export type Phase0RollingArtifactFamily =
  | 'channel'
  | 'gateway'
  | 'backend_pi_embedded'
  | 'backend_native'
  | 'backend_drift'
  | 'prune';

export interface Phase0RollingArtifactFile {
  file_name: string;
  family: Phase0RollingArtifactFamily;
  tag: string;
  tag_timestamp_ms: number;
}

export interface Phase0RollingArtifactRetentionPlan {
  keep: Phase0RollingArtifactFile[];
  remove: Phase0RollingArtifactFile[];
  families: Array<{
    family: Phase0RollingArtifactFamily;
    total_tags: number;
    keep_tags: number;
    remove_tags: number;
  }>;
}

const ROLLING_TAG_PATTERN = /^(\d{4})-(\d{2})-(\d{2})-(\d{6})$/;

const FAMILY_PATTERNS: Array<{ family: Phase0RollingArtifactFamily; pattern: RegExp }> = [
  {
    family: 'channel',
    pattern: /^phase0_baseline_live_(\d{4}-\d{2}-\d{2}-\d{6})\.(json|jsonl|md)$/,
  },
  {
    family: 'gateway',
    pattern: /^phase0_baseline_live_gateway_(\d{4}-\d{2}-\d{2}-\d{6})\.(json|jsonl|md)$/,
  },
  {
    family: 'backend_pi_embedded',
    pattern: /^phase0_baseline_live_backend_pi_embedded_(\d{4}-\d{2}-\d{2}-\d{6})\.(json|jsonl|md)$/,
  },
  {
    family: 'backend_native',
    pattern: /^phase0_baseline_live_backend_native_(\d{4}-\d{2}-\d{2}-\d{6})\.(json|jsonl|md)$/,
  },
  {
    family: 'backend_drift',
    pattern: /^phase0_baseline_live_backend_drift_(\d{4}-\d{2}-\d{2}-\d{6})\.(json|md)$/,
  },
  {
    family: 'prune',
    pattern: /^phase0_baseline_live_prune_(\d{4}-\d{2}-\d{2}-\d{6})\.(json|md)$/,
  },
];

function parseRollingTagTimestampMs(tag: string): number | undefined {
  const match = ROLLING_TAG_PATTERN.exec(tag);
  if (!match) {
    return undefined;
  }

  const year = Number(match[1]);
  const month = Number(match[2]);
  const day = Number(match[3]);
  const hhmmss = match[4] ?? '';

  if (!Number.isFinite(year) || !Number.isFinite(month) || !Number.isFinite(day) || hhmmss.length !== 6) {
    return undefined;
  }

  const hour = Number(hhmmss.slice(0, 2));
  const minute = Number(hhmmss.slice(2, 4));
  const second = Number(hhmmss.slice(4, 6));
  if (!Number.isFinite(hour) || !Number.isFinite(minute) || !Number.isFinite(second)) {
    return undefined;
  }
  if (month < 1 || month > 12 || day < 1 || day > 31 || hour < 0 || hour > 23 || minute < 0 || minute > 59 || second < 0 || second > 59) {
    return undefined;
  }

  const timestampMs = Date.UTC(year, month - 1, day, hour, minute, second);
  if (!Number.isFinite(timestampMs)) {
    return undefined;
  }

  const utc = new Date(timestampMs);
  if (
    utc.getUTCFullYear() !== year
    || utc.getUTCMonth() !== month - 1
    || utc.getUTCDate() !== day
    || utc.getUTCHours() !== hour
    || utc.getUTCMinutes() !== minute
    || utc.getUTCSeconds() !== second
  ) {
    return undefined;
  }

  return timestampMs;
}

function parseRollingArtifactFile(fileName: string): Phase0RollingArtifactFile | undefined {
  for (const entry of FAMILY_PATTERNS) {
    const match = entry.pattern.exec(fileName);
    if (!match) {
      continue;
    }
    const tag = match[1] ?? '';
    const timestampMs = parseRollingTagTimestampMs(tag);
    if (typeof timestampMs !== 'number') {
      continue;
    }
    return {
      file_name: fileName,
      family: entry.family,
      tag,
      tag_timestamp_ms: timestampMs,
    };
  }
  return undefined;
}

function sortByTagTimeDesc(a: { tag_timestamp_ms: number; tag: string }, b: { tag_timestamp_ms: number; tag: string }): number {
  const delta = b.tag_timestamp_ms - a.tag_timestamp_ms;
  if (delta !== 0) {
    return delta;
  }
  return b.tag.localeCompare(a.tag);
}

export function collectRollingPhase0ArtifactFiles(fileNames: string[]): Phase0RollingArtifactFile[] {
  const parsed: Phase0RollingArtifactFile[] = [];
  for (const fileName of fileNames) {
    const row = parseRollingArtifactFile(fileName);
    if (row) {
      parsed.push(row);
    }
  }
  return parsed;
}

export function planRollingPhase0ArtifactRetention(
  fileNames: string[],
  keepPerFamily: number,
): Phase0RollingArtifactRetentionPlan {
  if (!Number.isFinite(keepPerFamily)) {
    throw new Error('keepPerFamily must be a finite integer greater than or equal to 0.');
  }
  if (!Number.isInteger(keepPerFamily)) {
    throw new Error('keepPerFamily must be an integer greater than or equal to 0.');
  }
  if (keepPerFamily < 0) {
    throw new Error('keepPerFamily must be greater than or equal to 0.');
  }

  const keepLimit = keepPerFamily;
  const parsed = collectRollingPhase0ArtifactFiles(fileNames);

  const keep: Phase0RollingArtifactFile[] = [];
  const remove: Phase0RollingArtifactFile[] = [];
  const familyRows: Phase0RollingArtifactRetentionPlan['families'] = [];

  for (const familyPattern of FAMILY_PATTERNS) {
    const family = familyPattern.family;
    const familyFiles = parsed.filter((row) => row.family === family);
    const byTag = new Map<string, { tag_timestamp_ms: number; files: Phase0RollingArtifactFile[] }>();

    for (const row of familyFiles) {
      const existing = byTag.get(row.tag);
      if (existing) {
        existing.files.push(row);
        existing.tag_timestamp_ms = Math.max(existing.tag_timestamp_ms, row.tag_timestamp_ms);
      } else {
        byTag.set(row.tag, {
          tag_timestamp_ms: row.tag_timestamp_ms,
          files: [row],
        });
      }
    }

    const sortedTags = [...byTag.entries()]
      .map(([tag, row]) => ({ tag, tag_timestamp_ms: row.tag_timestamp_ms, files: row.files }))
      .sort(sortByTagTimeDesc);

    const keepTags = new Set(sortedTags.slice(0, keepLimit).map((row) => row.tag));

    for (const row of familyFiles) {
      if (keepTags.has(row.tag)) {
        keep.push(row);
      } else {
        remove.push(row);
      }
    }

    familyRows.push({
      family,
      total_tags: sortedTags.length,
      keep_tags: Math.min(sortedTags.length, keepLimit),
      remove_tags: Math.max(0, sortedTags.length - keepLimit),
    });
  }

  const sortFilesAsc = (a: Phase0RollingArtifactFile, b: Phase0RollingArtifactFile): number => {
    const familyDelta = a.family.localeCompare(b.family);
    if (familyDelta !== 0) {
      return familyDelta;
    }
    const tagDelta = sortByTagTimeDesc(a, b);
    if (tagDelta !== 0) {
      return tagDelta;
    }
    return a.file_name.localeCompare(b.file_name);
  };

  return {
    keep: [...keep].sort(sortFilesAsc),
    remove: [...remove].sort(sortFilesAsc),
    families: familyRows,
  };
}