import { FONT_STACKS } from '$lib/theme/presets';
import { readerSettingsSchema, type ReaderSettings } from '$lib/schema/reader';

export const READER_SETTINGS_STORAGE_KEY = 'chitai:reader-settings';

/** Georgia — the app's own title face, and a reasonable default for long prose. */
export const DEFAULT_READER_SETTINGS: ReaderSettings = {
	fontFamily: FONT_STACKS[1].value,
	fontSize: 18,
	fontWeight: 400,
	lineHeight: 1.6,
	letterSpacing: 0,
	margin: 48,
	gap: 6,
	// foliate caps the reading area at this times the column count, so 1000 gives
	// a 2000px spread — enough to fill a large display rather than leaving the
	// book as a narrow strip. Its own default of 720 is noticeably tight.
	maxInlineSize: 1000,
	maxColumnCount: 2,
	flow: 'paginated',
	justify: true,
	hyphenate: true
};

/** Reused from the app theme: system stacks only, so nothing silently falls back. */
export const READER_FONT_OPTIONS = FONT_STACKS;

/** Slider bounds, kept next to the schema they mirror. */
export const READER_BOUNDS = {
	fontSize: { min: 12, max: 32, step: 1 },
	fontWeight: { min: 300, max: 700, step: 100 },
	lineHeight: { min: 1, max: 2.5, step: 0.05 },
	letterSpacing: { min: -0.05, max: 0.2, step: 0.01 },
	margin: { min: 0, max: 120, step: 4 },
	gap: { min: 0, max: 15, step: 1 },
	maxInlineSize: { min: 400, max: 2400, step: 20 }
} as const;

/**
 * Reads stored settings, falling back to defaults on anything unusable.
 *
 * Unknown keys are stripped and missing ones filled, so settings added in a
 * later release do not invalidate what a reader already has stored.
 */
export function loadReaderSettings(): ReaderSettings {
	try {
		const raw = localStorage.getItem(READER_SETTINGS_STORAGE_KEY);
		if (!raw) return DEFAULT_READER_SETTINGS;
		const parsed = readerSettingsSchema.safeParse({
			...DEFAULT_READER_SETTINGS,
			...JSON.parse(raw)
		});
		return parsed.success ? parsed.data : DEFAULT_READER_SETTINGS;
	} catch {
		return DEFAULT_READER_SETTINGS;
	}
}

export function saveReaderSettings(settings: ReaderSettings) {
	try {
		localStorage.setItem(READER_SETTINGS_STORAGE_KEY, JSON.stringify(settings));
	} catch (error) {
		// A full quota must not stop anyone reading.
		console.warn('Could not save reader settings', error);
	}
}

/**
 * The half of the settings that foliate takes as renderer attributes.
 *
 * The renderer has no JS property API — these must be set with setAttribute.
 * Note there is no `margin` shorthand upstream, and no `spread`: on a reflowable
 * book a two-page spread is max-column-count 2.
 */
export function toRendererAttributes(s: ReaderSettings): Record<string, string> {
	return {
		flow: s.flow,
		gap: `${s.gap}%`,
		'margin-top': `${s.margin}px`,
		'margin-bottom': `${s.margin}px`,
		'margin-left': `${s.margin}px`,
		'margin-right': `${s.margin}px`,
		'max-inline-size': `${s.maxInlineSize}px`,
		'max-column-count': String(s.maxColumnCount)
	};
}