#include "protocol.h"
#include <stdio.h>
#include <stdarg.h>

#define PROTOCOL_VERSION 1

static inline int append(char* buf, size_t size, int pos, const char* fmt, ...) {
    if ((size_t)pos >= size) return -1;

    va_list args;
    va_start(args, fmt);
    int written = vsnprintf(buf + pos, size - pos, fmt, args);
    va_end(args);

    if (written < 0 || (size_t)(pos + written) >= size) {
        return -1;
    }

    return pos + written;
}

// --- TELEMETRY (single measurement) ---
int build_telemetry_single(
    char* buf,
    size_t buf_size,
    const char* id,
    const char* device_id,
    int64_t ts_ms,
    const char* metric,
    double value,
    const char* unit,
    const char* source,
    int64_t m_ts_ms
) {
    int pos = 0;

    // header
    pos = append(buf, buf_size, pos,
        "{\"v\":%d,\"id\":\"%s\",\"type\":\"telemetry\",\"ts\":%lld,"
        "\"deviceId\":\"%s\",\"payload\":{\"measurements\":[",
        PROTOCOL_VERSION,
        id,
        (long long)ts_ms,
        device_id
    );
    if (pos < 0) return -1;

    // measurement start
    pos = append(buf, buf_size, pos,
        "{\"metric\":\"%s\",\"value\":%.3f",
        metric,
        value
    );
    if (pos < 0) return -1;

    // optional
    if (unit) {
        pos = append(buf, buf_size, pos, ",\"unit\":\"%s\"", unit);
        if (pos < 0) return -1;
    }

    if (source) {
        pos = append(buf, buf_size, pos, ",\"source\":\"%s\"", source);
        if (pos < 0) return -1;
    }

    if (m_ts_ms > 0) {
        pos = append(buf, buf_size, pos, ",\"ts\":%lld", (long long)m_ts_ms);
        if (pos < 0) return -1;
    }

    // close measurement + payload
    pos = append(buf, buf_size, pos, "}]}}");
    if (pos < 0) return -1;

    return pos;
}

// --- EVENT ---
int build_event(
    char* buf,
    size_t buf_size,
    const char* id,
    const char* device_id,
    int64_t ts_ms,
    const char* name,
    const char* severity,
    const char* message
) {
    int pos = 0;

    // header
    pos = append(buf, buf_size, pos,
        "{\"v\":%d,\"id\":\"%s\",\"type\":\"event\",\"ts\":%lld,"
        "\"deviceId\":\"%s\",\"payload\":{",
        PROTOCOL_VERSION,
        id,
        (long long)ts_ms,
        device_id
    );
    if (pos < 0) return -1;

    // required
    pos = append(buf, buf_size, pos, "\"name\":\"%s\"", name);
    if (pos < 0) return -1;

    // optional
    if (severity) {
        pos = append(buf, buf_size, pos, ",\"severity\":\"%s\"", severity);
        if (pos < 0) return -1;
    }

    if (message) {
        pos = append(buf, buf_size, pos, ",\"message\":\"%s\"", message);
        if (pos < 0) return -1;
    }

    // close
    pos = append(buf, buf_size, pos, "}}");
    if (pos < 0) return -1;

    return pos;
}