str/src/vm/commands/enclose.ts

import {Command, ParseContext, StrTerm, unwrapString, wrapString} from "./command.js";
import {LexInput} from "../lexer.js";
import {StrVM} from "../vm.js";
import {Awaitable} from "../../util/types.js";

export type EncloseData = {
    left?: StrTerm,
    right?: StrTerm,
}

export class Enclose extends Command<EncloseData> {
    attemptParse(context: ParseContext): EncloseData {
        return {
            left: context.popOptionalTerm(),
            right: context.popOptionalTerm(),
        }
    }

    getDisplayName(): string {
        return 'enclose'
    }

    isParseCandidate(token: LexInput): boolean {
        return this.isKeyword(token, 'enclose')
    }

    execute(vm: StrVM, data: EncloseData): Awaitable<StrVM> {
        return vm.tapInPlace(ctx => {
            const [left, right] = this.determineSurroundingStrings(
                data.left ? ctx.resolveString(data.left) : undefined,
                data.right ? ctx.resolveString(data.right) : undefined,
            )

            return ctx.replaceSubjectAsString(sub => `${left}${sub}${right}`)
        })
    }

    private determineSurroundingStrings(left?: string, right?: string): [string, string] {
        if ( !left ) {
            left = '('
        }

        if ( !right ) {
            right = ({
                '(': ')',
                '[': ']',
                '{': '}',
                '<': '>',
            })[left] ?? left
        }

        return [left, right]
    }
}