// ─── Runtime ────────────────────────────────────────────────────────────────
// The heart of the harness: manages session state, orchestration, tool execution,
// budgets, retries, and structured planner/executor/evaluator roles.

import { nanoid } from 'nanoid';
import { EventBus, now, type HarnessEvent, type PlanItem, type TokenUsage, type ToolCallRecord } from '../events/index.js';
import type { ProviderAdapter, ModelInvocation, Message, ToolCallRequest, ModelResult } from '../provider/index.js';
import { ToolRegistry, type ToolDef, type ToolContext } from '../tools/index.js';
import { SkillRegistry } from '../skills/index.js';
import { PolicyEngine } from '../policy/index.js';
import { MetricsCollector } from '../observability/index.js';
import { ArtifactStore } from '../artifacts/index.js';
import { Evaluator, type EvalContext } from '../evaluators/index.js';

// ─── Session State ──────────────────────────────────────────────────────────
export interface SessionState {
  id: string;
  goal: string;
  plan: PlanItem[];
  messages: Message[];
  artifacts: string[]; // artifact IDs
  provider: string;
  model: string;
  skills: string[];
  budgetUsed: { tokens: number; costUsd: number };
  status: 'running' | 'completed' | 'failed' | 'paused';
  retries: number;
  maxRetries: number;
  createdAt: string;
}

export interface RuntimeConfig {
  provider: ProviderAdapter;
  model: string;
  tools: ToolRegistry;
  skills: SkillRegistry;
  policy: PolicyEngine;
  metrics: MetricsCollector;
  artifacts: ArtifactStore;
  evaluator: Evaluator;
  eventBus: EventBus;
  systemPrompt: string;
  activeSkills: string[];
  maxRetries?: number;
  maxTurns?: number;
  budgetTokens?: number;
  budgetCostUsd?: number;
  approvalHandler?: (toolCall: ToolCallRecord) => Promise<boolean>;
}

// ─── Runtime ────────────────────────────────────────────────────────────────
export class Runtime {
  private state: SessionState;
  private config: RuntimeConfig;
  private abortController = new AbortController();
  private turn = 0;

  constructor(config: RuntimeConfig, goal: string) {
    this.config = config;
    this.state = {
      id: nanoid(),
      goal,
      plan: [],
      messages: [],
      artifacts: [],
      provider: config.provider.id,
      model: config.model,
      skills: config.activeSkills,
      budgetUsed: { tokens: 0, costUsd: 0 },
      status: 'running',
      retries: 0,
      maxRetries: config.maxRetries ?? 3,
      createdAt: now(),
    };
  }

  get sessionId(): string { return this.state.id; }
  get status(): string { return this.state.status; }

  private emit(event: HarnessEvent): void {
    this.config.eventBus.emit(event);
  }

  async run(): Promise<SessionState> {
    this.emit({ type: 'session.started', sessionId: this.state.id, goal: this.state.goal, timestamp: now() });

    // Build system message
    const skillInstructions = this.config.skills.buildInstructions(this.config.activeSkills);
    const systemMsg: Message = {
      role: 'system',
      content: [this.config.systemPrompt, skillInstructions].filter(Boolean).join('\n\n---\n\n'),
    };
    this.state.messages = [systemMsg, { role: 'user', content: this.state.goal }];

    const maxTurns = this.config.maxTurns ?? 20;

    try {
      while (this.state.status === 'running' && this.turn < maxTurns) {
        this.turn++;

        // Budget check
        const budgetCheck = this.config.policy.checkBudget(this.state.budgetUsed);
        if (!budgetCheck.ok) {
          this.emit({ type: 'budget.warning', usage: { promptTokens: 0, completionTokens: 0, totalTokens: this.state.budgetUsed.tokens, estimatedCostUsd: this.state.budgetUsed.costUsd }, limit: this.config.budgetTokens ?? 0, timestamp: now() });
          break;
        }

        // Invoke model
        const toolDefs = this.config.tools.listForModel();
        const invocation: ModelInvocation = {
          model: this.config.model,
          messages: this.state.messages,
          tools: toolDefs,
          signal: this.abortController.signal,
        };

        this.emit({ type: 'model.request.start', provider: this.config.provider.id, model: this.config.model, timestamp: now() });
        const startMs = Date.now();

        let result: ModelResult;
        try {
          result = await this.config.provider.invoke(invocation);
        } catch (err) {
          const errMsg = err instanceof Error ? err.message : String(err);
          this.emit({ type: 'error', message: `Model call failed: ${errMsg}`, timestamp: now() });
          if (this.state.retries < this.state.maxRetries) {
            this.state.retries++;
            continue;
          }
          this.state.status = 'failed';
          break;
        }

        const durationMs = Date.now() - startMs;
        this.state.budgetUsed.tokens += result.usage.totalTokens;
        this.state.budgetUsed.costUsd += result.usage.estimatedCostUsd ?? 0;

        this.emit({ type: 'model.request.end', provider: this.config.provider.id, model: this.config.model, usage: result.usage, durationMs, timestamp: now() });
        this.config.metrics.record({ timestamp: now(), type: 'model-call', provider: this.config.provider.id, model: this.config.model, durationMs, usage: result.usage, success: true });

        // Handle assistant response
        if (result.content) {
          this.emit({ type: 'model.stream.end', fullText: result.content, timestamp: now() });
        }

        this.state.messages.push({
          role: 'assistant',
          content: result.content,
          toolCalls: result.toolCalls,
        });

        // If no tool calls, we're done
        if (!result.toolCalls || result.toolCalls.length === 0) {
          this.state.status = 'completed';
          break;
        }

        // Execute tool calls
        for (const tc of result.toolCalls) {
          const toolResult = await this.executeTool(tc);
          this.state.messages.push({
            role: 'tool',
            content: typeof toolResult === 'string' ? toolResult : JSON.stringify(toolResult),
            toolCallId: tc.id,
          });
        }
      }

      // Run evaluation
      if (this.state.status === 'completed') {
        this.emit({ type: 'evaluation.started', timestamp: now() });
        const evalCtx: EvalContext = {
          sessionId: this.state.id,
          goal: this.state.goal,
          artifacts: this.config.artifacts.list().map((a) => ({ path: a.path, content: a.content, type: a.type })),
          assistantOutput: this.state.messages.filter((m) => m.role === 'assistant').map((m) => m.content).join('\n'),
          workDir: process.cwd(),
        };
        const report = await this.config.evaluator.evaluate(evalCtx);
        this.emit({ type: 'evaluation.completed', report, timestamp: now() });
      }

      this.emit({ type: 'session.completed', sessionId: this.state.id, summary: `Completed in ${this.turn} turns.`, timestamp: now() });
    } catch (err) {
      const errMsg = err instanceof Error ? err.message : String(err);
      this.state.status = 'failed';
      this.emit({ type: 'session.failed', sessionId: this.state.id, error: errMsg, timestamp: now() });
    }

    return this.state;
  }

  private async executeTool(tc: ToolCallRequest): Promise<unknown> {
    const tool = this.config.tools.getByName(tc.name);
    if (!tool) {
      const errMsg = `Unknown tool: ${tc.name}`;
      this.emit({ type: 'tool.failed', toolCallId: tc.id, error: errMsg, durationMs: 0, timestamp: now() });
      return { error: errMsg };
    }

    // Parse input
    let input: unknown;
    try {
      const raw = JSON.parse(tc.arguments);
      input = tool.inputSchema.parse(raw);
    } catch (err) {
      const errMsg = `Invalid tool input: ${err instanceof Error ? err.message : String(err)}`;
      this.emit({ type: 'tool.failed', toolCallId: tc.id, error: errMsg, durationMs: 0, timestamp: now() });
      return { error: errMsg };
    }

    // Policy check
    if (this.config.policy.isBlocked(tool.name)) {
      this.emit({ type: 'tool.denied', toolCallId: tc.id, reason: 'Tool is blocked by policy.', timestamp: now() });
      return { error: 'Tool blocked by policy.' };
    }

    const needsApproval = this.config.policy.requiresApproval(tool.permission, tool.name);
    const record: ToolCallRecord = {
      id: tc.id,
      toolId: tool.id,
      toolName: tool.name,
      input,
      status: needsApproval ? 'awaiting-approval' : 'queued',
    };
    this.emit({ type: 'tool.requested', toolCall: record, timestamp: now() });

    if (needsApproval && this.config.approvalHandler) {
      const approved = await this.config.approvalHandler(record);
      if (!approved) {
        this.emit({ type: 'tool.denied', toolCallId: tc.id, reason: 'User denied.', timestamp: now() });
        return { error: 'Tool call denied by user.' };
      }
      this.emit({ type: 'tool.approved', toolCallId: tc.id, timestamp: now() });
    }

    // Execute
    this.emit({ type: 'tool.started', toolCallId: tc.id, timestamp: now() });
    const startMs = Date.now();

    const ctx: ToolContext = {
      sessionId: this.state.id,
      workDir: process.cwd(),
      signal: this.abortController.signal,
      emit: (msg) => this.emit({ type: 'tool.progress', toolCallId: tc.id, message: msg, timestamp: now() }),
    };

    let retries = 0;
    while (retries <= tool.retries) {
      try {
        const result = await Promise.race([
          tool.execute(input, ctx),
          new Promise((_, reject) => setTimeout(() => reject(new Error('Tool timeout')), tool.timeout)),
        ]);
        const durationMs = Date.now() - startMs;
        this.emit({ type: 'tool.finished', toolCallId: tc.id, result, durationMs, timestamp: now() });
        this.config.metrics.record({ timestamp: now(), type: 'tool-call', toolName: tool.name, durationMs, success: true });
        return result;
      } catch (err) {
        retries++;
        if (retries > tool.retries) {
          const durationMs = Date.now() - startMs;
          const errMsg = err instanceof Error ? err.message : String(err);
          this.emit({ type: 'tool.failed', toolCallId: tc.id, error: errMsg, durationMs, timestamp: now() });
          this.config.metrics.record({ timestamp: now(), type: 'tool-call', toolName: tool.name, durationMs, success: false, error: errMsg });
          return { error: errMsg };
        }
        this.config.metrics.record({ timestamp: now(), type: 'retry', toolName: tool.name, durationMs: 0, success: false });
      }
    }

    return { error: 'Unexpected tool execution path.' };
  }

  pause(): void { this.state.status = 'paused'; }
  resume(): void { if (this.state.status === 'paused') this.state.status = 'running'; }
  cancel(): void { this.abortController.abort(); this.state.status = 'failed'; }
  getState(): Readonly<SessionState> { return this.state; }
}