import {Command, ParseContext, processPath, StrTerm} from "./command.js";
import {LexInput} from "../lexer.js";
import {StrVM} from "../vm.js";
import {Awaitable} from "../../util/types.js";
import os from "node:os";
import fs from "node:fs/promises";
import {isSaveData} from "./save.js";

export class Load extends Command<{ path?: StrTerm }> {
    isParseCandidate(token: LexInput): boolean {
        return this.isKeyword(token, 'load')
    }

    attemptParse(context: ParseContext): { path?: StrTerm } {
        return { path: context.popOptionalTerm() }
    }

    getDisplayName(): string {
        return 'load'
    }

    execute(vm: StrVM, data: { path?: StrTerm }): Awaitable<StrVM> {
        return vm.replaceContextMatchingTerm(ctx => ({
            override: async () => {
                const path = processPath(
                    data.path
                        ? ctx.resolveString(data.path)
                        : `~/.str.json`)

                const content = await fs.readFile(path, 'utf8')
                const saveData = JSON.parse(content)
                if ( !isSaveData(saveData) ) {
                    throw new Error('Cannot load: invalid save data')
                }

                return saveData.subject
            }
        }))
    }
}