js__typescript__pluralsight2/course/index.ts

type PlayerOne = {
    kind: "playerOne";
    name: string;
};
type PlayerTwo = {
    kind: "playerTwo";
    name: string;
};
type Player = PlayerOne | PlayerTwo;
type Point = "love" | "15" | "30";
type Deuce = {
    kind: "deuce";
};
type PointsData = {
    kind: "points";
    playerOnePoint: Point;
    playerTwoPoint: Point;
};
type FortyData = {
    kind: "forty";
    player: Player;
    otherPlayerPoint: Point;
};
type Advantage = {
    kind: "advantage",
    player: Player
};
type Game = {
    kind: "game",
    player: Player
    // otherPlayerPoint: ? Not representable here.
};
type Score = Deuce | PointsData | FortyData | Advantage | Game;

function scoreWhenDeuce(player: Player): Advantage {
    return {
        kind: "advantage",
        player,
    }
}

function scoreWhenAdvantage(score: Advantage, player: Player): Game | Deuce {
    return score.player.kind === player.kind ? {
        kind: "game",
        player,
    } :
    {
        kind: "deuce",
    };
}

function incrementPoints(point: Point): "15" | "30" | undefined {
    switch (point) {
        case "love":
            return "15";
        case "15":
            return "30";
        case "30":
            return undefined;
    }
}

function scoreWhenForty(score: FortyData, player: Player): Game | Deuce | FortyData {
    if (score.player.kind === player.kind) {
        return {
            kind: "game",
            player,
        }
    }
    else {
        // "15" | "30" | undefined is a subset of Point | undefined
        const newPoints: Point | undefined = incrementPoints(score.otherPlayerPoint);
        return newPoints === undefined ?
            { kind: "deuce" } :
            { ...score, otherPlayerPoint: newPoints };
    }
}