import * as os from "os";
import * as path from "path";
import { increment } from "../../internal/util/metric";
import { logger } from "../../util/logger";
import {
    CloneDirectoryInfo,
    CloneOptions,
    DirectoryManager,
} from "./DirectoryManager";
import { StableDirectoryManager } from "./StableDirectoryManager";
import { TmpDirectoryManager } from "./tmpDirectoryManager";

const AtomistWorkingDirectory = path.join(".atomist", "cache");

const AbsoluteAtomistWorkingDirectory = path.join(os.homedir(), AtomistWorkingDirectory);

const cache = new StableDirectoryManager({
    reuseDirectories: true,
    baseDir: AbsoluteAtomistWorkingDirectory,
    cleanOnExit: false,
});

/**
 * Designed to accommodate occasional writes to the same repositories,
 * this keeps one clone available for each repository. Every time that repository is requested,
 * if that clone is available, we return it. (The caller gets to fetch, clean, etc. The directory could be dirty.)
 * If that clone is locked by some other automation invocation, this
 * DirectoryManager returns a temporary directory, and you get to clone into that.
 *
 * If the returned CloneDirectoryInfo has type: "empty-directory"
 * then the caller should clone into it (not from it, you're not in the parent directory).
 * If it has type: "existing-directory" then fetch, clean, checkout etc. given it's already cloned.
 *
 * @type {{directoryFor:
 * ((owner: string, repo: string, branch: string, opts: CloneOptions) => Promise<CloneDirectoryInfo>)}}
 */
export const CachingDirectoryManager: DirectoryManager = {

    directoryFor(owner: string, repo: string, branch: string, opts: CloneOptions): Promise<CloneDirectoryInfo> {

        return cache.directoryFor(owner, repo, branch, opts).then(existing =>
            pleaseLock(existing.path).then(lockResult => {
                if (lockResult.success) {
                    incrementReuse(owner, repo);
                    return {
                        ...existing,
                        release: () => {
                            logger.debug("Releasing lock on '%s'", existing.path);
                            return lockResult.release().then(existing.release);
                        },
                        invalidate: () => {
                            logger.debug("Invalidating '%s'", existing.path);
                            return cache.invalidate(existing)
                                .then(() => {
                                    logger.debug("Invalidated. Now releasing lock");
                                    return lockResult.release().then(existing.release);
                                });
                        },
                        provenance: (existing.provenance || "") + " successfully locked",
                    };
                } else {
                    logger.debug("Lock detected on '%s'", existing.path);
                    incrementFallback(owner, repo);
                    return TmpDirectoryManager.directoryFor(owner, repo, branch, opts).then(cdi =>
                        ({
                            ...cdi,
                            provenance: `Tried '${existing.path}' but it was locked. ` + (cdi.provenance || ""),
                        }));
                }
            }));
    },
};

export const ReuseKey = "directory_cache.reuse";
export const FallbackKey = "directory_cache.fallback";

function incrementReuse(owner: string, repo: string): void {
    increment(`${ReuseKey}.${keyFor(owner, repo)}`);
    increment(ReuseKey);
}

function incrementFallback(owner: string, repo: string): void {
    increment(`${FallbackKey}.${keyFor(owner, repo)}`);
    increment(FallbackKey);
}

function keyFor(owner: string, repo: string): string {
    return `${owner}/${repo}`;
}

/*
 * file locking. only used here
 */
import lockfile = require("proper-lockfile");

interface LockAcquired {
    success: true;
    release: () => Promise<void>;
}

interface NoLockForYou {
    success: false;
    error: Error;
}

// for testing
export { pleaseLock, LockResult, LockAcquired, NoLockForYou };

type LockResult = LockAcquired | NoLockForYou;

function pleaseLock(lockPath: string): Promise<LockResult> {
    return new Promise<LockResult>((resolve, reject) => {
        lockfile.lock(lockPath, (error, releaseCallback) => {
            if (error) {
                if (error.code === "ELOCKED") {
                    resolve({ success: false, error });
                }
                reject(error);
            } else {
                // make the release function return a promise too. Its callback accepts a possible error.
                const release = () =>
                    new Promise<void>((releaseResolve, releaseReject) => {
                        releaseCallback(err => {
                            if (err) {
                                releaseReject(err);
                            } else {
                                releaseResolve();
                            }
                        });
                    });
                resolve({ success: true, release });
            }
        });
    });
}