const fs = require('fs');
const os = require('os');
const path = require('path');

function executable(filename) {
    try {
        fs.accessSync(filename, fs.constants.X_OK);
        return true;
    } catch (_) {
        return false;
    }
}

function localPythonVersion(workspace) {
    if (!workspace) return null;
    let directory = path.resolve(workspace);
    while (directory !== path.dirname(directory)) {
        try {
            const version = fs.readFileSync(path.join(directory, '.python-version'),
                                            'utf8').trim().split(/\s+/)[0];
            return /^[A-Za-z0-9._-]+$/.test(version) ? version : null;
        } catch (_) {}
        directory = path.dirname(directory);
    }
    return null;
}

function installedPyenvPythons(home) {
    try {
        const versions = fs.readdirSync(path.join(home, '.pyenv', 'versions'));
        return versions.filter(version => /^3\.12(?:\.\d+)?$/.test(version))
            .sort((a, b) => Number(b.split('.')[2] || 0) -
                            Number(a.split('.')[2] || 0))
            .map(version => path.join(home, '.pyenv', 'versions', version,
                                      'bin', 'python'));
    } catch (_) {
        return [];
    }
}

function resolvePython(options = {}) {
    const command = String(options.command || 'auto').trim();
    const args = Array.isArray(options.args) ? options.args : [];
    if (command !== 'auto') {
        return {command, args};
    }

    const home = options.home || os.homedir();
    const workspace = options.workspace;
    const isExecutable = options.isExecutable || executable;
    const candidates = [];
    const shim = path.join(home, '.pyenv', 'shims', 'python');
    const version = options.localVersion === undefined ?
        localPythonVersion(workspace) : options.localVersion;
    const installed = options.installedPyenv === undefined ?
        installedPyenvPythons(home) : options.installedPyenv;
    if (version) candidates.push(shim);
    candidates.push(...installed);
    if (!version) candidates.push(shim);
    if (workspace) {
        candidates.push(path.join(workspace, '.venv', 'bin', 'python'));
    }
    candidates.push(
        '/opt/homebrew/bin/python3.12',
        '/usr/local/bin/python3.12',
        '/usr/bin/python3.12',
    );
    const found = candidates.find(isExecutable);
    if (!found) {
        throw new Error(
            'Не найден Python 3.12. Задайте абсолютный путь в ' +
            'sprinterDebugger.pythonCommand.');
    }
    return {command: found, args: []};
}

function pyenvEnvironment(command, workspace, home = os.homedir()) {
    const shim = path.join(home, '.pyenv', 'shims', 'python');
    const version = command === shim ? localPythonVersion(workspace) : null;
    return version ? {PYENV_VERSION: version} : undefined;
}

module.exports = {resolvePython, localPythonVersion, installedPyenvPythons,
                  pyenvEnvironment};