package main

import (
	"compress/gzip"
	"encoding/csv"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
)

const (
	imdbDataDir     = "imdbdata"
	basicsURL       = "https://datasets.imdbws.com/title.basics.tsv.gz"
	ratingsURL      = "https://datasets.imdbws.com/title.ratings.tsv.gz"
)

func dataPath(name string) string {
	return filepath.Join(imdbDataDir, name)
}

// downloadFile fetches url and writes to dst, overwriting if present.
func downloadFile(dst, url string) error {
	resp, err := http.Get(url)
	if err != nil {
		return fmt.Errorf("http get: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("http %d from %s", resp.StatusCode, url)
	}

	f, err := os.Create(dst)
	if err != nil {
		return fmt.Errorf("create %s: %w", dst, err)
	}
	defer f.Close()

	_, err = io.Copy(f, resp.Body)
	if err != nil {
		return fmt.Errorf("write %s: %w", dst, err)
	}
	log.Printf("downloaded %s", url)
	return nil
}

// gunzipFile decompresses src.gz to dst.
func gunzipFile(src, dst string) error {
	f, err := os.Open(src)
	if err != nil {
		return err
	}
	defer f.Close()

	gz, err := gzip.NewReader(f)
	if err != nil {
		return err
	}
	defer gz.Close()

	out, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer out.Close()

	_, err = io.Copy(out, gz)
	if err != nil {
		return fmt.Errorf("write %s: %w", dst, err)
	}
	return nil
}

// downloadImdbDatasets fetches and extracts the two TSV files into imdbdata/.
func (a *App) downloadImdbDatasets() error {
	if err := os.MkdirAll(imdbDataDir, 0755); err != nil {
		return fmt.Errorf("mkdir: %w", err)
	}

	type filePair struct {
		url string
		gz  string
		tsv string
	}

	pairs := []filePair{
		{basicsURL, dataPath("title.basics.tsv.gz"), dataPath("title.basics.tsv")},
		{ratingsURL, dataPath("title.ratings.tsv.gz"), dataPath("title.ratings.tsv")},
	}

	for _, p := range pairs {
		if err := downloadFile(p.gz, p.url); err != nil {
			return fmt.Errorf("download %s: %w", p.url, err)
		}
		if err := gunzipFile(p.gz, p.tsv); err != nil {
			return fmt.Errorf("gunzip %s: %w", p.gz, err)
		}
		log.Printf("extracted %s", p.tsv)
	}
	return nil
}

// ratingEntry holds data from title.ratings.tsv for one title.
type ratingEntry struct {
	AverageRating float64
	NumVotes      int
}

// basicEntry holds data from title.basics.tsv for one title.
type basicEntry struct {
	TitleType      string
	PrimaryTitle   string
	OriginalTitle  string
	StartYear      *int
	RuntimeMinutes *int
}

// parseTSV reads a TSV file and calls fn for each row (after header).
// Only rows where keep(tconst) is true are passed to fn.
func parseTSV(path string, keep func(string) bool, fn func(record []string) error) error {
	f, err := os.Open(path)
	if err != nil {
		return fmt.Errorf("open %s: %w", path, err)
	}
	defer f.Close()

	r := csv.NewReader(f)
	r.Comma = '\t'
	r.LazyQuotes = true
	r.FieldsPerRecord = -1

	// skip header
	if _, err := r.Read(); err != nil {
		return fmt.Errorf("read header: %w", err)
	}

	for {
		rec, err := r.Read()
		if err == io.EOF {
			break
		}
		if err != nil {
			return fmt.Errorf("read row: %w", err)
		}

		if len(rec) < 1 {
			continue
		}

		tconst := rec[0]
		if !keep(tconst) {
			continue
		}

		if err := fn(rec); err != nil {
			return err
		}
	}
	return nil
}

// parseTitleRatings reads the ratings TSV and collects entries for the given ids.
func (a *App) parseTitleRatings(ids map[string]bool) (map[string]ratingEntry, error) {
	result := make(map[string]ratingEntry)

	err := parseTSV(dataPath("title.ratings.tsv"),
		func(s string) bool { return ids[s] },
		func(rec []string) error {
			if len(rec) < 3 {
				return nil
			}
			rating, err := strconv.ParseFloat(rec[1], 64)
			if err != nil {
				return nil
			}
			votes, err := strconv.Atoi(rec[2])
			if err != nil {
				return nil
			}
			result[rec[0]] = ratingEntry{AverageRating: rating, NumVotes: votes}
			return nil
		},
	)
	return result, err
}

// parseTitleBasics reads the basics TSV and collects entries for the given ids.
func (a *App) parseTitleBasics(ids map[string]bool) (map[string]basicEntry, error) {
	result := make(map[string]basicEntry)

	err := parseTSV(dataPath("title.basics.tsv"),
		func(s string) bool { return ids[s] },
		func(rec []string) error {
			if len(rec) < 7 {
				return nil
			}

			entry := basicEntry{
				TitleType:     rec[1],
				PrimaryTitle:  rec[2],
				OriginalTitle: rec[3],
			}

			if rec[4] != "\\N" && rec[4] != "" {
				v, err := strconv.Atoi(rec[4])
				if err == nil {
					entry.StartYear = &v
				}
			}

			if rec[5] != "\\N" && rec[5] != "" {
				v, err := strconv.Atoi(rec[5])
				if err == nil {
					entry.RuntimeMinutes = &v
				}
			}

			result[rec[0]] = entry
			return nil
		},
	)
	return result, err
}

// applyImdbUpdates writes ratings and basics data into the imdb table.
func (a *App) applyImdbUpdates(ratings map[string]ratingEntry, basics map[string]basicEntry) error {
	tx := a.DB.MustBegin()

	rStmt, err := tx.Prepare(`UPDATE imdb SET average_rating = ?, num_votes = ? WHERE imdb_id = ?`)
	if err != nil {
		tx.Rollback()
		return fmt.Errorf("prepare rating update: %w", err)
	}
	defer rStmt.Close()

	bStmt, err := tx.Prepare(`
		UPDATE imdb SET title_type = ?, primary_title = ?, original_title = ?,
			start_year = ?, runtime_minutes = ? WHERE imdb_id = ?
	`)
	if err != nil {
		tx.Rollback()
		return fmt.Errorf("prepare basic update: %w", err)
	}
	defer bStmt.Close()

	rCount, bCount := 0, 0

	for id, r := range ratings {
		dec := float64(int(r.AverageRating*10+0.5)) / 10.0
		if _, err := rStmt.Exec(dec, r.NumVotes, id); err != nil {
			tx.Rollback()
			return fmt.Errorf("update rating %s: %w", id, err)
		}
		rCount++
	}

	for id, b := range basics {
		if _, err := bStmt.Exec(
			b.TitleType, b.PrimaryTitle, b.OriginalTitle,
			b.StartYear, b.RuntimeMinutes, id,
		); err != nil {
			tx.Rollback()
			return fmt.Errorf("update basic %s: %w", id, err)
		}
		bCount++
	}

	if err := tx.Commit(); err != nil {
		return fmt.Errorf("commit: %w", err)
	}

	log.Printf("applyImdbUpdates: %d ratings, %d basics updated", rCount, bCount)
	return nil
}

// getImdbIDsWithoutRating returns all imdb_id values where average_rating IS NULL.
func (a *App) getImdbIDsWithoutRating() (map[string]bool, error) {
	rows, err := a.DB.Query(`SELECT imdb_id FROM imdb WHERE average_rating IS NULL`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	ids := make(map[string]bool)
	for rows.Next() {
		var id string
		if err := rows.Scan(&id); err != nil {
			return nil, err
		}
		ids[id] = true
	}
	return ids, rows.Err()
}

// fetchAndUpdateImdbData is the main entry point.
// Checks if any imdb entry lacks average_rating. If so, downloads datasets,
// parses them, and updates matching rows with ratings and basic metadata.
func (a *App) fetchAndUpdateImdbData() error {
	var count int
	if err := a.DB.QueryRow(`SELECT COUNT(*) FROM imdb WHERE average_rating IS NULL`).Scan(&count); err != nil {
		return fmt.Errorf("count: %w", err)
	}
	if count == 0 {
		log.Println("fetchAndUpdateImdbData: all entries have ratings, skipping")
		return nil
	}
	log.Printf("fetchAndUpdateImdbData: %d entries without rating", count)

	// Download / refresh datasets
	if err := a.downloadImdbDatasets(); err != nil {
		return err
	}

	// Gather all imdb_ids needing updates
	ids, err := a.getImdbIDsWithoutRating()
	if err != nil {
		return err
	}
	if len(ids) == 0 {
		log.Println("fetchAndUpdateImdbData: no entries need updating")
		return nil
	}
	log.Printf("fetchAndUpdateImdbData: %d entries to update", len(ids))

	// Parse datasets
	ratings, err := a.parseTitleRatings(ids)
	if err != nil {
		return fmt.Errorf("parseTitleRatings: %w", err)
	}
	log.Printf("fetchAndUpdateImdbData: found ratings for %d entries", len(ratings))

	basics, err := a.parseTitleBasics(ids)
	if err != nil {
		return fmt.Errorf("parseTitleBasics: %w", err)
	}
	log.Printf("fetchAndUpdateImdbData: found basics for %d entries", len(basics))

	// Write to DB
	if err := a.applyImdbUpdates(ratings, basics); err != nil {
		return err
	}

	return nil
}