"""Tree-of-thought: multi-branch reasoning with evaluation and selection.

Tree-of-Thought (ToT) extends Chain-of-Thought by exploring multiple reasoning paths
and selecting the best one. This is useful for complex problems where the first
reasoning path may not be optimal.

Key concepts:
- Branch: A single reasoning path
- ThoughtNode: Hierarchical node with depth, unit_refs, children (Super Big Brain)
- Evaluation: Scoring each branch for quality
- Selection: Choosing the best branch based on evaluation
- Pruning: Discarding low-quality branches early
"""

import json
import uuid
from dataclasses import dataclass, field
from typing import Any

from fusionagi.adapters.base import LLMAdapter
from fusionagi.reasoning.cot import run_chain_of_thought, build_cot_messages
from fusionagi._logger import logger


@dataclass
class ThoughtNode:
    """Hierarchical reasoning node: supports arbitrary depth, subtree independence, unit_refs."""

    node_id: str = field(default_factory=lambda: f"node_{uuid.uuid4().hex[:12]}")
    parent_id: str | None = None
    thought: str = ""
    trace: list[str] = field(default_factory=list)
    score: float = 0.0
    children: list["ThoughtNode"] = field(default_factory=list)
    depth: int = 0
    unit_refs: list[str] = field(default_factory=list)
    metadata: dict[str, Any] = field(default_factory=dict)


def expand_node(
    node: ThoughtNode,
    new_thought: str,
    unit_refs: list[str] | None = None,
) -> ThoughtNode:
    """Create a child node under node."""
    child = ThoughtNode(
        parent_id=node.node_id,
        thought=new_thought,
        trace=node.trace + [new_thought],
        depth=node.depth + 1,
        unit_refs=unit_refs or list(node.unit_refs),
    )
    node.children.append(child)
    return child


def prune_subtree(node: ThoughtNode, prune_threshold: float) -> ThoughtNode:
    """Remove children below prune_threshold; return node."""
    node.children = [c for c in node.children if c.score >= prune_threshold]
    for c in node.children:
        prune_subtree(c, prune_threshold)
    return node


def merge_subtrees(nodes: list[ThoughtNode], threshold: float = 0.8) -> ThoughtNode | None:
    """Merge sibling nodes when they converge on same conclusion (similarity > threshold)."""
    if not nodes:
        return None
    if len(nodes) == 1:
        return nodes[0]
    best = max(nodes, key=lambda n: n.score)
    for n in nodes:
        if n is best:
            continue
        if n.score >= best.score * threshold:
            best.thought += "\n[Alternative] " + n.thought[:200]
    return best


@dataclass
class ThoughtBranch:
    """A single reasoning branch in the tree."""

    branch_id: int
    thought: str
    trace: list[str]
    score: float = 0.0
    is_terminal: bool = False
    children: list["ThoughtBranch"] = field(default_factory=list)
    metadata: dict[str, Any] = field(default_factory=dict)


@dataclass
class ToTResult:
    """Result of Tree-of-Thought reasoning."""

    best_response: str
    best_trace: list[str]
    best_score: float
    all_branches: list[ThoughtBranch]
    total_llm_calls: int
    selection_reason: str


# System prompts for ToT
TOT_GENERATION_SYSTEM = """You are exploring different approaches to solve a problem.
Generate a distinct reasoning approach. Be creative and consider different angles.
State your thought process clearly step by step."""

TOT_EVALUATION_SYSTEM = """You are evaluating the quality of reasoning approaches.
Score each approach from 0 to 1 based on:
- Logical soundness (is the reasoning valid?)
- Completeness (does it address all aspects?)
- Clarity (is it easy to follow?)
- Practicality (can it be implemented?)
Output ONLY a JSON object: {"score": 0.X, "reason": "brief explanation"}"""


def _generate_branch(
    adapter: LLMAdapter,
    query: str,
    context: str | None,
    branch_num: int,
    previous_branches: list[ThoughtBranch],
    **kwargs: Any,
) -> ThoughtBranch:
    """Generate a single reasoning branch."""
    # Build prompt that encourages diverse thinking
    diversity_hint = ""
    if previous_branches:
        prev_summaries = [
            f"Approach {b.branch_id}: {b.thought[:100]}..."
            for b in previous_branches
        ]
        diversity_hint = f"\n\nPrevious approaches tried:\n" + "\n".join(prev_summaries)
        diversity_hint += "\n\nGenerate a DIFFERENT approach."
    
    messages = [
        {"role": "system", "content": TOT_GENERATION_SYSTEM},
        {
            "role": "user",
            "content": f"Query: {query}{diversity_hint}" + (f"\n\nContext: {context}" if context else ""),
        },
    ]
    
    response = adapter.complete(messages, **kwargs)
    
    return ThoughtBranch(
        branch_id=branch_num,
        thought=response,
        trace=[response],
    )


def _evaluate_branch(
    adapter: LLMAdapter,
    branch: ThoughtBranch,
    query: str,
    **kwargs: Any,
) -> float:
    """Evaluate a reasoning branch and return a score."""
    messages = [
        {"role": "system", "content": TOT_EVALUATION_SYSTEM},
        {
            "role": "user",
            "content": f"Query: {query}\n\nReasoning approach:\n{branch.thought}\n\nScore this approach.",
        },
    ]
    
    response = adapter.complete(messages, **kwargs)
    
    # Parse score from response
    try:
        # Try to extract JSON
        if "{" in response:
            json_start = response.index("{")
            json_end = response.rindex("}") + 1
            json_str = response[json_start:json_end]
            result = json.loads(json_str)
            score = float(result.get("score", 0.5))
            branch.metadata["evaluation_reason"] = result.get("reason", "")
            return max(0.0, min(1.0, score))  # Clamp to [0, 1]
    except (json.JSONDecodeError, ValueError, KeyError):
        pass
    
    # Fallback: try to extract a number
    import re
    numbers = re.findall(r"0?\.\d+|1\.0|[01]", response)
    if numbers:
        try:
            return max(0.0, min(1.0, float(numbers[0])))
        except ValueError:
            pass
    
    return 0.5  # Default score if parsing fails


def _select_best_branch(branches: list[ThoughtBranch]) -> tuple[ThoughtBranch, str]:
    """Select the best branch based on scores."""
    if not branches:
        raise ValueError("No branches to select from")
    
    if len(branches) == 1:
        return branches[0], "Only one branch available"
    
    # Sort by score descending
    sorted_branches = sorted(branches, key=lambda b: b.score, reverse=True)
    best = sorted_branches[0]
    
    # Check if there's a clear winner
    if len(sorted_branches) > 1:
        score_diff = best.score - sorted_branches[1].score
        if score_diff > 0.2:
            reason = f"Clear winner with score {best.score:.2f} (next best: {sorted_branches[1].score:.2f})"
        else:
            reason = f"Selected highest score {best.score:.2f} among close alternatives"
    else:
        reason = f"Single branch with score {best.score:.2f}"
    
    return best, reason


def run_tree_of_thought(
    adapter: LLMAdapter,
    query: str,
    context: str | None = None,
    max_branches: int = 3,
    depth: int = 1,
    prune_threshold: float = 0.3,
    **kwargs: Any,
) -> tuple[str, list[str]]:
    """
    Run Tree-of-Thought reasoning with multiple branches.
    
    Args:
        adapter: LLM adapter for generation and evaluation.
        query: The question or problem to reason about.
        context: Optional context to include.
        max_branches: Maximum number of reasoning branches to explore.
        depth: Number of refinement iterations (1 = single pass, 2+ = iterative refinement).
        prune_threshold: Minimum score to keep a branch (branches below are pruned).
        **kwargs: Additional arguments passed to adapter.complete().
    
    Returns:
        Tuple of (best_response, trace_list).
    """
    if max_branches < 1:
        max_branches = 1
    
    if max_branches == 1:
        # Fall back to simple CoT for single branch
        return run_chain_of_thought(adapter, query, context=context, **kwargs)
    
    logger.info(
        "Starting Tree-of-Thought",
        extra={"query_length": len(query), "max_branches": max_branches, "depth": depth},
    )
    
    total_llm_calls = 0
    branches: list[ThoughtBranch] = []
    
    # Generate initial branches
    for i in range(max_branches):
        branch = _generate_branch(adapter, query, context, i, branches, **kwargs)
        total_llm_calls += 1
        branches.append(branch)
    
    # Evaluate all branches
    for branch in branches:
        branch.score = _evaluate_branch(adapter, branch, query, **kwargs)
        total_llm_calls += 1
    
    # Prune low-quality branches
    branches = [b for b in branches if b.score >= prune_threshold]
    
    if not branches:
        # All branches pruned - fall back to CoT
        logger.warning("All ToT branches pruned, falling back to CoT")
        return run_chain_of_thought(adapter, query, context=context, **kwargs)
    
    # Iterative refinement for depth > 1
    for d in range(1, depth):
        refined_branches = []
        for branch in branches:
            # Generate a refined version
            refinement_prompt = f"""Original approach:
{branch.thought}

Score: {branch.score:.2f}
Feedback: {branch.metadata.get('evaluation_reason', 'N/A')}

Improve this approach based on the feedback. Make it more complete and rigorous."""
            
            messages = [
                {"role": "system", "content": TOT_GENERATION_SYSTEM},
                {"role": "user", "content": f"Query: {query}\n\n{refinement_prompt}"},
            ]
            
            refined_thought = adapter.complete(messages, **kwargs)
            total_llm_calls += 1
            
            refined_branch = ThoughtBranch(
                branch_id=branch.branch_id,
                thought=refined_thought,
                trace=branch.trace + [f"[Refinement {d}] {refined_thought}"],
            )
            
            refined_branch.score = _evaluate_branch(adapter, refined_branch, query, **kwargs)
            total_llm_calls += 1
            
            # Keep the better version
            if refined_branch.score > branch.score:
                refined_branches.append(refined_branch)
            else:
                refined_branches.append(branch)
        
        branches = refined_branches
    
    # Select the best branch
    best_branch, selection_reason = _select_best_branch(branches)
    
    logger.info(
        "Tree-of-Thought completed",
        extra={
            "best_score": best_branch.score,
            "total_branches": len(branches),
            "total_llm_calls": total_llm_calls,
        },
    )
    
    # Build comprehensive trace
    trace = [
        f"[ToT Branch {best_branch.branch_id}] Score: {best_branch.score:.2f}",
        best_branch.thought,
    ]
    if best_branch.metadata.get("evaluation_reason"):
        trace.append(f"[Evaluation] {best_branch.metadata['evaluation_reason']}")
    trace.append(f"[Selection] {selection_reason}")
    
    return best_branch.thought, trace


def run_tree_of_thought_detailed(
    adapter: LLMAdapter,
    query: str,
    context: str | None = None,
    max_branches: int = 3,
    depth: int = 1,
    prune_threshold: float = 0.3,
    **kwargs: Any,
) -> ToTResult:
    """
    Run Tree-of-Thought and return detailed results including all branches.
    
    Same as run_tree_of_thought but returns a ToTResult with full information.
    """
    if max_branches < 1:
        max_branches = 1
    
    if max_branches == 1:
        response, trace = run_chain_of_thought(adapter, query, context=context, **kwargs)
        single_branch = ThoughtBranch(branch_id=0, thought=response, trace=trace, score=0.5)
        return ToTResult(
            best_response=response,
            best_trace=trace,
            best_score=0.5,
            all_branches=[single_branch],
            total_llm_calls=1,
            selection_reason="Single branch (CoT mode)",
        )
    
    total_llm_calls = 0
    branches: list[ThoughtBranch] = []
    
    # Generate and evaluate branches
    for i in range(max_branches):
        branch = _generate_branch(adapter, query, context, i, branches, **kwargs)
        total_llm_calls += 1
        branch.score = _evaluate_branch(adapter, branch, query, **kwargs)
        total_llm_calls += 1
        branches.append(branch)
    
    all_branches = list(branches)  # Keep all for result
    
    # Prune
    branches = [b for b in branches if b.score >= prune_threshold]
    
    if not branches:
        # Use best of all branches even if below threshold
        branches = sorted(all_branches, key=lambda b: b.score, reverse=True)[:1]
    
    # Select best
    best_branch, selection_reason = _select_best_branch(branches)
    
    return ToTResult(
        best_response=best_branch.thought,
        best_trace=best_branch.trace,
        best_score=best_branch.score,
        all_branches=all_branches,
        total_llm_calls=total_llm_calls,
        selection_reason=selection_reason,
    )