package handlers

import (
	"bufio"
	"context"
	"database/sql"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"time"

	"gitea.futuresens.co.uk/futuresens/hardlink/db"
	log "github.com/sirupsen/logrus"
)

type preauthSpoolRecord struct {
	CreatedAt    time.Time         `json:"createdAt"`
	CheckoutDate string            `json:"checkoutDate"` // keep as received
	Fields       map[string]string `json:"fields"`       // ChipDNA result.Fields
}

func (app *App) getDB(ctx context.Context) (*sql.DB, error) {
	app.dbMu.Lock()
	defer app.dbMu.Unlock()

	// Fast path: db exists and is alive
	if app.db != nil {
		pingCtx, cancel := context.WithTimeout(ctx, 1*time.Second)
		defer cancel()

		if err := app.db.PingContext(pingCtx); err == nil {
			return app.db, nil
		}

		// stale handle
		_ = app.db.Close()
		app.db = nil
	}

	// Reconnect once, bounded
	dialCtx, cancel := context.WithTimeout(ctx, 3*time.Second)
	defer cancel()

	dbConn, err := db.InitMSSQL(
		app.cfg.Dbport,
		app.cfg.Dbuser,
		app.cfg.Dbpassword,
		app.cfg.Dbname,
	)
	if err != nil {
		return nil, err
	}

	pingCtx, cancel2 := context.WithTimeout(dialCtx, 1*time.Second)
	defer cancel2()

	if err := dbConn.PingContext(pingCtx); err != nil {
		_ = dbConn.Close()
		return nil, err
	}

	app.db = dbConn
	return app.db, nil
}

func (app *App) spoolPath() string {
	// keep it near logs; adjust if you prefer a dedicated dir
	// ensure LogDir ends with separator in your config loader
	return filepath.Join(app.cfg.LogDir, "preauth_spool.ndjson")
}

// persistPreauth tries DB first; if DB is down or insert fails, it spools to file.
// It never returns an error to the caller (so your HTTP flow stays simple),
// but it logs failures.
func (app *App) persistPreauth(ctx context.Context, fields map[string]string, checkoutDate string) {
	// First, try DB (with your reconnect logic inside getDB)
	dbConn, err := app.getDB(ctx)
	if err == nil && dbConn != nil {
		if err := db.InsertPreauth(ctx, dbConn, fields, checkoutDate); err == nil {
			// opportunistic drain once DB is alive
			go app.drainPreauthSpool(context.Background())
			return
		} else {
			log.WithError(err).Warn("DB insert failed; will spool preauth")
		}
	} else {
		log.WithError(err).Warn("DB unavailable; will spool preauth")
	}

	// Fallback: spool to file
	rec := preauthSpoolRecord{
		CreatedAt:    time.Now().UTC(),
		CheckoutDate: checkoutDate,
		Fields:       fields,
	}
	if spErr := app.spoolPreauth(rec); spErr != nil {
		log.WithError(spErr).Error("failed to spool preauth")
	}
}

// append one line JSON (NDJSON)
func (app *App) spoolPreauth(rec preauthSpoolRecord) error {
	p := app.spoolPath()

	f, err := os.OpenFile(p, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
	if err != nil {
		return fmt.Errorf("open spool file: %w", err)
	}
	defer f.Close()

	b, err := json.Marshal(rec)
	if err != nil {
		return fmt.Errorf("marshal spool record: %w", err)
	}

	if _, err := f.Write(append(b, '\n')); err != nil {
		return fmt.Errorf("write spool record: %w", err)
	}

	return f.Sync() // ensure it's on disk
}

// Drain spool into DB.
// Strategy: read all lines, insert each; keep failures in a temp file; then replace original.
func (app *App) drainPreauthSpool(ctx context.Context) {
	dbConn, err := app.getDB(ctx)
	if err != nil {
		return // still down, nothing to do
	}

	spool := app.spoolPath()
	in, err := os.Open(spool)
	if err != nil {
		// no spool is fine
		return
	}
	defer in.Close()

	tmp := spool + ".tmp"
	out, err := os.OpenFile(tmp, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0666)
	if err != nil {
		log.WithError(err).Warn("drain spool: open tmp failed")
		return
	}
	defer out.Close()

	sc := bufio.NewScanner(in)
	// allow long lines if receipts ever sneak in (shouldn't, but safe)
	buf := make([]byte, 0, 64*1024)
	sc.Buffer(buf, 2*1024*1024)

	var (
		okCount   int
		failCount int
	)

	for sc.Scan() {
		line := sc.Bytes()
		if len(line) == 0 {
			continue
		}

		var rec preauthSpoolRecord
		if err := json.Unmarshal(line, &rec); err != nil {
			// malformed line: keep it so we don't lose evidence
			_, _ = out.Write(append(line, '\n'))
			failCount++
			continue
		}

		// attempt insert
		if err := db.InsertPreauth(ctx, dbConn, rec.Fields, rec.CheckoutDate); err != nil {
			// DB still flaky or data issue: keep it for later retry
			_, _ = out.Write(append(line, '\n'))
			failCount++
			continue
		}

		okCount++
	}

	if err := sc.Err(); err != nil {
		log.WithError(err).Warn("drain spool: scanner error")
		// best effort; do not replace spool
		return
	}

	_ = out.Sync()

	// Replace original spool with temp (atomic on Windows is best-effort; still OK here)
	_ = in.Close()
	_ = out.Close()

	if err := os.Rename(tmp, spool); err != nil {
		log.WithError(err).Warn("drain spool: rename failed")
		return
	}

	if okCount > 0 || failCount > 0 {
		log.WithFields(log.Fields{
			"inserted":  okCount,
			"remaining": failCount,
		}).Info("preauth spool drained")
	}
}