package com.baiyue.common.web;

import org.slf4j.MDC;

import java.util.UUID;
import java.util.regex.Pattern;

/** Immutable standard headers for one synchronous outbound child span. */
public record OutboundTraceHeaders(String requestId, String traceId, String traceParent) {
    private static final Pattern SAFE_REQUEST_ID = Pattern.compile("[A-Za-z0-9._:-]{1,128}");

    /** Builds a child span from the current MDC, safely starting a new trace when absent/invalid. */
    public static OutboundTraceHeaders fromCurrentOrNew() {
        String requestId = safeRequestId(MDC.get(CorrelationContext.REQUEST_ID));
        String traceId = TraceParent.normalizeTrustedTraceId(MDC.get(CorrelationContext.TRACE_ID))
                .orElseGet(() -> TraceParent.newRoot(null).traceId());
        return child(requestId, traceId);
    }

    /** Builds a local child from a trusted persisted trace value, or safely starts a new trace. */
    public static OutboundTraceHeaders fromTrustedTraceOrNew(String trustedTraceId) {
        String traceId = TraceParent.normalizeTrustedTraceId(trustedTraceId)
                .orElseGet(() -> TraceParent.newRoot(null).traceId());
        return child(UUID.randomUUID().toString(), traceId);
    }

    public String spanId() {
        return TraceParent.parse(traceParent).orElseThrow().parentId();
    }

    private static OutboundTraceHeaders child(String requestId, String traceId) {
        TraceParent child = TraceParent.outboundChild(traceId);
        return new OutboundTraceHeaders(requestId, child.traceId(), child.value());
    }

    private static String safeRequestId(String value) {
        return value != null && SAFE_REQUEST_ID.matcher(value).matches()
                ? value : UUID.randomUUID().toString();
    }
}