/**
 * What a swipe on a message row does, and what it should say it is about to do.
 *
 * The reader picks one action for each direction in Settings, but an action is
 * not a fixed thing: "delete" out of Deleted Items is permanent, "report spam"
 * inside Junk Mail is the opposite request, and "archive" while looking at the
 * archive is nothing at all. The strip revealed behind the row has to name the
 * thing that will actually happen, in the folder it is happening in -- a row
 * that slides open to reveal the word "Archive" and then does nothing is worse
 * than one that does not slide.
 *
 * So a direction with no meaning here resolves to `null`, and a null direction
 * is one the row simply will not move in.
 */

export type SwipeAction = "archive" | "delete" | "spam" | "read" | "star" | "move" | "none";

export interface SwipeContext {
  /** The role of the folder on screen, where it has one. */
  role?: string | null;
  /** Whether the row is unread — "mark as read" is a toggle, and says so. */
  unread: boolean;
  starred: boolean;
}

/**
 * Which glyph the strip shows. Named for the state it is offering rather than
 * the setting it came from: "mark as unread" and "not spam" are the same two
 * settings as their opposites but nothing like the same icon, and a strip that
 * says "Not spam" beside a spam icon is asking to be misread at a glance.
 */
export type SwipeIcon = "archive" | "delete" | "spam" | "not-spam" | "read" | "unread" | "star" | "unstar" | "move";

export interface SwipeDescriptor {
  action: Exclude<SwipeAction, "none">;
  label: string;
  icon: SwipeIcon;
  /** Which color the strip behind the row takes. */
  tone: "danger" | "warn" | "accent" | "neutral";
  /**
   * Whether firing it takes the row out of the list. Those slide the rest of
   * the way off before they fire, so the message is gone from under the finger
   * rather than snapping home and then vanishing a frame later.
   */
  removes: boolean;
  /**
   * For the two actions that are toggles, the state this swipe sets — so the
   * caller fires exactly what the strip promised. Read back off the row
   * instead and a slow finger can invert it: the strip that said "Mark as
   * read" would mark as unread if a push update landed mid-gesture.
   */
  on?: boolean;
}

export function describeSwipe(action: SwipeAction, ctx: SwipeContext): SwipeDescriptor | null {
  switch (action) {
    case "archive":
      // Archiving out of the archive is the one no-op worth refusing outright.
      return ctx.role === "archive" ? null : { action, label: "Archive", icon: "archive", tone: "accent", removes: true };
    case "delete":
      return { action, label: ctx.role === "trash" ? "Delete forever" : "Delete", icon: "delete", tone: "danger", removes: true };
    case "spam":
      // Nothing you wrote is spam you received, so the gesture stays inert in
      // the two folders that hold your own mail.
      if (ctx.role === "drafts" || ctx.role === "sent") return null;
      return ctx.role === "junk"
        ? { action, label: "Not spam", icon: "not-spam", tone: "warn", removes: true }
        : { action, label: "Report spam", icon: "spam", tone: "warn", removes: true };
    case "read":
      return { action, label: ctx.unread ? "Mark as read" : "Mark as unread", icon: ctx.unread ? "read" : "unread", tone: "neutral", removes: false, on: ctx.unread };
    case "star":
      return { action, label: ctx.starred ? "Remove star" : "Add star", icon: ctx.starred ? "unstar" : "star", tone: "warn", removes: false, on: !ctx.starred };
    case "move":
      // The folder picker opens over the list, so the row comes home first.
      return { action, label: "Move to…", icon: "move", tone: "accent", removes: false };
    case "none":
      return null;
  }
}

/** The Settings picker's options, in the order they are offered. */
export const SWIPE_CHOICES: ReadonlyArray<{ value: SwipeAction; label: string }> = [
  { value: "archive", label: "Archive" },
  { value: "delete", label: "Delete" },
  { value: "read", label: "Mark as read / unread" },
  { value: "star", label: "Star / unstar" },
  { value: "spam", label: "Report spam / not spam" },
  { value: "move", label: "Move to…" },
  { value: "none", label: "Nothing" },
];