/*
 * Copyright (C) 2024-present Puter Technologies Inc.
 *
 * This file is part of Puter.
 *
 * Puter is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
import { Exit } from './coreutil_lib/exit.js';
import { fileLines } from '../../util/file.js';

export default {
    name: 'head',
    usage: 'head [OPTIONS] [FILE]',
    description: 'Read a file and print the first lines to standard output.\n\n' +
        'Defaults to 10 lines unless --lines is given. ' +
        'If no FILE is provided, or FILE is `-`, read standard input.',
    input: {
        syncLines: true
    },
    args: {
        $: 'simple-parser',
        allowPositionals: true,
        options: {
            lines: {
                description: 'Print the last COUNT lines',
                type: 'string',
                short: 'n',
                valueName: 'COUNT',
            }
        }
    },
    execute: async ctx => {
        const { out, err } = ctx.externs;
        const { positionals, values } = ctx.locals;

        if (positionals.length > 1) {
            // TODO: Support multiple files (this is POSIX)
            await err.write('head: Only one FILE parameter is allowed\n');
            throw new Exit(1);
        }
        const relPath = positionals[0] || '-';

        let lineCount = 10;

        if (values.lines) {
            const parsedLineCount = Number.parseFloat(values.lines);
            if (isNaN(parsedLineCount) || ! Number.isInteger(parsedLineCount) || parsedLineCount < 1) {
                await err.write(`head: Invalid number of lines '${values.lines}'\n`);
                throw new Exit(1);
            }
            lineCount = parsedLineCount;
        }

        let processedLineCount = 0;
        for await (const line of fileLines(ctx, relPath)) {
            await out.write(line);
            processedLineCount++;
            if (processedLineCount >= lineCount)
                break;
        }
    }
};
