<?php

namespace Dashboard\Ticketing\Support;

use Dashboard\Ticketing\Models\EmailConnection;

/**
 * THE ONE WRITER OF THE EMAIL TAB'S AUDIT TRAIL — [central-ticketing] #6217.
 *
 * An email connection is a mailbox the help desk collects FROM: mail that
 * arrives in it becomes a ticket on the group named beside it. So the row
 * decides which mailbox the school's help-desk mail is pulled out of, with what
 * credentials, and whose queue it lands in — and until this class, creating
 * one, re-pointing one at a different mailbox or deleting one wrote NOTHING to
 * Admin → Logs → Changes. The delete confirm even says the credentials go
 * ("Tickets already created from it are kept; the saved credentials are not");
 * nothing recorded that they had been there.
 *
 * ── WHY THIS IS NOT `registerAuditedModels()` ───────────────────────────────
 *
 * Its three siblings on the same Settings page — `PriorityLevel`,
 * `TicketStatus`, `TicketingProject` — ARE declared to `AuditRegistry`, because
 * every column worth recording on them is a column. This one is different in
 * exactly one way, and it is the way that matters: the mailbox host, port,
 * username and PASSWORD all live inside a single `config` JSON column
 * (`EmailConnection::$casts = ['config' => 'array']`).
 *
 *   - Declaring `config` copies the PASSWORD into `audit_events.changes`.
 *     `Audit::redact()` masks by TOP-LEVEL FIELD NAME, and `normalize()` walks
 *     into an array without redacting inside it, so a declared `config` is a
 *     credential written in clear to a table read under `logs.view` alone.
 *   - Declaring only `group_id` / `type` / `active` — the scalar columns — is
 *     silent on the write the card is actually about: the observer records
 *     nothing when no DECLARED field moved, so re-pointing a connection at a
 *     different host, or changing its password, would still leave no trace.
 *
 * So the config is FLATTENED here into `config.host`, `config.username`,
 * `config.password`, … — which is the spelling `Audit::isSecretField()` masks,
 * because it matches the substring `password`. {@see write()} masks it at the
 * source as well, so the real credential is never handed to the logger at all
 * and the central redaction is the second of two layers rather than the only
 * one.
 *
 * ── THE RULES IT KEEPS, WHICH ARE THE OBSERVER'S OWN ────────────────────────
 *
 *  1. ONE ROW PER SAVE. A save that moves the type AND the host is one edit and
 *     reads as one row, the way an observer-written row would.
 *  2. NOTHING MOVED, NOTHING RECORDED. The Email tab re-posts every box it
 *     renders, so "somebody pressed Save" is not news. A blank password box
 *     means "keep the one you have" ({@see
 *     \Dashboard\Ticketing\Http\Controllers\TicketingSettingsController::mergedConnectionConfig()}),
 *     and keeping it is not a change.
 *  3. THE VERBS ARE `created` / `updated` / `deleted`. Not a private
 *     `ticketing.email.*` spelling: the other six tabs on this page are
 *     observer-written under exactly these three, the Changes page's Action
 *     filter is a SELECT DISTINCT over them, and an operator asking "what was
 *     deleted in Help Desk today" should not have to know that one tab writes
 *     its rows by hand.
 *
 * The `app` is left to `Audit::appFor()`, which answers `ticketing` from the
 * `Dashboard\Ticketing\…` namespace of the subject. The subject is the MODEL
 * and not a string for the same reason: a string subject files under `shell`
 * and leaves `EmailConnection` out of the Changes log's Subject-type facet,
 * which is the census the card read the gap off.
 *
 * central-logs is optional on any given host — guarded once, in {@see write()},
 * and not at the three call sites.
 */
final class EmailConnectionAudit
{
    /**
     * The config keys the Email tab writes, in the order the form asks for them.
     *
     * A fixed list and not `array_keys($config)`: the audit row should say the
     * same thing about every connection, and an unknown key arriving in the blob
     * is not something to copy into the log sight-unseen.
     */
    private const CONFIG_KEYS = ['host', 'port', 'encryption', 'username', 'password', 'mailbox'];

    public static function created(EmailConnection $connection): void
    {
        static::write('created', $connection, static::sided(static::state($connection), 'to'));
    }

    /**
     * @param  array<string,mixed>  $before  {@see state()}, taken BEFORE the save
     */
    public static function updated(EmailConnection $connection, array $before): void
    {
        $changes = [];

        foreach (static::state($connection) as $key => $now) {
            $was = $before[$key] ?? null;

            if (static::unchanged($was, $now)) {
                continue;
            }

            $changes[$key] = ['from' => $was, 'to' => $now];
        }

        if ($changes === []) {
            return;   // rule 2
        }

        static::write('updated', $connection, $changes);
    }

    public static function deleted(EmailConnection $connection): void
    {
        // What the row HELD when it was deleted is usually the whole question
        // being asked — the same side the observer snapshots on a delete.
        static::write('deleted', $connection, static::sided(static::state($connection), 'from'));
    }

    /**
     * The connection as the log describes it: the scalar columns, plus `config`
     * flattened one level into dotted keys.
     *
     * Public because `updateEmailConnection()` has to take the BEFORE side
     * itself, before the save — the two halves of an update's diff must be read
     * the same way or they cannot be compared.
     *
     * `last_polled_at` is deliberately absent: it is written by the collector,
     * not by a person, and a timestamp moving on its own is not a change
     * anybody made.
     *
     * @return array<string,mixed>
     */
    public static function state(EmailConnection $connection): array
    {
        $config = is_array($connection->config) ? $connection->config : [];

        $state = [
            'group_id' => $connection->group_id === null ? null : (int) $connection->group_id,
            'type'     => $connection->type,
            'active'   => (bool) $connection->active,
        ];

        foreach (self::CONFIG_KEYS as $key) {
            $value = $config[$key] ?? null;

            $state['config.'.$key] = ($value === '' ? null : $value);
        }

        return $state;
    }

    /**
     * A whole state as one-sided {from,to} pairs, for a create (`to`) or a
     * delete (`from`). Unset fields are dropped: an empty box is noise, not
     * information — `AuditObserver::snapshot()` drops them for the same reason.
     *
     * @param  array<string,mixed>  $state
     * @return array<string, array{from:mixed,to:mixed}>
     */
    private static function sided(array $state, string $side): array
    {
        $out = [];

        foreach ($state as $key => $value) {
            if ($value === null) {
                continue;
            }

            $out[$key] = $side === 'from'
                ? ['from' => $value, 'to' => null]
                : ['from' => null, 'to' => $value];
        }

        return $out;
    }

    /**
     * Did this field move?
     *
     * Compared as strings because the two sides come from different places — the
     * stored JSON on one and a freshly-posted form on the other — so a port that
     * was saved as `993` and re-posted as `"993"` is the same port, and recording
     * it as a change would make every Save look like an edit.
     */
    private static function unchanged(mixed $was, mixed $now): bool
    {
        return static::scalar($was) === static::scalar($now);
    }

    private static function scalar(mixed $value): string
    {
        if (is_bool($value)) {
            return $value ? '1' : '0';
        }

        return is_array($value) ? json_encode($value) : (string) ($value ?? '');
    }

    /**
     * Write one row, with every secret masked before it leaves this class.
     *
     * The mask is `Audit::isSecretField()`'s own answer, applied to the same
     * flattened key the row will carry, so this and `Audit::redact()` cannot
     * disagree about what a secret is. NULL is preserved on either side: "was
     * unset, now set" is information that gives nothing away, and it is the one
     * thing the trail can honestly say about a credential.
     *
     * @param  array<string, array{from:mixed,to:mixed}>  $changes
     */
    private static function write(string $action, EmailConnection $connection, array $changes): void
    {
        if (! class_exists(\Central\Logs\Support\Audit::class)) {
            return;
        }

        foreach ($changes as $key => $pair) {
            if (! \Central\Logs\Support\Audit::isSecretField((string) $key)) {
                continue;
            }

            $mask = fn ($v) => ($v === null || $v === '') ? null : \Central\Logs\Support\Audit::REDACTED;

            $changes[$key] = ['from' => $mask($pair['from'] ?? null), 'to' => $mask($pair['to'] ?? null)];
        }

        \Central\Logs\Support\Audit::record($action, $connection, $changes);
    }
}