/**
 * Token Counter Module
 * 
 * Estimates token counts for text and messages.
 * Uses a character-based approximation (GPT-style tokenization is roughly 4 chars per token).
 * For more accurate counting, you could integrate tiktoken or similar libraries.
 */

export interface TokenCountResult {
  tokens: number;
  characters: number;
  words: number;
}

export interface MessageTokenCount {
  role: string;
  content: string;
  tokens: number;
}

export interface TokenBudget {
  used: number;
  remaining: number;
  total: number;
  percentageUsed: number;
}

// Approximate tokens per character ratio (GPT-style)
const CHARS_PER_TOKEN = 4;

// Overhead for message formatting (role, delimiters, etc.)
const MESSAGE_OVERHEAD_TOKENS = 4;

/**
 * TokenCounter - Estimates token counts for text and conversations
 */
export class TokenCounter {
  private maxTokens: number;
  private reservedTokens: number;

  constructor(maxTokens: number = 128000, reservedTokens: number = 4096) {
    this.maxTokens = maxTokens;
    this.reservedTokens = reservedTokens;
  }

  /**
   * Count tokens in a text string
   */
  countText(text: string): TokenCountResult {
    const characters = text.length;
    const words = text.split(/\s+/).filter(w => w.length > 0).length;
    
    // Token estimation using character ratio
    // Also account for word boundaries and special characters
    const tokens = Math.ceil(characters / CHARS_PER_TOKEN);
    
    return {
      tokens,
      characters,
      words
    };
  }

  /**
   * Count tokens in a single message
   */
  countMessage(message: { role: string; content: string }): number {
    const contentTokens = this.countText(message.content).tokens;
    return contentTokens + MESSAGE_OVERHEAD_TOKENS;
  }

  /**
   * Count tokens in a conversation (array of messages)
   */
  countConversation(messages: Array<{ role: string; content: string }>): {
    total: number;
    breakdown: MessageTokenCount[];
  } {
    const breakdown: MessageTokenCount[] = messages.map(msg => ({
      role: msg.role,
      content: msg.content.substring(0, 100) + (msg.content.length > 100 ? '...' : ''),
      tokens: this.countMessage(msg)
    }));

    const total = breakdown.reduce((sum, msg) => sum + msg.tokens, 0);

    return { total, breakdown };
  }

  /**
   * Get current token budget
   */
  getBudget(usedTokens: number): TokenBudget {
    const availableTokens = this.maxTokens - this.reservedTokens;
    const remaining = Math.max(0, availableTokens - usedTokens);
    
    return {
      used: usedTokens,
      remaining,
      total: availableTokens,
      percentageUsed: (usedTokens / availableTokens) * 100
    };
  }

  /**
   * Check if adding a message would exceed the budget
   */
  wouldExceedBudget(
    currentTokens: number, 
    message: { role: string; content: string }
  ): boolean {
    const messageTokens = this.countMessage(message);
    const budget = this.getBudget(currentTokens);
    return messageTokens > budget.remaining;
  }

  /**
   * Calculate how many messages can fit in the remaining budget
   */
  calculateCapacity(
    currentTokens: number,
    averageMessageTokens: number = 500
  ): number {
    const budget = this.getBudget(currentTokens);
    return Math.floor(budget.remaining / averageMessageTokens);
  }

  /**
   * Split text into chunks that fit within token limits
   */
  chunkText(text: string, maxTokensPerChunk: number): string[] {
    const totalTokens = this.countText(text).tokens;
    
    if (totalTokens <= maxTokensPerChunk) {
      return [text];
    }

    const chunks: string[] = [];
    const sentences = text.split(/(?<=[.!?])\s+/);
    
    let currentChunk = '';
    let currentTokens = 0;

    for (const sentence of sentences) {
      const sentenceTokens = this.countText(sentence).tokens;
      
      if (currentTokens + sentenceTokens > maxTokensPerChunk) {
        if (currentChunk) {
          chunks.push(currentChunk.trim());
        }
        currentChunk = sentence;
        currentTokens = sentenceTokens;
      } else {
        currentChunk += ' ' + sentence;
        currentTokens += sentenceTokens;
      }
    }

    if (currentChunk.trim()) {
      chunks.push(currentChunk.trim());
    }

    return chunks;
  }

  /**
   * Find the optimal cutoff point for message truncation
   */
  findOptimalCutoff(
    messages: Array<{ role: string; content: string }>,
    targetTokens: number
  ): number {
    let accumulated = 0;
    
    for (let i = 0; i < messages.length; i++) {
      const msgTokens = this.countMessage(messages[i]);
      if (accumulated + msgTokens > targetTokens) {
        return i;
      }
      accumulated += msgTokens;
    }
    
    return messages.length;
  }

  /**
   * Estimate tokens for different content types
   */
  estimateContentTokens(content: unknown): number {
    if (typeof content === 'string') {
      return this.countText(content).tokens;
    }
    
    if (Array.isArray(content)) {
      return this.countText(JSON.stringify(content)).tokens;
    }
    
    if (typeof content === 'object' && content !== null) {
      return this.countText(JSON.stringify(content)).tokens;
    }
    
    return 0;
  }
}

// Singleton instance with default settings
export const defaultTokenCounter = new TokenCounter();

/**
 * Quick utility functions
 */
export function countTokens(text: string): number {
  return defaultTokenCounter.countText(text).tokens;
}

export function countMessagesTokens(
  messages: Array<{ role: string; content: string }>
): number {
  return defaultTokenCounter.countConversation(messages).total;
}