<?php

namespace App\Services\Deployment;

use Illuminate\Support\Carbon;
use Illuminate\Support\Facades\File;
use Illuminate\Support\Facades\Lang;
use Throwable;

/**
 * The panel's side of "update this installation".
 *
 * The panel cannot update anything itself, and it should not be able to. It
 * runs as www-data inside a container; the update runs on the host, as the
 * service account, and restarts the very container the request came from. A
 * button that shelled out would be a button that kills its own web server
 * mid-response — and it would need the app to hold host-level credentials,
 * which is a far worse thing to own than an out-of-date checkout.
 *
 * So this is a mailbox, not a command:
 *
 *   panel  → writes a request into storage/app/deploy/
 *   agent  → (deploy/update-agent.sh, on the host, on a timer) consumes it,
 *            runs deploy/update.sh, writes back what happened
 *   panel  → reads the result
 *
 * The directory is inside the bind-mounted checkout, so both sides see it
 * without anything being exposed over the network.
 *
 * The request carries a KIND, not a flag: "check" (look only — the agent
 * already fetches on every tick regardless, this just answers sooner than the
 * next one would on its own), "run" (apply it, downtime and all), or
 * "restart" (queue, queue-provisioning, scheduler, reverb only — picking up a
 * freshly-saved .env without a deployment). Three different things an
 * operator can ask for, not one request with a modifier — an operator who
 * only wants to know whether anything is new must not be routed through a
 * real deployment to find out, and one who only changed a credential must not
 * be routed through one either.
 *
 * Everything here degrades to "unknown" rather than throwing. A broken or
 * absent status file must leave the settings page readable — it is the page an
 * operator opens when something is already wrong.
 */
final class UpdateChannel
{
    /** Written by the panel, consumed by the agent. */
    private const REQUEST = 'deploy/update-request.json';

    /** A request the agent only checks against, and never acts on. */
    private const KIND_CHECK = 'check';

    /**
     * A request the agent actually applies.
     *
     * Also the fallback for a request with no `kind` at all — every request
     * meant this before "check" existed, so an older panel's request (or one
     * still in flight across a deploy of this very feature) must keep meaning
     * it rather than silently doing nothing.
     */
    private const KIND_RUN = 'run';

    /**
     * A request to restart the four workers that only read .env at their own
     * startup — queue, queue-provisioning, scheduler, reverb — and nothing
     * else. Not a deployment: no fetch is consulted, no maintenance mode, no
     * release is involved. `app` is deliberately never in that list — see
     * update-agent.sh's handling of this kind for why.
     */
    private const KIND_RESTART = 'restart';

    /**
     * A request to mint an SSH key that may do exactly one thing: read the
     * invoice archive over rsync.
     *
     * The panel cannot do any of it. Generating a keypair, installing the public
     * half restricted to one directory and handing over the private half all
     * happen on the HOST, in the service account's own home — and the panel is
     * www-data inside a container that owns none of that. So it asks, like it
     * asks for everything else here.
     */
    private const KIND_ARCHIVE_KEY = 'archive-key';

    /**
     * Where the agent leaves a freshly minted key, once.
     *
     * Read and deleted by the panel in one go: the private half exists on disk
     * for the seconds between the agent writing it and somebody looking at it,
     * and not a minute longer. Same shape as the initial admin password an
     * instance holds until it is acknowledged.
     */
    private const ARCHIVE_KEY = 'deploy/archive-key.json';

    /** Written by the agent after every check and every run. */
    private const STATUS = 'deploy/update-status.json';

    /**
     * The outcome of the last actual run, kept apart from the periodic check.
     *
     * In one file the next idle check would overwrite a failure a minute
     * later, and an operator would usually never learn that the update failed.
     */
    private const LAST_RUN = 'deploy/update-last-run.json';

    /** Tail of the last run, for the operator to read without shell access. */
    private const LOG = 'deploy/update-last-run.log';

    /**
     * The outcome of the last worker RESTART, kept apart from LAST_RUN.
     *
     * A restart is not a deployment and update.sh never runs for it, so it
     * gets its own tiny record rather than borrowing the deployment's — the
     * two must be able to fail independently and be reported independently.
     */
    private const RESTART_LAST_RUN = 'deploy/restart-last-run.json';

    /**
     * The step deploy/update.sh is on, written by update.sh itself.
     *
     * Read from here rather than from the status file, and that is the whole
     * point: the agent writes the status once, then blocks for the length of the
     * run. Anything taken from the status file is therefore frozen at "the run
     * started" and the step would never advance while it mattered. update.sh
     * rewrites this file at every step, so it is the only live source.
     *
     * Two tab-separated fields: the step key, and when it started.
     */
    private const PHASE = 'deploy/update-phase';

    /**
     * A request older than this is treated as abandoned.
     *
     * Without it a request written while the agent was stopped would fire the
     * moment the agent came back, which could be days later and no longer what
     * anyone wanted.
     */
    private const REQUEST_EXPIRES_MINUTES = 30;

    /**
     * How stale the agent's last check may be before it counts as gone.
     *
     * The timer runs every minute; twenty missed ticks in a row is a stopped
     * agent, not a slow one — comfortably more than one bad tick (a hung
     * fetch, a loaded host) can account for. Without this, a single status
     * file written once — by an agent since disabled, broken or uninstalled —
     * leaves the button enabled forever, and pressing it writes a request
     * nobody will ever collect while the page cheerfully reports an update in
     * progress.
     */
    private const AGENT_STALE_AFTER_MINUTES = 20;

    /**
     * What the panel needs to show, in one read.
     *
     * @return array<string, mixed>
     */
    public function state(): array
    {
        $release = Release::current();
        $status = $this->readJson(self::STATUS);
        $lastRun = $this->readJson(self::LAST_RUN);
        $restartLastRun = $this->readJson(self::RESTART_LAST_RUN);
        $request = $this->pendingRequest();

        $checkedAt = $this->timestamp($status['checked_at'] ?? null);
        $agentAlive = $this->agentIsAlive($status);
        // Missing on a request an older panel wrote — see KIND_RUN.
        $requestKind = $request['kind'] ?? self::KIND_RUN;

        // A figure from an agent that has since stopped is not current, and
        // "three updates behind" from last week reads exactly like now.
        $behind = $agentAlive && isset($status['behind']) ? (int) $status['behind'] : null;

        return [
            'version' => $release->version,
            'commit' => $release->commit,
            'source' => $release->source,
            'deployed_at' => $release->deployedAt,

            // Null means "we do not know", which is not the same as "up to
            // date" and must not be shown as it.
            'behind' => $behind,
            'available' => $behind !== null && $behind > 0,
            // The tag an update would install, e.g. "v1.1.0". An update is
            // always to a released version now — a commit landing on main is
            // not an update, and the console has nothing to say about it.
            'target_release' => $agentAlive && ! empty($status['target_release'])
                ? (string) $status['target_release']
                : null,
            'remote_commit' => isset($status['remote_commit']) ? (string) $status['remote_commit'] : null,
            'checked_at' => $checkedAt,

            'agent_seen' => $agentAlive,
            // A pending CHECK or RESTART must never read as "running": nothing
            // is being deployed, the site never enters maintenance mode, and
            // the full-screen overlay (layouts/admin.blade.php) exists only
            // for the case where it does. A worker restart used to slip
            // through this check by only excluding "check" — any kind that
            // was not a check counted as "running" — which would have shown
            // an operator saving .env the same maintenance screen as a real
            // deployment, for four containers that come back in seconds.
            // Matched on KIND_RUN explicitly instead, so a future kind added
            // here has to opt IN to the overlay rather than getting it by
            // accident.
            'running' => $agentAlive && (
                ($request !== null && $requestKind === self::KIND_RUN)
                || ($status['state'] ?? null) === 'running'
            ),
            // A pending check, still waiting for the agent to pick it up.
            'checking' => $agentAlive && $request !== null && $requestKind === self::KIND_CHECK,
            // A pending — or in-flight — worker restart. The agent handles a
            // restart within the same tick it consumes the request (no
            // maintenance mode, no phase file), so this is only ever true for
            // the short window before that tick runs; see RESTART_LAST_RUN
            // below for what happened once it has.
            'restarting' => $agentAlive && $request !== null && $requestKind === self::KIND_RESTART,
            'requested_at' => $request !== null ? $this->timestamp($request['requested_at'] ?? null) : null,
            'requested_by' => $request['requested_by'] ?? null,

            // Is the agent woken the moment a request lands, or does the
            // request wait for the next tick?
            //
            // Reported by the agent rather than decided here: the trigger is a
            // systemd path unit on the host (deploy/install-agent.sh), which
            // the panel cannot see from inside its container, and a server
            // that has not re-run install-agent.sh since this landed still
            // waits for the timer. It decides whether the console may say
            // "now" or has to name a time — and promising "now" on an
            // installation that will take five minutes is the failure this
            // whole field exists to avoid.
            'instant' => $agentAlive && ($status['request_watch'] ?? null) === true,

            // The step the deployment script is on — a key, translated here.
            // Read live from the phase file; older agents write none, so its
            // absence is normal rather than a fault.
            'phase' => $this->phase($this->currentPhase($status)),
            'started_at' => $this->timestamp($status['started_at'] ?? null),

            'last_state' => $lastRun['state'] ?? null,
            'last_phase' => $this->phase($lastRun['phase'] ?? null),
            'last_started_at' => $this->timestamp($lastRun['started_at'] ?? null),
            'last_finished_at' => $this->timestamp($lastRun['finished_at'] ?? null),
            // The run's own failure first; a check-level problem (the
            // repository being unreachable) only when the last run was fine.
            'last_error' => $this->errorMessage($lastRun) ?? $this->errorMessage($status),

            // The last worker restart, independent of the deployment fields
            // above — see RESTART_LAST_RUN.
            'last_restart_state' => $restartLastRun['state'] ?? null,
            'last_restart_finished_at' => $this->timestamp($restartLastRun['finished_at'] ?? null),
            'last_restart_error' => $this->errorMessage($restartLastRun),
        ];
    }

    /**
     * The deployment step, as something a German interface can print.
     *
     * The script writes a key precisely so this stays translatable. An unknown
     * key — a newer script against older translations — yields null rather than
     * a raw identifier in the middle of a sentence.
     */
    private function phase(mixed $key): ?string
    {
        if (! is_string($key) || $key === '') {
            return null;
        }

        $line = __('admin_settings.update_phase.'.$key);

        return is_string($line) && $line !== 'admin_settings.update_phase.'.$key ? $line : null;
    }

    /**
     * The step key update.sh last announced, or null.
     *
     * Its own tiny file rather than a field in the status document: update.sh
     * runs as the service account on the host and rewrites this at every step,
     * while the agent that owns the status document is blocked waiting for it.
     *
     * Only while a run is genuinely in flight, and only if the step is newer
     * than that run. A failed run deliberately LEAVES its file behind so the
     * failing step can be named; without these two checks, queueing the next
     * update would show it as already at "Migrating the database" — a step
     * nothing has started — and hide the one thing the operator needs, which is
     * when it will actually begin.
     *
     * @param  array<string, mixed>  $status
     */
    private function currentPhase(array $status): ?string
    {
        if (($status['state'] ?? null) !== 'running') {
            return null;
        }

        $path = storage_path('app/'.self::PHASE);

        if (! is_file($path)) {
            return null;
        }

        // Deliberately forgiving: this is a progress hint, and a half-written
        // line during the moment update.sh replaces it must not throw on a page
        // an operator is watching a deployment from.
        $parts = explode("\t", (string) @file_get_contents($path), 2);
        $key = trim($parts[0] ?? '');

        if ($key === '') {
            return null;
        }

        // Left over from a manual run of update.sh on the shell: newer than the
        // last agent status, older than this run.
        $startedAt = $this->timestamp($status['started_at'] ?? null);
        $phaseAt = $this->timestamp(trim($parts[1] ?? ''));

        if ($startedAt !== null && $phaseAt !== null && $phaseAt->lt($startedAt)) {
            return null;
        }

        return $key;
    }

    /*
     * There was a nextCheckAt() here, and a checkInterval() feeding it, so the
     * console could count down to the agent's next tick. Both are gone.
     *
     * It could not be made honest. `checked_at + interval` is in the past
     * whenever the interval the agent reports is shorter than the timer
     * actually installed on that host — which is every server that has not
     * re-run install-agent.sh — and the fallback then returned "now + interval"
     * afresh on every poll. The operator watched it run down four seconds and
     * snap back to a full minute, forever. Reported exactly that way.
     *
     * It is also no longer needed: the request wakes the agent (the path unit
     * in deploy/install-agent.sh), so there is no wait to describe.
     */

    /**
     * Has the agent checked in recently enough to be considered alive?
     *
     * @param  array<string, mixed>  $status
     */
    private function agentIsAlive(array $status): bool
    {
        $checkedAt = $this->timestamp($status['checked_at'] ?? null);

        return $checkedAt !== null
            && $checkedAt->gt(Carbon::now()->subMinutes(self::AGENT_STALE_AFTER_MINUTES));
    }

    /** Is the agent in the middle of a run right now? */
    public function isRunning(): bool
    {
        $status = $this->readJson(self::STATUS);

        return ($status['state'] ?? null) === 'running' && $this->agentIsAlive($status);
    }

    /** Is an update run already asked for, and still current? */
    public function pendingRequest(): ?array
    {
        $request = $this->readJson(self::REQUEST);

        if ($request === []) {
            return null;
        }

        $at = $this->timestamp($request['requested_at'] ?? null);

        if ($at === null || $at->lt(Carbon::now()->subMinutes(self::REQUEST_EXPIRES_MINUTES))) {
            return null;
        }

        return $request;
    }

    /**
     * Ask the agent to update — an actual run, downtime and all.
     *
     * Returns false when a request is already outstanding — clicking twice must
     * not queue two runs, and the second click is much more likely to be
     * impatience than intent.
     */
    public function request(string $by): bool
    {
        return $this->submit($by, self::KIND_RUN);
    }

    /**
     * Ask the agent only to look — never to apply anything.
     *
     * The agent already fetches on every tick regardless of this; the request
     * exists so an operator who asks gets an answer at the moment they ask,
     * and so the answer never runs through the "run" branch — no maintenance
     * mode, no restart, for a question that was only "is there something new".
     *
     * A question must not sit in a queue. Where the host runs the path unit
     * from deploy/install-agent.sh this file wakes the agent within a second;
     * where it does not, the timer is the fallback and the console says so
     * rather than counting down to a start that is not happening — see
     * 'instant' in state().
     */
    public function requestCheck(string $by): bool
    {
        return $this->submit($by, self::KIND_CHECK);
    }

    /**
     * Ask the agent to restart the four workers that only read .env at their
     * own startup — never `app`. See update-agent.sh's handling of this kind
     * for why `app` is excluded and always will be.
     *
     * The caller (App\Livewire\Admin\Integrations::saveEnv()) only calls this
     * when the agent is known to be alive; a submit() with no agent to
     * collect it would sit until it expires and tell the operator nothing.
     * Whether the agent is reachable at all is what makes the difference
     * between "handled automatically" and "saved, but still on the old
     * values" — the operator is told which one happened, never left to guess.
     */
    public function requestRestart(string $by): bool
    {
        return $this->submit($by, self::KIND_RESTART);
    }

    /**
     * Ask the host to mint a collection key for one archive directory.
     *
     * The path is passed rather than looked up on the host, because the panel
     * is the only side that knows which destination the operator pressed the
     * button on.
     */
    public function requestArchiveKey(string $by, string $path, string $label): bool
    {
        return $this->submit($by, self::KIND_ARCHIVE_KEY, [
            'archive_path' => $path,
            'label' => $label,
        ]);
    }

    /**
     * Take the minted key, if one is waiting.
     *
     * Taking, not reading: the file is deleted in the same call. A private key
     * that stays on disk after somebody has seen it is a private key on disk.
     *
     * @return array{created_at:string, label:string, path:string, private_key:string}|null
     */
    public function takeArchiveKey(): ?array
    {
        $data = $this->readJson(self::ARCHIVE_KEY);

        if ($data === [] || ! isset($data['private_key'])) {
            return null;
        }

        try {
            File::delete(storage_path('app/'.self::ARCHIVE_KEY));
        } catch (Throwable) {
            // Shown once regardless. Failing to delete it is a reason to warn,
            // not a reason to withhold the key from the person who asked for it
            // — they would simply ask again and leave a second one behind.
        }

        return $data;
    }

    /** @param array<string, mixed> $extra */
    private function submit(string $by, string $kind, array $extra = []): bool
    {
        // Both conditions, not just the request file. The agent DELETES the
        // request before it starts a run — so between that moment and the end
        // of the run there is nothing pending, and a second click from a
        // stale tab would queue a whole redundant deployment for the next
        // tick. One request slot for all three kinds: the agent handles one
        // tick at a time regardless of what it is asked for.
        if ($this->pendingRequest() !== null || $this->isRunning()) {
            return false;
        }

        $this->write(self::REQUEST, json_encode([
            'requested_at' => Carbon::now()->toIso8601String(),
            'requested_by' => $by,
            'kind' => $kind,
        ] + $extra, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES));

        return true;
    }

    /**
     * The agent's failure, in the operator's language.
     *
     * The agent is a shell script and is not translated; it reports a code and
     * the translation happens here. Anything unrecognised is passed through
     * rather than swallowed — a message nobody has worded yet still beats
     * silence when an update is failing.
     */
    private function errorMessage(array $status): ?string
    {
        $code = isset($status['error']) ? trim((string) $status['error']) : '';

        if ($code === '') {
            return null;
        }

        $key = 'admin_settings.update_error.'.$code;

        if (! Lang::has($key)) {
            return $code;
        }

        return __($key, ['code' => (string) ($status['exit_code'] ?? '?')]);
    }

    /** The tail of the last run, for showing what went wrong. */
    public function lastLog(int $lines = 40): ?string
    {
        $path = storage_path('app/'.self::LOG);

        try {
            if (! File::exists($path)) {
                return null;
            }

            $all = preg_split('/\R/', trim((string) File::get($path))) ?: [];

            return implode("\n", array_slice($all, -$lines));
        } catch (Throwable) {
            return null;
        }
    }

    /** @return array<string, mixed> */
    private function readJson(string $relative): array
    {
        try {
            $path = storage_path('app/'.$relative);

            if (! File::exists($path)) {
                return [];
            }

            $decoded = json_decode((string) File::get($path), true);

            return is_array($decoded) ? $decoded : [];
        } catch (Throwable) {
            return [];
        }
    }

    private function write(string $relative, string $contents): void
    {
        $path = storage_path('app/'.$relative);
        File::ensureDirectoryExists(dirname($path));
        File::put($path, $contents);
    }

    private function timestamp(mixed $value): ?Carbon
    {
        if (! is_string($value) || $value === '') {
            return null;
        }

        try {
            return Carbon::parse($value);
        } catch (Throwable) {
            return null;
        }
    }
}