<?php

namespace App\Libraries\Abdm\Fhir;

class FhirDocumentBuilder
{
    /** @var array<int,array<string,mixed>> */
    private array $entries = [];

    /** @var array<string,bool> */
    private array $resourceIds = [];

    /** @var array<string,mixed> */
    private array $bundleMeta = [];

    /** @var array<string,mixed>|null */
    private ?array $composition = null;

    public function buildBundleMeta(string $identifierValue, string $timestamp): self
    {
        $this->bundleMeta = [
            'resourceType' => 'Bundle',
            'id' => $identifierValue,
            'meta' => [
                'versionId' => '1',
                'lastUpdated' => $timestamp,
                'profile' => ['https://nrces.in/ndhm/fhir/r4/StructureDefinition/DocumentBundle'],
                'security' => [[
                    'system' => 'http://terminology.hl7.org/CodeSystem/v3-Confidentiality',
                    'code' => 'V',
                    'display' => 'very restricted'
                ]]
            ],
            'identifier' => [
                'system' => 'https://hms.local/fhir/document',
                'value' => $identifierValue,
            ],
            'type' => 'document',
            'timestamp' => $timestamp,
        ];

        return $this;
    }

    /** @param array<string,mixed> $values */
    public function updateBundleMeta(array $values): self
    {
        $this->bundleMeta = array_replace($this->bundleMeta, $values);

        return $this;
    }

    /**
     * @param array<string,mixed> $composition
     */
    public function buildComposition(array $composition): self
    {
        $this->composition = $composition;
        return $this;
    }

    /** @param array<string,mixed> $values */
    public function updateComposition(array $values): self
    {
        if (is_array($this->composition)) {
            $this->composition = array_replace($this->composition, $values);
        }

        return $this;
    }

    /**
     * @param array<string,mixed> $resource
     */
    public function addPatient(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addEncounter(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addPractitioner(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addOrganization(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addCondition(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addObservation(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addServiceRequest(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addAllergyIntolerance(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addCarePlan(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addDiagnosticReport(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addMedicationRequest(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addProcedure(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addClaim(array $resource): self
    {
        return $this->addResource($resource);
    }

    /** @param array<string,mixed> $resource */
    public function addDocumentReference(array $resource): self
    {
        return $this->addResource($resource);
    }

    /**
     * @return array<string,mixed>
     */
    public function toBundle(): array
    {
        $bundle = $this->bundleMeta;
        $entries = [];

        if (is_array($this->composition)) {
            $entries[] = $this->wrapEntry($this->composition);
        }

        foreach ($this->entries as $entry) {
            $entries[] = $entry;
        }

        $bundle['entry'] = $this->normalizeEntryReferences($entries);
        return $this->stripNulls($bundle);
    }

    /**
     * A urn:uuid fullUrl must contain an RFC 4122 UUID. Resource ids remain
     * human-readable while all document references use deterministic UUID URNs.
     *
     * @param array<int,array<string,mixed>> $entries
     * @return array<int,array<string,mixed>>
     */
    private function normalizeEntryReferences(array $entries): array
    {
        $referenceMap = [];
        $idMap = [];
        foreach ($entries as $entry) {
            $resource = (array) ($entry['resource'] ?? []);
            $id = (string) ($resource['id'] ?? '');
            if ($id === '') {
                continue;
            }
            $newUuid = $this->uuidForResource($resource);
            $referenceMap['urn:uuid:' . $id] = 'urn:uuid:' . $newUuid;
            $idMap[$id] = $newUuid;
        }

        foreach ($entries as &$entry) {
            $resource = (array) ($entry['resource'] ?? []);
            $id = (string) ($resource['id'] ?? '');
            if ($id !== '') {
                $entry['fullUrl'] = $referenceMap['urn:uuid:' . $id];
            }
            $resource = $this->rewriteReferences($resource, $referenceMap);
            if ($id !== '') {
                $resource['id'] = $idMap[$id];
            }
            $entry['resource'] = $resource;
        }
        unset($entry);

        return $entries;
    }

    /** @param array<string,mixed> $resource */
    private function uuidForResource(array $resource): string
    {
        $hex = md5((string) ($resource['resourceType'] ?? 'Resource') . '/' . (string) ($resource['id'] ?? ''));
        return substr($hex, 0, 8) . '-' . substr($hex, 8, 4) . '-4' . substr($hex, 13, 3)
            . '-a' . substr($hex, 17, 3) . '-' . substr($hex, 20, 12);
    }

    /**
     * @param mixed $value
     * @param array<string,string> $referenceMap
     * @return mixed
     */
    private function rewriteReferences($value, array $referenceMap)
    {
        if (is_string($value)) {
            return $referenceMap[$value] ?? $value;
        }
        if (! is_array($value)) {
            return $value;
        }

        foreach ($value as $key => $nested) {
            $value[$key] = $this->rewriteReferences($nested, $referenceMap);
        }

        return $value;
    }

    /**
     * @param array<string,mixed> $resource
     */
    private function addResource(array $resource): self
    {
        $id = (string) ($resource['id'] ?? '');
        if ($id === '') {
            $resource['id'] = $this->newId((string) ($resource['resourceType'] ?? 'resource'));
            $id = (string) $resource['id'];
        }

        $fullRef = (string) ($resource['resourceType'] ?? '') . '/' . $id;
        if (isset($this->resourceIds[$fullRef])) {
            return $this;
        }

        $this->resourceIds[$fullRef] = true;
        $this->entries[] = $this->wrapEntry($resource);
        return $this;
    }

    /**
     * @param array<string,mixed> $resource
     * @return array<string,mixed>
     */
    private function wrapEntry(array $resource): array
    {
        $id = (string) ($resource['id'] ?? $this->newId((string) ($resource['resourceType'] ?? 'resource')));
        $resource['id'] = $id;

        return [
            'fullUrl' => 'urn:uuid:' . $id,
            'resource' => $this->stripNulls($resource),
        ];
    }

    /**
     * @param array<string,mixed> $data
     * @return array<string,mixed>
     */
    private function stripNulls(array $data): array
    {
        $out = [];
        foreach ($data as $key => $value) {
            if ($value === null || $value === '' || $this->isPlaceholderValue($value)) {
                continue;
            }
            if (is_array($value)) {
                $clean = $this->stripNested($value);
                if ($clean === [] || $clean === null) {
                    continue;
                }
                $out[$key] = $clean;
                continue;
            }
            $out[$key] = $value;
        }
        return $out;
    }

    /**
     * @param array<int|string,mixed> $value
     * @return array<int|string,mixed>|null
     */
    private function stripNested(array $value): ?array
    {
        $clean = [];
        foreach ($value as $k => $v) {
            if ($v === null || $v === '' || $this->isPlaceholderValue($v)) {
                continue;
            }
            if (is_array($v)) {
                $nested = $this->stripNested($v);
                if ($nested === null || $nested === []) {
                    continue;
                }
                $clean[$k] = $nested;
                continue;
            }
            $clean[$k] = $v;
        }

        return $clean === [] ? null : $clean;
    }

    /**
     * Returns true only for display-level placeholder strings that should never
     * appear in a rendered FHIR bundle (pure "no data" sentinel values).
     * NOTE: '0' is intentionally excluded — it is a valid FHIR quantity value,
     * coded value, and identifier string. Its earlier inclusion caused silent
     * data loss in observation valueQuantity and numeric identifiers.
     *
     * @param mixed $value
     */
    private function isPlaceholderValue($value): bool
    {
        if (! is_string($value)) {
            return false;
        }

        return in_array(strtoupper(trim($value)), ['NA', 'N/A', 'N / A', 'NULL', 'NOT AVAILABLE', 'UNDEFINED'], true);
    }

    private function newId(string $prefix): string
    {
        $prefix = strtolower(preg_replace('/[^a-z0-9]/i', '-', $prefix) ?: 'resource');
        $bytes = bin2hex(random_bytes(6));
        return $prefix . '-' . $bytes;
    }
}