<?php

declare(strict_types=1);

namespace App\Services\TenantConfiguration;

final class EntraCoverageComparator
{
    /**
     * @var list<string>
     */
    private const MATERIAL_CHANGE_TYPES = [
        'added',
        'removed',
        'changed',
    ];

    public function __construct(
        private readonly EntraComparablePayloadNormalizer $normalizer,
    ) {}

    /**
     * @param  array<string, mixed>  $beforePayload
     * @param  array<string, mixed>  $afterPayload
     * @return array<string, mixed>
     */
    public function compare(string $canonicalType, array $beforePayload, array $afterPayload): array
    {
        if (! $this->normalizer->supports($canonicalType)) {
            return [
                'canonical_type' => $canonicalType,
                'supported' => false,
                'classification' => 'unsupported_field',
                'changed' => false,
                'changes' => [[
                    'field' => 'canonical_type',
                    'classification' => 'unsupported_field',
                    'importance' => 'informational',
                ]],
            ];
        }

        $before = $this->normalizer->normalize($canonicalType, $beforePayload);
        $after = $this->normalizer->normalize($canonicalType, $afterPayload);
        $changes = [
            ...$this->volatileChanges($beforePayload, $afterPayload),
            ...$this->diagnosticChanges($before, $after),
            ...$this->materialChanges(
                $this->materialPayload($before),
                $this->materialPayload($after),
            ),
        ];
        $hasMaterialChange = collect($changes)
            ->contains(fn (array $change): bool => in_array($change['classification'] ?? null, self::MATERIAL_CHANGE_TYPES, true));

        return [
            'canonical_type' => $canonicalType,
            'supported' => true,
            'classification' => $hasMaterialChange ? 'changed' : 'unchanged',
            'changed' => $hasMaterialChange,
            'changes' => $changes,
        ];
    }

    /**
     * @param  array<string, mixed>  $payload
     * @return array<string, mixed>
     */
    private function materialPayload(array $payload): array
    {
        unset($payload['diagnostics'], $payload['supported'], $payload['canonical_type']);

        return $payload;
    }

    /**
     * @param  array<string, mixed>  $before
     * @param  array<string, mixed>  $after
     * @return list<array<string, mixed>>
     */
    private function materialChanges(array $before, array $after, string $path = ''): array
    {
        $changes = [];
        $keys = array_values(array_unique([...array_keys($before), ...array_keys($after)]));
        sort($keys, SORT_NATURAL | SORT_FLAG_CASE);

        foreach ($keys as $key) {
            $field = $path === '' ? (string) $key : $path.'.'.(string) $key;
            $beforeValue = $before[$key] ?? null;
            $afterValue = $after[$key] ?? null;

            if (is_array($beforeValue) && is_array($afterValue) && ! array_is_list($beforeValue) && ! array_is_list($afterValue)) {
                foreach ($this->materialChanges($beforeValue, $afterValue, $field) as $nestedChange) {
                    $changes[] = $nestedChange;
                }

                continue;
            }

            if ($beforeValue === $afterValue) {
                continue;
            }

            $changes[] = [
                'field' => $field,
                'classification' => $this->changeClassification($beforeValue, $afterValue),
                'importance' => $this->importance($field),
                'before' => $beforeValue,
                'after' => $afterValue,
            ];
        }

        return $changes;
    }

    private function changeClassification(mixed $beforeValue, mixed $afterValue): string
    {
        if ($this->isEmptyValue($beforeValue) && ! $this->isEmptyValue($afterValue)) {
            return 'added';
        }

        if (! $this->isEmptyValue($beforeValue) && $this->isEmptyValue($afterValue)) {
            return 'removed';
        }

        return 'changed';
    }

    private function isEmptyValue(mixed $value): bool
    {
        return $value === null || $value === '' || $value === [];
    }

    private function importance(string $field): string
    {
        if ($field === 'state') {
            return 'critical';
        }

        if (str_starts_with($field, 'targets.')
            || str_starts_with($field, 'grant_controls.')
            || str_starts_with($field, 'session_controls.')
            || str_starts_with($field, 'conditions.')
        ) {
            return 'important';
        }

        return 'informational';
    }

    /**
     * @param  array<string, mixed>  $beforePayload
     * @param  array<string, mixed>  $afterPayload
     * @return list<array<string, mixed>>
     */
    private function volatileChanges(array $beforePayload, array $afterPayload): array
    {
        $changes = [];

        foreach ($this->normalizer->volatileRootFields() as $field) {
            $before = $beforePayload[$field] ?? null;
            $after = $afterPayload[$field] ?? null;

            if ($before === $after) {
                continue;
            }

            $changes[] = [
                'field' => $field,
                'classification' => 'ignored_volatile',
                'importance' => 'informational',
            ];
        }

        return $changes;
    }

    /**
     * @param  array<string, mixed>  $before
     * @param  array<string, mixed>  $after
     * @return list<array<string, mixed>>
     */
    private function diagnosticChanges(array $before, array $after): array
    {
        $changes = [];

        foreach ($this->diagnosticFieldUnion($before, $after, 'unsupported_fields') as $field) {
            $changes[] = [
                'field' => $field,
                'classification' => 'unsupported_field',
                'importance' => 'informational',
            ];
        }

        foreach ($this->diagnosticFieldUnion($before, $after, 'redacted_fields') as $field) {
            $changes[] = [
                'field' => $field,
                'classification' => 'redacted',
                'importance' => 'informational',
            ];
        }

        return $changes;
    }

    /**
     * @param  array<string, mixed>  $before
     * @param  array<string, mixed>  $after
     * @return list<string>
     */
    private function diagnosticFieldUnion(array $before, array $after, string $key): array
    {
        $fields = [
            ...$this->diagnosticFieldList($before, $key),
            ...$this->diagnosticFieldList($after, $key),
        ];
        $fields = array_values(array_unique($fields));
        sort($fields, SORT_NATURAL | SORT_FLAG_CASE);

        return $fields;
    }

    /**
     * @param  array<string, mixed>  $payload
     * @return list<string>
     */
    private function diagnosticFieldList(array $payload, string $key): array
    {
        $fields = data_get($payload, 'diagnostics.'.$key, []);

        if (! is_array($fields)) {
            return [];
        }

        return array_values(array_filter(
            array_map(static fn (mixed $field): string => is_string($field) ? trim($field) : '', $fields),
            static fn (string $field): bool => $field !== '',
        ));
    }
}