import type { OriginAction, MaybeOriginAction } from "../navigation";
import { useOrigin, type UseOrigin } from "../scene/scene";
import type { OriginContext, OriginOperationHandle } from "../scene/types";
import { clamp01, measureRect, type OriginRect } from "../shared";
import type {
  OriginGestureBinding,
  OriginGestureCompletionPredicate,
  OriginGestureDefinition,
  OriginGestureDirection,
  OriginGestureDistance,
  OriginGestureOptions,
  OriginGesturePoint,
  OriginGestureStart,
} from "./definition";

/*
 * Running gestures: pointer-down admission, movement tracking, and the
 * recognizer that turns one host's pointer events into a scene operation.
 */

// Direction ----------------------------------------------------------------

export const isHorizontal = (direction: OriginGestureDirection): boolean => {
  return direction === "left" || direction === "right";
};

/** Component of a movement `(dx, dy)` along `direction`. */
export const directedDistance = (
  direction: OriginGestureDirection,
  dx: number,
  dy: number,
): number => {
  switch (direction) {
    case "left":
      return -dx;
    case "right":
      return dx;
    case "up":
      return -dy;
    case "down":
      return dy;
  }
};

/** Absolute movement perpendicular to `direction`. */
export const crossDistance = (
  direction: OriginGestureDirection,
  dx: number,
  dy: number,
): number => {
  return isHorizontal(direction) ? Math.abs(dy) : Math.abs(dx);
};

/**
 * CSS `touch-action` for a host recognizing the given directions: native
 * scrolling is preserved on any axis no gesture claims.
 */
export const touchActionFor = (
  directions: Iterable<OriginGestureDirection>,
): "none" | "pan-x" | "pan-y" | "auto" => {
  let horizontal = false;
  let vertical = false;
  for (const direction of directions) {
    if (isHorizontal(direction)) horizontal = true;
    else vertical = true;
  }
  if (horizontal && vertical) return "none";
  if (horizontal) return "pan-y";
  if (vertical) return "pan-x";
  return "auto";
};

// Pointer-down admission ----------------------------------------------------

/*
 * Pointer-down admission: which events may begin a gesture at all.
 */

const IGNORED_TARGETS =
  '[data-origin-gesture="ignore"], input, textarea, select, option, [contenteditable="true"]';

/** Form controls and opted-out subtrees never start gestures. */
export const isIgnoredTarget = (target: EventTarget | null): boolean => {
  return (
    !(target instanceof Element) || Boolean(target.closest(IGNORED_TARGETS))
  );
};

export const pointOf = (
  event: Pick<PointerEvent, "clientX" | "clientY">,
  bounds: OriginRect,
): OriginGesturePoint => {
  return {
    clientX: event.clientX,
    clientY: event.clientY,
    localX: event.clientX - bounds.left,
    localY: event.clientY - bounds.top,
  };
};

const nonNegative = (value: number) =>
  Number.isFinite(value) ? Math.max(0, value) : 0;

/**
 * Resolve an arbitrary CSS length against a box with the gesture host's size.
 *
 * A short-lived off-screen box lets the browser handle `rem`, viewport units,
 * percentages, `calc()`, and `clamp()` consistently. This runs only during
 * pointer-down for edge-constrained definitions.
 */
export const resolveCssDistance = (
  distance: OriginGestureDistance,
  axis: "horizontal" | "vertical",
  host: HTMLElement,
  bounds: OriginRect,
): number => {
  if (typeof distance === "number") return nonNegative(distance);

  const document = host.ownerDocument;
  if (!document.body) return Math.max(0, Number.parseFloat(distance) || 0);

  const container = document.createElement("div");
  const probe = document.createElement("div");
  Object.assign(container.style, {
    position: "fixed",
    left: "-100000px",
    top: "-100000px",
    width: `${bounds.width}px`,
    height: `${bounds.height}px`,
    visibility: "hidden",
    pointerEvents: "none",
    contain: "strict",
  });
  Object.assign(probe.style, {
    position: "absolute",
    width: axis === "horizontal" ? distance : "0",
    height: axis === "vertical" ? distance : "0",
  });
  container.append(probe);
  document.body.append(container);
  const rect = probe.getBoundingClientRect();
  container.remove();
  return nonNegative(axis === "horizontal" ? rect.width : rect.height);
};

/** Whether a pointer-down satisfies a definition's start policy. */
export const matchesStart = (
  start: OriginGestureStart,
  event: PointerEvent,
  host: HTMLElement,
  origin: OriginContext,
  bounds: OriginRect,
): boolean => {
  if (start.kind === "anywhere") return true;
  const point = pointOf(event, bounds);
  if (start.kind === "when")
    return start.predicate({ event, origin, host, bounds, point });

  const horizontal = start.edge === "left" || start.edge === "right";
  const distance = resolveCssDistance(
    start.distance,
    horizontal ? "horizontal" : "vertical",
    host,
    bounds,
  );
  switch (start.edge) {
    case "left":
      return point.localX >= 0 && point.localX <= distance;
    case "right":
      return (
        point.localX <= bounds.width && bounds.width - point.localX <= distance
      );
    case "top":
      return point.localY >= 0 && point.localY <= distance;
    case "bottom":
      return (
        point.localY <= bounds.height &&
        bounds.height - point.localY <= distance
      );
  }
};

// Movement tracking ---------------------------------------------------------

type PointerSample = Pick<PointerEvent, "clientX" | "clientY" | "timeStamp">;

/** Shortest frame interval assumed when computing velocity, in ms. */
const MIN_SAMPLE_INTERVAL = 8;
/**
 * A release without movement after this many ms is treated as a hold, so the
 * last move's flick velocity no longer applies.
 */
const HOLD_RELEASE_INTERVAL = 80;

/**
 * Measures one pointer sequence's movement along a gesture direction.
 *
 * Progress and velocity are normalized by the host's size along the gesture
 * axis, so `1` means one full host width (or height).
 */
export class DirectionalTracker {
  /** Directed distance from the start, in CSS pixels. */
  distance = 0;
  /** Absolute cross-axis distance from the start, in CSS pixels. */
  crossDistance = 0;
  /** Directed distance as a fraction of host size, clamped to `0..1`. */
  progress = 0;
  /** Latest directed velocity in progress units per second. */
  velocity = 0;

  private readonly horizontal: boolean;
  /** Whether progress grows as the axis coordinate decreases. */
  private readonly reversed: boolean;
  private lastCoordinate: number;
  private lastTime: number;

  constructor(
    private readonly direction: OriginGestureDirection,
    private readonly start: PointerSample,
    /** Host size along the gesture axis, read at every sample. */
    private readonly axisSize: () => number,
  ) {
    this.horizontal = isHorizontal(direction);
    this.reversed = direction === "left" || direction === "up";
    this.lastCoordinate = this.coordinateOf(start);
    this.lastTime = start.timeStamp;
  }

  private coordinateOf(event: PointerSample) {
    return this.horizontal ? event.clientX : event.clientY;
  }

  /** Movement from the start without recording a sample. */
  displacement(event: PointerSample) {
    const dx = event.clientX - this.start.clientX;
    const dy = event.clientY - this.start.clientY;
    return {
      distance: directedDistance(this.direction, dx, dy),
      crossDistance: crossDistance(this.direction, dx, dy),
    };
  }

  /** Record a sample, updating distance, progress, and velocity. */
  sample(event: PointerSample, release = false): void {
    const { distance, crossDistance } = this.displacement(event);
    this.distance = distance;
    this.crossDistance = crossDistance;

    const size = Math.max(1, this.axisSize());
    const coordinate = this.coordinateOf(event);
    const step = this.reversed
      ? this.lastCoordinate - coordinate
      : coordinate - this.lastCoordinate;
    const interval = event.timeStamp - this.lastTime;
    this.progress = clamp01(distance / size);
    // Pointer-up commonly repeats the final pointer-move coordinate. Preserve
    // that move's flick velocity for a prompt release, but decay it when the
    // pointer was held still long enough for the flick to have ended.
    if (!release || step !== 0 || interval > HOLD_RELEASE_INTERVAL)
      this.velocity =
        (step * 1000) / (Math.max(MIN_SAMPLE_INTERVAL, interval) * size);

    this.lastCoordinate = coordinate;
    this.lastTime = event.timeStamp;
  }
}

// Recognizer ----------------------------------------------------------------

/** Directed movement in CSS pixels required before a gesture captures. */
const DEFAULT_THRESHOLD = 8;
/** Ratio by which directed movement must exceed cross-axis movement. */
const DEFAULT_AXIS_DOMINANCE = 1.15;

/** Legacy `edge` start side for each movement direction. */
const LEGACY_START_EDGE = {
  left: "right",
  right: "left",
  up: "bottom",
  down: "top",
} as const;

/**
 * The single shape the recognizer executes. Builder definitions and legacy
 * options objects are both normalized into it.
 */
export interface RecognizerPolicy {
  readonly direction: OriginGestureDirection;
  readonly start: OriginGestureStart;
  readonly threshold: number;
  readonly axisDominance: number;
  readonly completion?: OriginGestureCompletionPredicate;
  readonly action: (context: OriginContext) => MaybeOriginAction;
}

/** The origin capabilities a recognizer needs. */
export type RecognizerOrigin = Pick<UseOrigin, "context" | "begin">;

/** State of one admitted pointer sequence, from pointer-down to release. */
interface PointerSession {
  readonly pointerId: number;
  readonly host: HTMLElement;
  readonly bounds: OriginRect;
  /** Origin context captured at pointer-down. */
  readonly origin: OriginContext;
  readonly start: OriginGesturePoint;
  readonly startTime: number;
  readonly tracker: DirectionalTracker;
  /** Movement passed the recognition threshold and the pointer is captured. */
  captured: boolean;
  /** The scene operation, once the action resolved and `begin()` was called. */
  operation: Promise<OriginOperationHandle | null> | null;
}

/**
 * Turns one host's pointer events into a scene operation.
 *
 * Lifecycle of a session:
 *
 * 1. **down**: an eligible primary pointer opens a session.
 * 2. **move**: once directed movement passes the threshold, the pointer is
 *    captured and the policy's action is resolved; a non-null action begins
 *    an operation, while a declined one closes the session. Every later move
 *    updates the operation's progress.
 * 3. **up**: the session closes and the operation finishes, using the
 *    policy's completion predicate when present.
 * 4. **cancel**: the session closes and the operation is cancelled.
 *
 * Action resolution and `begin()` are asynchronous. Each continuation checks
 * that its session is still current, so a stale resolution never creates or
 * updates an orphan operation.
 */
export class GestureRecognizer {
  private session: PointerSession | null = null;

  constructor(
    readonly policy: RecognizerPolicy,
    private readonly origin: RecognizerOrigin,
  ) {}

  /** Create a recognizer for a builder definition or legacy options. */
  static create(
    definition: OriginGestureDefinition | OriginGestureOptions,
    origin: RecognizerOrigin,
  ): GestureRecognizer {
    return new GestureRecognizer(
      GestureRecognizer.policyFor(definition),
      origin,
    );
  }

  /**
   * Normalize a builder definition or legacy options object into the single
   * policy shape the recognizer executes.
   */
  static policyFor(
    definition: OriginGestureDefinition | OriginGestureOptions,
  ): RecognizerPolicy {
    return "kind" in definition &&
      definition.kind === "origin-gesture-definition"
      ? GestureRecognizer.policyFromDefinition(definition)
      : GestureRecognizer.policyFromOptions(definition as OriginGestureOptions);
  }

  private static policyFromDefinition(
    definition: OriginGestureDefinition,
  ): RecognizerPolicy {
    return {
      direction: definition.direction,
      start: definition.start,
      threshold: definition.recognition.threshold ?? DEFAULT_THRESHOLD,
      axisDominance:
        definition.recognition.axisDominance ?? DEFAULT_AXIS_DOMINANCE,
      completion: definition.completion,
      // Pair the resolved navigation intent with the definition's animation.
      action: async (context) => {
        const navigation = await definition.navigation(context);
        if (!navigation) return navigation;
        const action: OriginAction = {
          ...navigation,
          choreography: definition.choreography,
        };
        return action;
      },
    };
  }

  /** Legacy `edge` is measured from the side opposite the movement. */
  private static policyFromOptions(
    options: OriginGestureOptions,
  ): RecognizerPolicy {
    return {
      direction: options.direction,
      start:
        options.edge === undefined
          ? { kind: "anywhere" }
          : Object.freeze({
              kind: "edge",
              edge: LEGACY_START_EDGE[options.direction],
              distance: options.edge,
            }),
      threshold: options.threshold ?? DEFAULT_THRESHOLD,
      axisDominance: DEFAULT_AXIS_DOMINANCE,
      action: options.action,
    };
  }

  pointerDown(event: PointerEvent): void {
    const host = event.currentTarget;
    if (
      !event.isPrimary ||
      event.button !== 0 ||
      !(host instanceof HTMLElement) ||
      isIgnoredTarget(event.target)
    )
      return;

    const bounds = measureRect(host);
    const origin = this.origin.context.value;
    if (!matchesStart(this.policy.start, event, host, origin, bounds)) return;

    // The component containing this declaration is the operation's origin.
    event.stopPropagation();
    const horizontal = isHorizontal(this.policy.direction);
    this.session = {
      pointerId: event.pointerId,
      host,
      bounds,
      origin,
      start: pointOf(event, bounds),
      startTime: event.timeStamp,
      tracker: new DirectionalTracker(this.policy.direction, event, () =>
        horizontal ? host.clientWidth : host.clientHeight,
      ),
      captured: false,
      operation: null,
    };
  }

  async pointerMove(event: PointerEvent): Promise<void> {
    const session = this.sessionFor(event);
    if (!session) return;

    if (!session.captured) {
      if (!this.recognizes(session, event)) return;
      session.captured = true;
      session.host.setPointerCapture?.(session.pointerId);
      event.preventDefault();
      session.tracker.sample(event);
      const action = await this.resolveAction();
      // The pointer may have been released or cancelled meanwhile.
      if (this.session !== session) return;
      if (!action) {
        this.session = null;
        return;
      }
      session.operation = this.origin.begin(action).catch(() => null);
    } else {
      event.preventDefault();
      session.tracker.sample(event);
    }

    // Progress is read after the await so the latest buffered sample wins.
    const pending = session.operation;
    const handle = pending ? await pending : null;
    if (this.session === session && session.operation === pending)
      handle?.update(session.tracker.progress, session.tracker.velocity);
  }

  async pointerUp(event: PointerEvent): Promise<void> {
    const session = this.sessionFor(event);
    if (!session) return;
    this.session = null;
    if (!session.captured) return;

    const { tracker } = session;
    tracker.sample(event, true);
    const commit = this.policy.completion?.({
      origin: session.origin,
      direction: this.policy.direction,
      progress: tracker.progress,
      velocity: tracker.velocity,
      distance: tracker.distance,
      crossDistance: tracker.crossDistance,
      duration: Math.max(0, event.timeStamp - session.startTime),
      event,
      host: session.host,
      bounds: session.bounds,
      start: session.start,
      current: pointOf(event, session.bounds),
    });
    const { progress, velocity } = tracker;

    const handle = session.operation ? await session.operation : null;
    if (!handle) return;
    handle.update(progress, velocity);
    await handle.finish(commit === undefined ? undefined : { commit });
  }

  async pointerCancel(): Promise<void> {
    const session = this.session;
    this.session = null;
    if (!session?.captured) return;
    const handle = session.operation ? await session.operation : null;
    await handle?.cancel();
  }

  private sessionFor(event: PointerEvent) {
    const session = this.session;
    return session && session.pointerId === event.pointerId ? session : null;
  }

  /** Directed movement passed the threshold and dominates the cross axis. */
  private recognizes(session: PointerSession, event: PointerEvent) {
    const { distance, crossDistance } = session.tracker.displacement(event);
    return (
      distance >= this.policy.threshold &&
      distance >= crossDistance * this.policy.axisDominance
    );
  }

  /**
   * Resolve the policy's action against the origin's current context. A
   * declined or failed action resolves to `null`.
   */
  private resolveAction(): Promise<OriginAction | null | undefined> {
    try {
      return Promise.resolve(
        this.policy.action(this.origin.context.value),
      ).catch(() => null);
    } catch {
      return Promise.resolve(null);
    }
  }
}

// Composable ----------------------------------------------------------------

/**
 * Install a component-owned pointer recognizer.
 *
 * Recognition is local to the element receiving these handlers. There is no
 * application-wide gesture table and no lookup of a currently active view.
 *
 * Builder definitions may independently describe their pointer-down region
 * and movement direction. Omitting `.from` recognizes pointer-down across the
 * whole element. The legacy options object remains supported; its `edge` is
 * inferred from the opposite side of its movement direction.
 *
 * Interactive controls and anything inside
 * `[data-origin-gesture="ignore"]` are ignored automatically. The recognizer
 * preserves native scrolling on the cross-axis through its returned style.
 *
 * @param definition - An immutable builder result or legacy recognizer options.
 * @returns Pointer handlers and required host styles.
 * @throws If called outside a component rendered by `OriginScene`.
 *
 * @example Builder-defined backward gesture
 * ```ts
 * const swipeBack = useOriginGesture(
 *   gesture
 *     .from.left("32px")
 *     .to.right()
 *     .navigate((context) => context.canGoBack ? back() : null)
 *     .animate(slideRight),
 * );
 * ```
 */
export function useOriginGesture(
  definition: OriginGestureDefinition | OriginGestureOptions,
): OriginGestureBinding {
  const recognizer = GestureRecognizer.create(definition, useOrigin());

  return {
    style: {
      // Preserve native scrolling perpendicular to the declared gesture.
      touchAction: touchActionFor([recognizer.policy.direction]),
      // OriginGesture is commonly the root returned by a view component.
      width: "100%",
      height: "100%",
    },
    onPointerdown: (event) => recognizer.pointerDown(event),
    onPointermove: (event) => void recognizer.pointerMove(event),
    onPointerup: (event) => void recognizer.pointerUp(event),
    onPointercancel: () => void recognizer.pointerCancel(),
  };
}