(new): add threshold-based log level filtering and docs

- add threshold-aware LogLevel constructors
- add Logger.SetThresholdMode and SameThreshold
- preserve legacy SameLevel behavior for compatibility
- extend tests for threshold mode and compatibility
- update README and release notes for v2.2.0

README.md

@@ -71,6 +71,10 @@ func main() {
 
 Important: with the current level ordering, `Level(sneklog.FATAL)` allows `INFO`, `WARN`, `ERROR`, and `FATAL`, but not `DEBUG`. Use `Level(sneklog.DEBUG)` to enable every level.
 
+If you want classic threshold filtering instead, call `SetThresholdMode(true)` and
+configure levels with `NewThresholdLogLevel(...)` or
+`NewThresholdLogLevelWithColors(...)`.
+
 ## Writers and ownership
 
 `Logger.Close()` only closes writers created by the logger itself:
@@ -142,6 +146,29 @@ access := sneklog.NewInfoLogLevelWithColors("access", sneklog.FgCyan, sneklog.Bg
 audit := sneklog.NewWarnLogLevel("audit")
 ```
 
+These helpers keep the legacy severity index for backward compatibility and also
+assign default threshold values:
+
+- `INFO`: `th=10`
+- `WARN`: `th=20`
+- `ERROR`: `th=30`
+- `FATAL`: `th=40`
+- `DEBUG`: `th=0`
+
+To define custom threshold-based levels explicitly:
+
+```go
+trace := sneklog.NewThresholdLogLevelWithColors(4, 5, "trace", sneklog.FgHiBlack, sneklog.BgNone)
+audit := sneklog.NewThresholdLogLevel(1, 25, "audit")
+
+logger := sneklog.NewLogger().
+	SetLevel(audit).
+	SetThresholdMode(true)
+
+logger.Print(trace, "verbose trace") // filtered out
+logger.Print(audit, "audit event")   // allowed
+```
+
 HTTP method-specific predefined levels are available out of the box:
 
 ```go
@@ -149,8 +176,11 @@ level := sneklog.LogLevelForMethod(http.MethodPost)
 logger.Print(level, "POST /users")
 ```
 
-When comparing levels, use `SameLevel` if only the severity matters and `Equal`
-if the full configuration, including colors and attributes, must match.
+When comparing levels:
+
+- use `SameLevel` if only the legacy severity index matters;
+- use `SameThreshold` if only threshold filtering matters;
+- use `Equal` if the full configuration, including threshold, colors, and attributes, must match.
 
 ## Message replacement
 

README_ru.md

@@ -71,6 +71,10 @@ func main() {
 
 Важно: в текущей модели уровней `Level(sneklog.FATAL)` пропускает `INFO`, `WARN`, `ERROR` и `FATAL`, но не `DEBUG`. Чтобы включить все сообщения, используйте `Level(sneklog.DEBUG)`.
 
+Если нужна классическая threshold-фильтрация, включите `SetThresholdMode(true)` и
+задавайте уровни через `NewThresholdLogLevel(...)` или
+`NewThresholdLogLevelWithColors(...)`.
+
 ## Writer'ы и владение
 
 `Logger.Close()` закрывает только writer'ы, которые логгер создал сам:
@@ -142,6 +146,29 @@ access := sneklog.NewInfoLogLevelWithColors("access", sneklog.FgCyan, sneklog.Bg
 audit := sneklog.NewWarnLogLevel("audit")
 ```
 
+Эти helper'ы сохраняют legacy severity index для обратной совместимости и
+одновременно выставляют значения threshold по умолчанию:
+
+- `INFO`: `th=10`
+- `WARN`: `th=20`
+- `ERROR`: `th=30`
+- `FATAL`: `th=40`
+- `DEBUG`: `th=0`
+
+Чтобы явно создавать уровни для threshold-режима:
+
+```go
+trace := sneklog.NewThresholdLogLevelWithColors(4, 5, "trace", sneklog.FgHiBlack, sneklog.BgNone)
+audit := sneklog.NewThresholdLogLevel(1, 25, "audit")
+
+logger := sneklog.NewLogger().
+	SetLevel(audit).
+	SetThresholdMode(true)
+
+logger.Print(trace, "verbose trace") // будет отфильтровано
+logger.Print(audit, "audit event")   // будет записано
+```
+
 Для HTTP-методов доступны готовые уровни:
 
 ```go
@@ -149,9 +176,11 @@ level := sneklog.LogLevelForMethod(http.MethodPost)
 logger.Print(level, "POST /users")
 ```
 
-Если нужно сравнить только severity, используйте `SameLevel`. Если нужно
-полное совпадение конфигурации уровня, включая цвета и атрибуты, используйте
-`Equal`.
+При сравнении уровней:
+
+- используйте `SameLevel`, если важен только legacy severity index;
+- используйте `SameThreshold`, если важна только threshold-фильтрация;
+- используйте `Equal`, если нужно полное совпадение конфигурации, включая threshold, цвета и атрибуты.
 
 ## Замена сообщений
 

RELEASE_NOTES.md

@@ -1,6 +1,8 @@
 # Unreleased (planned v2.2.0)
 
-This release expands the public LogLevel API, adds HTTP method helpers, and improves package documentation and test coverage.
+This release expands the public LogLevel API, adds optional threshold-based
+filtering alongside the legacy severity ordering, and improves documentation
+and test coverage.
 
 ### Added
 
@@ -15,6 +17,9 @@ This release expands the public LogLevel API, adds HTTP method helpers, and impr
   - `NewFatalLogLevelWithColors`
   - `NewDebugLogLevel`
   - `NewDebugLogLevelWithColors`
+- Added threshold-aware log level constructors:
+  - `NewThresholdLogLevel`
+  - `NewThresholdLogLevelWithColors`
 - Added HTTP method-specific predefined log levels:
   - `HTTPGetLevel`
   - `HTTPHeadLevel`
@@ -28,24 +33,30 @@ This release expands the public LogLevel API, adds HTTP method helpers, and impr
   - `HTTPUnknownLevel`
 - Added `LogLevelForMethod(method string) LogLevel` to map HTTP methods to predefined log levels.
 - Added `Logger.Printf(level, format, args...)` for formatted logging with an explicit log level.
-- Added `LogLevel.SameLevel` and `LogLevel.Equal` for severity-only and full level comparisons.
+- Added `Logger.SetThresholdMode(bool)` to switch filtering from legacy severity-index ordering to threshold-based ordering.
+- Added `LogLevel.SameLevel`, `LogLevel.SameThreshold`, and `LogLevel.Equal` for severity-only, threshold-only, and full level comparisons.
 
 ### Changed
 
 - Refactored log level definitions into a dedicated `levels.go` file.
 - Unified `Logger.Print` and `Logger.Println` through a shared internal implementation without changing their behavior.
-- Expanded test coverage for `Logger.Printf`, HTTP level mapping, and new level constructors.
+- Common helper constructors such as `NewInfoLogLevel` now also assign threshold values while preserving legacy severity indexes.
+- `LogLevel.Equal` now includes threshold configuration in full equality checks.
+- Expanded test coverage for `Logger.Printf`, HTTP level mapping, constructor behavior, threshold filtering, and backward compatibility.
 
 ### Documentation
 
 - Improved GoDoc coverage for exported types, constructors, formatters, colors, HTTP helpers, and time layouts.
-- Documented level comparison helpers and explicit-level formatted logging.
+- Documented threshold mode, threshold-aware constructors, level comparison helpers, and explicit-level formatted logging.
 - Expanded inline documentation for formatter tokens and default formatter behavior.
+- Updated English and Russian README files with threshold-mode examples and comparison guidance.
 
 ### Compatibility
 
 - No breaking API changes.
-- Existing `Print`, `Println`, predefined levels, and color APIs remain compatible.
+- Existing `Print`, `Println`, predefined levels, `Level/SetLevel`, and color APIs remain compatible.
+- Legacy severity ordering remains the default; threshold filtering is enabled only when `SetThresholdMode(true)` is called.
+- `SameLevel` remains severity-only for backward compatibility, even when levels carry threshold metadata.
 
 # v2.1.0
 

doc.go

@@ -47,6 +47,7 @@
 // io.Writer values through CreateTextWriter or CreateJsonWriter remain owned by
 // the caller and are not closed by the logger.
 //
-// LogLevel values can be compared with SameLevel when only severity matters or
+// LogLevel values can be compared with SameLevel when only the legacy severity
+// index matters, with SameThreshold when only threshold filtering matters, or
 // with Equal when the full level configuration must match.
 package sneklog

io.go

@@ -84,7 +84,9 @@ func (l *Logger) Debugln(m ...any) {
 }
 
 func (l *Logger) print(level LogLevel, newline bool, m ...any) {
-	if l.level.n < level.n {
+	if l.threshold && l.level.th < level.th {
+		return
+	} else if l.level.n < level.n {
 		return
 	}
 	if len(l.writers) == 0 {

levels.go

@@ -11,8 +11,9 @@ var (
 
 // LogLevel describes a logging severity.
 type LogLevel struct {
-	n uint8
-	t string
+	n  uint8
+	th uint8
+	t  string
 
 	fg    FgColor
 	fg256 FgColor256
@@ -26,53 +27,68 @@ type LogLevel struct {
 }
 
 // NewLogLevel creates a log level without predefined colors.
+// Deprecated: use NewThresholdLogLevel. This function will be removed in v3.
 func NewLogLevel(index uint8, name string) LogLevel {
 	return NewLogLevelWithColors(index, name, 0, 0)
 }
 
 // NewLogLevelWithColors creates a log level with ANSI foreground and background colors.
+// Deprecated: use NewThresholdLogLevelWithColors. This function will be removed in v3.
 func NewLogLevelWithColors(index uint8, name string, fg FgColor, bg BgColor) LogLevel {
 	return LogLevel{n: index, t: name, fg: fg, bg: bg, attrs: []Attribute{}}
 }
 
+// NewThresholdLogLevel creates a log level with both a legacy severity index and
+// a threshold value used when Logger.SetThresholdMode(true) is enabled.
+func NewThresholdLogLevel(index, th uint8, name string) LogLevel {
+	return NewThresholdLogLevelWithColors(index, th, name, FgNone, BgNone)
+}
+
+// NewThresholdLogLevelWithColors creates a log level with both a legacy
+// severity index and a threshold value, plus ANSI foreground and background
+// colors.
+func NewThresholdLogLevelWithColors(index, th uint8, name string, fg FgColor, bg BgColor) LogLevel {
+	return LogLevel{n: index, th: th, t: name, fg: fg, bg: bg, attrs: []Attribute{}}
+}
+
 // NewInfoLogLevel creates an info-level log level without predefined colors.
-func NewInfoLogLevel(name string) LogLevel { return NewLogLevel(0, name) }
+func NewInfoLogLevel(name string) LogLevel { return NewThresholdLogLevel(0, 10, name) }
 
 // NewInfoLogLevelWithColors creates an info-level log level with ANSI colors.
 func NewInfoLogLevelWithColors(name string, fg FgColor, bg BgColor) LogLevel {
-	return NewLogLevelWithColors(0, name, fg, bg)
+	return NewThresholdLogLevelWithColors(0, 10, name, fg, bg)
 }
 
 // NewWarnLogLevel creates a warn-level log level without predefined colors.
-func NewWarnLogLevel(name string) LogLevel { return NewLogLevel(1, name) }
+func NewWarnLogLevel(name string) LogLevel { return NewThresholdLogLevel(1, 20, name) }
 
 // NewWarnLogLevelWithColors creates a warn-level log level with ANSI colors.
 func NewWarnLogLevelWithColors(name string, fg FgColor, bg BgColor) LogLevel {
-	return NewLogLevelWithColors(1, name, fg, bg)
+	return NewThresholdLogLevelWithColors(1, 20, name, fg, bg)
 }
 
 // NewErrorLogLevel creates an error-level log level without predefined colors.
-func NewErrorLogLevel(name string) LogLevel { return NewLogLevel(2, name) }
+func NewErrorLogLevel(name string) LogLevel { return NewThresholdLogLevel(2, 30, name) }
 
 // NewErrorLogLevelWithColors creates an error-level log level with ANSI colors.
 func NewErrorLogLevelWithColors(name string, fg FgColor, bg BgColor) LogLevel {
-	return NewLogLevelWithColors(2, name, fg, bg)
+	return NewThresholdLogLevelWithColors(2, 30, name, fg, bg)
 }
 
 // NewFatalLogLevel creates a fatal-level log level without predefined colors.
-func NewFatalLogLevel(name string) LogLevel { return NewLogLevel(3, name) }
+func NewFatalLogLevel(name string) LogLevel { return NewThresholdLogLevel(3, 40, name) }
 
 // NewFatalLogLevelWithColors creates a fatal-level log level with ANSI colors.
 func NewFatalLogLevelWithColors(name string, fg FgColor, bg BgColor) LogLevel {
-	return NewLogLevelWithColors(3, name, fg, bg)
+	return NewThresholdLogLevelWithColors(3, 40, name, fg, bg)
 }
 
 // NewDebugLogLevel creates a debug-level log level without predefined colors.
-func NewDebugLogLevel(name string) LogLevel { return NewLogLevel(4, name) }
+func NewDebugLogLevel(name string) LogLevel { return NewThresholdLogLevel(4, 0, name) }
 
 // NewDebugLogLevelWithColors creates a debug-level log level with ANSI colors.
 func NewDebugLogLevelWithColors(name string, fg FgColor, bg BgColor) LogLevel {
-	return NewLogLevelWithColors(4, name, fg, bg)
+	return NewThresholdLogLevelWithColors(4, 0, name, fg, bg)
 }
 
 // GetName returns the lowercase textual representation of the level.
@@ -198,13 +214,21 @@ func (l *LogLevel) GetAttributes() []Attribute {
 }
 
 // SameLevel reports whether two log levels have the same severity index.
+// Deprecated: use SameThreshold for threshold-only comparisons or Equal for the
+// full level configuration. SameLevel remains severity-only for backward
+// compatibility and ignores threshold values.
 func (l *LogLevel) SameLevel(other LogLevel) bool {
 	return l.n == other.n
 }
 
+// SameThreshold reports whether two log levels have the same threshold value.
+func (l *LogLevel) SameThreshold(other LogLevel) bool {
+	return l.th == other.th
+}
+
 // Equal reports whether two log levels have identical configuration.
 func (l *LogLevel) Equal(other LogLevel) bool {
-	if l.t != other.t || l.n != other.n {
+	if l.t != other.t || l.n != other.n || l.th != other.th {
 		return false
 	}
 	if l.fg != other.fg || l.bg != other.bg {

logger.go

@@ -18,12 +18,14 @@ type MethodTraceback struct {
 
 // Logger routes log records to one or more configured writers.
 type Logger struct {
-	prefix    string
-	level     LogLevel
+	prefix string
+	level  LogLevel
+
 	writers   []LoggerWriter
 	replacers []replacer
 
 	jsonPretty bool
+	threshold  bool
 }
 
 // CreateLogger creates a logger with default settings.
@@ -82,6 +84,13 @@ func (l *Logger) SetJSONPretty(b bool) *Logger {
 	return l
 }
 
+// SetThresholdMode switches Logger.Print filtering from legacy severity-index
+// ordering to LogLevel threshold ordering.
+func (l *Logger) SetThresholdMode(b bool) *Logger {
+	l.threshold = b
+	return l
+}
+
 // AddWriters appends multiple writers to the logger.
 func (l *Logger) AddWriters(writers ...LoggerWriter) *Logger {
 	l.writers = append(l.writers, writers...)

logger_test.go

@@ -120,6 +120,77 @@ func TestLoggerPrintfFormatsMessage(t *testing.T) {
 	}
 }
 
+func TestLoggerUsesSeverityOrderingWhenThresholdModeIsDisabled(t *testing.T) {
+	writer := &stubLoggerWriter{}
+	logger := CreateLogger().
+		SetLevel(NewThresholdLogLevel(1, 0, "warn")).
+		AddWriter(writer)
+
+	logger.Print(NewThresholdLogLevel(0, 100, "info"))
+	logger.Print(NewThresholdLogLevel(2, 0, "error"))
+
+	if writer.printCalls != 1 {
+		t.Fatalf("severity mode should allow only lower-or-equal severity levels, got %d writes", writer.printCalls)
+	}
+}
+
+func TestLoggerUsesThresholdOrderingWhenThresholdModeIsEnabled(t *testing.T) {
+	writer := &stubLoggerWriter{}
+	logger := CreateLogger().
+		SetLevel(NewThresholdLogLevel(4, 20, "custom")).
+		SetThresholdMode(true).
+		AddWriter(writer)
+
+	logger.Print(NewThresholdLogLevel(4, 10, "debug"))
+	logger.Print(NewThresholdLogLevel(0, 30, "info"))
+
+	if writer.printCalls != 1 {
+		t.Fatalf("threshold mode should allow only entries at or below the configured threshold, got %d writes", writer.printCalls)
+	}
+}
+
+func TestDeprecatedLevelMethodKeepsLegacySeverityBehavior(t *testing.T) {
+	writer := &stubLoggerWriter{}
+	logger := CreateLogger().
+		Level(FATAL).
+		AddWriter(writer)
+
+	logger.Print(INFO, "info")
+	logger.Print(WARN, "warn")
+	logger.Print(ERROR, "error")
+	logger.Print(FATAL, "fatal")
+	logger.Print(DEBUG, "debug")
+
+	if writer.printCalls != 4 {
+		t.Fatalf("Level(FATAL) should keep legacy behavior and allow INFO/WARN/ERROR/FATAL only, got %d writes", writer.printCalls)
+	}
+}
+
+func TestSameLevelIgnoresThresholdDifferencesForCompatibility(t *testing.T) {
+	legacy := NewLogLevel(1, "warn")
+	threshold := NewThresholdLogLevel(1, 20, "warn")
+
+	if !legacy.SameLevel(threshold) {
+		t.Fatalf("SameLevel() should continue comparing only severity index")
+	}
+	if legacy.Equal(threshold) {
+		t.Fatalf("Equal() should distinguish levels with different threshold configuration")
+	}
+}
+
+func TestSameThresholdComparesOnlyThresholdValue(t *testing.T) {
+	first := NewThresholdLogLevel(1, 20, "warn")
+	second := NewThresholdLogLevel(9, 20, "custom")
+	third := NewThresholdLogLevel(1, 30, "warn")
+
+	if !first.SameThreshold(second) {
+		t.Fatalf("SameThreshold() should ignore severity and compare threshold only")
+	}
+	if first.SameThreshold(third) {
+		t.Fatalf("SameThreshold() should detect different threshold values")
+	}
+}
+
 func TestLogLevelForMethodReturnsExpectedLevels(t *testing.T) {
 	tests := []struct {
 		name   string
@@ -150,15 +221,16 @@ func TestLogLevelForMethodReturnsExpectedLevels(t *testing.T) {
 
 func TestNewLevelConstructorsSetExpectedSeverity(t *testing.T) {
 	tests := []struct {
-		name string
-		got  LogLevel
-		want LogLevel
+		name   string
+		got    LogLevel
+		want   LogLevel
+		wantTh uint8
 	}{
-		{name: "info", got: NewInfoLogLevel("custom"), want: INFO},
-		{name: "warn", got: NewWarnLogLevel("custom"), want: WARN},
-		{name: "error", got: NewErrorLogLevel("custom"), want: ERROR},
-		{name: "fatal", got: NewFatalLogLevel("custom"), want: FATAL},
-		{name: "debug", got: NewDebugLogLevel("custom"), want: DEBUG},
+		{name: "info", got: NewInfoLogLevel("custom"), want: INFO, wantTh: 10},
+		{name: "warn", got: NewWarnLogLevel("custom"), want: WARN, wantTh: 20},
+		{name: "error", got: NewErrorLogLevel("custom"), want: ERROR, wantTh: 30},
+		{name: "fatal", got: NewFatalLogLevel("custom"), want: FATAL, wantTh: 40},
+		{name: "debug", got: NewDebugLogLevel("custom"), want: DEBUG, wantTh: 0},
 	}
 
 	for _, tt := range tests {
@@ -166,6 +238,9 @@ func TestNewLevelConstructorsSetExpectedSeverity(t *testing.T) {
 			if tt.got.n != tt.want.n {
 				t.Fatalf("%s severity = %d, want %d", tt.name, tt.got.n, tt.want.n)
 			}
+			if tt.got.th != tt.wantTh {
+				t.Fatalf("%s threshold = %d, want %d", tt.name, tt.got.th, tt.wantTh)
+			}
 			if tt.got.GetName() != "custom" {
 				t.Fatalf("%s constructor should preserve name, got %q", tt.name, tt.got.GetName())
 			}