<?php

namespace App\Services;

use Illuminate\Database\Eloquent\Builder;
use Illuminate\Support\Facades\DB;

class QueryOptimizationService
{
    /**
     * Add eager loading constraints to prevent N+1 queries
     */
    public function eagerLoadJobRelations(Builder $query): Builder
    {
        return $query->with([
            'source:id,name',
            'category:id,name,slug,icon',
            'jobLocation:id,city,state,country',
        ]);
    }

    /**
     * Optimize job listing query
     */
    public function optimizeJobListingQuery(Builder $query): Builder
    {
        return $query
            ->select([
                'id',
                'title',
                'company',
                'location',
                'job_type',
                'experience_level',
                'salary_min',
                'salary_max',
                'salary_currency',
                'remote_allowed',
                'posted_at',
                'job_source_id',
                'job_category_id',
                'job_location_id',
                'created_at',
            ])
            ->with([
                'source:id,name',
                'category:id,name,slug,icon',
                'jobLocation:id,city,state,country',
            ]);
    }

    /**
     * Analyze slow queries
     */
    public function analyzeSlowQueries(int $threshold = 1000): array
    {
        // Enable query logging
        DB::enableQueryLog();

        // Get queries that took longer than threshold (in milliseconds)
        $queries = DB::getQueryLog();

        $slowQueries = array_filter($queries, function ($query) use ($threshold) {
            return ($query['time'] ?? 0) > $threshold;
        });

        return array_map(function ($query) {
            return [
                'query' => $query['query'],
                'bindings' => $query['bindings'],
                'time' => $query['time'] . 'ms',
            ];
        }, $slowQueries);
    }

    /**
     * Get query explain plan
     */
    public function explainQuery(string $sql, array $bindings = []): array
    {
        $explained = DB::select('EXPLAIN ' . $sql, $bindings);

        return array_map(function ($row) {
            return (array) $row;
        }, $explained);
    }

    /**
     * Optimize table (defragment and rebuild indexes)
     */
    public function optimizeTable(string $table): void
    {
        DB::statement("OPTIMIZE TABLE {$table}");
    }

    /**
     * Analyze table statistics for query optimizer
     */
    public function analyzeTable(string $table): void
    {
        DB::statement("ANALYZE TABLE {$table}");
    }

    /**
     * Get table size and index statistics
     */
    public function getTableStats(string $table): array
    {
        $stats = DB::select("
            SELECT
                table_name,
                ROUND(((data_length + index_length) / 1024 / 1024), 2) AS size_mb,
                table_rows,
                ROUND((data_length / 1024 / 1024), 2) AS data_size_mb,
                ROUND((index_length / 1024 / 1024), 2) AS index_size_mb
            FROM information_schema.TABLES
            WHERE table_schema = DATABASE()
            AND table_name = ?
        ", [$table]);

        return $stats ? (array) $stats[0] : [];
    }

    /**
     * Get index usage statistics
     */
    public function getIndexStats(string $table): array
    {
        $stats = DB::select("
            SELECT
                index_name,
                column_name,
                seq_in_index,
                cardinality,
                index_type
            FROM information_schema.STATISTICS
            WHERE table_schema = DATABASE()
            AND table_name = ?
            ORDER BY index_name, seq_in_index
        ", [$table]);

        return array_map(function ($row) {
            return (array) $row;
        }, $stats);
    }

    /**
     * Check for missing indexes based on slow queries
     */
    public function suggestIndexes(string $table): array
    {
        $suggestions = [];

        // Get columns that are frequently used in WHERE clauses without indexes
        $unindexedColumns = DB::select("
            SELECT DISTINCT column_name
            FROM information_schema.COLUMNS
            WHERE table_schema = DATABASE()
            AND table_name = ?
            AND column_name NOT IN (
                SELECT column_name
                FROM information_schema.STATISTICS
                WHERE table_schema = DATABASE()
                AND table_name = ?
            )
        ", [$table, $table]);

        foreach ($unindexedColumns as $column) {
            $suggestions[] = [
                'type' => 'missing_index',
                'table' => $table,
                'column' => $column->column_name,
                'suggestion' => "Consider adding an index on {$column->column_name}",
            ];
        }

        return $suggestions;
    }

    /**
     * Chunk large queries to reduce memory usage
     */
    public function chunkQuery(Builder $query, int $chunkSize, callable $callback): void
    {
        $query->chunk($chunkSize, $callback);
    }

    /**
     * Use cursor for memory-efficient iteration
     */
    public function cursorQuery(Builder $query): \Illuminate\Support\LazyCollection
    {
        return $query->cursor();
    }
}