package api

import (
	"context"
	"encoding/json"
	"net/http"
	"sort"
	"strings"
	"time"

	"github.com/ponzischeme89/memby/server/internal/sonarr"
	"github.com/ponzischeme89/memby/server/internal/store"
)

// The TV calendar is the schedule row's other shape: the same Sonarr episodes, laid out a
// month at a time rather than as the next five days. It shares the row's item builder on
// purpose — a card is a card, and the availability badges, lifecycle tags and Emby series
// link have to mean the same thing on both screens or the calendar becomes a second,
// slightly different account of the same week.
//
// Bump the prefix when the item contract changes, so an older layout cannot survive a
// deployment until the cached months expire.
const calendarCachePrefix = "sonarr:calendar:month:v2:"

// How far either side of the present a viewer may travel. Sonarr answers for any date it
// has been asked about, and a held D-pad on the month header would otherwise walk it into
// the 2050s one request at a time. A year each way covers "when does the new season start"
// and "what did we miss in March" and stops there.
const calendarMonthRange = 12

type calendarResponse struct {
	// Available is false when the household runs no Sonarr. The page says so rather than
	// drawing an empty grid that looks like a month in which nothing airs.
	Available bool `json:"available"`
	// Month is the machine key ("2026-08"); Label is what the header prints.
	Month string `json:"month"`
	Label string `json:"label"`
	// Empty when the month is at the end of the travelable range, which is what makes the
	// header's arrows disappear rather than fail.
	Previous string `json:"previous,omitempty"`
	Next     string `json:"next,omitempty"`
	// The household's today, sent only when it falls inside this month — the client has no
	// business deciding which cell to ring from a television's own clock when the gateway
	// already knows the household's zone.
	Today string `json:"today,omitempty"`
	// The grid's shape. Sending it rather than a date per cell keeps civil-calendar
	// arithmetic in one place: the television draws DayCount cells after FirstWeekday
	// blanks and never has to know which years are leap years.
	FirstWeekday int           `json:"firstWeekday"`
	DayCount     int           `json:"dayCount"`
	Days         []calendarDay `json:"days"`
}

// calendarDay carries only the days that have something on them. A month of empty cells is
// the client's to draw, and sending thirty-one mostly-empty objects would triple the
// response for nothing.
type calendarDay struct {
	Date  string            `json:"date"`
	Day   int               `json:"day"`
	Items []json.RawMessage `json:"items"`
}

func (s *Server) handleCalendar(w http.ResponseWriter, r *http.Request, _ store.Session) {
	ctx := r.Context()
	if !s.sonarrEnabled(ctx) || !s.featureEnabled(ctx, featureTVCalendar) {
		writeJSON(w, http.StatusOK, emptyCalendar())
		return
	}
	location := s.sonarrLocation()
	now := time.Now().In(location)
	month, ok := parseCalendarMonth(r.URL.Query().Get("month"), now, location)
	if !ok {
		writeError(w, http.StatusBadRequest, "invalid month")
		return
	}
	calendar, err := s.sonarrCalendarMonth(ctx, month, now, location)
	if err != nil {
		// A month nobody can fetch is reported as an empty month rather than as a failure:
		// the page is informational, and a viewer pressing Right past a Sonarr hiccup
		// should land on a quiet month and be able to press Left back out of it.
		s.loggerFor(ctx).Warn("calendar month unavailable",
			"month", month.Format("2006-01"), "error", err)
		calendar = buildCalendarMonth(nil, month, now, location, nil)
	}
	writeJSON(w, http.StatusOK, calendar)
}

func (s *Server) sonarrLocation() *time.Location {
	if s.cfg.SonarrLocation != nil {
		return s.cfg.SonarrLocation
	}
	return time.Local
}

func (s *Server) sonarrCalendarMonth(
	ctx context.Context,
	month, now time.Time,
	location *time.Location,
) (calendarResponse, error) {
	key := calendarCachePrefix + month.Format("2006-01")
	if cached := s.cachedCalendar(ctx, key); cached != nil {
		return *cached, nil
	}

	// The same shared lock the schedule row takes, for the same reason: several televisions
	// opening the calendar together must not each stampede Sonarr on the one miss.
	s.sonarrMu.Lock()
	defer s.sonarrMu.Unlock()
	if cached := s.cachedCalendar(ctx, key); cached != nil {
		return *cached, nil
	}

	episodes, err := s.sonarr.Calendar(ctx, month, month.AddDate(0, 1, 0))
	if err != nil {
		return calendarResponse{}, err
	}
	calendar := buildCalendarMonth(episodes, month, now, location, s.embySeriesIndex(ctx))
	if body, marshalErr := json.Marshal(calendar); marshalErr == nil {
		if cacheErr := s.cache.Set(ctx, key, body, s.cfg.SonarrTTL); cacheErr != nil {
			s.loggerFor(ctx).Warn("calendar cache write failed", "error", cacheErr)
		}
	}
	return calendar, nil
}

// cachedCalendar refuses an entry whose Today no longer agrees with the household's, so a
// month cached before midnight cannot leave the ring on yesterday. Everything else in the
// response is fixed for the month and safely reusable.
func (s *Server) cachedCalendar(ctx context.Context, key string) *calendarResponse {
	raw, err := s.cache.Get(ctx, key)
	if err != nil {
		return nil
	}
	var cached calendarResponse
	if json.Unmarshal(raw, &cached) != nil {
		return nil
	}
	now := time.Now().In(s.sonarrLocation())
	if cached.Today != "" && cached.Today != now.Format("2006-01-02") {
		return nil
	}
	return &cached
}

// parseCalendarMonth turns the client's `month` parameter into the first instant of that
// month in the household's zone. An empty parameter is the present month, which is what a
// television asks for when it opens the page and the only request an older client makes.
//
// Out-of-range months are refused rather than clamped: a clamp would answer a request for
// 2031 with this year's August and the header would then disagree with the grid.
func parseCalendarMonth(value string, now time.Time, location *time.Location) (time.Time, bool) {
	now = now.In(location)
	current := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, location)
	trimmed := strings.TrimSpace(value)
	if trimmed == "" {
		return current, true
	}
	parsed, err := time.ParseInLocation("2006-01", trimmed, location)
	if err != nil {
		return time.Time{}, false
	}
	month := time.Date(parsed.Year(), parsed.Month(), 1, 0, 0, 0, 0, location)
	if month.Before(current.AddDate(0, -calendarMonthRange, 0)) ||
		month.After(current.AddDate(0, calendarMonthRange, 0)) {
		return time.Time{}, false
	}
	return month, true
}

// buildCalendarMonth is the whole layout rule, pure so the edges — a month starting on a
// Sunday, a February, the day either side of the travel limit — are testable without a
// Sonarr to hand.
func buildCalendarMonth(
	episodes []sonarr.Episode,
	month, now time.Time,
	location *time.Location,
	series seriesIndex,
) calendarResponse {
	month = month.In(location)
	monthEnd := month.AddDate(0, 1, 0)
	current := time.Date(now.In(location).Year(), now.In(location).Month(), 1, 0, 0, 0, 0, location)

	calendar := calendarResponse{
		Available: true,
		Month:     month.Format("2006-01"),
		Label:     month.Format("January 2006"),
		// Sunday is 0, matching the weekday header the grid draws.
		FirstWeekday: int(month.Weekday()),
		DayCount:     int(monthEnd.Sub(month).Hours() / 24),
		Days:         []calendarDay{},
	}
	if previous := month.AddDate(0, -1, 0); !previous.Before(current.AddDate(0, -calendarMonthRange, 0)) {
		calendar.Previous = previous.Format("2006-01")
	}
	if next := month.AddDate(0, 1, 0); !next.After(current.AddDate(0, calendarMonthRange, 0)) {
		calendar.Next = next.Format("2006-01")
	}
	if today := now.In(location); !today.Before(month) && today.Before(monthEnd) {
		calendar.Today = today.Format("2006-01-02")
	}

	sort.SliceStable(episodes, func(i, j int) bool {
		if episodes[i].AirDateUTC == nil {
			return false
		}
		if episodes[j].AirDateUTC == nil {
			return true
		}
		return episodes[i].AirDateUTC.Before(*episodes[j].AirDateUTC)
	})

	// A map plus one ordered slice, rather than a slice searched per episode: a busy month
	// is a few hundred episodes and the days they land on are already in order.
	byDate := make(map[string]int, 31)
	for _, episode := range episodes {
		if episode.AirDateUTC == nil {
			continue
		}
		// Sonarr is asked in the household's zone but answers in UTC, so an episode airing
		// late on the 31st elsewhere can fall outside this month once converted back.
		airTime := episode.AirDateUTC.In(location)
		if airTime.Before(month) || !airTime.Before(monthEnd) {
			continue
		}
		raw, err := json.Marshal(toSonarrScheduleItem(episode, now, location, series))
		if err != nil {
			continue
		}
		date := airTime.Format("2006-01-02")
		index, seen := byDate[date]
		if !seen {
			calendar.Days = append(calendar.Days, calendarDay{
				Date:  date,
				Day:   airTime.Day(),
				Items: []json.RawMessage{},
			})
			index = len(calendar.Days) - 1
			byDate[date] = index
		}
		calendar.Days[index].Items = append(calendar.Days[index].Items, raw)
	}
	return calendar
}

func emptyCalendar() calendarResponse {
	return calendarResponse{Days: []calendarDay{}}
}