package service

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"path"
	"strings"
	"time"

	"github.com/prabhupadasays/spsays-bff/internal/model"
	"github.com/prabhupadasays/spsays-bff/internal/repository"
)

// UserService handles profile-edit + avatar-upload flows.
type UserService struct {
	users *repository.UserRepo
	r2    *repository.R2
}

func NewUserService(users *repository.UserRepo, r2 *repository.R2) *UserService {
	return &UserService{users: users, r2: r2}
}

// UpdateProfile updates the user's name, avatar URL, and/or handle.
//
// `avatarURL` semantics:
//
//	nil  → don't touch
//	""   → clear (remove avatar)
//	"x"  → set to "x"
//
// `handle` is normalized to the project's slug format before being passed
// to the DB so users can't sneak in spaces or punctuation. Empty after
// normalization → 400.
func (s *UserService) UpdateProfile(ctx context.Context, id string, name, avatarURL, handle *string) (*model.User, error) {
	if name != nil {
		trimmed := strings.TrimSpace(*name)
		if trimmed == "" {
			return nil, errors.New("name cannot be empty")
		}
		if len(trimmed) > 120 {
			return nil, errors.New("name too long (max 120)")
		}
		name = &trimmed
	}
	if handle != nil {
		clean := normalizeHandle(*handle)
		if len(clean) < 3 {
			return nil, errors.New("handle must be at least 3 characters (letters, digits, dashes)")
		}
		if len(clean) > 32 {
			return nil, errors.New("handle too long (max 32)")
		}
		handle = &clean
	}
	return s.users.UpdateProfile(ctx, id, name, avatarURL, handle)
}

// Search returns users matching the query (handle or name substring).
// Used by the public user-search endpoint on the /search page.
func (s *UserService) Search(ctx context.Context, q string, limit int) ([]model.User, error) {
	return s.users.Search(ctx, q, limit)
}

// GetReadingPrefs returns the user's reading prefs blob (opaque JSON).
// Used by the frontend to hydrate ReadingSettings on sign-in so the
// theme/palette/font choices roam across devices.
func (s *UserService) GetReadingPrefs(ctx context.Context, id string) ([]byte, error) {
	return s.users.GetReadingPrefs(ctx, id)
}

// UpdateReadingPrefs overwrites the user's reading prefs blob. The
// handler re-marshals the decoded request before calling in here so we
// know `prefsJSON` is well-formed by the time it hits the DB.
func (s *UserService) UpdateReadingPrefs(ctx context.Context, id string, prefsJSON []byte) error {
	return s.users.UpdateReadingPrefs(ctx, id, prefsJSON)
}

// normalizeHandle lowercases and strips anything that isn't [a-z0-9-]. Same
// rules as slugForHandle in auth_service, but exposed here because the
// profile-update path doesn't go through auth.
func normalizeHandle(raw string) string {
	var b strings.Builder
	for _, r := range strings.ToLower(strings.TrimSpace(raw)) {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
			b.WriteRune(r)
		case r == '-', r == '.', r == '_':
			b.WriteByte('-')
		}
	}
	out := strings.Trim(b.String(), "-")
	// Collapse runs of dashes.
	for strings.Contains(out, "--") {
		out = strings.ReplaceAll(out, "--", "-")
	}
	return out
}

// AvatarPresign issues a one-shot presigned PUT URL the frontend uses to
// upload an avatar directly to R2.
//
// The key is namespaced under `avatars/<user_id>/<random>.<ext>` so:
//   - we can list / clean up a user's avatars with one prefix scan
//   - the random suffix forces cache invalidation when the avatar changes
//   - a malicious user can't overwrite someone else's avatar (their JWT
//     scopes the user_id portion of the key)
//
// Returns (uploadURL, publicURL, error). The frontend then PUTs to uploadURL
// and POSTs publicURL back as the new avatar.
func (s *UserService) AvatarPresign(ctx context.Context, userID, contentType string) (uploadURL, publicURL string, err error) {
	if s.r2 == nil {
		return "", "", errors.New("avatar uploads are not configured")
	}
	ext, ok := extensionFor(contentType)
	if !ok {
		return "", "", fmt.Errorf("unsupported content type: %s", contentType)
	}

	suffix := make([]byte, 8)
	if _, err := rand.Read(suffix); err != nil {
		return "", "", err
	}
	key := path.Join("avatars", userID, hex.EncodeToString(suffix)+ext)

	return s.r2.PresignPut(ctx, key, contentType, 5*time.Minute)
}

// extensionFor whitelists the image content types we accept. Restricting
// here is the cheap-but-effective defence against users uploading arbitrary
// binaries to our R2 bucket.
func extensionFor(ct string) (string, bool) {
	switch ct {
	case "image/png":
		return ".png", true
	case "image/jpeg":
		return ".jpg", true
	case "image/webp":
		return ".webp", true
	case "image/gif":
		return ".gif", true
	default:
		return "", false
	}
}