<?php

declare(strict_types=1);

namespace App\Services;

use App\Enums\IdentityMatchConfidence;
use App\Enums\IdentityMatchMethod;
use App\Enums\IdentityMatchStatus;
use App\Models\Event;
use App\Models\Person;
use App\Models\PersonIdentityMatch;
use App\Models\User;
use App\Services\FormBuilder\FormTagSyncService;
use Illuminate\Support\Collection;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Facades\Log;
use Illuminate\Validation\ValidationException;

final class PersonIdentityService
{
    public function __construct(
        private readonly ?FormTagSyncService $tagSyncService = null,
    ) {}


    /**
     * Calculate whether two name strings are a fuzzy match using Levenshtein distance
     * with a length-adaptive threshold.
     */
    private function isFuzzyNameMatch(string $a, string $b): bool
    {
        $a = mb_strtolower(trim($a));
        $b = mb_strtolower(trim($b));

        if ($a === $b) {
            return true;
        }

        $maxLen = max(strlen($a), strlen($b));

        // For very short names (< 4 chars), require exact match
        if ($maxLen < 4) {
            return false;
        }

        // Adaptive threshold: 2 for names ≤ 10 chars, 3 for longer
        $threshold = $maxLen <= 10 ? 2 : 3;

        return levenshtein($a, $b) <= $threshold;
    }

    /**
     * Detect potential matches for a person.
     * Called when a Person is created or email is updated.
     *
     * Detection strategy (in order of confidence):
     * 1. Exact email match within org → HIGH confidence
     * 2. Fuzzy name match + optional DOB tiebreaker → MEDIUM (or HIGH if DOB matches)
     */
    public function detectMatchForPerson(Person $person): ?PersonIdentityMatch
    {
        $matches = $this->detectMatches($person);

        return $matches->first();
    }

    /**
     * Detect all potential matches for a person.
     */
    public function detectMatches(Person $person): Collection
    {
        if ($person->user_id !== null) {
            return collect();
        }

        if ($person->trashed()) {
            return collect();
        }

        if (! $person->email && ! $person->first_name) {
            return collect();
        }

        $event = $person->event;
        if (! $event) {
            return collect();
        }

        $organisationId = $event->organisation_id;
        $matches = collect();

        // Get all users in this organisation (one query, reuse for all checks)
        $orgUsers = User::whereHas('organisations', fn ($q) => $q->where('organisations.id', $organisationId))->get();

        // === Strategy 1: Exact email match ===
        if ($person->email) {
            $normalised = strtolower(trim($person->email));
            $emailMatches = $orgUsers->filter(
                fn (User $u) => strtolower(trim($u->email)) === $normalised
            );

            foreach ($emailMatches as $user) {
                $match = $this->createMatchIfEligible(
                    $person, $user, IdentityMatchMethod::EMAIL, IdentityMatchConfidence::HIGH,
                    ['email'], $organisationId
                );
                if ($match) {
                    $matches->push($match);
                }
            }
        }

        // === Strategy 2: Fuzzy name match (only if no email match found) ===
        // Skip fuzzy matching for self-registered persons — they provided their
        // own email, so that's the canonical identity. Fuzzy name matching with
        // a different user would be confusing.
        if ($matches->isEmpty() && $person->first_name && $person->last_name
            && ($person->registration_source ?? 'organizer') !== 'self') {
            $nameMatches = $orgUsers->filter(function (User $user) use ($person) {
                // Skip if same email (already handled above, or would be email match)
                if ($person->email && strtolower(trim($user->email)) === strtolower(trim($person->email))) {
                    return false;
                }
                if (! $user->first_name || ! $user->last_name) {
                    return false;
                }

                return $this->isFuzzyNameMatch($person->first_name, $user->first_name)
                    && $this->isFuzzyNameMatch($person->last_name, $user->last_name);
            });

            foreach ($nameMatches as $user) {
                $confidence = IdentityMatchConfidence::MEDIUM;
                $matchedFields = [];

                // Check exact name match vs fuzzy
                if (mb_strtolower(trim($person->first_name)) === mb_strtolower(trim($user->first_name))
                    && mb_strtolower(trim($person->last_name)) === mb_strtolower(trim($user->last_name))) {
                    $matchedFields[] = 'first_name';
                    $matchedFields[] = 'last_name';
                } else {
                    $matchedFields[] = 'first_name_fuzzy';
                    $matchedFields[] = 'last_name_fuzzy';
                }

                // DOB tiebreaker: upgrades medium → high
                if ($person->date_of_birth && $user->date_of_birth
                    && $person->date_of_birth->equalTo($user->date_of_birth)) {
                    $confidence = IdentityMatchConfidence::HIGH;
                    $matchedFields[] = 'date_of_birth';
                }

                $match = $this->createMatchIfEligible(
                    $person, $user, IdentityMatchMethod::NAME_FUZZY, $confidence,
                    $matchedFields, $organisationId
                );
                if ($match) {
                    $matches->push($match);
                }
            }
        }

        return $matches;
    }

    /**
     * Create a match record if eligible (no existing match, no conflict).
     */
    private function createMatchIfEligible(
        Person $person,
        User $user,
        IdentityMatchMethod $method,
        IdentityMatchConfidence $confidence,
        array $matchedFields,
        string $organisationId,
    ): ?PersonIdentityMatch {
        // Skip if user already linked to a person at this event with same crowd type
        $alreadyLinked = Person::withoutGlobalScopes()
            ->where('event_id', $person->event_id)
            ->where('user_id', $user->id)
            ->where('crowd_type_id', $person->crowd_type_id)
            ->where('id', '!=', $person->id)
            ->exists();
        if ($alreadyLinked) {
            return null;
        }

        // Skip if there's already a pending or confirmed match for this person+user pair
        $existingMatch = PersonIdentityMatch::where('person_id', $person->id)
            ->where('matched_user_id', $user->id)
            ->whereIn('status', [IdentityMatchStatus::PENDING, IdentityMatchStatus::CONFIRMED])
            ->first();
        if ($existingMatch) {
            return $existingMatch;
        }

        // Skip if previously dismissed (don't re-suggest)
        $wasDismissed = PersonIdentityMatch::where('person_id', $person->id)
            ->where('matched_user_id', $user->id)
            ->where('status', IdentityMatchStatus::DISMISSED)
            ->exists();
        if ($wasDismissed) {
            return null;
        }

        $match = PersonIdentityMatch::create([
            'person_id' => $person->id,
            'matched_user_id' => $user->id,
            'matched_on' => $method,
            'confidence' => $confidence,
            'status' => IdentityMatchStatus::PENDING,
            'match_details' => [
                'person_email' => $person->email,
                'user_email' => $user->email,
                'person_name' => $person->full_name,
                'user_name' => $user->full_name,
                'person_dob' => $person->date_of_birth?->toDateString(),
                'user_dob' => $user->date_of_birth?->toDateString(),
                'matched_fields' => $matchedFields,
                'organisation_id' => $organisationId,
            ],
        ]);

        $activityLogger = activity('identity')
            ->performedOn($person)
            ->withProperties([
                'match_id' => $match->id,
                'matched_user_id' => $user->id,
                'matched_on' => $method->value,
                'confidence' => $confidence->value,
                'matched_fields' => $matchedFields,
            ]);

        if (auth()->user()) {
            $activityLogger->causedBy(auth()->user());
        }

        $activityLogger->log('person.identity.match_detected');

        return $match;
    }

    /**
     * Detect all unlinked persons matching a user's email.
     * Called after a user account is created. Creates pending matches.
     * Returns the number of matches created.
     */
    public function detectMatchesForUser(User $user): int
    {
        // 1. Fetch all matching unlinked persons
        $normalised = strtolower(trim($user->email));
        $persons = Person::whereNull('user_id')
            ->whereRaw('LOWER(email) = ?', [$normalised])
            ->get();

        if ($persons->isEmpty()) {
            return 0;
        }

        // 2. Batch-check which events already have this user linked (no N+1)
        $alreadyLinkedEventIds = Person::withoutGlobalScopes()
            ->where('user_id', $user->id)
            ->whereIn('event_id', $persons->pluck('event_id'))
            ->pluck('event_id')
            ->toArray();

        // 3. Batch-check existing match records (no N+1)
        $existingMatchPersonIds = PersonIdentityMatch::where('matched_user_id', $user->id)
            ->whereIn('person_id', $persons->pluck('id'))
            ->pluck('person_id')
            ->toArray();

        // 4. Filter — no queries inside this loop
        $toCreate = $persons
            ->reject(fn (Person $p) => in_array($p->event_id, $alreadyLinkedEventIds))
            ->reject(fn (Person $p) => in_array($p->id, $existingMatchPersonIds));

        // 5. Create matches
        foreach ($toCreate as $person) {
            PersonIdentityMatch::create([
                'person_id' => $person->id,
                'matched_user_id' => $user->id,
                'matched_on' => IdentityMatchMethod::EMAIL,
                'confidence' => IdentityMatchConfidence::HIGH,
                'status' => IdentityMatchStatus::PENDING,
                'match_details' => [
                    'person_email' => $person->email,
                    'user_email' => $user->email,
                    'person_name' => $person->full_name,
                    'user_name' => $user->full_name,
                    'matched_fields' => ['email'],
                    'organisation_id' => $person->event?->organisation_id,
                ],
            ]);

            $activityLogger = activity('identity')
                ->performedOn($person)
                ->withProperties([
                    'matched_user_id' => $user->id,
                    'matched_on' => IdentityMatchMethod::EMAIL->value,
                    'confidence' => IdentityMatchConfidence::HIGH->value,
                ]);

            if (auth()->user()) {
                $activityLogger->causedBy(auth()->user());
            }

            $activityLogger->log('person.identity.match_detected');
        }

        return $toCreate->count();
    }

    /**
     * Confirm a match: link the person to the matched user.
     * Also syncs registration tags and dismisses other pending matches.
     *
     * @throws \DomainException if match is not pending or would violate uniqueness
     */
    public function confirmMatch(PersonIdentityMatch $match, User $resolvedBy): void
    {
        if ($match->status !== IdentityMatchStatus::PENDING) {
            throw new \DomainException('Match is not pending and cannot be confirmed.');
        }

        $person = $match->person;

        // Safety check: no duplicate user_id in the same event + crowd type
        $conflict = Person::withoutGlobalScopes()
            ->where('event_id', $person->event_id)
            ->where('user_id', $match->matched_user_id)
            ->where('crowd_type_id', $person->crowd_type_id)
            ->exists();

        if ($conflict) {
            throw new \DomainException('User already has a person record with this crowd type in this event.');
        }

        DB::transaction(function () use ($match, $person, $resolvedBy): void {
            $match->update([
                'status' => IdentityMatchStatus::CONFIRMED,
                'confirmed_by_user_id' => $resolvedBy->id,
                'confirmed_at' => now(),
                'resolved_by_user_id' => $resolvedBy->id,
                'resolved_at' => now(),
            ]);

            // Set user_id explicitly (not mass-assignable)
            $person->user_id = $match->matched_user_id;
            $person->save();

            // ARCH §31.10 — deferred TAG_PICKER sync: previously submitted
            // event_registration forms now have a user account to attach
            // self_reported tags to. No-op if null path surfaces.
            ($this->tagSyncService ?? app(FormTagSyncService::class))
                ->rebuildForPerson($person->fresh() ?? $person);

            // Dismiss other pending matches for this person
            PersonIdentityMatch::where('person_id', $person->id)
                ->where('id', '!=', $match->id)
                ->where('status', IdentityMatchStatus::PENDING)
                ->update([
                    'status' => IdentityMatchStatus::DISMISSED->value,
                    'dismissed_by_user_id' => $resolvedBy->id,
                    'dismissed_at' => now(),
                    'resolved_by_user_id' => $resolvedBy->id,
                    'resolved_at' => now(),
                ]);
        });

        activity('identity')
            ->causedBy($resolvedBy)
            ->performedOn($person)
            ->withProperties([
                'match_id' => $match->id,
                'old' => ['user_id' => null],
                'new' => ['user_id' => $match->matched_user_id],
            ])
            ->log('person.identity.match_confirmed');
    }

    /**
     * Dismiss a match: mark as dismissed so it's not shown again.
     *
     * @throws \DomainException if match is not pending
     */
    public function dismissMatch(PersonIdentityMatch $match, User $resolvedBy): void
    {
        if ($match->status !== IdentityMatchStatus::PENDING) {
            throw new \DomainException('Match is not pending and cannot be dismissed.');
        }

        $match->update([
            'status' => IdentityMatchStatus::DISMISSED,
            'dismissed_by_user_id' => $resolvedBy->id,
            'dismissed_at' => now(),
            'resolved_by_user_id' => $resolvedBy->id,
            'resolved_at' => now(),
        ]);

        activity('identity')
            ->causedBy($resolvedBy)
            ->performedOn($match->person)
            ->withProperties(['match_id' => $match->id])
            ->log('person.identity.match_dismissed');
    }

    /**
     * Revert a confirmed match — unlinks person.user_id (the "split" action).
     *
     * @throws \DomainException if match is not confirmed
     */
    public function revertMatch(PersonIdentityMatch $match, User $revertedBy): void
    {
        if ($match->status !== IdentityMatchStatus::CONFIRMED) {
            throw new \DomainException('Only confirmed matches can be reverted.');
        }

        $person = $match->person;
        $previousUserId = $person->user_id;

        DB::transaction(function () use ($match, $person, $revertedBy): void {
            $person->user_id = null;
            $person->save();

            $match->update([
                'status' => IdentityMatchStatus::REVERTED,
                'reverted_by_user_id' => $revertedBy->id,
                'reverted_at' => now(),
            ]);
        });

        activity('identity')
            ->causedBy($revertedBy)
            ->performedOn($person)
            ->withProperties([
                'match_id' => $match->id,
                'unlinked_user_id' => $previousUserId,
            ])
            ->log('person.identity.match_reverted');
    }

    /**
     * Manually link a person to a user (organiser-initiated, no detection).
     *
     * @throws ValidationException if person already linked or conflict exists
     */
    public function manualLink(Person $person, User $user, User $linkedBy): PersonIdentityMatch
    {
        if ($person->user_id !== null) {
            throw ValidationException::withMessages([
                'person_id' => ['Deze persoon is al gekoppeld aan een platformaccount. Ontkoppel eerst.'],
            ]);
        }

        // Check for conflict at event level (same crowd type)
        $alreadyLinked = Person::withoutGlobalScopes()
            ->where('event_id', $person->event_id)
            ->where('user_id', $user->id)
            ->where('crowd_type_id', $person->crowd_type_id)
            ->where('id', '!=', $person->id)
            ->exists();

        if ($alreadyLinked) {
            throw ValidationException::withMessages([
                'user_id' => ['Dit platformaccount is al gekoppeld aan een andere deelnemer met hetzelfde type bij dit evenement.'],
            ]);
        }

        $match = null;

        DB::transaction(function () use ($person, $user, $linkedBy, &$match): void {
            $match = PersonIdentityMatch::create([
                'person_id' => $person->id,
                'matched_user_id' => $user->id,
                'matched_on' => IdentityMatchMethod::MANUAL,
                'confidence' => IdentityMatchConfidence::HIGH,
                'status' => IdentityMatchStatus::CONFIRMED,
                'confirmed_by_user_id' => $linkedBy->id,
                'confirmed_at' => now(),
                'resolved_by_user_id' => $linkedBy->id,
                'resolved_at' => now(),
                'match_details' => [
                    'person_email' => $person->email,
                    'user_email' => $user->email,
                    'person_name' => $person->full_name,
                    'user_name' => $user->full_name,
                    'matched_fields' => ['manual'],
                    'organisation_id' => $person->event?->organisation_id,
                ],
            ]);

            $person->user_id = $user->id;
            $person->save();

            // Dismiss pending matches
            PersonIdentityMatch::where('person_id', $person->id)
                ->where('id', '!=', $match->id)
                ->where('status', IdentityMatchStatus::PENDING)
                ->update([
                    'status' => IdentityMatchStatus::DISMISSED->value,
                    'dismissed_by_user_id' => $linkedBy->id,
                    'dismissed_at' => now(),
                    'resolved_by_user_id' => $linkedBy->id,
                    'resolved_at' => now(),
                ]);
        });

        activity('identity')
            ->causedBy($linkedBy)
            ->performedOn($person)
            ->withProperties([
                'match_id' => $match->id,
                'linked_user_id' => $user->id,
            ])
            ->log('person.identity.manually_linked');

        return $match;
    }

    /**
     * Unlink a person that was linked (with or without a match record).
     *
     * @throws ValidationException if person is not linked
     */
    public function unlinkDirect(Person $person, User $unlinkedBy): Person
    {
        if ($person->user_id === null) {
            throw ValidationException::withMessages([
                'person_id' => ['Deze persoon is niet gekoppeld aan een platformaccount.'],
            ]);
        }

        // Check for confirmed match record first
        $confirmedMatch = PersonIdentityMatch::where('person_id', $person->id)
            ->where('status', IdentityMatchStatus::CONFIRMED)
            ->latest()
            ->first();

        if ($confirmedMatch) {
            $this->revertMatch($confirmedMatch, $unlinkedBy);
        } else {
            // Direct unlink (no match record exists)
            $previousUserId = $person->user_id;
            $person->user_id = null;
            $person->save();

            activity('identity')
                ->causedBy($unlinkedBy)
                ->performedOn($person)
                ->withProperties(['previous_user_id' => $previousUserId])
                ->log('person.identity.unlinked_directly');
        }

        return $person->fresh();
    }

}