"""
Deterministic ensemble merge for semantic index generation.

All functions are pure Python with zero LLM calls. Fully testable with mock data.

Cross-references N semantic_index outputs (generated with different temperatures)
and produces a single merged index with confidence scores.

Used by: step1_semantic_index.py
Tested by: tests/test_ensemble_merge.py
"""

from collections import defaultdict
from difflib import SequenceMatcher


# =============================================================================
# Concept Name Similarity
# =============================================================================

def concept_name_similarity(name_a: str, name_b: str) -> float:
    """Compute similarity between two concept names for cross-version matching.

    Strategy (in order of precedence):
      1. Exact string match -> 1.0
      2. Substring containment (one is a substring of the other) -> 0.9
      3. SequenceMatcher ratio on character sequences -> 0.0-1.0

    Returns:
        float in [0.0, 1.0] where >= 0.7 means "likely the same concept".
    """
    if name_a == name_b:
        return 1.0

    # Substring containment: one name is contained in the other
    if name_a in name_b or name_b in name_a:
        # Only count as similar if they're of comparable length
        # (avoid matching "国内" with "国内行车娱乐限制")
        len_ratio = min(len(name_a), len(name_b)) / max(len(name_a), len(name_b))
        if len_ratio >= 0.5:
            return 0.85 + 0.05 * len_ratio  # range 0.875-0.90
        return 0.55  # too different in length → below threshold

    return SequenceMatcher(None, name_a, name_b).ratio()


# =============================================================================
# Concept Clustering & Merging
# =============================================================================

def cluster_concepts(
    all_concepts_lists: list[list[dict]],
    similarity_threshold: float = 0.7,
) -> list[list[tuple[int, dict]]]:
    """Group concepts across ensemble versions by name similarity.

    Uses greedy single-pass clustering: for each concept, find the best-matching
    existing cluster. If max similarity >= threshold, add to it; otherwise,
    create a new cluster.

    Args:
        all_concepts_lists: List of concept lists, one per ensemble version.
                            all_concepts_lists[i] = concepts from version i.
        similarity_threshold: Minimum name similarity to join a cluster.

    Returns:
        List of clusters. Each cluster is list of (version_idx, concept_dict).
    """
    clusters = []  # type: list[list[tuple[int, dict]]]

    for version_idx, concepts in enumerate(all_concepts_lists):
        for c in concepts:
            name = c.get("name", "")
            if not name:
                continue

            best_cluster = None
            best_sim = 0.0

            for cluster in clusters:
                # Compare against the first member of the cluster (seed)
                seed_name = cluster[0][1].get("name", "")
                sim = concept_name_similarity(name, seed_name)
                if sim > best_sim:
                    best_sim = sim
                    best_cluster = cluster

            if best_cluster is not None and best_sim >= similarity_threshold:
                best_cluster.append((version_idx, c))
            else:
                clusters.append([(version_idx, c)])

    return clusters


def merge_concept_cluster(
    cluster: list[tuple[int, dict]],
    total_versions: int,
) -> tuple[dict, str]:
    """Merge a single cluster of matched concepts into one concept dict.

    Rules:
      - name: Longest name (most specific). Tie-break by lower version_idx.
      - aliases: Union of all aliases across versions.
      - defined_in: Union of all defined_in across versions.
      - parent: Most common non-null parent (voting). Tie-break by lower version_idx.

    Returns:
        (merged_concept_dict, confidence_level) where confidence is "high"/"medium"/"low".
    """
    if not cluster:
        return {}, "low"

    # --- name: longest (most specific) ---
    best_name = ""
    best_name_len = 0
    for v_idx, c in cluster:
        n = c.get("name", "")
        if len(n) > best_name_len:
            best_name = n
            best_name_len = len(n)
        elif len(n) == best_name_len and v_idx < cluster[0][0]:  # lower version idx
            best_name = n

    # --- aliases: union ---
    aliases = set()
    for _, c in cluster:
        for a in c.get("aliases", []):
            aliases.add(a)

    # --- defined_in: union ---
    defined_in = set()
    for _, c in cluster:
        for d in c.get("defined_in", []):
            defined_in.add(d)

    # --- parent: most common non-null parent (vote) ---
    parent_votes = defaultdict(int)
    for v_idx, c in cluster:
        p = c.get("parent")
        if p is not None:
            parent_votes[p] += 1

    if parent_votes:
        best_parent = max(parent_votes, key=lambda p: (parent_votes[p], -1))
    else:
        best_parent = None

    # --- confidence ---
    versions_present = len({v_idx for v_idx, _ in cluster})
    confidence = compute_confidence_versions(versions_present, total_versions,
                                              any(v_idx == 0 for v_idx, _ in cluster))

    merged = {
        "name": best_name,
        "aliases": sorted(aliases),
        "defined_in": sorted(defined_in),
        "parent": best_parent,
        "confidence": confidence,
    }
    return merged, confidence


# =============================================================================
# Unit Similarity Functions
# =============================================================================

def _collect_logic_tree_nodes(unit: dict) -> set[str]:
    """Extract the flattened set of all logic tree node IDs from a function_unit."""
    nodes = set()
    for src in unit.get("sources", []):
        if src.get("type") == "logic_tree":
            nodes.update(src.get("logic_tree_nodes", []))
    return nodes


def unit_node_jaccard(unit_a: dict, unit_b: dict) -> float:
    """Compute Jaccard similarity on logic tree node sets between two units.

    Jaccard(A, B) = |A ∩ B| / |A ∪ B|. Returns 0.0 if both have no nodes.
    """
    nodes_a = _collect_logic_tree_nodes(unit_a)
    nodes_b = _collect_logic_tree_nodes(unit_b)

    if not nodes_a and not nodes_b:
        return 0.0
    if not nodes_a or not nodes_b:
        return 0.0

    intersection = nodes_a & nodes_b
    union = nodes_a | nodes_b
    return len(intersection) / len(union)


def path_similarity(path_a: list[str], path_b: list[str]) -> float:
    """Compute similarity between two path arrays.

    Hybrid approach:
      - Sequential similarity (order-aware): SequenceMatcher on joined strings.
      - Set similarity (order-independent): Jaccard on path element sets.
      - Final score: 0.5 * seq_sim + 0.5 * set_sim

    Returns:
        float in [0.0, 1.0].
    """
    if not path_a and not path_b:
        return 1.0
    if not path_a or not path_b:
        return 0.0

    # Sequential similarity
    joined_a = "|".join(path_a)
    joined_b = "|".join(path_b)
    seq_sim = SequenceMatcher(None, joined_a, joined_b).ratio()

    # Set similarity
    set_a = set(path_a)
    set_b = set(path_b)
    set_sim = len(set_a & set_b) / len(set_a | set_b)

    return 0.5 * seq_sim + 0.5 * set_sim


def unit_similarity(unit_a: dict, unit_b: dict) -> float:
    """Combined similarity between two function_units.

    Weighted combination:
      - 0.6 * unit_node_jaccard  (primary signal: same logic tree nodes = same rule)
      - 0.4 * path_similarity    (secondary signal: semantic agreement)

    Returns:
        float in [0.0, 1.0]. >= 0.5 means "likely the same function_unit".
    """
    return 0.6 * unit_node_jaccard(unit_a, unit_b) + 0.4 * path_similarity(
        unit_a.get("path", []), unit_b.get("path", [])
    )


# =============================================================================
# Function Unit Clustering & Merging
# =============================================================================

def cluster_function_units(
    all_units_lists: list[list[dict]],
    similarity_threshold: float = 0.5,
) -> list[list[tuple[int, dict]]]:
    """Group function_units across ensemble versions by content similarity.

    Lowest-temperature versions are processed first (most stable → cluster seeds).
    Higher-temperature variants join existing clusters if similar enough.

    Args:
        all_units_lists: List of unit lists, one per ensemble version.
        similarity_threshold: Minimum unit_similarity to join a cluster.

    Returns:
        List of clusters. Each cluster is list of (version_idx, unit_dict).
    """
    clusters = []  # type: list[list[tuple[int, dict]]]

    for version_idx, units in enumerate(all_units_lists):
        for unit in units:
            best_cluster = None
            best_sim = 0.0

            for cluster in clusters:
                # Compare against all members already in the cluster
                cluster_sim = max(
                    unit_similarity(unit, existing_unit)
                    for (_, existing_unit) in cluster
                )
                if cluster_sim > best_sim:
                    best_sim = cluster_sim
                    best_cluster = cluster

            if best_cluster is not None and best_sim >= similarity_threshold:
                best_cluster.append((version_idx, unit))
            else:
                clusters.append([(version_idx, unit)])

    return clusters


def pick_best_representative(
    cluster: list[tuple[int, dict]],
) -> dict:
    """Select the best function_unit from a cluster as the merged representative.

    Scoring formula (all normalized to [0, 1]):
      - 0.35: Node count (more logic_tree_nodes = more complete trace)
      - 0.25: Source count (more sources = more evidence)
      - 0.20: Description length (longer = more detail, capped at 500 chars)
      - 0.20: Temperature rank (lower version_idx = lower temp = more stable)

    Returns a deep copy of the winning unit dict.
    """
    if not cluster:
        return {}

    # Compute max values for normalization
    max_nodes = max(
        len(_collect_logic_tree_nodes(unit)) for _, unit in cluster
    )
    max_sources = max(
        len(unit.get("sources", [])) for _, unit in cluster
    )
    max_desc_len = max(
        len(unit.get("description", "")) for _, unit in cluster
    )
    max_version_idx = max(v_idx for v_idx, _ in cluster)
    num_versions = len(cluster)

    def score(v_idx: int, unit: dict) -> float:
        nodes = len(_collect_logic_tree_nodes(unit))
        sources = len(unit.get("sources", []))
        desc_len = min(len(unit.get("description", "")), 500)
        temp_rank = 1.0 - (v_idx / max(num_versions, max_version_idx + 1))

        return (
            0.35 * (nodes / max(1, max_nodes))
            + 0.25 * (sources / max(1, max_sources))
            + 0.20 * (desc_len / max(1, max_desc_len))
            + 0.20 * temp_rank
        )

    best = max(cluster, key=lambda x: score(x[0], x[1]))
    return dict(best[1])  # deep-ish copy (1 level)


def merge_unit_sources(
    cluster: list[tuple[int, dict]],
) -> list[dict]:
    """Union all sources from units in a cluster, deduplicating by (type, image_id, section).

    When the same source key appears in multiple versions, keeps the one with
    the most logic_tree_nodes.
    """
    # Group by dedup key
    source_groups = defaultdict(list)

    for v_idx, unit in cluster:
        for src in unit.get("sources", []):
            # Build a dedup key
            src_type = src.get("type", "")
            if src_type == "logic_tree":
                key = ("logic_tree", src.get("image_id", ""))
            else:
                key = (src_type, src.get("section", ""), src.get("row", ""))

            source_groups[key].append(src)

    # Pick best per group
    result = []
    for key, sources in source_groups.items():
        # Pick the source with the most logic_tree_nodes (if any)
        best = max(sources, key=lambda s: len(s.get("logic_tree_nodes", [])))
        result.append(dict(best))

    return result


def compute_confidence_versions(
    versions_present: int,
    total_versions: int,
    includes_lowest_temp: bool = False,
) -> str:
    """Compute 3-level confidence based on cross-version agreement.

    - "high": Appears in all versions, OR >= 2/3 with lowest-temp version (T=0.0).
    - "medium": Appears in >= half the versions but not all.
    - "low": Appears in fewer than half (singleton in ensemble).

    Args:
        versions_present: Number of versions this item appeared in.
        total_versions: Total number of ensemble versions.
        includes_lowest_temp: Whether the item appeared in the T=0.0 version.
    """
    ratio = versions_present / total_versions

    if ratio >= 1.0:
        return "high"
    if ratio >= 0.5 and includes_lowest_temp:
        return "high"
    if ratio >= 0.5:
        return "medium"
    return "low"


def ensemble_merge_concepts(
    all_concepts_lists: list[list[dict]],
) -> list[dict]:
    """Merge concepts across all ensemble versions.

    Returns:
        List of merged concept dicts, each with added "confidence" field.
    """
    total = len(all_concepts_lists)
    clusters = cluster_concepts(all_concepts_lists)
    merged = []
    seen_names = set()

    for cluster in clusters:
        concept, confidence = merge_concept_cluster(cluster, total)
        name = concept.get("name", "")
        if name and name not in seen_names:
            concept["ensemble_support"] = f"{len({v for v, _ in cluster})}/{total}"
            merged.append(concept)
            seen_names.add(name)

    # Sort: high confidence first, then by name
    conf_order = {"high": 0, "medium": 1, "low": 2}
    merged.sort(key=lambda c: (conf_order.get(c.get("confidence", "low"), 3), c.get("name", "")))

    # Validate and fix parent references
    merged = _validate_concept_parents(merged)

    return merged


def _validate_concept_parents(concepts: list[dict]) -> list[dict]:
    """Post-merge: validate that every concept's parent exists in the list.

    Strategy for dangling parents:
      1. Fuzzy match (concept_name_similarity >= 0.7) → fix reference
      2. No match → set parent to null, downgrade confidence to "low"
    """
    concept_names = {c["name"] for c in concepts}
    conf_order = {"high": 0, "medium": 1, "low": 2}

    for c in concepts:
        parent = c.get("parent")
        if parent is None:
            continue
        if parent in concept_names:
            continue

        # Dangling parent — try fuzzy match
        best_match = None
        best_sim = 0.0
        for name in concept_names:
            sim = concept_name_similarity(parent, name)
            if sim > best_sim:
                best_sim = sim
                best_match = name

        if best_match and best_sim >= 0.7:
            c["parent"] = best_match
            # Downgrade if match was fuzzy (not exact)
            if best_sim < 1.0:
                current_conf = c.get("confidence", "low")
                c["confidence"] = _downgrade_confidence(current_conf)
        else:
            c["parent"] = None
            c["confidence"] = _downgrade_confidence(c.get("confidence", "low"))

    # Re-sort after confidence changes
    concepts.sort(key=lambda c: (conf_order.get(c.get("confidence", "low"), 3), c.get("name", "")))
    return concepts


def _downgrade_confidence(current: str) -> str:
    """Drop confidence one level."""
    if current == "high":
        return "medium"
    return "low"


def ensemble_merge_function_units(
    all_units_lists: list[list[dict]],
) -> list[dict]:
    """Merge function_units across all ensemble versions.

    1. Cluster units across versions.
    2. For each cluster: pick best, merge sources, compute confidence.
    3. Reassign stable unit_ids: FU-ENS-001, FU-ENS-002, ...

    Returns:
        List of merged function_unit dicts with added "confidence",
        "ensemble_support", "source_versions" fields.
    """
    total = len(all_units_lists)
    clusters = cluster_function_units(all_units_lists)

    merged = []
    for cluster in clusters:
        # Pick best representative
        best = pick_best_representative(cluster)

        # Merge sources from all cluster members
        best["sources"] = merge_unit_sources(cluster)

        # Compute confidence
        versions_present = len({v_idx for v_idx, _ in cluster})
        includes_t0 = any(v_idx == 0 for v_idx, _ in cluster)
        confidence = compute_confidence_versions(
            versions_present, total, includes_t0
        )

        best["confidence"] = confidence
        best["ensemble_support"] = f"{versions_present}/{total}"
        best["source_versions"] = versions_present

        merged.append(best)

    # Sort by confidence desc, then by unit_id
    conf_order = {"high": 0, "medium": 1, "low": 2}
    merged.sort(key=lambda u: (conf_order.get(u.get("confidence", "low"), 3),
                                 u.get("unit_id", "")))

    # Reassign stable unit_ids
    for i, unit in enumerate(merged):
        # Preserve original unit_id for traceability
        if "original_unit_id" not in unit:
            unit["original_unit_id"] = unit.get("unit_id", "")
        unit["unit_id"] = f"FU-ENS-{i + 1:03d}"

    return merged


# =============================================================================
# Top-Level Ensemble Merge
# =============================================================================

def ensemble_merge(
    semantic_indices: list[dict],
) -> dict:
    """Merge N semantic index outputs into one ensemble result.

    Args:
        semantic_indices: List of semantic_index dicts from each temperature run.
                          semantic_indices[0] should be the lowest-temperature version.

    Returns:
        Merged semantic_index dict with structure:
        {
            "feature_name": str,
            "ensemble_versions": int,
            "concepts": [...],
            "function_units": [...],
            "confidence_summary": {...},
        }
    """
    if not semantic_indices:
        return {
            "feature_name": "",
            "ensemble_versions": 0,
            "concepts": [],
            "function_units": [],
            "confidence_summary": {},
        }

    total = len(semantic_indices)

    # Extract concepts and function_units from each version
    all_concepts = [si.get("concepts", []) for si in semantic_indices]
    all_units = [si.get("function_units", []) for si in semantic_indices]

    # Merge
    merged_concepts = ensemble_merge_concepts(all_concepts)
    merged_units = ensemble_merge_function_units(all_units)

    # Feature name: majority vote across versions
    feature_names = [si.get("feature_name", "") for si in semantic_indices]
    name_counts = defaultdict(int)
    for fn in feature_names:
        if fn:
            name_counts[fn] += 1
    feature_name = max(name_counts, key=name_counts.get) if name_counts else ""

    # Confidence summary
    unit_conf = defaultdict(int)
    for u in merged_units:
        unit_conf[u.get("confidence", "low")] += 1
    concept_conf = defaultdict(int)
    for c in merged_concepts:
        concept_conf[c.get("confidence", "low")] += 1

    return {
        "feature_name": feature_name,
        "ensemble_versions": total,
        "concepts": merged_concepts,
        "function_units": merged_units,
        "confidence_summary": {
            "total_units": len(merged_units),
            "high": unit_conf.get("high", 0),
            "medium": unit_conf.get("medium", 0),
            "low": unit_conf.get("low", 0),
            "total_concepts": len(merged_concepts),
            "concept_high": concept_conf.get("high", 0),
            "concept_medium": concept_conf.get("medium", 0),
            "concept_low": concept_conf.get("low", 0),
        },
    }