package domain

import "context"

// Language is the spoken language an upload is transcribed as. It is chosen by the user on
// the upload form and reaches the engines as one request field, so it is a closed set,
// never free text (tapir#61).
type Language string

const (
	// LangSwedish sends language=sv: the Swedish engines' own language, and what every
	// upload was transcribed as before the choice existed.
	LangSwedish Language = "sv"
	// LangAuto sends no language, so the engine detects it. It is what "Other" on the form
	// means: the Swedish-only engines are not used for it.
	LangAuto Language = "auto"
)

// ParseLanguage reads a form value. An empty value is Swedish (a client that predates the
// field); anything that is not exactly a known value is refused rather than normalised.
func ParseLanguage(s string) (Language, bool) {
	switch Language(s) {
	case "", LangSwedish:
		return LangSwedish, true
	case LangAuto:
		return LangAuto, true
	}
	return "", false
}

type languageKey struct{}

// WithLanguage returns a context that carries the language of the job it serves. The
// Transcriber interface does not change: engines read it with LanguageFrom, the same way
// they read the progress Reporter (ADR-035).
func WithLanguage(ctx context.Context, l Language) context.Context {
	return context.WithValue(ctx, languageKey{}, l)
}

// LanguageFrom returns the language carried by ctx, or Swedish when it carries none, so a
// caller that sets nothing behaves as it always did.
func LanguageFrom(ctx context.Context) Language {
	if l, ok := ctx.Value(languageKey{}).(Language); ok && l != "" {
		return l
	}
	return LangSwedish
}