/**
 * Geometry for the rectification timeline: clock strings in, percentages out.
 *
 * Kept apart from the component so the scale is testable without a DOM. The
 * component renders what this returns and decides nothing itself.
 *
 * Two rules this module exists to hold:
 *
 * - The axis is the **current** search window (`candidate_range`), never the
 *   opening one. The window widens (BUG-572: ±15 → ±30 → ±60 → ±120) and
 *   narrows (a chosen block), so an axis pinned to the opening window would be
 *   overrun by its own band.
 * - Candidate marks carry no confidence. BUG-560 is blocked: relative support
 *   between candidate minutes is 7–9 out of 100 and calibration found no
 *   minute-level discriminating power, so a graded mark would render a
 *   difference the engine cannot support. The only encoding is in-range or
 *   excluded.
 */

const MINUTES_PER_DAY = 1440;

export type RectificationTimelineStage = "minute" | "block_scan";

export type TimelineMark = Readonly<{
  /** Stable across re-renders so CSS transitions animate rather than restart. */
  key: string;
  percent: number;
  /** Binary by design; see the module note on BUG-560. */
  state: "in" | "out";
}>;

export type TimelineTick = Readonly<{
  key: string;
  percent: number;
  label: string;
}>;

export type RectificationTimelineView = Readonly<{
  /** Inclusive clock labels for the axis ends, for assistive text. */
  axisStartLabel: string;
  axisEndLabel: string;
  bandStartPercent: number;
  bandWidthPercent: number;
  marks: readonly TimelineMark[];
  ticks: readonly TimelineTick[];
  /** `05:07–05:09` */
  rangeLabel: string;
  /** `3 分钟` */
  widthLabel: string;
}>;

/** `HH:MM` or `HH:MM:SS` to minutes past midnight; null when unparseable. */
export function parseClockMinutes(value: unknown): number | null {
  if (typeof value !== "string") return null;
  const match = /^(\d{1,2}):(\d{2})(?::\d{2})?$/.exec(value.trim());
  if (!match) return null;
  const hours = Number(match[1]);
  const minutes = Number(match[2]);
  if (!Number.isInteger(hours) || !Number.isInteger(minutes)) return null;
  if (hours > 23 || minutes > 59) return null;
  return hours * 60 + minutes;
}

export function formatClockMinutes(value: number): string {
  const wrapped = ((Math.round(value) % MINUTES_PER_DAY) + MINUTES_PER_DAY) % MINUTES_PER_DAY;
  const hours = Math.floor(wrapped / 60);
  const minutes = wrapped % 60;
  return `${String(hours).padStart(2, "0")}:${String(minutes).padStart(2, "0")}`;
}

/**
 * Declared periods may cross midnight (`late_night` is 23:00–03:59), which
 * arrives as an end earlier than its start. Unrolling onto a second day keeps
 * the axis monotonic; every other calculation then works on plain numbers.
 */
export function unrollWindowEnd(start: number, end: number): number {
  return end >= start ? end : end + MINUTES_PER_DAY;
}

/** Place a clock reading on an axis that may run past midnight. */
export function alignToAxis(minute: number, axisStart: number, axisEnd: number): number {
  if (minute >= axisStart) return minute;
  const shifted = minute + MINUTES_PER_DAY;
  return shifted <= axisEnd ? shifted : minute;
}

/** Coarser ticks as the window grows; the labels stay on round clock values. */
export function timelineTickStepMinutes(span: number): number {
  if (span <= 40) return 5;
  if (span <= 90) return 10;
  if (span <= 180) return 20;
  if (span <= 400) return 60;
  if (span <= 900) return 120;
  return 240;
}

export function timelineDurationLabel(minutes: number): string {
  const total = Math.max(0, Math.round(minutes));
  if (total < 60) return `${total} 分钟`;
  const hours = Math.floor(total / 60);
  const rest = total % 60;
  return rest === 0 ? `${hours} 小时` : `${hours} 小时 ${rest} 分`;
}

function clampPercent(value: number): number {
  if (!Number.isFinite(value)) return 0;
  if (value < 0) return 0;
  if (value > 100) return 100;
  return value;
}

/** Position on the axis as a percentage; callers clamp-safe by construction. */
export function timelinePercent(minute: number, axisStart: number, axisEnd: number): number {
  const span = axisEnd - axisStart;
  if (span <= 0) return 0;
  return clampPercent(((minute - axisStart) / span) * 100);
}

function buildTicks(axisStart: number, axisEnd: number): TimelineTick[] {
  const span = axisEnd - axisStart;
  const step = timelineTickStepMinutes(span);
  const ticks: TimelineTick[] = [];
  const first = Math.ceil(axisStart / step) * step;
  for (let at = first; at <= axisEnd; at += step) {
    ticks.push({
      key: `t${at}`,
      percent: timelinePercent(at, axisStart, axisEnd),
      label: formatClockMinutes(at),
    });
  }
  return ticks;
}

export type TimelineInferenceMark = Readonly<{
  time: string;
  eliminated: boolean;
}>;

export type RectificationTimelineInput = Readonly<{
  /** `candidate_range`: the case's current search window, and the axis. */
  searchWindow: readonly [string, string] | null;
  /** `credible_range`; absent during block scan, where the band is the window. */
  credibleRange: readonly [string, string] | null;
  candidateTimes: readonly string[];
  /**
   * Inference-layer minutes with elimination status. When present and non-empty,
   * these are the marks; `eliminated` is the only in/out judge. When absent,
   * engine `candidateTimes` are drawn solid.
   */
  inferenceMarks?: readonly TimelineInferenceMark[];
  stage: RectificationTimelineStage | null;
}>;

/**
 * Returns null when the bar has nothing truthful to draw — the caller renders
 * an equal-height skeleton rather than shrinking, because the bar sits outside
 * the scroll container and a height change would silently break stick-to-bottom.
 */
export function buildRectificationTimeline(
  input: RectificationTimelineInput,
): RectificationTimelineView | null {
  const windowStart = parseClockMinutes(input.searchWindow?.[0]);
  const windowEndRaw = parseClockMinutes(input.searchWindow?.[1]);
  if (windowStart === null || windowEndRaw === null) return null;

  const axisStart = windowStart;
  const axisEnd = unrollWindowEnd(windowStart, windowEndRaw);
  if (axisEnd <= axisStart) return null;

  // Block scan has no scored candidates yet, so the credible range is the whole
  // window. Saying "24 小时" there is accurate, not a placeholder.
  const bandStartRaw = parseClockMinutes(input.credibleRange?.[0]);
  const bandEndRaw = parseClockMinutes(input.credibleRange?.[1]);
  const hasBand = bandStartRaw !== null && bandEndRaw !== null;
  const bandStart = hasBand
    ? Math.max(axisStart, alignToAxis(bandStartRaw, axisStart, axisEnd))
    : axisStart;
  const bandEnd = hasBand
    ? Math.min(axisEnd, Math.max(bandStart, alignToAxis(unrollWindowEnd(bandStartRaw, bandEndRaw), axisStart, axisEnd)))
    : axisEnd;

  const bandStartPercent = timelinePercent(bandStart, axisStart, axisEnd);
  const bandWidthPercent = clampPercent(
    timelinePercent(bandEnd, axisStart, axisEnd) - bandStartPercent,
  );

  // Minute stage only: during block scan the marks would be blocks, and their
  // boundaries do not reach the client as structured data (see PROGRESS).
  const marks: TimelineMark[] = [];
  if (input.stage === "minute") {
    const sourced = input.inferenceMarks && input.inferenceMarks.length > 0
      ? input.inferenceMarks.map((mark) => ({ time: mark.time, eliminated: mark.eliminated }))
      : input.candidateTimes.map((time) => ({ time, eliminated: false }));
    const seen = new Set<number>();
    for (const item of sourced) {
      const parsed = parseClockMinutes(item.time);
      if (parsed === null) continue;
      const at = alignToAxis(parsed, axisStart, axisEnd);
      if (at < axisStart || at > axisEnd) continue;
      if (seen.has(at)) continue;
      seen.add(at);
      marks.push({
        key: `m${at}`,
        percent: timelinePercent(at, axisStart, axisEnd),
        // Status from the inference layer, never band position (BUG-603).
        state: item.eliminated ? "out" : "in",
      });
    }
    marks.sort((left, right) => left.percent - right.percent);
  }

  return {
    axisStartLabel: formatClockMinutes(axisStart),
    axisEndLabel: formatClockMinutes(axisEnd),
    bandStartPercent,
    bandWidthPercent,
    marks,
    ticks: buildTicks(axisStart, axisEnd),
    rangeLabel: `${formatClockMinutes(bandStart)}–${formatClockMinutes(bandEnd)}`,
    widthLabel: timelineDurationLabel(bandEnd - bandStart + 1),
  };
}