import { replacePlaceholders } from '../src/expression.js';
import { SchemaPageArray } from '../src/index.js';

describe('replacePlaceholders', () => {
  it('should return content as is if there are no placeholders', () => {
    const content = 'Hello, world!';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe(content);
  });

  it('should replace placeholders with variables', () => {
    const content = 'Hello, {name}!';
    const variables = { name: 'Alice' };
    const result = replacePlaceholders({ content, variables, schemas: [] });
    expect(result).toBe('Hello, Alice!');
  });

  it('should evaluate expressions within placeholders', () => {
    const content = 'The sum is {1 + 2}.';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('The sum is 3.');
  });

  it('should handle date and dateTime placeholders', () => {
    const content = 'Today is {date} and now is {dateTime}.';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    const date = new Date();
    const padZero = (num: number) => String(num).padStart(2, '0');
    const formattedDate = `${date.getFullYear()}/${padZero(date.getMonth() + 1)}/${padZero(
      date.getDate()
    )}`;
    const formattedDateTime = `${formattedDate} ${padZero(date.getHours())}:${padZero(
      date.getMinutes()
    )}`;
    expect(result).toBe(`Today is ${formattedDate} and now is ${formattedDateTime}.`);
  });

  it('should handle data from schemas', () => {
    const content = 'Schema content: {name}';
    const variables = {};
    const schemas = [
      [
        {
          name: 'name',
          type: 'text',
          content: 'SchemaName',
          readOnly: true,
        },
      ],
    ] as SchemaPageArray;
    const result = replacePlaceholders({ content, variables, schemas });
    expect(result).toBe('Schema content: SchemaName');
  });

  it('should prioritize variables over schemas', () => {
    const content = 'Name: {name}';
    const variables = { name: 'VariableName' };
    const schemas = [
      [
        {
          name: 'name',
          type: 'text',
          content: 'SchemaName',
          readOnly: true,
        },
      ],
    ] as SchemaPageArray;
    const result = replacePlaceholders({ content, variables, schemas });
    expect(result).toBe('Name: VariableName');
  });

  it('should handle nested placeholders in variables', () => {
    const content = 'Nested variable: {greeting}';
    const variables = { greeting: 'Hello, {name}!' };
    const schemas = [
      [
        {
          name: 'name',
          type: 'text',
          content: 'Bob',
          readOnly: true,
        },
      ],
    ] as SchemaPageArray;
    const result = replacePlaceholders({ content, variables, schemas });
    expect(result).toBe('Nested variable: Hello, Bob!');
  });

  it('should return content unchanged when placeholders are invalid', () => {
    const content = 'Invalid placeholder: {name';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('Invalid placeholder: {name');
  });

  it('should evaluate expressions even if they result in Infinity', () => {
    const content = 'Divide by zero: {1 / 0}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('Divide by zero: Infinity');
  });

  it('should handle complex expressions', () => {
    const content = 'Result: {Math.max(1, 2, 3)}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('Result: 3');
  });

  it('should parse JSON strings in variables', () => {
    const content = 'Data: {data.value}';
    const variables = { data: '{"value": "42"}' };
    const result = replacePlaceholders({ content, variables, schemas: [] });
    expect(result).toBe('Data: 42');
  });

  it('should handle variables of different types', () => {
    const content = 'Number: {num}, Boolean: {bool}, Array: {arr[0]}, Object: {obj.key}';
    const variables = {
      num: 42,
      bool: true,
      arr: ['first', 'second'],
      obj: { key: 'value' },
    };
    const result = replacePlaceholders({ content, variables, schemas: [] });
    expect(result).toBe('Number: 42, Boolean: true, Array: first, Object: value');
  });

  it('should use content from readOnly schemas', () => {
    const content = 'Content: {readOnlyField}';
    const variables = {};
    const schemas = [
      [
        {
          name: 'readOnlyField',
          type: 'text',
          content: 'ReadOnlyContent',
          readOnly: true,
        },
      ],
    ] as SchemaPageArray;
    const result = replacePlaceholders({ content, variables, schemas });
    expect(result).toBe('Content: ReadOnlyContent');
  });

  it('should use empty string for non-readOnly schema content', () => {
    const content = 'Content: {editableField}';
    const variables = {};
    const schemas = [
      [
        {
          name: 'editableField',
          type: 'text',
          content: 'Should not be used',
          readOnly: false,
        },
      ],
    ] as SchemaPageArray;
    const result = replacePlaceholders({ content, variables, schemas });
    expect(result).toBe('Content: ');
  });

  it('should allow method chaining on permitted global objects', () => {
    const content = 'Chained: {Math.random().toString()}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Math.random() generates a random number, which is then converted to a string using toString()
    const regex = /^Chained: \d+\.\d+$/;
    expect(regex.test(result)).toBe(true);
  });
});

describe('replacePlaceholders - Security Tests', () => {
  it('should prevent access to __proto__ property', () => {
    const content = 'Proto: {__proto__}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Since __proto__ access is prohibited, the placeholder should remain unchanged
    expect(result).toBe('Proto: {__proto__}');
  });

  it('should prevent access to constructor property', () => {
    const content = 'Constructor: {constructor}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // 'constructor' is allowed if defined in context or globals; assuming it's not, placeholder remains
    expect(result).toBe('Constructor: {constructor}');
  });

  it('should prevent access to prototype property', () => {
    const content = 'Prototype: {prototype}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // 'prototype' access is prohibited
    expect(result).toBe('Prototype: {prototype}');
  });

  it('should prevent access to nested prohibited properties', () => {
    const content = 'Nested: {user.__proto__.polluted}';
    const variables = { user: {} };
    const result = replacePlaceholders({ content, variables, schemas: [] });
    // Access to '__proto__' is prohibited; placeholder remains unchanged
    expect(result).toBe('Nested: {user.__proto__.polluted}');
  });

  it('should prevent use of Function constructor', () => {
    const content = 'Function: {Function("return 42")()}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Use of Function constructor is not allowed; placeholder remains unchanged
    expect(result).toBe('Function: {Function("return 42")()}');
  });

  it('should prevent access to disallowed global variables', () => {
    const content = 'Process: {process.env}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // 'process' is not in allowedGlobals; placeholder remains unchanged
    expect(result).toBe('Process: {process.env}');
  });

  it('should prevent prototype pollution via JSON.parse', () => {
    const content = 'Polluted: {JSON.parse(\'{"__proto__":{"polluted":true}}\').polluted}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Even if 'polluted' is accessed, the prototype is not polluted, so undefined is returned.
    expect(result).toBe('Polluted: undefined');
  });

  it('should prevent accessing nested prohibited properties in functions', () => {
    const content = 'Access: {( () => { return this.constructor } )()}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Attempting to access 'constructor' via 'this' should be prohibited; placeholder remains unchanged
    expect(result).toBe('Access: {( () => { return this.constructor } )()}');
  });

  it('should prevent accessing global objects not in allowedGlobals', () => {
    const content = 'Global: {global}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // 'global' is not in allowedGlobals; placeholder remains unchanged
    expect(result).toBe('Global: {global}');
  });

  it('should prevent accessing Object constructor via allowed globals', () => {
    const content = 'ObjectConstructor: {Object.constructor}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Accessing 'constructor' of 'Object' is prohibited
    expect(result).toBe('ObjectConstructor: {Object.constructor}');
  });

  it('should prevent accessing Function from allowed globals', () => {
    const content = 'FunctionAccess: {Function("return 42")()}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // 'Function' is not in allowedGlobals, so this should fail
    expect(result).toBe('FunctionAccess: {Function("return 42")()}');
  });

  it('should prevent accessing nested properties via allowed globals', () => {
    const content = 'NestedAccess: {Math.__proto__.polluted}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Accessing '__proto__' of allowed global 'Math' is prohibited
    expect(result).toBe('NestedAccess: {Math.__proto__.polluted}');
  });

  it('should prevent execution of arbitrary code via ternary operator', () => {
    const content = 'ArbitraryCode: {true ? (() => { return "Hacked" })() : "Safe"}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Execution of arbitrary functions is not allowed; placeholder remains unchanged
    expect(result).toBe('ArbitraryCode: {true ? (() => { return "Hacked" })() : "Safe"}');
  });

  it('should handle attempts to override context variables', () => {
    const content = 'Override: {date = "Hacked"} {date}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Assignment operations are not supported; placeholders remain unchanged
    const date = new Date();
    const padZero = (num: number) => String(num).padStart(2, '0');
    const dateFmt = `${date.getFullYear()}/${padZero(date.getMonth() + 1)}/${padZero(
      date.getDate()
    )}`;
    expect(result).toBe(`Override: {date = "Hacked"} ${dateFmt}`);
  });

  it('should prevent using eval-like expressions', () => {
    const content = 'Eval: {eval("2 + 2")';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // 'eval' is not in allowedGlobals; placeholder remains unchanged
    expect(result).toBe('Eval: {eval("2 + 2")');
  });

  it('should prevent accessing undefined variables', () => {
    const content = 'Undefined: {undefinedVar}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // 'undefinedVar' is not defined; placeholder remains unchanged
    expect(result).toBe('Undefined: {undefinedVar}');
  });

  it('should prevent accessing nested properties of undefined variables', () => {
    const content = 'NestedUndefined: {user.name}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // 'user' is undefined; accessing 'name' should fail and placeholder remains unchanged
    expect(result).toBe('NestedUndefined: {user.name}');
  });

  it('should prevent accessing nested prohibited properties in objects', () => {
    const content = 'Nested: {user.__proto__.polluted}';
    const variables = { user: {} };
    const result = replacePlaceholders({ content, variables, schemas: [] });
    // Since access to '__proto__' is prohibited, the placeholder remains unchanged.
    expect(result).toBe('Nested: {user.__proto__.polluted}');
  });

  it('should prevent using Function constructor', () => {
    const content = 'Function: {Function("return 42")()}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Since 'Function' is not included in allowedGlobals, the placeholder remains unchanged.
    expect(result).toBe('Function: {Function("return 42")()}');
  });
});

describe('replacePlaceholders - Comparison Operators Tests', () => {
  it('should evaluate expressions with == operator', () => {
    const content = 'Equals: {1 == 1}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('Equals: true');
  });

  it('should evaluate expressions with != operator', () => {
    const content = 'NotEquals: {1 != 2}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('NotEquals: true');
  });

  it('should evaluate expressions with === operator', () => {
    const content = 'StrictEquals: {1 === 1}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('StrictEquals: true');
  });

  it('should evaluate expressions with !== operator', () => {
    const content = 'StrictNotEquals: {1 !== "1"}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('StrictNotEquals: true');
  });

  it('should evaluate expressions with < operator', () => {
    const content = 'LessThan: {1 < 2}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('LessThan: true');
  });

  it('should evaluate expressions with > operator', () => {
    const content = 'GreaterThan: {2 > 1}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('GreaterThan: true');
  });

  it('should evaluate expressions with <= operator', () => {
    const content = 'LessThanOrEquals: {1 <= 1}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('LessThanOrEquals: true');
  });

  it('should evaluate expressions with >= operator', () => {
    const content = 'GreaterThanOrEquals: {2 >= 1}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('GreaterThanOrEquals: true');
  });

  it('should handle complex expressions with comparison operators', () => {
    const content = 'Complex: {1 + 2 > 2 && 4 - 1 < 5}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe('Complex: true');
  });

  it('should prevent execution of arbitrary code via comparison operators', () => {
    const content = 'ArbitraryCode: {1 < (() => { return "Hacked" })()}';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Execution of arbitrary functions is not allowed; placeholder remains unchanged
    expect(result).toBe('ArbitraryCode: {1 < (() => { return "Hacked" })()}');
  });
});

describe('replacePlaceholders - XSS Vulnerability Prevention Tests', () => {
  it('should prevent XSS via Object.getOwnPropertyDescriptor and Object.getPrototypeOf (CVE payload 1)', () => {
    const content = '{ ((f, g) => f(g(Object), "constructor").value)(Object.getOwnPropertyDescriptor, Object.getPrototypeOf)("alert(location)")() }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // The dangerous expression should not be evaluated and should return as-is
    expect(result).toBe(content);
  });

  it('should prevent XSS via object property assignment (CVE payload 2)', () => {
    const content = '{ { f: Object.getOwnPropertyDescriptor }.f({ g: Object.getPrototypeOf }.g(Object), "constructor").value("alert(location)")() }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // The dangerous expression should not be evaluated and should return as-is
    expect(result).toBe(content);
  });

  it('should prevent direct access to Object.getOwnPropertyDescriptor', () => {
    const content = '{ Object.getOwnPropertyDescriptor(Object, "constructor") }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Direct access to dangerous method should be blocked
    expect(result).toBe(content);
  });

  it('should prevent direct access to Object.getPrototypeOf', () => {
    const content = '{ Object.getPrototypeOf(Object) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Direct access to dangerous method should be blocked
    expect(result).toBe(content);
  });

  it('should prevent access to Object.setPrototypeOf', () => {
    const content = '{ Object.setPrototypeOf({}, null) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Direct access to dangerous method should be blocked
    expect(result).toBe(content);
  });

  it('should prevent access to Object.defineProperty', () => {
    const content = '{ Object.defineProperty({}, "prop", { value: 42 }) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Direct access to dangerous method should be blocked
    expect(result).toBe(content);
  });

  it('should prevent access to Object.defineProperties', () => {
    const content = '{ Object.defineProperties({}, { prop: { value: 42 } }) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Direct access to dangerous method should be blocked
    expect(result).toBe(content);
  });

  it('should prevent access to Object.getOwnPropertyNames', () => {
    const content = '{ Object.getOwnPropertyNames(Object) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Direct access to dangerous method should be blocked
    expect(result).toBe(content);
  });

  it('should prevent access to Object.getOwnPropertySymbols', () => {
    const content = '{ Object.getOwnPropertySymbols(Object) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Direct access to dangerous method should be blocked
    expect(result).toBe(content);
  });

  it('should allow safe Object methods', () => {
    // Test Object.keys
    const keysContent = '{ Object.keys({ a: 1, b: 2 }) }';
    const keysResult = replacePlaceholders({ content: keysContent, variables: {}, schemas: [] });
    expect(keysResult).toBe('a,b');

    // Test Object.values
    const valuesContent = '{ Object.values({ a: 1, b: 2 }) }';
    const valuesResult = replacePlaceholders({ content: valuesContent, variables: {}, schemas: [] });
    expect(valuesResult).toBe('1,2');

    // Test Object.entries
    const entriesContent = '{ Object.entries({ a: 1 })[0] }';
    const entriesResult = replacePlaceholders({ content: entriesContent, variables: {}, schemas: [] });
    expect(entriesResult).toBe('a,1');

    // Test safe Object.assign
    const assignContent = '{ Object.assign({}, { a: 1 }, { b: 2 }).a }';
    const assignResult = replacePlaceholders({ content: assignContent, variables: {}, schemas: [] });
    expect(assignResult).toBe('1'); // Safe assign should work
  });

  it('should prevent complex XSS attempts via nested function calls', () => {
    const content = '{ [].map.call("abc", Object.getOwnPropertyDescriptor) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Complex attempts to access dangerous functions should be blocked
    expect(result).toBe(content);
  });

  it('should prevent Function constructor access via constructor property', () => {
    const content = '{ "".constructor.constructor("alert(1)")() }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Attempts to access Function constructor should be blocked
    expect(result).toBe(content);
  });

  it('should prevent prototype pollution via Object.assign and __lookupGetter__', () => {
    const content = '{ { assign: Object.assign }.assign({ f: {}.__lookupGetter__("__proto__") }.f(), { polluted: "yes" }) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // The dangerous expression should not be evaluated due to __lookupGetter__ being blocked
    expect(result).toBe(content);
    // Verify that prototype is not polluted
    expect(({} as any).polluted).toBeUndefined();
  });

  it('should prevent access to __lookupGetter__', () => {
    const content = '{ {}.__lookupGetter__("__proto__") }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe(content);
  });

  it('should prevent access to __lookupSetter__', () => {
    const content = '{ {}.__lookupSetter__("__proto__") }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe(content);
  });

  it('should prevent access to __defineGetter__', () => {
    const content = '{ {}.__defineGetter__("test", () => "hacked") }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe(content);
  });

  it('should prevent access to __defineSetter__', () => {
    const content = '{ {}.__defineSetter__("test", () => {}) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    expect(result).toBe(content);
  });

  it('should allow safe Object.assign but prevent prototype pollution', () => {
    const content = '{ Object.assign({}, { a: 1 }) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Safe assign should work
    expect(result).toBe('[object Object]');
  });

  it('should prevent prototype pollution via Object.assign', () => {
    const pollutionContent = '{ Object.assign({}, { "__proto__": { polluted: "yes" } }) }';
    const result = replacePlaceholders({ content: pollutionContent, variables: {}, schemas: [] });
    // Should execute but not pollute prototype
    expect(result).toBe('[object Object]');
    expect(({} as any).polluted).toBeUndefined();
    
    // Test with constructor
    const constructorContent = '{ Object.assign({}, { "constructor": { polluted: "yes" } }) }';
    const result2 = replacePlaceholders({ content: constructorContent, variables: {}, schemas: [] });
    expect(result2).toBe('[object Object]');
    expect(({} as any).constructor.polluted).toBeUndefined();
  });

  it('should no longer allow Object.create due to security concerns', () => {
    const content = '{ Object.create(null) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Object.create is now blocked
    expect(result).toBe(content);
  });

  it('should no longer allow Object.freeze due to security concerns', () => {
    const content = '{ Object.freeze({}) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Object.freeze is now blocked
    expect(result).toBe(content);
  });

  it('should no longer allow Object.seal due to security concerns', () => {
    const content = '{ Object.seal({}) }';
    const result = replacePlaceholders({ content, variables: {}, schemas: [] });
    // Object.seal is now blocked
    expect(result).toBe(content);
  });
});

describe('replacePlaceholders memory safety', () => {
  // Regression guard: before the fix, `parseData` memoized results in a
  // module-level `parseDataCache` keyed by `JSON.stringify(data)` that was
  // never evicted. Every unique inputs state added a permanent Map key
  // whose byte length matched the input byte length, so any consumer
  // passing varying large string values (image base64 in schema content,
  // embedded fonts, large text) leaked memory for the app's lifetime.
  //
  // This test stress-tests the API with many unique large inputs and
  // asserts that no multi-hundred-KB strings are retained afterwards. It
  // uses `v8.writeHeapSnapshot` to capture ground truth from V8 instead
  // of relying on `process.memoryUsage()` (which is too coarse and noisy
  // to catch a cache that grows by tens of MB per burst).
  //
  // The test is deterministic in direction: pre-fix, retained "big
  // string" bytes is O(inputs × inputSize) ≈ 15 MB, far above the
  // threshold. Post-fix, retained is effectively zero (the strings are
  // temporaries freed when the call returns).
  it('does not retain call inputs in a module-level cache', () => {
    const schemas: SchemaPageArray = [
      [
        {
          name: 'blob',
          type: 'text',
          content: '',
          position: { x: 0, y: 0 },
          width: 100,
          height: 10,
        },
      ],
    ] as unknown as SchemaPageArray;

    // 30 unique payloads × ~500 KB each. If the fix regresses, at least
    // 15 MB of string data will be pinned as parseDataCache keys. The
    // content MUST contain a placeholder (`{blob}`) — otherwise
    // replacePlaceholders short-circuits and parseData is never called.
    const PAYLOAD_COUNT = 30;
    const PAYLOAD_SIZE = 500_000;
    for (let i = 0; i < PAYLOAD_COUNT; i++) {
      replacePlaceholders({
        content: 'value: {blob}',
        variables: { blob: `${i}-${'x'.repeat(PAYLOAD_SIZE)}` },
        schemas,
      });
    }

    // Force full GC if `--expose-gc` is available. If not, V8 will still
    // have collected most transients by the time writeHeapSnapshot runs,
    // and the threshold is generous enough that transient tails don't
    // matter. On CI where --expose-gc is absent the test can still
    // distinguish +15 MB (leak) from <1 MB (fixed).
    const gc = (globalThis as { gc?: () => void }).gc;
    if (gc) gc();

    // v8.writeHeapSnapshot is available in all Node versions the pdfme
    // monorepo supports. The snapshot JSON can be tens of MB; we parse it
    // once and discard.
    // eslint-disable-next-line @typescript-eslint/no-require-imports
    const v8: typeof import('v8') = require('v8');
    // eslint-disable-next-line @typescript-eslint/no-require-imports
    const fs: typeof import('fs') = require('fs');
    // eslint-disable-next-line @typescript-eslint/no-require-imports
    const os: typeof import('os') = require('os');
    // eslint-disable-next-line @typescript-eslint/no-require-imports
    const path: typeof import('path') = require('path');

    const snapPath = path.join(
      os.tmpdir(),
      `pdfme-expression-memtest-${process.pid}-${Date.now()}.heapsnapshot`,
    );
    v8.writeHeapSnapshot(snapPath);
    const rawSnap = fs.readFileSync(snapPath, 'utf8');
    fs.unlinkSync(snapPath);
    const snap = JSON.parse(rawSnap) as {
      nodes: number[];
      snapshot: { meta: { node_fields: string[]; node_types: string[][] } };
    };
    const fieldCount = snap.snapshot.meta.node_fields.length;
    const typeFieldIdx = snap.snapshot.meta.node_fields.indexOf('type');
    const selfSizeIdx = snap.snapshot.meta.node_fields.indexOf('self_size');
    const typeNames = snap.snapshot.meta.node_types[typeFieldIdx];

    // Sum self_size of all 'string' nodes whose size exceeds 200 KB. A
    // healthy post-fix run has ~0 such nodes (strings are freed after
    // each call). A leaking pre-fix run has at least PAYLOAD_COUNT
    // nodes totalling >= PAYLOAD_COUNT * PAYLOAD_SIZE bytes.
    const MIN_STRING_BYTES = 200_000;
    let retainedLargeStringBytes = 0;
    for (let i = 0; i < snap.nodes.length; i += fieldCount) {
      if (typeNames[snap.nodes[i + typeFieldIdx]] !== 'string') continue;
      const size = snap.nodes[i + selfSizeIdx];
      if (size >= MIN_STRING_BYTES) retainedLargeStringBytes += size;
    }

    // Generous threshold: healthy is ~0, leak is ~15 MB. 2 MB cleanly
    // separates the two without being sensitive to unrelated large
    // strings (e.g. inline source maps in test fixtures).
    expect(retainedLargeStringBytes).toBeLessThan(2_000_000);
  }, 60_000);
});