import { createMacro } from 'babel-plugin-macros';
import { types } from '@babel/core';

import { ensureImport } from './helpers'

type MobExprMacro = <T>(expr: T) => T;

/**
 * Macro version of mobx-utils/expr.
 * 
 * Upon transpilation, converts `mexpr(a.b.c)` -> `computed(() => a.b.c).get()`
 * and ensures that `computed` is imported from MobX
 * 
 * @name mexpr
 * @param expr Expression to be converted into a computed
 */
export default createMacro(({ references, state, babel: { types: t } }) => {
    references.default.forEach(ref => {
        // TODO: Extract expressions into class properties?
        const call_expr = ref.container as types.CallExpression;
        const comp_expr = call_expr.arguments[0] as any;

        const cf_expr = t.arrowFunctionExpression([], comp_expr);
        const comp_inst_expr = t.callExpression(t.identifier('computed'), [cf_expr]);
        const get_expr = t.memberExpression(comp_inst_expr, t.identifier('get'))
        const get_call_expr = t.callExpression(get_expr, []);

        const program = ref.scope.getProgramParent().path;
        ensureImport(t, program, 'computed', 'mobx')

        ref.parentPath.replaceWith(get_call_expr)
    })
}) as MobExprMacro;