import * as _ from "lodash-commonjs-es";
import * as utils from "../../utils";
import type { RuleListener } from "@typescript-eslint/utils/dist/ts-eslint";
import { is } from "typescript-misc";

export enum MessageId {
  inexhaustiveSwitch = "inexhaustiveSwitch"
}

export const exhaustiveSwitch = utils.createRule({
  name: "exhaustive-switch",
  messages: { [MessageId.inexhaustiveSwitch]: "Inexhaustive switch" },
  docs: {
    description: "Checks exhaustiveness of switch statement.",
    failExamples: `
      function f(x: 1 | 2): void {
        switch (x) {
          case 1:
        }
      }
    `,
    passExamples: `
      function f(x: 1 | 2): void {
        switch (x) {
          case 1:
          case 2:
        }
      }
    `
  },
  create: (context, typeCheck): RuleListener => {
    return {
      SwitchStatement: node => {
        if (node.cases.some(switchCase => is.null(switchCase.test))) {
          // Has default
        } else {
          const got = node.cases
            .map(switchCase => switchCase.test)
            .filter(is.not.empty)
            .flatMap(expression => typeCheck.typeParts(expression));

          const expected = typeCheck.typeParts(node.discriminant);

          if (_.difference(expected, got).length > 0)
            context.report({
              messageId: MessageId.inexhaustiveSwitch,
              node: node.discriminant
            });
        }
      }
    };
  }
});