import type { Message, ContentBlock } from '../core/session/session-jsonl.js';
import { estimateTokensForText } from './tokens.js';

export interface TailToolSnipConfig {
  
  hardKeepLatest: number;
  
  softBand: number;
  
  maxChars: number;
}

export const DEFAULT_TAIL_SNIP_CONFIG: TailToolSnipConfig = {
  hardKeepLatest: 2,
  softBand: 8,
  maxChars: 12_000,
};

export interface TailToolSnipResult {
  messages: Message[];
  snippedCount: number;
  
  savedChars: number;
  
  savedTokens: number;
}

function shortSnipLine(toolName?: string): string {
  const n = toolName?.trim() || 'tool';
  return `[超长输出已省略 · ${n}；若仍需原文请在本轮再调用该工具。]`;
}




export function snipTailOversizedToolResults(
  messages: Message[],
  config: Partial<TailToolSnipConfig> = {}
): TailToolSnipResult {
  const cfg = { ...DEFAULT_TAIL_SNIP_CONFIG, ...config };

  const allToolResults: Array<{
    msgIdx: number;
    blockIdx: number;
    content: string;
    name?: string;
  }> = [];

  for (let mi = 0; mi < messages.length; mi++) {
    const msg = messages[mi];
    if (typeof msg.content === 'string') continue;
    for (let bi = 0; bi < msg.content.length; bi++) {
      const block = msg.content[bi];
      if (block.type !== 'tool_result' || typeof block.content !== 'string') continue;
      allToolResults.push({
        msgIdx: mi,
        blockIdx: bi,
        content: block.content,
        name: typeof block.name === 'string' ? block.name : undefined,
      });
    }
  }

  if (allToolResults.length <= cfg.hardKeepLatest) {
    return { messages, snippedCount: 0, savedChars: 0, savedTokens: 0 };
  }

  const n = allToolResults.length;
  const bandStart = Math.max(0, n - cfg.hardKeepLatest - cfg.softBand);
  const bandEnd = n - cfg.hardKeepLatest;

  const snipKeys = new Set<string>();
  let wouldSnip = 0;
  let savedChars = 0;
  let savedTokens = 0;

  for (let i = bandStart; i < bandEnd; i++) {
    const tr = allToolResults[i];
    if (tr.content.length < cfg.maxChars) continue;
    const line = shortSnipLine(tr.name);
    if (tr.content === line) continue;
    snipKeys.add(`${tr.msgIdx}:${tr.blockIdx}`);
    wouldSnip++;
    savedChars += tr.content.length - line.length;
    savedTokens += Math.max(0, estimateTokensForText(tr.content) - estimateTokensForText(line));
  }

  if (wouldSnip === 0) {
    return { messages, snippedCount: 0, savedChars: 0, savedTokens: 0 };
  }

  let snippedCount = 0;
  const result: Message[] = messages.map((msg, mi) => {
    if (typeof msg.content === 'string') return msg;
    let modified = false;
    const newContent: ContentBlock[] = msg.content.map((block, bi) => {
      const key = `${mi}:${bi}`;
      if (!snipKeys.has(key) || block.type !== 'tool_result') return block;
      const line = shortSnipLine(block.name);
      modified = true;
      snippedCount++;
      return { ...block, content: line };
    });
    return modified ? { ...msg, content: newContent } : msg;
  });

  return { messages: result, snippedCount, savedChars, savedTokens };
}