import time

import cv2
import numpy as np
from django.conf import settings
from django.db.models import Max
from django.utils import timezone

from .algorithms import ProcessingError, average_images, decode_image, histogram, histogram_payload, normalize_to_uint8, process_image, verify_registration
from .models import ImageSession, ImageState, ProcessingJob
from .registry import apply_registered_operation
from .storage import delete_relative_file, load_image_array, payload_for_image, save_image_array
from .tasks import run_batch_job


def image_session_create(*, uploaded_file=None, image_base64=None):
    """Create a new image session and its initial S0 upload state.

    The session groups all later processing states so a user can present the full workflow.
    """

    if uploaded_file and uploaded_file.size > settings.MAX_UPLOAD_MB * 1024 * 1024:
        raise ProcessingError(f"Upload exceeds {settings.MAX_UPLOAD_MB} MB.")

    image = compact_workspace_image(decode_image(uploaded_file=uploaded_file, base64_image=image_base64))
    relative_path = save_image_array(image, "original")
    hist = histogram(image)
    session = ImageSession.objects.create(
        original_image=relative_path,
        width=image.shape[1],
        height=image.shape[0],
        channels=image.shape[2] if image.ndim == 3 else 1,
        color_mode="RGB" if image.ndim == 3 else "L",
        original_histogram=hist,
        expires_at=timezone.now() + timezone.timedelta(hours=settings.IMAGE_SESSION_TTL_HOURS),
    )
    state = image_state_create(
        session=session,
        parent=None,
        image=image,
        operation="upload",
        params={},
        label="S0 Upload",
        prefix="state-upload",
    )
    payload = {
        "session_id": str(session.id),
        "active_state_id": str(state.id),
        "width": session.width,
        "height": session.height,
        "channels": session.channels,
        "color_mode": session.color_mode,
        "original_histogram": hist,
        "histogram": state.histogram,
        "expires_at": session.expires_at.isoformat(),
        "states": [image_state_payload(state=state, include_image=True)],
    }
    payload.update(payload_for_image(image, relative_path))
    return payload


def compact_workspace_image(image):
    """Resize large uploads to the configured maximum dimension for faster processing.

    This keeps classroom-sized experiments responsive even when the uploaded file is very large.
    """

    max_dimension = int(getattr(settings, "IMAGE_WORKSPACE_MAX_DIMENSION", 1400))
    if max_dimension <= 0:
        return image
    height, width = image.shape[:2]
    longest = max(width, height)
    if longest <= max_dimension:
        return image
    scale = max_dimension / float(longest)
    next_size = (max(1, int(round(width * scale))), max(1, int(round(height * scale))))
    return cv2.resize(image, next_size, interpolation=cv2.INTER_AREA).astype(np.uint8)


def image_state_create(*, session, parent, image, operation, params, label=None, prefix="state"):
    """Persist one processed image state with its metadata, parent, and histogram.

    Saving every result makes it possible to compare steps and combine previous states later.
    """

    relative_path = save_image_array(image, prefix)
    max_sequence = session.states.aggregate(value=Max("sequence"))["value"]
    sequence = 0 if max_sequence is None else max_sequence + 1
    state = ImageState.objects.create(
        session=session,
        parent=parent,
        sequence=sequence,
        label=label or f"S{sequence} {operation}",
        operation=operation,
        params=params or {},
        image=relative_path,
        width=image.shape[1],
        height=image.shape[0],
        channels=image.shape[2] if image.ndim == 3 else 1,
        color_mode="RGB" if image.ndim == 3 else "L",
        histogram=histogram_payload(image),
    )
    return state


def image_state_payload(*, state, include_image=True):
    """Serialize an image state for the frontend workspace."""

    payload = {
        "state_id": str(state.id),
        "session_id": str(state.session_id),
        "parent_state_id": str(state.parent_id) if state.parent_id else None,
        "sequence": state.sequence,
        "label": state.label,
        "operation": state.operation,
        "params": state.params,
        "width": state.width,
        "height": state.height,
        "channels": state.channels,
        "color_mode": state.color_mode,
        "histogram": state.histogram,
        "created_at": state.created_at.isoformat(),
    }
    if include_image:
        image = load_image_array(state.image)
        payload.update(payload_for_image(image, state.image))
    else:
        payload["image_path"] = state.image
        payload["image_url"] = f"{settings.MEDIA_URL}{state.image}"
    return payload


def image_states_payload(*, states):
    """Serialize a list of image states."""

    return [image_state_payload(state=state, include_image=True) for state in states]


def image_state_delete(*, state):
    """Delete a non-S0 state while keeping child states available.

    Use it to remove unhelpful experiments without losing later useful results.
    """

    if state.sequence == 0 or state.operation == "upload":
        raise ProcessingError("The original S0 upload state cannot be deleted.")
    image_path = state.image
    state.children.update(parent=None)
    state.delete()
    delete_relative_file(image_path)


def image_state_apply_operation(*, state, operation, params):
    """Apply one registered algorithm to a selected state and save the result as a new state.

    This is the main workspace action: every filter or transform becomes a reproducible step.
    """

    if state.session.expired:
        raise ProcessingError("Image session has expired.")
    source = load_image_array(state.image)
    result = apply_registered_operation(source, operation, params or {})
    new_state = image_state_create(
        session=state.session,
        parent=state,
        image=result,
        operation=operation,
        params=params or {},
        label=None,
        prefix=f"state-{operation}",
    )
    return image_state_payload(state=new_state, include_image=True)


def combine_states(*, states, operation, params=None):
    """Combine registered states using add, subtract, dot product, average, and/or.

    Use it for MATLAB-like image arithmetic, change detection, masking, and K-image denoising.
    """

    params = params or {}
    if len(states) < 2:
        raise ProcessingError("At least two states are required.")
    session = states[0].session
    if any(state.session_id != session.id for state in states):
        raise ProcessingError("All states must belong to the same session.")
    images = [load_image_array(state.image) for state in states]
    verify_registration(images)

    if operation == "average":
        result = average_images(images)
    elif operation == "add":
        result = np_clip_sum(images)
    elif operation == "subtract":
        result = normalize_to_uint8(images[0].astype("float32") - images[1].astype("float32"))
    elif operation == "dot_product":
        result = normalize_to_uint8(np.prod([image.astype("float32") / 255.0 for image in images], axis=0))
    elif operation == "and":
        result = images[0].copy()
        for image in images[1:]:
            result = result & image
    elif operation == "or":
        result = images[0].copy()
        for image in images[1:]:
            result = result | image
    else:
        raise ProcessingError(f"Unsupported combine operation '{operation}'.")

    new_state = image_state_create(
        session=session,
        parent=states[0],
        image=result,
        operation=f"combine_{operation}",
        params={**params, "state_ids": [str(state.id) for state in states]},
        label=None,
        prefix=f"state-combine-{operation}",
    )
    return image_state_payload(state=new_state, include_image=True)


def np_clip_sum(images):
    """Add several registered images and clip the result to [0, 255].

    Use it to combine brightness/detail contributions while keeping the output displayable.
    """

    total = np.zeros_like(images[0], dtype="float32")
    for image in images:
        total += image.astype("float32")
    return np.clip(total, 0, 255).astype("uint8")


def image_session_process(*, session, operation, params):
    """Run a legacy single-image operation against the original session image.

    This keeps the older API working while the state workspace handles the main presentation flow.
    """

    if session.expired:
        raise ProcessingError("Image session has expired.")

    started_at = time.perf_counter()
    source = load_image_array(session.original_image)
    result = process_image(source, operation, params)
    relative_path = save_image_array(result, f"processed-{operation}")
    hist = histogram(result)

    session.processed_image = relative_path
    session.processed_histogram = hist
    session.save(update_fields=["processed_image", "processed_histogram"])

    payload = {
        "session_id": str(session.id),
        "operation": operation,
        "params": params,
        "processed_histogram": hist,
        "elapsed_ms": round((time.perf_counter() - started_at) * 1000, 2),
    }
    payload.update(payload_for_image(result, relative_path))
    return payload


def batch_job_create(*, operation, session_ids, params=None):
    """Create a Celery-backed processing job for heavier batch operations.

    Use it when an operation may take longer than an interactive request should block.
    """

    job = ProcessingJob.objects.create(operation=operation, params=params or {})
    run_batch_job.delay(str(job.id), operation, [str(session_id) for session_id in session_ids])
    return job


def processing_job_payload(*, job):
    """Serialize a processing job, including result image data when available."""

    payload = {
        "job_id": str(job.id),
        "operation": job.operation,
        "status": job.status,
        "progress": job.progress,
        "error": job.error,
        "result_histogram": job.result_histogram,
    }
    if job.result_image:
        image = load_image_array(job.result_image)
        payload.update(payload_for_image(image, job.result_image))
    return payload