source as any)[key]);
      }
    }
  }
  return target;
}

export type Processor<T extends schemas.$ZodType = schemas.$ZodType> = (
  schema: T,
  ctx: ToJSONSchemaContext,
  json: JSONSchema.BaseSchema,
  params: ProcessParams
) => void;

/**
 * Called for each schema that has no JSON Schema equivalent. Return a JSON Schema to use in its
 * place, `"any"` to fall back to the `unrepresentable: "any"` behavior, or `"throw"`/`undefined` to
 * throw the default error. Throwing from the handler propagates, so custom errors work too.
 */
export type UnrepresentableHandler<T extends schemas.$ZodType = schemas.$ZodType> = (ctx: {
  zodSchema: T;
  path: (string | number)[];
  /** The error Zod would throw. Distinguishes sites that share a `zodSchema`, e.g. an `undefined`
   *  vs a `bigint` member of the same literal. */
  message: string;
}) => JSONSchema.BaseSchema | "throw" | "any" | undefined;

export interface JSONSchemaGeneratorParams {
  processors: Record<string, Processor>;
  /** A registry used to look up metadata for each schema. Any schema with an `id` property will be extracted as a $def.
   *  @default globalRegistry */
  metadata?: $ZodRegistry<Record<string, any>>;
  /** The JSON Schema version to target.
   * - `"draft-2020-12"` — Default. JSON Schema Draft 2020-12
   * - `"draft-07"` — JSON Schema Draft 7
   * - `"draft-04"` — JSON Schema Draft 4
   * - `"openapi-3.0"` — OpenAPI 3.0 Schema Object */
  target?: "draft-04" | "draft-07" | "draft-2020-12" | "openapi-3.0" | ({} & string) | undefined;
  /** How to handle unrepresentable types.
   * - `"throw"` — Default. Unrepresentable types throw an error
   * - `"any"` — Unrepresentable types become `{}`
   * - A function — called once per unrepresentable schema; see {@link UnrepresentableHandler}. */
  unrepresentable?: "throw" | "any" | UnrepresentableHandler<schemas.$ZodTypes>;
  /** Arbitrary custom logic that can be used to modify the generated JSON Schema. */
  override?: (ctx: {
    zodSchema: schemas.$ZodTypes;
    jsonSchema: JSONSchema.BaseSchema;
    path: (string | number)[];
  }) => void;
  /** Whether to extract the `"input"` or `"output"` type. Relevant to transforms, defaults, coerced primitives, etc.
   * - `"output"` — Default. Convert the output schema.
   * - `"input"` — Convert the input schema. */
  io?: "input" | "output";
  cycles?: "ref" | "throw";
  reused?: "ref" | "inline";
  external?:
    | {
        registry: $ZodRegistry<{ id?: string | undefined }>;
        uri?: ((id: string) => string) | undefined;
        defs: Record<string, JSONSchema.BaseSchema>;
      }
    | undefined;
}

/**
 * Parameters for the toJSONSchema function.
 */
export type ToJSONSchemaParams = Omit<JSONSchemaGeneratorParams, "processors" | "external">;

/**
 * Parameters for the toJSONSchema function when passing a registry.
 */
export interface RegistryToJSONSchemaParams extends ToJSONSchemaParams {
  uri?: (id: string) => string;
}

export interface ProcessParams {
  schemaPath: schemas.$ZodType[];
  path: (string | number)[];
}

export interface Seen {
  /** JSON Schema result for this Zod schema */
  schema: JSONSchema.BaseSchema;
  /** A cached version of the schema that doesn't get overwritten during ref resolution */
  def?: JSONSchema.BaseSchema;
  defId?: string | undefined;
  /** Number of times this schema was encountered during traversal */
  count: number;
  /** Cycle path */
  cycle?: (string | number)[] | undefined;
  isParent?: boolean | undefined;
  /** Schema to inherit JSON Schema properties from (set by processor for wrappers) */
  ref?: schemas.$ZodType | null;
  /** JSON Schema property path for this schema */
  path?: (string | number)[] | undefined;
}

export interface ToJSONSchemaContext {
  processors: Record<string, Processor>;
  metadataRegistry: $ZodRegistry<Record<string, any>>;
  target: "draft-04" | "draft-07" | "draft-2020-12" | "openapi-3.0" | ({} & string);
  // must be schemas.$ZodType to prevent recursive type resolution error
  unrepresentable: "throw" | "any" | UnrepresentableHandler;
  override: (ctx: {
    // must be schemas.$ZodType to prevent recursive type resolution error
    zodSchema: schemas.$ZodType;
    jsonSchema: JSONSchema.BaseSchema;
    path: (string | number)[];
  }) => void;
  io: "input" | "output";
  counter: number;
  seen: Map<schemas.$ZodType, Seen>;
  /** Registry conversions share one `seen` map across every emitted schema. These hold the
   * `external` the whole-map passes below last ran for, so the passes are not repeated once per
   * schema — and still re-run if the map grows or `external` is swapped. `sharedEmitDoneFor`
   * covers both passes in `finalize`: the ref flattening and the `$defs` build.
   *
   * The passes are valid only while nothing they read has changed, so both are cleared in
   * `processSchema()` when the map grows, and in `JSONSchemaGenerator.emit()`, which can also change
   * the `cycles` and `reused` they branch on.
   *
   * One case is deliberately not covered: an `override` callback that writes to
   * `metadataRegistry` mid-conversion. It runs inside `finalize`, so a registry conversion has
   * nowhere left to clear the guards, and later schemas keep the ids the first pass saw. That
   * output was never coherent — before this, whether a shared subschema was inlined or extracted
   * depended on which registry entry happened to be emitted when the callback fired. */
  sharedDefsExtractedFor?: ToJSONSchemaContext["external"];
  sharedEmitDoneFor?: ToJSONSchemaContext["external"];
  cycles: "ref" | "throw";
  reused: "ref" | "inline";
  /** The `allOf` array of each intersection encountered during traversal, innermost first. `finalize` folds every emitted object holding one; see `foldIntersection`. */
  intersections: JSONSchema.BaseSchema[][];
  /** Rewrites a processor deferred to `finalize`, where the flatten has resolved every ref and the union branches are in place. */
  deferred: (() => void)[];
  external?:
    | {
        registry: $ZodRegistry<{ id?: string | undefined }>;
        uri?: ((id: string) => string) | undefined;
        defs: Record<string, JSONSchema.BaseSchema>;
      }
    | undefined;
}

// function initializeContext<T extends schemas.$ZodType>(inputs: JSONSchemaGeneratorParams<T>): ToJSONSchemaContext<T> {
//   return {
//     processor: inputs.processor,
//     metadataRegistry: inputs.metadata ?? globalRegistry,
//     target: inputs.target ?? "draft-2020-12",
//     unrepresentable: inputs.unrepresentable ?? "throw",
//   };
// }

export function initializeContext(params: JSONSchemaGeneratorParams): ToJSONSchemaContext {
  // Normalize target: convert old non-hyphenated versions to hyphenated versions
  let target: ToJSONSchemaContext["target"] = params?.target ?? "draft-2020-12";
  if (target === "draft-4") target = "draft-04";
  if (target === "draft-7") target = "draft-07";

  return {
    processors: params.processors ?? {},
    metadataRegistry: params?.metadata ?? globalRegistry,
    target,
    unrepresentable: (params?.unrepresentable as ToJSONSchemaContext["unrepresentable"]) ?? "throw",
    override: (params?.override as any) ?? (() => {}),
    io: params?.io ?? "output",
    counter: 0,
    seen: new Map(),
    sharedDefsExtractedFor: undefined,
    sharedEmitDoneFor: undefined,
    cycles: params?.cycles ?? "ref",
    reused: params?.reused ?? "inline",
    intersections: [],
    deferred: [],
    external: params?.external ?? undefined,
  };
}

/**
 * Applies the `unrepresentable` setting at a site that has no JSON Schema equivalent. Throws
 * `message` unless the setting (or the handler's return value) says otherwise. Returns `true` if a
 * custom JSON Schema was written into `json`, in which case the caller must not write its own.
 */
export function handleUnrepresentable(
  schema: schemas.$ZodType,
  ctx: ToJSONSchemaContext,
  json: JSONSchema.BaseSchema,
  params: ProcessParams,
  message: string
): boolean {
  const result =
    typeof ctx.unrepresentable === "function"
      ? ctx.unrepresentable({ zodSchema: schema, path: params.path, message })
      : ctx.unrepresentable;
  if (result === "any") return false;
  if (result === undefined || result === "throw") throw new Error(message);
  Object.assign(json, result);
  return true;
}

// never rename this back to `process`: bundler polyfills inject a top-level `const process` that a lexical declaration of the same name collides with (#6397)
export function processSchema<T extends schemas.$ZodType>(
  schema: T,
  ctx: ToJSONSchemaContext,
  _params: ProcessParams = { path: [], schemaPath: [] }
): JSONSchema.BaseSchema {
  const def = schema._zod.def as schemas.$ZodTypes["_zod"]["def"];

  // check for schema in seens
  const seen = ctx.seen.get(schema);

  if (seen) {
    seen.count++;

    // check if cycle
    const isCycle = _params.schemaPath.includes(schema);
    if (isCycle) {
      seen.cycle = _params.path;
    }

    return seen.schema;
  }

  // initialize
  const result: Seen = { schema: {}, count: 1, cycle: undefined, path: _params.path };
  ctx.seen.set(schema, result);
  ctx.sharedDefsExtractedFor = undefined;
  ctx.sharedEmitDoneFor = undefined;

  // custom method overrides default behavior
  const overrideSchema = schema._zod.toJSONSchema?.();
  if (overrideSchema) {
    result.schema = overrideSchema as any;
  } else {
    const params = {
      ..._params,
      schemaPath: [..._params.schemaPath, schema],
      path: _params.path,
    };

    if (schema._zod.processJSONSchema) {
      schema._zod.processJSONSchema(ctx, result.schema, params);
    } else {
      const _json = result.schema;
      const processor = ctx.processors[def.type];
      if (!processor) {
        throw new Error(`[toJSONSchema]: Non-representable type encountered: ${def.type}`);
      }
      processor(schema, ctx, _json, params);
    }

    const parent = schema._zod.parent as T;

    if (parent) {
      // Also set ref if processor didn't (for inheritance)
      if (!result.ref) result.ref = parent;
      processSchema(parent, ctx, params);
      ctx.seen.get(parent)!.isParent = true;
    }
  }

  // metadata
  const meta = ctx.metadataRegistry.get(schema);
  if (meta) assignProps(result.schema, meta);

  if (ctx.io === "input" && isTransforming(schema)) {
    // examples/defaults only apply to output type of pipe
    delete result.schema.examples;
    delete result.schema.default;
  }

  // set prefault as default
  if (ctx.io === "input" && "_prefault" in result.schema) result.schema.default ??= result.schema._prefault;
  delete result.schema._prefault;

  // pulling fresh from ctx.seen in case it was overwritten
  const _result = ctx.seen.get(schema)!;

  return _result.schema;
}

/** @deprecated Renamed to `processSchema`. An export alias declares no binding, so it is safe to keep. */
export { processSchema as process };

// Escape a reference token for use in a JSON Pointer fragment (RFC 6901): `~` becomes `~0` and `/` becomes `~1`. The `~` replacement must run first.
function encodeJSONPointerSegment(segment: string): string {
  return segment.replace(/~/g, "~0").replace(/\//g, "~1");
}

export function extractDefs<T extends schemas.$ZodType>(
  ctx: ToJSONSchemaContext,
  schema: T
  // params: EmitParams
): void {
  // iterate over seen map;
  const root = ctx.seen.get(schema);

  if (!root) throw new Error("Unprocessed schema. This is a bug in Zod.");

  // With `external` set, every registered schema resolves through the external branch of `makeURI`, so the root branch below produces the same ref the external branch would — this pass is identical whichever schema it is called with, and only needs to run once.
  if (ctx.external && ctx.sharedDefsExtractedFor === ctx.external) return;

  // Track ids to detect duplicates across different schemas
  const idToSchema = new Map<string, schemas.$ZodType>();
  for (const entry of ctx.seen.entries()) {
    const id = ctx.metadataRegistry.get(entry[0])?.id;
    if (id) {
      const existing = idToSchema.get(id);
      if (existing && existing !== entry[0]) {
        throw new Error(
          `Duplicate schema id "${id}" detected during JSON Schema conversion. Two different schemas cannot share the same id when converted together.`
        );
      }
      idToSchema.set(id, entry[0]);
    }
  }

  // returns a ref to the schema defId will be empty if the ref points to an external schema (or #)
  const makeURI = (entry: [schemas.$ZodType<unknown, unknown>, Seen]): { ref: string; defId?: string } => {
    // comparing the seen objects because sometimes multiple schemas map to the same seen object. e.g. lazy

    // external is configured
    const defsSegment = ctx.target === "draft-2020-12" ? "$defs" : "definitions";
    if (ctx.external) {
      const externalId = ctx.external.registry.get(entry[0])?.id; // ?? "__shared";// `__schema${ctx.counter++}`;

      // check if schema is in the external registry
      const uriGenerator = ctx.external.uri ?? ((id: string) => id);
      if (externalId) {
        return { ref: uriGenerator(externalId) };
      }

      // otherwise, add to __shared
      const id: string = entry[1].defId ?? (entry[1].schema.id as string) ?? `schema${ctx.counter++}`;
      entry[1].defId = id; // set defId so it will be reused if needed
      return { defId: id, ref: `${uriGenerator("__shared")}#/${defsSegment}/${encodeJSONPointerSegment(id)}` };
    }

    const uriPrefix = `#`;
    const defUriPrefix = `${uriPrefix}/${defsSegment}/`;

    // an id-less root has nowhere to be extracted to, so it stays inline and self-references as `#`
    if (entry[1] === root && !entry[1].schema.id) {
      return { ref: uriPrefix };
    }

    // self-contained schema
    const defId = entry[1].schema.id ?? `__schema${ctx.counter++}`;
    return { defId, ref: defUriPrefix + encodeJSONPointerSegment(defId) };
  };

  // stored cached version in `def` property remove all properties, set $ref
  const extractToDef = (entry: [schemas.$ZodType<unknown, unknown>, Seen]): void => {
    // if the schema is already a reference, do not extract it
    if (entry[1].schema.$ref) {
      return;
    }
    const seen = entry[1];
    const { ref, defId } = makeURI(entry);

    seen.def = { ...seen.schema };
    // defId won't be set if the schema is a reference to an external schema or if the schema is the root schema
    if (defId) seen.defId = defId;
    // wipe away all properties except $ref
    const schema = seen.schema;
    for (const key in schema) {
      delete schema[key];
    }
    schema.$ref = ref;
  };

  // throw on cycles

  // break cycles
  if (ctx.cycles === "throw") {
    for (const entry of ctx.seen.entries()) {
      const seen = entry[1];
      if (seen.cycle) {
        throw new Error(
          "Cycle detected: " +
            `#/${seen.cycle?.join("/")}/<root>` +
            '\n\nSet the `cycles` parameter to `"ref"` to resolve cyclical schemas with defs.'
        );
      }
    }
  }

  // extract schemas into $defs
  for (const entry of ctx.seen.entries()) {
    const seen = entry[1];

    // convert root schema to # $ref
    if (schema === entry[0]) {
      extractToDef(entry); // this has special handling for the root schema
      continue;
    }

    // extract schemas that are in the external registry
    if (ctx.external) {
      const ext = ctx.external.registry.get(entry[0])?.id;
      if (schema !== entry[0] && ext) {
        extractToDef(entry);
        continue;
      }
    }

    // extract schemas with `id` meta
    const id = ctx.metadataRegistry.get(entry[0])?.id;
    if (id) {
      extractToDef(entry);
      continue;
    }

    // break cycles
    if (seen.cycle) {
      // any
      extractToDef(entry);
      continue;
    }

    // extract reused schemas
    if (seen.count > 1) {
      if (ctx.reused === "ref") {
        extractToDef(entry);
      }
    }
  }

  if (ctx.external) ctx.sharedDefsExtractedFor = ctx.external;
}

/** Rewrites `anyOf: [{type: "a"}, {type: "b"}]` to `type: ["a", "b"]`, which every JSON Schema draft treats as equivalent and most consumers render far better for the nullable case. Only branches that are a bare type assertion qualify — anything carrying a constraint, `$ref`, `const` or metadata is left alone. Runs after `flattenRef`, so a branch an override decorated or `$defs` extraction turned into a `$ref` is no longer bare and correctly stays in `anyOf`. `oneOf` is excluded: `integer` and `number` overlap, so "exactly one" and "at least one" are not the same there. OpenAPI 3.0 is excluded: its `type` must be a single string. */
function compactTypeUnion(schema: JSONSchema.BaseSchema): void {
  const options = schema.anyOf;
  if (!Array.isArray(options) || options.length === 0 || schema.type !== undefined) return;

  const types: JSONSchema.SchemaType[] = [];
  for (const option of options) {
    if (!option || typeof option !== "object") return;
    // A branch that is itself a compactible union folds into this one — nested `anyOf` and a flat `type` array say the same thing. Compacting it first also makes the result independent of the order this pass walks the seen map in.
    compactTypeUnion(option as JSONSchema.BaseSchema);
    const keys = Object.keys(option);
    if (keys.length !== 1 || keys[0] !== "type") return;
    const type = (option as JSONSchema.BaseSchema).type;
    for (const member of Array.isArray(type) ? type : [type]) {
      if (typeof member !== "string") return;
      if (!types.includes(member)) types.push(member);
    }
  }

  delete schema.anyOf;
  // A `type` array must be non-empty and unique (metaschema); a single member is spelled as a bare string.
  schema.type = types.length === 1 ? types[0] : types;
}

/** Keywords `foldIntersection` knows how to combine. Anything else — `$ref`, `patternProperties`,
 * an annotation like `description` — makes a member unfoldable, so a constraint this does not
 * understand leaves the `allOf` alone instead of being silently dropped or misattributed. */
const FOLDABLE_KEYS = new Set(["type", "properties", "required", "additionalProperties"]);
const UNION_KEYS = ["oneOf", "anyOf"] as const;

/** A member's constraint on a key it does not declare itself. A `catchall` states one; `false`, an absent `additionalProperties`, and the empty schema a loose object emits state nothing. */
function undeclaredConstraint(member: JSONSchema.ObjectSchema): JSONSchema.BaseSchema | null {
  const extra = member.additionalProperties;
  if (extra === undefined || extra === false || typeof extra !== "object" || extra === null) return null;
  return Object.keys(extra).length ? (extra as JSONSchema.BaseSchema) : null;
}

/** Combines object members into the single object they describe together, or returns `null` if any of them carries a keyword outside {@link FOLDABLE_KEYS}. */
function foldObjects(members: JSONSchema._JSONSchema[]): JSONSchema.ObjectSchema | null {
  const objects: JSONSchema.ObjectSchema[] = [];
  for (const member of members) {
    // A boolean subschema is legal JSON Schema and carries no keywords to fold.
    if (typeof member !== "object" || member.type !== "object") return null;
    for (const key in member) {
      if (!FOLDABLE_KEYS.has(key)) return null;
    }
    objects.push(member as JSONSchema.ObjectSchema);
  }

  const properties: Record<string, JSONSchema._JSONSchema> = {};
  const required = new Set<string>();
  for (const object of objects) {
    for (const key in object.properties) {
      // `in` would report a `__proto__` key as already present via the prototype chain and skip it.
      if (Object.prototype.hasOwnProperty.call(properties, key)) continue;
      // Every member constrains this key: the ones that declare it say how, and a `catchall` member constrains it too even though it does not name it. The key has to satisfy all of them, which is the same intersection one level down.
      const parts: JSONSchema._JSONSchema[] = [];
      for (const other of objects) {
        const part = other.properties?.[key] ?? undeclaredConstraint(other);
        if (part === null || part === undefined) continue;
        if (!parts.some((seen) => JSON.stringify(seen) === JSON.stringify(part))) parts.push(part);
      }
      const merged =
        parts.length === 1
          ? parts[0]!
          : (foldObjects(parts) ?? ({ allOf: parts as JSONSchema.BaseSchema[] } as JSONSchema.BaseSchema));
      assignProp(properties, key, merged);
    }
    for (const key of object.required ?? []) required.add(key);
  }

  const folded: JSONSchema.ObjectSchema = { type: "object", properties };
  if (required.size) folded.required = [...required];
  // A key no member declares is rejected only when every member rejects it, so the fold is closed only when every member is. Otherwise it carries whatever the `catchall` members demand of such a key.
  if (objects.every((object) => object.additionalProperties === false)) {
    folded.additionalProperties = false;
  } else {
    const constraints: JSONSchema.BaseSchema[] = [];
    for (const object of objects) {
      const constraint = undeclaredConstraint(object);
      if (constraint && !constraints.some((seen) => JSON.stringify(seen) === JSON.stringify(constraint)))
        constraints.push(constraint);
    }
    if (constraints.length === 1) folded.additionalProperties = constraints[0]!;
    else if (constraints.length > 1) folded.additionalProperties = { allOf: constraints };
  }
  return folded;
}

/** `additionalProperties` in an `allOf` member sees only that member's own `properties`, so two
 * closed object members reject each other's keys and the schema validates nothing. Zod's parser
 * pools the key sets instead — `handleIntersectionResults` reports a key as unrecognized only when
 * *every* side rejects it — so the emitted schema has to pool them too, and folding the members
 * into one object is the encoding that says so on every target.
 *
 * This runs from `finalize`, after `extractDefs`, which is what keeps it clear of the `$ref`
 * machinery: a member extracted into `$defs` is already a `$ref` by now and declines to fold, so it
 * keeps its reference and its own closedness rather than being inlined as a stale copy. */
function foldIntersection(json: JSONSchema.BaseSchema): void {
  const allOf = json.allOf;
  if (!Array.isArray(allOf) || allOf.length < 2) return;
  // An `override` runs before this pass and may have written object keywords onto the intersection itself. Those are deliberate, so decline rather than overwrite them.
  for (const key of FOLDABLE_KEYS) if (key in json) return;

  // An intersection distributes over a union: `A & (X | Y)` is `(A & X) | (A & Y)`. Only the first union is distributed over; a second one stays among the members every branch folds against, where it fails the object check and declines the whole intersection rather than multiplying out.
  const unions = allOf.filter((m) => UNION_KEYS.some((k) => Array.isArray(m[k])));

  let folded: JSONSchema.BaseSchema | null = null;
  if (!unions.length) {
    folded = foldObjects(allOf);
  } else {
    const union = unions[0]!;
    const keyword = UNION_KEYS.find((k) => Array.isArray(union[k]))!;
    if (Object.keys(union).length !== 1) return;
    const rest = allOf.filter((m) => m !== union);
    const branches = (union[keyword] as JSONSchema._JSONSchema[]).map((branch) => foldObjects([...rest, branch]));
    if (branches.some((b) => !b)) return;
    folded = { [keyword]: branches } as JSONSchema.BaseSchema;
  }
  if (!folded) return;

  delete json.allOf;
  assignProps(json, folded);
}

export function finalize<T extends schemas.$ZodType>(
  ctx: ToJSONSchemaContext,
  schema: T
): ZodStandardJSONSchemaPayload<T> {
  const root = ctx.seen.get(schema);
  if (!root) throw new Error("Unprocessed schema. This is a bug in Zod.");

  // flatten refs - inherit properties from parent schemas
  const flattenRef = (zodSchema: schemas.$ZodType) => {
    const seen = ctx.seen.get(zodSchema)!;

    // already processed
    if (seen.ref === null) return;

    const schema = seen.def ?? seen.schema;
    const _cached = { ...schema };

    const ref = seen.ref;
    seen.ref = null; // prevent infinite recursion

    if (ref) {
      flattenRef(ref);

      const refSeen = ctx.seen.get(ref)!;
      const refSchema = refSeen.schema;

      // merge referenced schema into current
      if (refSchema.$ref && (ctx.target === "draft-07" || ctx.target === "draft-04" || ctx.target === "openapi-3.0")) {
        // older drafts can't combine $ref with other properties
        schema.allOf = schema.allOf ?? [];
        schema.allOf.push(refSchema);
      } else {
        assignProps(schema, refSchema);
      }
      // restore child's own properties (child wins)
      assignProps(schema, _cached);

      const isParentRef = zodSchema._zod.parent === ref;

      // For parent chain, child is a refinement - remove parent-only properties
      if (isParentRef) {
        for (const key in schema) {
          if (key === "$ref" || key === "allOf") continue;
          if (!(key in _cached)) {
            delete schema[key];
          }
        }
      }

      // When ref was extracted to $defs, remove properties that match the definition
      if (refSchema.$ref && refSeen.def) {
        for (const key in schema) {
          if (key === "$ref" || key === "allOf") continue;
          if (key in refSeen.def && JSON.stringify(schema[key]) === JSON.stringify(refSeen.def[key])) {
            delete schema[key];
          }
        }
      }
    }

    // If parent was extracted (has $ref), propagate $ref to this schema. This handles cases like: readonly().meta({id}).describe() where processor sets ref to innerType but parent should be referenced
    const parent = zodSchema._zod.parent;
    if (parent && parent !== ref) {
      // Ensure parent is processed first so its def has inherited properties
      flattenRef(parent);
      const parentSeen = ctx.seen.get(parent);
      if (parentSeen?.schema.$ref) {
        schema.$ref = parentSeen.schema.$ref;
        // De-duplicate with parent's definition
        if (parentSeen.def) {
          for (const key in schema) {
            if (key === "$ref" || key === "allOf") continue;
            if (key in parentSeen.def && JSON.stringify(schema[key]) === JSON.stringify(parentSeen.def[key])) {
              delete schema[key];
            }
          }
        }
      }
    }

    // execute overrides
    ctx.override({
      zodSchema: zodSchema as schemas.$ZodTypes,
      jsonSchema: schema,
      path: seen.path ?? [],
    });
  };

  // Flattening walks the whole map and clears each `ref` as it goes, so a second call over the same map is a no-op scan. Skip it outright once it has run for a registry conversion.
  if (!ctx.external || ctx.sharedEmitDoneFor !== ctx.external) {
    for (const entry of [...ctx.seen.entries()].reverse()) {
      flattenRef(entry[0]);
    }

    if (ctx.target !== "openapi-3.0") {
      for (const entry of ctx.seen.entries()) {
        compactTypeUnion(entry[1].def ?? entry[1].schema);
      }
    }

    for (const rewrite of ctx.deferred) rewrite();

    // After flattening, every member that was extracted is a `$ref`, so the fold sees the final shape. A schema that inherits an intersection — through `z.lazy`, or any `ref` chain — holds the same `allOf` array, so fold by array identity to catch every copy.
    if (ctx.intersections.length) {
      const carriers = new Map<JSONSchema.BaseSchema[], JSONSchema.BaseSchema[]>();
      for (const seen of ctx.seen.values()) {
        for (const json of [seen.schema, seen.def]) {
          const allOf = json?.allOf as JSONSchema.BaseSchema[] | undefined;
          if (!Array.isArray(allOf)) continue;
          const existing = carriers.get(allOf);
          if (existing) existing.push(json!);
          else carriers.set(allOf, [json!]);
        }
      }
      for (const allOf of ctx.intersections) {
        for (const json of carriers.get(allOf) ?? []) foldIntersection(json);
      }
    }
  }

  const result: JSONSchema.BaseSchema = {};
  if (ctx.target === "draft-2020-12") {
    result.$schema = "https://json-schema.org/draft/2020-12/schema";
  } else if (ctx.target === "draft-07") {
    result.$schema = "http://json-schema.org/draft-07/schema#";
  } else if (ctx.target === "draft-04") {
    result.$schema = "http://json-schema.org/draft-04/schema#";
  } else if (ctx.target === "openapi-3.0") {
    // OpenAPI 3.0 schema objects should not include a $schema property
  } else {
    // Arbitrary string values are allowed but won't have a $schema property set
  }

  if (ctx.external?.uri) {
    const id = ctx.external.registry.get(schema)?.id;
    if (!id) throw new Error("Schema is missing an `id` property");
    result.$id = ctx.external.uri(id);
  }

  // when the root was extracted into $defs, `root.schema` is the `$ref` wrapper and `root.def` is the body that now lives under $defs
  assignProps(result, root.defId ? root.schema : (root.def ?? root.schema));

  // The `id` in `.meta()` is a Zod-specific registration tag used to extract schemas into $defs — it is not user-facing JSON Schema metadata. Strip it from the output body where it would otherwise leak. The id is preserved implicitly via the $defs key (and via $ref paths).
  const rootMetaId = ctx.metadataRegistry.get(schema)?.id;
  if (rootMetaId !== undefined && result.id === rootMetaId) delete result.id;

  // build defs object. With `external`, `defs` is the shared object every schema writes into, so the same entries are reassigned on every call. Without it, `defs` is fresh per call and must be rebuilt.
  const defs: JSONSchema.BaseSchema["$defs"] = ctx.external?.defs ?? {};
  if (!ctx.external || ctx.sharedEmitDoneFor !== ctx.external) {
    for (const entry of ctx.seen.entries()) {
      const seen = entry[1];
      if (seen.def && seen.defId) {
        if (seen.def.id === seen.defId) delete seen.def.id;
        assignProp(defs, seen.defId, seen.def);
      }
    }
  }
  if (ctx.external) ctx.sharedEmitDoneFor = ctx.external;

  // set definitions in result
  if (ctx.external) {
  } else {
    if (Object.keys(defs).length > 0) {
      if (ctx.target === "draft-2020-12") {
        result.$defs = defs;
      } else {
        result.definitions = defs;
      }
    }
  }

  try {
    // this "finalizes" this schema and ensures all cycles are removed each call to finalize() is functionally independent though the seen map is shared
    const finalized = JSON.parse(JSON.stringify(result));
    Object.defineProperty(finalized, "~standard", {
      value: {
        ...schema["~standard"],
        jsonSchema: {
          input: createStandardJSONSchemaMethod(schema, "input", ctx.processors),
          output: createStandardJSONSchemaMethod(schema, "output", ctx.processors),
        },
      },
      enumerable: false,
      writable: false,
    });

    return finalized;
  } catch (_err) {
    throw new Error("Error converting schema to JSON.");
  }
}

function isTransforming(
  _schema: schemas.$ZodType,
  _ctx?: {
    seen: Set<schemas.$ZodType>;
  }
): boolean {
  const ctx = _ctx ?? { seen: new Set() };

  if (ctx.seen.has(_schema)) return false;
  ctx.seen.add(_schema);

  const def = (_schema as schemas.$ZodTypes)._zod.def;

  if (def.type === "transform") return true;

  if (def.type === "array") return isTransforming(def.element, ctx);
  if (def.type === "set") return isTransforming(def.valueType, ctx);
  if (def.type === "lazy") return isTransforming(def.getter(), ctx);

  if (
    def.type === "promise" ||
    def.type === "optional" ||
    def.type === "nonoptional" ||
    def.type === "nullable" ||
    def.type === "readonly" ||
    def.type === "default" ||
    def.type === "prefault" ||
    def.type === "catch"
  ) {
    return isTransforming(def.innerType, ctx);
  }

  if (def.type === "intersection") {
    return isTransforming(def.left, ctx) || isTransforming(def.right, ctx);
  }
  if (def.type === "record" || def.type === "map") {
    return isTransforming(def.keyType, ctx) || isTransforming(def.valueType, ctx);
  }
  if (def.type === "pipe") {
    if (_schema._zod.traits.has("$ZodCodec")) return true;
    return isTransforming(def.in, ctx) || isTransforming(def.out, ctx);
  }

  if (def.type === "object") {
    for (const key in def.shape) {
      if (isTransforming(def.shape[key]!, ctx)) return true;
    }
    return false;
  }
  if (def.type === "union") {
    for (const option of def.options) {
      if (isTransforming(option, ctx)) return true;
    }
    return false;
  }
  if (def.type === "tuple") {
    for (const item of def.items) {
      if (isTransforming(item, ctx)) return true;
    }
    if (def.rest && isTransforming(def.rest, ctx)) return true;
    return false;
  }

  return false;
}

export type ZodStandardSchemaWithJSON<T> = StandardSchemaWithJSONProps<core.input<T>, core.output<T>>;
export interface ZodStandardJSONSchemaPayload<T> extends JSONSchema.BaseSchema {
  "~standard": ZodStandardSchemaWithJSON<T>;
}

/**
 * Creates a toJSONSchema method for a schema instance.
 * This encapsulates the logic of initializing context, processing, extracting defs, and finalizing.
 */
export const createToJSONSchemaMethod =
  <T extends schemas.$ZodType>(schema: T, processors: Record<string, Processor> = {}) =>
  (params?: ToJSONSchemaParams): ZodStandardJSONSchemaPayload<T> => {
    const ctx = initializeContext({ ...params, processors });
    processSchema(schema, ctx);
    extractDefs(ctx, schema);
    return finalize(ctx, schema);
  };

/**
 * Creates a toJSONSchema method for a schema instance.
 * This encapsulates the logic of initializing context, processing, extracting defs, and finalizing.
 */
type StandardJSONSchemaMethodParams = Parameters<StandardJSONSchemaV1["~standard"]["jsonSchema"]["input"]>[0];
export const createStandardJSONSchemaMethod =
  <T extends schemas.$ZodType>(schema: T, io: "input" | "output", processors: Record<string, Processor> = {}) =>
  (params?: StandardJSONSchemaMethodParams): JSONSchema.BaseSchema => {
    const { libraryOptions, target } = params ?? {};
    const ctx = initializeContext({ ...(libraryOptions ?? {}), target, io, processors });
    processSchema(schema, ctx);
    extractDefs(ctx, schema);
    return finalize(ctx, schema);
  };