<?php

namespace App\Support\VideoWorkflow;

use App\Models\VideoProject;
use App\Models\WorkflowStep;
use App\Models\WorkflowTemplate;

/**
 * Drives a VideoProject's pipeline: creates its step sequence and manages
 * step state transitions (execution, approval, failure, retry).
 *
 * Steps run strictly in `order`. Each step is one of:
 *   pending -> in_progress -> awaiting_approval -> completed
 *                          \-> completed (skips approval if not required)
 *                          \-> failed -> in_progress (retry)
 *              awaiting_approval -> rejected -> in_progress (retry)
 *   pending | in_progress -> skipped
 *
 * This class only manages state — it doesn't know how to actually generate
 * a script, render video, etc. Whatever does that work (a future AI
 * provider integration, a human, an Artisan command) calls completeStep()/
 * failStep() to report the result.
 */
class WorkflowEngine
{
    /**
     * Create the step sequence for a project and activate the first one.
     *
     * @param  array<int, array{type: string, requires_approval?: bool}>  $steps
     */
    public function start(VideoProject $project, array $steps): WorkflowStep
    {
        if ($project->steps()->exists()) {
            throw new WorkflowTransitionException("Video project {$project->id} already has workflow steps.");
        }

        if (empty($steps)) {
            throw new WorkflowTransitionException('Cannot start a workflow with no steps.');
        }

        foreach (array_values($steps) as $order => $step) {
            $project->steps()->create([
                'type' => $step['type'],
                'order' => $order,
                'status' => 'pending',
                'requires_approval' => $step['requires_approval'] ?? false,
            ]);
        }

        $project->update(['status' => 'in_progress']);

        $first = $project->steps()->orderBy('order')->firstOrFail();

        return $this->activate($first);
    }

    public function startFromTemplate(VideoProject $project, WorkflowTemplate $template): WorkflowStep
    {
        $project->update(['workflow_template_id' => $template->id]);

        return $this->start($project, $template->steps);
    }

    /**
     * The step currently blocking progress — pending, running, awaiting
     * approval, or stuck on failure/rejection. Null once every step is
     * completed or skipped.
     */
    public function currentStep(VideoProject $project): ?WorkflowStep
    {
        return $project->steps()
            ->whereNotIn('status', ['completed', 'skipped'])
            ->orderBy('order')
            ->first();
    }

    public function completeStep(WorkflowStep $step, array $output = []): WorkflowStep
    {
        $this->assertStatus($step, 'in_progress');

        $step->update([
            'output' => $output,
            'error' => null,
            'completed_at' => now(),
            'status' => $step->requires_approval ? 'awaiting_approval' : 'completed',
        ]);

        if ($step->status === 'completed') {
            $this->activateNext($step);
        }

        return $step->fresh();
    }

    public function approveStep(WorkflowStep $step): WorkflowStep
    {
        $this->assertStatus($step, 'awaiting_approval');

        $step->update(['status' => 'completed']);

        $this->activateNext($step);

        return $step->fresh();
    }

    /**
     * Rejecting does not advance the pipeline — it stays blocked on this
     * step until retryStep() is called.
     */
    public function rejectStep(WorkflowStep $step, ?string $reason = null): WorkflowStep
    {
        $this->assertStatus($step, 'awaiting_approval');

        $step->update(['status' => 'rejected', 'error' => $reason]);

        return $step->fresh();
    }

    public function failStep(WorkflowStep $step, string $error): WorkflowStep
    {
        $this->assertStatus($step, 'in_progress');

        $step->update(['status' => 'failed', 'error' => $error]);

        return $step->fresh();
    }

    public function retryStep(WorkflowStep $step): WorkflowStep
    {
        if (! in_array($step->status, ['failed', 'rejected'], true)) {
            throw new WorkflowTransitionException("Step {$step->id} can only be retried from failed or rejected, currently '{$step->status}'.");
        }

        $step->update([
            'status' => 'in_progress',
            'error' => null,
            'output' => null,
            'started_at' => now(),
            'completed_at' => null,
        ]);

        return $step->fresh();
    }

    public function skipStep(WorkflowStep $step): WorkflowStep
    {
        if (! in_array($step->status, ['pending', 'in_progress'], true)) {
            throw new WorkflowTransitionException("Step {$step->id} can only be skipped from pending or in_progress, currently '{$step->status}'.");
        }

        $step->update(['status' => 'skipped', 'completed_at' => now()]);

        $this->activateNext($step);

        return $step->fresh();
    }

    private function activate(WorkflowStep $step): WorkflowStep
    {
        $step->update(['status' => 'in_progress', 'started_at' => now()]);

        return $step->fresh();
    }

    private function activateNext(WorkflowStep $justFinished): void
    {
        $project = $justFinished->videoProject;

        $next = $project->steps()
            ->where('order', '>', $justFinished->order)
            ->whereNotIn('status', ['completed', 'skipped'])
            ->orderBy('order')
            ->first();

        if ($next) {
            $this->activate($next);

            return;
        }

        $project->update(['status' => 'completed']);
    }

    private function assertStatus(WorkflowStep $step, string $expected): void
    {
        if ($step->status !== $expected) {
            throw new WorkflowTransitionException("Step {$step->id} must be '{$expected}' for this transition, currently '{$step->status}'.");
        }
    }
}