// Copyright (C) 2025 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.

package slogutil

import (
	"log/slog"
	"maps"
	"sync"
)

// A levelTracker keeps track of log level per package. This enables the
// traditional STTRACE variable to set certain packages to debug level, but
// also allows setting packages to other levels such as WARN to silence
// INFO-level messages.
//
// The STTRACE environment variable is one way of controlling this, where
// mentioning a package makes it DEBUG level:
//     STTRACE="model,protocol"  # model and protocol are at DEBUG level
// however you can also give specific levels after a colon:
//     STTRACE="model:WARNING,protocol:DEBUG"

func PackageDescrs() map[string]string {
	return globalLevels.Descrs()
}

func PackageLevels() map[string]slog.Level {
	return globalLevels.Levels()
}

func SetPackageLevel(pkg string, level slog.Level) {
	globalLevels.Set(pkg, level)
}

func SetDefaultLevel(level slog.Level) {
	globalLevels.SetDefault(level)
}

type levelTracker struct {
	mut      sync.RWMutex
	defLevel slog.Level
	descrs   map[string]string     // package name to description
	levels   map[string]slog.Level // package name to level
}

func (t *levelTracker) Get(pkg string) slog.Level {
	t.mut.RLock()
	defer t.mut.RUnlock()
	if level, ok := t.levels[pkg]; ok {
		return level
	}
	return t.defLevel
}

func (t *levelTracker) Set(pkg string, level slog.Level) {
	t.mut.Lock()
	changed := t.levels[pkg] != level
	t.levels[pkg] = level
	t.mut.Unlock()
	if changed {
		slog.Info("Changed package log level", "package", pkg, "level", level)
	}
}

func (t *levelTracker) SetDefault(level slog.Level) {
	t.mut.Lock()
	changed := t.defLevel != level
	t.defLevel = level
	t.mut.Unlock()
	if changed {
		slog.Info("Changed default log level", "level", level)
	}
}

func (t *levelTracker) SetDescr(pkg, descr string) {
	t.mut.Lock()
	t.descrs[pkg] = descr
	t.mut.Unlock()
}

func (t *levelTracker) Descrs() map[string]string {
	t.mut.RLock()
	defer t.mut.RUnlock()
	m := make(map[string]string, len(t.descrs))
	maps.Copy(m, t.descrs)
	return m
}

func (t *levelTracker) Levels() map[string]slog.Level {
	t.mut.RLock()
	defer t.mut.RUnlock()
	m := make(map[string]slog.Level, len(t.descrs))
	for pkg := range t.descrs {
		if level, ok := t.levels[pkg]; ok {
			m[pkg] = level
		} else {
			m[pkg] = t.defLevel
		}
	}
	return m
}