package account

import (
	"context"
	"errors"
	"fmt"
	"math/rand/v2"
	"regexp"
	"strings"
	"time"
	"unicode"
	"unicode/utf8"

	"github.com/go-jet/jet/v2/postgres"
	"github.com/go-jet/jet/v2/qrm"
	"github.com/google/uuid"

	"scrabble/backend/internal/postgres/jet/backend/model"
	"scrabble/backend/internal/postgres/jet/backend/table"
)

// maxDisplayName caps an editable display name's length in runes (the column itself
// is unbounded; auto-provisioned platform names bypass this editor validation).
const maxDisplayName = 32

// maxDisplayNameSpecials caps the total special characters (the "." / "_" separators —
// every name rune that is neither a letter nor a space) an editable display name may
// carry, so a still-well-formed name cannot be made of mostly punctuation (Stage 17).
const maxDisplayNameSpecials = 5

// maxAwayWindow bounds the daily away window's duration (midnight-wrap aware).
const maxAwayWindow = 12 * time.Hour

// displayNameRe enforces the editable display-name format (Stage 8): Unicode letters
// joined by single space / "." / "_" separators, where a "." or "_" may be followed
// by a single space. No leading separator and no two adjacent separators (except
// "<dot|underscore> <space>"); a single trailing "." is allowed (Stage 17), so
// "Name_P. Last" and "Anna B." are valid, "Name P._Last" is not.
var displayNameRe = regexp.MustCompile(`^\p{L}+(?:(?:[._] ?| )\p{L}+)*\.?$`)

// ErrInvalidProfile is returned when a profile update carries an unacceptable
// field (an unknown language, an invalid timezone, or an over-long display name).
var ErrInvalidProfile = errors.New("account: invalid profile")

// ProfileUpdate is the full set of player-editable profile fields. UpdateProfile
// overwrites every field, so callers send the complete desired profile. AwayStart
// and AwayEnd carry only the hour and minute of the daily away window, in the
// account's TimeZone.
type ProfileUpdate struct {
	DisplayName            string
	PreferredLanguage      string // "en" or "ru"
	TimeZone               string // an IANA location name
	AwayStart              time.Time
	AwayEnd                time.Time
	BlockChat              bool
	BlockFriendRequests    bool
	NotificationsInAppOnly bool
}

// UpdateProfile validates and overwrites the editable fields of the account, then
// returns the stored row. It reports ErrInvalidProfile for a bad language,
// timezone or display name and ErrNotFound when no account matches id.
func (s *Store) UpdateProfile(ctx context.Context, id uuid.UUID, p ProfileUpdate) (Account, error) {
	lang := strings.TrimSpace(p.PreferredLanguage)
	if lang != "en" && lang != "ru" {
		return Account{}, fmt.Errorf("%w: preferred_language %q", ErrInvalidProfile, p.PreferredLanguage)
	}
	tz := strings.TrimSpace(p.TimeZone)
	if !validZone(tz) {
		return Account{}, fmt.Errorf("%w: time_zone %q", ErrInvalidProfile, p.TimeZone)
	}
	name, err := ValidateDisplayName(p.DisplayName)
	if err != nil {
		return Account{}, err
	}
	if err := validateAwayWindow(p.AwayStart, p.AwayEnd); err != nil {
		return Account{}, err
	}

	stmt := table.Accounts.UPDATE(
		table.Accounts.DisplayName, table.Accounts.PreferredLanguage, table.Accounts.TimeZone,
		table.Accounts.AwayStart, table.Accounts.AwayEnd,
		table.Accounts.BlockChat, table.Accounts.BlockFriendRequests,
		table.Accounts.NotificationsInAppOnly, table.Accounts.UpdatedAt,
	).SET(
		postgres.String(name), postgres.String(lang), postgres.String(tz),
		postgres.TimeT(p.AwayStart), postgres.TimeT(p.AwayEnd),
		postgres.Bool(p.BlockChat), postgres.Bool(p.BlockFriendRequests),
		postgres.Bool(p.NotificationsInAppOnly), postgres.TimestampzT(time.Now().UTC()),
	).WHERE(table.Accounts.AccountID.EQ(postgres.UUID(id))).
		RETURNING(table.Accounts.AllColumns)

	var row model.Accounts
	if err := stmt.QueryContext(ctx, s.db, &row); err != nil {
		if errors.Is(err, qrm.ErrNoRows) {
			return Account{}, ErrNotFound
		}
		return Account{}, fmt.Errorf("account: update profile %s: %w", id, err)
	}
	return modelToAccount(row), nil
}

// ValidateDisplayName trims surrounding whitespace and checks the editable
// display-name length (<= maxDisplayName runes) and format (displayNameRe),
// returning the cleaned name or ErrInvalidProfile. It is exported so the gateway
// boundary could reuse it; the UI mirrors the same rule.
func ValidateDisplayName(raw string) (string, error) {
	name := strings.TrimSpace(raw)
	if name == "" {
		return "", fmt.Errorf("%w: display name is empty", ErrInvalidProfile)
	}
	if utf8.RuneCountInString(name) > maxDisplayName {
		return "", fmt.Errorf("%w: display name exceeds %d characters", ErrInvalidProfile, maxDisplayName)
	}
	if !displayNameRe.MatchString(name) {
		return "", fmt.Errorf("%w: display name has an invalid character or layout", ErrInvalidProfile)
	}
	specials := 0
	for _, r := range name {
		if r != ' ' && !unicode.IsLetter(r) {
			specials++
		}
	}
	if specials > maxDisplayNameSpecials {
		return "", fmt.Errorf("%w: display name has more than %d special characters", ErrInvalidProfile, maxDisplayNameSpecials)
	}
	return name, nil
}

// sanitizeDisplayName best-effort cleans a platform-supplied name (e.g. a Telegram
// first name) to the editable display-name format: it keeps the maximal runs of
// Unicode letters and joins them with a single space, dropping every other rune
// (emoji, digits, punctuation), then caps the result to maxDisplayName runes. The
// result therefore always satisfies ValidateDisplayName, or is empty when the input
// carries no letters — in which case the caller substitutes placeholderDisplayName.
// Mirroring the profile editor's rule means a connector-provisioned name is editable
// later without first failing validation.
func sanitizeDisplayName(raw string) string {
	fields := strings.FieldsFunc(raw, func(r rune) bool { return !unicode.IsLetter(r) })
	if len(fields) == 0 {
		return ""
	}
	name := strings.Join(fields, " ")
	if utf8.RuneCountInString(name) > maxDisplayName {
		name = strings.TrimRight(string([]rune(name)[:maxDisplayName]), " ")
	}
	return name
}

// placeholderDisplayName builds a fallback display name for a platform account whose
// supplied name had no usable letters: "Player-NNNNN" for lang "en" (the default) or
// "Игрок-NNNNN" for "ru", with five random digits. The generated name intentionally
// carries digits and a hyphen, so it lies outside the editable format and the player
// is expected to rename it; provisioned names bypass that editor validation.
func placeholderDisplayName(lang string) string {
	prefix := "Player"
	if lang == "ru" {
		prefix = "Игрок"
	}
	return fmt.Sprintf("%s-%05d", prefix, rand.IntN(100000))
}

// validateAwayWindow checks that the daily away window's duration, wrapping across
// midnight, does not exceed maxAwayWindow. A zero-length window (start == end) means
// "no away time" and is allowed.
func validateAwayWindow(start, end time.Time) error {
	mins := (end.Hour()*60 + end.Minute()) - (start.Hour()*60 + start.Minute())
	if mins < 0 {
		mins += 24 * 60
	}
	if time.Duration(mins)*time.Minute > maxAwayWindow {
		return fmt.Errorf("%w: away window exceeds %s", ErrInvalidProfile, maxAwayWindow)
	}
	return nil
}