SubMiner/src/core/services/subtitle-cue-parser.ts

import {
  assOverrideSignature,
  assToPlainText,
  collectAssOverrideCommands,
  parseAssEffectField,
  type AssEffectKind,
  type AssOverrideCommand,
} from './ass-text';
import { hasAssAnimationEvidence, mergeDuplicateCues } from './subtitle-cue-dedup';

export interface SubtitleCue {
  startTime: number;
  endTime: number;
  text: string;
  /** A complete authored line recovered from matching generated ASS animation events. */
  source?: 'canonical-ass';
  /**
   * Full span of the generated animation events a canonical cue replaced. Entrance and
   * exit frames routinely run past the authored `startTime`/`endTime`, so live-text
   * matching must use this envelope while display and history keep the authored timing.
   */
  animationStartTime?: number;
  animationEndTime?: number;
}

/**
 * Everything the parser knows about a source event, shared only with the dedup engine.
 * Deduplication needs the authoring context -- which style the line belongs to, which
 * override commands it carries, whether the `Effect` column was set -- to tell a karaoke
 * burst apart from two characters saying the same word in turn. None of it is meaningful
 * outside the parser, so the public API exposes only timing, text, and the optional
 * canonical-source marker used by live subtitle consumers.
 */
export interface AnnotatedSubtitleCue extends SubtitleCue {
  /** Text exactly as authored, override blocks and all. */
  rawText: string;
  style: string;
  layer: number;
  /** ASS `Name`/`Actor` column. */
  name: string;
  /** ASS `Effect` column, verbatim. */
  effect: string;
  effectKind: AssEffectKind;
  /** Override commands found in `{...}` blocks, with their arguments. */
  overrides: readonly AssOverrideCommand[];
  /** Canonical form of `overrides`, for spotting values that change across a run. */
  overrideSignature: string;
  /** Position in the source file, so sorting by time stays deterministic across layers. */
  order: number;
}

export type SubtitleSourceFormat = 'ass' | 'srt';

const HTML_SUBTITLE_TAG_PATTERN = /<\/?[A-Za-z][^>\n]*>/g;

const SRT_TIMING_PATTERN =
  /^\s*(?:(\d{1,2}):)?(\d{2}):(\d{2})[,.](\d{1,3})\s*-->\s*(?:(\d{1,2}):)?(\d{2}):(\d{2})[,.](\d{1,3})/;

function parseTimestamp(
  hours: string | undefined,
  minutes: string,
  seconds: string,
  millis: string,
): number {
  return (
    Number(hours || 0) * 3600 +
    Number(minutes) * 60 +
    Number(seconds) +
    Number(millis.padEnd(3, '0')) / 1000
  );
}

/**
 * The single ASS decode for the file path: cues leave the parser as plain text with real
 * line breaks, matching what mpv hands over for the same line played live. No layer
 * downstream decodes ASS again.
 */
function sanitizeSubtitleCueText(text: string): string {
  return assToPlainText(text, '\n').replace(HTML_SUBTITLE_TAG_PATTERN, '').trim();
}

function toPublicCues(cues: AnnotatedSubtitleCue[]): SubtitleCue[] {
  return cues.map(({ startTime, endTime, text, source, animationStartTime, animationEndTime }) =>
    source
      ? { startTime, endTime, text, source, animationStartTime, animationEndTime }
      : { startTime, endTime, text },
  );
}

function parseAnnotatedSrtCues(content: string): AnnotatedSubtitleCue[] {
  const cues: AnnotatedSubtitleCue[] = [];
  const lines = content.split(/\r?\n/);
  let i = 0;

  while (i < lines.length) {
    const line = lines[i]!;
    const timingMatch = SRT_TIMING_PATTERN.exec(line);
    if (!timingMatch) {
      i += 1;
      continue;
    }

    const startTime = parseTimestamp(
      timingMatch[1],
      timingMatch[2]!,
      timingMatch[3]!,
      timingMatch[4]!,
    );
    const endTime = parseTimestamp(
      timingMatch[5],
      timingMatch[6]!,
      timingMatch[7]!,
      timingMatch[8]!,
    );

    i += 1;
    const textLines: string[] = [];
    while (i < lines.length && lines[i]!.trim() !== '') {
      textLines.push(lines[i]!);
      i += 1;
    }

    const rawText = textLines.join('\n');
    const text = sanitizeSubtitleCueText(rawText);
    if (text) {
      cues.push({
        startTime,
        endTime,
        text,
        rawText,
        style: '',
        layer: 0,
        name: '',
        effect: '',
        effectKind: 'none',
        // SRT and VTT carry no authoring metadata, and the dedup engine never reads
        // overrides for those formats -- collecting them would be parsing for nobody.
        overrides: [],
        overrideSignature: '',
        order: cues.length,
      });
    }
  }

  return cues;
}

export function parseSrtCues(content: string): SubtitleCue[] {
  return toPublicCues(parseAnnotatedSrtCues(content));
}

const ASS_TIMING_PATTERN = /^(\d+):(\d{2}):(\d{2})\.(\d{1,2})$/;
const ASS_FORMAT_PREFIX = 'Format:';
const ASS_DIALOGUE_PREFIX = 'Dialogue:';
const ASS_COMMENT_PREFIX = 'Comment:';
const ASS_NAME_FIELD_ALIASES = ['name', 'actor'];
const CANONICAL_MATCH_MARGIN_SECONDS = 1;
const MIN_CANONICAL_ANIMATION_EVENTS = 3;
// A tiny animated fragment can itself be composed from still smaller glyph events. It is
// not enough evidence that the fragment represents an authored line boundary.
const MIN_CANONICAL_DIALOGUE_TEXT_LENGTH = 4;

function parseAssTimestamp(raw: string): number | null {
  const match = ASS_TIMING_PATTERN.exec(raw.trim());
  if (!match) {
    return null;
  }
  const hours = Number(match[1]);
  const minutes = Number(match[2]);
  const seconds = Number(match[3]);
  const centiseconds = Number(match[4]!.padEnd(2, '0'));
  return hours * 3600 + minutes * 60 + seconds + centiseconds / 100;
}

function readField(fields: string[], index: number): string {
  return index >= 0 && index < fields.length ? fields[index]!.trim() : '';
}

function findFieldIndex(formatFields: string[], aliases: string[]): number {
  for (const alias of aliases) {
    const index = formatFields.indexOf(alias);
    if (index >= 0) {
      return index;
    }
  }
  return -1;
}

interface ParsedAssEvents {
  dialogue: AnnotatedSubtitleCue[];
  comments: AnnotatedSubtitleCue[];
}

// Every candidate line re-reads the compacted text of each event in its window, so on
// fragment-heavy scripts the same event compacts thousands of times without this cache.
const compactMatchTextCache = new WeakMap<AnnotatedSubtitleCue, string>();

function compactAssMatchText(text: string): string {
  return text.replace(/\s+/gu, '');
}

function compactCueMatchText(cue: AnnotatedSubtitleCue): string {
  let compact = compactMatchTextCache.get(cue);
  if (compact === undefined) {
    compact = compactAssMatchText(cue.text);
    compactMatchTextCache.set(cue, compact);
  }
  return compact;
}

function assEventGroupKey(cue: AnnotatedSubtitleCue): string {
  return `${cue.style}\0${cue.name}`;
}

/**
 * Windowed lookup over one style/name group. Every candidate line queries its time
 * neighborhood, and fragment-heavy scripts put thousands of candidates in one group, so
 * a linear rescan per candidate is quadratic in practice. Events are sorted by start
 * once; `prefixMaxEnd` lets the backward walk stop as soon as no earlier event can still
 * reach the window.
 */
interface AssEventGroupIndex {
  byStart: AnnotatedSubtitleCue[];
  prefixMaxEnd: number[];
}

function buildAssEventGroupIndex(events: readonly AnnotatedSubtitleCue[]): AssEventGroupIndex {
  const byStart = [...events].sort((a, b) => a.startTime - b.startTime || a.order - b.order);
  const prefixMaxEnd: number[] = [];
  let maxEnd = -Infinity;
  for (const event of byStart) {
    maxEnd = Math.max(maxEnd, event.endTime);
    prefixMaxEnd.push(maxEnd);
  }
  return { byStart, prefixMaxEnd };
}

/** Group events overlapping `[startTime, endTime]`, returned in source order. */
function eventsOverlappingWindow(
  index: AssEventGroupIndex,
  startTime: number,
  endTime: number,
): AnnotatedSubtitleCue[] {
  const { byStart, prefixMaxEnd } = index;
  let low = 0;
  let high = byStart.length;
  while (low < high) {
    const mid = (low + high) >>> 1;
    if (byStart[mid]!.startTime <= endTime) {
      low = mid + 1;
    } else {
      high = mid;
    }
  }
  const matches: AnnotatedSubtitleCue[] = [];
  for (let i = low - 1; i >= 0 && prefixMaxEnd[i]! >= startTime; i -= 1) {
    if (byStart[i]!.endTime >= startTime) {
      matches.push(byStart[i]!);
    }
  }
  return matches.sort((a, b) => a.order - b.order);
}

interface FragmentGroup {
  text: string;
  events: AnnotatedSubtitleCue[];
}

function fragmentPlacementAnchors(event: AnnotatedSubtitleCue): Set<string> {
  const anchors = new Set<string>();
  for (const command of event.overrides) {
    const name = command.name.toLowerCase();
    const args = command.args.split(',').map((value) => value.trim());
    if (name === 'pos' && args.length >= 2) {
      anchors.add(`pos:${args[0]},${args[1]}`);
    } else if (name === 'move' && args.length >= 4) {
      anchors.add(`move:${args[0]},${args[1]}`);
      anchors.add(`move:${args[2]},${args[3]}`);
    }
  }
  return anchors;
}

function isRepeatedFragmentCopy(
  previous: AnnotatedSubtitleCue,
  current: AnnotatedSubtitleCue,
): boolean {
  const previousAnchors = fragmentPlacementAnchors(previous);
  if ([...fragmentPlacementAnchors(current)].some((anchor) => previousAnchors.has(anchor))) {
    return true;
  }
  return (
    previous.startTime === current.startTime &&
    previous.endTime === current.endTime &&
    previous.overrideSignature === current.overrideSignature
  );
}

function groupConsecutiveAssFragments(events: readonly AnnotatedSubtitleCue[]): FragmentGroup[] {
  const groups: FragmentGroup[] = [];
  for (const event of events) {
    const text = compactCueMatchText(event);
    if (!text) {
      continue;
    }
    const previous = groups.at(-1);
    if (
      previous?.text === text &&
      previous.events.some((previousEvent) => isRepeatedFragmentCopy(previousEvent, event))
    ) {
      previous.events.push(event);
    } else {
      groups.push({ text, events: [event] });
    }
  }
  return groups;
}

function findCanonicalFragmentEvents(
  events: readonly AnnotatedSubtitleCue[],
  canonicalText: string,
): AnnotatedSubtitleCue[] {
  const groups = groupConsecutiveAssFragments(events);
  const matches = new Set<AnnotatedSubtitleCue>();

  for (let start = 0; start < groups.length; start += 1) {
    let combined = '';
    for (let end = start; end < groups.length; end += 1) {
      const group = groups[end]!;
      // A complete rendered copy cannot prove that the neighboring events are its
      // fragments. Exact full-line animation is handled separately for comments.
      if (group.text.length >= canonicalText.length) {
        break;
      }
      const next = combined + group.text;
      if (!canonicalText.startsWith(next)) {
        break;
      }
      combined = next;
      if (combined !== canonicalText) {
        continue;
      }
      for (let index = start; index <= end; index += 1) {
        for (const event of groups[index]!.events) {
          matches.add(event);
        }
      }
      start = end;
      break;
    }
  }

  return [...matches];
}

function matchingAssAnimationEvents(options: {
  candidate: AnnotatedSubtitleCue;
  group: AssEventGroupIndex;
  allowFullLineFrames: boolean;
}): AnnotatedSubtitleCue[] {
  const canonicalText = compactCueMatchText(options.candidate);
  // The group index already restricts to the candidate's style and name.
  const nearby = eventsOverlappingWindow(
    options.group,
    options.candidate.startTime - CANONICAL_MATCH_MARGIN_SECONDS,
    options.candidate.endTime + CANONICAL_MATCH_MARGIN_SECONDS,
  );
  const fragments = findCanonicalFragmentEvents(nearby, canonicalText);
  if (fragments.length >= MIN_CANONICAL_ANIMATION_EVENTS && hasAssAnimationEvidence(fragments)) {
    return fragments;
  }

  if (!options.allowFullLineFrames) {
    return [];
  }
  const fullLineFrames = nearby.filter((cue) => compactCueMatchText(cue) === canonicalText);
  return fullLineFrames.length >= MIN_CANONICAL_ANIMATION_EVENTS &&
    hasAssAnimationEvidence(fullLineFrames)
    ? fullLineFrames
    : [];
}

// Reductions rather than `Math.min(...events)`: one generated line can carry an
// unbounded number of events, and spreading them all as arguments risks the engine's
// argument-count limit.
function earliestStartTime(events: readonly AnnotatedSubtitleCue[], seed = Infinity): number {
  return events.reduce((earliest, event) => Math.min(earliest, event.startTime), seed);
}

function latestEndTime(events: readonly AnnotatedSubtitleCue[], seed = -Infinity): number {
  return events.reduce((latest, event) => Math.max(latest, event.endTime), seed);
}

function includeCanonicalBoundaryEvents(options: {
  candidate: AnnotatedSubtitleCue;
  group: AssEventGroupIndex;
  animationEvents: readonly AnnotatedSubtitleCue[];
}): AnnotatedSubtitleCue[] {
  const canonicalText = compactCueMatchText(options.candidate);
  const startTime = earliestStartTime(options.animationEvents);
  const endTime = latestEndTime(options.animationEvents);
  return eventsOverlappingWindow(
    options.group,
    startTime - CANONICAL_MATCH_MARGIN_SECONDS,
    endTime + CANONICAL_MATCH_MARGIN_SECONDS,
  ).filter((cue) => compactCueMatchText(cue) === canonicalText);
}

function recoverCanonicalAssEvents({
  dialogue,
  comments,
}: ParsedAssEvents): AnnotatedSubtitleCue[] {
  const recovered: AnnotatedSubtitleCue[] = [];
  const suppressed = new Set<AnnotatedSubtitleCue>();
  // A recovery is only as good as its owning event. When a later candidate proves that
  // an earlier candidate was itself a generated frame of its animation, the earlier
  // recovery is a duplicate of the same authored line and must be withdrawn.
  const recoveredByOwner = new Map<AnnotatedSubtitleCue, AnnotatedSubtitleCue>();
  const withdrawn = new Set<AnnotatedSubtitleCue>();
  const eventsByGroup = new Map<string, AnnotatedSubtitleCue[]>();
  for (const cue of dialogue) {
    const key = assEventGroupKey(cue);
    const group = eventsByGroup.get(key);
    if (group) {
      group.push(cue);
    } else {
      eventsByGroup.set(key, [cue]);
    }
  }
  const indexByGroup = new Map<string, AssEventGroupIndex>();
  for (const [key, events] of eventsByGroup) {
    indexByGroup.set(key, buildAssEventGroupIndex(events));
  }
  const emptyGroupIndex: AssEventGroupIndex = { byStart: [], prefixMaxEnd: [] };
  const candidates = [
    ...comments.map((cue) => ({ cue, kind: 'comment' as const })),
    ...dialogue
      .filter(
        (cue) =>
          compactCueMatchText(cue).length >= MIN_CANONICAL_DIALOGUE_TEXT_LENGTH &&
          hasAssAnimationEvidence([cue]),
      )
      .sort((left, right) => right.text.length - left.text.length || left.order - right.order)
      .map((cue) => ({ cue, kind: 'dialogue' as const })),
  ];

  for (const { cue: candidate, kind } of candidates) {
    if (candidate.endTime <= candidate.startTime || suppressed.has(candidate)) {
      continue;
    }
    const canonicalText = compactCueMatchText(candidate);
    if (!canonicalText) {
      continue;
    }

    const group = indexByGroup.get(assEventGroupKey(candidate)) ?? emptyGroupIndex;
    const animationEvents = matchingAssAnimationEvents({
      candidate,
      group,
      allowFullLineFrames: kind === 'comment',
    });
    if (animationEvents.length === 0) {
      continue;
    }

    const boundaryEvents = includeCanonicalBoundaryEvents({
      candidate,
      group,
      animationEvents,
    });
    const generatedEvents = [...new Set([...animationEvents, ...boundaryEvents])];
    const animationStartTime = earliestStartTime(generatedEvents, candidate.startTime);
    const animationEndTime = latestEndTime(generatedEvents, candidate.endTime);
    const startTime = kind === 'comment' ? candidate.startTime : animationStartTime;
    const endTime = kind === 'comment' ? candidate.endTime : animationEndTime;
    const recoveredCue: AnnotatedSubtitleCue = {
      ...candidate,
      startTime,
      endTime,
      animationStartTime,
      animationEndTime,
      source: 'canonical-ass',
    };
    recovered.push(recoveredCue);
    recoveredByOwner.set(candidate, recoveredCue);
    for (const event of generatedEvents) {
      suppressed.add(event);
      if (event === candidate) {
        continue;
      }
      const priorRecovery = recoveredByOwner.get(event);
      if (priorRecovery) {
        // No text is lost by withdrawing: a fragment claim means the withdrawn line is
        // a contiguous piece of this candidate's text, and a boundary claim means the
        // texts are equal, so the surviving canonical cue always contains it.
        withdrawn.add(priorRecovery);
      }
    }
  }

  const survivingRecovered = recovered.filter((cue) => !withdrawn.has(cue));
  if (survivingRecovered.length === 0) {
    return dialogue;
  }
  return [...dialogue.filter((cue) => !suppressed.has(cue)), ...survivingRecovered].sort(
    (a, b) => a.startTime - b.startTime || a.endTime - b.endTime || a.order - b.order,
  );
}

function parseAnnotatedAssEvents(content: string): ParsedAssEvents {
  const cues: AnnotatedSubtitleCue[] = [];
  const comments: AnnotatedSubtitleCue[] = [];
  const lines = content.split(/\r?\n/);
  let inEventsSection = false;
  let eventOrder = 0;
  const fieldIndex = {
    start: -1,
    end: -1,
    text: -1,
    style: -1,
    layer: -1,
    name: -1,
    effect: -1,
  };

  const resetFieldIndex = () => {
    fieldIndex.start = -1;
    fieldIndex.end = -1;
    fieldIndex.text = -1;
    fieldIndex.style = -1;
    fieldIndex.layer = -1;
    fieldIndex.name = -1;
    fieldIndex.effect = -1;
  };

  for (const line of lines) {
    const trimmed = line.trim();

    if (trimmed.startsWith('[') && trimmed.endsWith(']')) {
      inEventsSection = trimmed.toLowerCase() === '[events]';
      if (!inEventsSection) {
        resetFieldIndex();
      }
      continue;
    }

    if (!inEventsSection) {
      continue;
    }

    if (trimmed.startsWith(ASS_FORMAT_PREFIX)) {
      const formatFields = trimmed
        .slice(ASS_FORMAT_PREFIX.length)
        .split(',')
        .map((field) => field.trim().toLowerCase());
      fieldIndex.start = formatFields.indexOf('start');
      fieldIndex.end = formatFields.indexOf('end');
      fieldIndex.text = formatFields.indexOf('text');
      fieldIndex.style = formatFields.indexOf('style');
      fieldIndex.layer = formatFields.indexOf('layer');
      // Aegisub writes the speaker column as `Actor`; the v4+ spec calls it `Name`.
      // Missing it costs the burst check its speaker guard, so both spellings count.
      fieldIndex.name = findFieldIndex(formatFields, ASS_NAME_FIELD_ALIASES);
      fieldIndex.effect = formatFields.indexOf('effect');
      continue;
    }

    const eventPrefix = trimmed.startsWith(ASS_DIALOGUE_PREFIX)
      ? ASS_DIALOGUE_PREFIX
      : trimmed.startsWith(ASS_COMMENT_PREFIX)
        ? ASS_COMMENT_PREFIX
        : null;
    if (!eventPrefix) {
      continue;
    }

    if (fieldIndex.start < 0 || fieldIndex.end < 0 || fieldIndex.text < 0) {
      continue;
    }

    const fields = trimmed.slice(eventPrefix.length).split(',');
    if (
      fieldIndex.start >= fields.length ||
      fieldIndex.end >= fields.length ||
      fieldIndex.text >= fields.length
    ) {
      continue;
    }

    const startTime = parseAssTimestamp(fields[fieldIndex.start]!);
    const endTime = parseAssTimestamp(fields[fieldIndex.end]!);
    if (startTime === null || endTime === null) {
      continue;
    }

    const rawText = fields.slice(fieldIndex.text).join(',');
    const text = sanitizeSubtitleCueText(rawText);
    if (!text) {
      continue;
    }

    const effect = readField(fields, fieldIndex.effect);
    const layer = Number(readField(fields, fieldIndex.layer));
    const overrides = collectAssOverrideCommands(rawText);
    const cue: AnnotatedSubtitleCue = {
      startTime,
      endTime,
      text,
      rawText,
      style: readField(fields, fieldIndex.style),
      layer: Number.isFinite(layer) ? layer : 0,
      name: readField(fields, fieldIndex.name),
      effect,
      effectKind: parseAssEffectField(effect),
      overrides,
      overrideSignature: assOverrideSignature(overrides),
      order: eventOrder,
    };
    eventOrder += 1;
    if (eventPrefix === ASS_COMMENT_PREFIX) {
      comments.push(cue);
    } else {
      cues.push(cue);
    }
  }

  return { dialogue: cues, comments };
}

function parseAnnotatedAssCues(content: string): AnnotatedSubtitleCue[] {
  return recoverCanonicalAssEvents(parseAnnotatedAssEvents(content));
}

export function parseAssCues(content: string): SubtitleCue[] {
  return toPublicCues(parseAnnotatedAssCues(content));
}

function detectSubtitleFormat(source: string): 'srt' | 'vtt' | 'ass' | 'ssa' | null {
  const [normalizedSource = source] =
    (() => {
      try {
        return /^[a-z]+:\/\//i.test(source) ? new URL(source).pathname : source;
      } catch {
        return source;
      }
    })().split(/[?#]/, 1)[0] ?? '';
  const ext = normalizedSource.split('.').pop()?.toLowerCase() ?? '';
  if (ext === 'srt') return 'srt';
  if (ext === 'vtt') return 'vtt';
  if (ext === 'ass' || ext === 'ssa') return 'ass';
  return null;
}

export function parseSubtitleCues(content: string, filename: string): SubtitleCue[] {
  const format = detectSubtitleFormat(filename);
  let cues: AnnotatedSubtitleCue[];
  let sourceFormat: SubtitleSourceFormat = 'srt';

  switch (format) {
    case 'srt':
    case 'vtt':
      cues = parseAnnotatedSrtCues(content);
      break;
    case 'ass':
    case 'ssa':
      cues = parseAnnotatedAssCues(content);
      sourceFormat = 'ass';
      break;
    default:
      cues = [];
  }

  if (cues.length === 0) {
    const assCues = parseAnnotatedAssCues(content);
    const srtCues = parseAnnotatedSrtCues(content);
    const preferAss = assCues.length >= srtCues.length;
    cues = preferAss ? assCues : srtCues;
    sourceFormat = preferAss && assCues.length > 0 ? 'ass' : 'srt';
  }

  cues.sort((a, b) => a.startTime - b.startTime || a.endTime - b.endTime || a.order - b.order);
  return toPublicCues(mergeDuplicateCues(cues, sourceFormat));
}