import QtQuick

// Tiny SSE client implemented in pure QML.
// Caveat: relies on QML's XMLHttpRequest delivering partial responses
// during readyState === LOADING. If that proves unreliable, this gets
// replaced by a C++ class in Phase 1 (per PLAN.md §7, MercureClient).
QtObject {
    id: root

    property string url: ""
    property bool active: false

    signal eventReceived(string data, string id)
    signal stateChanged(string state)

    property var _xhr: null
    property int _offset: 0
    property string _accumulated: ""

    function connect() {
        if (active) return
        _offset = 0
        _accumulated = ""

        const xhr = new XMLHttpRequest()
        xhr.open("GET", url)
        xhr.setRequestHeader("Accept", "text/event-stream")
        xhr.onreadystatechange = function() {
            if (xhr.readyState === XMLHttpRequest.LOADING ||
                xhr.readyState === XMLHttpRequest.DONE) {
                const text = xhr.responseText
                if (text.length > _offset) {
                    const fresh = text.substring(_offset)
                    _offset = text.length
                    _ingest(fresh)
                }
            }
            if (xhr.readyState === XMLHttpRequest.DONE) {
                active = false
                stateChanged("disconnected")
            }
        }
        xhr.send()
        _xhr = xhr
        active = true
        stateChanged("connected")
    }

    function disconnect() {
        if (!active) return
        if (_xhr) _xhr.abort()
        active = false
        stateChanged("disconnected")
    }

    function _ingest(chunk) {
        _accumulated += chunk
        const parts = _accumulated.split("\n\n")
        _accumulated = parts.pop()
        for (let i = 0; i < parts.length; ++i) {
            _emit(parts[i])
        }
    }

    function _emit(message) {
        const lines = message.split("\n")
        let id = ""
        let dataLines = []
        for (let i = 0; i < lines.length; ++i) {
            const line = lines[i]
            if (line.length === 0 || line.charAt(0) === ":") continue
            const colon = line.indexOf(":")
            if (colon < 0) continue
            const field = line.substring(0, colon)
            let value = line.substring(colon + 1)
            if (value.length > 0 && value.charAt(0) === " ") value = value.substring(1)
            if (field === "data") dataLines.push(value)
            else if (field === "id") id = value
        }
        if (dataLines.length > 0) {
            eventReceived(dataLines.join("\n"), id)
        }
    }
}