package main

import (
	"context"
	"log/slog"
	"net/http"
)

// A song needs this many reviews to qualify for any ranking: with ten members it means a third of
// the club has weighed in, which is a real threshold rather than a formality.
const minReviews = 3

type songStat struct {
	ID          int64
	Title       string
	Artist      string
	Value       float64
	ReviewCount int
}

type userStat struct {
	ID     int64
	Name   string
	Value  float64
	Count  int
	Avatar *string
}

func (u *userStat) Initials() string { m := member{Name: u.Name}; return m.Initials() }

type stats struct {
	MinReviews int

	TopSongs     []songStat
	BottomSongs  []songStat
	MostDivisive []songStat
	MostUnified  []songStat
	MostReviewed []songStat

	Harshest     []userStat
	MostGenerous []userStat
	MostActive   []userStat
	MostProlific []userStat
}

// Every leaderboard is ordered and limited in SQL, and every one carries a deterministic tie-break:
// ties are common in a ten-person club, and without one Postgres may return a different ten each
// time, so the page visibly reshuffles between reloads for no reason.
func (a *app) songLeaderboard(ctx context.Context, valueExpr, direction string) ([]songStat, error) {
	rows, err := a.pool.Query(ctx, `
		select s.id, s.title, s.artist, `+valueExpr+`::float as value, count(r.id)::int as reviews
		  from songs s join reviews r on r.song_id = s.id
		 group by s.id
		having count(r.id) >= $1
		 order by value `+direction+`, reviews desc, s.id asc
		 limit 10`, minReviews)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []songStat
	for rows.Next() {
		var s songStat
		if err := rows.Scan(&s.ID, &s.Title, &s.Artist, &s.Value, &s.ReviewCount); err != nil {
			return nil, err
		}
		out = append(out, s)
	}
	return out, rows.Err()
}

// Reviewer boards need a minimum too, or one enthusiastic 100 makes someone the most generous
// member in the club forever.
func (a *app) reviewerLeaderboard(ctx context.Context, valueExpr, direction string) ([]userStat, error) {
	rows, err := a.pool.Query(ctx, `
		select u.id, u.name, u.avatar, `+valueExpr+`::float as value, count(r.id)::int as n
		  from users u join reviews r on r.reviewer_id = u.id
		 group by u.id
		having count(r.id) >= $1
		 order by value `+direction+`, n desc, u.id asc
		 limit 10`, minReviews)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []userStat
	for rows.Next() {
		var u userStat
		if err := rows.Scan(&u.ID, &u.Name, &u.Avatar, &u.Value, &u.Count); err != nil {
			return nil, err
		}
		out = append(out, u)
	}
	return out, rows.Err()
}

func (a *app) mostProlific(ctx context.Context) ([]userStat, error) {
	rows, err := a.pool.Query(ctx, `
		select u.id, u.name, u.avatar, count(s.id)::float, count(s.id)::int
		  from users u join songs s on s.submitted_by = u.id
		 group by u.id
		 order by count(s.id) desc, u.id asc
		 limit 10`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []userStat
	for rows.Next() {
		var u userStat
		if err := rows.Scan(&u.ID, &u.Name, &u.Avatar, &u.Value, &u.Count); err != nil {
			return nil, err
		}
		out = append(out, u)
	}
	return out, rows.Err()
}

// The reveal rule does not apply here: leaderboards are always public. That is the whole point of
// /stats being a page you walk to deliberately.
func (a *app) statsPage(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()
	s := stats{MinReviews: minReviews}

	var err error
	for _, load := range []func() error{
		func() (err error) { s.TopSongs, err = a.songLeaderboard(ctx, "avg(r.score)", "desc"); return },
		func() (err error) { s.BottomSongs, err = a.songLeaderboard(ctx, "avg(r.score)", "asc"); return },
		func() (err error) {
			s.MostDivisive, err = a.songLeaderboard(ctx, "stddev_pop(r.score)", "desc")
			return
		},
		func() (err error) { s.MostUnified, err = a.songLeaderboard(ctx, "stddev_pop(r.score)", "asc"); return },
		func() (err error) { s.MostReviewed, err = a.songLeaderboard(ctx, "count(r.id)", "desc"); return },
		func() (err error) { s.Harshest, err = a.reviewerLeaderboard(ctx, "avg(r.score)", "asc"); return },
		func() (err error) { s.MostGenerous, err = a.reviewerLeaderboard(ctx, "avg(r.score)", "desc"); return },
		func() (err error) { s.MostActive, err = a.reviewerLeaderboard(ctx, "count(r.id)", "desc"); return },
		func() (err error) { s.MostProlific, err = a.mostProlific(ctx); return },
	} {
		if err = load(); err != nil {
			slog.Error("stats", "ctx", "songs", "error", err)
			http.Error(w, "virhe", http.StatusInternalServerError)
			return
		}
	}

	a.render(w, r, http.StatusOK, "stats.html", page{Title: "Tilastot", Data: s})
}