// Sessions remain resident after creation so their open Remote sources keep running off-screen.

import type { Context } from '@deepseek-ai/cordis'
import { randomUUID } from '@deepseek-ai/dsh-util-crypto'
import type { AttachmentIdType, ImageAttachmentRef } from '@deepseek-ai/dsh-attachment'
import type {
  IApiClient, SubagentAddress,
} from '@deepseek-ai/dsh-client-connection/client'
import type { MessageId } from '@deepseek-ai/dsh-llm/brand'
import type { SessionId } from '@deepseek-ai/dsh-session/types'
import {
  SessionEventStream,
  sessionStreamFailure,
} from '../transport.ts'
import type { SessionJournalChange } from '../transport.ts'
import type {
  PromptContentPart,
  QueueAction,
  SessionAddress,
  SessionControlFrame,
  SessionQueuedItem,
  SessionRequestId,
  SessionError,
} from '../../types.ts'
import type { ClientFailure, ClientResult } from '../contract/result.ts'
import { transportResult } from '../contract/result.ts'
import type { SessionFace } from '../contract/session.ts'
import type {
  OpenState, PromptError, SessionSnapshot,
} from '../contract/snapshot.ts'
import { MutableSessionEventSource } from '../contract/events.ts'
import type {
  SessionEventLikeEntry, SessionLiveEventEntry,
} from '../contract/events.ts'
import { Notifier } from './notifier.ts'
import type { RemoteResult } from '@deepseek-ai/dsh-typert-protocol'
import type { SessionRemotes } from './remotes.ts'
import { ProjectionValueStore } from './projection-store.ts'
import type { ProjectionsBaseline } from './projection-store.ts'
import { resolvedClientTimeZone } from '../time-zone.ts'
import { SessionQueueMirror } from './queue-mirror.ts'

/** Messages requested per history page. */
export const PAGE_MESSAGES = 50

/** Manager-owned observers of a Session object's local state edges. */
export interface SessionOptions {
  /** Catalog-discovered address selecting non-activating subagent transport. */
  address?: SubagentAddress
  /** Whether the exact direct parent Agent was live at the latest catalog read; absent before that read. */
  parentAvailable?: boolean
  /**
   * First ACCEPTED prompt on a blank session (fires at most once, on the
   * prompt RPC's success response): the manager mirrors the blank→false flip
   * into its list row so the session surfaces without waiting for a host
   * frame. Acceptance is the flip point because it proves the user message
   * is in the host log; a rejected first prompt keeps the session blank
   * (hidden, still reusable by connectWorkspace).
   */
  onEngaged?(session: Session): void
  /**
   * Manager-owned projection value store to adopt (frames route through the
   * manager and values outlive instantiation); omitted, the Session owns a
   * private store (bare object-layer construction).
   */
  projections?: ProjectionValueStore
}

/**
 * Owns a session's event window, lifecycle state, and observable
 * snapshot. React bindings remain outside this data layer. Features see only
 * the {@link SessionFace} slice (ISession verbs + the snapshot source); the
 * remaining public members are Session Controller internals.
 */
export class Session implements SessionFace {
  // ---- Window and derived state (all private; the snapshot is the only read API) ----
  private baseSeq = 0
  private hasMore = false
  private openState: OpenState = 'cold'
  private openError: ClientFailure | null = null
  private openPromise: Promise<void> | null = null
  /** Bumped by stream replacement to invalidate an in-flight doOpen. Stale
   *  passes drop all writes once the generation moves on. */
  private openGeneration = 0
  private loadingOlder = false
  /** Authoritative stream-only inbox snapshot; pending work never hits history. */
  private readonly queueMirror = new SessionQueueMirror()
  private running = false
  private address: SubagentAddress | undefined
  private parentAvailable: boolean | undefined
  /**
   * Sticky send marker, private input of the composerPhase derivation: set
   * synchronously before prompt()'s first await, never reset — the blank →
   * engaging edge of the phase machine (see ComposerPhase).
   */
  private promptAttempted = false
  /** A first accepted prompt stays in the engaging phase until its turn is observable. */
  private firstPromptPendingTurn = false
  /** Empty-log mirror (see ConversationSnapshot.blank); unknown bare sessions begin conservatively blank. */
  private blankBit = true
  private removed = false
  private promptError: PromptError | null = null
  private lastAgentError: string | null = null
  /** Owns the addressed page/follow lifecycle while this Session is open. */
  private events: SessionEventStream | undefined

  /**
   * Per-session projection value store (push model; see the session-projection
   * subsystem page, docs/subsystems/session-projection.md): finished whole
   * values computed on the Host, seeded by the tail page's
   * projections block and updated by Session Controller control frames under the
   * one higher-seq-wins rule. Keys are read via `projections.faceOf(key)`
   * (the useProjection resolution face); the conversation snapshot never
   * carries projection values, and no client-side domain folding exists.
   * Manager-owned when constructed through SessionManager (frames route and
   * the store outlives instantiation, the title-snapshot precedent); a bare
   * construction gets a private store.
   */
  readonly projections: ProjectionValueStore

  /** Contiguous history and live tail consumed by Conversation assembly. */
  readonly eventSource = new MutableSessionEventSource()
  private snapshotCache: SessionSnapshot
  private readonly notifier: Notifier
  /**
   * Agent-scoped cordis context, bound once by ClientSessions when it
   * mints the scope (the client mirror of the host Agent's loopCtx). The
   * Session dispatches its own scoped events through it; undefined means
   * unbound (bare object-layer construction) or already pruned — both skip
   * dispatch-dependent behavior rather than fail.
   */
  private actx: Context | undefined

  /**
   * @param sessionId - Host session identity (client sessions are always Host-born).
   * @param api - shared wire client.
   * @param remote - generated Remote namespaces this session calls.
   * @param options - optional manager-owned state observers.
   */
  constructor(
    readonly sessionId: SessionId,
    private readonly api: IApiClient,
    private readonly remote: SessionRemotes,
    private readonly options: SessionOptions = {},
  ) {
    this.projections = options.projections ?? new ProjectionValueStore()
    this.address = options.address
    this.parentAvailable = options.parentAvailable
    this.notifier = new Notifier(() => {
      this.snapshotCache = this.buildSnapshot()
    })
    this.snapshotCache = this.buildSnapshot()
  }

  /**
   * Bind the Agent-scoped context minted by ClientSessions (single write;
   * a second bind is a wiring error and throws). Direction stays one-way at
   * this binding boundary: consumers still reach the Session via `sessions.sessionOf`,
   * while the Session holds its own dispatch point (host Agent.loopCtx
   * mirror).
   * @param actx - the agent's scoped context.
   */
  bindScope(actx: Context): void {
    if (this.actx !== undefined) throw new Error(`session ${this.sessionId} already has a bound scope`)
    this.actx = actx
  }

  /** Release the bound scope at prune time (a later rebind accompanies a freshly minted scope). */
  unbindScope(): void {
    this.actx = undefined
  }

  // ---- Operations ----

  /**
   * Send (queue/steer passed through 1:1); failures land in the snapshot's promptError.
   * @param content - text plus browser-owned temporary image uploads.
   * @param mode - queue appends after the current turn; steer interrupts it.
   * @returns the prompt result (also mirrored into promptError on failure).
   */
  async prompt(
    content: PromptContentPart[],
    mode: 'queue' | 'steer',
    signal?: AbortSignal,
  ): Promise<ClientResult<{ accepted: true }>> {
    this.promptError = null
    this.lastAgentError = null
    // Synchronous, before the first await: the blank → engaging edge must be
    // visible on the session area's very first frame when a caller sends
    // ahead of navigation (first-send flow).
    this.promptAttempted = true
    if (this.blankBit) this.firstPromptPendingTurn = true
    this.notifier.markDirty()
    let result: ClientResult<{ accepted: true }>
    try {
      if (this.address === undefined) {
        const clientTimeZone = resolvedClientTimeZone()
        result = toSessionResult(await this.remote.session.prompt({
          requestId: randomUUID() as SessionRequestId,
          sessionId: this.sessionId,
          mode,
          content,
          clientTimeZone,
        }, signal))
      } else if (this.address.mode === 'one-shot') {
        result = {
          ok: false,
          error: {
            code: 'subagent-not-resumable',
            message: 'one-shot subagent conversations are read-only',
            details: { childSessionId: this.address.childSessionId },
          },
        }
      } else {
        if (content.some(part => part.type === 'image')) {
          result = {
            ok: false,
            error: {
              code: 'attachment-error',
              message: 'Image input is unavailable for subagent continuations.',
              details: { reason: 'SUBAGENT_IMAGE_UNSUPPORTED' },
            },
          }
        } else {
          const routed = (await this.api.subagents.prompt({
            ...this.address,
            content: content.flatMap(part => part.type === 'text'
              ? [{ type: 'text' as const, text: part.text }]
              : []),
            clientTimeZone: resolvedClientTimeZone(),
          }, signal)).result
          result = routed.ok ? { ok: true, value: { accepted: true } } : routed
        }
      }
    } catch (error) {
      result = transportResult(error)
    }
    if (!result.ok) {
      this.promptError = { op: 'send', error: result.error }
      this.notifier.markDirty()
      return result
    }
    // Blank flips on ACCEPTANCE, not attempt: an accepted prompt starts the
    // conversation's first turn on the host (the host criterion — a logged
    // turn/start — is fact, not optimism; standalone command and projection
    // events never flip it), while a rejected first prompt must keep the
    // session blank — the client-side blank mirror only ever lowers, so
    // flipping early on a failure would surface the session forever and
    // strip its connectWorkspace reuse eligibility against the host's
    // authority.
    if (this.blankBit) {
      this.blankBit = false
      this.options.onEngaged?.(this)
      this.notifier.markDirty()
    }
    return result
  }

  /**
   * Resolve one image referenced by this session into browser-consumable bytes.
   * @param attachmentId - opaque id found in the folded session log.
   * @returns the authenticated reference and decoded bytes.
   */
  async readAttachment(
    attachmentId: AttachmentIdType,
  ): Promise<ClientResult<{ attachment: ImageAttachmentRef; data: Uint8Array }>> {
    try {
      const result = await this.remote.session.attachment({
        sessionId: this.sessionId,
        attachmentId,
      })
      if (!result.ok) return toSessionResult(result)
      const binary = atob(result.value.data)
      const data = Uint8Array.from(binary, char => char.charCodeAt(0))
      return { ok: true, value: { attachment: result.value.attachment, data } }
    } catch (error) {
      return transportResult(error)
    }
  }

  /** Apply one operation to a still-pending queue occurrence. */
  async updateQueue(itemId: MessageId, action: QueueAction): Promise<ClientResult<{ accepted: true }>> {
    try {
      return toSessionResult(await this.remote.session.updateQueue({ sessionId: this.sessionId, itemId, action }))
    } catch (error) {
      return transportResult(error)
    }
  }

  /**
   * Stop the active turn while the Host preserves pending inbox work; failures
   * land in promptError (same error-strip display slot). A continuable
   * subagent address routes through `subagent.interrupt`, whose durable
   * parent-address authority works without a live parent Agent; a one-shot
   * address stays uncancellable (the UI offers no stop action, so this arm is
   * defensive).
   * @returns the cancel result.
   */
  async cancel(): Promise<ClientResult<{ accepted: true }>> {
    const address = this.address
    if (address !== undefined && address.mode === 'one-shot') {
      const result: ClientResult<{ accepted: true }> = {
        ok: false,
        error: {
          code: 'subagent-delivery-unavailable',
          message: 'subagent activation cancellation is unavailable',
          details: { childSessionId: address.childSessionId },
        },
      }
      this.promptError = { op: 'stop', error: result.error }
      this.notifier.markDirty()
      return result
    }
    let result: ClientResult<{ accepted: true }>
    try {
      result = address !== undefined
        ? (await this.api.subagents.interrupt(address)).result
        : toSessionResult(await this.remote.session.cancel({ sessionId: this.sessionId }))
    } catch (error) {
      result = transportResult(error)
    }
    if (!result.ok) {
      this.promptError = { op: 'stop', error: result.error }
      this.notifier.markDirty()
    }
    return result
  }

  /**
   * Rename: contract session.rename 1:1. On success settle the 'title'
   * projection cell from the response's `{title, seq}` under the store's
   * higher-seq-wins rule (the push frame arriving later is a no-op replay),
   * so the list row and any useProjection('title') reader update without
   * waiting for the control-stream projection update.
   * @param title - raw title text (the host normalizes acceptance).
   * @returns the rename result (normalized accepted title + title event seq).
   */
  async rename(title: string): Promise<ClientResult<{ title: string; seq: number }>> {
    try {
      const result = toSessionResult(await this.remote.session.rename({ sessionId: this.sessionId, title }))
      if (result.ok) this.projections.apply('title', result.value.title, result.value.seq)
      return result
    } catch (error) {
      return transportResult(error)
    }
  }

  /**
   * Execute one slash-command line against this session's agent — pure
   * admission semantics (the host executor durably logs the lifecycle;
   * outcomes render as flow nodes, never as a response echo).
   * @param line - the full command line, leading slash included.
   * @returns the admission result, or the error branch on transport failure.
   */
  async command(line: string): Promise<RemoteResult<{ matched: boolean }>> {
    const result = await this.remote.commands.execute(this.sessionId, line, [])
    if (!result.ok) return result
    return { ok: true, value: { matched: result.value !== undefined } }
  }

  /** First open: pull the tail page (idempotent — in-flight/already-open returns the existing promise). */
  open(): Promise<void> {
    if (this.openState === 'open') return Promise.resolve()
    if (this.openPromise !== null) return this.openPromise
    const promise = this.doOpen(this.openGeneration).finally(() => {
      // Identity-guarded: a superseded open must not null out the promise resync just started.
      if (this.openPromise === promise) this.openPromise = null
    })
    this.openPromise = promise
    return promise
  }

  /** Page up: pull one earlier page with the window's first seq as beforeSeq and prepend. */
  async loadOlder(): Promise<void> {
    if (this.openState !== 'open' || !this.hasMore || this.loadingOlder) return
    const events = this.events
    if (events === undefined) return
    this.loadingOlder = true
    this.notifier.markDirty()
    try {
      await events.prepend({ beforeSeq: this.baseSeq, maxMessages: PAGE_MESSAGES })
    } catch (error) {
      if (sessionStreamFailure(error) === undefined) {
        console.error('[session-controller] loadOlder failed:', error)
      }
    } finally {
      this.loadingOlder = false
      this.notifier.markDirty()
    }
  }

  /** Rebuild an opened history source after address replacement.
   *  Invalidates any in-flight open first; queue state belongs to the independently
   *  reconnecting control stream and remains untouched. */
  async resync(): Promise<void> {
    if (this.openState === 'cold') return // never opened: no window to rebuild (doOpen flips to 'loading' synchronously, so cold implies no in-flight open)
    this.openGeneration++
    const events = this.events
    this.events = undefined
    await events?.dispose()
    this.openPromise = null
    this.openState = 'cold'
    this.openError = null
    this.baseSeq = 0
    this.notifier.markDirty()
    await this.open()
  }

  // ---- Subscription API (useSyncExternalStore direct wiring) ----

  /**
   * uSES subscription entry.
   * @param listener - change callback.
   * @returns the unsubscribe function.
   */
  subscribe(listener: () => void): () => void {
    return this.notifier.subscribe(listener)
  }

  /**
   * Cached Session snapshot (rebuilt lazily when dirty with no listeners).
   * @returns the cached reference (stable until the next flush).
   */
  getSnapshot(): SessionSnapshot {
    this.notifier.ensureFresh()
    return this.snapshotCache
  }

  // ---- Manager-only entry points (@internal; never called by the UI) ----

  /**
   * Replace every transient control value for this Session from one stream baseline.
   * @param queue - complete pending queue for this Session.
   */
  replaceControl(queue: readonly SessionQueuedItem[]): void {
    this.queueMirror.replace(queue)
    this.notifier.markDirty()
  }

  /**
   * Apply one Session-addressed live control update.
   * @param frame - queue replacement addressed to this Session.
   */
  handleControlFrame(frame: Extract<SessionControlFrame, { type: 'queue' }>): void {
    this.queueMirror.replace(frame.items)
    this.notifier.markDirty()
  }

  /**
   * Running-bit relay from the host stream (list entry and snapshot stay consistent).
   * @param running - the new running state.
   */
  handleRunning(running: boolean): void {
    // Turn-start conversion: a blank session never runs, so the first
    // running:true proves another side's first message landed.
    if (running && this.blankBit) {
      this.blankBit = false
      this.notifier.markDirty()
    }
    if (running) this.firstPromptPendingTurn = false
    if (this.running === running) return
    this.running = running
    this.notifier.markDirty()
  }

  /**
   * Install or clear the catalog-discovered transport address. A changed
   * address rebuilds an already-open window through its new history route.
   * @param address - direct parent/child address, or undefined for ordinary transport.
   * @param parentAvailable - latest exact-parent availability hint, or undefined before a catalog read.
   */
  configureSubagent(address: SubagentAddress | undefined, parentAvailable?: boolean): void {
    const same = this.address?.parentSessionId === address?.parentSessionId
      && this.address?.childSessionId === address?.childSessionId
      && this.address?.mode === address?.mode
    this.address = address
    this.parentAvailable = parentAvailable
    if (!same && this.openState !== 'cold') void this.resync()
    else this.notifier.markDirty()
  }

  /**
   * Update only the parent availability hint from a catalog refresh.
   * @param available - whether the exact direct parent is live.
   */
  handleSubagentParentAvailable(available: boolean): void {
    if (this.parentAvailable === available) return
    this.parentAvailable = available
    this.notifier.markDirty()
  }

  /**
   * Blank-bit relay from the authoritative summary source (`session.list` and
   * `api-session/added`). Monotone: once any signal (local first send,
   * running flip, an earlier summary) cleared it, a stale true never
   * re-blanks.
   * @param blank - the summary's derived empty-log bit.
   */
  handleBlank(blank: boolean): void {
    if (blank === this.blankBit) return
    if (blank && (this.promptAttempted || this.running)) return
    this.blankBit = blank
    this.notifier.markDirty()
  }

  /** `api-session/removed` relay: flag the snapshot while retaining the resident instance. */
  handleRemoved(): void {
    this.removed = true
    this.notifier.markDirty()
  }

  /**
   * `api-session/error` relay: the outlet for live failures with no turn position.
   * @param message - the stringified error.
   */
  handleAgentError(message: string): void {
    this.lastAgentError = message
    this.notifier.markDirty()
  }

  /**
   * Stop the Session's live Remote source.
   * @returns when the Remote iterator has completed teardown.
   */
  async dispose(): Promise<void> {
    this.openGeneration++
    const events = this.events
    this.events = undefined
    await events?.dispose()
  }

  // ---- Private ----

  /** @param generation - openGeneration at launch; stale passes cannot publish after replacement. */
  private async doOpen(generation: number): Promise<void> {
    this.openState = 'loading'
    this.openError = null
    this.notifier.markDirty()
    const events = new SessionEventStream(this.remote, this.sessionAddress(), {
      publish: (change) => {
        if (generation !== this.openGeneration || this.events !== events) return
        this.acceptEventChange(change)
      },
      failed: (error) => {
        this.failEventStream(events, generation, error)
      },
    })
    this.events = events
    try {
      await events.open({ maxMessages: PAGE_MESSAGES })
      if (generation !== this.openGeneration || this.events !== events) return
      this.openState = 'open'
    } catch (error) {
      if (generation !== this.openGeneration || this.events !== events) return
      this.events = undefined
      this.openState = 'error'
      this.openError = openFailure(error)
    } finally {
      if (generation === this.openGeneration) this.notifier.markDirty()
    }
  }

  /** Apply one contiguous journal update already reconciled by the Remote stream. */
  private acceptEventChange(change: SessionJournalChange): void {
    switch (change.type) {
      case 'replace':
        this.installWindow(change.entries, change.hasMore, change.page.projections)
        return
      case 'prepend':
        this.prependWindow(change.entries, change.hasMore)
        return
      case 'append':
        if (this.appendLive(change.entry)) this.notifier.markDirty()
    }
  }

  /** Replace the complete contiguous window and apply page-owned projection metadata. */
  private installWindow(entries: readonly SessionEventLikeEntry[], hasMore: boolean, projections?: ProjectionsBaseline): void {
    this.baseSeq = entries[0]?.event.seq ?? 0
    this.hasMore = hasMore
    if (entries.some(entry => entry.event.type === 'turn/start')) this.firstPromptPendingTurn = false
    if (projections !== undefined) this.projections.seed(projections)
    this.eventSource.replace(entries, hasMore)
    this.notifier.markDirty()
  }

  /** Prepend one stream-validated history page. */
  private prependWindow(entries: readonly SessionEventLikeEntry[], hasMore: boolean): void {
    this.baseSeq = entries[0]?.event.seq ?? this.baseSeq
    this.hasMore = hasMore
    this.eventSource.prepend(entries, hasMore)
  }

  /** Append one stream-validated live event. */
  private appendLive(entry: SessionLiveEventEntry): boolean {
    const event = entry.event
    const awaitingFirstTurn = this.firstPromptPendingTurn
    if (event.type === 'turn/start') this.firstPromptPendingTurn = false
    const queueChanged = this.queueMirror.acceptDurable(event)
    this.eventSource.append(entry)
    return queueChanged || awaitingFirstTurn !== this.firstPromptPendingTurn
  }

  /** Publish a terminal background failure only while this stream still owns the Session. */
  private failEventStream(events: SessionEventStream, generation: number, error: unknown): void {
    if (generation !== this.openGeneration || this.events !== events) return
    this.openGeneration++
    this.events = undefined
    this.openPromise = null
    this.openState = 'error'
    this.openError = openFailure(error)
    void events.dispose()
    this.notifier.markDirty()
  }

  private buildSnapshot(): SessionSnapshot {
    return {
      sessionId: this.sessionId,
      queue: this.queueMirror.snapshot(),
      running: this.running,
      subagent: this.address === undefined
        ? null
        : {
          address: this.address,
          ...(this.parentAvailable === undefined ? {} : { parentAvailable: this.parentAvailable }),
        },
      removed: this.removed,
      openState: this.openState,
      openError: this.openError,
      hasMore: this.hasMore,
      loadingOlder: this.loadingOlder,
      promptError: this.promptError,
      blank: this.blankBit,
      lastAgentError: this.lastAgentError,
      promptAttempted: this.promptAttempted,
      awaitingFirstTurn: this.firstPromptPendingTurn,
    }
  }

  private sessionAddress(): SessionAddress {
    return this.address === undefined
      ? { kind: 'session', sessionId: this.sessionId }
      : { kind: 'subagent', ...this.address }
  }
}

/** Convert a terminal Session stream failure to the Client error vocabulary. */
function openFailure(error: unknown): ClientFailure {
  const failure = sessionStreamFailure(error)
  if (failure !== undefined) return failure as SessionError
  const folded = transportResult<never>(error)
  /* v8 ignore next -- transportResult never returns an ok result. */
  if (folded.ok) throw new Error('transportResult returned an unexpected success')
  return folded.error
}
/** Narrow a generated Session Remote failure to its service-owned error vocabulary. */
function toSessionResult<T>(result: RemoteResult<T>): ClientResult<T> {
  return result.ok ? result : { ok: false, error: result.error as SessionError }
}