/**
 * @fileoverview Reads a claude session's edit history on request: the new bytes of its
 * transcripts (main + subagents) go into its `EditHistoryStore`, and the Bash image
 * candidates that came with them are confirmed against the files on disk.
 *
 * WHEN. Only when the panel asks (`GET …/edits?sync=1` on open and while it follows the
 * session, `POST …/edits/older`): no timer, no hook, no background read for sessions nobody
 * looks at. One sync per session runs at a time; requests during a run are folded into one
 * more forward read and/or one more older read afterwards.
 *
 * HOW MUCH. A forward read shares one budget over all files, main first. A file whose chunk
 * the shared budget cut short is not applied (the store would take a chunk with no line end
 * for a line longer than the budget) but read in the next pass; up to
 * {@link MAX_FORWARD_PASSES} passes per sync, the rest with the next one.
 *
 * NEW CONVERSATION. When the transcript path names another conversation (`/clear`, resume),
 * the previous transcript (same directory) is first read to its end, so edits it got after
 * the last read are not lost with its cursors; then the new one is read from its end.
 * "Load older" reaches back within the current conversation only.
 *
 * MEMORY. At most {@link MAX_LOADED_STORES} stores stay loaded; past that the least recently
 * used one without a run is written (if it changed) and dropped, and loaded again on demand.
 *
 * GONE. `remove()` (the session's record is deleted) marks the session gone, deletes the file
 * and then drops the session's slot: a run in flight stops after its current read and its
 * store no longer writes; a request during the removal reads nothing (`unavailable`, reason
 * `removed`). A session that comes back with the same id (reboot restore) starts afresh.
 * `sweep()` deletes, at startup, the stored history of sessions that no longer exist. A
 * subagent transcript that vanished loses its cursor (`dropSource`), not its entries.
 *
 * OLDER. "Load older" reads a full budget block of up to {@link MAX_OLDER_SOURCES} sources
 * with older lines per click; with more sources they take turns.
 *
 * WHICH SESSIONS. Claude sessions, local and remote. Docker and non-claude sessions answer
 * `unsupported` and are never read. The deps get the session and read a remote one over ssh
 * (`remote-files.ts`): one round trip to find its transcript, one per read (more for a
 * conversation with hundreds of subagents). A remote read never wakes its host; a sleeping one
 * is a connect timeout (`unavailable`, stored entries kept).
 *
 * IMAGES. A Bash candidate counts only when the file's mtime lies in the call's window
 * (start − 2 s … end + 2 s), so `ls *.png` lists nothing. Transcript times and mtimes come
 * from the same host, so a remote host's clock skew to this server does not matter.
 *
 * Tests: `test/edit-history-sync.test.ts`.
 *
 * @module web/edit-history-sync
 */

import { basename, dirname, join } from 'node:path';
import type { SessionRemote } from '../types/session.js';
import type { EditSourceReadOptions, EditSourceRequest, EditSources, PathProbe } from '../edit-history-local-source.js';
import type { ImageCandidate } from '../edit-history-parse.js';
import { EditHistoryStore, READ_BUDGET_BYTES, type ConfirmedImage } from '../edit-history-store.js';
import { getCli } from '../config/cli-registry/registry.js';

/** Slack around a Bash call's window for the image mtime check. */
export const IMAGE_MTIME_SLACK_MS = 2000;
/** Forward passes per sync when files grew by more than one budget. */
export const MAX_FORWARD_PASSES = 3;
/** Sources read back per "Load older" click, a full budget each. */
export const MAX_OLDER_SOURCES = 3;
/** Stores kept in memory; the least recently used one past this is dropped. */
export const MAX_LOADED_STORES = 3;
/** `reason` when the session has no transcript yet (no prompt yet, or not found). */
export const NO_TRANSCRIPT = 'no-transcript';
/** `reason` once the session's history was deleted. */
export const REMOVED = 'removed';

export type EditHistoryState = 'ok' | 'unavailable' | 'unsupported';

export interface EditHistoryStatus {
  state: EditHistoryState;
  reason?: string;
}

/** The slice of a session this needs. */
export interface EditHistorySession {
  id: string;
  mode: string;
  remote: SessionRemote | undefined;
  docker?: unknown;
  /** Set on a wrapper around a foreign tmux session: Codeman holds no transcript id for what runs there. */
  adopt?: unknown;
  claudeSessionId: string | null;
  /** The session's own `CLAUDE_CONFIG_DIR` (Codeman env override), if it has one. */
  claudeConfigDir?: string;
}

export interface EditHistorySyncDeps {
  /**
   * The session's main transcript path, or null when it has none yet. `storedTranscriptId` is
   * the conversation the stored history holds (null before the first read); see
   * {@link remoteTranscriptIds}.
   */
  transcriptPath(session: EditHistorySession, storedTranscriptId: string | null): Promise<string | null>;
  /** The session's transcripts (a remote session's on its host). */
  readSources(
    session: EditHistorySession,
    mainPath: string,
    requests: readonly EditSourceRequest[],
    budget: number,
    opts?: EditSourceReadOptions
  ): Promise<EditSources | null>;
  /** Bash image candidates of the session, on the host it runs on. */
  probe(session: EditHistorySession, paths: readonly string[]): Promise<Array<PathProbe | null>>;
  loadStore(sessionId: string): Promise<EditHistoryStore>;
  /** Delete a session's stored history without loading it. */
  deleteStore(sessionId: string): Promise<void>;
  /** Delete the stored history of every session `keep` rejects; returns how many. */
  sweepStores(keep: (sessionId: string) => boolean): Promise<number>;
  budget?: number;
}

export interface SyncOptions {
  older?: boolean;
}

/**
 * The conversation ids a REMOTE session's transcript lookup considers when its claude writes
 * none now; the most recently written of them wins (`buildRemoteClaudeTranscriptLocateCommand`).
 * The stored history's conversation must be among them: no hook tells Codeman of a remote
 * `/clear`, so `claudeSessionId` stays the launch id, and without the stored one the panel
 * would flip back to the cleared conversation as soon as the remote claude exits.
 */
export function remoteTranscriptIds(session: EditHistorySession, storedTranscriptId: string | null): string[] {
  return [...new Set([storedTranscriptId, session.claudeSessionId || session.id, session.id])].filter(
    (id): id is string => !!id
  );
}

/** Why a session has no edit history, or undefined when it can have one. */
export function unsupportedReason(session: EditHistorySession): string | undefined {
  if (session.docker) return 'docker';
  if (session.adopt) return 'adopted';
  if (getCli(session.mode)?.capabilities.transcript !== 'claude-jsonl') return 'mode';
  return undefined;
}

/** One turn of the event loop, between synchronous parses of up to one budget each. */
function breathe(): Promise<void> {
  return new Promise((resolve) => setImmediate(resolve));
}

/**
 * Bash candidates whose probed file is a regular file with an mtime inside the call's window
 * (files claude sent to the user skip the window: they exist and were shown on purpose).
 * A candidate whose file version is already recorded is skipped: `known(path)` is the newest
 * entry time for that path, and an entry at or after `mtime − slack` saw this version: the
 * `ls *.png` right after the render, or a Write followed by a listing. Candidates are taken
 * in call order so a batch dedupes itself the same way.
 */
export function confirmImages(
  candidates: readonly ImageCandidate[],
  probe: (path: string) => PathProbe | null | undefined,
  known: (path: string) => number | undefined = () => undefined
): ConfirmedImage[] {
  const out: ConfirmedImage[] = [];
  const seen = new Map<string, number>();
  for (const c of [...candidates].sort((a, b) => a.end - b.end)) {
    for (const path of c.paths) {
      const p = probe(path);
      if (!p || p.kind !== 'file' || !p.mtimeMs) continue;
      const inWindow = p.mtimeMs >= c.start - IMAGE_MTIME_SLACK_MS && p.mtimeMs <= c.end + IMAGE_MTIME_SLACK_MS;
      if (!c.sent && !inWindow) continue;
      const entryPath = path.startsWith('~/') ? p.realPath : path;
      const last = Math.max(seen.get(entryPath) ?? -Infinity, known(entryPath) ?? -Infinity);
      if (last >= p.mtimeMs - IMAGE_MTIME_SLACK_MS) continue;
      seen.set(entryPath, c.end);
      const img: ConfirmedImage = {
        toolUseId: c.toolUseId,
        path: entryPath,
        ts: c.end,
        tool: c.sent ? 'sent' : 'bash',
      };
      if (c.agentId) img.agentId = c.agentId;
      out.push(img);
    }
  }
  return out;
}

interface SyncWant {
  forward: boolean;
  older: boolean;
}

interface SessionSlot {
  store?: Promise<EditHistoryStore>;
  status: EditHistoryStatus;
  running?: Promise<void>;
  again?: SyncWant;
  /** The history was deleted: nothing reads for this session any more. */
  gone?: boolean;
  /** The last source the previous "Load older" read; the next one starts after it. */
  olderAfter?: string;
}

export class EditHistorySync {
  /** By session, least recently used first. */
  private readonly slots = new Map<string, SessionSlot>();
  /** Writes of dropped stores; loading that session again waits for its write. */
  private readonly unloading = new Map<string, Promise<void>>();
  private readonly budget: number;

  constructor(private readonly deps: EditHistorySyncDeps) {
    this.budget = deps.budget ?? READ_BUDGET_BYTES;
  }

  /** The session's store, loaded from disk on first use (one load for concurrent callers). */
  getStore(sessionId: string): Promise<EditHistoryStore> {
    return this.storeOf(sessionId, this.slot(sessionId));
  }

  getStatus(sessionId: string): EditHistoryStatus {
    return { ...this.slot(sessionId).status };
  }

  /**
   * Read what is new (or, with `older`, the next older block). Resolves when this
   * request's run is done; never rejects. A call during a run queues one more run.
   */
  async sync(session: EditHistorySession, opts: SyncOptions = {}): Promise<EditHistoryStatus> {
    const why = unsupportedReason(session);
    const slot = this.slot(session.id);
    if (slot.gone) return { ...slot.status };
    if (why) {
      slot.status = { state: 'unsupported', reason: why };
      return { ...slot.status };
    }
    const want: SyncWant = { forward: !opts.older, older: !!opts.older };
    if (slot.running) {
      slot.again = {
        forward: (slot.again?.forward ?? false) || want.forward,
        older: (slot.again?.older ?? false) || want.older,
      };
      await slot.running;
      // The queued run starts when the current one ends; wait for it too.
      if (slot.running) await slot.running;
      return { ...slot.status };
    }
    slot.running = this.runLoop(session, slot, want);
    try {
      await slot.running;
    } finally {
      slot.running = undefined;
      this.unloadIdle(slot);
    }
    return { ...slot.status };
  }

  /** Write every loaded store's pending changes (server shutdown). */
  async flushAll(): Promise<void> {
    await Promise.all([
      ...[...this.slots.values()].map(async (slot) => (await slot.store?.catch(() => undefined))?.settle()),
      ...this.unloading.values(),
    ]);
  }

  /**
   * Delete a session's stored history (its record is gone). While it runs the session is
   * marked, so a run in flight or a request meanwhile cannot load and write a new store for
   * it; then its slot goes, and a session that comes back with this id starts afresh.
   */
  async remove(sessionId: string): Promise<void> {
    const slot = this.slot(sessionId);
    slot.gone = true;
    slot.again = undefined;
    slot.status = { state: 'unavailable', reason: REMOVED };
    try {
      const store = await slot.store?.catch(() => undefined);
      if (store) {
        await store.remove();
      } else {
        await this.unloading.get(sessionId);
        await this.deps.deleteStore(sessionId);
      }
      await slot.running;
    } finally {
      if (this.slots.get(sessionId) === slot) this.slots.delete(sessionId);
    }
  }

  /**
   * Delete the stored history of sessions that no longer exist (startup: left behind by a
   * crash during deletion, or by an older build). A session in use here is kept.
   */
  sweep(exists: (sessionId: string) => boolean): Promise<number> {
    return this.deps.sweepStores((id) => this.slots.has(id) || exists(id));
  }

  /** The session's slot, now the most recently used. */
  private slot(sessionId: string): SessionSlot {
    const slot = this.slots.get(sessionId) ?? { status: { state: 'ok' } };
    this.slots.delete(sessionId);
    this.slots.set(sessionId, slot);
    return slot;
  }

  private storeOf(sessionId: string, slot: SessionSlot): Promise<EditHistoryStore> {
    if (!slot.store) {
      const loading = (async () => {
        await this.unloading.get(sessionId);
        return this.deps.loadStore(sessionId);
      })();
      slot.store = loading;
      loading.catch(() => {
        if (slot.store === loading) slot.store = undefined;
      });
      this.unloadIdle(slot);
    }
    return slot.store;
  }

  /**
   * Past {@link MAX_LOADED_STORES}, drop the least recently used stores no run uses: each is
   * written if it changed, and a later request loads it again (after that write).
   */
  private unloadIdle(keep?: SessionSlot): void {
    let loaded = 0;
    for (const slot of this.slots.values()) if (slot.store) loaded++;
    for (const [sessionId, slot] of this.slots) {
      if (loaded <= MAX_LOADED_STORES) break;
      if (!slot.store || slot.running || slot.gone || slot === keep) continue;
      this.slots.delete(sessionId);
      loaded--;
      const writing: Promise<void> = slot.store
        .then((store) => store.settle())
        .catch((err) => {
          console.warn(`[EditHistory] Saving the history of ${sessionId} failed:`, err);
        })
        .finally(() => {
          if (this.unloading.get(sessionId) === writing) this.unloading.delete(sessionId);
        });
      this.unloading.set(sessionId, writing);
    }
  }

  private async runLoop(session: EditHistorySession, slot: SessionSlot, want: SyncWant): Promise<void> {
    let next: SyncWant | undefined = want;
    while (next && !slot.gone) {
      if (next.forward) await this.runOnce(session, slot, false);
      if (next.older && !slot.gone) await this.runOnce(session, slot, true);
      next = slot.again;
      slot.again = undefined;
    }
  }

  private async runOnce(session: EditHistorySession, slot: SessionSlot, older: boolean): Promise<void> {
    let status: EditHistoryStatus;
    try {
      // This slot's store: a run still in flight after `remove()` cannot reach a later one.
      const store = await this.storeOf(session.id, slot);
      const path = slot.gone ? null : await this.deps.transcriptPath(session, store.getTranscriptId());
      let found: boolean;
      if (!path) {
        found = false;
      } else if (older) {
        found = await this.readOlder(session, path, store, slot);
      } else {
        found = true;
        for (let pass = 0; pass < MAX_FORWARD_PASSES && found && !slot.gone; pass++) {
          const r = await this.readForward(session, path, store);
          found = r.found;
          if (!r.more) break;
        }
      }
      status = found ? { state: 'ok' } : { state: 'unavailable', reason: NO_TRANSCRIPT };
    } catch (err) {
      status = { state: 'unavailable', reason: err instanceof Error ? err.message : String(err) };
    }
    if (!slot.gone) slot.status = status;
  }

  private forwardRequests(store: EditHistoryStore): EditSourceRequest[] {
    const out: EditSourceRequest[] = [];
    for (const relPath of store.knownSources()) {
      const c = store.getCursor(relPath);
      if (c) out.push({ relPath, offset: c.offset });
    }
    return out;
  }

  /**
   * One forward read of all sources. `more` = some file has unread bytes after it, or was cut
   * short by the shared budget and left for the next pass. A transcript other than the stored
   * one (`/clear`, resume) is read like a first read, once the stored one is read to its end.
   */
  private async readForward(
    session: EditHistorySession,
    path: string,
    store: EditHistoryStore
  ): Promise<{ found: boolean; more: boolean }> {
    const own = this.storedTranscript(path, store);
    if (own !== path && store.knownSources().length > 0) {
      const previous = await this.readFrom(session, own, store, this.forwardRequests(store));
      if (previous.more) return { found: true, more: true };
    }
    return this.readFrom(session, path, store, own === path ? this.forwardRequests(store) : []);
  }

  /**
   * The path of the conversation the store holds cursors for: `path` itself, or the previous
   * conversation's transcript next to it (`/clear` and resume keep the project directory).
   */
  private storedTranscript(path: string, store: EditHistoryStore): string {
    const known = store.getTranscriptId();
    return known === null || basename(path) === `${known}.jsonl` ? path : join(dirname(path), `${known}.jsonl`);
  }

  private async readFrom(
    session: EditHistorySession,
    path: string,
    store: EditHistoryStore,
    requests: EditSourceRequest[]
  ): Promise<{ found: boolean; more: boolean }> {
    const res = await this.deps.readSources(session, path, requests, this.budget);
    if (!res) return { found: false, more: false };
    this.dropMissing(store, requests, res);
    for (const [agentId, text] of Object.entries(res.metas)) {
      if (!store.hasAgentMeta(agentId)) store.setAgentMeta(agentId, text);
    }
    const requested = new Set(requests.map((r) => r.relPath));
    let more = false;
    const candidates: ImageCandidate[] = [];
    let parsed = false;
    for (const f of res.files) {
      // Each file is up to one budget (8 MiB) of synchronous parsing: yield between them.
      if (parsed) await breathe();
      if (store.isRemoved()) break;
      // A requested file reads on from its cursor, a new one its tail.
      const available = requested.has(f.relPath) ? f.size - f.startOffset : f.size;
      if (f.chunk.length < Math.min(this.budget, available)) {
        more = true;
        continue;
      }
      parsed = true;
      const r = store.apply({
        transcriptId: res.transcriptId,
        source: f.relPath,
        startOffset: f.startOffset,
        chunk: f.chunk,
        size: f.size,
      });
      candidates.push(...r.candidates);
      if (f.startOffset + f.chunk.length < f.size) more = true;
    }
    await this.addImages(session, store, candidates);
    return { found: true, more };
  }

  private async readOlder(
    session: EditHistorySession,
    path: string,
    store: EditHistoryStore,
    slot: SessionSlot
  ): Promise<boolean> {
    if (!store.backfillTruncated) return true;
    // Older lines belong to the stored conversation, even before a forward read moved on.
    path = this.storedTranscript(path, store);
    const sources = store.sourcesWithOlder().sort();
    if (sources.length === 0) return true;
    // Take turns: start after the last source the previous click read.
    const after = slot.olderAfter;
    const first =
      after === undefined
        ? 0
        : Math.max(
            0,
            sources.findIndex((s) => s > after)
          );
    const picked = [...sources.slice(first), ...sources.slice(0, first)].slice(0, MAX_OLDER_SOURCES);
    const requests: EditSourceRequest[] = [];
    for (const relPath of picked) {
      const range = store.olderRange(relPath, this.budget);
      if (range) requests.push({ relPath, offset: range.offset, len: range.len });
    }
    if (requests.length === 0) return true;
    slot.olderAfter = picked[picked.length - 1];
    const res = await this.deps.readSources(session, path, requests, this.budget * requests.length, {
      onlyRequested: true,
    });
    if (!res) return false;
    if (res.transcriptId !== store.getTranscriptId()) return true;
    this.dropMissing(store, requests, res);
    const wanted = new Set(requests.map((r) => r.relPath));
    const candidates: ImageCandidate[] = [];
    let parsed = false;
    for (const f of res.files) {
      if (!wanted.has(f.relPath)) continue;
      // Each file is up to one budget (8 MiB) of synchronous parsing: yield between them.
      if (parsed) await breathe();
      parsed = true;
      if (slot.gone) return true;
      const r = store.applyOlder({
        transcriptId: res.transcriptId,
        source: f.relPath,
        startOffset: f.startOffset,
        chunk: f.chunk,
        size: f.size,
      });
      candidates.push(...r.candidates);
    }
    await this.addImages(session, store, candidates);
    return true;
  }

  /** Requested files the reader no longer lists are gone: their cursors go too. */
  private dropMissing(store: EditHistoryStore, requests: readonly EditSourceRequest[], res: EditSources): void {
    const listed = new Set(res.files.map((f) => f.relPath));
    for (const r of requests) if (!listed.has(r.relPath)) store.dropSource(r.relPath);
  }

  private async addImages(
    session: EditHistorySession,
    store: EditHistoryStore,
    candidates: readonly ImageCandidate[]
  ): Promise<void> {
    const paths = [...new Set(candidates.flatMap((c) => c.paths))];
    // A removed store keeps nothing: do not probe agent-printed paths for it.
    if (paths.length === 0 || store.isRemoved()) return;
    let probes: Array<PathProbe | null>;
    try {
      probes = await this.deps.probe(session, paths);
    } catch {
      // The edits of this read are in; only its images are lost. The read itself succeeded.
      return;
    }
    const byPath = new Map(paths.map((p, i) => [p, probes[i]]));
    const newest = new Map<string, number>();
    for (const e of store.list()) newest.set(e.path, Math.max(newest.get(e.path) ?? -Infinity, e.ts));
    store.addImageEntries(
      confirmImages(
        candidates,
        (p) => byPath.get(p),
        (p) => newest.get(p)
      )
    );
  }
}