package shared

import (
	"fmt"

	"galaxy/authsession/internal/domain/sessionlimit"
	"galaxy/authsession/internal/ports"
)

// EvaluateSessionLimit evaluates the Stage-4 active-session creation decision
// from the loaded configuration and current active-session count.
func EvaluateSessionLimit(config ports.SessionLimitConfig, activeSessionCount int) (sessionlimit.Decision, error) {
	if err := config.Validate(); err != nil {
		return sessionlimit.Decision{}, InternalError(fmt.Errorf("evaluate session limit: %w", err))
	}
	if activeSessionCount < 0 {
		return sessionlimit.Decision{}, InternalError(fmt.Errorf("evaluate session limit: active session count %d is negative", activeSessionCount))
	}

	decision := sessionlimit.Decision{
		ActiveSessionCount: activeSessionCount,
		NextSessionCount:   activeSessionCount + 1,
	}

	if config.ActiveSessionLimit == nil {
		decision.Kind = sessionlimit.KindDisabled
	} else {
		decision.ConfiguredLimit = config.ActiveSessionLimit
		if decision.NextSessionCount <= *config.ActiveSessionLimit {
			decision.Kind = sessionlimit.KindAllowed
		} else {
			decision.Kind = sessionlimit.KindExceeded
		}
	}
	if err := decision.Validate(); err != nil {
		return sessionlimit.Decision{}, InternalError(fmt.Errorf("evaluate session limit: %w", err))
	}

	return decision, nil
}