"""
Cross-dataset early integration (ADR-0001, Mode A — T7).

Build ONE combined AnnData from >=2 registered datasets by:
  1. harmonising each to a shared gene-symbol feature axis,
  2. intersecting features (join="inner"), and
  3. concatenating samples with a ``batch`` obs column = dataset_id.

The result is a *standard* AnnData that the existing single-dataset tools
(``decoupler_differential_expression`` and the enrichment tools) consume
unchanged — Mode A pools the matrices and a downstream DE models ``dataset_id``
as a batch covariate (see ``decoupler_differential_expression``'s
``batch_column``, T8). Whether a set of datasets is eligible for early pooling is
decided upstream by ``get_integration_plan`` (mode == "early"); this module
performs the mechanics once that verdict is in (the gating lives in the
``decoupler_integrate_datasets`` tool, T9).

Pure core: ``combine_anndatas(adatas, ...)`` operates on already-loaded AnnData
objects (unit-testable, no network). ``build_combined_anndata(dataset_ids, ...)``
is the thin loader wrapper that resolves each manifest's hosted h5ad.

v1 scope / limitations:
- Harmonises to gene symbols: a dataset whose ``feature_id_type`` is
  "gene_symbol" uses var_names directly; otherwise a var column named
  SYMBOL/gene_symbol/gene_name is used if present; anything else raises (probe
  collapse / ortholog mapping / entrez without a symbol column are NOT handled
  here — such datasets do not reach an ``early`` verdict in v1).
- Duplicate symbols within a dataset are collapsed keep-first (preserves raw
  integer counts for the DESeq2 path — no averaging).
"""

from __future__ import annotations

from collections.abc import Sequence
from pathlib import Path
from typing import TYPE_CHECKING

import anndata as ad
import numpy as np

from src.core.paths import OUTPUT_DIR

if TYPE_CHECKING:
    from anndata import AnnData

# var columns checked, in order, for a gene-symbol axis when feature_id_type
# is not already "gene_symbol".
_SYMBOL_VAR_COLUMNS = ("SYMBOL", "gene_symbol", "Gene_Symbol", "symbol", "gene_name")


def _symbol_axis(adata: AnnData, feature_id_type: str) -> list[str]:
    """Return a per-var list of gene symbols for ``adata``, or raise if unavailable."""
    if feature_id_type == "gene_symbol":
        return [str(v) for v in adata.var_names]
    for col in _SYMBOL_VAR_COLUMNS:
        if col in adata.var.columns:
            return [str(v) for v in adata.var[col].tolist()]
    raise ValueError(
        f"cannot resolve gene symbols: feature_id_type='{feature_id_type}' and no "
        f"symbol column {list(_SYMBOL_VAR_COLUMNS)} in var. Mode-A v1 needs a "
        f"gene-symbol axis (probe collapse / id-mapping is not handled here)."
    )


def _to_symbol_adata(adata: AnnData, feature_id_type: str) -> AnnData:
    """Return a copy of ``adata`` whose var_names are unique gene symbols.

    Drops features with empty/missing symbols; collapses duplicate symbols
    keep-first (preserves raw counts — no averaging)."""
    symbols = _symbol_axis(adata, feature_id_type)
    a = adata.copy()
    a.var_names = [str(s) for s in symbols]
    keep = np.array([bool(s) and s.strip().lower() not in ("nan", "none", "") for s in a.var_names])
    a = a[:, keep].copy()
    # keep-first on duplicate symbols (np.unique returns the first index per value)
    _, first_idx = np.unique(np.asarray(a.var_names, dtype=object), return_index=True)
    a = a[:, np.sort(first_idx)].copy()
    return a


def combine_anndatas(
    adatas: Sequence[AnnData],
    dataset_ids: Sequence[str],
    feature_id_types: Sequence[str],
    *,
    design_factor: str | None = None,
    batch_key: str = "batch",
    min_shared_features: int = 200,
) -> AnnData:
    """Pure core: feature-intersection concat of >=2 AnnData into one combined AnnData.

    Each input is harmonised to a unique gene-symbol var axis, the var
    intersection is taken (``join="inner"``), a ``batch_key`` obs column is set to
    the dataset_id, and samples are concatenated (obs names disambiguated per
    batch with a ``-<dataset_id>`` suffix).

    Raises
    ------
    ValueError
        on <2 inputs, mismatched argument lengths, an unresolvable symbol axis,
        a missing ``design_factor`` column in any dataset, or a feature
        intersection smaller than ``min_shared_features``.
    """
    if len(adatas) < 2:
        raise ValueError(f"early integration needs >=2 datasets; got {len(adatas)}")
    if not (len(adatas) == len(dataset_ids) == len(feature_id_types)):
        raise ValueError(
            "adatas, dataset_ids, and feature_id_types must be the same length "
            f"({len(adatas)}, {len(dataset_ids)}, {len(feature_id_types)})"
        )

    prepared: list[AnnData] = []
    for a, did, fit in zip(adatas, dataset_ids, feature_id_types, strict=True):
        sa = _to_symbol_adata(a, fit)
        if design_factor is not None and design_factor not in sa.obs.columns:
            raise ValueError(
                f"dataset '{did}' has no obs column '{design_factor}' required for "
                f"the requested contrast."
            )
        prepared.append(sa)

    shared = set(prepared[0].var_names)
    for sa in prepared[1:]:
        shared &= set(sa.var_names)
    if len(shared) < min_shared_features:
        raise ValueError(
            f"only {len(shared)} shared gene symbols across {list(dataset_ids)} "
            f"(minimum {min_shared_features}); the datasets likely do not share a "
            f"feature space and are not eligible for early pooling."
        )

    combined = ad.concat(
        prepared,
        axis=0,
        join="inner",  # feature intersection
        label=batch_key,
        keys=[str(d) for d in dataset_ids],
        index_unique="-",  # disambiguate duplicate sample barcodes across cohorts
        merge="same",
    )
    combined.obs[batch_key] = combined.obs[batch_key].astype("category")
    return combined


def _resolve_to_local(url_or_path: str) -> tuple[str, bool]:
    """Return (local_path, is_temp). Downloads http(s)/ftp URLs to a temp file.

    Delegates to the shared authenticated resolver so private huggingface.co
    files download with HF_TOKEN (see src/core/data_io.py)."""
    from src.core.data_io import resolve_to_local_path

    return resolve_to_local_path(url_or_path)


def build_combined_anndata(
    dataset_ids: Sequence[str],
    *,
    design_factor: str | None = None,
    batch_key: str = "batch",
    min_shared_features: int = 200,
    out_prefix: str | None = None,
) -> dict:
    """Loader wrapper: resolve each registered dataset's hosted h5ad and combine.

    Resolves each ``dataset_id`` to its manifest's ``expression_source.url``,
    reads the AnnData, and delegates to :func:`combine_anndatas`. Writes the
    combined AnnData to ``OUTPUT_DIR`` and returns a summary dict.
    """
    import scanpy as sc

    from src.datasets.registry import load_manifest

    if len(dataset_ids) < 2:
        raise ValueError(f"early integration needs >=2 datasets; got {len(dataset_ids)}")

    adatas: list[AnnData] = []
    feature_id_types: list[str] = []
    temps: list[str] = []
    try:
        for did in dataset_ids:
            m = load_manifest(did)
            url = (m.expression_source or {}).get("url")
            if not url:
                raise ValueError(f"dataset '{did}' has no expression_source.url")
            local, is_temp = _resolve_to_local(url)
            if is_temp:
                temps.append(local)
            adatas.append(sc.read_h5ad(local))
            feature_id_types.append(m.feature_id_type)

        combined = combine_anndatas(
            adatas,
            dataset_ids,
            feature_id_types,
            design_factor=design_factor,
            batch_key=batch_key,
            min_shared_features=min_shared_features,
        )
    finally:
        for t in temps:
            Path(t).unlink(missing_ok=True)

    out_prefix = out_prefix or ("combined_" + "_".join(str(d) for d in dataset_ids))[:80]
    OUTPUT_DIR.mkdir(parents=True, exist_ok=True)
    out_path = OUTPUT_DIR / f"{out_prefix}.h5ad"
    combined.write_h5ad(out_path)

    per_batch = combined.obs[batch_key].value_counts().to_dict()
    return {
        "output_path": str(out_path.resolve()),
        "n_obs": int(combined.n_obs),
        "n_vars": int(combined.n_vars),
        "batch_key": batch_key,
        "shared_feature_space": "gene_symbol",
        "per_batch_n": {str(k): int(v) for k, v in per_batch.items()},
        "dataset_ids": list(dataset_ids),
    }


# ---------------------------------------------------------------------------
# ComBat pre-correction for the per-sample activity-scoring path (ADR-0001 #10)
# ---------------------------------------------------------------------------
#
# The DE path models `dataset` as a covariate (decoupler_integrate_datasets). The
# per-sample activity-scoring path has no design matrix to carry one, so the pooled
# matrix is batch-corrected with ComBat BEFORE scoring. Standard ComBat (empirical
# Bayes, scanpy.pp.combat) on the log-normalised matrix is used — NOT ComBat-seq —
# because the scoring path log-normalises anyway and the corrected matrix never feeds
# a count model (that path uses the covariate route). See ADR-0001 item 10.
#
# Data levels that ARE log-scale already (ComBat applied directly, no transform).
_LOG_SCALE_LEVELS = ("log_expression", "log_ratio")
# Linear-but-not-count levels: log1p before ComBat.
_LINEAR_LEVELS = ("tpm", "fpkm")


def _looks_like_raw_counts(X) -> bool:
    """Heuristic: does this matrix look like raw integer counts?

    Non-negative, (near-)integer, and a large dynamic range — the same signal the
    DE tool uses to guard DESeq2. Used as a safety net when the declared
    ``data_level`` is missing or disagrees with the values."""
    import numpy as np

    arr = np.asarray(X.toarray() if hasattr(X, "toarray") else X, dtype=float)
    sample = arr[: min(50, arr.shape[0])]
    finite = sample[np.isfinite(sample)]
    if finite.size == 0:
        return False
    return (
        float(finite.min()) >= 0
        and float(finite.max()) > 30
        and bool(np.allclose(finite, np.round(finite), atol=1e-6))
    )


def _genes_variable_within_each_batch(adata: AnnData, batch_key: str, tol: float = 1e-12):
    """Boolean mask of genes with non-zero variance within EVERY batch.

    ComBat estimates a per-batch location/scale per gene; a gene that is constant
    inside any batch yields a zero-variance estimate and NaNs. Drop those first."""
    import numpy as np

    X = np.asarray(adata.X.toarray() if hasattr(adata.X, "toarray") else adata.X, dtype=float)
    keep = np.ones(adata.n_vars, dtype=bool)
    batches = adata.obs[batch_key].astype(str).to_numpy()
    for b in np.unique(batches):
        sub = X[batches == b]
        keep &= sub.std(axis=0) > tol
    return keep


def batch_correct_for_scoring(
    adata: AnnData,
    *,
    batch_key: str = "batch",
    data_level: str | None = None,
    min_per_batch: int = 2,
) -> tuple[AnnData, dict]:
    """ComBat-correct a pooled AnnData for per-sample activity scoring.

    Brings the matrix to a log scale appropriate for decoupleR scoring (keyed on
    ``data_level``, with a raw-counts safety detector), drops genes that are
    constant within any batch, then applies ``scanpy.pp.combat`` keyed on
    ``batch_key``. Returns ``(corrected_adata, info)``.

    This is the **no-design-matrix** counterpart to the DE covariate route — use it
    only for per-sample scoring / clustering / PCA, NEVER as a pre-step to DE
    testing (ComBat + naive DE inflates false positives; ADR-0001). ComBat runs
    without a biological covariate, so dataset-level structure is removed wholesale.

    Raises
    ------
    ValueError
        when ``batch_key`` is absent, a batch has < ``min_per_batch`` samples
        (ComBat cannot estimate it), or < 2 non-constant genes remain.
    """
    import numpy as np
    import scanpy as sc

    if batch_key not in adata.obs.columns:
        raise ValueError(f"batch_key '{batch_key}' not found in obs.")

    counts = adata.obs[batch_key].value_counts()
    too_small = counts[counts < min_per_batch]
    if len(too_small):
        raise ValueError(
            f"ComBat needs >= {min_per_batch} samples per batch; too small: "
            f"{ {str(k): int(v) for k, v in too_small.items()} }."
        )

    a = adata.copy()
    a.X = np.asarray(a.X.toarray() if hasattr(a.X, "toarray") else a.X, dtype=np.float64)

    level = (data_level or "").lower()
    if level == "raw_counts" or (level not in _LOG_SCALE_LEVELS and _looks_like_raw_counts(a.X)):
        sc.pp.normalize_total(a, target_sum=1e4)
        sc.pp.log1p(a)
        normalization = "normalize_total(1e4)+log1p"
    elif level in _LINEAR_LEVELS:
        sc.pp.log1p(a)
        normalization = "log1p"
    else:
        normalization = "none (already log-scale)"

    keep = _genes_variable_within_each_batch(a, batch_key)
    n_dropped = int((~keep).sum())
    if n_dropped:
        a = a[:, keep].copy()
    if a.n_vars < 2:
        raise ValueError(
            "fewer than 2 genes are non-constant within every batch; cannot ComBat-"
            "correct (the cohorts likely share almost no usable feature space)."
        )

    sc.pp.combat(a, key=batch_key)

    info = {
        "method": "ComBat (scanpy.pp.combat)",
        "normalization": normalization,
        "n_genes_corrected": int(a.n_vars),
        "n_genes_dropped_constant_within_batch": n_dropped,
        "batch_key": batch_key,
        "data_level": data_level,
    }
    return a, info