<?php

declare(strict_types=1);

// Instance registry. Replaces the backup server's plain name allowlist and
// gives the update server the client identity it never had. One record per
// deployed client instance, stored in storage/instances.json.
//
// Tokens are stored as a SHA-256 hash only. The plaintext is returned exactly
// once, when it is created or rotated, and can never be recovered afterwards.

require_once __DIR__ . "/bootstrap.php";

function manageInstanceValidateId(string $id): string
{
    $id = trim($id);
    if (
        $id === "" ||
        strlen($id) > 120 ||
        preg_match('/^[A-Za-z0-9][A-Za-z0-9._-]*$/', $id) !== 1
    ) {
        throw new RuntimeException(
            "Ungültige Instanz-Kennung. Erlaubt sind Buchstaben, Zahlen, Punkt, Unterstrich und Bindestrich.",
        );
    }

    return $id;
}

function manageInstanceGenerateToken(): string
{
    return bin2hex(random_bytes(32));
}

function manageInstanceHashToken(string $token): string
{
    return hash("sha256", $token);
}

// Fills in every field a caller may read, so the rest of the code never has to
// guard against records written by an older version.
function manageInstanceNormalize(array $record): array
{
    return [
        "id" => (string) ($record["id"] ?? ""),
        "label" => (string) ($record["label"] ?? ""),
        "enabled" => (bool) ($record["enabled"] ?? true),
        "token_hash" => (string) ($record["token_hash"] ?? ""),
        "created_at" => (string) ($record["created_at"] ?? ""),
        "token_rotated_at" => (string) ($record["token_rotated_at"] ?? ""),
        "last_seen_at" => (string) ($record["last_seen_at"] ?? ""),
        "last_ip" => (string) ($record["last_ip"] ?? ""),
        "version" => (string) ($record["version"] ?? ""),
        "php_version" => (string) ($record["php_version"] ?? ""),
        "disk_free" => (int) ($record["disk_free"] ?? 0),
        "pending_migrations" => (int) ($record["pending_migrations"] ?? 0),
        "last_backup_at" => (string) ($record["last_backup_at"] ?? ""),
        "backup_count" => (int) ($record["backup_count"] ?? 0),
        "notes" => (string) ($record["notes"] ?? ""),
    ];
}

function manageInstanceList(): array
{
    $data = manageReadJsonFile(manageInstancesFile());
    $records = isset($data["instances"]) && is_array($data["instances"])
        ? $data["instances"]
        : [];

    $instances = [];
    foreach ($records as $record) {
        if (!is_array($record)) {
            continue;
        }
        $normalized = manageInstanceNormalize($record);
        if ($normalized["id"] === "") {
            continue;
        }
        $instances[] = $normalized;
    }

    usort($instances, static function (array $left, array $right): int {
        return strcmp($left["id"], $right["id"]);
    });

    return $instances;
}

function manageInstanceWriteAll(array $instances): void
{
    manageWriteJsonFile(manageInstancesFile(), [
        "instances" => array_values($instances),
    ]);
}

function manageInstanceFind(string $id): ?array
{
    foreach (manageInstanceList() as $instance) {
        if ($instance["id"] === $id) {
            return $instance;
        }
    }

    return null;
}

function manageInstanceExists(string $id): bool
{
    return manageInstanceFind($id) !== null;
}

/**
 * @return array{instance: array, token: string} the plaintext token is shown once
 */
function manageInstanceCreate(string $id, string $label = "", string $notes = ""): array
{
    $id = manageInstanceValidateId($id);
    if (manageInstanceExists($id)) {
        throw new RuntimeException("Eine Instanz mit dieser Kennung existiert bereits.");
    }

    $token = manageInstanceGenerateToken();
    $instance = manageInstanceNormalize([
        "id" => $id,
        "label" => trim($label),
        "enabled" => true,
        "token_hash" => manageInstanceHashToken($token),
        "created_at" => date(DATE_ATOM),
        "token_rotated_at" => date(DATE_ATOM),
        "notes" => trim($notes),
    ]);

    $instances = manageInstanceList();
    $instances[] = $instance;
    manageInstanceWriteAll($instances);

    manageLogAccess("Instance created", ["instance" => $id]);

    return ["instance" => $instance, "token" => $token];
}

// Applies a partial update to one instance. Unknown keys are ignored, so a
// caller can hand over a heartbeat payload directly.
function manageInstanceUpdate(string $id, array $changes): array
{
    $instances = manageInstanceList();
    $updated = null;

    foreach ($instances as $position => $instance) {
        if ($instance["id"] !== $id) {
            continue;
        }

        foreach ($changes as $key => $value) {
            if ($key === "id" || $key === "token_hash" || !array_key_exists($key, $instance)) {
                continue;
            }
            $instance[$key] = $value;
        }

        $updated = manageInstanceNormalize($instance);
        $instances[$position] = $updated;
        break;
    }

    if ($updated === null) {
        throw new RuntimeException("Instanz wurde nicht gefunden: " . $id);
    }

    manageInstanceWriteAll($instances);

    return $updated;
}

function manageInstanceRotateToken(string $id): string
{
    $instances = manageInstanceList();
    $token = manageInstanceGenerateToken();
    $found = false;

    foreach ($instances as $position => $instance) {
        if ($instance["id"] !== $id) {
            continue;
        }
        $instance["token_hash"] = manageInstanceHashToken($token);
        $instance["token_rotated_at"] = date(DATE_ATOM);
        $instances[$position] = $instance;
        $found = true;
        break;
    }

    if (!$found) {
        throw new RuntimeException("Instanz wurde nicht gefunden: " . $id);
    }

    manageInstanceWriteAll($instances);
    manageLogAccess("Instance token rotated", ["instance" => $id]);

    return $token;
}

// Removes the registry entry. Stored backups are kept on purpose: a deleted
// instance can no longer upload, but its history stays available for download.
function manageInstanceDelete(string $id): void
{
    $instances = manageInstanceList();
    $remaining = [];
    $found = false;

    foreach ($instances as $instance) {
        if ($instance["id"] === $id) {
            $found = true;
            continue;
        }
        $remaining[] = $instance;
    }

    if (!$found) {
        throw new RuntimeException("Instanz wurde nicht gefunden: " . $id);
    }

    manageInstanceWriteAll($remaining);
    manageLogAccess("Instance deleted", ["instance" => $id]);
}

/**
 * Constant-time token check.
 *
 * @return array|null the instance record, or null when id/token do not match
 */
function manageInstanceAuthenticate(string $id, string $token): ?array
{
    $instance = manageInstanceFind($id);
    if ($instance === null || $instance["token_hash"] === "") {
        return null;
    }

    if (!hash_equals($instance["token_hash"], manageInstanceHashToken($token))) {
        return null;
    }

    return $instance;
}

// Records what a client reported. Called from every authenticated API request
// so the dashboard stays current even without an explicit heartbeat.
function manageInstanceTouch(string $id, array $report = []): void
{
    $changes = [
        "last_seen_at" => date(DATE_ATOM),
        "last_ip" => (string) ($_SERVER["REMOTE_ADDR"] ?? ""),
    ];

    foreach (["version", "php_version", "disk_free", "pending_migrations"] as $key) {
        if (array_key_exists($key, $report)) {
            $changes[$key] = $report[$key];
        }
    }

    try {
        manageInstanceUpdate($id, $changes);
    } catch (Throwable $exception) {
        // A missing instance cannot happen here (the caller authenticated
        // first) and a failed status write must never break the request.
        manageLogError("Instance touch failed", [
            "instance" => $id,
            "error" => $exception->getMessage(),
        ]);
    }
}