interpreter.ts

import * as ts from "typescript";
import { taskEither, TaskEither, left, right } from "fp-ts/lib/TaskEither";
import { task, Task } from "fp-ts/lib/Task";
import { left as eitherLeft, right as _eitherRight, Either } from "fp-ts/lib/Either";
import { sequence } from "fp-ts/lib/Traversable"
import { array } from "fp-ts/lib/Array"

export type INode = ts.StringLiteral | ts.NumericLiteral | ts.BinaryExpression | ts.ExpressionStatement

export type IValue = string | number | boolean | any

export type IReference = {
    node: INode
    base: IValue
    propertyName: string
}

export type IScope = {
    parent: IScope | null
    value: IValue
}

export type IExecutionContext = {
    scope: IScope
    strict: boolean
    result: IValue

    withResult(v: IValue): IExecutionContext
}

export type IUnknownNodeError = {
    type: 'UnknownNode',
    node: any
}

export type INodeExecutor<N extends INode, E, A> = (n: N) => (x: IExecutionContext) => TaskEither<E | IUnknownNodeError, [A, IExecutionContext]>
export type INodeExecutorResult<E, A> = (x: IExecutionContext) => TaskEither<E| IUnknownNodeError, [A, IExecutionContext]>

export interface ICompileNode {
    compileNode(node: INode): (x: IExecutionContext) => TaskEither<any, any>
}

export enum ExecutionContextType {
    GLOBAL_CODE
}

// TaskEither.all
const all = <L, A, B>(fa: TaskEither<L, A>, fb: TaskEither<L, B>) => fb.ap(fa.map(a => (b: B) => [a, b])) as TaskEither<L, [A, B]>
const toVoid = (x: IExecutionContext) => <A>(a: A) => [undefined, x] as [void, IExecutionContext]
function eitherRight<A, B>(r: [A, B]): Either<never, [A, B]>{
  return _eitherRight(r)
}

const newTaskEither = <L, A>(fn: () => Either<L, A>): TaskEither<L, A> => {
  return new TaskEither(new Task(() => Promise.resolve(fn())))
}
function newTaskEitherOf<A, B>(r: [A, B]): TaskEither<never, [A, B]>{
  return taskEither.of(r)
}
function newTaskEitherLeftOf<L>(r: L): TaskEither<L, never>{
  return newTaskEither(() => eitherLeft(r))
}
function newUnknownNodeError(node: any): IUnknownNodeError{
  return {type: 'UnknownNode', node}
}

// Scope
class Scope {
  constructor(
    public readonly value: IValue,
    public readonly parent: IScope | null = null
  ){

  }
}
const GLOBAL_OBJECT = {}

// ExecutionContext
class ExecutionContext implements IExecutionContext {

  constructor(
    public readonly type: ExecutionContextType,
    public readonly strict: boolean = true,
    public readonly scope: Scope = new Scope(GLOBAL_OBJECT, null),
    public readonly result: any = undefined
  ){
  }

  withResult(r: any){
    return new ExecutionContext(this.type, this.strict, this.scope, r)
  }
}

// getValue
function getValue(r: any): TaskEither<never, IValue>{
  // TODO: intercept Reference and resolve value
  return r
}

// NumericLiteral
export const runNumericLiteral: INodeExecutor<
  ts.NumericLiteral,
  never,
  number
> = node => x => newTaskEitherOf([+node.text, x]);

// StringLiteral
export const runStringLiteral: INodeExecutor<
  ts.StringLiteral,
  never,
  string
> = node => x => newTaskEitherOf([node.text, x]);

// BinaryExpression
export const runBinaryExpression: INodeExecutor<
  ts.BinaryExpression,
  never,
  IValue
> = node => {
  const left = compileNode(node.left)
  const right = compileNode(node.right)

  return x => all(left(x), right(x))
    .chain(([l, r]) => all(getValue(l), getValue(r)))
    .chain(([l, r]) => newTaskEither(() => {
      switch(node.operatorToken.kind){
        case ts.SyntaxKind.LessThanToken: return eitherRight([l < r, x])
        case ts.SyntaxKind.GreaterThanToken: return eitherRight([l > r, x])
        case ts.SyntaxKind.LessThanEqualsToken: return eitherRight([l <= r, x])
        case ts.SyntaxKind.GreaterThanEqualsToken: return eitherRight([l >= r, x])
        case ts.SyntaxKind.EqualsEqualsToken: return eitherRight([l == r, x])
        case ts.SyntaxKind.ExclamationEqualsToken: return eitherRight([l != r, x])
        case ts.SyntaxKind.EqualsEqualsEqualsToken: return eitherRight([l === r, x])
        case ts.SyntaxKind.ExclamationEqualsEqualsToken: return eitherRight([l !== r, x])
        case ts.SyntaxKind.PlusToken: return eitherRight([l + r, x])
        case ts.SyntaxKind.MinusToken: return eitherRight([l - r, x])
        default: return eitherLeft(newUnknownNodeError(`Unknown operatorToken kind #${node.operatorToken.kind}`))
      }
    }))
};

// ExpressionStatement
export const runExpressionStatement: INodeExecutor<
  ts.ExpressionStatement,
  never,
  void
> = node => {
  const expression = compileNode(node.expression)
  return x => expression(x)
    .chain(([v, x]) => all(getValue(v), taskEither.of(x)))
    .map<[void, IExecutionContext]>(([v, x]) => [undefined, x.withResult(v)])
};

function compileNode(node: ts.NumericLiteral): INodeExecutorResult<never, number>
function compileNode(node: ts.StringLiteral): INodeExecutorResult<never, string>
function compileNode(node: ts.BinaryExpression): INodeExecutorResult<never, any>
function compileNode(node: ts.ExpressionStatement): INodeExecutorResult<never, void>
function compileNode(node: ts.Node): INodeExecutorResult<never, any>
function compileNode(node: ts.Node): INodeExecutorResult<never, any>{
    if(ts.isStringLiteral(node)) return runStringLiteral(node)
    if(ts.isNumericLiteral(node)) return runNumericLiteral(node)
    if(ts.isBinaryExpression(node)) return runBinaryExpression(node)
    if(ts.isExpressionStatement(node)) return runExpressionStatement(node)
    return x => newTaskEitherLeftOf(newUnknownNodeError(`Unknown node kind #${node.kind}`))
}

const seq = sequence(taskEither, array)
function compileNodeSequence(nodes: ReadonlyArray<ts.Node>): INodeExecutorResult<never, any>{
  // TODO: when ExecutionContext will be immutable, we need to pass each written "x" to the next one
  return x => seq(nodes.map(node => compileNode(node)(x))).map<[any, IExecutionContext]>(v => v.pop() || [undefined, x])
}

export function compileCode(code: string) {
  // create the file source
  const sourceFile = ts.createSourceFile(
    "code.ts",
    code,
    ts.ScriptTarget.Latest,
    true
  );
  // make the execution context
  const x = new ExecutionContext(ExecutionContextType.GLOBAL_CODE, true);
  // make the AST transforms
  return compileNodeSequence(sourceFile.statements)(x)
}