import type { CSSProperties } from "vue";
import type { OriginChoreography } from "../choreography";
import type { MaybeOriginAction, OriginNavigationIntent } from "../navigation";
import type { OriginContext } from "../scene/types";
import type { OriginRect } from "../shared";

/*
 * What a gesture is: the public gesture types, component props, and the
 * immutable builder that produces executable definitions. Running them is
 * the recognizer's job.
 */

/** Direction in which pointer movement advances operation progress. */
export type OriginGestureDirection = "left" | "right" | "up" | "down";

/** Physical side of the gesture host used to admit pointer-down. */
export type OriginGestureEdge = "left" | "right" | "top" | "bottom";

/**
 * CSS length accepted by an edge-based gesture start rule.
 *
 * Numbers are interpreted as CSS pixels. Strings may use normal CSS lengths,
 * percentages, `calc()`, or `clamp()`, and are resolved against the gesture
 * host when pointer-down occurs.
 */
export type OriginGestureDistance = number | string;

/** A pointer position measured in viewport and gesture-host coordinates. */
export interface OriginGesturePoint {
  /** Viewport-relative horizontal position. */
  readonly clientX: number;
  /** Viewport-relative vertical position. */
  readonly clientY: number;
  /** Horizontal position relative to the gesture host's left edge. */
  readonly localX: number;
  /** Vertical position relative to the gesture host's top edge. */
  readonly localY: number;
}

/** Context supplied to a custom `.from.when()` start predicate. */
export interface OriginGestureStartContext {
  /** Native pointer-down event being considered. */
  readonly event: PointerEvent;
  /** Component instance from which the gesture would originate. */
  readonly origin: OriginContext;
  /** Element carrying the gesture's pointer handlers. */
  readonly host: HTMLElement;
  /** Gesture-host bounds captured at pointer-down. */
  readonly bounds: OriginRect;
  /** Pointer position at pointer-down. */
  readonly point: OriginGesturePoint;
}

/**
 * Synchronous predicate deciding whether a pointer-down may become a gesture.
 *
 * Directional recognition still occurs later, after movement passes the
 * configured intent threshold.
 */
export type OriginGestureStartPredicate = (
  context: OriginGestureStartContext,
) => boolean;

/** Start policy stored in a completed gesture definition. */
export type OriginGestureStart =
  | {
      /** Recognize pointer-down anywhere on the host. */
      readonly kind: "anywhere";
    }
  | {
      /** Recognize pointer-down within a CSS distance of one host side. */
      readonly kind: "edge";
      readonly edge: OriginGestureEdge;
      readonly distance: OriginGestureDistance;
    }
  | {
      /** Recognize pointer-down when application policy returns `true`. */
      readonly kind: "when";
      readonly predicate: OriginGestureStartPredicate;
    };

/** Direction-recognition tuning accepted by `.to.left()` and its siblings. */
export interface OriginGestureDirectionOptions {
  /**
   * Minimum directed movement in CSS pixels before the gesture captures.
   *
   * @defaultValue `8`
   */
  readonly threshold?: number;
  /**
   * Ratio by which directed movement must exceed cross-axis movement.
   *
   * @defaultValue `1.15`
   */
  readonly axisDominance?: number;
}

/** Values available when a custom `.complete()` policy runs on pointer-up. */
export interface OriginGestureCompletionContext {
  /** Component instance that originated the gesture. */
  readonly origin: OriginContext;
  /** Recognized movement direction. */
  readonly direction: OriginGestureDirection;
  /** Normalized directed distance, clamped to `0..1`. */
  readonly progress: number;
  /** Latest normalized progress units per second. */
  readonly velocity: number;
  /** Directed movement from pointer-down in CSS pixels. */
  readonly distance: number;
  /** Absolute cross-axis movement from pointer-down in CSS pixels. */
  readonly crossDistance: number;
  /** Elapsed time since pointer-down in milliseconds. */
  readonly duration: number;
  /** Native pointer-up event that ended the interaction. */
  readonly event: PointerEvent;
  /** Element carrying the gesture's pointer handlers. */
  readonly host: HTMLElement;
  /** Gesture-host bounds captured at pointer-down. */
  readonly bounds: OriginRect;
  /** Pointer position captured at pointer-down. */
  readonly start: OriginGesturePoint;
  /** Pointer position at release. */
  readonly current: OriginGesturePoint;
}

/** Synchronous commit/cancel policy installed by `.complete()`. */
export type OriginGestureCompletionPredicate = (
  context: OriginGestureCompletionContext,
) => boolean;

/**
 * Values accepted from a gesture builder's `.navigate()` factory.
 *
 * A promise supports lazy view selection. Stale resolutions are discarded if
 * the pointer has already ended or been cancelled.
 */
export type MaybeOriginNavigationIntent =
  | OriginNavigationIntent
  | null
  | undefined
  | Promise<OriginNavigationIntent | null | undefined>;

/** Factory that resolves navigation after directional recognition succeeds. */
export type OriginGestureNavigationFactory = (
  context: OriginContext,
) => MaybeOriginNavigationIntent;

/**
 * Immutable, executable result of a complete gesture builder chain.
 *
 * Pass this object to {@link useOriginGesture}. An omitted `.from` step is
 * represented as an `anywhere` start rule.
 */
export interface OriginGestureDefinition {
  /** Discriminator used by the compatibility recognizer overload. */
  readonly kind: "origin-gesture-definition";
  /** Pointer-down eligibility policy. */
  readonly start: OriginGestureStart;
  /** Direction in which movement advances operation progress. */
  readonly direction: OriginGestureDirection;
  /** Directional intent recognition tuning. */
  readonly recognition: Readonly<OriginGestureDirectionOptions>;
  /**
   * Optional release decision. When omitted, choreography thresholds decide.
   */
  readonly completion?: OriginGestureCompletionPredicate;
  /** Node-local destination/history resolver. */
  readonly navigation: OriginGestureNavigationFactory;
  /** Visual routine paired with the navigation intent. */
  readonly choreography: OriginChoreography;
  /** Handlers run, in order, when a release commits. See `.onCommit()`. */
  readonly commitHandlers?: readonly OriginGestureCommitHandler[];
}

/**
 * Side effect run when a released gesture commits, such as haptic feedback.
 *
 * It runs once, synchronously at release, after the commit decision and
 * before the settling animation. It receives the same context as a
 * `.complete()` predicate. Errors are reported without interrupting the
 * operation.
 */
export type OriginGestureCommitHandler = (
  context: OriginGestureCompletionContext,
) => void;

/** Direction-selection stage shared by `gesture.to` and `.from.*().to`. */
export interface OriginGestureToBuilder {
  /** Recognize leftward pointer movement. */
  left(options?: OriginGestureDirectionOptions): OriginGestureDirectedBuilder;
  /** Recognize rightward pointer movement. */
  right(options?: OriginGestureDirectionOptions): OriginGestureDirectedBuilder;
  /** Recognize upward pointer movement. */
  up(options?: OriginGestureDirectionOptions): OriginGestureDirectedBuilder;
  /** Recognize downward pointer movement. */
  down(options?: OriginGestureDirectionOptions): OriginGestureDirectedBuilder;
}

/** Stage produced after a `.from` policy has been selected. */
export interface OriginGestureFromSelection {
  /** Select the direction that advances this gesture. */
  readonly to: OriginGestureToBuilder;
}

/** Optional pointer-down policy exposed at the start of a gesture chain. */
export interface OriginGestureFromBuilder {
  /** Admit pointer-down within `distance` of the host's left edge. */
  left(distance: OriginGestureDistance): OriginGestureFromSelection;
  /** Admit pointer-down within `distance` of the host's right edge. */
  right(distance: OriginGestureDistance): OriginGestureFromSelection;
  /** Admit pointer-down within `distance` of the host's top edge. */
  top(distance: OriginGestureDistance): OriginGestureFromSelection;
  /** Admit pointer-down within `distance` of the host's bottom edge. */
  bottom(distance: OriginGestureDistance): OriginGestureFromSelection;
  /** Admit pointer-down anywhere on the gesture host. */
  anywhere(): OriginGestureFromSelection;
  /** Admit pointer-down when a synchronous application predicate succeeds. */
  when(predicate: OriginGestureStartPredicate): OriginGestureFromSelection;
}

/** Builder stage after direction is known and completion remains optional. */
export interface OriginGestureDirectedBuilder {
  /** Override the choreography's default release decision. */
  complete(
    predicate: OriginGestureCompletionPredicate,
  ): OriginGestureCompletedBuilder;
  /** Select the target/history mutation while retaining default completion. */
  navigate(
    factory: OriginGestureNavigationFactory,
  ): OriginGestureNavigationBuilder;
  /** Run `handler` when a release commits. Handlers accumulate in order. */
  onCommit(handler: OriginGestureCommitHandler): OriginGestureDirectedBuilder;
}

/** Builder stage after a custom completion policy has been selected. */
export interface OriginGestureCompletedBuilder {
  /** Select the target/history mutation performed on commit. */
  navigate(
    factory: OriginGestureNavigationFactory,
  ): OriginGestureNavigationBuilder;
  /** Run `handler` when a release commits. Handlers accumulate in order. */
  onCommit(handler: OriginGestureCommitHandler): OriginGestureCompletedBuilder;
}

/** Final builder stage waiting for visual choreography. */
export interface OriginGestureNavigationBuilder {
  /** Attach visual choreography and produce an executable definition. */
  animate(choreography: OriginChoreography): OriginGestureDefinition;
  /** Run `handler` when a release commits. Handlers accumulate in order. */
  onCommit(handler: OriginGestureCommitHandler): OriginGestureNavigationBuilder;
}

/** Root of the immutable fluent gesture-definition API. */
export interface OriginGestureBuilder {
  /** Optionally constrain where pointer-down may begin. */
  readonly from: OriginGestureFromBuilder;
  /**
   * Select movement direction with an implicit `from.anywhere()` start.
   */
  readonly to: OriginGestureToBuilder;
}

/** Configuration consumed by {@link useOriginGesture}. */
export interface OriginGestureOptions {
  /**
   * Direction in which the pointer moves to advance the operation.
   *
   * The starting edge is the opposite side: `right` begins at the left edge,
   * `left` at the right edge, `down` at the top, and `up` at the bottom.
   */
  direction: OriginGestureDirection;
  /**
   * Restrict pointer-down to this many CSS pixels from the gesture host's
   * starting edge. Omit it to recognize across the entire host.
   *
   * This is relative to the bound element, not necessarily the browser
   * viewport. Use a positive number such as `24` or `36`.
   */
  edge?: number;
  /**
   * Minimum directed movement in CSS pixels before the gesture captures.
   *
   * Movement must also dominate the cross-axis by a factor of `1.15`.
   *
   * @defaultValue `8`
   */
  threshold?: number;
  /**
   * Resolve the scene action after directional recognition succeeds.
   *
   * Returning no action abandons recognition without modifying the scene.
   */
  action(context: OriginContext): MaybeOriginAction;
}

/**
 * DOM bindings returned by {@link useOriginGesture}.
 *
 * Spread or attach all four handlers to the same `HTMLElement`. Apply
 * {@link style} as well so native scrolling is preserved on the cross-axis.
 */
export interface OriginGestureBinding {
  /** Required size and `touch-action` styles for the gesture host. */
  readonly style: Readonly<CSSProperties>;
  /** Pointer-down handler that records a potentially eligible gesture. */
  readonly onPointerdown: (event: PointerEvent) => void;
  /** Pointer-move handler that recognizes and updates the operation. */
  readonly onPointermove: (event: PointerEvent) => void;
  /** Pointer-up handler that commits or cancels using progress and velocity. */
  readonly onPointerup: (event: PointerEvent) => void;
  /** Pointer-cancel handler that abandons any captured operation. */
  readonly onPointercancel: () => void;
}

// Component props ----------------------------------------------------------

/** Props shared by both `OriginGesture` declaration styles. */
export interface OriginGestureBaseProps {
  /**
   * Native HTML tag rendered as the gesture host.
   *
   * @defaultValue `"div"`
   */
  as?: string;
}

/** Builder-definition props accepted by the `OriginGesture` component. */
export interface OriginGestureDefinitionProps extends OriginGestureBaseProps {
  /** Immutable definition produced by the {@link gesture} builder. */
  gesture: OriginGestureDefinition;
  /** Builder definitions already contain direction. */
  direction?: never;
  /** Builder definitions already contain their start policy. */
  edge?: never;
  /** Builder definitions already contain recognition tuning. */
  threshold?: never;
  /** Builder definitions already contain their navigation factory. */
  action?: never;
}

/** Legacy option props accepted by the `OriginGesture` component. */
export interface OriginGestureLegacyProps extends OriginGestureBaseProps {
  /** Legacy component declarations do not provide a builder definition. */
  gesture?: never;
  /** Direction in which pointer movement advances operation progress. */
  direction: OriginGestureDirection;
  /**
   * Eligible pointer-down width in CSS pixels from the host's starting edge.
   * Omit it to allow the full component surface.
   */
  edge?: number;
  /**
   * Directed movement required before capture.
   *
   * @defaultValue `8`
   */
  threshold?: number;
  /** Node-local action factory invoked only after recognition succeeds. */
  action(context: OriginContext): MaybeOriginAction;
}

/**
 * Public props accepted by the `OriginGesture` convenience component.
 *
 * Prefer the builder-definition form. The legacy direction/action form remains
 * available for compatibility.
 */
export type OriginGestureProps =
  OriginGestureDefinitionProps | OriginGestureLegacyProps;

/** Public props accepted by the multi-definition gesture surface component. */
export interface OriginGestureSurfaceProps {
  /**
   * Native HTML tag rendered as the shared gesture host.
   *
   * @defaultValue `"div"`
   */
  as?: string;
  /**
   * Complete immutable definitions installed on the shared host.
   *
   * The surface adds no start, direction, completion, navigation, or animation
   * policy. Definitions should be created by the owning page component.
   */
  gestures: readonly OriginGestureDefinition[];
}

// Builder ------------------------------------------------------------------

/*
 * Immutable fluent builder. Each stage is a frozen object holding the choices
 * made so far in a frozen draft; the final `.animate()` produces a frozen
 * definition. `.onCommit()` is available at every stage after the direction
 * and returns the same stage with the handler appended.
 *
 *   gesture[.from.<start>].to.<direction>()[.complete()].navigate().animate()
 */

/** Choices accumulated by the builder before `.animate()`. */
interface GestureDraft {
  readonly start: OriginGestureStart;
  readonly direction: OriginGestureDirection;
  readonly recognition: Readonly<OriginGestureDirectionOptions>;
  readonly completion?: OriginGestureCompletionPredicate;
  readonly commitHandlers: readonly OriginGestureCommitHandler[];
}

const withCommitHandler = <Draft extends GestureDraft>(
  draft: Draft,
  handler: OriginGestureCommitHandler,
): Draft =>
  Object.freeze({
    ...draft,
    commitHandlers: Object.freeze([...draft.commitHandlers, handler]),
  });

function navigationStage(
  draft: GestureDraft & { readonly navigation: OriginGestureNavigationFactory },
): OriginGestureNavigationBuilder {
  return Object.freeze({
    animate: (choreography: OriginChoreography): OriginGestureDefinition =>
      Object.freeze({
        kind: "origin-gesture-definition",
        start: draft.start,
        direction: draft.direction,
        recognition: draft.recognition,
        completion: draft.completion,
        navigation: draft.navigation,
        choreography,
        commitHandlers: draft.commitHandlers,
      }),
    onCommit: (handler: OriginGestureCommitHandler) =>
      navigationStage(withCommitHandler(draft, handler)),
  });
}

const navigateFrom =
  (draft: GestureDraft) => (navigation: OriginGestureNavigationFactory) =>
    navigationStage(Object.freeze({ ...draft, navigation }));

function completedStage(draft: GestureDraft): OriginGestureCompletedBuilder {
  return Object.freeze({
    navigate: navigateFrom(draft),
    onCommit: (handler: OriginGestureCommitHandler) =>
      completedStage(withCommitHandler(draft, handler)),
  });
}

function directedStage(draft: GestureDraft): OriginGestureDirectedBuilder {
  return Object.freeze({
    complete: (completion: OriginGestureCompletionPredicate) =>
      completedStage(Object.freeze({ ...draft, completion })),
    navigate: navigateFrom(draft),
    onCommit: (handler: OriginGestureCommitHandler) =>
      directedStage(withCommitHandler(draft, handler)),
  });
}

function toStage(start: OriginGestureStart): OriginGestureToBuilder {
  const direct =
    (direction: OriginGestureDirection) =>
    (options: OriginGestureDirectionOptions = {}) =>
      directedStage(
        Object.freeze({
          start,
          direction,
          recognition: Object.freeze({ ...options }),
          commitHandlers: Object.freeze([]),
        }),
      );
  return Object.freeze({
    left: direct("left"),
    right: direct("right"),
    up: direct("up"),
    down: direct("down"),
  });
}

function fromStage(start: OriginGestureStart): OriginGestureFromSelection {
  return Object.freeze({ to: toStage(Object.freeze(start)) });
}

const fromEdge =
  (edge: OriginGestureEdge) => (distance: OriginGestureDistance) =>
    fromStage({ kind: "edge", edge, distance });

const fromBuilder: OriginGestureFromBuilder = Object.freeze({
  left: fromEdge("left"),
  right: fromEdge("right"),
  top: fromEdge("top"),
  bottom: fromEdge("bottom"),
  anywhere: () => fromStage({ kind: "anywhere" }),
  when: (predicate: OriginGestureStartPredicate) =>
    fromStage({ kind: "when", predicate }),
});

/**
 * Root of the immutable gesture builder.
 *
 * `.from` is optional. Starting at `.to` admits pointer-down anywhere on the
 * bound host, exactly like `.from.anywhere().to`.
 *
 * @example Anywhere-to-right back gesture
 * ```ts
 * const swipeBack = gesture
 *   .to.right()
 *   .navigate((context) => context.canGoBack ? back() : null)
 *   .animate(slideRight);
 * ```
 *
 * @example Predicate-gated gesture with custom completion
 * ```ts
 * const openPanel = gesture
 *   .from.when(({ point, bounds }) => point.localX <= bounds.width * 0.08)
 *   .to.down()
 *   .complete(({ progress, velocity }) => progress > 0.5 || velocity > 1)
 *   .navigate(() => above(originView(PanelView)))
 *   .animate(dropPanel);
 * ```
 */
export const gesture: OriginGestureBuilder = Object.freeze({
  from: fromBuilder,
  to: toStage(Object.freeze({ kind: "anywhere" })),
});