typocomath/src/plugins/typeInferPlugin.ts

import ts from 'typescript'

const transformer: ts.TransformerFactory<ts.SourceFile> = context => {
  // TODO: get a reference to the program instance that the plugin is running in instead of creating a new program?
  const program = ts.createProgram([],  {})
  const checker = program.getTypeChecker()

  return sourceFile => {
    const visitor = (node: ts.Node): ts.Node => {
      // @ts-ignore
      if (ts.isStringLiteral(node) && node.text === '__infer__') {
        console.log('PLUGIN: FOUND AN OCCURRENCE OF __infer__')

        // we're looking for a function call like typed('name', '__infer__', deps => ...)
        const parentNode = node.parent
        if (ts.isCallExpression(parentNode) && ts.isIdentifier(parentNode.expression) && parentNode.expression.escapedText === '$reflect') {
          // console.log('PARENT')
          // console.log(parentNode)

          // TODO: validate that argNode is an ArrowFunction
          // @ts-ignore
          const argNode = parentNode.arguments[1]
          // @ts-ignore
          const returnType = argNode.type.getText(sourceFile)
          console.log('PLUGIN: RETURN TYPE')
          console.log(returnType)
          // (a: number) => number

          // @ts-ignore
          const paramNode = argNode.parameters[0]
          const paramTypeSrc = paramNode.type.getText(sourceFile)
          console.log('PLUGIN: PARAM TYPE SRC', paramTypeSrc)
          // {
          //   multiply: (a: number, b: number) => number,
          //   unaryMinus: (x: number) => number, // just for the experiment
          // }

          const type = checker.getTypeAtLocation(paramNode)
          const paramType = checker.typeToString(type, paramNode, ts.TypeFormatFlags.InTypeAlias)
          console.log('PLUGIN: PARAM TYPE STRING', paramType)
          // { multiply: (a: number, b: number) => number; unaryMinus: (x: number) => number; }

          const depsAndReturnType = `{ deps: ${paramType}; return: ${returnType} }`

          return ts.factory.createStringLiteral(depsAndReturnType)
        }
      }

      return ts.visitEachChild(node, visitor, context)
    }

    return ts.visitNode(sourceFile, visitor)
  }
}

export default transformer