from shapely.geometry import box as shapely_box, Point
from collections import defaultdict, deque
import math


MAX_FALLBACK_DIST = 150  # pixels

def map_arrows(nodes, arrows):
    """
    Map arrows to node boxes using geometric containment with fallback to nearest box.
    Returns directional edges (source_id, target_id, label).

    Args:
        nodes (list): List of node dicts with 'bbox' field.
        arrows (list): List of arrow dicts with 'tail' and 'head' coordinates.

    Returns:
        list: List of (source, target, label) tuples.
    """
    for node in nodes:
        node["shape"] = shapely_box(*node["bbox"])
        node["center"] = (
            (node["bbox"][0] + node["bbox"][2]) // 2,
            (node["bbox"][1] + node["bbox"][3]) // 2
        )

    edges = []

    def find_nearest_node(pt):
        min_dist = float("inf")
        nearest_id = None
        for n in nodes:
            cx, cy = n["center"]
            dist = math.dist(pt, (cx, cy))
            if dist < min_dist:
                min_dist = dist
                nearest_id = n["id"]
        return nearest_id, min_dist

    for arrow in arrows:
        if not isinstance(arrow, dict) or not isinstance(arrow.get("tail"), (tuple, list)) or not isinstance(arrow.get("head"), (tuple, list)):
            print(f"⚠️ Skipping malformed arrow: {arrow}")
            continue

        tail_pt = Point(arrow["tail"])
        head_pt = Point(arrow["head"])
        label = arrow.get("label", "").strip()

        source = next((n["id"] for n in nodes if n["shape"].buffer(10).contains(tail_pt)), None)
        target = next((n["id"] for n in nodes if n["shape"].buffer(10).contains(head_pt)), None)

        # Fallback to nearest node if not found
        if not source:
            source, dist = find_nearest_node(arrow["tail"])
            if dist > MAX_FALLBACK_DIST:
                source = None
        if not target:
            target, dist = find_nearest_node(arrow["head"])
            if dist > MAX_FALLBACK_DIST:
                target = None

        if source and target and source != target:
            print(f"✅ Mapped arrow from {source} → {target} [{label}]")
            edges.append((source, target, label))
        else:
            print(f"⚠️ Could not map arrow endpoints to nodes: tail={arrow.get('tail')} head={arrow.get('head')}")

    return edges


def detect_node_type(text, default_type="process"):
    """
    Heuristically infer the node type from its text.

    Args:
        text (str): Node label.
        default_type (str): Fallback type.

    Returns:
        str: Inferred node type.
    """
    text_lower = text.lower()
    if "start" in text_lower:
        return "start"
    if "end" in text_lower or "full" in text_lower:
        return "end"
    if "?" in text or "yes" in text_lower or "no" in text_lower:
        return "decision"
    return default_type


def build_flowchart_json(nodes, arrows):
    """
    Construct a structured flowchart JSON using basic graph traversal.

    Args:
        nodes (list): Detected node dicts.
        arrows (list): Detected arrow dicts.

    Returns:
        dict: JSON with 'start' and 'steps'.
    """
    edges = map_arrows(nodes, arrows)

    # Build adjacency and reverse mappings
    graph = defaultdict(list)
    reverse_links = defaultdict(list)
    edge_labels = {}

    for src, tgt, label in edges:
        graph[src].append(tgt)
        reverse_links[tgt].append(src)
        edge_labels[(src, tgt)] = label.lower()

    all_node_ids = {n["id"] for n in nodes}
    start_candidates = [nid for nid in all_node_ids if nid not in reverse_links]

    flowchart = {
        "start": start_candidates[0] if start_candidates else None,
        "steps": []
    }

    visited = set()
    queue = deque(start_candidates)
    id_to_node = {n["id"]: n for n in nodes}

    while queue:
        curr = queue.popleft()
        if curr in visited:
            continue
        visited.add(curr)

        node = id_to_node.get(curr, {})
        text = node.get("text", "").strip()
        node_type = node.get("type") or detect_node_type(text)

        step = {
            "id": curr,
            "text": text,
            "type": node_type
        }

        parents = list(set(reverse_links[curr]))
        if len(parents) == 1:
            step["parent"] = parents[0]
        elif len(parents) > 1:
            step["parents"] = parents

        next_nodes = list(set(graph[curr]))
        if node_type == "decision" and next_nodes:
            step["branches"] = {}
            for tgt in next_nodes:
                label = edge_labels.get((curr, tgt), "")
                if "yes" in label:
                    step["branches"]["yes"] = tgt
                elif "no" in label:
                    step["branches"]["no"] = tgt
                else:
                    step["branches"].setdefault("unknown", []).append(tgt)
                if tgt not in visited:
                    queue.append(tgt)
        elif len(next_nodes) == 1:
            step["next"] = next_nodes[0]
            if next_nodes[0] not in visited:
                queue.append(next_nodes[0])
        elif len(next_nodes) > 1:
            step["next"] = next_nodes
            for n in next_nodes:
                if n not in visited:
                    queue.append(n)

        flowchart["steps"].append(step)

    return flowchart