#!/usr/bin/env python3
"""
session_reader.py — Parse Hermes session JSONL transcripts.

Each line in a session file is a JSON object representing a message.
Standard fields: role (user|assistant|system), content (str), timestamp (str).
Tool calls and tool results are also captured.
"""

import json
import sys
from pathlib import Path
from typing import Iterator, Optional


def read_session(path: str) -> list[dict]:
    """Read a session JSONL file and return all messages as a list."""
    messages = []
    with open(path, 'r', encoding='utf-8') as f:
        for line_num, line in enumerate(f, 1):
            line = line.strip()
            if not line:
                continue
            try:
                msg = json.loads(line)
                messages.append(msg)
            except json.JSONDecodeError as e:
                print(f"WARNING: Skipping malformed JSON at line {line_num}: {e}", file=sys.stderr)
    return messages


def read_session_iter(path: str) -> Iterator[dict]:
    """Iterate over session messages without loading all into memory."""
    with open(path, 'r', encoding='utf-8') as f:
        for line_num, line in enumerate(f, 1):
            line = line.strip()
            if not line:
                continue
            try:
                yield json.loads(line)
            except json.JSONDecodeError as e:
                print(f"WARNING: Skipping malformed JSON at line {line_num}: {e}", file=sys.stderr)


def extract_conversation(messages: list[dict]) -> list[dict]:
    """Extract user/assistant conversation turns, skipping tool-only messages."""
    conversation = []
    for msg in messages:
        role = msg.get('role', '')
        content = msg.get('content', '')
        
        # Skip empty messages and pure tool calls
        if role in ('user', 'assistant', 'system'):
            if isinstance(content, str) and content.strip():
                conversation.append({
                    'role': role,
                    'content': content.strip(),
                    'timestamp': msg.get('timestamp', '')
                })
            elif isinstance(content, list):
                # Multimodal content — extract text parts
                text_parts = []
                for part in content:
                    if isinstance(part, dict) and part.get('type') == 'text':
                        text_parts.append(part.get('text', ''))
                if text_parts:
                    conversation.append({
                        'role': role,
                        'content': '\n'.join(text_parts),
                        'timestamp': msg.get('timestamp', '')
                    })
    return conversation


def truncate_for_context(messages: list[dict], head: int = 50, tail: int = 50) -> list[dict]:
    """Truncate long sessions: keep first N + last N messages.
    
    This preserves session start (initial context) and end (final results),
    skipping the messy middle of long debugging sessions.
    """
    if len(messages) <= head + tail:
        return messages
    
    truncated = messages[:head]
    truncated.append({
        'role': 'system',
        'content': f'[{len(messages) - head - tail} messages truncated]',
        'timestamp': ''
    })
    truncated.extend(messages[-tail:])
    return truncated


def messages_to_text(messages: list[dict]) -> str:
    """Convert message list to plain text for LLM consumption."""
    lines = []
    for msg in messages:
        role = msg.get('role', 'unknown').upper()
        content = msg.get('content', '')
        if msg.get('role') == 'system' and 'truncated' in content:
            lines.append(f'--- {content} ---')
        else:
            lines.append(f'{role}: {content}')
    return '\n\n'.join(lines)


def get_session_metadata(path: str) -> dict:
    """Extract metadata from a session file (first message often has config info)."""
    messages = read_session(path)
    if not messages:
        return {'path': path, 'message_count': 0}
    
    first = messages[0]
    last = messages[-1]
    
    return {
        'path': path,
        'message_count': len(messages),
        'first_timestamp': first.get('timestamp', ''),
        'last_timestamp': last.get('timestamp', ''),
        'first_role': first.get('role', ''),
        'has_tool_calls': any(m.get('tool_calls') for m in messages),
    }


if __name__ == '__main__':
    if len(sys.argv) < 2:
        print(f"Usage: {sys.argv[0]} <session.jsonl>")
        sys.exit(1)
    
    path = sys.argv[1]
    meta = get_session_metadata(path)
    print(json.dumps(meta, indent=2))
    
    messages = read_session(path)
    conv = extract_conversation(messages)
    print(f"\nConversation: {len(conv)} turns")
    
    truncated = truncate_for_context(conv)
    print(f"After truncation: {len(truncated)} turns")
    print(f"\nPreview (first 500 chars):")
    print(messages_to_text(truncated[:5])[:500])