package main

import (
	"database/sql"
	"fmt"
	"log"
)

func CalculateEpisodeNumbers(db *sql.DB) error {
	log.Printf("Calculating episode numbers")

	// Start a transaction
	tx, err := db.Begin()
	if err != nil {
		return fmt.Errorf("error starting transaction: %w", err)
	}
	defer tx.Rollback()

	// First find all years that still need episodes numbers
	rows, err := tx.Query("select year, max((select max(episode) from videos where year = year)) from videos where episode is null group by year")
	if err != nil {
		return fmt.Errorf("error retrieving rows: %w", err)
	}

	// Loop over each year and set the missing episode numbers
	for rows.Next() {
		var year, lastEpisode int
		err = rows.Scan(&year, &lastEpisode)
		log.Printf("Last episode is %d", lastEpisode)
		if err != nil {
			return fmt.Errorf("error getting row: %w", err)
		}

		// Find all episodes that need updating
		episodes, err := tx.Query("select id from videos where year = ? and episode is null order by run, id desc", year)
		if err != nil {
			return fmt.Errorf("error retrieving episodes: %w", err)
		}

		// Update each episode
		for episodes.Next() {
			var episodeId int
			err = episodes.Scan(&episodeId)
			if err != nil {
				return fmt.Errorf("error retrieving episode id: %w", err)
			}

			// Set the episode ID
			lastEpisode++
			_, err = tx.Exec("update videos set episode = ? where id = ?", &lastEpisode, &episodeId)
			if err != nil {
				return fmt.Errorf("error updating episode id: %w", err)
			}
		}
	}

	// Commit all changes
	err = tx.Commit()
	if err != nil {
		return fmt.Errorf("error commiting changes: %w", err)
	}

	return nil
}