oslstats/pkg/slapshotapi/tampering.go

package slapshotapi

import (
	"fmt"
	"strings"

	"github.com/pkg/errors"
)

// DetectTampering analyzes 3 period logs for modification signs.
// Returns (isTampering bool, reason string, error).
func DetectTampering(logs []*MatchLog) (bool, string, error) {
	if len(logs) != 3 {
		return false, "", errors.New("exactly 3 period logs are required")
	}

	reasons := []string{}

	// Check metadata consistency
	tampered, reason, err := ValidateMetadataConsistency(logs)
	if err != nil {
		return false, "", errors.Wrap(err, "ValidateMetadataConsistency")
	}
	if tampered {
		reasons = append(reasons, reason)
	}

	// Check score progression
	tampered, reason, err = ValidateScoreProgression(logs)
	if err != nil {
		return false, "", errors.Wrap(err, "ValidateScoreProgression")
	}
	if tampered {
		reasons = append(reasons, reason)
	}

	// Check player consistency
	tampered, reason, err = ValidatePlayerConsistency(logs)
	if err != nil {
		return false, "", errors.Wrap(err, "ValidatePlayerConsistency")
	}
	if tampered {
		reasons = append(reasons, reason)
	}

	if len(reasons) > 0 {
		return true, strings.Join(reasons, "; "), nil
	}
	return false, "", nil
}

// ValidateMetadataConsistency checks that arena, match_length, and
// custom_mercy_rule are consistent across all periods, and warns if any
// period has periods_enabled set to "False" (periods disabled).
func ValidateMetadataConsistency(logs []*MatchLog) (bool, string, error) {
	if len(logs) != 3 {
		return false, "", errors.New("exactly 3 period logs are required")
	}

	ref := logs[0]
	inconsistencies := []string{}

	for i := 1; i < len(logs); i++ {
		log := logs[i]
		if log.Arena != ref.Arena {
			inconsistencies = append(inconsistencies,
				fmt.Sprintf("arena differs in period %d (%q vs %q)", i+1, log.Arena, ref.Arena))
		}
		if log.MatchLength != ref.MatchLength {
			inconsistencies = append(inconsistencies,
				fmt.Sprintf("match_length differs in period %d (%s vs %s)", i+1, log.MatchLength, ref.MatchLength))
		}
		if log.CustomMercyRule != ref.CustomMercyRule {
			inconsistencies = append(inconsistencies,
				fmt.Sprintf("custom_mercy_rule differs in period %d (%s vs %s)", i+1, log.CustomMercyRule, ref.CustomMercyRule))
		}
	}

	// Warn if any period has periods disabled
	for i, log := range logs {
		if strings.EqualFold(log.PeriodsEnabled, "False") {
			inconsistencies = append(inconsistencies,
				fmt.Sprintf("periods_enabled is False in period %d", i+1))
		}
	}

	if len(inconsistencies) > 0 {
		return true, "metadata inconsistency: " + strings.Join(inconsistencies, ", "), nil
	}
	return false, "", nil
}

// ValidateScoreProgression checks that scores only increase or stay the same
// across periods (cumulative stats).
func ValidateScoreProgression(logs []*MatchLog) (bool, string, error) {
	if len(logs) != 3 {
		return false, "", errors.New("exactly 3 period logs are required")
	}

	issues := []string{}

	for i := 1; i < len(logs); i++ {
		prev := logs[i-1]
		curr := logs[i]
		if curr.Score.Home < prev.Score.Home {
			issues = append(issues,
				fmt.Sprintf("home score decreased from period %d (%d) to period %d (%d)",
					i, prev.Score.Home, i+1, curr.Score.Home))
		}
		if curr.Score.Away < prev.Score.Away {
			issues = append(issues,
				fmt.Sprintf("away score decreased from period %d (%d) to period %d (%d)",
					i, prev.Score.Away, i+1, curr.Score.Away))
		}
	}

	if len(issues) > 0 {
		return true, "score regression: " + strings.Join(issues, ", "), nil
	}
	return false, "", nil
}

// ValidatePlayerConsistency checks that player rosters remain relatively stable
// across periods. A player present in period 1 should ideally still be present
// in later periods. Drastic roster changes are suspicious.
func ValidatePlayerConsistency(logs []*MatchLog) (bool, string, error) {
	if len(logs) != 3 {
		return false, "", errors.New("exactly 3 period logs are required")
	}

	// Build player sets per period
	periodPlayers := make([]map[string]string, 3) // game_user_id -> team
	for i, log := range logs {
		periodPlayers[i] = make(map[string]string)
		for _, p := range log.Players {
			periodPlayers[i][p.GameUserID] = p.Team
		}
	}

	issues := []string{}

	// Check for team-switching between periods (same player, different team)
	for i := 1; i < len(logs); i++ {
		for id, prevTeam := range periodPlayers[i-1] {
			if currTeam, exists := periodPlayers[i][id]; exists {
				if currTeam != prevTeam {
					issues = append(issues,
						fmt.Sprintf("player %s switched teams between period %d and %d",
							id, i, i+1))
				}
			}
		}
	}

	// Check for drastic roster changes (more than 50% different players)
	for i := 1; i < len(logs); i++ {
		prev := periodPlayers[i-1]
		curr := periodPlayers[i]
		if len(prev) == 0 {
			continue
		}
		missing := 0
		for id := range prev {
			if _, exists := curr[id]; !exists {
				missing++
			}
		}
		ratio := float64(missing) / float64(len(prev))
		if ratio > 0.5 {
			issues = append(issues,
				fmt.Sprintf("more than 50%% of players changed between period %d and %d (%d/%d missing)",
					i, i+1, missing, len(prev)))
		}
	}

	if len(issues) > 0 {
		return true, "player inconsistency: " + strings.Join(issues, ", "), nil
	}
	return false, "", nil
}