// Package verbose provides a process-wide verbosity level and a pluggable
// log sink so verbose output integrates with the downloader's progress bars.
//
// Level meaning:
//
//	0 (Off) - no extra output
//	1 (V)   - log per-track CDN URLs from the downloader
//	2 (VV)  - additionally log every outbound HTTP request via the
//	          netutil-wrapped transport (covers all provider API calls
//	          and downloads)
package verbose

import (
	"fmt"
	"os"
	"sync/atomic"
)

const (
	Off byte = 0
	V   byte = 1
	VV  byte = 2
)

var (
	level atomic.Uint32
	sink  atomic.Pointer[func(string)]
)

// SetLevel clamps and stores the verbosity level. Pass 0 to disable.
func SetLevel(l int) {
	if l < 0 {
		l = 0
	}
	if l > int(VV) {
		l = int(VV)
	}
	level.Store(uint32(l))
}

func Level() byte { return byte(level.Load()) }

func Enabled(l byte) bool { return Level() >= l }

// SetSink installs a writer for verbose output. Use this to route logs
// through the downloader so they don't tear progress bars. Pass nil to
// fall back to stderr.
func SetSink(fn func(string)) {
	if fn == nil {
		sink.Store(nil)
		return
	}
	sink.Store(&fn)
}

// Printf emits a line at the given level if verbosity is enabled. The
// caller is responsible for including a trailing newline.
func Printf(l byte, format string, args ...any) {
	if !Enabled(l) {
		return
	}
	msg := fmt.Sprintf(format, args...)
	if p := sink.Load(); p != nil {
		(*p)(msg)
		return
	}
	_, _ = fmt.Fprint(os.Stderr, msg)
}