silverbullet/common/space_lua/runtime.ts

import type { LuaFunctionBody } from "./ast.ts";
import { evalStatement } from "$common/space_lua/eval.ts";

export class LuaEnv implements ILuaSettable, ILuaGettable {
  variables = new Map<string, LuaValue>();

  constructor(readonly parent?: LuaEnv) {
  }

  setLocal(name: string, value: LuaValue) {
    this.variables.set(name, value);
  }

  set(key: string, value: LuaValue): void {
    if (this.variables.has(key) || !this.parent) {
      this.variables.set(key, value);
    } else {
      this.parent.set(key, value);
    }
  }

  get(name: string): LuaValue | undefined {
    if (this.variables.has(name)) {
      return this.variables.get(name);
    }
    if (this.parent) {
      return this.parent.get(name);
    }
    return undefined;
  }
}

export class LuaMultiRes {
  constructor(readonly values: any[]) {
  }

  unwrap(): any {
    if (this.values.length !== 1) {
      throw new Error("Cannot unwrap multiple values");
    }
    return this.values[0];
  }
}

export function singleResult(value: any): any {
  if (value instanceof LuaMultiRes) {
    return value.unwrap();
  } else {
    return value;
  }
}

// These types are for documentation only
export type LuaValue = any;
export type JSValue = any;

export interface ILuaFunction {
  call(...args: LuaValue[]): Promise<LuaValue> | LuaValue;
}

export interface ILuaSettable {
  set(key: LuaValue, value: LuaValue): void;
}

export interface ILuaGettable {
  get(key: LuaValue): LuaValue | undefined;
}

export class LuaFunction implements ILuaFunction {
  constructor(private body: LuaFunctionBody, private closure: LuaEnv) {
  }

  call(...args: LuaValue[]): Promise<LuaValue> | LuaValue {
    // Create a new environment for this function call
    const env = new LuaEnv(this.closure);
    // Assign the passed arguments to the parameters
    for (let i = 0; i < this.body.parameters.length; i++) {
      let arg = args[i];
      if (arg === undefined) {
        arg = null;
      }
      env.set(this.body.parameters[i], arg);
    }
    return evalStatement(this.body.block, env).catch((e: any) => {
      if (e instanceof LuaReturn) {
        if (e.values.length === 0) {
          return;
        } else if (e.values.length === 1) {
          return e.values[0];
        } else {
          return new LuaMultiRes(e.values);
        }
      } else {
        throw e;
      }
    });
  }
}

export class LuaNativeJSFunction implements ILuaFunction {
  constructor(readonly fn: (...args: JSValue[]) => JSValue) {
  }

  call(...args: LuaValue[]): Promise<LuaValue> | LuaValue {
    const result = this.fn(...args.map(luaValueToJS));
    if (result instanceof Promise) {
      return result.then(jsToLuaValue);
    } else {
      return jsToLuaValue(result);
    }
  }
}

export class LuaTable implements ILuaSettable, ILuaGettable {
  // To optimize the table implementation we use a combination of different data structures
  // When tables are used as maps, the common case is that they are string keys, so we use a simple object for that
  private stringKeys: Record<string, any>;
  // Other keys we can support using a Map as a fallback
  private otherKeys: Map<any, any> | null;
  // When tables are used as arrays, we use a native JavaScript array for that
  private arrayPart: any[];

  // TODO: Actually implement metatables
  private metatable: LuaTable | null;

  constructor() {
    // For efficiency and performance reasons we pre-allocate these (modern JS engines are very good at optimizing this)
    this.stringKeys = {};
    this.arrayPart = [];
    this.otherKeys = null; // Only create this when needed
    this.metatable = null;
  }

  get length(): number {
    return this.arrayPart.length;
  }

  set(key: LuaValue, value: LuaValue) {
    if (typeof key === "string") {
      this.stringKeys[key] = value;
    } else if (Number.isInteger(key) && key >= 1) {
      this.arrayPart[key - 1] = value;
    } else {
      if (!this.otherKeys) {
        this.otherKeys = new Map();
      }
      this.otherKeys.set(key, value);
    }
  }

  get(key: LuaValue): LuaValue | undefined {
    if (typeof key === "string") {
      return this.stringKeys[key];
    } else if (Number.isInteger(key) && key >= 1) {
      return this.arrayPart[key - 1];
    } else if (this.otherKeys) {
      return this.otherKeys.get(key);
    }
    return undefined;
  }

  toArray(): JSValue[] {
    return this.arrayPart;
  }

  toObject(): Record<string, JSValue> {
    const result = { ...this.stringKeys };
    for (const i in this.arrayPart) {
      result[parseInt(i) + 1] = this.arrayPart[i];
    }
    return result;
  }

  static fromArray(arr: JSValue[]): LuaTable {
    const table = new LuaTable();
    for (let i = 0; i < arr.length; i++) {
      table.set(i + 1, arr[i]);
    }
    return table;
  }

  static fromObject(obj: Record<string, JSValue>): LuaTable {
    const table = new LuaTable();
    for (const key in obj) {
      table.set(key, obj[key]);
    }
    return table;
  }
}

export type LuaLValueContainer = { env: ILuaSettable; key: LuaValue };

export function luaSet(obj: any, key: any, value: any) {
  if (obj instanceof LuaTable) {
    obj.set(key, value);
  } else {
    obj[key] = value;
  }
}

export function luaGet(obj: any, key: any): any {
  if (obj instanceof LuaTable) {
    return obj.get(key);
  } else {
    return obj[key];
  }
}

export function luaLen(obj: any): number {
  if (obj instanceof LuaTable) {
    return obj.toArray().length;
  } else if (Array.isArray(obj)) {
    return obj.length;
  } else {
    return 0;
  }
}

export class LuaBreak extends Error {
}

export class LuaReturn extends Error {
  constructor(readonly values: LuaValue[]) {
    super();
  }
}

export function luaTruthy(value: any): boolean {
  if (value === undefined || value === null || value === false) {
    return false;
  }
  if (value instanceof LuaTable) {
    return value.length > 0;
  }
  return true;
}

export function jsToLuaValue(value: any): any {
  if (value instanceof LuaTable) {
    return value;
  } else if (Array.isArray(value)) {
    return LuaTable.fromArray(value.map(jsToLuaValue));
  } else if (typeof value === "object") {
    return LuaTable.fromObject(value);
  } else {
    return value;
  }
}

export function luaValueToJS(value: any): any {
  if (value instanceof LuaTable) {
    // This is a heuristic: if this table is used as an array, we return an array
    if (value.length > 0) {
      return value.toArray();
    } else {
      return value.toObject();
    }
  } else {
    return value;
  }
}