package main

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"os"
	"strconv"
	"time"

	"github.com/jackc/pgx/v5"
)

const pageSize = 20

type songSummary struct {
	ID          int64
	Title       string
	Artist      string
	Genre       string
	Duration    int
	CreatedAt   time.Time
	Submitter   string
	SubmitterID int64
	ReviewCount int
	// Nil unless the viewer has revealed the song. The reveal rule is applied in the query, not
	// in the template — a hidden average is never sent.
	Average  *float64
	Own      bool
	Reviewed bool
}

func (s *songSummary) GenreLabel() string { return genreLabel(s.Genre) }
func (s *songSummary) Revealed() bool     { return s.Own || s.Reviewed }

func (s *songSummary) Length() string {
	return fmt.Sprintf("%d.%02d", s.Duration/60, s.Duration%60)
}

type songList struct {
	Items      []*songSummary
	NextCursor int64 // 0 when there is no next page
	Queue      bool
}

// The select list is identical for both lists, so the reveal rule cannot drift between them.
const songColumns = `
	s.id, s.title, s.artist, s.genre, s.duration_seconds, s.created_at, u.id, u.name,
	(select count(*) from reviews r where r.song_id = s.id),
	case when s.submitted_by = $1
	          or exists (select 1 from reviews r where r.song_id = s.id and r.reviewer_id = $1)
	     then (select avg(r.score)::float from reviews r where r.song_id = s.id)
	end,
	s.submitted_by = $1,
	exists (select 1 from reviews r where r.song_id = s.id and r.reviewer_id = $1)`

func scanSongs(rows pgx.Rows) ([]*songSummary, error) {
	defer rows.Close()
	var out []*songSummary
	for rows.Next() {
		var s songSummary
		if err := rows.Scan(&s.ID, &s.Title, &s.Artist, &s.Genre, &s.Duration, &s.CreatedAt,
			&s.SubmitterID, &s.Submitter, &s.ReviewCount, &s.Average, &s.Own, &s.Reviewed); err != nil {
			return nil, err
		}
		out = append(out, &s)
	}
	return out, rows.Err()
}

// The queue is a worklist: songs you can still review, oldest first, and never your own — you can
// never act on those, so they would sit at the front forever.
func (a *app) queue(ctx context.Context, viewerID, cursor int64) (*songList, error) {
	rows, err := a.pool.Query(ctx, `select`+songColumns+`
		  from songs s join users u on u.id = s.submitted_by
		 where s.submitted_by <> $1
		   and not exists (select 1 from reviews r where r.song_id = s.id and r.reviewer_id = $1)
		   and ($2 = 0 or s.id > $2)
		 order by s.created_at, s.id
		 limit $3`, viewerID, cursor, pageSize+1)
	if err != nil {
		return nil, err
	}
	items, err := scanSongs(rows)
	if err != nil {
		return nil, err
	}
	return paginate(items, true), nil
}

// Everything, newest first. This is where a song lives once it has left the queue.
func (a *app) browse(ctx context.Context, viewerID, cursor int64) (*songList, error) {
	rows, err := a.pool.Query(ctx, `select`+songColumns+`
		  from songs s join users u on u.id = s.submitted_by
		 where ($2 = 0 or s.id < $2)
		 order by s.created_at desc, s.id desc
		 limit $3`, viewerID, cursor, pageSize+1)
	if err != nil {
		return nil, err
	}
	items, err := scanSongs(rows)
	if err != nil {
		return nil, err
	}
	return paginate(items, false), nil
}

// One row over the page size is fetched so "is there more" needs no second count query.
func paginate(items []*songSummary, isQueue bool) *songList {
	l := &songList{Items: items, Queue: isQueue}
	if len(items) > pageSize {
		l.Items = items[:pageSize]
		l.NextCursor = l.Items[pageSize-1].ID
	}
	return l
}

func cursorOf(r *http.Request) int64 {
	n, _ := strconv.ParseInt(r.URL.Query().Get("cursor"), 10, 64)
	return n
}

func (a *app) queuePage(w http.ResponseWriter, r *http.Request) {
	list, err := a.queue(r.Context(), memberFrom(r.Context()).ID, cursorOf(r))
	if err != nil {
		slog.Error("queue", "ctx", "songs", "error", err)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	a.render(w, r, http.StatusOK, "queue.html", page{Title: "Jono", Data: list})
}

func (a *app) browsePage(w http.ResponseWriter, r *http.Request) {
	list, err := a.browse(r.Context(), memberFrom(r.Context()).ID, cursorOf(r))
	if err != nil {
		slog.Error("browse", "ctx", "songs", "error", err)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	a.render(w, r, http.StatusOK, "songs.html", page{Title: "Kappaleet", Data: list})
}

// --- detail ---

type songDetail struct {
	songSummary
	Description  string
	SourceURL    *string
	Reviews      []*review // nil when the reveal rule is withholding them
	ViewerReview *review
	CanReview    bool
	CanEdit      bool // submitter, and the song is unlocked
	Genres       []genre
}

func (s *songDetail) Locked() bool { return s.ReviewCount > 0 }

func (a *app) song(ctx context.Context, viewerID, songID int64) (*songDetail, error) {
	var d songDetail
	err := a.pool.QueryRow(ctx, `select`+songColumns+`, coalesce(s.description, ''), s.source_url
		  from songs s join users u on u.id = s.submitted_by
		 where s.id = $2`, viewerID, songID).
		Scan(&d.ID, &d.Title, &d.Artist, &d.Genre, &d.Duration, &d.CreatedAt,
			&d.SubmitterID, &d.Submitter, &d.ReviewCount, &d.Average, &d.Own, &d.Reviewed,
			&d.Description, &d.SourceURL)
	if err != nil {
		return nil, err
	}
	d.Genres = genres
	d.CanReview = !d.Own && !d.Reviewed
	d.CanEdit = d.Own && d.ReviewCount == 0

	if d.Reviewed {
		d.ViewerReview, err = a.viewerReview(ctx, songID, viewerID)
		if err != nil {
			return nil, err
		}
	}
	// The query only runs when the song is revealed: hidden reviews are never fetched, let alone
	// sent and hidden with CSS.
	if d.Revealed() {
		d.Reviews, err = a.reviewsFor(ctx, songID, viewerID)
		if err != nil {
			return nil, err
		}
	}
	return &d, nil
}

func (a *app) songPage(w http.ResponseWriter, r *http.Request) {
	id, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	d, err := a.song(r.Context(), memberFrom(r.Context()).ID, id)
	if errors.Is(err, pgx.ErrNoRows) {
		http.NotFound(w, r)
		return
	} else if err != nil {
		slog.Error("song", "ctx", "songs", "error", err, "song", id)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	a.render(w, r, http.StatusOK, "song.html", page{Title: d.Title, Data: d})
}

// --- edit and delete ---

// The submitter may change the four text fields while the song is unlocked. Once people have
// reviewed it, the thing they reviewed stops changing under them.
func (a *app) editSong(w http.ResponseWriter, r *http.Request) {
	id, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	genre := r.FormValue("genre")
	if !validGenre(genre) {
		http.Error(w, "tuntematon genre", http.StatusUnprocessableEntity)
		return
	}
	title, artist := clean(r.FormValue("title"), maxTitle), clean(r.FormValue("artist"), maxArtist)
	if title == "" || artist == "" {
		a.flash(w, "Nimi ja esittäjä ovat pakollisia.")
		http.Redirect(w, r, fmt.Sprintf("/songs/%d", id), http.StatusSeeOther)
		return
	}

	tag, err := a.pool.Exec(r.Context(), `
		update songs set title = $3, artist = $4, genre = $5, description = nullif($6, '')
		 where id = $1 and submitted_by = $2
		   and not exists (select 1 from reviews r where r.song_id = songs.id)`,
		id, memberFrom(r.Context()).ID, title, artist, genre,
		clean(r.FormValue("description"), maxDescription))
	if err != nil {
		slog.Error("edit song", "ctx", "songs", "error", err, "song", id)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	if tag.RowsAffected() == 0 {
		a.flash(w, "Kappaletta ei voi enää muokata — sitä on jo arvosteltu.")
	} else {
		a.flash(w, "Tiedot tallennettu.")
	}
	http.Redirect(w, r, fmt.Sprintf("/songs/%d", id), http.StatusSeeOther)
}

// The row and the file go together, always.
func (a *app) deleteSong(w http.ResponseWriter, r *http.Request) {
	id, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	tag, err := a.pool.Exec(r.Context(), `
		delete from songs where id = $1 and submitted_by = $2
		  and not exists (select 1 from reviews r where r.song_id = songs.id)`,
		id, memberFrom(r.Context()).ID)
	if err != nil {
		slog.Error("delete song", "ctx", "songs", "error", err, "song", id)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}
	if tag.RowsAffected() == 0 {
		a.flash(w, "Kappaletta ei voi enää poistaa — sitä on jo arvosteltu.")
		http.Redirect(w, r, fmt.Sprintf("/songs/%d", id), http.StatusSeeOther)
		return
	}
	os.Remove(a.audioPath(id))
	slog.Info("song deleted", "ctx", "songs", "song", id)
	a.flash(w, "Kappale poistettu.")
	http.Redirect(w, r, "/songs", http.StatusSeeOther)
}

// --- audio ---

// Auth-gated, Range-capable, and not under /api because it serves bytes rather than JSON.
// Parsing the id as an integer is the traversal check.
func (a *app) audio(w http.ResponseWriter, r *http.Request) {
	id, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	var name string
	err = a.pool.QueryRow(r.Context(), `select audio_file from songs where id = $1`, id).Scan(&name)
	if errors.Is(err, pgx.ErrNoRows) {
		http.NotFound(w, r)
		return
	} else if err != nil {
		slog.Error("audio lookup", "ctx", "songs", "error", err, "song", id)
		http.Error(w, "virhe", http.StatusInternalServerError)
		return
	}

	f, err := os.Open(a.audioPath(id))
	if err != nil {
		slog.Error("audio open", "ctx", "songs", "error", err, "song", id)
		http.NotFound(w, r)
		return
	}
	defer f.Close()
	info, err := f.Stat()
	if err != nil {
		http.NotFound(w, r)
		return
	}
	w.Header().Set("Content-Type", "audio/ogg")
	// ServeContent handles 206, 416 and If-Range correctly, which hand-rolled Range parsing does not.
	http.ServeContent(w, r, name, info.ModTime(), f)
}