import json
import logging
import importlib.util
import uuid
from pathlib import Path
from typing import AsyncGenerator, Optional, Dict, Any, List, Set
import tiktoken

logger = logging.getLogger(__name__)

# ------------------------------------------------------------------------------
# Tokenizer
# ------------------------------------------------------------------------------

try:
    # cl100k_base is used by gpt-4, gpt-3.5-turbo, text-embedding-ada-002
    ENCODING = tiktoken.get_encoding("cl100k_base")
except Exception:
    ENCODING = None

THINKING_START_TAG = "<thinking>"
THINKING_END_TAG = "</thinking>"

def _pending_tag_suffix(buffer: str, tag: str) -> int:
    """Length of the suffix of buffer that matches the prefix of tag (for partial matches)."""
    if not buffer or not tag:
        return 0
    max_len = min(len(buffer), len(tag) - 1)
    for length in range(max_len, 0, -1):
        if buffer[-length:] == tag[:length]:
            return length
    return 0

def count_tokens(text: str) -> int:
    """Counts tokens with tiktoken."""
    if not text or not ENCODING:
        return 0
    return len(ENCODING.encode(text))

# ------------------------------------------------------------------------------
# Dynamic Loader
# ------------------------------------------------------------------------------

def _load_claude_parser():
    """Dynamically load claude_parser module."""
    base_dir = Path(__file__).resolve().parent
    spec = importlib.util.spec_from_file_location("v2_claude_parser", str(base_dir / "claude_parser.py"))
    module = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(module)
    return module

try:
    _parser = _load_claude_parser()
    build_message_start = _parser.build_message_start
    build_content_block_start = _parser.build_content_block_start
    build_content_block_delta = _parser.build_content_block_delta
    build_content_block_stop = _parser.build_content_block_stop
    build_ping = _parser.build_ping
    build_message_stop = _parser.build_message_stop
    build_tool_use_start = _parser.build_tool_use_start
    build_tool_use_input_delta = _parser.build_tool_use_input_delta
except Exception as e:
    logger.error(f"Failed to load claude_parser: {e}")
    # Fallback definitions
    def build_message_start(*args, **kwargs): return ""
    def build_content_block_start(*args, **kwargs): return ""
    def build_content_block_delta(*args, **kwargs): return ""
    def build_content_block_stop(*args, **kwargs): return ""
    def build_ping(*args, **kwargs): return ""
    def build_message_stop(*args, **kwargs): return ""
    def build_tool_use_start(*args, **kwargs): return ""
    def build_tool_use_input_delta(*args, **kwargs): return ""

class ClaudeStreamHandler:
    def __init__(self, model: str, input_tokens: int = 0, conversation_id: Optional[str] = None):
        self.model = model
        self.input_tokens = input_tokens
        self.response_buffer: List[str] = []
        self.content_block_index: int = -1
        self.content_block_started: bool = False
        self.content_block_start_sent: bool = False
        self.content_block_stop_sent: bool = False
        self.message_start_sent: bool = False
        self.conversation_id: Optional[str] = conversation_id

        # Tool use state
        self.current_tool_use: Optional[Dict[str, Any]] = None
        self.tool_input_buffer: List[str] = []
        self.tool_use_id: Optional[str] = None
        self.tool_name: Optional[str] = None
        self._processed_tool_use_ids: Set[str] = set()
        self.all_tool_inputs: List[str] = []
        self.has_tool_use: bool = False  # Track if any tool_use was emitted

        # Think tag state
        self.in_think_block: bool = False
        self.think_buffer: str = ""
        self.pending_start_tag_chars: int = 0

        # Response termination flag
        self.response_ended: bool = False

    async def handle_event(self, event_type: str, payload: Dict[str, Any]) -> AsyncGenerator[str, None]:
        """Process a single Amazon Q event and yield Claude SSE events."""

        # Early return if response has already ended
        if self.response_ended:
            return

        # 1. Message Start (initial-response)
        if event_type == "initial-response":
            if not self.message_start_sent:
                # Use conversation_id from payload if available, otherwise use the one passed to constructor
                conv_id = payload.get('conversationId') or self.conversation_id or str(uuid.uuid4())
                self.conversation_id = conv_id
                yield build_message_start(conv_id, self.model, self.input_tokens)
                self.message_start_sent = True
                yield build_ping()

        # 2. Content Block Delta (assistantResponseEvent)
        elif event_type == "assistantResponseEvent":
            content = payload.get("content", "")

            # Close any open tool use block
            if self.current_tool_use and not self.content_block_stop_sent:
                yield build_content_block_stop(self.content_block_index)
                self.content_block_stop_sent = True
                self.current_tool_use = None

            # Process content with think tag detection
            if content:
                self.think_buffer += content
                while self.think_buffer:
                    if self.pending_start_tag_chars > 0:
                        if len(self.think_buffer) < self.pending_start_tag_chars:
                            self.pending_start_tag_chars -= len(self.think_buffer)
                            self.think_buffer = ""
                            break
                        else:
                            self.think_buffer = self.think_buffer[self.pending_start_tag_chars:]
                            self.pending_start_tag_chars = 0
                            if not self.think_buffer:
                                break
                            continue

                    if not self.in_think_block:
                        think_start = self.think_buffer.find(THINKING_START_TAG)
                        if think_start == -1:
                            pending = _pending_tag_suffix(self.think_buffer, THINKING_START_TAG)
                            if pending == len(self.think_buffer) and pending > 0:
                                if self.content_block_start_sent:
                                    yield build_content_block_stop(self.content_block_index)
                                    self.content_block_stop_sent = True
                                    self.content_block_start_sent = False

                                self.content_block_index += 1
                                yield build_content_block_start(self.content_block_index, "thinking")
                                self.content_block_start_sent = True
                                self.content_block_started = True
                                self.content_block_stop_sent = False
                                self.in_think_block = True
                                self.pending_start_tag_chars = len(THINKING_START_TAG) - pending
                                self.think_buffer = ""
                                break

                            emit_len = len(self.think_buffer) - pending
                            if emit_len <= 0:
                                break
                            text_chunk = self.think_buffer[:emit_len]
                            if text_chunk:
                                if not self.content_block_start_sent:
                                    self.content_block_index += 1
                                    yield build_content_block_start(self.content_block_index, "text")
                                    self.content_block_start_sent = True
                                    self.content_block_started = True
                                    self.content_block_stop_sent = False
                                self.response_buffer.append(text_chunk)
                                yield build_content_block_delta(self.content_block_index, text_chunk)
                            self.think_buffer = self.think_buffer[emit_len:]
                        else:
                            before_text = self.think_buffer[:think_start]
                            if before_text:
                                if not self.content_block_start_sent:
                                    self.content_block_index += 1
                                    yield build_content_block_start(self.content_block_index, "text")
                                    self.content_block_start_sent = True
                                    self.content_block_started = True
                                    self.content_block_stop_sent = False
                                self.response_buffer.append(before_text)
                                yield build_content_block_delta(self.content_block_index, before_text)
                            self.think_buffer = self.think_buffer[think_start + len(THINKING_START_TAG):]

                            if self.content_block_start_sent:
                                yield build_content_block_stop(self.content_block_index)
                                self.content_block_stop_sent = True
                                self.content_block_start_sent = False

                            self.content_block_index += 1
                            yield build_content_block_start(self.content_block_index, "thinking")
                            self.content_block_start_sent = True
                            self.content_block_started = True
                            self.content_block_stop_sent = False
                            self.in_think_block = True
                            self.pending_start_tag_chars = 0
                    else:
                        think_end = self.think_buffer.find(THINKING_END_TAG)
                        if think_end == -1:
                            pending = _pending_tag_suffix(self.think_buffer, THINKING_END_TAG)
                            emit_len = len(self.think_buffer) - pending
                            if emit_len <= 0:
                                break
                            thinking_chunk = self.think_buffer[:emit_len]
                            if thinking_chunk:
                                yield build_content_block_delta(
                                    self.content_block_index,
                                    thinking_chunk,
                                    delta_type="thinking_delta",
                                    field_name="thinking"
                                )
                            self.think_buffer = self.think_buffer[emit_len:]
                        else:
                            thinking_chunk = self.think_buffer[:think_end]
                            if thinking_chunk:
                                yield build_content_block_delta(
                                    self.content_block_index,
                                    thinking_chunk,
                                    delta_type="thinking_delta",
                                    field_name="thinking"
                                )
                            self.think_buffer = self.think_buffer[think_end + len(THINKING_END_TAG):]

                            yield build_content_block_stop(self.content_block_index)
                            self.content_block_stop_sent = True
                            self.content_block_start_sent = False
                            self.in_think_block = False

        # 3. Tool Use (toolUseEvent)
        elif event_type == "toolUseEvent":
            tool_use_id = payload.get("toolUseId")
            tool_name = payload.get("name")
            tool_input = payload.get("input", {})
            is_stop = payload.get("stop", False)

            # Deduplication: skip if this tool_use_id was already processed and no tool is active
            # (allows input deltas to pass through when current_tool_use is set)
            if tool_use_id and tool_use_id in self._processed_tool_use_ids and not self.current_tool_use:
                logger.warning(f"Detected duplicate tool use event, toolUseId={tool_use_id}, skipping")
                return

            # Start new tool use
            if tool_use_id and tool_name and not self.current_tool_use:
                # Close previous text block if open
                if self.content_block_start_sent and not self.content_block_stop_sent:
                    yield build_content_block_stop(self.content_block_index)
                    self.content_block_stop_sent = True

                self._processed_tool_use_ids.add(tool_use_id)
                self.content_block_index += 1
                
                yield build_tool_use_start(self.content_block_index, tool_use_id, tool_name)
                
                self.content_block_started = True
                self.current_tool_use = {"toolUseId": tool_use_id, "name": tool_name}
                self.tool_use_id = tool_use_id
                self.tool_name = tool_name
                self.tool_input_buffer = []
                self.content_block_stop_sent = False
                self.content_block_start_sent = True
                self.has_tool_use = True  # Mark that we have tool_use

            # Accumulate input
            if self.current_tool_use and tool_input:
                fragment = ""
                if isinstance(tool_input, str):
                    fragment = tool_input
                else:
                    fragment = json.dumps(tool_input, ensure_ascii=False)
                
                self.tool_input_buffer.append(fragment)
                yield build_tool_use_input_delta(self.content_block_index, fragment)

            # Stop tool use
            if is_stop and self.current_tool_use:
                full_input = "".join(self.tool_input_buffer)
                self.all_tool_inputs.append(full_input)

                yield build_content_block_stop(self.content_block_index)
                # Reset state to allow next content block
                self.content_block_stop_sent = False  # Reset to False to allow next block
                self.content_block_started = False
                self.content_block_start_sent = False  # Important: reset start flag for next block
                self.current_tool_use = None
                self.tool_use_id = None
                self.tool_name = None
                self.tool_input_buffer = []

        # 4. Assistant Response End (assistantResponseEnd)
        elif event_type == "assistantResponseEnd":
            # Close any open block
            if self.content_block_started and not self.content_block_stop_sent:
                yield build_content_block_stop(self.content_block_index)
                self.content_block_stop_sent = True

            # Mark as finished to prevent processing further events
            self.response_ended = True

            # Immediately send message_stop (instead of waiting for finish())
            full_text = "".join(self.response_buffer)
            full_tool_input = "".join(self.all_tool_inputs)
            output_tokens = count_tokens(full_text) + count_tokens(full_tool_input)
            # Use "tool_use" stop_reason if any tool_use was emitted, otherwise "end_turn"
            stop_reason = "tool_use" if self.has_tool_use else "end_turn"
            yield build_message_stop(self.input_tokens, output_tokens, stop_reason)

    async def finish(self) -> AsyncGenerator[str, None]:
        """Send final events."""
        # Skip if response already ended (message_stop already sent)
        if self.response_ended:
            return

        # Flush any remaining think_buffer content
        if self.think_buffer:
            if self.in_think_block:
                # Emit remaining thinking content
                yield build_content_block_delta(
                    self.content_block_index,
                    self.think_buffer,
                    delta_type="thinking_delta",
                    field_name="thinking"
                )
            else:
                # Emit remaining text content
                if not self.content_block_start_sent:
                    self.content_block_index += 1
                    yield build_content_block_start(self.content_block_index, "text")
                    self.content_block_start_sent = True
                    self.content_block_started = True
                    self.content_block_stop_sent = False
                self.response_buffer.append(self.think_buffer)
                yield build_content_block_delta(self.content_block_index, self.think_buffer)
            self.think_buffer = ""

        # Ensure last block is closed
        if self.content_block_started and not self.content_block_stop_sent:
            yield build_content_block_stop(self.content_block_index)
            self.content_block_stop_sent = True

        # Calculate output tokens (approximate)
        full_text = "".join(self.response_buffer)
        full_tool_input = "".join(self.all_tool_inputs)
        # Simple approximation: 4 chars per token
        # output_tokens = max(1, (len(full_text) + len(full_tool_input)) // 4)
        output_tokens = count_tokens(full_text) + count_tokens(full_tool_input)

        # Use "tool_use" stop_reason if any tool_use was emitted, otherwise "end_turn"
        stop_reason = "tool_use" if self.has_tool_use else "end_turn"
        yield build_message_stop(self.input_tokens, output_tokens, stop_reason)