Seed from go-template-repo, renamed to simplexcalc

The template's files at a77fd30, without its history or LICENSE, after
script/rename simplexcalc.

Model: opus-5-5

internal/logger/logger.go

@@ -0,0 +1,92 @@
+// Package logger provides structured logging using stdlib log/slog.
+//
+// JSON output always, one format for every environment, TTY or not. A
+// log line is a record to be queried, not prose to be read.
+package logger
+
+import (
+	"fmt"
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+
+	"go.uber.org/fx"
+	"sneak.berlin/go/simplexcalc/internal/globals"
+)
+
+// Params defines dependencies for Logger.
+type Params struct {
+	fx.In
+
+	Globals *globals.Globals
+
+	// Output is the log destination. Optional in the fx graph: when
+	// absent (production) it defaults to os.Stdout; tests inject a
+	// buffer here to assert on the output contract.
+	Output io.Writer `optional:"true"`
+}
+
+// Logger wraps slog with application-specific functionality.
+type Logger struct {
+	log     *slog.Logger
+	level   *slog.LevelVar
+	globals *globals.Globals
+}
+
+// New creates a new Logger instance.
+func New(_ fx.Lifecycle, params Params) (*Logger, error) {
+	l := &Logger{
+		level:   new(slog.LevelVar),
+		globals: params.Globals,
+	}
+	l.level.Set(slog.LevelInfo)
+
+	out := params.Output
+	if out == nil {
+		out = os.Stdout
+	}
+
+	// replaceAttr simplifies the source attribute to "file.go:line".
+	replaceAttr := func(_ []string, a slog.Attr) slog.Attr {
+		if a.Key == slog.SourceKey {
+			if src, ok := a.Value.Any().(*slog.Source); ok {
+				a.Value = slog.StringValue(
+					fmt.Sprintf("%s:%d", filepath.Base(src.File), src.Line),
+				)
+			}
+		}
+
+		return a
+	}
+
+	handler := slog.NewJSONHandler(out, &slog.HandlerOptions{
+		Level:       l.level,
+		AddSource:   true,
+		ReplaceAttr: replaceAttr,
+	})
+
+	l.log = slog.New(handler)
+
+	return l, nil
+}
+
+// EnableDebugLogging sets the log level to debug.
+func (l *Logger) EnableDebugLogging() {
+	l.level.Set(slog.LevelDebug)
+	l.log.Debug("debug logging enabled", "debug", true)
+}
+
+// Get returns the underlying slog.Logger.
+func (l *Logger) Get() *slog.Logger {
+	return l.log
+}
+
+// Identify logs application startup information.
+func (l *Logger) Identify() {
+	l.log.Info("starting",
+		"appname", l.globals.Appname,
+		"version", l.globals.Version,
+		"arch", l.globals.Buildarch,
+	)
+}