<?php

declare(strict_types=1);

namespace NetBoxStore\Database;

use JsonException;
use RuntimeException;
use Throwable;

final class JsonStoreRepository implements StoreRepository
{
    private const MAX_DATABASE_BYTES = 134_217_728;
    private string $lockPath;

    public function __construct(private readonly string $path, private readonly int $maxDatabaseBytes = self::MAX_DATABASE_BYTES)
    {
        $this->lockPath = $path . '.lock';
    }

    public function initialize(): void
    {
        $directory = dirname($this->path);
        if (!is_dir($directory) && !mkdir($directory, 0700, true) && !is_dir($directory)) {
            throw new RuntimeException('Could not create datastore directory.');
        }
        if (!is_file($this->path)) {
            $lock = $this->lock(LOCK_EX);
            try {
                if (!is_file($this->path)) {
                    $this->atomicWrite(State::empty());
                }
            } finally {
                $this->unlock($lock);
            }
        }
        @chmod($this->path, 0600);
        $this->read();
    }

    public function read(): array
    {
        $lock = $this->lock(LOCK_SH);
        try {
            return $this->readUnlocked();
        } finally {
            $this->unlock($lock);
        }
    }

    public function acquireLease(string $name): ?ExclusiveLease
    {
        $leasePath = $this->path . '.lease-' . substr(hash('sha256', $name), 0, 24) . '.lock';
        $handle = fopen($leasePath, 'c+b');
        if ($handle === false) {
            throw new RuntimeException('Could not open exclusive lease file.');
        }
        @chmod($leasePath, 0600);
        if (!flock($handle, LOCK_EX | LOCK_NB)) {
            fclose($handle);
            return null;
        }
        return new CallbackLease(static function () use ($handle): void {
            flock($handle, LOCK_UN);
            fclose($handle);
        });
    }

    public function transaction(callable $callback): mixed
    {
        $lock = $this->lock(LOCK_EX);
        try {
            $draft = $this->readUnlocked();
            $result = $callback($draft);
            State::validate($draft);
            $this->atomicWrite($draft);
            return $result;
        } finally {
            $this->unlock($lock);
        }
    }

    /** @return resource */
    private function lock(int $operation): mixed
    {
        $handle = fopen($this->lockPath, 'c+b');
        if ($handle === false || !flock($handle, $operation)) {
            throw new RuntimeException('Could not acquire datastore lock.');
        }
        @chmod($this->lockPath, 0600);
        return $handle;
    }

    /** @param resource $handle */
    private function unlock(mixed $handle): void
    {
        flock($handle, LOCK_UN);
        fclose($handle);
    }

    /** @return array<string,mixed> */
    private function readUnlocked(): array
    {
        $size = @filesize($this->path);
        if ($size === false || $size > $this->maxDatabaseBytes) {
            throw new RuntimeException('JSON datastore is missing or exceeds 128 MB.');
        }
        $contents = file_get_contents($this->path);
        if ($contents === false) {
            throw new RuntimeException('Could not read JSON datastore.');
        }
        try {
            $state = json_decode($contents, true, 512, JSON_THROW_ON_ERROR);
        } catch (JsonException $exception) {
            throw new RuntimeException('JSON datastore is malformed.', 0, $exception);
        }
        if (!is_array($state)) {
            throw new RuntimeException('JSON datastore root is invalid.');
        }
        State::validate($state);
        return $state;
    }

    /** @param array<string,mixed> $state */
    private function atomicWrite(array $state): void
    {
        $payload = json_encode($state, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_THROW_ON_ERROR) . "\n";
        if (strlen($payload) > $this->maxDatabaseBytes) {
            throw new RuntimeException('JSON datastore would exceed its configured 128 MB safety limit.');
        }
        $temporary = dirname($this->path) . '/.' . basename($this->path) . '.tmp-' . bin2hex(random_bytes(8));
        $handle = fopen($temporary, 'x+b');
        if ($handle === false) {
            throw new RuntimeException('Could not create temporary datastore file.');
        }
        try {
            $written = 0;
            while ($written < strlen($payload)) {
                $chunk = fwrite($handle, substr($payload, $written));
                if ($chunk === false || $chunk === 0) {
                    throw new RuntimeException('Could not write temporary datastore file.');
                }
                $written += $chunk;
            }
            if (!fflush($handle)) {
                throw new RuntimeException('Could not flush temporary datastore file.');
            }
            if (function_exists('fsync')) {
                fsync($handle);
            }
            fclose($handle);
            $handle = null;
            @chmod($temporary, 0600);
            if (!rename($temporary, $this->path)) {
                throw new RuntimeException('Atomic datastore rename failed.');
            }
        } catch (Throwable $exception) {
            if (is_resource($handle)) {
                fclose($handle);
            }
            @unlink($temporary);
            throw $exception;
        }
    }
}