"""Token-usage estimation for the active chain of a JSONL transcript.

v0.1 ships only `char_div_3_5` — count characters of the active chain's content
fields and divide by 3.5. This is a rough but cheap heuristic; tiktoken-based
estimation can be added later behind the same interface.
"""
from __future__ import annotations
import json
from pathlib import Path
from typing import Any

from .jsonl_ops import find_active_chain, load_messages


def _char_count(content: Any) -> int:
    if content is None:
        return 0
    if isinstance(content, str):
        return len(content)
    if isinstance(content, list):
        total = 0
        for item in content:
            if isinstance(item, dict):
                if "text" in item and isinstance(item["text"], str):
                    total += len(item["text"])
                elif "input" in item:
                    total += len(json.dumps(item.get("input", {}), ensure_ascii=False))
                elif "content" in item:
                    total += _char_count(item["content"])
            else:
                total += len(str(item))
        return total
    if isinstance(content, dict):
        return _char_count(content.get("content"))
    return len(str(content))


def _message_chars(msg: dict[str, Any]) -> int:
    inner = msg.get("message")
    if isinstance(inner, dict):
        return _char_count(inner.get("content"))
    if "tool_use_id" in msg and "content" in msg:
        return _char_count(msg.get("content"))
    return 0


def estimate_active_chain_tokens(transcript: Path, *, method: str = "char_div_3_5") -> int:
    if method != "char_div_3_5":
        raise ValueError(f"Unsupported estimate_method: {method}")
    msgs = load_messages(transcript)
    chain = find_active_chain(msgs)
    chars = sum(_message_chars(m) for m in chain)
    return int(chars / 3.5)