package rain

import (
	"context"
	"errors"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"weatherstation/internal/database"
)

// Options controls the rain (CMPA hourly precip) scheduler behavior.
type Options struct {
	Enable     bool
	OutputDir  string
	BaseURL    string // template with %Y%m%d/%H/%M and {z}/{y}/{x}; time is UTC
	MaxRetries int
	StoreToDB  bool
	Tiles      [][3]int // list of (z,y,x); defaults to [[7,40,102],[7,40,104]]
}

// Start starts the CMPA hourly rain tile downloader.
// Runs every 10 minutes aligned to 10-minute boundaries. For each tick at local time T,
// constructs the slot as floor_to_hour(T) - 1h (last completed hour), converts to UTC
// (slot_utc = slot_local - 8h), and downloads 0-minute tile for each configured (z,y,x).
func Start(ctx context.Context, opts Options) error {
	if !opts.Enable && !envEnabledDefaultTrue() {
		log.Println("[rain] scheduler disabled")
		return nil
	}
	if opts.OutputDir == "" {
		opts.OutputDir = getenvDefault("RAIN_DIR", "rain_data")
	}
	if opts.MaxRetries == 0 {
		opts.MaxRetries = getenvIntDefault("RAIN_MAX_RETRIES", 2)
	}
	if opts.BaseURL == "" {
		opts.BaseURL = getenvDefault("RAIN_BASE_URL", "https://image.data.cma.cn/tiles/China/CMPA_RT_China_0P01_HOR-PRE_GISJPG_Tiles/%Y%m%d/%H/%M/{z}/{y}/{x}.bin")
	}
	if len(opts.Tiles) == 0 {
		opts.Tiles = [][3]int{{7, 40, 102}, {7, 40, 104}}
	}
	if err := os.MkdirAll(opts.OutputDir, 0o755); err != nil {
		return fmt.Errorf("create rain output dir: %w", err)
	}

	loc, _ := time.LoadLocation("Asia/Shanghai")
	if loc == nil {
		loc = time.FixedZone("CST", 8*3600)
	}

	// immediate first run
	go func() {
		if err := runOnce(ctx, opts, loc); err != nil {
			log.Printf("[rain] first run error: %v", err)
		}
	}()

	// every 10 minutes
	go func() {
		for {
			if ctx.Err() != nil {
				return
			}
			now := time.Now().In(loc)
			runAt := roundDownN(now, 10*time.Minute).Add(10 * time.Minute)
			sleep := time.Until(runAt)
			if sleep < 0 {
				sleep = 0
			}
			timer := time.NewTimer(sleep)
			select {
			case <-ctx.Done():
				timer.Stop()
				return
			case <-timer.C:
				if err := runOnce(ctx, opts, loc); err != nil {
					log.Printf("[rain] run error: %v", err)
				}
			}
		}
	}()

	log.Printf("[rain] scheduler started (10m, dir=%s, tiles=%d)", opts.OutputDir, len(opts.Tiles))
	return nil
}

func runOnce(ctx context.Context, opts Options, loc *time.Location) error {
	// target hour: current hour at 00 (floor_to_hour(now))
	// e.g., 10:15 -> 10:00; if尚未发布则下载可能失败，等待下一次10分钟重试
	now := time.Now().In(loc)
	slotLocal := now.Truncate(time.Hour)
	// UTC for URL path
	slotUTC := slotLocal.Add(-8 * time.Hour).In(time.UTC)
	log.Printf("[rain] tick target hour: local=%s (CST), utc=%s (UTC)", slotLocal.Format("2006-01-02 15:04"), slotUTC.Format("2006-01-02 15:04"))
	dateStr := slotUTC.Format("20060102")
	hh := slotUTC.Format("15")
	mm := "00" // hourly product uses minute 00

	for _, t := range opts.Tiles {
		z, y, x := t[0], t[1], t[2]
		if err := downloadAndStoreTile(ctx, slotLocal, dateStr, hh, mm, z, y, x, opts); err != nil {
			log.Printf("[rain] download/store z=%d y=%d x=%d failed: %v", z, y, x, err)
		}
	}
	return nil
}

func downloadAndStoreTile(ctx context.Context, local time.Time, dateStr, hh, mm string, z, y, x int, opts Options) error {
	url := fmt.Sprintf("https://image.data.cma.cn/tiles/China/CMPA_RT_China_0P01_HOR-PRE_GISJPG_Tiles/%s/%s/%s/%d/%d/%d.bin", dateStr, hh, mm, z, y, x)
	// skip if exists in DB
	if ref, err := ParseCMPATileURL(url); err == nil {
		exists, err := databaseHas(ctx, ref.Product, ref.DT, z, y, x)
		if err != nil {
			return err
		}
		if exists {
			log.Printf("[rain] skip: already in DB z=%d y=%d x=%d dt(local)=%s url=%s", z, y, x, ref.DT.Format("2006-01-02 15:04"), url)
			return nil
		}
	}

	fname := fmt.Sprintf("rain_z%d_y%d_x%d_%s.bin", z, y, x, local.Format("20060102_1504"))
	dest := filepath.Join(opts.OutputDir, fname)
	if _, err := os.Stat(dest); err == nil {
		log.Printf("[rain] skip: file exists %s", dest)
		return nil
	}

	if err := httpDownloadTo(ctx, url, dest); err != nil {
		return err
	}
	log.Printf("[rain] saved %s (url=%s)", dest, url)

	if opts.StoreToDB {
		b, rerr := os.ReadFile(dest)
		if rerr != nil {
			return fmt.Errorf("read saved tile: %w", rerr)
		}
		if err := StoreTileBytes(ctx, url, b); err != nil {
			return fmt.Errorf("store tile db: %w", err)
		}
		log.Printf("[rain] stored to DB: %s", fname)
	}
	return nil
}

func httpDownloadTo(ctx context.Context, url, dest string) error {
	client := &http.Client{Timeout: 20 * time.Second}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return fmt.Errorf("build request: %w", err)
	}
	req.Header.Set("Referer", "https://data.cma.cn/")
	req.Header.Set("Origin", "https://data.cma.cn")
	req.Header.Set("User-Agent", "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/137.0.0.0 Safari/537.36")
	resp, err := client.Do(req)
	if err != nil {
		return fmt.Errorf("http get: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("unexpected status: %d", resp.StatusCode)
	}
	tmp := dest + ".part"
	f, err := os.Create(tmp)
	if err != nil {
		return fmt.Errorf("create temp: %w", err)
	}
	_, copyErr := io.Copy(f, resp.Body)
	closeErr := f.Close()
	if copyErr != nil {
		_ = os.Remove(tmp)
		return fmt.Errorf("write body: %w", copyErr)
	}
	if closeErr != nil {
		_ = os.Remove(tmp)
		return fmt.Errorf("close temp: %w", closeErr)
	}
	if err := os.Rename(tmp, dest); err != nil {
		// Cross-device fallback
		if !errors.Is(err, os.ErrInvalid) {
			return fmt.Errorf("rename: %w", err)
		}
		data, rerr := os.ReadFile(tmp)
		if rerr != nil {
			return fmt.Errorf("read temp: %w", rerr)
		}
		if werr := os.WriteFile(dest, data, 0o644); werr != nil {
			return fmt.Errorf("write final: %w", werr)
		}
		_ = os.Remove(tmp)
	}
	return nil
}

// small env helpers (duplicated minimal set to avoid cross-package deps)
func getenvDefault(k, def string) string {
	if v := os.Getenv(k); v != "" {
		return v
	}
	return def
}
func getenvIntDefault(k string, def int) int {
	if v := os.Getenv(k); v != "" {
		if n, err := strconv.Atoi(v); err == nil {
			return n
		}
	}
	return def
}
func envEnabledDefaultTrue() bool {
	v := strings.ToLower(os.Getenv("RAIN_ENABLED"))
	if v == "" {
		return true
	}
	return v == "1" || v == "true" || v == "yes"
}

func databaseHas(ctx context.Context, product string, dt time.Time, z, y, x int) (bool, error) {
	return database.HasRainTile(ctx, database.GetDB(), product, dt, z, y, x)
}

func roundDownN(t time.Time, d time.Duration) time.Time { return t.Truncate(d) }