"""Hydra-free checkpoint -> optimizer construction.

Rebuilds the learned optimizer (architecture + weights) from a checkpoint
*without* going through Hydra. Only ``_load_checkpoint_cfg`` +
``load_typed_config`` are used (both Hydra-free); the Hydra coupling lives in
``setup_cfg`` / ``merge_config_from_file`` / ``setup_output_dir`` which we never
call. All heavy imports are deferred into the functions so ``import optgs``
stays cheap.
"""

from __future__ import annotations

from functools import lru_cache
from pathlib import Path
from typing import TYPE_CHECKING

from optgs.experimental.api.integration.scene_protocol import OptGSError


@lru_cache(maxsize=8)
def _load_ckpt_cfg_cached(cfg_path_str: str):
    """Load + migrate a checkpoint config once per path (read-only callers).

    ``build_optimizer_cfg`` / ``build_decoder`` / ``get_scene_trainer_scalar``
    all need the same DictConfig; caching avoids re-parsing the file.
    """
    from optgs.config import _load_checkpoint_cfg  # Hydra-free

    return _load_checkpoint_cfg(Path(cfg_path_str))


def get_scene_trainer_scalar(cfg_path: Path, key: str, default):
    """Read ``scene_trainer.<key>`` from a checkpoint config (or ``default``).

    Used for scalars that live on the (Hydra-free unavailable) scene-trainer
    config rather than the optimizer cfg: ``num_update_steps``,
    ``iter_batch_size``, ``sh_degree_interval``.
    """
    from omegaconf import OmegaConf

    cfg = _load_ckpt_cfg_cached(str(cfg_path))
    return OmegaConf.select(cfg, f"scene_trainer.{key}", default=default)

if TYPE_CHECKING:  # pragma: no cover - typing only
    from torch import nn

    from optgs.scene_trainer.optimizer.optimizer_knn_based import KnnBasedOptimizerCfg


def _optimizer_class_by_cfg_name():
    """Map a checkpoint config's ``scene_optimizer.name`` -> optimizer class.

    The registry (``SCENE_OPTIMIZERS``) keys on registry names (e.g.
    ``"depthsplat"``), but a checkpoint config's ``scene_optimizer.name`` is the
    cfg literal (``"knn_based"`` / ``"l2s"`` / ``"resplat_v1"`` /
    ``"resplat_v2"``). Each class asserts ``cfg.name`` is its ``OPTIMIZER_NAME``
    or one of its ``OPTIMIZER_NAME_ALIASES`` (e.g. legacy ``"clogs"`` for
    ``Learn2SplatOptimizer``), so we dispatch on both.
    """
    from optgs.scene_trainer.optimizer.optimizer_knn_based import KnnBasedOptimizer
    from optgs.scene_trainer.optimizer.optimizer_learn2splat import (
        Learn2SplatOptimizer,
    )
    from optgs.scene_trainer.optimizer.optimizer_resplat import (
        ResplatOptimizerV1,
        ResplatOptimizerV2,
    )

    classes = (
        KnnBasedOptimizer,
        Learn2SplatOptimizer,
        ResplatOptimizerV1,
        ResplatOptimizerV2,
    )
    mapping = {}
    for cls in classes:
        for name in (cls.OPTIMIZER_NAME, *getattr(cls, "OPTIMIZER_NAME_ALIASES", ())):
            mapping[name] = cls
    return mapping


def _initializer_cfg_class(name: str):
    """Map ``scene_initializer.name`` -> its concrete typed Cfg dataclass.

    ``InitializerCfg`` is a PEP-604 union; dacite needs a concrete dataclass
    as the top-level target (a union is only resolvable as a *field* type).
    Keyed to match both ``SCENE_INITIALIZERS`` and each Cfg's ``name``
    Literal.
    """
    from optgs.scene_trainer.initializer import (
        InitializerColmapCfg,
        InitializerEdgsCfg,
        InitializerPlyCfg,
        InitializerPointcloudCfg,
        InitializerRandomCfg,
        ResplatInitializerCfg,
    )

    return {
        "resplat_v1": ResplatInitializerCfg,
        "resplat_v2": ResplatInitializerCfg,
        "colmap": InitializerColmapCfg,
        "ply": InitializerPlyCfg,
        "edgs": InitializerEdgsCfg,
        "random": InitializerRandomCfg,
        "pointcloud": InitializerPointcloudCfg,
    }.get(name)


def _compose_default_group(group: str, value: str):
    """Hydra-compose the bundled default for ``scene_trainer.<group>=<value>``.

    Released checkpoints predate fields later added to the typed configs
    (e.g. ``scene_optimizer.refiner.fallback_means_lr``). The training/eval
    pipeline reconciles this by merging the checkpoint config over the
    *current* default config (config.py:merge_config_from_file). We mirror
    that: compose the bundled default for the group (e.g.
    ``scene_optimizer=knn_based`` -> base -> refiner:none, or
    ``scene_initializer=colmap``) so missing fields can be backfilled with
    current defaults while checkpoint values win for shared keys.

    Scoped use of ``hydra.compose`` (no ``@hydra.main`` / ``HydraConfig.get``,
    no app context); lazily imported so ``import optgs`` stays light. Returns
    ``None`` if composition fails (caller falls back to a strict parse).
    """
    try:
        import optgs
        from hydra import compose, initialize_config_dir
        from hydra.core.global_hydra import GlobalHydra
        from omegaconf import OmegaConf

        config_dir = str(Path(optgs.__file__).resolve().parent / "config")
        GlobalHydra.instance().clear()
        try:
            with initialize_config_dir(version_base=None, config_dir=config_dir):
                composed = compose(
                    config_name="main",
                    overrides=[f"scene_trainer/{group}={value}"],
                )
        finally:
            GlobalHydra.instance().clear()
        return OmegaConf.select(composed, f"scene_trainer.{group}")
    except Exception as e:  # noqa: BLE001 - best-effort backfill
        print(
            f"[optgs] warning: could not compose default scene_trainer.{group}"
            f"={value} for back-compat merge ({type(e).__name__}: {e}); "
            f"parsing checkpoint config as-is."
        )
        return None


def build_optimizer_cfg(cfg_path: Path) -> tuple["KnnBasedOptimizerCfg", int | None]:
    """Load a checkpoint's saved config and return its typed optimizer cfg.

    Returns ``(KnnBasedOptimizerCfg, num_update_steps)`` where
    ``num_update_steps`` (the per-scene optimization step count) is read from
    ``scene_trainer.num_update_steps`` if present (it is NOT part of the
    optimizer cfg), else ``None``.
    """
    from omegaconf import OmegaConf

    from optgs.config import load_typed_config
    from optgs.scene_trainer.optimizer.optimizer_knn_based import KnnBasedOptimizerCfg

    cfg = _load_ckpt_cfg_cached(str(cfg_path))  # read_omega_cfg + migrate; NO Hydra
    so = OmegaConf.select(cfg, "scene_trainer.scene_optimizer")
    name = OmegaConf.select(cfg, "scene_trainer.scene_optimizer.name")
    if so is None or name in (None, "none"):
        raise OptGSError(
            f"checkpoint config at {cfg_path} has no learned scene_optimizer "
            f"(scene_trainer.scene_optimizer={name!r}). OptGS needs a learned "
            f"optimizer checkpoint (knn_based / clogs / resplat_v1 / resplat_v2)."
        )
    # Backfill fields a released (older) checkpoint config lacks with the
    # current defaults, then let checkpoint values win for shared keys
    # (mirrors config.py:merge_config_from_file's OmegaConf.merge).
    default_so = _compose_default_group("scene_optimizer", "knn_based")
    if default_so is not None:
        OmegaConf.set_struct(default_so, False)
        merged_so = OmegaConf.merge(default_so, so)
    else:
        merged_so = so
    try:
        opt_cfg = load_typed_config(merged_so, KnnBasedOptimizerCfg)
    except Exception as e:  # dacite/omegaconf errors -> actionable message
        raise OptGSError(
            f"failed to parse scene_optimizer from {cfg_path} into "
            f"KnnBasedOptimizerCfg ({type(e).__name__}: {e})."
        ) from e

    # Mirror SceneTrainerCfg (scene_trainer_cfg.py: scene_optimizer.update(
    # scene_initializer)): wire the checkpoint's initializer cfg into the
    # optimizer cfg so the runtime-only fields init_gaussian_param_num /
    # init_sh_d / sh_d — absent from every config file — are populated before
    # the optimizer nn.Module is built.
    si = OmegaConf.select(cfg, "scene_trainer.scene_initializer")
    si_name = OmegaConf.select(cfg, "scene_trainer.scene_initializer.name")
    if si is None or si_name in (None, "none"):
        raise OptGSError(
            f"checkpoint config at {cfg_path} has no scene_initializer "
            f"(name={si_name!r}); cannot derive init_gaussian_param_num "
            f"required to build the optimizer."
        )
    init_cls = _initializer_cfg_class(str(si_name))
    if init_cls is None:
        raise OptGSError(
            f"unsupported scene_initializer.name={si_name!r} in {cfg_path}; "
            f"cannot derive init_gaussian_param_num for the optimizer."
        )
    default_si = _compose_default_group("scene_initializer", str(si_name))
    if default_si is not None:
        OmegaConf.set_struct(default_si, False)
        merged_si = OmegaConf.merge(default_si, si)
    else:
        merged_si = si
    try:
        init_cfg = load_typed_config(merged_si, init_cls)
        opt_cfg.update(init_cfg)  # sets init_gaussian_param_num/init_sh_d/sh_d
    except Exception as e:
        raise OptGSError(
            f"failed to wire scene_initializer ({si_name!r}) into the "
            f"optimizer cfg from {cfg_path} ({type(e).__name__}: {e})."
        ) from e

    num_update_steps = OmegaConf.select(
        cfg, "scene_trainer.num_update_steps", default=None
    )
    return opt_cfg, num_update_steps


def build_decoder(
    cfg_path: Path, dataset_cfg: object, decoder_overrides: dict | None = None
) -> "nn.Module":
    """Build the renderer the checkpoint was trained with.

    Uses ``scene_trainer.decoder`` from the checkpoint config (NOT a hardcoded
    backend): the learned optimizer's in-loop render gradients must match the
    backend it trained with, and only the registered/available backends are
    usable (e.g. ``gsplat`` — the optgs default; the ``inria`` backend needs
    ``diff_gaussian_rasterization``, which is optional). ``dataset_cfg`` only
    needs a ``background_color`` attribute. ``decoder_overrides`` (e.g.
    ``rasterize_mode`` / ``eps2d``) take precedence over the checkpoint config.
    """
    from omegaconf import OmegaConf

    from optgs.config import load_typed_config
    from optgs.model.decoder import DecoderCfg, get_decoder

    cfg = _load_ckpt_cfg_cached(str(cfg_path))
    node = OmegaConf.select(cfg, "scene_trainer.decoder")
    if node is None:
        raise OptGSError(
            f"checkpoint config at {cfg_path} has no scene_trainer.decoder; "
            f"cannot rebuild the renderer the optimizer trained with."
        )
    # gsplat decoder rasterize_mode / eps2d, by precedence:
    #   caller override  >  checkpoint config  >  gsplat rasterization() default
    # (so an older checkpoint that omits a field behaves as plain gsplat would).
    if OmegaConf.select(node, "name") == "gsplat":
        import inspect

        from gsplat.rendering import rasterization

        sig = inspect.signature(rasterization).parameters
        node = OmegaConf.merge(
            OmegaConf.create(
                {f: sig[f].default for f in ("rasterize_mode", "eps2d") if f in sig}
            ),
            node,
            OmegaConf.create(dict(decoder_overrides or {})),
        )
    try:
        decoder_cfg = load_typed_config(node, DecoderCfg)
    except Exception as e:
        raise OptGSError(
            f"failed to parse scene_trainer.decoder from {cfg_path} "
            f"({type(e).__name__}: {e})."
        ) from e
    try:
        return get_decoder(decoder_cfg, dataset_cfg)
    except (KeyError, ImportError) as e:
        raise OptGSError(
            f"decoder backend {decoder_cfg.name!r} is not available in this "
            f"environment ({type(e).__name__}: {e}). Install its backend "
            f"(e.g. diff_gaussian_rasterization for 'inria') or use a "
            f"checkpoint trained with the 'gsplat' decoder."
        ) from e


def build_optimizer(opt_cfg: "KnnBasedOptimizerCfg") -> "nn.Module":
    """Construct the concrete learned optimizer for ``opt_cfg`` (no weights)."""
    from optgs.misc.io import FrequencyScheduler

    mapping = _optimizer_class_by_cfg_name()
    cls = mapping.get(opt_cfg.name)
    if cls is None:
        raise OptGSError(
            f"unsupported scene_optimizer.name={opt_cfg.name!r}; OptGS supports "
            f"{sorted(mapping)}."
        )
    optimizer = cls(opt_cfg)
    # The optimizer's save_every (info/context/target/debug artifact dumps) is
    # wired by SceneTrainer during training; the optimizer calls it
    # unconditionally, so the API inference path — which has nothing to dump —
    # installs a disabled scheduler instead of leaving it None.
    save_every = FrequencyScheduler(last_step=0)
    save_every.disable(True)
    optimizer.save_every = save_every
    return optimizer


def build_adam_baseline(num_refine: int) -> "nn.Module":
    """Build the codebase's 3DGS Adam optimizer for a fair baseline comparison.

    Uses the bundled ``scene_optimizer=3dgs`` config — gsplat's example
    hyperparameters (LRs, betas). Densification is disabled so the baseline
    refines the same fixed Gaussian set as the learned optimizer (a
    like-for-like update-rule comparison), and the means-LR decay horizon is set
    to ``num_refine``. Returns a ready-to-run ``AdamOptimizer``.
    """
    from omegaconf import OmegaConf

    from optgs.config import load_typed_config
    from optgs.misc.io import FrequencyScheduler
    from optgs.scene_trainer.optimizer.optimizer_adam import (
        AdamOptimizer,
        AdamOptimizerCfg,
    )

    composed = _compose_default_group("scene_optimizer", "3dgs")
    if composed is None:
        raise OptGSError(
            "could not Hydra-compose the bundled 'scene_optimizer=3dgs' config "
            "for the Adam baseline."
        )
    OmegaConf.set_struct(composed, False)
    # gsplat decays the means LR over the full step budget.
    composed.means_lr_max_steps = int(num_refine)
    # Disable densification — the baseline refines the same fixed Gaussian set
    # as the learned optimizer (a like-for-like comparison of the update rule).
    for flag in ("do_densify", "do_prune", "do_opacity_reset"):
        if flag in composed.refiner:
            composed.refiner[flag] = False
    try:
        adam_cfg = load_typed_config(composed, AdamOptimizerCfg)
    except Exception as e:
        raise OptGSError(
            f"failed to parse the bundled '3dgs' config into AdamOptimizerCfg "
            f"({type(e).__name__}: {e})."
        ) from e

    optimizer = AdamOptimizer(adam_cfg)
    save_every = FrequencyScheduler(last_step=0)  # nothing to dump (see build_optimizer)
    save_every.disable(True)
    optimizer.save_every = save_every
    # AdamOptimizer is a NonlearnedOptimizer — already pinned to eval mode.
    return optimizer


# Module-attribute renames applied when the legacy Resplat encoder was split
# into separate initializer/optimizer modules (transcribed from
# optgs/main.py:load_optimizer).
_ORIG_OPTIMIZER_ATTR_RENAMES = {
    "render_error_mv_attn": "update_error_attn",
}


def load_optimizer_state(
    optimizer: "nn.Module",
    ckpt_path: str,
    init_state_wo_features: bool,
    strict: bool,
) -> None:
    """Load optimizer weights from ``ckpt_path`` into ``optimizer``.

    Transcribes the prefix-stripping / legacy-rename / feature-drop logic from
    ``optgs/main.py:load_optimizer`` (we cannot call that function: it needs a
    full Hydra ``cfg`` and a ``scene_trainer``).
    """
    import torch

    state = torch.load(ckpt_path, map_location="cpu")
    if isinstance(state, dict) and "state_dict" in state:
        state = state["state_dict"]
    # Strip the Lightning "scene_trainer." prefix if present.
    state = {k.replace("scene_trainer.", ""): v for k, v in state.items()}

    if any(k.startswith("optimizer.") for k in state):
        # Unified repo format: keys are optimizer.*
        osd = {
            k[len("optimizer."):]: v
            for k, v in state.items()
            if k.startswith("optimizer.")
        }
    else:
        # Legacy Resplat format: keys are encoder.* (before init/opt split).
        osd = {
            k[len("encoder."):]: v
            for k, v in state.items()
            if k.startswith("encoder.")
        }
        renamed = {}
        for k, v in osd.items():
            for old, new in _ORIG_OPTIMIZER_ATTR_RENAMES.items():
                if k == old or k.startswith(old + "."):
                    k = new + k[len(old):]
                    break
            renamed[k] = v
        osd = renamed

    if not osd:
        raise OptGSError(
            f"no optimizer weights found in {ckpt_path} (looked for "
            f"'optimizer.*' or legacy 'encoder.*' keys)."
        )

    if init_state_wo_features:
        osd = {k: v for k, v in osd.items() if "update_proj" not in k}

    optimizer.load_state_dict(osd, strict=strict)