package mysql

import (
	"context"
	"database/sql"
	"strings"

	"hyapp/pkg/appcode"
)

const missingClientSessionID = "__missing_client_session__"

type socialIdentityDayKey struct {
	StatTZ  string
	StatDay string
}

// applySocialTrackingIdentity records only identity evidence. It deliberately
// never moves or rewrites stat_social_user_day rows: that table contains additive
// money and duration fields which cannot be safely undone when events arrive out
// of order. Query-time canonicalization consumes the small day-resolution table
// and leaves the financial read model untouched.
func applySocialTrackingIdentity(ctx context.Context, tx *sql.Tx, event AppTrackingEvent, nowMS int64) error {
	app := appcode.Normalize(event.AppCode)
	deviceID := strings.TrimSpace(event.DeviceID)
	clientSessionID := strings.TrimSpace(event.ClientSessionID)
	if app == "" || deviceID == "" {
		return nil
	}

	if event.UserID <= 0 {
		// Only events that actually create a d: row may participate in the
		// device-day resolution. page_open and failed actions otherwise introduce
		// phantom unresolved sessions that permanently block a valid login merge.
		contributesSocialRow := false
		for _, scope := range statDayScopesFromContext(ctx, event.OccurredAtMS) {
			if _, ok := socialDeltaForAppTrackingEvent(event, scope, nowMS); ok {
				contributesSocialRow = true
				break
			}
		}
		if !contributesSocialRow {
			return nil
		}
	} else if clientSessionID == "" {
		// Old authenticated clients still produce a direct u: fact, but without
		// the process session they cannot link any earlier anonymous row. Return
		// before taking a device lock on this high-volume compatibility path.
		return nil
	}
	if err := lockSocialIdentityDevice(ctx, tx, app, deviceID, nowMS); err != nil {
		return err
	}

	if event.UserID <= 0 {
		// Old clients do not send client_session_id. A single unresolved sentinel
		// per device/day blocks a different resolved session from swallowing those
		// anonymous events; conservative under-count correction is safer than a
		// false account merge on shared devices.
		if clientSessionID == "" {
			clientSessionID = missingClientSessionID
		}
		for _, scope := range statDayScopesFromContext(ctx, event.OccurredAtMS) {
			affected, err := insertUnique(ctx, tx, `
				INSERT IGNORE INTO stat_social_identity_session_day (
					app_code, stat_tz, stat_day, device_id, client_session_id, first_seen_at_ms, updated_at_ms
				) VALUES (?, ?, ?, ?, ?, ?, ?)
			`, app, scope.tz, scope.day, deviceID, clientSessionID, event.OccurredAtMS, nowMS)
			if err != nil {
				return err
			}
			if affected > 0 {
				if err := recomputeSocialIdentityDay(ctx, tx, app, scope.tz, scope.day, deviceID, nowMS); err != nil {
					return err
				}
			}
		}
		return nil
	}

	inserted, err := insertUnique(ctx, tx, `
		INSERT IGNORE INTO stat_social_identity_session_user (
			app_code, device_id, client_session_id, user_id, first_seen_at_ms, updated_at_ms
		) VALUES (?, ?, ?, ?, ?, ?)
	`, app, deviceID, clientSessionID, normalizeID(event.UserID), event.OccurredAtMS, nowMS)
	if err != nil || inserted == 0 {
		return err
	}

	// A session can cross a Beijing/UTC midnight. When its first authenticated
	// event arrives, recompute every earlier anonymous day observed for that same
	// device+client session so D1/D3/D7 retention sees one canonical account.
	rows, err := tx.QueryContext(ctx, `
		SELECT stat_tz, DATE_FORMAT(stat_day, '%Y-%m-%d')
		FROM stat_social_identity_session_day
		WHERE app_code = ? AND device_id = ? AND client_session_id = ?
		ORDER BY stat_tz, stat_day
		FOR UPDATE
	`, app, deviceID, clientSessionID)
	if err != nil {
		return err
	}
	days := make([]socialIdentityDayKey, 0, 2)
	for rows.Next() {
		var key socialIdentityDayKey
		if err := rows.Scan(&key.StatTZ, &key.StatDay); err != nil {
			_ = rows.Close()
			return err
		}
		days = append(days, key)
	}
	if err := rows.Err(); err != nil {
		_ = rows.Close()
		return err
	}
	if err := rows.Close(); err != nil {
		return err
	}
	for _, day := range days {
		if err := recomputeSocialIdentityDay(ctx, tx, app, day.StatTZ, day.StatDay, deviceID, nowMS); err != nil {
			return err
		}
	}
	return nil
}

func recomputeSocialIdentityDay(ctx context.Context, tx *sql.Tx, app, statTZ, statDay, deviceID string, nowMS int64) error {
	rows, err := tx.QueryContext(ctx, `
		SELECT d.client_session_id, u.user_id
		FROM stat_social_identity_session_day d
		LEFT JOIN stat_social_identity_session_user u
		  ON u.app_code = d.app_code
		 AND u.device_id = d.device_id
		 AND u.client_session_id = d.client_session_id
		WHERE d.app_code = ? AND d.stat_tz = ? AND d.stat_day = ? AND d.device_id = ?
		ORDER BY d.client_session_id, u.user_id
		FOR UPDATE
	`, app, normalizeStatTZ(statTZ), statDay, deviceID)
	if err != nil {
		return err
	}
	sessionUsers := map[string]map[int64]struct{}{}
	for rows.Next() {
		var sessionID string
		var userID sql.NullInt64
		if err := rows.Scan(&sessionID, &userID); err != nil {
			_ = rows.Close()
			return err
		}
		if sessionUsers[sessionID] == nil {
			sessionUsers[sessionID] = map[int64]struct{}{}
		}
		if userID.Valid && userID.Int64 > 0 {
			sessionUsers[sessionID][userID.Int64] = struct{}{}
		}
	}
	if err := rows.Err(); err != nil {
		_ = rows.Close()
		return err
	}
	if err := rows.Close(); err != nil {
		return err
	}

	state, resolvedUserID := "unresolved", int64(0)
	resolutionSource := "client_session"
	ambiguous := false
	unresolved := false
	for _, users := range sessionUsers {
		if len(users) == 0 {
			unresolved = true
			continue
		}
		if len(users) > 1 {
			ambiguous = true
			continue
		}
		for userID := range users {
			if resolvedUserID == 0 {
				resolvedUserID = userID
			} else if resolvedUserID != userID {
				ambiguous = true
			}
		}
	}
	if ambiguous {
		state, resolvedUserID = "ambiguous", 0
	} else if !unresolved && len(sessionUsers) > 0 && resolvedUserID > 0 {
		state = "resolved"
	} else {
		resolvedUserID = 0
	}
	if len(sessionUsers) == 1 {
		if _, onlyMissingSession := sessionUsers[missingClientSessionID]; onlyMissingSession {
			// A legacy client cannot establish an exact session bridge. Keep that
			// evidence conservative, but let a later bounded historical replay
			// replace it instead of giving it permanent client-session authority.
			resolutionSource = "missing_client_session"
		}
	}

	_, err = tx.ExecContext(ctx, `
		INSERT INTO stat_social_identity_day (
			app_code, stat_tz, stat_day, device_id, resolved_user_id,
			resolution_state, resolution_source, updated_at_ms
		) VALUES (?, ?, ?, ?, ?, ?, ?, ?)
		ON DUPLICATE KEY UPDATE
			resolved_user_id = VALUES(resolved_user_id),
			resolution_state = VALUES(resolution_state),
			resolution_source = VALUES(resolution_source),
			updated_at_ms = VALUES(updated_at_ms)
	`, app, normalizeStatTZ(statTZ), statDay, deviceID, resolvedUserID, state, resolutionSource, nowMS)
	return err
}

func lockSocialIdentityDevice(ctx context.Context, tx *sql.Tx, app, deviceID string, nowMS int64) error {
	if _, err := tx.ExecContext(ctx, `
		INSERT IGNORE INTO stat_social_identity_device_lock (app_code, device_id, created_at_ms)
		VALUES (?, ?, ?)
	`, appcode.Normalize(app), strings.TrimSpace(deviceID), nowMS); err != nil {
		return err
	}
	var lockedDeviceID string
	return tx.QueryRowContext(ctx, `
		SELECT device_id
		FROM stat_social_identity_device_lock
		WHERE app_code = ? AND device_id = ?
		FOR UPDATE
	`, appcode.Normalize(app), strings.TrimSpace(deviceID)).Scan(&lockedDeviceID)
}