import type { LLMMessage } from '../types.js'

/**
 * Estimate token count using a lightweight character heuristic.
 * This intentionally avoids model-specific tokenizer dependencies.
 */
export function estimateTokens(messages: LLMMessage[]): number {
  let chars = 0

  for (const message of messages) {
    for (const block of message.content) {
      if (block.type === 'text') {
        chars += block.text.length
      } else if (block.type === 'tool_result') {
        chars += block.content.length
      } else if (block.type === 'tool_use') {
        chars += JSON.stringify(block.input).length
      } else if (block.type === 'image') {
        // Account for non-text payloads with a small fixed cost.
        chars += 64
      }
    }
  }

  // Conservative English heuristic: ~4 chars per token.
  return Math.ceil(chars / 4)
}