<?php

namespace App\Services;

class WhisperTranscriptionStream
{
    /**
     * Pull complete SSE `data:` payloads out of a rolling buffer.
     *
     * @return list<string>
     */
    public function extractPayloads(string &$buffer): array
    {
        $frames = explode("\n\n", str_replace("\r\n", "\n", $buffer));
        $buffer = array_pop($frames) ?? '';
        $payloads = [];

        foreach ($frames as $frame) {
            foreach ($this->dataLines($frame) as $payload) {
                if ($payload === '[DONE]' || $payload === '') {
                    continue;
                }

                $payloads[] = $payload;
            }
        }

        return $payloads;
    }

    /**
     * Flush a trailing incomplete frame at end-of-stream.
     *
     * @return list<string>
     */
    public function flushBuffer(string &$buffer): array
    {
        $trimmed = trim($buffer);

        if ($trimmed === '') {
            $buffer = '';

            return [];
        }

        $buffer .= "\n\n";

        return $this->extractPayloads($buffer);
    }

    /**
     * Parse one SSE JSON payload into append/replace/end/done fields.
     *
     * @return array{append: ?string, replace: ?string, end: ?float, done: bool, legacy: bool}|null
     */
    public function parseEvent(string $json): ?array
    {
        $data = json_decode($json, true);

        if (! is_array($data)) {
            return null;
        }

        $type = $data['type'] ?? null;

        if ($type === 'transcript.text.delta') {
            $delta = $data['delta'] ?? '';

            if (! is_string($delta) || $delta === '') {
                return null;
            }

            return [
                'append' => $delta,
                'replace' => null,
                'end' => $this->nullableFloat($data['end'] ?? null),
                'done' => false,
                'legacy' => false,
            ];
        }

        if ($type === 'transcript.text.done') {
            $text = $data['text'] ?? '';

            return [
                'append' => null,
                'replace' => is_string($text) ? $text : '',
                'end' => $this->nullableFloat($data['end'] ?? null),
                'done' => true,
                'legacy' => false,
            ];
        }

        if ($type === null && isset($data['text']) && is_string($data['text']) && $data['text'] !== '') {
            return [
                'append' => $data['text'],
                'replace' => null,
                'end' => $this->nullableFloat($data['end'] ?? null),
                'done' => false,
                'legacy' => true,
            ];
        }

        return null;
    }

    /**
     * Apply a parsed event to the accumulated transcript.
     *
     * @param  array{append: ?string, replace: ?string, end: ?float, done: bool, legacy: bool}  $event
     */
    public function applyEvent(string $accumulated, array $event): string
    {
        if (is_string($event['replace'])) {
            return $event['replace'];
        }

        $chunk = $event['append'] ?? '';

        if ($chunk === '') {
            return $accumulated;
        }

        if ($event['legacy']) {
            $chunk = trim($chunk);

            if ($accumulated === '') {
                return $chunk;
            }

            return rtrim($accumulated).' '.$chunk;
        }

        return $accumulated.$chunk;
    }

    /**
     * @return list<string>
     */
    private function dataLines(string $frame): array
    {
        $payloads = [];

        foreach (explode("\n", $frame) as $line) {
            if (str_starts_with($line, 'data:')) {
                $payloads[] = ltrim(substr($line, 5));
            }
        }

        return $payloads;
    }

    private function nullableFloat(mixed $value): ?float
    {
        if (! is_numeric($value)) {
            return null;
        }

        return (float) $value;
    }
}