// Package alert owns durable, one-shot fall-event evidence.
package alert

import (
	"encoding/json"
	"fmt"
	"image"
	"image/png"
	"os"
	"path/filepath"
	"regexp"
	"sync"
	"time"

	"silverpose/v2/internal/fall"
)

var eventIDPattern = regexp.MustCompile(`^[A-Za-z0-9-]+$`)

type Record struct {
	Event          fall.Event
	ScreenshotPath string
	LogPath        string
	CreatedAtUTC   time.Time
	Written        bool
}

// Dispatcher de-duplicates events before writing to avoid screenshot overwrite,
// duplicate JSONL records, duplicate sound, or duplicate popups downstream.
type Dispatcher struct {
	eventDirectory string
	sourceID       string
	mu             sync.Mutex
	seen           map[string]struct{}
}

func NewDispatcher(eventDirectory, sourceID string) *Dispatcher {
	return &Dispatcher{
		eventDirectory: eventDirectory,
		sourceID:       sourceID,
		seen:           make(map[string]struct{}),
	}
}

func (dispatcher *Dispatcher) Dispatch(event fall.Event, canvas image.Image, now time.Time) (Record, error) {
	if event.State != fall.Confirmed {
		return Record{}, fmt.Errorf("only confirmed events can be persisted")
	}
	if !eventIDPattern.MatchString(event.EventID) {
		return Record{}, fmt.Errorf("event ID is invalid")
	}
	if canvas == nil {
		return Record{}, fmt.Errorf("event screenshot is missing")
	}
	if now.IsZero() {
		now = time.Now()
	}
	now = now.UTC()

	dispatcher.mu.Lock()
	if _, alreadyWritten := dispatcher.seen[event.EventID]; alreadyWritten {
		dispatcher.mu.Unlock()
		return Record{Event: event, Written: false}, nil
	}
	dispatcher.seen[event.EventID] = struct{}{}
	dispatcher.mu.Unlock()

	record, err := dispatcher.write(event, canvas, now)
	if err != nil {
		dispatcher.mu.Lock()
		delete(dispatcher.seen, event.EventID)
		dispatcher.mu.Unlock()
		return Record{}, err
	}
	return record, nil
}

func (dispatcher *Dispatcher) write(event fall.Event, canvas image.Image, now time.Time) (Record, error) {
	if dispatcher.eventDirectory == "" || dispatcher.sourceID == "" {
		return Record{}, fmt.Errorf("event directory and source ID must be configured")
	}
	dayDirectory := filepath.Join(dispatcher.eventDirectory, now.Format("20060102"))
	if err := os.MkdirAll(dayDirectory, 0o755); err != nil {
		return Record{}, fmt.Errorf("create event directory: %w", err)
	}
	screenshotPath := filepath.Join(dayDirectory, event.EventID+".png")
	file, err := os.Create(screenshotPath)
	if err != nil {
		return Record{}, fmt.Errorf("create screenshot: %w", err)
	}
	encodeErr := png.Encode(file, canvas)
	closeErr := file.Close()
	if encodeErr != nil || closeErr != nil {
		_ = os.Remove(screenshotPath)
		if encodeErr != nil {
			return Record{}, fmt.Errorf("encode screenshot: %w", encodeErr)
		}
		return Record{}, fmt.Errorf("close screenshot: %w", closeErr)
	}

	logPath := filepath.Join(dayDirectory, "events.jsonl")
	relativeScreenshot := filepath.ToSlash(filepath.Join(now.Format("20060102"), event.EventID+".png"))
	line, err := json.Marshal(struct {
		EventID              string     `json:"event_id"`
		TrackID              string     `json:"track_id"`
		ConfigVersion        string     `json:"config_version"`
		SourceID             string     `json:"source_id"`
		State                fall.State `json:"state"`
		ConfirmedAtUTC       string     `json:"confirmed_at_utc"`
		SuspectedAtMonotonic float64    `json:"suspected_at_monotonic"`
		ConfirmedAtMonotonic float64    `json:"confirmed_at_monotonic"`
		LatencySeconds       float64    `json:"latency_seconds"`
		Screenshot           string     `json:"screenshot"`
	}{
		EventID: event.EventID, TrackID: event.TrackID, ConfigVersion: event.ConfigVersion,
		SourceID: dispatcher.sourceID, State: event.State, ConfirmedAtUTC: now.Format(time.RFC3339Nano),
		SuspectedAtMonotonic: event.SuspectedAtMonotonic,
		ConfirmedAtMonotonic: event.ConfirmedAtMonotonic,
		LatencySeconds:       event.LatencySeconds, Screenshot: relativeScreenshot,
	})
	if err != nil {
		_ = os.Remove(screenshotPath)
		return Record{}, fmt.Errorf("encode event record: %w", err)
	}
	log, err := os.OpenFile(logPath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o600)
	if err != nil {
		_ = os.Remove(screenshotPath)
		return Record{}, fmt.Errorf("open event log: %w", err)
	}
	if _, err := log.Write(append(line, '\n')); err != nil {
		_ = log.Close()
		_ = os.Remove(screenshotPath)
		return Record{}, fmt.Errorf("write event log: %w", err)
	}
	if err := log.Close(); err != nil {
		return Record{}, fmt.Errorf("close event log: %w", err)
	}
	return Record{
		Event: event, ScreenshotPath: screenshotPath, LogPath: logPath, CreatedAtUTC: now, Written: true,
	}, nil
}