/**
 * Session scan — parity with `get-shit-done/bin/lib/profile-pipeline.cjs` `cmdScanSessions`.
 * Used by `scanSessions` query handler so SDK JSON matches `gsd-tools.cjs scan-sessions --json`.
 */
import { existsSync, readdirSync, readFileSync, statSync } from 'node:fs';
import { basename, join } from 'node:path';
import { homedir } from 'node:os';

/** One project entry in the JSON array emitted by `scan-sessions --json`. */
export type ScanSessionsProject = {
  name: string;
  directory: string;
  sessionCount: number;
  totalSize: number;
  totalSizeHuman: string;
  lastActive: string;
  dateRange: { first: string; last: string };
  sessions?: Array<{
    sessionId: string;
    size: number;
    sizeHuman: string;
    /** Full ISO-8601, same as CJS `scan-sessions --json --verbose`. */
    modified: string;
    summary?: string;
    messageCount?: number;
    created?: string;
  }>;
};

function formatBytes(bytes: number): string {
  if (bytes < 1024) return `${bytes} B`;
  if (bytes < 1048576) return `${(bytes / 1024).toFixed(1)} KB`;
  if (bytes < 1073741824) return `${(bytes / 1048576).toFixed(1)} MB`;
  return `${(bytes / 1073741824).toFixed(1)} GB`;
}

/** Same as CJS `scanProjectDir` in profile-pipeline.cjs (sessions sorted newest-first). */
export function scanProjectDir(projectDirPath: string): Array<{
  sessionId: string;
  filePath: string;
  size: number;
  modified: Date;
}> {
  const entries = readdirSync(projectDirPath);
  const sessions: Array<{ sessionId: string; filePath: string; size: number; modified: Date }> = [];

  for (const entry of entries) {
    if (!entry.endsWith('.jsonl')) continue;
    const sessionId = entry.replace('.jsonl', '');
    const filePath = join(projectDirPath, entry);
    const stat = statSync(filePath);

    sessions.push({
      sessionId,
      filePath,
      size: stat.size,
      modified: stat.mtime,
    });
  }

  sessions.sort((a, b) => b.modified.getTime() - a.modified.getTime());
  return sessions;
}

export function readSessionIndex(projectDirPath: string): {
  originalPath: string | null;
  entries: Map<string, { sessionId?: string; summary?: string; messageCount?: number; created?: string }>;
} {
  try {
    const indexPath = join(projectDirPath, 'sessions-index.json');
    const raw = readFileSync(indexPath, 'utf-8');
    const parsed = JSON.parse(raw) as { entries?: unknown[]; originalPath?: string | null };
    const entries = new Map<string, { sessionId?: string; summary?: string; messageCount?: number; created?: string }>();
    for (const entry of parsed.entries || []) {
      const e = entry as { sessionId?: string; summary?: string; messageCount?: number; created?: string };
      if (e.sessionId) {
        entries.set(e.sessionId, e);
      }
    }
    return { originalPath: parsed.originalPath ?? null, entries };
  } catch {
    return { originalPath: null, entries: new Map() };
  }
}

export function getProjectName(projectDirName: string, indexData: ReturnType<typeof readSessionIndex>): string {
  if (indexData.originalPath) {
    return basename(indexData.originalPath);
  }
  return projectDirName;
}

/** Same resolution as CJS `getSessionsDir` in profile-pipeline.cjs. */
export function getScanSessionsRoot(overridePath: string | null): string | null {
  const dir = overridePath || join(homedir(), '.claude', 'projects');
  if (!existsSync(dir)) return null;
  return dir;
}

/**
 * Build the same project array as CJS `cmdScanSessions` (stdout JSON when `--json`).
 */
export function buildScanSessionsProjects(
  overridePath: string | null,
  options: { verbose: boolean },
): ScanSessionsProject[] {
  const sessionsDir = getScanSessionsRoot(overridePath);
  if (!sessionsDir) {
    return [];
  }

  let projectDirs: string[];
  try {
    projectDirs = readdirSync(sessionsDir).filter((entry) => {
      const fullPath = join(sessionsDir, entry);
      try {
        return statSync(fullPath).isDirectory();
      } catch {
        return false;
      }
    });
  } catch {
    return [];
  }

  const projects: ScanSessionsProject[] = [];

  for (const dirName of projectDirs) {
    const projectPath = join(sessionsDir, dirName);
    const sessions = scanProjectDir(projectPath);
    if (sessions.length === 0) continue;

    const indexData = readSessionIndex(projectPath);
    const projectName = getProjectName(dirName, indexData);

    const totalSize = sessions.reduce((sum, s) => sum + s.size, 0);
    const lastActive = sessions[0].modified.toISOString();
    const oldest = sessions[sessions.length - 1].modified.toISOString();
    const newest = sessions[0].modified.toISOString();

    const project: ScanSessionsProject = {
      name: projectName,
      directory: dirName,
      sessionCount: sessions.length,
      totalSize,
      totalSizeHuman: formatBytes(totalSize),
      lastActive: lastActive.replace('T', ' ').substring(0, 19),
      dateRange: { first: oldest, last: newest },
    };

    if (options.verbose) {
      project.sessions = sessions.map((s) => {
        const indexed = indexData.entries.get(s.sessionId);
        const session: NonNullable<ScanSessionsProject['sessions']>[number] = {
          sessionId: s.sessionId,
          size: s.size,
          sizeHuman: formatBytes(s.size),
          modified: s.modified.toISOString(),
        };
        if (indexed) {
          if (indexed.summary) session.summary = indexed.summary;
          if (indexed.messageCount !== undefined) session.messageCount = indexed.messageCount;
          if (indexed.created) session.created = indexed.created;
        }
        return session;
      });
    }

    projects.push(project);
  }

  projects.sort((a, b) => b.dateRange.last.localeCompare(a.dateRange.last));
  return projects;
}