/**
 * v2.6 Phase 1 — OpenCodeServerBackend (slimmed, v2.7 audit reshape).
 *
 * Warm, multi-turn backend for the `opencode` agent. One `opencode serve` HTTP
 * server per BooCoder process; one opencode session per BooCode session (resumed
 * on switch-back); one SSE read loop PER session, each scoped to that session's
 * worktree directory so sessions in different directories stream concurrently.
 *
 * This file is now just the `AgentBackend` SURFACE — ensureSession / prompt /
 * accumulateUsage / closeSession + the per-session demux side effects (watchdog,
 * reconcile, usage). It composes three extracted collaborators:
 *   - `OpenCodeServerSupervisor` (opencode-server-process.ts) — child/client/port/
 *     health lifecycle, spawn/crash/restart/dispose.
 *   - the per-session SSE loop (opencode-sse.ts) — subscribe + reconnect/backoff.
 *   - the pure event map (opencode-event-map.ts) — Event → AgentEvent translation,
 *     dedup gate, dcp-strip, tool-snapshot.
 *
 * Implements the Phase 0 `AgentBackend` interface. Emits transport-agnostic
 * `AgentEvent`s; the dispatcher maps them to WS frames.
 *
 * Spec: openspec/changes/v2-6-persistent-agent-sessions/design.md §2 / §2a.
 */
import { createHash } from 'node:crypto';
import type { FastifyBaseLogger } from 'fastify';
import type { Event, AssistantMessage } from '@opencode-ai/sdk/v2/client';
import type { Sql } from '../../db.js';
import { armAbortGuard, noteTurnActivity, consumeTerminal } from './turn-guard.js';
import { stepEndedToUsage, type StepUsage } from './opencode-usage.js';
import { OpenCodeServerSupervisor, type ServerDownInfo } from './opencode-server-process.js';
import {
  startSessionEventLoop,
  type SessionState,
  type TurnState,
  type SseLoopDeps,
} from './opencode-sse.js';
import {
  classifyPartDelta,
  classifyUpdatedPart,
  toolCalledSnapshot,
  toolSuccessSnapshot,
  toolFailedSnapshot,
  stripDcpTags,
  errMsg,
  errToString,
} from './opencode-event-map.js';
import type {
  AgentBackend,
  AgentSessionHandle,
  EnsureSessionOpts,
  PromptCtx,
  TurnResult,
} from '../agent-backend.js';

/**
 * No-activity backstop for an in-flight turn. opencode streams reasoning/text/tool
 * deltas continuously while working, so "zero events for this long" means the turn
 * is wedged or its terminal event (session.idle) was lost. Generous so a
 * legitimately slow turn never trips it.
 */
const TURN_INACTIVITY_MS = 180_000;

export interface OpenCodeServerBackendDeps {
  sql: Sql;
  log: FastifyBaseLogger;
  /** Absolute path to the opencode binary (resolved from available_agents at wiring time, Phase 1.7). */
  opencodeBinary: string;
}

export class OpenCodeServerBackend implements AgentBackend {
  readonly backend = 'opencode_server' as const;

  private readonly sql: Sql;
  private readonly log: FastifyBaseLogger;
  private readonly supervisor: OpenCodeServerSupervisor;

  /** opencode session id → demux state. Maintained by ensureSession; read by the SSE loop. */
  private readonly byOpencodeId = new Map<string, SessionState>();
  /** Coalesces concurrent ensureSession calls for the same (chat, agent) key. */
  private readonly ensuring = new Map<string, Promise<AgentSessionHandle>>();

  constructor(deps: OpenCodeServerBackendDeps) {
    this.sql = deps.sql;
    this.log = deps.log;
    this.supervisor = new OpenCodeServerSupervisor({
      opencodeBinary: deps.opencodeBinary,
      log: deps.log,
      hooks: {
        isBusy: () => this.isBusy(),
        onServerDown: (info) => this.onServerDown(info),
      },
    });
  }

  /** §2: liveness for the health endpoint + dispatcher fallback decision. */
  health(): 'up' | 'down' {
    return this.supervisor.health();
  }

  /** Phase 3: busy iff ANY pooled opencode session has an in-flight turn. */
  isBusy(): boolean {
    for (const st of this.byOpencodeId.values()) {
      if (st.activeTurn) return true;
    }
    return false;
  }

  /** Phase 3 proactive health probe + busy-aware self-restart, run by the pool's
   *  periodic sweep. Delegates to the supervisor. */
  async tickHealth(now: number = Date.now()): Promise<void> {
    await this.supervisor.tickHealth(now);
  }

  /**
   * Server down (crash-exit or forced restart): fail every in-flight turn so its
   * dispatcher unblocks, mark each session crashed so ensureSession won't resume a
   * now-dead native id, and tear down the SSE loops + demux state. Invoked by the
   * supervisor (it owns the process/port reset). Mirrors the original
   * handleServerCrash session-half byte-for-byte.
   */
  private onServerDown(info: ServerDownInfo): void {
    const states = [...this.byOpencodeId.values()];
    this.log.warn(
      { code: info.code, signal: info.signal, port: info.port, liveSessions: states.length },
      'opencode-server: child exited — recovering (fail in-flight, mark crashed, re-spawn next turn)',
    );

    const crashedIds: string[] = [];
    for (const st of states) {
      st.sseAbort?.abort();
      if (st.activeTurn) {
        st.activeTurn.settle({ ok: false, error: 'opencode server crashed mid-turn' });
        st.activeTurn = null;
      }
      if (st.watchdog) {
        clearTimeout(st.watchdog);
        st.watchdog = null;
      }
      crashedIds.push(st.agentSessionId);
    }
    // Drop the demux map: every session id is stale against a fresh server.
    this.byOpencodeId.clear();

    if (crashedIds.length > 0) {
      this.sql`
        UPDATE agent_sessions SET status = 'crashed'
        WHERE agent_session_id = ANY(${crashedIds}) AND status <> 'closed'
      `.catch((err) => {
        this.log.warn({ err: errMsg(err) }, 'opencode-server: failed to mark crashed sessions (non-fatal)');
      });
    }
  }

  // ─── SSE loop wiring ─────────────────────────────────────────────────────────

  /** The dependency bundle the per-session SSE loop reads. */
  private sseDeps(): SseLoopDeps {
    return {
      isUp: () => this.supervisor.isUp(),
      getClient: () => this.supervisor.client,
      dispatchEvent: (ev) => this.dispatchEvent(ev),
      reconcile: (st) => this.reconcile(st),
      onReconnectGiveUp: (st) => this.onReconnectGiveUp(st),
      log: this.log,
    };
  }

  /** Demux one event to the owning session's active turn. Unknown/between-turns → drop. */
  private dispatchEvent(ev: Event): void {
    switch (ev.type) {
      // ─── session.next.* — live streaming events (the primary path) ─────────
      case 'session.next.text.delta': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        const cleaned = stripDcpTags(p.delta);
        if (cleaned) st.activeTurn.onEvent({ type: 'text', text: cleaned });
        return;
      }
      case 'session.next.reasoning.delta': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        st.activeTurn.onEvent({ type: 'reasoning', text: p.delta });
        return;
      }
      case 'session.next.tool.called': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        st.activeTurn.onEvent({ type: 'tool_call', toolCall: toolCalledSnapshot(p) });
        return;
      }
      case 'session.next.tool.success': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        st.activeTurn.onEvent({ type: 'tool_update', toolCall: toolSuccessSnapshot(p) });
        return;
      }
      case 'session.next.tool.failed': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        st.activeTurn.onEvent({ type: 'tool_update', toolCall: toolFailedSnapshot(p) });
        return;
      }
      // ─── per-step usage (U.6) — token/cost accounting for opencode sessions ──
      case 'session.next.step.ended': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        // Accumulate this step's normalized usage onto the (chat_id, agent) row.
        // Fire-and-forget: a DB hiccup must not stall the turn.
        const usage = stepEndedToUsage(p);
        void this.accumulateUsage(st, usage);
        return;
      }
      // ─── message.part.* — terminal/post-hoc events (dedup gate) ────────────
      case 'message.part.delta': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        const e = classifyPartDelta(p, st);
        if (e) st.activeTurn.onEvent(e);
        return;
      }
      case 'message.part.updated': {
        const part = ev.properties.part;
        const st = this.byOpencodeId.get(part.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        const e = classifyUpdatedPart(part, st);
        if (e) st.activeTurn.onEvent(e);
        return;
      }
      // ─── lifecycle ─────────────────────────────────────────────────────────
      case 'session.idle': {
        const st = this.byOpencodeId.get(ev.properties.sessionID);
        if (!st) return;
        if (consumeTerminal(st) === 'swallow') return; // F.1: drop the post-abort orphan
        st.activeTurn?.settle({ ok: true });
        return;
      }
      case 'session.error': {
        const sid = ev.properties.sessionID;
        if (!sid) return;
        const st = this.byOpencodeId.get(sid);
        if (!st) return;
        if (consumeTerminal(st) === 'swallow') return; // F.1: drop the post-abort orphan
        st.activeTurn?.settle({ ok: false, error: errToString(ev.properties.error) });
        return;
      }
      default:
        return;
    }
  }

  // ─── turn-completion resilience (watchdog + reconnect reconcile) ─────────────

  /** Reset the inactivity backstop on any event routed to a session's active turn. */
  private bumpActivity(st: SessionState): void {
    if (!st.activeTurn) return;
    // A live turn is producing → the post-abort orphan-terminal window is over.
    noteTurnActivity(st);
    if (st.watchdog) clearTimeout(st.watchdog);
    st.watchdog = setTimeout(() => {
      void this.onTurnStall(st);
    }, TURN_INACTIVITY_MS);
    st.watchdog.unref?.();
  }

  /** Watchdog fired: reconcile once; if still-running we can't tell, so fail closed.
   *  Also mark the agent_sessions row crashed so a stale session isn't resumed. */
  private async onTurnStall(st: SessionState): Promise<void> {
    const settled = await this.reconcile(st);
    if (!settled) {
      this.log.warn({ agentSessionId: st.agentSessionId }, 'opencode-server: turn stalled (no activity), failing + marking crashed');
      await this.sql`
        UPDATE agent_sessions SET status = 'crashed'
        WHERE agent_session_id = ${st.agentSessionId}
      `.catch(() => {});
      st.activeTurn?.settle({ ok: false, error: 'turn timed out (no activity)' });
    }
  }

  /** SSE circuit-breaker fired (reconnect gave up): fail the active turn + mark the
   *  session crashed so it isn't resumed. The next turn re-creates a fresh session. */
  private async onReconnectGiveUp(st: SessionState): Promise<void> {
    if (!st.activeTurn) return;
    await this.sql`
      UPDATE agent_sessions SET status = 'crashed'
      WHERE agent_session_id = ${st.agentSessionId}
    `.catch(() => {});
    st.activeTurn?.settle({ ok: false, error: 'opencode SSE stream lost (reconnect gave up)' });
  }

  /**
   * Ask the server whether this session's turn already finished — recovers a
   * session.idle/error lost during an SSE gap. Returns true if it settled the turn.
   */
  private async reconcile(st: SessionState): Promise<boolean> {
    const turn = st.activeTurn;
    const client = this.supervisor.client;
    if (!turn || !client) return false;
    try {
      const res = await client.session.messages({
        sessionID: st.agentSessionId,
        directory: st.worktreePath,
      });
      if (res.error || !res.data) return false;
      let lastAssistant: AssistantMessage | undefined;
      for (let i = res.data.length - 1; i >= 0; i--) {
        const info = res.data[i]!.info;
        if (info.role === 'assistant') {
          lastAssistant = info;
          break;
        }
      }
      if (!lastAssistant) return false;
      if (lastAssistant.error != null) {
        turn.settle({ ok: false, error: errToString(lastAssistant.error) });
        return true;
      }
      if (lastAssistant.time.completed != null) {
        turn.settle({ ok: true });
        return true;
      }
      return false; // still running — the live stream will deliver session.idle
    } catch {
      return false; // inconclusive — watchdog backstop covers it
    }
  }

  // ─── per-step usage persistence (U.6) ────────────────────────────────────────

  /**
   * Accumulate one `session.next.step.ended`'s normalized usage onto the session's
   * agent_sessions row. Running totals for the whole conversation context. Zero-delta
   * steps are skipped. Errors are swallowed: usage telemetry must never fail a turn.
   */
  private async accumulateUsage(st: SessionState, u: StepUsage): Promise<void> {
    if (u.input === 0 && u.output === 0 && u.cost === 0) return;
    try {
      await this.sql`
        UPDATE agent_sessions SET
          input_tokens = input_tokens + ${u.input},
          output_tokens = output_tokens + ${u.output},
          cost = cost + ${u.cost}
        WHERE agent_session_id = ${st.agentSessionId}
      `;
    } catch (err) {
      this.log.warn(
        { err: errMsg(err), agentSessionId: st.agentSessionId },
        'opencode-server: failed to persist step usage (non-fatal)',
      );
    }
  }

  // ─── ensureSession: create-or-resume against agent_sessions (1.5) ────────────

  async ensureSession(sessionId: string, opts: EnsureSessionOpts): Promise<AgentSessionHandle> {
    // Coalesce concurrent first-turns for the same (chat, agent) so the SELECT…
    // create…upsert can't race into two opencode sessions (the second orphaning
    // the first). A single (non-concurrent) call is unaffected — the entry is set
    // and removed within this call. Defensive: the dispatcher already serializes
    // turns per (chat, agent) via its inflight map.
    const key = `${opts.chatId}:${opts.agent}`;
    const existing = this.ensuring.get(key);
    if (existing) return existing;
    const p = this.ensureSessionInner(sessionId, opts).finally(() => {
      if (this.ensuring.get(key) === p) this.ensuring.delete(key);
    });
    this.ensuring.set(key, p);
    return p;
  }

  private async ensureSessionInner(sessionId: string, opts: EnsureSessionOpts): Promise<AgentSessionHandle> {
    await this.supervisor.ensureServer();
    const client = this.supervisor.client;
    if (!client) throw new Error('opencode-server: client not ready after ensureServer');

    const configHash = sessionConfigHash(opts.model);
    // P1.5-b: agent_sessions is keyed (chat_id, agent) — the tab/chat is the
    // context unit (two tabs in one session = two contexts sharing one worktree).
    const [row] = await this.sql<{ agent_session_id: string | null; status: string; config_hash: string | null }[]>`
      SELECT agent_session_id, status, config_hash FROM agent_sessions
      WHERE chat_id = ${opts.chatId} AND agent = ${opts.agent}
    `;
    let agentSessionId = row?.agent_session_id ?? null;

    // Don't resume crashed sessions or sessions whose config drifted (model change).
    const shouldResume = agentSessionId
      && row!.status !== 'crashed'
      && (row!.config_hash == null || row!.config_hash === configHash);

    if (!shouldResume) {
      if (agentSessionId) {
        this.log.info({ sessionId, oldStatus: row!.status, hashMatch: row!.config_hash === configHash },
          'opencode-server: not resuming stale session, creating fresh');
        this.byOpencodeId.delete(agentSessionId);
      }
      const created = await client.session.create({ directory: opts.worktreePath });
      if (created.error || !created.data) {
        throw new Error(`opencode-server: session.create failed: ${errToString(created.error)}`);
      }
      agentSessionId = created.data.id;
      await this.sql`
        INSERT INTO agent_sessions
          (chat_id, session_id, worktree_id, agent, backend, agent_session_id, server_port, status, last_active_at, config_hash)
        VALUES
          (${opts.chatId}, ${sessionId}, ${opts.worktreeId}, ${opts.agent}, 'opencode_server', ${agentSessionId}, ${this.supervisor.port}, 'active', clock_timestamp(), ${configHash})
        ON CONFLICT (chat_id, agent) DO UPDATE SET
          session_id = EXCLUDED.session_id,
          worktree_id = EXCLUDED.worktree_id,
          backend = 'opencode_server',
          agent_session_id = EXCLUDED.agent_session_id,
          server_port = EXCLUDED.server_port,
          status = 'active',
          last_active_at = clock_timestamp(),
          config_hash = EXCLUDED.config_hash
      `;
    } else {
      await this.sql`
        UPDATE agent_sessions
        SET status = 'active', last_active_at = clock_timestamp(), server_port = ${this.supervisor.port}, config_hash = ${configHash}
        WHERE chat_id = ${opts.chatId} AND agent = ${opts.agent}
      `;
    }

    // Both branches above guarantee agentSessionId is non-null.
    const ocSessionId = agentSessionId!;

    // Register / refresh the demux entry the SSE loop keys on. Preserve an existing
    // entry (and any in-flight turn) — just refresh the routing fields.
    let state = this.byOpencodeId.get(ocSessionId);
    if (state) {
      state.boocodeSessionId = sessionId;
      state.worktreePath = opts.worktreePath;
    } else {
      state = this.makeSessionState(sessionId, ocSessionId, opts.worktreePath);
      this.byOpencodeId.set(ocSessionId, state);
    }

    // Start this session's own SSE loop, scoped to its worktree directory. Both
    // fresh-create and resume reach here; idempotent.
    startSessionEventLoop(state, this.sseDeps());

    return {
      sessionId,
      agent: opts.agent,
      backend: 'opencode_server',
      chatId: opts.chatId,
      worktreeId: opts.worktreeId,
      agentSessionId: ocSessionId,
      serverPort: this.supervisor.port,
    };
  }

  /** Fresh per-(opencode session) demux state. */
  private makeSessionState(boocodeSessionId: string, agentSessionId: string, worktreePath: string): SessionState {
    return {
      boocodeSessionId,
      agentSessionId,
      worktreePath,
      streamedPartKeys: new Set(),
      partTypeById: new Map(),
      activeTurn: null,
      watchdog: null,
      sseAbort: null,
      swallowNextTerminal: false,
    };
  }

  // ─── prompt: send one turn (1.6) ─────────────────────────────────────────────

  async prompt(handle: AgentSessionHandle, input: string, ctx: PromptCtx): Promise<TurnResult> {
    const client = this.supervisor.client;
    if (!client) throw new Error('opencode-server: client not ready');
    const oc = handle.agentSessionId;
    if (!oc) throw new Error('opencode-server: handle has no agentSessionId');

    let state = this.byOpencodeId.get(oc);
    if (!state) {
      state = this.makeSessionState(handle.sessionId, oc, ctx.worktreePath);
      this.byOpencodeId.set(oc, state);
    }
    const session = state;

    // v2.7 busy-assert: one in-flight turn per session. The dispatcher serializes
    // turns per (chat, agent), so this never fires in normal dispatch — but if a
    // second prompt arrives while one is live it would silently overwrite the slot
    // and orphan the first turn, so reject instead.
    if (session.activeTurn) {
      return { ok: false, error: 'opencode-server: session already has an in-flight turn' };
    }

    // Authoritative per-turn directory for SDK routing + reconcile.
    session.worktreePath = ctx.worktreePath;
    // Defensive: ensureSession normally starts the loop, but if prompt is reached
    // with a freshly-created state (no loop yet), start it so the turn streams.
    startSessionEventLoop(session, this.sseDeps());

    return await new Promise<TurnResult>((resolve) => {
      let settled = false;
      const cleanup = () => {
        session.activeTurn = null;
        if (session.watchdog) {
          clearTimeout(session.watchdog);
          session.watchdog = null;
        }
        session.streamedPartKeys.clear();
        session.partTypeById.clear();
        ctx.signal.removeEventListener('abort', onAbort);
      };
      const settle = (r: TurnResult) => {
        if (settled) return;
        settled = true;
        cleanup();
        resolve(r);
      };
      const onAbort = () => {
        // Abort the turn only — never the server.
        client.session.abort({ sessionID: oc, directory: ctx.worktreePath }).catch(() => {});
        // F.1: opencode emits one trailing session.idle/error for the cancelled
        // turn — arm the guard so it's swallowed, not used to settle the next turn.
        armAbortGuard(session);
        settle({ ok: false, error: 'aborted' });
      };

      const turn: TurnState = { onEvent: ctx.onEvent, settle };
      session.activeTurn = turn;
      this.bumpActivity(session); // arm the inactivity backstop

      if (ctx.signal.aborted) {
        onAbort();
        return;
      }
      ctx.signal.addEventListener('abort', onAbort, { once: true });

      const model = parseModel(ctx.model);
      client.session
        .promptAsync({
          sessionID: oc,
          directory: ctx.worktreePath,
          parts: [{ type: 'text', text: input }],
          ...(model ? { model } : {}),
        })
        .then((res) => {
          // promptAsync is fire-and-forget (204); the turn completes via session.idle.
          // Only a submission error settles here.
          if (res.error) settle({ ok: false, error: errToString(res.error) });
        })
        .catch((err) => settle({ ok: false, error: errMsg(err) }));
    });
  }

  // ─── teardown ────────────────────────────────────────────────────────────────

  async closeSession(handle: AgentSessionHandle): Promise<void> {
    if (handle.agentSessionId) {
      // Stop this session's SSE loop before dropping its demux entry.
      this.byOpencodeId.get(handle.agentSessionId)?.sseAbort?.abort();
      this.byOpencodeId.delete(handle.agentSessionId);
    }
    await this.sql`
      UPDATE agent_sessions SET status = 'closed'
      WHERE chat_id = ${handle.chatId} AND agent = ${handle.agent}
    `.catch(() => {});
  }

  async dispose(): Promise<void> {
    // Abort every per-session SSE loop so none survive the teardown.
    for (const st of this.byOpencodeId.values()) st.sseAbort?.abort();
    this.byOpencodeId.clear();
    await this.supervisor.dispose();
  }
}

// ─── helpers ──────────────────────────────────────────────────────────────────

/** BooCoder model string "provider/model" → opencode's structured {providerID, modelID}. */
function parseModel(model: string | undefined): { providerID: string; modelID: string } | undefined {
  if (!model || !model.trim()) return undefined;
  const trimmed = model.trim();
  const idx = trimmed.indexOf('/');
  if (idx > 0 && idx < trimmed.length - 1) {
    return { providerID: trimmed.slice(0, idx), modelID: trimmed.slice(idx + 1) };
  }
  // No slash but non-empty → infer llama-swap (the only configured provider).
  if (idx < 0 && trimmed.length > 0) {
    return { providerID: 'llama-swap', modelID: trimmed };
  }
  return undefined;
}

/** Hash of stable config — detects model changes across sessions without
 *  invalidating on ephemeral state like the random server port. */
function sessionConfigHash(model: string): string {
  return createHash('sha256').update(`opencode_server|${model}`).digest('hex').slice(0, 16);
}