<?php

namespace App\Services\Projection;

use App\Enums\BucketTypeEnum;
use App\Enums\DistributionModeEnum;
use App\Models\Bucket;
use App\Models\Draw;
use App\Models\Scenario;
use Carbon\Carbon;
use Illuminate\Support\Collection;

readonly class PipelineAllocationService
{
    private const string CAP_BASE = 'base';

    private const string CAP_FILL = 'fill';

    /**
     * Allocate an inflow amount across scenario buckets using phased distribution.
     *
     * Phases:
     * 1. Needs to base (allocation_value)
     * 2. Wants to base (allocation_value)
     * 3. Needs to buffer (getEffectiveCapacity)
     * 4. Wants to buffer (getEffectiveCapacity)
     * 5. Overflow (all remaining)
     *
     * @return Collection<int, Draw> Collection of Draw models (unsaved)
     */
    public function allocateInflow(Scenario $scenario, int $amount, ?Carbon $date = null, ?string $description = null): Collection
    {
        if ($amount <= 0) {
            return collect();
        }

        $buckets = $scenario->buckets()
            ->orderBy('priority')
            ->get();

        if ($buckets->isEmpty()) {
            return collect();
        }

        $mode = $scenario->distribution_mode ?? DistributionModeEnum::EVEN;
        $allocationDate = $date ?? now();
        $allocationDescription = $description ?? 'Allocation from inflow';

        // Track cumulative allocations per bucket across phases
        /** @var array<int, int> $allocated bucket_id => total allocated cents */
        $allocated = [];

        $needs = $buckets->filter(fn (Bucket $b) => $b->type === BucketTypeEnum::NEED);
        $wants = $buckets->filter(fn (Bucket $b) => $b->type === BucketTypeEnum::WANT);
        $overflow = $buckets->first(fn (Bucket $b) => $b->type === BucketTypeEnum::OVERFLOW);

        $remaining = $amount;

        // Phases 1-4: needs/wants to base/buffer
        $phases = [
            [$needs, self::CAP_BASE],
            [$wants, self::CAP_BASE],
            [$needs, self::CAP_FILL],
            [$wants, self::CAP_FILL],
        ];

        foreach ($phases as [$group, $cap]) {
            $remaining = $this->allocateToGroup($group, $remaining, $mode, $cap, $allocated);
        }

        // Phase 5: Overflow
        if ($remaining > 0 && $overflow !== null) {
            $allocated[$overflow->id] = ($allocated[$overflow->id] ?? 0) + $remaining;
        }

        // Build Draw models from cumulative allocations
        $draws = collect();
        foreach ($allocated as $bucketId => $totalAmount) {
            if ($totalAmount <= 0) {
                continue;
            }

            $draws->push(new Draw([
                'bucket_id' => $bucketId,
                'amount' => $totalAmount,
                'date' => $allocationDate,
                'description' => $allocationDescription,
                'is_projected' => true,
            ]));
        }

        return $draws;
    }

    /**
     * Allocate money to a group of buckets up to a capacity target.
     *
     * @param  Collection<int, Bucket>  $buckets  Buckets ordered by priority
     * @param  int  $amount  Available money in cents
     * @param  DistributionModeEnum  $mode  Even or priority distribution
     * @param  string  $capMethod  self::CAP_BASE = allocation_value, self::CAP_FILL = getEffectiveCapacity()
     * @param  array<int, int>  &$allocated  Cumulative allocations per bucket (mutated)
     * @return int Remaining amount after allocation
     */
    private function allocateToGroup(Collection $buckets, int $amount, DistributionModeEnum $mode, string $capMethod, array &$allocated): int
    {
        if ($amount <= 0 || $buckets->isEmpty()) {
            return $amount;
        }

        return match ($mode) {
            DistributionModeEnum::PRIORITY => $this->allocatePriority($buckets, $amount, $capMethod, $allocated),
            DistributionModeEnum::EVEN => $this->allocateEven($buckets, $amount, $capMethod, $allocated),
        };
    }

    /**
     * Priority mode: fill highest-priority bucket first, then next.
     */
    private function allocatePriority(Collection $buckets, int $amount, string $capMethod, array &$allocated): int
    {
        $remaining = $amount;

        foreach ($buckets as $bucket) {
            if ($remaining <= 0) {
                break;
            }

            $space = $this->getAvailableSpace($bucket, $capMethod, $allocated);
            if ($space <= 0) {
                continue;
            }

            $allocation = min($space, $remaining);
            $allocated[$bucket->id] = ($allocated[$bucket->id] ?? 0) + $allocation;
            $remaining -= $allocation;
        }

        return $remaining;
    }

    /**
     * Even mode: split evenly across eligible buckets, redistributing when one fills up.
     */
    private function allocateEven(Collection $buckets, int $amount, string $capMethod, array &$allocated): int
    {
        $remaining = $amount;

        // Filter to buckets that still have space
        $eligible = $buckets->filter(fn (Bucket $b) => $this->getAvailableSpace($b, $capMethod, $allocated) > 0);

        while ($remaining > 0 && $eligible->isNotEmpty()) {
            $share = intdiv($remaining, $eligible->count());
            $remainder = $remaining % $eligible->count();

            $spent = 0;
            $filledUp = [];

            foreach ($eligible as $index => $bucket) {
                $bucketShare = $share + ($remainder > 0 ? 1 : 0);
                if ($remainder > 0) {
                    $remainder--;
                }

                if ($bucketShare <= 0) {
                    break;
                }

                $space = $this->getAvailableSpace($bucket, $capMethod, $allocated);
                $allocation = min($bucketShare, $space);

                if ($allocation > 0) {
                    $allocated[$bucket->id] = ($allocated[$bucket->id] ?? 0) + $allocation;
                    $spent += $allocation;
                }

                if ($allocation >= $space) {
                    $filledUp[] = $index;
                }
            }

            $remaining -= $spent;

            if (empty($filledUp)) {
                // No bucket filled up, so we're done (all money placed or share was 0)
                break;
            }

            // Remove filled buckets and retry with remaining money
            $eligible = $eligible->forget($filledUp)->values();
        }

        return $remaining;
    }

    /**
     * Get available space for a bucket given the cap method and already-allocated amounts.
     */
    private function getAvailableSpace(Bucket $bucket, string $capMethod, array $allocated): int
    {
        // Non-fixed-limit buckets (percentage, unlimited) have no meaningful cap in phased distribution
        if (! $bucket->hasFiniteCapacity()) {
            return 0;
        }

        $cap = $capMethod === self::CAP_BASE
            ? ($bucket->allocation_value ?? 0)
            : $bucket->getEffectiveCapacity();

        $currentBalance = $bucket->getCurrentBalance();
        $alreadyAllocated = $allocated[$bucket->id] ?? 0;

        return max(0, $cap - $currentBalance - $alreadyAllocated);
    }
}