/*
 * Original source: https://github.com/rafaelcaricio/gradient-parser/blob/master/lib/parser.js
 */

type GradientType =
	| "linear-gradient"
	| "repeating-linear-gradient"
	| "radial-gradient"
	| "repeating-radial-gradient";

type DirectionalOrientation = { type: "directional"; value: string };
type AngularOrientation = { type: "angular"; value: string };
type LinearOrientation = DirectionalOrientation | AngularOrientation;

type Distance =
	| { type: "%"; value: string }
	| { type: "position-keyword"; value: string }
	| { type: "calc"; value: string }
	| { type: "px"; value: string }
	| { type: "em"; value: string };

type PositionValue = { x?: Distance; y?: Distance };
type Position = { type: "position"; value: PositionValue };

type ExtentKeyword = { type: "extent-keyword"; value: string };

type ShapeValue = "circle" | "ellipse";
type Shape = {
	type: "shape";
	value: ShapeValue;
	style?: Distance | ExtentKeyword | Position;
	at?: Position;
};

type DefaultRadial = { type: "default-radial"; at: Position };

type RadialOrientation =
	| Shape
	| (ExtentKeyword & { at?: Position })
	| DefaultRadial;

export type GradientOrientation = LinearOrientation | Array<RadialOrientation>;

export type Color =
	| { type: "hex"; value: string }
	| { type: "literal"; value: string }
	| { type: "rgb"; value: Array<string> }
	| { type: "rgba"; value: Array<string> }
	| { type: "hsl"; value: [string, string, string] }
	| { type: "hsla"; value: [string, string, string, string] }
	| { type: "var"; value: string };

export type ColorStop = Color & { length?: Distance };

export type GradientAst = {
	type: GradientType;
	orientation: GradientOrientation | undefined;
	colorStops: Array<ColorStop>;
};

type Tokens = {
	linearGradient: RegExp;
	repeatingLinearGradient: RegExp;
	radialGradient: RegExp;
	repeatingRadialGradient: RegExp;
	sideOrCorner: RegExp;
	extentKeywords: RegExp;
	positionKeywords: RegExp;
	pixelValue: RegExp;
	percentageValue: RegExp;
	emValue: RegExp;
	angleValue: RegExp;
	radianValue: RegExp;
	startCall: RegExp;
	endCall: RegExp;
	comma: RegExp;
	hexColor: RegExp;
	literalColor: RegExp;
	rgbColor: RegExp;
	rgbaColor: RegExp;
	varColor: RegExp;
	calcValue: RegExp;
	variableName: RegExp;
	number: RegExp;
	hslColor: RegExp;
	hslaColor: RegExp;
};

const tokens: Tokens = {
	linearGradient: /^(-(webkit|o|ms|moz)-)?(linear-gradient)/i,
	repeatingLinearGradient:
		/^(-(webkit|o|ms|moz)-)?(repeating-linear-gradient)/i,
	radialGradient: /^(-(webkit|o|ms|moz)-)?(radial-gradient)/i,
	repeatingRadialGradient:
		/^(-(webkit|o|ms|moz)-)?(repeating-radial-gradient)/i,
	sideOrCorner:
		/^to (left (top|bottom)|right (top|bottom)|top (left|right)|bottom (left|right)|left|right|top|bottom)/i,
	extentKeywords:
		/^(closest-side|closest-corner|farthest-side|farthest-corner|contain|cover)/,
	positionKeywords: /^(left|center|right|top|bottom)/i,
	pixelValue: /^(-?(([0-9]*\.[0-9]+)|([0-9]+\.?)))px/,
	percentageValue: /^(-?(([0-9]*\.[0-9]+)|([0-9]+\.?)))%/,
	emValue: /^(-?(([0-9]*\.[0-9]+)|([0-9]+\.?)))em/,
	angleValue: /^(-?(([0-9]*\.[0-9]+)|([0-9]+\.?)))deg/,
	radianValue: /^(-?(([0-9]*\.[0-9]+)|([0-9]+\.?)))rad/,
	startCall: /^\(/,
	endCall: /^\)/,
	comma: /^,/,
	hexColor: /^#([0-9a-fA-F]+)/,
	literalColor: /^([a-zA-Z]+)/,
	rgbColor: /^rgb/i,
	rgbaColor: /^rgba/i,
	varColor: /^var/i,
	calcValue: /^calc/i,
	variableName: /^(--[a-zA-Z0-9-,\s#]+)/,
	number: /^(([0-9]*\.[0-9]+)|([0-9]+\.?))/,
	hslColor: /^hsl/i,
	hslaColor: /^hsla/i,
};

let input = "";

const error = ({ message }: { message: string }): never => {
	const err = new Error(`${input}: ${message}`);
	(err as Error & { source?: string }).source = input;
	throw err;
};

const getAst = (): Array<GradientAst> => {
	const ast = matchListDefinitions();

	if (input.length > 0) {
		error({ message: "Invalid input not EOF" });
	}

	return ast;
};

const matchListDefinitions = (): Array<GradientAst> =>
	matchListing({ matcher: matchDefinition });

const matchDefinition = (): GradientAst | undefined =>
	matchGradient({
		gradientType: "linear-gradient",
		pattern: tokens.linearGradient,
		orientationMatcher: matchLinearOrientation,
	}) ||
	matchGradient({
		gradientType: "repeating-linear-gradient",
		pattern: tokens.repeatingLinearGradient,
		orientationMatcher: matchLinearOrientation,
	}) ||
	matchGradient({
		gradientType: "radial-gradient",
		pattern: tokens.radialGradient,
		orientationMatcher: matchListRadialOrientations,
	}) ||
	matchGradient({
		gradientType: "repeating-radial-gradient",
		pattern: tokens.repeatingRadialGradient,
		orientationMatcher: matchListRadialOrientations,
	});

const matchGradient = ({
	gradientType,
	pattern,
	orientationMatcher,
}: {
	gradientType: GradientType;
	pattern: RegExp;
	orientationMatcher: () => GradientOrientation | undefined;
}): GradientAst | undefined =>
	matchCall({
		pattern,
		callback: () => {
			const orientation = orientationMatcher();
			if (orientation && !scan({ regexp: tokens.comma })) {
				error({ message: "Missing comma before color stops" });
			}

			return {
				type: gradientType,
				orientation,
				colorStops: matchListing({ matcher: matchColorStop }),
			};
		},
	});

const matchCall = <T>({
	pattern,
	callback,
}: {
	pattern: RegExp;
	callback: (captures: RegExpExecArray) => T;
}): T | undefined => {
	const captures = scan({ regexp: pattern });

	if (!captures) {
		return undefined;
	}

	if (!scan({ regexp: tokens.startCall })) {
		error({ message: "Missing (" });
	}

	const result = callback(captures);

	if (!scan({ regexp: tokens.endCall })) {
		error({ message: "Missing )" });
	}

	return result;
};

const matchLinearOrientation = (): LinearOrientation | undefined => {
	const sideOrCorner = matchSideOrCorner();
	if (sideOrCorner) {
		return sideOrCorner;
	}

	const legacyDirection = match({
		type: "position-keyword",
		pattern: tokens.positionKeywords,
		captureIndex: 1,
	});
	if (legacyDirection) {
		return {
			type: "directional",
			value: legacyDirection.value,
		};
	}

	return matchAngle();
};

const matchSideOrCorner = (): DirectionalOrientation | undefined =>
	match({ type: "directional", pattern: tokens.sideOrCorner, captureIndex: 1 });

const matchAngle = (): AngularOrientation | undefined =>
	match({ type: "angular", pattern: tokens.angleValue, captureIndex: 1 }) ||
	match({ type: "angular", pattern: tokens.radianValue, captureIndex: 1 });

const matchListRadialOrientations = ():
	| Array<RadialOrientation>
	| undefined => {
	const radialOrientation = matchRadialOrientation();
	if (!radialOrientation) {
		return undefined;
	}

	const radialOrientations: Array<RadialOrientation> = [radialOrientation];
	const lookaheadCache = input;

	if (!scan({ regexp: tokens.comma })) {
		return radialOrientations;
	}

	const nextRadial = matchRadialOrientation();
	if (!nextRadial) {
		input = lookaheadCache;
		return radialOrientations;
	}

	radialOrientations.push(nextRadial);
	return radialOrientations;
};

const matchRadialOrientation = (): RadialOrientation | undefined => {
	const radialType = matchCircle() || matchEllipse();
	if (radialType) {
		radialType.at = matchAtPosition();
		return radialType;
	}

	const extent = matchExtentKeyword();
	if (extent) {
		const positionAt = matchAtPosition();
		if (positionAt) {
			return { ...extent, at: positionAt };
		}
		return extent;
	}

	const implicitEllipse = matchImplicitEllipse();
	if (implicitEllipse) {
		return implicitEllipse;
	}

	const atPosition = matchAtPosition();
	if (atPosition) {
		return { type: "default-radial", at: atPosition };
	}

	const defaultPosition = matchPositioning();
	if (defaultPosition) {
		return { type: "default-radial", at: defaultPosition };
	}

	return undefined;
};

const matchImplicitEllipse = (): Shape | undefined => {
	const lookaheadCache = input;

	const width = matchDistance();
	if (!width) {
		return undefined;
	}

	const height = matchDistance();
	if (!height) {
		input = lookaheadCache;
		return undefined;
	}

	const atPos = matchAtPosition();
	if (!atPos) {
		input = lookaheadCache;
		return undefined;
	}

	return {
		type: "shape",
		value: "ellipse",
		style: { type: "position", value: { x: width, y: height } },
		at: atPos,
	};
};

const matchCircle = (): Shape | undefined => {
	const circle = match({
		type: "shape",
		pattern: /^(circle)/i,
		captureIndex: 0,
	}) as Shape | undefined;

	if (!circle) {
		return undefined;
	}

	circle.style = matchLength() || matchExtentKeyword();
	circle.value = "circle";
	return circle;
};

const matchEllipse = (): Shape | undefined => {
	const ellipse = match({
		type: "shape",
		pattern: /^(ellipse)/i,
		captureIndex: 0,
	}) as Shape | undefined;

	if (!ellipse) {
		return undefined;
	}

	ellipse.style = matchPositioning() || matchDistance() || matchExtentKeyword();
	ellipse.value = "ellipse";
	return ellipse;
};

const matchExtentKeyword = (): ExtentKeyword | undefined =>
	match({
		type: "extent-keyword",
		pattern: tokens.extentKeywords,
		captureIndex: 1,
	});

const matchAtPosition = (): Position | undefined => {
	if (!match({ type: "position", pattern: /^at/, captureIndex: 0 })) {
		return undefined;
	}

	const positioning = matchPositioning();
	if (!positioning) {
		error({ message: "Missing positioning value" });
	}

	return positioning;
};

const matchPositioning = (): Position | undefined => {
	const location = matchCoordinates();

	if (!location.x && !location.y) {
		return undefined;
	}

	return {
		type: "position",
		value: location,
	};
};

const matchCoordinates = (): PositionValue => ({
	x: matchDistance(),
	y: matchDistance(),
});

const matchListing = <T>({
	matcher,
}: {
	matcher: () => T | undefined;
}): Array<T> => {
	const captures = matcher();
	const result: Array<T> = [];

	if (!captures) {
		return result;
	}

	result.push(captures);
	while (scan({ regexp: tokens.comma })) {
		const nextCapture = matcher() ?? error({ message: "One extra comma" });
		result.push(nextCapture);
	}

	return result;
};

const matchColorStop = (): ColorStop => {
	const color = matchColor() ?? error({ message: "Expected color definition" });
	const length = matchDistance();
	return { ...color, length };
};

const matchColor = (): Color | undefined =>
	matchHexColor() ||
	matchHSLAColor() ||
	matchHSLColor() ||
	matchRGBAColor() ||
	matchRGBColor() ||
	matchVarColor() ||
	matchLiteralColor();

const matchLiteralColor = (): Color | undefined =>
	match({ type: "literal", pattern: tokens.literalColor, captureIndex: 0 });

const matchHexColor = (): Color | undefined =>
	match({ type: "hex", pattern: tokens.hexColor, captureIndex: 1 });

const matchRGBColor = (): Color | undefined =>
	matchCall({
		pattern: tokens.rgbColor,
		callback: () => ({
			type: "rgb",
			value: matchListing({ matcher: matchNumber }),
		}),
	});

const matchRGBAColor = (): Color | undefined =>
	matchCall({
		pattern: tokens.rgbaColor,
		callback: () => ({
			type: "rgba",
			value: matchListing({ matcher: matchNumber }),
		}),
	});

const matchVarColor = (): Color | undefined =>
	matchCall({
		pattern: tokens.varColor,
		callback: () => ({
			type: "var",
			value: matchVariableName(),
		}),
	});

const matchHSLColor = (): Color | undefined =>
	matchCall({
		pattern: tokens.hslColor,
		callback: () => {
			const lookahead = scan({ regexp: tokens.percentageValue });
			if (lookahead) {
				error({
					message:
						"HSL hue value must be a number in degrees (0-360) or normalized (-360 to 360), not a percentage",
				});
			}

			const hue = matchNumber();
			scan({ regexp: tokens.comma });
			let captures = scan({ regexp: tokens.percentageValue });
			const sat = captures ? captures[1] : null;
			scan({ regexp: tokens.comma });
			captures = scan({ regexp: tokens.percentageValue });
			const light = captures ? captures[1] : null;
			const ensuredSat =
				sat ??
				error({
					message:
						"Expected percentage value for saturation and lightness in HSL",
				});
			const ensuredLight =
				light ??
				error({
					message:
						"Expected percentage value for saturation and lightness in HSL",
				});
			return {
				type: "hsl",
				value: [hue, ensuredSat, ensuredLight],
			};
		},
	});

const matchHSLAColor = (): Color | undefined =>
	matchCall({
		pattern: tokens.hslaColor,
		callback: () => {
			const hue = matchNumber();
			scan({ regexp: tokens.comma });
			let captures = scan({ regexp: tokens.percentageValue });
			const sat = captures ? captures[1] : null;
			scan({ regexp: tokens.comma });
			captures = scan({ regexp: tokens.percentageValue });
			const light = captures ? captures[1] : null;
			scan({ regexp: tokens.comma });
			const alpha = matchNumber();
			const ensuredSat =
				sat ??
				error({
					message:
						"Expected percentage value for saturation and lightness in HSLA",
				});
			const ensuredLight =
				light ??
				error({
					message:
						"Expected percentage value for saturation and lightness in HSLA",
				});
			return {
				type: "hsla",
				value: [hue, ensuredSat, ensuredLight, alpha],
			};
		},
	});

const matchVariableName = (): string => {
	const captures =
		scan({ regexp: tokens.variableName }) ??
		error({ message: "Expected CSS variable name" });
	return captures[1];
};

const matchNumber = (): string => {
	const captures =
		scan({ regexp: tokens.number }) ?? error({ message: "Expected number" });
	return captures[1];
};

const matchDistance = (): Distance | undefined =>
	match({ type: "%", pattern: tokens.percentageValue, captureIndex: 1 }) ||
	matchPositionKeyword() ||
	matchCalc() ||
	matchLength();

const matchPositionKeyword = (): Distance | undefined =>
	match({
		type: "position-keyword",
		pattern: tokens.positionKeywords,
		captureIndex: 1,
	});

const matchCalc = (): Distance | undefined =>
	matchCall({
		pattern: tokens.calcValue,
		callback: () => {
			let openParenCount = 1;
			let index = 0;

			while (openParenCount > 0 && index < input.length) {
				const char = input.charAt(index);
				if (char === "(") {
					openParenCount++;
				} else if (char === ")") {
					openParenCount--;
				}
				index++;
			}

			if (openParenCount > 0) {
				error({ message: "Missing closing parenthesis in calc() expression" });
			}

			const calcContent = input.slice(0, index - 1);
			consume({ size: index - 1 });

			return {
				type: "calc",
				value: calcContent,
			};
		},
	});

const matchLength = (): Distance | undefined =>
	match({ type: "px", pattern: tokens.pixelValue, captureIndex: 1 }) ||
	match({ type: "em", pattern: tokens.emValue, captureIndex: 1 });

const match = <TType extends string>({
	type,
	pattern,
	captureIndex,
}: {
	type: TType;
	pattern: RegExp;
	captureIndex: number;
}): { type: TType; value: string } | undefined => {
	const captures = scan({ regexp: pattern });
	if (!captures) {
		return undefined;
	}

	return {
		type,
		value: captures[captureIndex],
	};
};

const scan = ({ regexp }: { regexp: RegExp }): RegExpExecArray | null => {
	const blankCaptures = /^[\n\r\t\s]+/.exec(input);
	if (blankCaptures) {
		consume({ size: blankCaptures[0].length });
	}

	const captures = regexp.exec(input);
	if (captures) {
		consume({ size: captures[0].length });
	}

	return captures;
};

const consume = ({ size }: { size: number }): void => {
	input = input.slice(size);
};

export const parseGradient = ({
	code,
}: {
	code: string;
}): Array<GradientAst> => {
	input = code.toString().trim();
	if (input.endsWith(";")) {
		input = input.slice(0, -1);
	}
	return getAst();
};

export const GradientParser = {
	parse: parseGradient,
};