import { Inject, Injectable, Logger, Optional, type OnModuleDestroy } from '@nestjs/common';
import {
  createAgentSession,
  DefaultResourceLoader,
  SessionManager,
  type AgentSession as PiAgentSession,
  type AgentSessionEvent,
  type ToolDefinition,
} from '@mariozechner/pi-coding-agent';
import type { Brain } from '@mosaic/brain';
import type { Memory } from '@mosaic/memory';
import { BRAIN } from '../brain/brain.tokens.js';
import { MEMORY } from '../memory/memory.tokens.js';
import { EmbeddingService } from '../memory/embedding.service.js';
import { CoordService } from '../coord/coord.service.js';
import { ProviderService } from './provider.service.js';
import { McpClientService } from '../mcp-client/mcp-client.service.js';
import { SkillLoaderService } from './skill-loader.service.js';
import { createBrainTools } from './tools/brain-tools.js';
import { createCoordTools } from './tools/coord-tools.js';
import { createMemoryTools } from './tools/memory-tools.js';
import { createFileTools } from './tools/file-tools.js';
import { createGitTools } from './tools/git-tools.js';
import { createShellTools } from './tools/shell-tools.js';
import { createWebTools } from './tools/web-tools.js';
import { createSearchTools } from './tools/search-tools.js';
import type { SessionInfoDto, SessionMetrics } from './session.dto.js';
import { SystemOverrideService } from '../preferences/system-override.service.js';
import { PreferencesService } from '../preferences/preferences.service.js';
import { SessionGCService } from '../gc/session-gc.service.js';

/** A single message from DB conversation history, used for context injection. */
export interface ConversationHistoryMessage {
  role: 'user' | 'assistant' | 'system';
  content: string;
  createdAt: Date;
}

export interface AgentSessionOptions {
  provider?: string;
  modelId?: string;
  /**
   * Sandbox working directory for the session.
   * File, git, and shell tools will be restricted to this directory.
   * Falls back to AGENT_FILE_SANDBOX_DIR env var or process.cwd().
   */
  sandboxDir?: string;
  /**
   * Platform-level system prompt for this session.
   * Merged with skill prompt additions (platform prompt first, then skills).
   * Falls back to AGENT_SYSTEM_PROMPT env var when omitted.
   */
  systemPrompt?: string;
  /**
   * Explicit allowlist of tool names available in this session.
   * When set, only listed tools are registered with the agent.
   * When omitted for non-admin users, falls back to AGENT_USER_TOOLS env var.
   * Admins (isAdmin=true) always receive the full tool set unless explicitly restricted.
   */
  allowedTools?: string[];
  /** Whether the requesting user has admin privileges. Controls default tool access. */
  isAdmin?: boolean;
  /**
   * DB agent config ID. When provided, loads agent config from DB and merges
   * provider, model, systemPrompt, and allowedTools. Explicit call-site options
   * take precedence over config values.
   */
  agentConfigId?: string;
  /** ID of the user who owns this session. Used for preferences and system override lookups. */
  userId?: string;
  /**
   * Prior conversation messages to inject as context when resuming a session.
   * These messages are formatted and prepended to the system prompt so the
   * agent is aware of what was discussed in previous sessions.
   */
  conversationHistory?: ConversationHistoryMessage[];
}

export interface AgentSession {
  id: string;
  provider: string;
  modelId: string;
  piSession: PiAgentSession;
  listeners: Set<(event: AgentSessionEvent) => void>;
  unsubscribe: () => void;
  createdAt: number;
  promptCount: number;
  channels: Set<string>;
  /** System prompt additions injected from enabled prompt-type skills. */
  skillPromptAdditions: string[];
  /** Resolved sandbox directory for this session. */
  sandboxDir: string;
  /** Tool names available in this session, or null when all tools are available. */
  allowedTools: string[] | null;
  /** User ID that owns this session, used for preference lookups. */
  userId?: string;
  /** Agent config ID applied to this session, if any (M5-001). */
  agentConfigId?: string;
  /** Human-readable agent name applied to this session, if any (M5-001). */
  agentName?: string;
  /** M5-007: per-session metrics. */
  metrics: SessionMetrics;
}

@Injectable()
export class AgentService implements OnModuleDestroy {
  private readonly logger = new Logger(AgentService.name);
  private readonly sessions = new Map<string, AgentSession>();
  private readonly creating = new Map<string, Promise<AgentSession>>();

  constructor(
    @Inject(ProviderService) private readonly providerService: ProviderService,
    @Inject(BRAIN) private readonly brain: Brain,
    @Inject(MEMORY) private readonly memory: Memory,
    @Inject(EmbeddingService) private readonly embeddingService: EmbeddingService,
    @Inject(CoordService) private readonly coordService: CoordService,
    @Inject(McpClientService) private readonly mcpClientService: McpClientService,
    @Inject(SkillLoaderService) private readonly skillLoaderService: SkillLoaderService,
    @Optional()
    @Inject(SystemOverrideService)
    private readonly systemOverride: SystemOverrideService | null,
    @Optional()
    @Inject(PreferencesService)
    private readonly preferencesService: PreferencesService | null,
    @Inject(SessionGCService) private readonly gc: SessionGCService,
  ) {}

  /**
   * Build the full set of custom tools scoped to the given sandbox directory and session user.
   * Brain/coord/memory/web tools are stateless with respect to cwd; file/git/shell
   * tools receive the resolved sandboxDir so they operate within the sandbox.
   * Memory tools are bound to sessionUserId so the LLM cannot access another user's data.
   */
  private buildToolsForSandbox(
    sandboxDir: string,
    sessionUserId: string | undefined,
  ): ToolDefinition[] {
    return [
      ...createBrainTools(this.brain),
      ...createCoordTools(this.coordService),
      ...createMemoryTools(
        this.memory,
        this.embeddingService.available ? this.embeddingService : null,
        sessionUserId,
      ),
      ...createFileTools(sandboxDir),
      ...createGitTools(sandboxDir),
      ...createShellTools(sandboxDir),
      ...createWebTools(),
      ...createSearchTools(),
    ];
  }

  /**
   * Resolve the tool allowlist for a session.
   * - Admin users: all tools unless an explicit allowedTools list is passed.
   * - Regular users: use allowedTools if provided, otherwise parse AGENT_USER_TOOLS env var.
   * Returns null when all tools should be available.
   */
  private resolveAllowedTools(isAdmin: boolean, allowedTools?: string[]): string[] | null {
    if (allowedTools !== undefined) {
      return allowedTools.length === 0 ? [] : allowedTools;
    }
    if (isAdmin) {
      return null; // admins get everything
    }
    const envTools = process.env['AGENT_USER_TOOLS'];
    if (!envTools) {
      return null; // no restriction configured
    }
    return envTools
      .split(',')
      .map((t) => t.trim())
      .filter((t) => t.length > 0);
  }

  async createSession(sessionId: string, options?: AgentSessionOptions): Promise<AgentSession> {
    const existing = this.sessions.get(sessionId);
    if (existing) return existing;

    const inflight = this.creating.get(sessionId);
    if (inflight) return inflight;

    const promise = this.doCreateSession(sessionId, options).finally(() => {
      this.creating.delete(sessionId);
    });
    this.creating.set(sessionId, promise);
    return promise;
  }

  private async doCreateSession(
    sessionId: string,
    options?: AgentSessionOptions,
  ): Promise<AgentSession> {
    // Merge DB agent config when agentConfigId is provided (M5-001)
    let mergedOptions = options;
    let resolvedAgentName: string | undefined;
    if (options?.agentConfigId) {
      const agentConfig = await this.brain.agents.findById(options.agentConfigId);
      if (agentConfig) {
        resolvedAgentName = agentConfig.name;
        mergedOptions = {
          provider: options.provider ?? agentConfig.provider,
          modelId: options.modelId ?? agentConfig.model,
          systemPrompt: options.systemPrompt ?? agentConfig.systemPrompt ?? undefined,
          allowedTools: options.allowedTools ?? agentConfig.allowedTools ?? undefined,
          sandboxDir: options.sandboxDir,
          isAdmin: options.isAdmin,
          agentConfigId: options.agentConfigId,
          userId: options.userId,
          conversationHistory: options.conversationHistory,
        };
        this.logger.log(
          `Merged agent config "${agentConfig.name}" (${agentConfig.id}) into session ${sessionId}`,
        );
      }
    }

    const model = this.resolveModel(mergedOptions);
    const providerName = model?.provider ?? 'default';
    const modelId = model?.id ?? 'default';

    // Resolve sandbox directory: option > env var > process.cwd()
    const sandboxDir =
      mergedOptions?.sandboxDir ?? process.env['AGENT_FILE_SANDBOX_DIR'] ?? process.cwd();

    // Resolve allowed tool set
    const allowedTools = this.resolveAllowedTools(
      mergedOptions?.isAdmin ?? false,
      mergedOptions?.allowedTools,
    );

    this.logger.log(
      `Creating agent session: ${sessionId} (provider=${providerName}, model=${modelId}, sandbox=${sandboxDir}, tools=${allowedTools === null ? 'all' : allowedTools.join(',') || 'none'})`,
    );

    // Load skill tools from the catalog
    const { metaTools: skillMetaTools, promptAdditions } =
      await this.skillLoaderService.loadForSession();
    if (skillMetaTools.length > 0) {
      this.logger.log(`Attaching ${skillMetaTools.length} skill tool(s) to session ${sessionId}`);
    }
    if (promptAdditions.length > 0) {
      this.logger.log(
        `Injecting ${promptAdditions.length} skill prompt addition(s) into session ${sessionId}`,
      );
    }

    // Build per-session tools scoped to the sandbox directory and authenticated user
    const sandboxTools = this.buildToolsForSandbox(sandboxDir, mergedOptions?.userId);

    // Combine static tools with dynamically discovered MCP client tools and skill tools
    const mcpTools = this.mcpClientService.getToolDefinitions();
    let allCustomTools = [...sandboxTools, ...skillMetaTools, ...mcpTools];
    if (mcpTools.length > 0) {
      this.logger.log(`Attaching ${mcpTools.length} MCP client tool(s) to session ${sessionId}`);
    }

    // Filter tools by allowlist when a restriction is in effect
    if (allowedTools !== null) {
      const allowedSet = new Set(allowedTools);
      const before = allCustomTools.length;
      allCustomTools = allCustomTools.filter((t) => allowedSet.has(t.name));
      this.logger.log(
        `Tool restriction applied: ${allCustomTools.length}/${before} tools allowed for session ${sessionId}`,
      );
    }

    // Build system prompt: platform prompt + skill additions appended
    const platformPrompt =
      mergedOptions?.systemPrompt ?? process.env['AGENT_SYSTEM_PROMPT'] ?? undefined;

    // Format conversation history for context injection (M1-004 / M1-005)
    const historyPromptSection = mergedOptions?.conversationHistory?.length
      ? this.buildHistoryPromptSection(
          mergedOptions.conversationHistory,
          model?.contextWindow ?? 8192,
          sessionId,
        )
      : undefined;

    const appendParts: string[] = [];
    if (promptAdditions.length > 0) appendParts.push(promptAdditions.join('\n\n'));
    if (historyPromptSection) appendParts.push(historyPromptSection);
    const appendSystemPrompt = appendParts.length > 0 ? appendParts.join('\n\n') : undefined;

    // Construct a resource loader that injects the configured system prompt
    const resourceLoader = new DefaultResourceLoader({
      cwd: sandboxDir,
      noExtensions: true,
      noSkills: true,
      noPromptTemplates: true,
      noThemes: true,
      systemPrompt: platformPrompt,
      appendSystemPrompt: appendSystemPrompt,
    });
    await resourceLoader.reload();

    let piSession: PiAgentSession;
    try {
      const result = await createAgentSession({
        sessionManager: SessionManager.inMemory(),
        modelRegistry: this.providerService.getRegistry(),
        model: model ?? undefined,
        cwd: sandboxDir,
        tools: [],
        customTools: allCustomTools,
        resourceLoader,
      });
      piSession = result.session;
    } catch (err) {
      this.logger.error(
        `Failed to create agent session for ${sessionId}`,
        err instanceof Error ? err.stack : String(err),
      );
      throw new Error(`Agent session creation failed for ${sessionId}: ${String(err)}`);
    }

    const listeners = new Set<(event: AgentSessionEvent) => void>();

    const unsubscribe = piSession.subscribe((event) => {
      for (const listener of listeners) {
        try {
          listener(event);
        } catch (err) {
          this.logger.error(`Event listener error in session ${sessionId}`, err);
        }
      }
    });

    const session: AgentSession = {
      id: sessionId,
      provider: providerName,
      modelId,
      piSession,
      listeners,
      unsubscribe,
      createdAt: Date.now(),
      promptCount: 0,
      channels: new Set(),
      skillPromptAdditions: promptAdditions,
      sandboxDir,
      allowedTools,
      userId: mergedOptions?.userId,
      agentConfigId: mergedOptions?.agentConfigId,
      agentName: resolvedAgentName,
      metrics: {
        tokens: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
        modelSwitches: 0,
        messageCount: 0,
        lastActivityAt: new Date().toISOString(),
      },
    };

    this.sessions.set(sessionId, session);
    this.logger.log(`Agent session ${sessionId} ready (${providerName}/${modelId})`);
    if (resolvedAgentName) {
      this.logger.log(
        `Agent session ${sessionId} using agent config "${resolvedAgentName}" (M5-001)`,
      );
    }

    return session;
  }

  /**
   * Estimate token count for a string using a rough 4-chars-per-token heuristic.
   */
  private estimateTokens(text: string): number {
    return Math.ceil(text.length / 4);
  }

  /**
   * Build a conversation history section for injection into the system prompt.
   * Implements M1-004 (history loading) and M1-005 (context window management).
   *
   * - Formats messages as a readable conversation transcript.
   * - If the full history exceeds 80% of the model's context window, older messages
   *   are summarized and only the most recent messages are kept verbatim.
   * - Summarization is a simple extractive approach (no LLM required).
   */
  private buildHistoryPromptSection(
    history: ConversationHistoryMessage[],
    contextWindow: number,
    sessionId: string,
  ): string {
    const TOKEN_BUDGET = Math.floor(contextWindow * 0.8);
    const HISTORY_HEADER = '## Conversation History (resumed session)\n\n';

    const formatMessage = (msg: ConversationHistoryMessage): string => {
      const roleLabel =
        msg.role === 'user' ? 'User' : msg.role === 'assistant' ? 'Assistant' : 'System';
      return `**${roleLabel}:** ${msg.content}`;
    };

    const formatted = history.map((msg) => formatMessage(msg));
    const fullHistory = formatted.join('\n\n');
    const fullTokens = this.estimateTokens(HISTORY_HEADER + fullHistory);

    if (fullTokens <= TOKEN_BUDGET) {
      this.logger.debug(
        `Session ${sessionId}: injecting full history (${history.length} msgs, ~${fullTokens} tokens)`,
      );
      return HISTORY_HEADER + fullHistory;
    }

    // History exceeds budget — summarize oldest messages, keep recent verbatim
    this.logger.log(
      `Session ${sessionId}: history (~${fullTokens} tokens) exceeds ${TOKEN_BUDGET} token budget; summarizing oldest messages`,
    );

    // Reserve 20% of the budget for the summary prefix, rest for verbatim messages
    const SUMMARY_RESERVE = Math.floor(TOKEN_BUDGET * 0.2);
    const verbatimBudget = TOKEN_BUDGET - SUMMARY_RESERVE;

    let verbatimTokens = 0;
    let verbatimCutIndex = history.length;
    for (let i = history.length - 1; i >= 0; i--) {
      const t = this.estimateTokens(formatted[i]!);
      if (verbatimTokens + t > verbatimBudget) break;
      verbatimTokens += t;
      verbatimCutIndex = i;
    }

    const summarizedMessages = history.slice(0, verbatimCutIndex);
    const verbatimMessages = history.slice(verbatimCutIndex);

    let summaryText = '';
    if (summarizedMessages.length > 0) {
      const topics = summarizedMessages
        .filter((m) => m.role === 'user')
        .map((m) => m.content.slice(0, 120).replace(/\n/g, ' '))
        .join('; ');
      summaryText =
        `**Previous conversation summary** (${summarizedMessages.length} messages omitted for brevity):\n` +
        `Topics discussed: ${topics || '(no user messages in summarized portion)'}`;
    }

    const verbatimSection = verbatimMessages.map((m) => formatMessage(m)).join('\n\n');

    const parts: string[] = [HISTORY_HEADER];
    if (summaryText) parts.push(summaryText);
    if (verbatimSection) parts.push(verbatimSection);

    const result = parts.join('\n\n');
    this.logger.log(
      `Session ${sessionId}: summarized ${summarizedMessages.length} messages, kept ${verbatimMessages.length} verbatim (~${this.estimateTokens(result)} tokens)`,
    );
    return result;
  }

  private resolveModel(options?: AgentSessionOptions) {
    if (!options?.provider && !options?.modelId) {
      return this.providerService.getDefaultModel() ?? null;
    }

    if (options.provider && options.modelId) {
      const model = this.providerService.findModel(options.provider, options.modelId);
      if (!model) {
        throw new Error(`Model not found: ${options.provider}/${options.modelId}`);
      }
      return model;
    }

    if (options.modelId) {
      const available = this.providerService.listAvailableModels();
      const match = available.find((m) => m.id === options.modelId);
      if (match) {
        return this.providerService.findModel(match.provider, match.id) ?? null;
      }
    }

    return this.providerService.getDefaultModel() ?? null;
  }

  getSession(sessionId: string): AgentSession | undefined {
    return this.sessions.get(sessionId);
  }

  listSessions(): SessionInfoDto[] {
    const now = Date.now();
    return Array.from(this.sessions.values()).map((s) => ({
      id: s.id,
      provider: s.provider,
      modelId: s.modelId,
      ...(s.agentName ? { agentName: s.agentName } : {}),
      createdAt: new Date(s.createdAt).toISOString(),
      promptCount: s.promptCount,
      channels: Array.from(s.channels),
      durationMs: now - s.createdAt,
      metrics: { ...s.metrics },
    }));
  }

  getSessionInfo(sessionId: string): SessionInfoDto | undefined {
    const s = this.sessions.get(sessionId);
    if (!s) return undefined;
    return {
      id: s.id,
      provider: s.provider,
      modelId: s.modelId,
      ...(s.agentName ? { agentName: s.agentName } : {}),
      createdAt: new Date(s.createdAt).toISOString(),
      promptCount: s.promptCount,
      channels: Array.from(s.channels),
      durationMs: Date.now() - s.createdAt,
      metrics: { ...s.metrics },
    };
  }

  /**
   * Record token usage for a session turn (M5-007).
   * Accumulates tokens across the session lifetime.
   */
  recordTokenUsage(
    sessionId: string,
    tokens: { input: number; output: number; cacheRead: number; cacheWrite: number; total: number },
  ): void {
    const session = this.sessions.get(sessionId);
    if (!session) return;
    session.metrics.tokens.input += tokens.input;
    session.metrics.tokens.output += tokens.output;
    session.metrics.tokens.cacheRead += tokens.cacheRead;
    session.metrics.tokens.cacheWrite += tokens.cacheWrite;
    session.metrics.tokens.total += tokens.total;
    session.metrics.lastActivityAt = new Date().toISOString();
  }

  /**
   * Record a model switch event for a session (M5-007).
   */
  recordModelSwitch(sessionId: string): void {
    const session = this.sessions.get(sessionId);
    if (!session) return;
    session.metrics.modelSwitches += 1;
    session.metrics.lastActivityAt = new Date().toISOString();
  }

  /**
   * Increment message count for a session (M5-007).
   */
  recordMessage(sessionId: string): void {
    const session = this.sessions.get(sessionId);
    if (!session) return;
    session.metrics.messageCount += 1;
    session.metrics.lastActivityAt = new Date().toISOString();
  }

  /**
   * Update the model tracked on a live session (M5-002).
   * This records the model change in the session metadata so subsequent
   * session:info emissions reflect the new model.  The Pi session itself is
   * not reconstructed — the model is used on the next createSession call for
   * the same conversationId when the session is torn down or a new one is created.
   */
  updateSessionModel(sessionId: string, modelId: string): void {
    const session = this.sessions.get(sessionId);
    if (!session) return;
    const prev = session.modelId;
    session.modelId = modelId;
    this.recordModelSwitch(sessionId);
    this.logger.log(`Session ${sessionId}: model updated ${prev} → ${modelId} (M5-002)`);
  }

  /**
   * Apply a new agent config to a live session mid-conversation (M5-003).
   * Updates agentName, agentConfigId, and modelId on the session object.
   * System prompt and tools take effect when the next session is created for
   * this conversationId (they are baked in at session creation time).
   */
  applyAgentConfig(
    sessionId: string,
    agentConfigId: string,
    agentName: string,
    modelId?: string,
  ): void {
    const session = this.sessions.get(sessionId);
    if (!session) return;
    session.agentConfigId = agentConfigId;
    session.agentName = agentName;
    if (modelId) {
      this.updateSessionModel(sessionId, modelId);
    }
    this.logger.log(
      `Session ${sessionId}: agent switched to "${agentName}" (${agentConfigId}) (M5-003)`,
    );
  }

  addChannel(sessionId: string, channel: string): void {
    const session = this.sessions.get(sessionId);
    if (session) {
      session.channels.add(channel);
    }
  }

  removeChannel(sessionId: string, channel: string): void {
    const session = this.sessions.get(sessionId);
    if (session) {
      session.channels.delete(channel);
    }
  }

  async prompt(sessionId: string, message: string): Promise<void> {
    const session = this.sessions.get(sessionId);
    if (!session) {
      throw new Error(`No agent session found: ${sessionId}`);
    }
    session.promptCount += 1;

    // Prepend session-scoped system override if present (renew TTL on each turn)
    let effectiveMessage = message;
    if (this.systemOverride) {
      const override = await this.systemOverride.get(sessionId);
      if (override) {
        effectiveMessage = `[System Override]\n${override}\n\n${message}`;
        await this.systemOverride.renew(sessionId);
        this.logger.debug(`Applied system override for session ${sessionId}`);
      }
    }

    try {
      await session.piSession.prompt(effectiveMessage);
    } catch (err) {
      this.logger.error(
        `Prompt failed for session=${sessionId}, messageLength=${message.length}`,
        err instanceof Error ? err.stack : String(err),
      );
      throw err;
    }
  }

  onEvent(sessionId: string, listener: (event: AgentSessionEvent) => void): () => void {
    const session = this.sessions.get(sessionId);
    if (!session) {
      throw new Error(`No agent session found: ${sessionId}`);
    }
    session.listeners.add(listener);
    return () => session.listeners.delete(listener);
  }

  async destroySession(sessionId: string): Promise<void> {
    const session = this.sessions.get(sessionId);
    if (!session) return;
    this.logger.log(`Destroying agent session ${sessionId}`);
    try {
      session.unsubscribe();
    } catch (err) {
      this.logger.error(`Failed to unsubscribe session ${sessionId}`, String(err));
    }
    try {
      session.piSession.dispose();
    } catch (err) {
      this.logger.error(`Failed to dispose piSession for ${sessionId}`, String(err));
    }
    session.listeners.clear();
    session.channels.clear();
    this.sessions.delete(sessionId);

    // Run GC cleanup for this session (fire and forget, errors are logged)
    this.gc.collect(sessionId).catch((err: unknown) => {
      this.logger.error(
        `GC collect failed for session ${sessionId}`,
        err instanceof Error ? err.stack : String(err),
      );
    });
  }

  async onModuleDestroy(): Promise<void> {
    this.logger.log('Shutting down all agent sessions');
    const stops = Array.from(this.sessions.keys()).map((id) => this.destroySession(id));
    const results = await Promise.allSettled(stops);
    for (const result of results) {
      if (result.status === 'rejected') {
        this.logger.error('Session shutdown failure', String(result.reason));
      }
    }
  }
}