package theme

import (
	"sort"
	"strings"

	"github.com/gdamore/tcell/v2"
)

// Theme maps style keys to the styles the editor draws with.
//
// Use Style to read a key: it falls back along the dots, so asking for
// "syntax.keyword" in a theme that only defines "syntax" gets the latter, and
// a theme that defines neither gets KeyDefault.
type Theme struct {
	name        string
	description string
	styles      map[string]tcell.Style
}

// Name returns the theme's display name, which is what the Options menu lists.
func (t *Theme) Name() string { return t.name }

// Description returns the one-line description from the theme file, or the
// empty string when it has none.
func (t *Theme) Description() string { return t.description }

// Style returns the style for a key, falling back along the dots and finally
// onto KeyDefault.
//
//	s := th.Style(theme.KeySyntaxKeyword)
//	// a theme defining only "syntax" answers that; one defining neither
//	// answers "default".
func (t *Theme) Style(key string) tcell.Style {
	for {
		if style, ok := t.styles[key]; ok {
			return style
		}
		dot := strings.LastIndexByte(key, '.')
		if dot < 0 {
			break
		}
		key = key[:dot]
	}
	return t.styles[KeyDefault]
}

// Keys returns every key the theme defines, sorted. It exists for tooling and
// for tests that check a theme file is complete.
func (t *Theme) Keys() []string {
	keys := make([]string, 0, len(t.styles))
	for key := range t.styles {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	return keys
}

// Defines reports whether the theme sets this exact key, without any fallback.
func (t *Theme) Defines(key string) bool {
	_, ok := t.styles[key]
	return ok
}

// fallbackStyle is what a theme resolves to before any file is read: white on
// black, which stays legible on every terminal.
func fallbackStyle() tcell.Style {
	return tcell.StyleDefault.
		Foreground(tcell.ColorWhite).
		Background(tcell.ColorBlack)
}