import fs from 'node:fs';

import { sync as commandExistsSync } from 'command-exists';
import git from 'isomorphic-git';
import http from 'isomorphic-git/http/node';
import simpleGit from 'simple-git';

/** @type {{ AUTO: 'auto', SYSTEM: 'system', BUILTIN: 'builtin' }} */
export const GIT_BACKENDS = {
    AUTO: 'auto',
    SYSTEM: 'system',
    BUILTIN: 'builtin',
};

/**
 * @param {string | undefined | null} preferredBackend
 * @returns {'system' | 'builtin'}
 */
function resolveBackend(preferredBackend) {
    const normalized = typeof preferredBackend === 'string' ? preferredBackend.trim().toLowerCase() : GIT_BACKENDS.AUTO;
    const backend = normalized === GIT_BACKENDS.SYSTEM
        ? GIT_BACKENDS.SYSTEM
        : normalized === GIT_BACKENDS.BUILTIN
            ? GIT_BACKENDS.BUILTIN
            : GIT_BACKENDS.AUTO;
    const systemGitAvailable = commandExistsSync('git');

    if (backend === GIT_BACKENDS.SYSTEM && !systemGitAvailable) {
        throw new Error('System git backend is configured, but no git binary was found in PATH.');
    }

    if (backend === GIT_BACKENDS.SYSTEM || (backend === GIT_BACKENDS.AUTO && systemGitAvailable)) {
        return GIT_BACKENDS.SYSTEM;
    }

    return GIT_BACKENDS.BUILTIN;
}

/**
 * @typedef {object} GitCloneOptions
 * @property {number} [depth]
 * @property {string} [branch]
 */

const SUPPORTED_CLONE_OPTIONS = new Set(['depth', 'branch']);

/**
 * @param {GitCloneOptions} [options]
 * @returns {{ depth?: number, branch?: string }}
 */
function normalizeCloneOptions(options = {}) {
    for (const key of Object.keys(options)) {
        if (!SUPPORTED_CLONE_OPTIONS.has(key)) {
            throw new Error(`Unsupported clone option: ${key}`);
        }
    }
    return { depth: options.depth, branch: options.branch };
}

/**
 * @typedef {object} GitClient
 * @property {'system' | 'builtin'} backend
 * @property {(url: string, localPath: string, options?: GitCloneOptions) => Promise<void>} clone
 */

/**
 * @param {{ backend?: string }} [options]
 * @returns {GitClient}
 */
export function createGitClient(options = {}) {
    const backend = resolveBackend(options.backend);
    if (backend === GIT_BACKENDS.SYSTEM) {
        return new SimpleGitClient();
    }

    return new IsomorphicGitClient();
}

/**
 * @implements {GitClient}
 */
class SimpleGitClient {
    constructor() {
        this.backend = GIT_BACKENDS.SYSTEM;
        this.git = simpleGit();
    }

    /**
     * @param {string} url
     * @param {string} localPath
     * @param {GitCloneOptions} [options]
     * @returns {Promise<void>}
     */
    async clone(url, localPath, options = {}) {
        const { depth, branch } = normalizeCloneOptions(options);
        /** @type {Record<string, any>} */
        const cloneOptions = {};

        if (depth !== undefined) {
            cloneOptions['--depth'] = depth;
        }

        if (branch) {
            cloneOptions['--branch'] = branch;
        }

        await this.git.clone(url, localPath, cloneOptions);
    }
}

/**
 * @implements {GitClient}
 */
class IsomorphicGitClient {
    constructor() {
        this.backend = GIT_BACKENDS.BUILTIN;
    }

    /**
     * @param {string} url
     * @param {string} localPath
     * @param {GitCloneOptions} [options]
     * @returns {Promise<void>}
     */
    async clone(url, localPath, options = {}) {
        const { depth, branch } = normalizeCloneOptions(options);

        await git.clone({
            fs,
            http,
            dir: localPath,
            url,
            depth,
            ref: branch,
            singleBranch: depth !== undefined || Boolean(branch),
        });
    }
}