package com.suno.android.common_networking.sse

import javax.inject.Inject

private const val ID_LINE_PREFIX = "id:"
private const val DATA_LINE_PREFIX = "data:"
private const val EVENT_LINE_PREFIX = "event:"
private const val RETRY_LINE_PREFIX = "retry:"
private const val COMMENT_PREFIX = ":"

/**
 * Parses Server-Sent Events lines according to the WHATWG SSE specification.
 * https://html.spec.whatwg.org/multipage/server-sent-events.html
 */
class SseLineParser @Inject constructor() {
    /**
     * Parses a single SSE line according to the specification.
     */
    fun parseLine(
        rawLine: String,
    ): ParsedLine =
        when {
            rawLine.startsWith(ID_LINE_PREFIX) -> ParsedLine.Id(rawLine.substringAfter(ID_LINE_PREFIX).trim())
            rawLine.startsWith(DATA_LINE_PREFIX) -> ParsedLine.Data(rawLine.substringAfter(DATA_LINE_PREFIX).trim())
            rawLine.startsWith(EVENT_LINE_PREFIX) -> ParsedLine.Event(rawLine.substringAfter(EVENT_LINE_PREFIX).trim())
            rawLine.startsWith(RETRY_LINE_PREFIX) -> {
                val retryValue = rawLine.substringAfter(RETRY_LINE_PREFIX).trim()
                val retryMs = retryValue.toLongOrNull()
                ParsedLine.Retry(retryMs)
            }
            rawLine.startsWith(COMMENT_PREFIX) -> ParsedLine.Comment(rawLine)
            rawLine.isBlank() -> ParsedLine.EndOfEvent(rawLine)
            else -> ParsedLine.Other(rawLine)
        }

    sealed class ParsedLine {
        /**
         * Event ID for reconnection via lastEventId param.
         */
        data class Id(
            val id: String,
        ) : ParsedLine()

        /**
         * Event data. Multiple data lines are joined with newlines per SSE spec.
         */
        data class Data(
            val data: String,
        ) : ParsedLine()

        /**
         * Event type.
         */
        data class Event(
            val eventType: String,
        ) : ParsedLine()

        /**
         * Reconnection time in milliseconds.
         */
        data class Retry(
            val retryMs: Long?,
        ) : ParsedLine()

        /**
         * Comment line starting with ':'. Ignored per SSE spec.
         */
        data class Comment(
            val rawLine: String,
        ) : ParsedLine()

        /**
         * Blank line indicating end of event. Triggers event dispatch per SSE spec.
         */
        data class EndOfEvent(
            val rawLine: String,
        ) : ParsedLine()

        /**
         * Unrecognized line format. Ignored per SSE spec.
         */
        data class Other(
            val rawLine: String,
        ) : ParsedLine()
    }
}