<?php

namespace App\Services\Document;

use App\Jobs\ReindexChunkJob;
use App\Models\ChunkAudit;
use App\Models\DocumentChunk;
use App\Services\KnowledgeBase\AuditService;
use App\Services\Qdrant\QdrantService;
use Illuminate\Support\Facades\DB;
use Illuminate\Support\Str;
use InvalidArgumentException;
use RuntimeException;

/**
 * ChunkSplitService
 *
 * Menguruskan operasi split chunk:
 *   1. Tandakan parent sebagai 'superseded'
 *   2. Deactivate Qdrant point parent
 *   3. Cipta child chunks dengan final_text dari admin
 *   4. Rekod audit trail (parent + setiap child)
 *   5. Dispatch ReindexChunkJob untuk setiap child
 *
 * PRINSIP:
 *   - Parent chunk TIDAK DIPADAM — hanya ditandakan superseded
 *   - content (raw_text) parent DISIMPAN dalam setiap child untuk audit trail
 *   - Child chunks mendapat chunk_index baharu (selepas max sedia ada)
 *   - Semua children dalam satu split operation berkongsi split_group_id yang sama
 */
class ChunkSplitService
{
    public function __construct(
        private readonly QdrantService $qdrant,
        private readonly AuditService  $audit,
    ) {}

    /**
     * Split satu chunk kepada beberapa chunk kecil.
     *
     * @param  DocumentChunk $parent   Chunk asal yang akan di-split
     * @param  string[]      $segments Array teks untuk setiap child chunk
     * @param  string|null   $notes    Nota admin (sebab split)
     * @return DocumentChunk[]         Array child chunks yang baru dicipta
     *
     * @throws InvalidArgumentException Jika segments tidak valid
     * @throws RuntimeException         Jika chunk tidak boleh di-split
     */
    public function split(
        DocumentChunk $parent,
        array $segments,
        ?string $notes = null
    ): array {
        $this->validateSegments($parent, $segments);

        // Index maksimum untuk version ini — child chunks akan guna index selepas ini
        $maxIndex = DocumentChunk::where('document_version_id', $parent->document_version_id)
            ->max('chunk_index') ?? 0;

        $splitGroupId = (string) Str::uuid();
        $children     = [];

        DB::transaction(function () use ($parent, $segments, $notes, $maxIndex, $splitGroupId, &$children) {
            $parentOldStatus = $parent->chunk_status;

            // ── Langkah 1: Tandakan parent sebagai superseded ────────────────
            $parent->markAsSuperseded();

            // ── Langkah 2: Deactivate Qdrant point parent ───────────────────
            if ($parent->qdrant_point_id) {
                $this->qdrant->updatePayload($parent->qdrant_point_id, [
                    'is_active' => false,
                    'status'    => 'superseded',
                ]);
            }

            // ── Langkah 3: Log audit untuk parent ───────────────────────────
            ChunkAudit::record($parent->id, ChunkAudit::OP_SPLIT_PARENT, [
                'old_status' => $parentOldStatus,
                'new_status' => DocumentChunk::STATUS_SUPERSEDED,
                'metadata'   => [
                    'split_group_id'   => $splitGroupId,
                    'segment_count'    => count($segments),
                    'original_length'  => mb_strlen($parent->content),
                    'original_words'   => str_word_count($parent->content),
                    'had_qdrant_point' => (bool) $parent->qdrant_point_id,
                ],
            ], $notes);

            // ── Langkah 4: Cipta child chunks ────────────────────────────────
            foreach ($segments as $i => $segmentText) {
                $cleanSegment = trim($segmentText);

                $child = DocumentChunk::create([
                    // Warisi metadata penting dari parent
                    'document_id'         => $parent->document_id,
                    'document_version_id' => $parent->document_version_id,
                    'page_number'         => $parent->page_number,
                    'section_heading'     => $parent->section_heading,

                    // content = raw_text parent (untuk audit trail — teks penuh sebelum split)
                    // Admin boleh rujuk ini untuk memahami konteks asal
                    'content'             => $parent->content,

                    // final_text = teks baharu yang admin tetapkan untuk chunk ini
                    'final_text'          => $cleanSegment,
                    'cleaned_text'        => null,

                    // Index dan ordering
                    'chunk_index'         => $maxIndex + $i + 1,
                    'split_order'         => $i,
                    'split_group_id'      => $splitGroupId,
                    'parent_chunk_id'     => $parent->id,

                    // Token estimate berdasarkan final_text
                    'token_count'         => (int) ceil(mb_strlen($cleanSegment) / 4),

                    // Status
                    'chunk_status'        => DocumentChunk::STATUS_PENDING,
                    'is_embedded'         => false,
                    'is_active'           => true,
                    'is_edited'           => true,
                    'exclude_from_index'  => false,
                    'needs_reindex'       => true,

                    // Admin yang buat split
                    'edited_by'           => auth()->id(),
                    'edited_at'           => now(),
                    'notes'               => "Dicipta dari split chunk #{$parent->chunk_index} "
                        . "(segmen " . ($i + 1) . "/" . count($segments) . ")",
                ]);

                // ── Langkah 5: Log audit untuk setiap child ─────────────────
                ChunkAudit::record($child->id, ChunkAudit::OP_SPLIT_CHILD, [
                    'old_status'    => null,
                    'new_status'    => DocumentChunk::STATUS_PENDING,
                    'new_final_text' => $cleanSegment,
                    'metadata'      => [
                        'parent_chunk_id'  => $parent->id,
                        'parent_chunk_idx' => $parent->chunk_index,
                        'split_group_id'   => $splitGroupId,
                        'split_order'      => $i,
                        'segment_length'   => mb_strlen($cleanSegment),
                        'segment_words'    => str_word_count($cleanSegment),
                    ],
                ], $notes);

                $children[] = $child;
            }
        }); // akhir DB::transaction

        // ── Langkah 6: Log ke audit_logs sistem ─────────────────────────────
        $this->audit->chunkSplit($parent, $children, $splitGroupId);

        // ── Langkah 7: Dispatch ReindexChunkJob untuk setiap child ──────────
        foreach ($children as $child) {
            ReindexChunkJob::dispatch($child->id);
        }

        return $children;
    }

    // =========================================================================
    // PRIVATE HELPERS
    // =========================================================================

    /**
     * Validasi input sebelum split dijalankan.
     *
     * @throws InvalidArgumentException
     * @throws RuntimeException
     */
    private function validateSegments(DocumentChunk $parent, array $segments): void
    {
        if ($parent->isSuperseded()) {
            throw new RuntimeException(
                'Chunk yang telah digantikan (superseded) tidak boleh di-split semula.'
            );
        }

        if (count($segments) < 2) {
            throw new InvalidArgumentException(
                'Split memerlukan sekurang-kurangnya 2 segmen.'
            );
        }

        if (count($segments) > 10) {
            throw new InvalidArgumentException(
                'Maksimum 10 segmen dibenarkan dalam satu operasi split.'
            );
        }

        foreach ($segments as $i => $seg) {
            $trimmed = trim($seg);

            if (empty($trimmed)) {
                throw new InvalidArgumentException(
                    'Segmen ' . ($i + 1) . ' tidak boleh kosong.'
                );
            }

            if (mb_strlen($trimmed) < 20) {
                throw new InvalidArgumentException(
                    'Segmen ' . ($i + 1) . ' terlalu pendek (minimum 20 aksara).'
                );
            }
        }
    }
}