/**
 * usmrad — USM Rapid Application Deployment supervisor.
 *
 * Tracks a git branch, builds and installs the branch's manifest into an
 * A/B slot layout under the application directory, and keeps an instance of
 * the application's executable running from the active slot. A deployment
 * failure never disturbs a running instance; a successful deployment
 * terminates the old instance and launches the new one. When the supervised
 * executable exits, usmrad exits with its exit code.
 *
 * Configuration is entirely environmental; see {@link Config}.
 */
namespace Usm.Rad {

/**
 * Failure modes of the rapid-deployment supervisor.
 */
public errordomain RadError {
    /** A USMRAD_* environment variable is missing or malformed */
    CONFIGURATION,
    /** A git operation (clone, fetch, reset) failed */
    GIT,
    /** A build or install step failed */
    DEPLOY,
    /** A dependency resource could not be satisfied by the SPM or USM repositories */
    DEPENDENCY
}

/**
 * Bracketed-origin logging for the usmrad supervisor, per STYLE.md.
 */
public class Log {

    /**
     * Prints an informational line to stdout with the {@link Log} origin
     * prefix.
     */
    public static void info(string message) {
        print("[usmrad] %s\n", message);
    }

    /**
     * Prints a warning line to stderr with the {@link Log} origin prefix.
     */
    public static void warning(string message) {
        printerr("[usmrad] %s\n", message);
    }
}

/**
 * argv construction for spawned commands and joined argument strings.
 *
 * Invercargill's {@link Invercargill.DataStructures.Vector.to_array} returns
 * exactly-sized arrays without the NULL sentinel GLib's spawn helpers and
 * {@link string.joinv} require — an unterminated argv crashes inside
 * g_subprocess_newv's g_strdupv. Every vector-built argument list therefore
 * flows through {@link from_vector}, whose trailing zeroed slot terminates
 * the array the same way a Vala literal or explicit `new string[n]` fill
 * does.
 */
public class Argv {

    /**
     * A NULL-terminated copy of {@link command}: one slot longer than the
     * vector, with the final slot left zeroed as the sentinel.
     */
    public static string[] from_vector(Invercargill.DataStructures.Vector<string> command) {
        var size = (int)command.length;
        var argv = new string[size + 1];
        var index = 0;
        foreach(var argument in command) {
            argv[index++] = argument;
        }
        return argv;
    }
}

/**
 * usmrad configuration, parsed from the USMRAD_* environment.
 */
public class Config : Object {

    /** Git repository URL to deploy (USMRAD_REPO, required). */
    public string repo { get; set; }
    /** Branch to track (USMRAD_BRANCH, default "master"). */
    public string branch { get; set; default = "master"; }
    /** Poll interval in minutes; 0 disables polling (USMRAD_POLL). */
    public double poll_minutes { get; set; default = 0; }
    /** Application directory (USMRAD_APPDIR, default "/app"). */
    public string appdir { get; set; default = "/app"; }
    /** USMR URIs wired into usm at startup (USMRAD_USM_REPOS, semicolon-delimited). */
    public string[] usm_repos { get; set; default = new string[] {}; }
    /** Seconds between SIGTERM and SIGKILL when terminating an instance (USMRAD_TERM_GRACE). */
    public int term_grace_seconds { get; set; default = 10; }

    /**
     * Poll interval in whole seconds; 0 when polling is disabled. Fractional
     * minutes round down, so USMRAD_POLL=0.25 polls every 15 seconds.
     */
    public uint poll_interval_seconds {
        get {
            return (uint)(poll_minutes * 60.0);
        }
    }

    /**
     * Reads the USMRAD_* environment applying defaults, throwing
     * {@link RadError.CONFIGURATION} with a user-facing message when a
     * variable is missing or malformed.
     */
    public static Config from_environment() throws RadError {
        var config = new Config();

        var repo = Environment.get_variable("USMRAD_REPO");
        if(repo == null || repo.strip().length == 0) {
            throw new RadError.CONFIGURATION("USMRAD_REPO is required (a git repository URL)");
        }
        config.repo = repo.strip();

        var branch = Environment.get_variable("USMRAD_BRANCH");
        if(branch != null && branch.strip().length > 0) {
            config.branch = branch.strip();
        }

        var poll = Environment.get_variable("USMRAD_POLL");
        if(poll != null && poll.strip().length > 0) {
            double parsed_poll;
            if(!double.try_parse(poll.strip(), out parsed_poll) || parsed_poll < 0) {
                throw new RadError.CONFIGURATION(@"USMRAD_POLL must be a non-negative number of minutes, got \"$poll\"");
            }
            config.poll_minutes = parsed_poll;
        }

        var appdir = Environment.get_variable("USMRAD_APPDIR");
        if(appdir != null && appdir.strip().length > 0) {
            config.appdir = appdir.strip();
        }

        var repos = Environment.get_variable("USMRAD_USM_REPOS");
        if(repos != null && repos.strip().length > 0) {
            var entries = new Invercargill.DataStructures.Vector<string>();
            foreach(var entry in repos.split(";")) {
                if(entry.strip().length > 0) {
                    entries.add(entry.strip());
                }
            }
            config.usm_repos = entries.to_array();
        }

        var grace = Environment.get_variable("USMRAD_TERM_GRACE");
        if(grace != null && grace.strip().length > 0) {
            int64 parsed_grace;
            if(!int64.try_parse(grace.strip(), out parsed_grace) || parsed_grace < 0) {
                throw new RadError.CONFIGURATION(@"USMRAD_TERM_GRACE must be a non-negative number of seconds, got \"$grace\"");
            }
            config.term_grace_seconds = (int)parsed_grace;
        }

        return config;
    }
}

Config rad_config;
Slots rad_slots;
Source rad_source;
System rad_system;
Deployer rad_deployer;
Supervisor rad_supervisor;
MainLoop rad_loop;
string rad_exec_name;
string[] rad_exec_args;
int rad_exit_code = 0;
bool rad_cycle_busy = false;
bool rad_instance_running = false;

// The test target links every rad source for pure-logic coverage; only the
// real executable may own the process entry point
#if !USMRAD_TESTS
public static int main(string[] args) {
    if(args.length < 2 || args[1].has_prefix("-")) {
        usage();
        return 255;
    }
    rad_exec_name = args[1];
    rad_exec_args = args[2:args.length];

    try {
        rad_config = Config.from_environment();
    }
    catch(RadError e) {
        Log.warning(e.message);
        usage();
        return 255;
    }

    rad_slots = new Slots(rad_config.appdir);
    try {
        rad_slots.ensure_layout();
    }
    catch(Error e) {
        Log.warning(@"Could not create the appdir layout in \"$(rad_config.appdir)\": $(e.message)");
        return 255;
    }

    var usm_binary = find_usm_binary();
    if(usm_binary == null) {
        Log.warning("Could not locate the usm executable next to usmrad or on PATH");
        return 255;
    }

    rad_source = new Source(rad_config.repo, rad_config.branch, rad_slots.repo_dir);
    rad_system = new System(rad_config, usm_binary);
    rad_deployer = new Deployer(rad_config, rad_slots, rad_source, rad_system, usm_binary);
    rad_supervisor = new Supervisor(rad_slots.pwd, rad_config.term_grace_seconds);

    rad_loop = new MainLoop();
    rad_supervisor.exited.connect(status => {
        rad_exit_code = status;
        rad_loop.quit();
    });
    rad_supervisor.shutdown.connect(signal_number => {
        rad_exit_code = 128 + signal_number;
        rad_loop.quit();
    });
    rad_supervisor.run();

    // Launch the previous good instance first so a running deployment cycle
    // never adds downtime for an instance that already works
    rad_instance_running = launch_from_current();
    if(rad_instance_running) {
        Log.info(@"Launched previous instance from slot \"$(rad_slots.read_current_slot())\"");
    }

    Idle.add(() => {
        startup_cycle.begin();
        return false;
    });

    if(rad_config.poll_interval_seconds > 0) {
        Timeout.add_seconds(rad_config.poll_interval_seconds, () => {
            run_cycle.begin();
            return true;
        });
    }

    rad_loop.run();
    return rad_exit_code;
}

/**
 * Runs the startup check cycle: enrollment, repository wiring and one
 * deployment check. With no previous instance a failed first deployment is
 * fatal (exit 251); with one, failures merely warn.
 */
private static async void startup_cycle() {
    try {
        rad_system.ensure_enrolled();
    }
    catch(RadError e) {
        Log.warning(@"usm enroll failed: $(e.message)");
        rad_exit_code = 245;
        rad_loop.quit();
        return;
    }

    try {
        rad_system.wire_repos();
    }
    catch(RadError e) {
        Log.warning(@"Could not wire USMRAD_USM_REPOS repositories: $(e.message); continuing");
    }

    var deployed = yield run_cycle();
    if(!deployed && !rad_instance_running) {
        Log.warning("First deployment failed and no previous instance exists");
        rad_exit_code = 251;
        rad_loop.quit();
    }
}

/**
 * Runs one check cycle, guarded against re-entry: synchronise the source
 * repository, refresh and update USM packages, and when new commits or
 * package updates are available, deploy into the inactive slot and swap.
 * Returns true when a deployment went through and a new instance launched.
 */
private static async bool run_cycle() {
    if(rad_cycle_busy) {
        return false;
    }
    rad_cycle_busy = true;
    var deployed = false;
    try {
        deployed = yield run_cycle_inner();
    }
    finally {
        rad_cycle_busy = false;
    }
    return deployed;
}

private static async bool run_cycle_inner() {
    try {
        rad_source.ensure_cloned();
        rad_source.fetch();
    }
    catch(RadError e) {
        Log.warning(@"Could not synchronise \"$(rad_config.repo)\": $(e.message); skipping cycle");
        return false;
    }

    var deployed_commit = rad_slots.read_deployed_commit();
    string remote_head = null;
    try {
        remote_head = rad_source.remote_head();
    }
    catch(RadError e) {
        Log.warning(@"Could not resolve the remote head: $(e.message); skipping cycle");
        return false;
    }
    var new_commits = deployed_commit == null || deployed_commit != remote_head;

    var deps_changed = false;
    try {
        deps_changed = yield rad_system.refresh_and_update();
    }
    catch(RadError e) {
        Log.warning(@"usm update failed: $(e.message); continuing with the commit check");
    }

    if(!new_commits && !deps_changed) {
        return false;
    }

    Log.info(new_commits
        ? @"New commits on \"$(rad_config.branch)\" ($remote_head)"
        : "Upstream USM package updates detected");

    var inactive_slot = rad_slots.inactive_slot() ?? "a";
    try {
        yield rad_deployer.deploy(inactive_slot);
    }
    catch(RadError e) {
        Log.warning(@"Deployment into slot \"$inactive_slot\" failed: $(e.message)");
        return false;
    }

    if(rad_instance_running) {
        Log.info("Terminating previous instance");
        yield rad_supervisor.terminate();
        rad_instance_running = false;
    }

    if(launch_from_current()) {
        rad_instance_running = true;
        Log.info(@"Launched new instance from slot \"$(rad_slots.read_current_slot())\" ($remote_head)");
        return true;
    }

    // The deployment succeeded but nothing launchable came out of it; the
    // container supervisor is better placed to recover than a dead poll loop
    Log.warning(@"\"$(rad_exec_name)\" does not resolve or launch from the deployed slot");
    rad_exit_code = 251;
    rad_loop.quit();
    return true;
}

/**
 * Launches the configured exec from the current slot. Returns false without
 * ceremony when no slot is current; warns when a current slot exists but the
 * exec does not resolve or launch within it.
 */
private static bool launch_from_current() {
    var current_slot = rad_slots.read_current_slot();
    if(current_slot == null) {
        return false;
    }

    var executable = rad_slots.resolve_exec(current_slot, rad_exec_name);
    if(executable == null) {
        Log.warning(@"\"$(rad_exec_name)\" does not resolve in slot \"$current_slot\" (PATH-style search within the slot)");
        return false;
    }

    try {
        rad_supervisor.launch(executable, rad_exec_args);
    }
    catch(Error e) {
        Log.warning(@"Could not launch \"$executable\": $(e.message)");
        return false;
    }
    return true;
}

/**
 * Locates the usm executable: a sibling of usmrad's own executable first
 * (both install into the same bindir), then the PATH.
 */
private static string? find_usm_binary() {
    try {
        var own_path = FileUtils.read_link("/proc/self/exe");
        var candidate = Path.build_filename(Path.get_dirname(own_path), "usm");
        if(FileUtils.test(candidate, FileTest.IS_EXECUTABLE)) {
            return candidate;
        }
    }
    catch(Error e) {
        // Fall through to the PATH search
    }
    return Environment.find_program_in_path("usm");
}

private static void usage() {
    printerr("USAGE:\n\tusmrad <exec> [args...]\n\nEnvironment:\n");
    printerr("\tUSMRAD_REPO (required) git repository URL\n");
    printerr("\tUSMRAD_BRANCH branch to track (default: master)\n");
    printerr("\tUSMRAD_POLL poll interval in minutes, 0 disables (default: 0)\n");
    printerr("\tUSMRAD_APPDIR application directory (default: /app)\n");
    printerr("\tUSMRAD_USM_REPOS semicolon-delimited .usmr URIs\n");
    printerr("\tUSMRAD_TERM_GRACE seconds between SIGTERM and SIGKILL (default: 10)\n");
}
#endif
}