package journslog

import (
	"log/slog"

	"src.lwithers.me.uk/go/journal"
)

// LevelMapper maps [slog.Level] values onto [journal.Priority] values.
type LevelMapper interface {
	LevelMap(slogLevel slog.Level) journal.Priority
}

// DefaultLevelMapper returns a [LevelMapper] with the package's default
// behaviour.
//
// The mapping for the four defined [slog.Level] constants is as follows:
//
//	slog.Level                journal.Priority
//	----------                ----------------
//	slog.LevelDebug (-4)      journal.PriDebug
//	slog.LevelInfo  (0)       journal.PriInfo
//	slog.LevelWarn  (4)       journal.PriWarning
//	slog.LevelError (8)       journal.PriErr
//
// Other integer values are mapped as follows:
//
//	integer slog.Level     journal.Priority
//	------------------     ----------------
//	-∞ ... -4              journal.PriDebug
//	-3 ...  0              journal.PriInfo
//	 1 ...  3              journal.PriNotice
//	 4 ...  7              journal.PriWarning
//	 8                     journal.PriErr
//	 9 ...  ∞              journal.PriCrit
func DefaultLevelMapper() LevelMapper {
	return &defaultLevelMapper{}
}

type defaultLevelMapper struct{}

func (*defaultLevelMapper) LevelMap(slogLevel slog.Level) journal.Priority {
	switch {
	case slogLevel <= slog.LevelDebug:
		return journal.PriDebug
	case slogLevel <= slog.LevelInfo:
		return journal.PriInfo
	case slogLevel < slog.LevelWarn:
		return journal.PriNotice
	case slogLevel < slog.LevelError:
		return journal.PriWarning
	case slogLevel == slog.LevelError:
		return journal.PriErr
	default:
		return journal.PriCrit
	}
}