package notifications

import (
	"context"
	"fmt"
	"log"
	"time"

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

// Service is the entry point for the daily notification scan. It reads
// cal_school_event + parent_account + tt_class, decides which (event,
// lead_days, audience) pairs are due today, dispatches via the configured
// upstream URLs, and writes a notification_log row for idempotency.
type Service struct {
	db           *pgxpool.Pool
	matrixURL    string // empty → status=skipped
	emailURL     string // empty → status=skipped
	httpTimeout  time.Duration
}

// Dispatch is the contract our upstream services (Matrix bridge + Email
// gateway, owned by the colleague) must implement. We POST a body with
// these fields; they figure out delivery. Stub mode (URL == "") logs
// instead, useful for dev + tests.
type DispatchPayload struct {
	Channel   string `json:"channel"`   // "matrix" | "email"
	Recipient string `json:"recipient"` // email address; for Matrix the bridge maps it
	Language  string `json:"language"`
	Subject   string `json:"subject"`
	Body      string `json:"body"`
	EventID   string `json:"event_id"`
	LeadDays  int    `json:"lead_days"`
}

func NewService(db *pgxpool.Pool, matrixURL, emailURL string) *Service {
	return &Service{
		db:          db,
		matrixURL:   matrixURL,
		emailURL:    emailURL,
		httpTimeout: 10 * time.Second,
	}
}

// LogRow is the read shape for the notification_log table.
type LogRow struct {
	LeadDays  int       `json:"lead_days"`
	Audience  string    `json:"audience"`
	Channel   string    `json:"channel"`
	Status    string    `json:"status"`
	Error     string    `json:"error_message,omitempty"`
	RunDate   string    `json:"run_date"`
	CreatedAt time.Time `json:"created_at"`
}

// ListLog returns the notification_log rows for one event, scoped to a
// teacher so the UI can't query someone else's log.
func (s *Service) ListLog(ctx context.Context, eventID, ownerUserID string) ([]LogRow, error) {
	rows, err := s.db.Query(ctx, `
		SELECT nl.lead_days, nl.audience, nl.channel, nl.status,
		       COALESCE(nl.error_message, ''), nl.run_date::text, nl.created_at
		FROM notification_log nl
		JOIN cal_school_event ev ON ev.id = nl.event_id
		WHERE ev.id = $1 AND ev.created_by_user_id = $2
		ORDER BY nl.lead_days DESC, nl.audience, nl.channel
	`, eventID, ownerUserID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := []LogRow{}
	for rows.Next() {
		var r LogRow
		if err := rows.Scan(&r.LeadDays, &r.Audience, &r.Channel, &r.Status, &r.Error, &r.RunDate, &r.CreatedAt); err != nil {
			return nil, err
		}
		out = append(out, r)
	}
	return out, nil
}

// RunForDate scans every active cal_school_event with a lead_day equal to
// (event_start - runDate). For each due (audience, channel) pair it
// renders + dispatches + logs. Idempotent via the UNIQUE constraint on
// notification_log.
type RunResult struct {
	Date    string `json:"date"`
	Sent    int    `json:"sent"`
	Failed  int    `json:"failed"`
	Skipped int    `json:"skipped"`
	AlreadyLogged int `json:"already_logged"`
}

func (s *Service) RunForDate(ctx context.Context, runDate time.Time) (*RunResult, error) {
	res := &RunResult{Date: runDate.Format("2006-01-02")}

	events, err := s.dueEvents(ctx, runDate)
	if err != nil {
		return nil, fmt.Errorf("query due events: %w", err)
	}

	for _, e := range events {
		// For each event we may notify parents and/or students depending on
		// the row's flags. Channels are derived from the audience:
		//   parents  → email + matrix
		//   students → matrix only (students don't always have email)
		audiences := []string{}
		if e.NotifyParents {
			audiences = append(audiences, "parents")
		}
		if e.NotifyStudents {
			audiences = append(audiences, "students")
		}
		for _, audience := range audiences {
			channels := []string{"matrix"}
			if audience == "parents" {
				channels = append(channels, "email")
			}
			for _, channel := range channels {
				status, err := s.dispatchOne(ctx, e, audience, channel, runDate)
				switch status {
				case "sent":
					res.Sent++
				case "failed":
					res.Failed++
					if err != nil {
						log.Printf("notification dispatch failed: %v", err)
					}
				case "skipped":
					res.Skipped++
				case "already":
					res.AlreadyLogged++
				}
			}
		}
	}
	return res, nil
}

// dueEvent holds the small slice of cal_school_event row we need plus the
// matched lead_day for this run.
type dueEvent struct {
	ID               string
	Title            string
	EventType        string
	StartDate        time.Time
	ClassName        string // optional, may be empty for "alle Klassen"
	OwnerUserID      string
	NotifyParents    bool
	NotifyStudents   bool
	LeadDays         int
}

func (s *Service) dueEvents(ctx context.Context, runDate time.Time) ([]dueEvent, error) {
	// A row is due when (start_date - runDate) appears in
	// notification_lead_days. Lead=0 means "today the event starts".
	rows, err := s.db.Query(ctx, `
		SELECT ev.id::text, ev.title, ev.event_type, ev.start_date, ev.created_by_user_id::text,
		       ev.notify_parents, ev.notify_students, ev.notification_lead_days,
		       COALESCE(
		         (SELECT string_agg(cl.name, ', ' ORDER BY cl.name)
		          FROM tt_class cl
		          WHERE cl.id = ANY(ev.affected_class_ids)),
		         ''
		       ) AS class_names
		FROM cal_school_event ev
		WHERE ev.start_date >= $1::date
		  AND (ev.notify_parents OR ev.notify_students)
	`, runDate.Format("2006-01-02"))
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var out []dueEvent
	for rows.Next() {
		var (
			id, title, eventType, ownerUserID, classNames string
			notifyParents, notifyStudents                  bool
			startDate                                      time.Time
			leadDays                                       []int32
		)
		if err := rows.Scan(&id, &title, &eventType, &startDate, &ownerUserID,
			&notifyParents, &notifyStudents, &leadDays, &classNames); err != nil {
			return nil, err
		}
		distanceDays := int(startDate.Sub(runDate).Hours() / 24)
		for _, lead := range leadDays {
			if int(lead) == distanceDays {
				out = append(out, dueEvent{
					ID: id, Title: title, EventType: eventType,
					StartDate: startDate, ClassName: classNames,
					OwnerUserID:    ownerUserID,
					NotifyParents:  notifyParents,
					NotifyStudents: notifyStudents,
					LeadDays:       int(lead),
				})
				break
			}
		}
	}
	return out, nil
}