<?php

namespace classes;

/**
 * Ensures additive audit columns used when invoice collections are superseded.
 */
class invoice_collection_schema_bootstrap
{
    private const TABLE = 'collected_order_invoices';
    private const LOCK_NAME = 'invoice_collection_schema_v1';

    /** @var array<string, string> */
    private const REQUIRED_COLUMNS = [
        'superseded_by_collection_id' => 'INT NULL',
        'superseded_at' => 'DATETIME NULL',
        'superseded_by_user_id' => 'INT NULL',
    ];

    public static function hasRequiredColumns(): bool
    {
        try {
            global $db;
            if (!self::canInspectSchema($db) || !self::tableExists($db)) {
                return false;
            }
            if (self::allColumnsExist($db)) {
                return true;
            }
            if (!self::acquireLock($db)) {
                return false;
            }

            try {
                // Another worker may have completed the additive migration while
                // this request waited for the advisory lock.
                foreach (self::REQUIRED_COLUMNS as $column => $definition) {
                    if (self::columnExists($db, $column)) {
                        continue;
                    }
                    $result = $db->query(
                        "ALTER TABLE `" . self::TABLE . "` ADD COLUMN `{$column}` {$definition}"
                    );
                    if ($result === false) {
                        return false;
                    }
                }

                if (!self::allColumnsExist($db)) {
                    return false;
                }
                return true;
            } finally {
                self::releaseLock($db);
            }
        } catch (\Throwable) {
            // Schema readiness is a capability gate. It must never break the
            // legacy invoicing routes when DDL or metadata access is unavailable.
            return false;
        }
    }

    private static function canInspectSchema(mixed $db): bool
    {
        return is_object($db)
            && method_exists($db, 'query')
            && method_exists($db, 'escape_string')
            && method_exists($db, 'getDatabase');
    }

    private static function tableExists(object $db): bool
    {
        return self::informationSchemaCount(
            $db,
            'information_schema.TABLES',
            'TABLE_NAME',
            self::TABLE
        ) > 0;
    }

    private static function columnExists(object $db, string $column): bool
    {
        return self::informationSchemaCount(
            $db,
            'information_schema.COLUMNS',
            'COLUMN_NAME',
            $column
        ) > 0;
    }

    private static function informationSchemaCount(
        object $db,
        string $informationSchemaTable,
        string $nameField,
        string $name
    ): int {
        $database = $db->escape_string((string)$db->getDatabase());
        $name = $db->escape_string($name);
        $result = $db->query(
            "SELECT COUNT(*) AS c FROM {$informationSchemaTable} "
            . "WHERE TABLE_SCHEMA = '{$database}' AND TABLE_NAME = '" . self::TABLE . "' "
            . "AND {$nameField} = '{$name}'"
        );
        if (!is_object($result) || !method_exists($result, 'fetch_assoc')) {
            throw new \RuntimeException('Invoice collection schema inspection failed');
        }
        $row = $result->fetch_assoc();
        if (!is_array($row) || !array_key_exists('c', $row)) {
            throw new \RuntimeException('Invoice collection schema inspection returned an invalid result');
        }
        return (int)$row['c'];
    }

    private static function allColumnsExist(object $db): bool
    {
        foreach (array_keys(self::REQUIRED_COLUMNS) as $column) {
            if (!self::columnExists($db, $column)) {
                return false;
            }
        }
        return true;
    }

    private static function acquireLock(object $db): bool
    {
        $result = $db->query("SELECT GET_LOCK('" . self::LOCK_NAME . "', 5) AS acquired");
        if (!is_object($result) || !method_exists($result, 'fetch_assoc')) {
            return false;
        }
        $row = $result->fetch_assoc();
        return is_array($row) && (int)($row['acquired'] ?? 0) === 1;
    }

    private static function releaseLock(object $db): void
    {
        try {
            $db->query("SELECT RELEASE_LOCK('" . self::LOCK_NAME . "')");
        } catch (\Throwable) {
            // The connection also releases advisory locks automatically.
        }
    }
}