"""Pipeline step executor - runs steps asynchronously.

Each step function receives (pipeline_id, manifest, params) and returns output data.
The executor handles state transitions, artifact storage, and dependency resolution.
"""

import asyncio
import logging
from typing import Dict, Optional

from .state import (
    STATE_PENDING, STATE_RUNNING, STATE_COMPLETED, STATE_FAILED,
    PIPELINE_RUNNING, PIPELINE_COMPLETED, PIPELINE_FAILED, PIPELINE_PAUSED,
    build_dependency_map,
)
from .storage import (
    get_manifest, save_manifest, save_artifact,
    update_step_state, create_new_version, reset_steps,
)

logger = logging.getLogger("pipeline.executor")

# Active pipeline execution tasks (pipeline_id -> asyncio.Task)
_active_tasks: Dict[str, asyncio.Task] = {}


async def start_pipeline(pipeline_id: str):
    """Start executing a pipeline from the beginning."""
    task = asyncio.create_task(_run_pipeline(pipeline_id))
    _active_tasks[pipeline_id] = task
    return task


async def resume_pipeline(pipeline_id: str):
    """Resume a paused pipeline."""
    task = asyncio.create_task(_run_pipeline(pipeline_id))
    _active_tasks[pipeline_id] = task
    return task


async def stop_pipeline(pipeline_id: str):
    """Cancel a running pipeline."""
    task = _active_tasks.get(pipeline_id)
    if task and not task.done():
        task.cancel()
        del _active_tasks[pipeline_id]
        return True
    return False


def is_running(pipeline_id: str) -> bool:
    """Check if a pipeline is currently running."""
    task = _active_tasks.get(pipeline_id)
    return task is not None and not task.done()


async def _run_pipeline(pipeline_id: str):
    """Main pipeline execution loop."""
    try:
        while True:
            manifest = get_manifest(pipeline_id)
            if not manifest:
                logger.error(f"Pipeline {pipeline_id} not found")
                break

            if manifest["state"] == PIPELINE_PAUSED:
                logger.info(f"Pipeline {pipeline_id} paused, waiting for user action")
                break

            if manifest["state"] == PIPELINE_COMPLETED:
                logger.info(f"Pipeline {pipeline_id} already completed")
                break

            # Find next pending step with all deps completed
            next_step = _find_next_step(manifest)
            if not next_step:
                # All steps done
                manifest["state"] = PIPELINE_COMPLETED
                save_manifest(pipeline_id, manifest)
                logger.info(f"Pipeline {pipeline_id} completed")
                break

            # Execute the step
            await _execute_step(pipeline_id, next_step)

    except asyncio.CancelledError:
        logger.info(f"Pipeline {pipeline_id} cancelled")
    except Exception as e:
        logger.error(f"Pipeline {pipeline_id} error: {e}")
    finally:
        _active_tasks.pop(pipeline_id, None)


def _find_next_step(manifest: dict) -> Optional[str]:
    """Find the next step to execute (pending, all deps completed)."""
    steps = manifest.get("steps", {})
    for name, info in sorted(steps.items(), key=lambda x: x[1].get("order", 0)):
        if info["state"] != STATE_PENDING:
            continue
        # Check all dependencies are completed
        deps_ok = all(
            steps.get(dep, {}).get("state") == STATE_COMPLETED
            for dep in info.get("deps", [])
        )
        if deps_ok:
            return name
    return None


async def _execute_step(pipeline_id: str, step_name: str):
    """Execute a single pipeline step."""
    update_step_state(pipeline_id, step_name, STATE_RUNNING)

    try:
        # Load input artifacts from dependencies
        manifest = get_manifest(pipeline_id)
        version = manifest["current_version"]
        input_data = await _gather_step_inputs(pipeline_id, step_name, version, manifest)

        # Save input artifact
        save_artifact(pipeline_id, version, step_name, "input", input_data)

        # Execute step handler
        handler = STEP_HANDLERS.get(step_name, _default_handler)
        output_data = await handler(pipeline_id, step_name, input_data, manifest)

        # Save output artifact
        save_artifact(pipeline_id, version, step_name, "output", output_data)
        update_step_state(pipeline_id, step_name, STATE_COMPLETED)

        logger.info(f"Step {step_name} completed for {pipeline_id}")

    except Exception as e:
        logger.error(f"Step {step_name} failed for {pipeline_id}: {e}")
        update_step_state(pipeline_id, step_name, STATE_FAILED, str(e))


async def _gather_step_inputs(pipeline_id: str, step_name: str, version: int, manifest: dict) -> dict:
    """Gather input data for a step from its dependencies' outputs."""
    from .storage import get_artifact
    steps = manifest.get("steps", {})
    step_info = steps.get(step_name, {})
    deps = step_info.get("deps", [])

    inputs = {}
    for dep in deps:
        dep_artifact = get_artifact(pipeline_id, version, dep, "output")
        if dep_artifact:
            inputs[dep] = dep_artifact.get("data", {})

    # Also include initial params
    if "_params" in inputs:
        inputs["params"] = inputs.pop("_params")

    # Check if there's a user-modified input for this step
    user_input = get_artifact(pipeline_id, version, step_name, "input")
    if user_input and user_input.get("data"):
        # User modified input exists, use it
        return user_input["data"]

    return inputs


# === Step Handlers ===

async def _default_handler(pipeline_id: str, step_name: str, input_data: dict, manifest: dict) -> dict:
    """Default handler - stub that returns input as output (for testing)."""
    logger.info(f"Default handler for {step_name}, pipeline {pipeline_id}")
    # Simulate some processing time
    await asyncio.sleep(0.5)
    return {"step": step_name, "status": "completed", "input_summary": str(input_data)[:200]}


# Real handlers will be registered here
STEP_HANDLERS = {
    # Will be populated by actual KTV pipeline step implementations
}


def register_handler(step_name: str, handler):
    """Register a step handler function."""
    STEP_HANDLERS[step_name] = handler