package main

import (
	"crypto/rand"
	"crypto/sha256"
	"database/sql"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"time"

	"golang.org/x/crypto/bcrypt"
)

func (s *Server) handleRegister(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		jsonErr(w, 405, "POST required")
		return
	}
	var req struct {
		Username string `json:"username"`
		Email    string `json:"email"`
		Password string `json:"password"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		jsonErr(w, 400, "invalid JSON")
		return
	}
	if req.Username == "" || req.Email == "" || req.Password == "" {
		jsonErr(w, 400, "username, email and password required")
		return
	}
	if err := validatePassword(req.Password); err != "" {
		jsonErr(w, 400, err)
		return
	}
	if !strings.Contains(req.Email, "@") || !strings.Contains(req.Email, ".") {
		jsonErr(w, 400, "invalid email")
		return
	}
	hash, err := bcrypt.GenerateFromPassword([]byte(req.Password), bcrypt.DefaultCost)
	if err != nil {
		jsonErr(w, 500, "internal error")
		return
	}
	now := time.Now().UTC().Format(time.RFC3339)
	id := make([]byte, 12)
	rand.Read(id)
	userID := hex.EncodeToString(id)
	_, err = s.db.Exec(
		"INSERT INTO server_users (id, username, email, password_hash, confirmed, created_at) VALUES (?, ?, ?, ?, 0, ?)",
		userID, req.Username, strings.ToLower(req.Email), string(hash), now,
	)
	if err != nil {
		if strings.Contains(err.Error(), "UNIQUE") {
			jsonErr(w, 409, "username or email already taken")
			return
		}
		jsonErr(w, 500, err.Error())
		return
	}
	// Confirmation token.
	tok := make([]byte, 24)
	rand.Read(tok)
	tokenStr := hex.EncodeToString(tok)
	exp := time.Now().Add(48 * time.Hour).UTC().Format(time.RFC3339)
	s.db.Exec("INSERT INTO server_email_tokens (token, user_id, purpose, expires_at, created_at) VALUES (?, ?, 'confirm', ?, ?)",
		tokenStr, userID, exp, now)
	// Try to send email.
	host := s.smtpGet("smtp_host")
	if host != "" {
		srvURL := s.smtpGet("server_url")
		var confirmURL string
		if srvURL != "" {
			confirmURL = fmt.Sprintf("%s/confirm?token=%s", srvURL, tokenStr)
		} else {
			confirmURL = fmt.Sprintf("/api/v1/auth/confirm?token=%s", tokenStr)
		}
		body := fmt.Sprintf("Welcome to Verstak Sync!\n\nPlease confirm your email by clicking:\n%s\n\nIf you did not register, ignore this message.", confirmURL)
		if err := s.smtpSend(req.Email, "Confirm your Verstak Sync account", body); err != nil {
			log.Printf("register: failed to send confirm email: %v", err)
		}
	} else {
		log.Printf("register: SMTP not configured, confirmation token=%s for user %s", tokenStr, req.Username)
	}
	jsonOK(w, map[string]string{"status": "confirmation_sent"})
}

func (s *Server) handleConfirm(w http.ResponseWriter, r *http.Request) {
	if r.Method != "GET" {
		jsonErr(w, 405, "GET required")
		return
	}
	tokenStr := r.URL.Query().Get("token")
	if tokenStr == "" {
		jsonErr(w, 400, "token required")
		return
	}
	var userID, expiresAt string
	err := s.db.QueryRow("SELECT user_id, expires_at FROM server_email_tokens WHERE token=? AND purpose='confirm'",
		tokenStr).Scan(&userID, &expiresAt)
	if err != nil {
		jsonErr(w, 400, "invalid or expired token")
		return
	}
	exp, err := time.Parse(time.RFC3339, expiresAt)
	if err != nil || time.Now().After(exp) {
		jsonErr(w, 400, "token expired")
		return
	}
	s.db.Exec("UPDATE server_users SET confirmed=1 WHERE id=?", userID)
	log.Printf("confirm: user %s confirmed email", userID)
	s.db.Exec("DELETE FROM server_email_tokens WHERE token=?", tokenStr)
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Write([]byte(confirmedHTML(s.locale())))
}

func (s *Server) handleUserLogin(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		jsonErr(w, 405, "POST required")
		return
	}
	var req struct {
		Username string `json:"username"`
		Password string `json:"password"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		jsonErr(w, 400, "invalid JSON")
		return
	}
	if req.Username == "" || req.Password == "" {
		jsonErr(w, 400, "username and password required")
		return
	}
	var userID, hash string
	var confirmed, blocked int
	err := s.db.QueryRow("SELECT id, password_hash, confirmed, blocked FROM server_users WHERE username=? OR email=?",
		req.Username, strings.ToLower(req.Username)).Scan(&userID, &hash, &confirmed, &blocked)
	if err != nil {
		jsonErr(w, 401, "invalid credentials")
		return
	}
	if blocked != 0 {
		jsonErr(w, 403, "account blocked")
		return
	}
	if confirmed == 0 {
		jsonErr(w, 403, "email not confirmed")
		return
	}
	if bcrypt.CompareHashAndPassword([]byte(hash), []byte(req.Password)) != nil {
		jsonErr(w, 401, "invalid credentials")
		return
	}
	s.db.Exec("UPDATE server_users SET last_seen=? WHERE id=?", time.Now().UTC().Format(time.RFC3339), userID)
	tok := s.userTokens.Create(userID)
	jsonOK(w, map[string]string{"token": tok, "user_id": userID})
}

func (s *Server) handleForgot(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		jsonErr(w, 405, "POST required")
		return
	}
	var req struct {
		Email string `json:"email"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		jsonErr(w, 400, "invalid JSON")
		return
	}
	if req.Email == "" {
		jsonErr(w, 400, "email required")
		return
	}
	var userID string
	err := s.db.QueryRow("SELECT id FROM server_users WHERE email=?", strings.ToLower(req.Email)).Scan(&userID)
	if err != nil {
		jsonOK(w, map[string]string{"status": "if email exists, reset link sent"})
		return
	}
	tok := make([]byte, 24)
	rand.Read(tok)
	tokenStr := hex.EncodeToString(tok)
	exp := time.Now().Add(1 * time.Hour).UTC().Format(time.RFC3339)
	now := time.Now().UTC().Format(time.RFC3339)
	s.db.Exec("INSERT INTO server_email_tokens (token, user_id, purpose, expires_at, created_at) VALUES (?, ?, 'reset', ?, ?)",
		tokenStr, userID, exp, now)
	host := s.smtpGet("smtp_host")
	if host != "" {
		srvURL := s.smtpGet("server_url")
		resetURL := fmt.Sprintf("/api/v1/auth/reset?token=%s", tokenStr)
		if srvURL != "" {
			resetURL = fmt.Sprintf("%s/api/v1/auth/reset?token=%s", srvURL, tokenStr)
		}
		body := fmt.Sprintf("Reset your Verstak Sync password:\n\n%s\n\nThis link expires in 1 hour.", resetURL)
		s.smtpSend(req.Email, "Verstak Sync password reset", body)
	}
	jsonOK(w, map[string]string{"status": "if email exists, reset link sent"})
}

func (s *Server) handleReset(w http.ResponseWriter, r *http.Request) {
	if r.Method != "POST" {
		jsonErr(w, 405, "POST required")
		return
	}
	var req struct {
		Token       string `json:"token"`
		NewPassword string `json:"new_password"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		jsonErr(w, 400, "invalid JSON")
		return
	}
	if req.Token == "" || req.NewPassword == "" {
		jsonErr(w, 400, "token and new_password required")
		return
	}
	if err := validatePassword(req.NewPassword); err != "" {
		jsonErr(w, 400, err)
		return
	}
	var userID, expiresAt string
	err := s.db.QueryRow("SELECT user_id, expires_at FROM server_email_tokens WHERE token=? AND purpose='reset'",
		req.Token).Scan(&userID, &expiresAt)
	if err != nil {
		jsonErr(w, 400, "invalid or expired token")
		return
	}
	exp, err := time.Parse(time.RFC3339, expiresAt)
	if err != nil || time.Now().After(exp) {
		jsonErr(w, 400, "token expired")
		return
	}
	hash, err := bcrypt.GenerateFromPassword([]byte(req.NewPassword), bcrypt.DefaultCost)
	if err != nil {
		jsonErr(w, 500, "internal error")
		return
	}
	s.db.Exec("UPDATE server_users SET password_hash=? WHERE id=?", string(hash), userID)
	s.db.Exec("DELETE FROM server_email_tokens WHERE token=?", req.Token)
	jsonOK(w, map[string]string{"status": "password reset"})
}

func (s *Server) handleUserDevices(w http.ResponseWriter, r *http.Request) {
	userID, ok := s.requireUser(w, r)
	if !ok {
		return
	}
	if r.Method != "GET" {
		jsonErr(w, 405, "GET required")
		return
	}
	rows, err := s.db.Query(`
		SELECT d.id, d.name, d.last_seen, d.created_at
		FROM server_devices d
		JOIN server_user_devices ud ON ud.device_id = d.id
		WHERE ud.user_id = ?
		ORDER BY d.created_at`, userID)
	if err != nil {
		jsonErr(w, 500, err.Error())
		return
	}
	defer rows.Close()
	type deviceDTO struct {
		ID        string `json:"id"`
		Name      string `json:"name"`
		LastSeen  string `json:"last_seen"`
		CreatedAt string `json:"created_at"`
	}
	var devices []deviceDTO
	for rows.Next() {
		var d deviceDTO
		var lastSeen sql.NullString
		if err := rows.Scan(&d.ID, &d.Name, &lastSeen, &d.CreatedAt); err != nil {
			continue
		}
		d.LastSeen = lastSeen.String
		devices = append(devices, d)
	}
	if devices == nil {
		devices = []deviceDTO{}
	}
	jsonOK(w, map[string]interface{}{"devices": devices})
}

func (s *Server) handleSyncPush(w http.ResponseWriter, r *http.Request) {
	if !s.requireAPIKey(w, r) {
		return
	}
	if r.Method != "POST" {
		jsonErr(w, 405, "POST required")
		return
	}
	var req struct {
		DeviceID       string `json:"device_id"`
		IdempotencyKey string `json:"idempotency_key"`
		Ops            []struct {
			OpID              string `json:"op_id"`
			EntityType        string `json:"entity_type"`
			EntityID          string `json:"entity_id"`
			OpType            string `json:"op_type"`
			PayloadJSON       string `json:"payload_json"`
			ClientSequence    int    `json:"client_sequence"`
			LastSeenServerSeq int    `json:"last_seen_server_seq"`
			CreatedAt         string `json:"created_at"`
		} `json:"ops"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		jsonErr(w, 400, "invalid JSON: "+err.Error())
		return
	}

	// Idempotency: if request-level key provided, check for cached response.
	if req.IdempotencyKey != "" {
		var cachedJSON string
		err := s.db.QueryRow("SELECT response_json FROM server_idempotency_keys WHERE idempotency_key=?", req.IdempotencyKey).Scan(&cachedJSON)
		if err == nil {
			w.Header().Set("Content-Type", "application/json")
			w.Write([]byte(cachedJSON))
			return
		}
	}

	now := time.Now().UTC().Format(time.RFC3339)
	var accepted []string
	var conflicts []map[string]interface{}

	for _, op := range req.Ops {
		if op.OpID == "" || op.EntityType == "" || op.EntityID == "" || op.OpType == "" {
			continue
		}
		// Conflict detection: check if another device already created ops for this entity
		// with a server_sequence higher than what this client last saw.
		if op.LastSeenServerSeq > 0 {
			conflictRows, err := s.db.Query(`
				SELECT op_id, device_id, op_type, server_sequence FROM server_ops
				WHERE entity_type=? AND entity_id=? AND device_id!=?
				  AND server_sequence > ? AND op_type != 'delete'
				ORDER BY server_sequence`, op.EntityType, op.EntityID, req.DeviceID, op.LastSeenServerSeq)
			if err == nil {
				for conflictRows.Next() {
					var cOpID, cDevID, cOpType string
					var cSeq int
					conflictRows.Scan(&cOpID, &cDevID, &cOpType, &cSeq)
					conflicts = append(conflicts, map[string]interface{}{
						"op_id":           cOpID,
						"device_id":       cDevID,
						"op_type":         cOpType,
						"server_sequence": cSeq,
						"entity_type":     op.EntityType,
						"entity_id":       op.EntityID,
					})
				}
				conflictRows.Close()
			}
		}

		res, err := s.db.Exec(
			`INSERT OR IGNORE INTO server_ops (op_id, server_sequence, device_id, entity_type, entity_id, op_type, payload_json, idempotency_key, client_sequence, last_seen_server_seq, created_at, pushed_at)
			 VALUES (?, NULL, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
			op.OpID, req.DeviceID, op.EntityType, op.EntityID, op.OpType, op.PayloadJSON,
			req.IdempotencyKey, op.ClientSequence, op.LastSeenServerSeq, op.CreatedAt, now,
		)
		if err != nil {
			continue
		}
		n, _ := res.RowsAffected()
		if n == 0 {
			continue // duplicate op_id
		}
		seqRes, err := s.db.Exec("INSERT INTO server_revisions (op_id, device_id) VALUES (?, ?)", op.OpID, req.DeviceID)
		if err != nil {
			continue
		}
		seq, _ := seqRes.LastInsertId()
		s.db.Exec("UPDATE server_ops SET server_sequence=? WHERE op_id=?", seq, op.OpID)

		if op.OpType == "delete" {
			s.db.Exec(`INSERT OR REPLACE INTO server_tombstones (entity_type, entity_id, op_id, deleted_at) VALUES (?, ?, ?, ?)`,
				op.EntityType, op.EntityID, op.OpID, now)
		}

		accepted = append(accepted, op.OpID)
	}

	resp := map[string]interface{}{
		"accepted":  accepted,
		"count":     len(accepted),
		"conflicts": conflicts,
	}

	// Cache response for idempotency.
	if req.IdempotencyKey != "" {
		if respJSON, err := json.Marshal(resp); err == nil {
			s.db.Exec("INSERT OR IGNORE INTO server_idempotency_keys (idempotency_key, response_json, created_at) VALUES (?, ?, ?)",
				req.IdempotencyKey, string(respJSON), now)
		}
	}

	jsonOK(w, resp)
}

func (s *Server) handleSyncPull(w http.ResponseWriter, r *http.Request) {
	if !s.requireAPIKey(w, r) {
		return
	}
	if r.Method != "POST" {
		jsonErr(w, 405, "POST required")
		return
	}
	var req struct {
		SinceSequence int `json:"since_sequence"`
	}
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		jsonErr(w, 400, "invalid JSON")
		return
	}

	var serverSeq int
	s.db.QueryRow("SELECT COALESCE(MAX(server_sequence), 0) FROM server_ops").Scan(&serverSeq)

	rows, err := s.db.Query(`
		SELECT op_id, server_sequence, device_id, entity_type, entity_id, op_type, payload_json, created_at
		FROM server_ops
		WHERE server_sequence > ? AND server_sequence IS NOT NULL
		ORDER BY server_sequence`, req.SinceSequence)
	if err != nil {
		jsonErr(w, 500, err.Error())
		return
	}
	defer rows.Close()

	type opDTO struct {
		OpID           string `json:"op_id"`
		ServerSequence int    `json:"server_sequence"`
		DeviceID       string `json:"device_id"`
		EntityType     string `json:"entity_type"`
		EntityID       string `json:"entity_id"`
		OpType         string `json:"op_type"`
		PayloadJSON    string `json:"payload_json"`
		CreatedAt      string `json:"created_at"`
	}
	var ops []opDTO
	for rows.Next() {
		var o opDTO
		if err := rows.Scan(&o.OpID, &o.ServerSequence, &o.DeviceID, &o.EntityType, &o.EntityID, &o.OpType, &o.PayloadJSON, &o.CreatedAt); err != nil {
			continue
		}
		ops = append(ops, o)
	}

	jsonOK(w, map[string]interface{}{
		"server_sequence": serverSeq,
		"ops":             ops,
	})
}

func (s *Server) handleBlobs(w http.ResponseWriter, r *http.Request) {
	if !s.requireAPIKey(w, r) {
		return
	}
	switch r.Method {
	case "POST":
		// Upload: accept multipart file, store by SHA-256.
		if err := r.ParseMultipartForm(200 << 20); err != nil {
			jsonErr(w, 400, "multipart error: "+err.Error())
			return
		}
		file, header, err := r.FormFile("file")
		if err != nil {
			jsonErr(w, 400, "file field required")
			return
		}
		defer file.Close()

		// Read content and compute SHA-256.
		data, err := io.ReadAll(file)
		if err != nil {
			jsonErr(w, 500, "read error")
			return
		}
		hash := sha256.Sum256(data)
		shaHex := hex.EncodeToString(hash[:])

		// Store at blobs/ab/cd/sha256.
		blobDir := filepath.Join(s.blobsDir, shaHex[:2], shaHex[2:4])
		if err := os.MkdirAll(blobDir, 0750); err != nil {
			jsonErr(w, 500, "mkdir error")
			return
		}
		blobPath := filepath.Join(blobDir, shaHex)
		if err := os.WriteFile(blobPath, data, 0640); err != nil {
			jsonErr(w, 500, "write error")
			return
		}
		_ = header

		// Record in blobs table.
		now := time.Now().UTC().Format(time.RFC3339)
		s.db.Exec("INSERT OR IGNORE INTO server_blobs (sha256, size, created_at) VALUES (?, ?, ?)",
			shaHex, len(data), now)

		jsonOK(w, map[string]interface{}{
			"sha256": shaHex,
			"size":   len(data),
		})

	case "GET":
		// Download: GET /api/v1/blobs/{sha256}
		shaHex := strings.TrimPrefix(r.URL.Path, "/api/v1/blobs/")
		if len(shaHex) != 64 {
			jsonErr(w, 400, "invalid SHA-256")
			return
		}
		blobPath := filepath.Join(s.blobsDir, shaHex[:2], shaHex[2:4], shaHex)
		if _, err := os.Stat(blobPath); os.IsNotExist(err) {
			jsonErr(w, 404, "blob not found")
			return
		}
		data, err := os.ReadFile(blobPath)
		if err != nil {
			jsonErr(w, 500, "read error")
			return
		}
		w.Header().Set("Content-Type", "application/octet-stream")
		w.Header().Set("Content-Disposition", "attachment; filename=\""+shaHex+"\"")
		w.Write(data)

	default:
		jsonErr(w, 405, "method not allowed")
	}
}