// Package service — SadhnaService is the sādhana-streak brain. It folds a
// user's chanting logs (sadhna_logs) together with their quote posts
// (posts table) into the single dashboard the /sadhna-streak page reads:
// today's two disciplines, the trailing 7-day strip, the streak counters,
// and the growing-plant state.
//
// A day is "complete" only when BOTH daily disciplines were done that UTC
// calendar day: the target rounds were chanted AND at least one quote was
// posted. The streak counts consecutive complete days; the plant's growth
// is a 0–100 score that rises a little each complete day and falls faster
// for each missed day, eventually decaying to 0 ("dead") — and revives as
// soon as the practice resumes. The whole thing is recomputed from the
// underlying rows on every read, so there's no derived state to keep in
// sync and back-dated edits can never drift.
package service

import (
	"context"
	"math/rand"
	"time"

	"github.com/prabhupadasays/spsays-bff/internal/model"
	"github.com/prabhupadasays/spsays-bff/internal/repository"
	"go.uber.org/zap"
)

// Tunables for the streak + plant. Kept together so the growth feel is
// easy to adjust in one place.
const (
	// defaultChantTarget is the fallback daily rounds when a user hasn't
	// set daily_chanting_rounds on their profile (Śrīla Prabhupāda's
	// minimum for initiated devotees).
	defaultChantTarget = 16

	// growthMax is the score at which the plant is a full mature tree.
	growthMax = 100
	// growthPerDay is added for each complete day (≈25 perfect days from
	// seed to full tree).
	growthPerDay = 4
	// regressPerDay is subtracted for each missed day. Deliberately larger
	// than growthPerDay so neglect undoes progress faster than practice
	// builds it (a full tree withers to nothing in ~12 missed days).
	regressPerDay = 9

	// streakWindowDays bounds how far back the recompute walks. Comfortably
	// longer than any growth/decay can persist, so the [0,100] clamp washes
	// out the unknown state before the window's start.
	streakWindowDays = 400

	// vineMaxDays caps how many folds the creeper payload carries. The
	// client only renders as many as fit the pole anyway; CurrentStreak
	// still reports the true length.
	vineMaxDays = 60
)

// rewardEveryDays is the streak cadence for gifts: one reward every 7
// completed days, counted from the start of the current unbroken streak
// (days 7, 14, 21, …). A broken streak restarts the count.
const rewardEveryDays = 7

// SadhnaService computes streak/plant state and records chanting progress.
type SadhnaService struct {
	logs    *repository.SadhnaRepo
	posts   *repository.PostRepo
	users   *repository.UserRepo
	rewards *repository.RewardRepo
	logger  *zap.Logger
}

func NewSadhnaService(
	logs *repository.SadhnaRepo,
	posts *repository.PostRepo,
	users *repository.UserRepo,
	rewards *repository.RewardRepo,
	logger *zap.Logger,
) *SadhnaService {
	return &SadhnaService{logs: logs, posts: posts, users: users, rewards: rewards, logger: logger}
}

const dayFmt = "2006-01-02"

// utcToday returns today's UTC calendar date truncated to midnight, the
// anchor every day-bucket comparison uses.
func utcToday() time.Time {
	now := time.Now().UTC()
	return time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, time.UTC)
}

// SaveChant records the user's chanting progress for today and returns the
// freshly recomputed dashboard. Rounds outside [0,1008] are clamped.
// chant_done is frozen as rounds >= the user's current target.
func (s *SadhnaService) SaveChant(ctx context.Context, userID string, rounds int) (*model.SadhnaDashboard, error) {
	if rounds < 0 {
		rounds = 0
	}
	if rounds > 1008 {
		rounds = 1008
	}
	target := s.targetFor(ctx, userID)
	chantDone := rounds >= target

	if _, err := s.logs.UpsertToday(ctx, userID, utcToday(), rounds, chantDone); err != nil {
		return nil, err
	}
	return s.Dashboard(ctx, userID)
}

// Dashboard recomputes the user's full sādhana state from their chanting
// logs and quote posts over the trailing window.
func (s *SadhnaService) Dashboard(ctx context.Context, userID string) (*model.SadhnaDashboard, error) {
	target := s.targetFor(ctx, userID)
	today := utcToday()
	since := today.AddDate(0, 0, -(streakWindowDays - 1))

	logs, err := s.logs.ListSince(ctx, userID, since)
	if err != nil {
		return nil, err
	}
	postsByDay, err := s.posts.PostCountsByDate(ctx, userID, since)
	if err != nil {
		return nil, err
	}

	// Index the chanting half by day.
	chantByDay := make(map[string]bool, len(logs))
	roundsByDay := make(map[string]int, len(logs))
	for _, l := range logs {
		key := l.LogDate.UTC().Format(dayFmt)
		chantByDay[key] = l.ChantDone
		roundsByDay[key] = l.RoundsCompleted
	}

	// posted[day] = at least one quote that day; postsByDay[day] = how many.
	posted := func(day string) bool { return postsByDay[day] > 0 }
	// completed[day] = both disciplines done that day.
	completed := func(day string) bool { return chantByDay[day] && posted(day) }

	todayKey := today.Format(dayFmt)

	// --- Growth: forward-simulate the window, day by day. Today never
	// regresses the plant (the day isn't over yet) — it only adds growth
	// once complete. ---
	growth := 0
	for d := since; !d.After(today); d = d.AddDate(0, 0, 1) {
		key := d.Format(dayFmt)
		isToday := key == todayKey
		switch {
		case completed(key):
			growth += growthPerDay
			if growth > growthMax {
				growth = growthMax
			}
		case isToday:
			// in-progress day — leave growth as-is
		default:
			growth -= regressPerDay
			if growth < 0 {
				growth = 0
			}
		}
	}

	// --- Streaks. Current streak ends at today if today is complete,
	// otherwise at yesterday (so an unfinished today doesn't read as a
	// broken streak mid-day). ---
	current := 0
	cursor := today
	if !completed(todayKey) {
		cursor = today.AddDate(0, 0, -1)
	}
	for !cursor.Before(since) && completed(cursor.Format(dayFmt)) {
		current++
		cursor = cursor.AddDate(0, 0, -1)
	}

	// Longest run of complete days anywhere in the window.
	longest, run := 0, 0
	for d := since; !d.After(today); d = d.AddDate(0, 0, 1) {
		if completed(d.Format(dayFmt)) {
			run++
			if run > longest {
				longest = run
			}
		} else {
			run = 0
		}
	}
	if current > longest {
		longest = current
	}

	// --- The trailing 7-day strip, oldest first. ---
	week := make([]model.SadhnaDay, 0, 7)
	for i := 6; i >= 0; i-- {
		d := today.AddDate(0, 0, -i)
		key := d.Format(dayFmt)
		week = append(week, model.SadhnaDay{
			Date:      key,
			ChantDone: chantByDay[key],
			QuoteDone: posted(key),
			Completed: completed(key),
		})
	}

	// --- The creeper: one fold per day of the current streak (oldest
	// first), plus a final in-progress fold for an unfinished today. The
	// streak's complete days end at today when today is complete, else at
	// yesterday; an unfinished today is appended as the growing tip. ---
	vine := make([]model.VineDay, 0, current+1)
	if current >= 1 {
		end := today
		if !completed(todayKey) {
			end = today.AddDate(0, 0, -1)
		}
		start := end.AddDate(0, 0, -(current - 1))
		for d := start; !d.After(end); d = d.AddDate(0, 0, 1) {
			key := d.Format(dayFmt)
			vine = append(vine, model.VineDay{
				Date:      key,
				Rounds:    roundsByDay[key],
				Posts:     postsByDay[key],
				Completed: true,
			})
		}
	}
	if !completed(todayKey) {
		vine = append(vine, model.VineDay{
			Date:       todayKey,
			Rounds:     roundsByDay[todayKey],
			Posts:      postsByDay[todayKey],
			InProgress: true,
		})
	}
	if len(vine) > vineMaxDays {
		vine = vine[len(vine)-vineMaxDays:]
	}

	// --- Rewards: a gift every 7 streak-days. When today completes a
	// multiple-of-7 streak day, grant one (idempotently). Surface any
	// not-yet-celebrated grant + the projected date of the next gift. ---
	var pending *model.SadhnaRewardGrant
	var nextReward *string
	if s.rewards != nil {
		todayDone := completed(todayKey)
		if todayDone && current > 0 && current%rewardEveryDays == 0 {
			s.ensureGrant(ctx, userID, current)
		}
		pending, _ = s.rewards.PendingGrant(ctx, userID)
		nextReward = nextRewardDate(today, current, todayDone)
	}

	return &model.SadhnaDashboard{
		TargetRounds:    target,
		RoundsCompleted: roundsByDay[todayKey],
		ChantDone:       chantByDay[todayKey],
		QuoteDone:       posted(todayKey),
		TodayCompleted:  completed(todayKey),
		CurrentStreak:   current,
		LongestStreak:   longest,
		Growth:          growth,
		Stage:           stageFor(growth),
		Alive:           growth > 0,
		Week:            week,
		VineDays:        vine,
		NextRewardDate:  nextReward,
		PendingReward:   pending,
	}, nil
}

// ensureGrant idempotently awards a gift for the given streak milestone,
// picking a reward the user hasn't received yet. Once every reward has been
// collected the pool resets (avoiding an immediate back-to-back repeat) so
// the gifts cycle. Best-effort: any error leaves the milestone ungranted,
// to be retried on the next recompute.
func (s *SadhnaService) ensureGrant(ctx context.Context, userID string, milestone int) {
	has, err := s.rewards.HasMilestone(ctx, userID, milestone)
	if err != nil || has {
		return
	}
	pool, err := s.rewards.ListGiftable(ctx)
	if err != nil || len(pool) == 0 {
		return
	}
	granted, err := s.rewards.GrantedRewardIDs(ctx, userID)
	if err != nil {
		return
	}

	// Prefer rewards not yet received.
	cand := make([]model.SadhnaReward, 0, len(pool))
	for _, r := range pool {
		if !granted[r.ID] {
			cand = append(cand, r)
		}
	}
	// All collected → cycle, excluding the most recent to avoid a repeat.
	if len(cand) == 0 {
		last, _ := s.rewards.LastGrantedRewardID(ctx, userID)
		for _, r := range pool {
			if r.ID != last {
				cand = append(cand, r)
			}
		}
		if len(cand) == 0 {
			cand = pool
		}
	}

	pick := cand[rand.Intn(len(cand))]
	if err := s.rewards.CreateGrant(ctx, userID, pick.ID, milestone); err != nil {
		s.logger.Warn("sadhna: could not grant reward", zap.Error(err))
	}
}

// nextRewardDate projects the UTC date the next gift lands if the streak
// continues unbroken — the date the streak count next reaches a multiple of
// rewardEveryDays. An unfinished today is assumed to be completed.
func nextRewardDate(today time.Time, current int, todayCompleted bool) *string {
	next := (current/rewardEveryDays + 1) * rewardEveryDays // first multiple > current
	days := next - current
	if !todayCompleted {
		// today isn't counted yet; completing it is the first of the
		// remaining days, so it lands one day sooner.
		days--
	}
	if days < 0 {
		days = 0
	}
	d := today.AddDate(0, 0, days).Format(dayFmt)
	return &d
}

// Rewards returns the user's collected gifts (newest first) and the size of
// the giftable catalog (for "N of M" framing on the client).
func (s *SadhnaService) Rewards(ctx context.Context, userID string) ([]model.SadhnaRewardGrant, int, error) {
	grants, err := s.rewards.GrantsByUser(ctx, userID)
	if err != nil {
		return nil, 0, err
	}
	pool, err := s.rewards.ListGiftable(ctx)
	if err != nil {
		return nil, 0, err
	}
	return grants, len(pool), nil
}

// AckRewards clears the user's pending celebration(s) after the client has
// shown the confetti.
func (s *SadhnaService) AckRewards(ctx context.Context, userID string) error {
	return s.rewards.MarkCelebrated(ctx, userID)
}

// History returns the per-day sādhana state for every UTC calendar day in
// the inclusive range [from, to] — what the calendar needs to render an
// arbitrary week or month. Days with no activity (including future days)
// come back as all-false. The caller is expected to bound the range.
func (s *SadhnaService) History(ctx context.Context, userID string, from, to time.Time) ([]model.SadhnaDay, error) {
	logs, err := s.logs.ListSince(ctx, userID, from)
	if err != nil {
		return nil, err
	}
	postsByDay, err := s.posts.PostCountsByDate(ctx, userID, from)
	if err != nil {
		return nil, err
	}

	chantByDay := make(map[string]bool, len(logs))
	for _, l := range logs {
		chantByDay[l.LogDate.UTC().Format(dayFmt)] = l.ChantDone
	}

	out := make([]model.SadhnaDay, 0, 42)
	for d := from; !d.After(to); d = d.AddDate(0, 0, 1) {
		key := d.Format(dayFmt)
		quote := postsByDay[key] > 0
		out = append(out, model.SadhnaDay{
			Date:      key,
			ChantDone: chantByDay[key],
			QuoteDone: quote,
			Completed: chantByDay[key] && quote,
		})
	}
	return out, nil
}

// targetFor returns the user's daily rounds goal, falling back to the
// default when unset/out of range or when the user can't be loaded (the
// dashboard should still render).
func (s *SadhnaService) targetFor(ctx context.Context, userID string) int {
	u, err := s.users.FindByID(ctx, userID)
	if err != nil || u == nil || u.DailyChantingRounds == nil {
		return defaultChantTarget
	}
	if r := *u.DailyChantingRounds; r >= 1 && r <= 1008 {
		return r
	}
	return defaultChantTarget
}

// stageFor maps a growth score to the plant's visual stage. The client
// renders the matching artwork and interpolates within the stage by the
// raw growth value.
func stageFor(growth int) string {
	switch {
	case growth <= 0:
		return "dead"
	case growth <= 15:
		return "sprout"
	case growth <= 35:
		return "seedling"
	case growth <= 60:
		return "sapling"
	case growth <= 85:
		return "young"
	default:
		return "mature"
	}
}