// 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,
	)
}