// Purge-errors strategy — removes failed/empty tool_result entries.
// Clean-room implementation.

import type { DcpMessage } from '../messages.js';

const ERROR_PREFIXES = ['Error:', 'error:', 'Error: '];
const DEFAULT_WINDOW = 5;

export function purgeErrors(
  messages: DcpMessage[],
  windowSize: number = DEFAULT_WINDOW,
): { messages: DcpMessage[]; stats: { removedCount: number; freedTokens: number } } {
  const result: DcpMessage[] = [];
  let removedCount = 0;
  let freedTokens = 0;

  for (const msg of messages) {
    if (msg.role === 'tool') {
      const shouldRemove =
        msg.isError ||
        ERROR_PREFIXES.some((p) => msg.content.startsWith(p)) ||
        msg.content.trim() === '';

      if (shouldRemove) {
        removedCount++;
        freedTokens += Math.ceil(msg.content.length / 4);
        continue; // Skip this message
      }
    }
    result.push(msg);
  }

  return { messages: result, stats: { removedCount, freedTokens } };
}