/**
 * Side Chat routes of the /sidebar JSON API ('sidechat.start' /
 * 'sidechat.prompt' / 'sidechat.cancel' / 'sidechat.dispose' /
 * 'sidechat.info' / 'sidechat.events').
 *
 * A side thread is a child session the plugin creates ITSELF with a custom
 * seed — the parent's full event log up to the click moment, honestly closed
 * at an in-progress turn (see sidechat-core.ts). The child is marked
 * `origin: 'subagent'` so the main session list hides it, and EVERY
 * operation goes through these routes because the generic session RPCs are
 * fenced away from subagent-origin identities (the api-remotes
 * agent-lookup ownership fence). No DSH source is touched:
 *
 * - creation uses the public AgentRegistry.create seam (the same one
 *   api-proxy's session.fork and the subagent fork provider use), with the
 *   parent's preset composition and provider/model selection so the child's
 *   first request shares the parent's token prefix (provider-side prefix
 *   cache reuse);
 * - the first prompt (boundary + question) and every follow-up are admitted
 *   with the stock `agent.followup`;
 * - a cold thread (DSH restart, or a closed thread) is resumed with
 *   AgentRegistry.resume, composing the preset the child recorded.
 */
import { randomUUID } from 'node:crypto'
import { createUserMessage, type ContentBlock, type UserMessage } from '@deepseek-ai/dsh-llm'
import type { Agent, AgentSetup, CreateAgentOptions, ResumeAgentOptions } from '@deepseek-ai/dsh-agent'
import { snapshotSubagentDescriptor } from '@deepseek-ai/dsh-subagent'
import type { Context as CordisContext } from '@deepseek-ai/cordis'
import type { SessionEvent, SessionId } from '@deepseek-ai/dsh-session'
import { SessionLogOffset } from '@deepseek-ai/dsh-session'
import type {
  Context,
  SidebarAgentPresetsService,
  SidebarSessionPersistenceService,
  SidebarSessionTitleService,
} from './context-types.ts'
import {
  boundaryDelivered,
  buildSidechatInheritance,
  resolvePresetId,
  SIDE_BOUNDARY_PROMPT,
  SIDE_INJECTION_PLUGIN,
  SIDE_NEW_THREAD_TITLE,
  sideLabel,
  type SeedEvent,
  type SidechatLogEvent,
  type SidechatThreadInfo,
  threadOwnLogEvents,
} from './sidechat-core.ts'
import { requireString, SidebarError } from './wire.ts'

/** The six Side Chat routes of the sidebar API (wire method names). */
export interface SidechatRoutes {
  /** Create a side thread child seeded with the parent's log up to now.
   *  `question` is optional: empty creates an EMPTY thread (Codex-style
   *  immediate create); the first `sidechat.prompt` then carries the
   *  boundary + snapshot and earns the thread its real label. */
  'sidechat.start'(payload: unknown): Promise<{ childId: string }>
  /** Deliver one follow-up message to a thread (live, or cold-resumed). */
  'sidechat.prompt'(payload: unknown): Promise<{ accepted: true }>
  /** Abort the thread's running turn (queued work is preserved). */
  'sidechat.cancel'(payload: unknown): Promise<{ accepted: true }>
  /** Release the thread's live agent (session and history stay persisted). */
  'sidechat.dispose'(payload: unknown): Promise<{ accepted: true }>
  /** Live state + agent identity for the thread header. */
  'sidechat.info'(payload: unknown): Promise<SidechatThreadInfo>
  /** The thread's OWN transcript events, seed-cut host-side (the inherited
   *  parent log never crosses the wire); `afterSeq` narrows the response to
   *  the delta beyond it (poll tail). */
  'sidechat.events'(payload: unknown): Promise<{ events: SidechatLogEvent[] }>
}

/** Timeout guarding the create call (the registry detaches it before the
 *  handle becomes visible, so the child is never cancelled by it). */
const CREATE_TIMEOUT_MS = 15_000

/** Head cap of one `sidechat.events` response (the ceiling the old
 *  client-side walk could load: 40 pages × 200 events). A pathological
 *  thread beyond it renders its tail window — the same degradation the
 *  capped walk had, never a failed poll. */
const EVENTS_CAP = 8_000

/** Per-activation disposers of created thread agents (the dispose route
 *  releases them; the session and its history always stay persisted). */
const threadDisposers = new Map<string, () => Promise<void>>()

/** The in-progress-turn snapshot captured at creation of an EMPTY thread,
 *  waiting to ride the first prompt (lost on a host restart — the boundary
 *  prompt is then delivered alone, a logged degradation). */
const pendingSnapshots = new Map<string, string>()

/** Resolve the parent's preset and build the child's composition setup
 *  (mirror of api-proxy's composeAgent minus the model-selection install —
 *  the child carries the parent's provider/model in agentOptions). */
async function composeChildSetup(
  ctx: Context,
  presetId: string | undefined,
): Promise<{ agentPreset?: string; setup: AgentSetup }> {
  const presets = ctx.get('agentPresets') as SidebarAgentPresetsService | undefined
  if (presets === undefined) {
    return { setup: () => Promise.resolve() }
  }
  const resolved = await presets.resolve(presetId)
  return {
    agentPreset: resolved.id,
    setup: async (agentCtx: CordisContext) => { await presets.mount(agentCtx, resolved.id) },
  }
}

/** Build the cold-resume setup from the thread's PERSISTED record (the
 *  recorded preset wins, newest selection event first). */
async function composePersistedSetup(
  ctx: Context,
  childId: string,
): Promise<AgentSetup> {
  const persistence = ctx.get('sessionPersistence') as SidebarSessionPersistenceService | undefined
  if (persistence === undefined) {
    return () => Promise.resolve()
  }
  const inspected = await persistence.inspect(childId)
  const presetId = resolvePresetId(inspected.meta, inspected.events)
  const presets = ctx.get('agentPresets') as SidebarAgentPresetsService | undefined
  if (presets === undefined || presetId === undefined) {
    return () => Promise.resolve()
  }
  const resolved = await presets.resolve(presetId)
  return async (agentCtx: CordisContext) => { await presets.mount(agentCtx, resolved.id) }
}

/** One text-block prompt (the thread boundary + question, or a follow-up). */
function textPrompt(text: string): ContentBlock[] {
  return [{ type: 'text', text }]
}

/** Admit one user message to a live agent through the stock followup path. */
function admitFollowup(agent: Agent, blocks: ContentBlock[]): void {
  const message: UserMessage = createUserMessage({ content: blocks, source: { kind: 'user' } })
  agent.followup(message)
}

/**
 * Deliver the thread's FIRST contact as TWO log-separated messages: the
 * boundary prompt (+ the parked in-progress snapshot) rides `agent.inject`
 * — queued model-facing context that does NOT wake the driver and is
 * claimed FIRST at the opening step (Inbox.claim drains next-step before
 * next-turn) — and the user's question is the follow-up that wakes it. The
 * log therefore records two user/message events (injection, then question)
 * instead of one wrapped blob: the transcript shows the question as a user
 * bubble and collapses the injection as a context row. The injection source
 * is stamped `kind: 'plugin'` so recognition is structural; its text still
 * opens with SIDE_BOUNDARY_PREFIX, keeping boundaryDelivered intact.
 */
function admitFirstContact(agent: Agent, injectionText: string, question: string): void {
  agent.inject(createUserMessage({
    content: textPrompt(injectionText),
    source: { kind: 'plugin', plugin: SIDE_INJECTION_PLUGIN },
  }))
  admitFollowup(agent, textPrompt(question))
}

/** The live thread agent, or undefined (cold — the caller resumes). */
function liveThreadAgent(ctx: Context, childId: string): Agent | undefined {
  const agents = ctx.get('agents') as { get(id: string): Agent | undefined } | undefined
  return agents?.get(childId)
}

/**
 * The thread's event log (seed + its own events, already expanded): the live
 * agent's in-memory log while the thread is attached — the freshest read,
 * including events not yet flushed — else the persisted logical log. Both
 * DSH generations expose these seams with the same shape (the 0.1.2
 * persistence layer packs chunk rows on disk but expands them on inspect;
 * the live log is `Session.snapshotEvents()`, the 0.1.2-alpha.4 rename of
 * the `Session.events` property), which is why the transcript reads here
 * instead of the client's session-history RPC: that face
 * (`ctx.connection.api`) was removed in 0.1.2-alpha.1's Remote-gateway
 * migration.
 */
async function threadLogEvents(ctx: Context, childId: string): Promise<readonly SidechatLogEvent[]> {
  const agent = liveThreadAgent(ctx, childId)
  if (agent !== undefined) {
    return agent.session.snapshotEvents() as unknown as readonly SidechatLogEvent[]
  }
  const persistence = ctx.get('sessionPersistence') as SidebarSessionPersistenceService | undefined
  if (persistence === undefined) {
    throw new SidebarError('sidechat-error', 'the session persistence service is unavailable', 503)
  }
  try {
    const inspected = await persistence.inspect(childId)
    return inspected.events as unknown as readonly SidechatLogEvent[]
  } catch (error: unknown) {
    throw new SidebarError(
      'not-found',
      `thread "${childId}" is not available: ${error instanceof Error ? error.message : String(error)}`,
      404,
    )
  }
}

/** Build the Side Chat routes (all optional services degrade to a wire
 *  error the tab surfaces inline). The record keys are the FULL wire method
 *  names the /sidebar/api dispatcher looks up (`api[method]`). */
export function buildSidechatApi(ctx: Context): SidechatRoutes {
  return {
    'sidechat.start': async (payload: unknown) => {
      const sessionId = requireString(payload, 'sessionId')
      const rawQuestion = (payload as { question?: unknown }).question
      const question = typeof rawQuestion === 'string' ? rawQuestion.trim() : ''
      const parent = liveThreadAgent(ctx, sessionId)
      if (parent === undefined) {
        throw new SidebarError('sidechat-error', `parent session "${sessionId}" is not running`, 409)
      }
      const parentSession = parent.session
      const inheritance = buildSidechatInheritance(
        parentSession.snapshotEvents() as unknown as readonly SidechatLogEvent[],
      )
      const { agentPreset, setup } = await composeChildSetup(
        ctx,
        resolvePresetId(parentSession.header, parentSession.snapshotEvents()),
      )
      const childId = `session-${randomUUID()}` as SessionId
      const label = question === '' ? SIDE_NEW_THREAD_TITLE : sideLabel(question)
      // Honest catalog citizenship: the durable descriptor keeps the thread
      // a HEALTHY row in the host's subagents.list — a cold child without
      // one is deterministically rendered as a 'corrupt' diagnostic. The
      // SubagentView filters the 'Side: ' label out, so the topology UI
      // stays noise-free; the row only serves enumeration correctness.
      const descriptor = snapshotSubagentDescriptor({
        mode: 'continuable',
        provider: 'sidechat',
        label,
        ...(parent.options.provider === undefined ? {} : { agentProvider: parent.options.provider }),
        ...(parent.options.model === undefined ? {} : { agentModel: parent.options.model }),
      })
      const descriptorEvent: SeedEvent = {
        type: 'subagent/descriptor',
        seq: inheritance.seed.length,
        time: Date.now(),
        data: descriptor as unknown as Record<string, unknown>,
      }
      const seed = [...inheritance.seed, descriptorEvent]
      // Fork-marker fields (the exact shape the host's own session.fork uses,
      // api-session-controller): without `isSeeded` + `inheritedEventCount` the
      // session treats the whole seed as the child's OWN events, so the child's
      // Inbox constructor replays the parent's `agent/inbox/spliced` events and
      // inherits whatever input sat UNCLAIMED in the parent at the click moment
      // (a queued follow-up, or a tool-result context spliced into next-step
      // between step boundaries of a long-running turn). The first side prompt
      // would then claim and send that stale message BEFORE the boundary +
      // question. The marker keeps `ownEvents()` at the end-seed boundary, so
      // the inherited inbox replays to empty.
      const options: CreateAgentOptions = {
        sessionId: childId,
        meta: {
          ...(parentSession.header.cwd === undefined ? {} : { cwd: parentSession.header.cwd }),
          parentSession: parentSession.id,
          isSeeded: true,
          origin: 'subagent',
          delegationDepth: (parentSession.header.delegationDepth ?? 0) + 1,
          ...(agentPreset === undefined ? {} : { agentPreset }),
        },
        seed: seed as unknown as readonly SessionEvent[],
        inheritedEventCount: SessionLogOffset(seed.length),
        agentOptions: { ...parent.options },
        setup,
        signal: AbortSignal.timeout(CREATE_TIMEOUT_MS),
      }
      const agents = ctx.get('agents') as { create(options: CreateAgentOptions): Promise<{ agent: Agent; dispose(): Promise<void> }> } | undefined
      if (agents?.create === undefined) {
        throw new SidebarError('sidechat-error', 'the agents service is unavailable', 503)
      }
      let handle: { agent: Agent; dispose(): Promise<void> }
      try {
        handle = await agents.create(options)
      } catch (error) {
        throw new SidebarError('sidechat-error', `thread creation failed: ${error instanceof Error ? error.message : String(error)}`, 500)
      }
      threadDisposers.set(childId, () => handle.dispose())
      // Pin the thread label so the client can identify its threads by
      // title prefix (the rename is a live-session op, no RPC fence).
      const titles = ctx.get('sessionTitle') as SidebarSessionTitleService | undefined
      const pinTitle = (label: string): void => {
        if (titles === undefined) return
        try {
          titles.rename(handle.agent.session, label)
        } catch {
          // Keep the auto-generated title; the thread stays usable.
        }
      }
      if (question === '') {
        // Codex-style immediate create: no prompt yet — the composer owns
        // the first message; the snapshot waits for it.
        if (inheritance.snapshot !== null) pendingSnapshots.set(childId, inheritance.snapshot)
        pinTitle(SIDE_NEW_THREAD_TITLE)
      } else {
        const promptParts = [SIDE_BOUNDARY_PROMPT]
        if (inheritance.snapshot !== null) promptParts.push(inheritance.snapshot)
        admitFirstContact(handle.agent, promptParts.join('\n\n'), question)
        pinTitle(sideLabel(question))
      }
      return { childId }
    },

    'sidechat.prompt': async (payload: unknown) => {
      const childId = requireString(payload, 'childId')
      const text = requireString(payload, 'text').trim()
      if (text === '') {
        throw new SidebarError('bad-request', 'text is required')
      }
      let agent = liveThreadAgent(ctx, childId)
      if (agent === undefined) {
        // Cold thread: resume the persisted session under its recorded
        // composition, then deliver the follow-up.
        const agents = ctx.get('agents') as { resume(options: ResumeAgentOptions): Promise<{ agent: Agent; dispose(): Promise<void> }> } | undefined
        if (agents?.resume === undefined) {
          throw new SidebarError('sidechat-error', 'the agents service is unavailable', 503)
        }
        const setup = await composePersistedSetup(ctx, childId)
        try {
          const handle = await agents.resume({ resumeSessionId: childId as SessionId, setup })
          threadDisposers.set(childId, () => handle.dispose())
          agent = handle.agent
        } catch (error) {
          throw new SidebarError('sidechat-error', `thread resume failed: ${error instanceof Error ? error.message : String(error)}`, 500)
        }
      }
      if (boundaryDelivered(agent.session.snapshotEvents() as unknown as readonly SidechatLogEvent[])) {
        admitFollowup(agent, textPrompt(text))
      } else {
        // First message of an immediately-created thread: it carries the
        // boundary (+ the snapshot parked at creation, if still around)
        // and earns the thread its real label.
        const parts = [SIDE_BOUNDARY_PROMPT]
        const snapshot = pendingSnapshots.get(childId)
        pendingSnapshots.delete(childId)
        if (snapshot !== undefined) parts.push(snapshot)
        admitFirstContact(agent, parts.join('\n\n'), text)
        const titles = ctx.get('sessionTitle') as SidebarSessionTitleService | undefined
        if (titles !== undefined) {
          try {
            titles.rename(agent.session, sideLabel(text))
          } catch {
            // Keep the placeholder title; the thread stays usable.
          }
        }
      }
      return { accepted: true as const }
    },

    'sidechat.cancel': async (payload: unknown) => {
      const childId = requireString(payload, 'childId')
      const agent = liveThreadAgent(ctx, childId)
      if (agent !== undefined) {
        agent.cancel({ kind: 'user' }, { keepInbox: true })
      }
      return { accepted: true as const }
    },

    'sidechat.dispose': async (payload: unknown) => {
      const childId = requireString(payload, 'childId')
      pendingSnapshots.delete(childId)
      const dispose = threadDisposers.get(childId)
      if (dispose !== undefined) {
        threadDisposers.delete(childId)
        try {
          await dispose()
        } catch {
          // The agent may already be gone (restart); the session persists.
        }
      }
      return { accepted: true as const }
    },

    'sidechat.info': async (payload: unknown) => {
      const childId = requireString(payload, 'childId')
      const agent = liveThreadAgent(ctx, childId)
      if (agent !== undefined) {
        const preset = agent.session.header.agentPreset
        return {
          live: true,
          status: agent.status,
          ...(agent.options.provider === undefined ? {} : { provider: agent.options.provider }),
          ...(agent.options.model === undefined ? {} : { model: agent.options.model }),
          ...(preset === undefined ? {} : { preset }),
        }
      }
      // Cold thread: only the persisted preset is worth reading back.
      const persistence = ctx.get('sessionPersistence') as SidebarSessionPersistenceService | undefined
      if (persistence !== undefined) {
        try {
          const inspected = await persistence.inspect(childId)
          const preset = resolvePresetId(inspected.meta, inspected.events)
          return { live: false, ...(preset === undefined ? {} : { preset }) }
        } catch {
          // Unknown/gone session: report a bare cold info.
        }
      }
      return { live: false }
    },

    'sidechat.events': async (payload: unknown) => {
      const childId = requireString(payload, 'childId')
      const rawAfter = (payload as { afterSeq?: unknown }).afterSeq
      if (rawAfter !== undefined
        && (typeof rawAfter !== 'number' || !Number.isSafeInteger(rawAfter) || rawAfter < 0)) {
        throw new SidebarError('bad-request', 'afterSeq must be a non-negative integer')
      }
      const events = await threadLogEvents(ctx, childId)
      const own = threadOwnLogEvents(events)
      const fresh = rawAfter === undefined ? own : own.filter(event => event.seq > rawAfter)
      return { events: fresh.length > EVENTS_CAP ? fresh.slice(fresh.length - EVENTS_CAP) : fresh }
    },
  }
}