import type { ReactNode } from "react";
import "@app/ui/MetricCard.css";

export type DeltaDirection = "up" | "down" | "flat";

export interface MetricCardProps {
  label: string;
  value: string | number;
  /** Optional description shown under the delta line. */
  description?: string;
  /** Numeric delta as a fraction (0.12 = +12%). The sign drives direction unless `deltaDirection` is set. */
  delta?: number;
  /** Override the inferred direction — useful when you only want the colour, not the value. */
  deltaDirection?: DeltaDirection;
  /** Visual emphasis. `primary` = darker surface, used for hero metrics. */
  emphasis?: "default" | "primary";
  /** Density. `sm` tightens padding + value size for narrow rails/strips. */
  size?: "sm" | "md";
  /** Optional icon shown in the top-right corner. */
  icon?: ReactNode;
  onClick?: () => void;
  className?: string;
}

function inferDirection(delta?: number): DeltaDirection {
  if (delta === undefined || delta === 0) return "flat";
  return delta > 0 ? "up" : "down";
}

function formatDelta(delta: number) {
  const pct = Math.round(Math.abs(delta) * 100);
  return `${pct}%`;
}

/**
 * Stirling's standard KPI card. Used on Home, Sources, Documents, Audit and
 * every Infrastructure tab — the prototype calls these the metric strip.
 */
export function MetricCard({
  label,
  value,
  description,
  delta,
  deltaDirection,
  emphasis = "default",
  size = "md",
  icon,
  onClick,
  className,
}: MetricCardProps) {
  const dir = deltaDirection ?? inferDirection(delta);
  const interactive = !!onClick;

  const classes = [
    "sui-metric",
    `sui-metric--${size}`,
    emphasis === "primary" ? "sui-metric--primary" : "",
    interactive ? "sui-metric--interactive" : "",
    className ?? "",
  ]
    .filter(Boolean)
    .join(" ");

  const body = (
    <>
      <div className="sui-metric__header">
        <span className="sui-metric__label">{label}</span>
        {icon && (
          <span className="sui-metric__icon" aria-hidden>
            {icon}
          </span>
        )}
      </div>
      <div className="sui-metric__value">{value}</div>
      {(delta !== undefined || description) && (
        <div className="sui-metric__footer">
          {delta !== undefined && (
            <span className={`sui-metric__delta sui-metric__delta--${dir}`}>
              <span className="sui-metric__delta-arrow" aria-hidden>
                {dir === "up" ? "↑" : dir === "down" ? "↓" : "·"}
              </span>
              {formatDelta(delta)}
            </span>
          )}
          {description && (
            <span className="sui-metric__desc">{description}</span>
          )}
        </div>
      )}
    </>
  );

  if (interactive) {
    return (
      <button type="button" className={classes} onClick={onClick}>
        {body}
      </button>
    );
  }

  return <div className={classes}>{body}</div>;
}
