import * as http from 'http';
import { URL } from 'url';

export type CodexReasoningEffort = 'medium' | 'high' | 'xhigh';

export interface CodexReasoningModelMap {
  opusModel?: string;
  sonnetModel?: string;
  haikuModel?: string;
  defaultModel?: string;
}

export interface CodexReasoningProxyConfig {
  upstreamBaseUrl: string;
  verbose?: boolean;
  timeoutMs?: number;
  modelMap: CodexReasoningModelMap;
  defaultEffort?: CodexReasoningEffort;
  traceFilePath?: string;
}

function isNonEmptyString(value: unknown): value is string {
  return typeof value === 'string' && value.trim().length > 0;
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return typeof value === 'object' && value !== null && !Array.isArray(value);
}

function parseModelEffortSuffix(
  model: string
): { upstreamModel: string; effort: CodexReasoningEffort } | null {
  const match = model.match(/^(.*)-(xhigh|high|medium)$/);
  if (!match) return null;
  const upstreamModel = match[1]?.trim();
  const effort = match[2] as CodexReasoningEffort;
  if (!upstreamModel) return null;
  return { upstreamModel, effort };
}

const EFFORT_RANK: Record<CodexReasoningEffort, number> = {
  medium: 1,
  high: 2,
  xhigh: 3,
};

function minEffort(a: CodexReasoningEffort, b: CodexReasoningEffort): CodexReasoningEffort {
  return EFFORT_RANK[a] <= EFFORT_RANK[b] ? a : b;
}

export function buildCodexModelEffortMap(
  models: CodexReasoningModelMap,
  defaultEffort: CodexReasoningEffort = 'medium'
): Map<string, CodexReasoningEffort> {
  const map = new Map<string, CodexReasoningEffort>();

  const upsertMin = (model: string | undefined, effort: CodexReasoningEffort) => {
    if (!isNonEmptyString(model)) return;
    const existing = map.get(model);
    map.set(model, existing ? minEffort(existing, effort) : effort);
  };

  upsertMin(models.defaultModel, 'xhigh');
  upsertMin(models.opusModel, 'xhigh');
  upsertMin(models.sonnetModel, 'high');
  upsertMin(models.haikuModel, 'medium');

  if (map.size === 0 && isNonEmptyString(models.defaultModel)) {
    map.set(models.defaultModel, defaultEffort);
  }

  return map;
}

export function getEffortForModel(
  model: string | null,
  modelEffort: Map<string, CodexReasoningEffort>,
  defaultEffort: CodexReasoningEffort
): CodexReasoningEffort {
  if (!model) return defaultEffort;
  return modelEffort.get(model) ?? defaultEffort;
}

export function injectReasoningEffortIntoBody(
  body: unknown,
  effort: CodexReasoningEffort
): unknown {
  if (!isRecord(body)) return body;

  // OpenAI Responses API knob: reasoning: { effort: "..." }
  // Always override effort (user expectation).
  const existingReasoning = isRecord(body.reasoning) ? body.reasoning : {};
  return {
    ...body,
    reasoning: {
      ...existingReasoning,
      effort,
    },
  };
}

export class CodexReasoningProxy {
  private server: http.Server | null = null;
  private port: number | null = null;
  private readonly config: Required<
    Pick<
      CodexReasoningProxyConfig,
      'upstreamBaseUrl' | 'verbose' | 'timeoutMs' | 'defaultEffort' | 'traceFilePath'
    >
  > &
    Pick<CodexReasoningProxyConfig, 'modelMap'>;
  private readonly modelEffort: Map<string, CodexReasoningEffort>;
  private readonly recent: Array<{
    at: string;
    model: string | null;
    upstreamModel: string | null;
    effort: CodexReasoningEffort;
    path: string;
  }> = [];
  private readonly counts: Record<CodexReasoningEffort, number> = { medium: 0, high: 0, xhigh: 0 };

  constructor(config: CodexReasoningProxyConfig) {
    this.config = {
      upstreamBaseUrl: config.upstreamBaseUrl,
      verbose: config.verbose ?? false,
      timeoutMs: config.timeoutMs ?? 120000,
      modelMap: config.modelMap,
      defaultEffort: config.defaultEffort ?? 'medium',
      traceFilePath: config.traceFilePath ?? '',
    };
    this.modelEffort = buildCodexModelEffortMap(this.config.modelMap, this.config.defaultEffort);
  }

  private log(message: string): void {
    if (this.config.verbose) {
      console.error(`[codex-reasoning-proxy] ${message}`);
    }
  }

  private trace(line: string): void {
    if (!this.config.traceFilePath) return;
    try {
      // Intentionally best-effort: tracing must never break requests.
      const fs = require('fs') as typeof import('fs');
      const pathMod = require('path') as typeof import('path');

      // Security: validate trace path against safe directories to prevent path traversal
      const resolvedPath = pathMod.resolve(this.config.traceFilePath);
      const home = process.env.HOME || process.env.USERPROFILE || '';
      const safeDirs = ['/tmp/', '/var/log/', home ? `${home}/.ccs/` : ''];
      const isSafe = safeDirs.some((base) => base && resolvedPath.startsWith(base));
      if (!isSafe) {
        this.log(`[SECURITY] Trace path rejected (outside allowed dirs): ${resolvedPath}`);
        return;
      }

      const dir = pathMod.dirname(resolvedPath);
      fs.mkdirSync(dir, { recursive: true });
      fs.appendFileSync(resolvedPath, line + '\n');
    } catch {
      // ignore
    }
  }

  private record(
    model: string | null,
    upstreamModel: string | null,
    effort: CodexReasoningEffort,
    path: string
  ): void {
    this.counts[effort] += 1;
    this.recent.push({ at: new Date().toISOString(), model, upstreamModel, effort, path });
    if (this.recent.length > 50) this.recent.shift();
  }

  async start(): Promise<number> {
    if (this.server) return this.port ?? 0;

    return new Promise((resolve, reject) => {
      this.server = http.createServer((req, res) => {
        void this.handleRequest(req, res);
      });

      this.server.listen(0, '127.0.0.1', () => {
        const address = this.server?.address();
        this.port = typeof address === 'object' && address ? address.port : 0;
        resolve(this.port);
      });

      this.server.on('error', (err) => reject(err));
    });
  }

  stop(): void {
    if (!this.server) return;
    this.server.close();
    this.server = null;
    this.port = null;
  }

  private readBody(req: http.IncomingMessage): Promise<string> {
    return new Promise((resolve, reject) => {
      const chunks: Buffer[] = [];
      const maxSize = 10 * 1024 * 1024; // 10MB
      let total = 0;

      req.on('data', (chunk: Buffer) => {
        total += chunk.length;
        if (total > maxSize) {
          req.destroy(); // Signal client to stop sending
          reject(new Error('Request body too large (max 10MB)'));
          return;
        }
        chunks.push(chunk);
      });

      req.on('end', () => resolve(Buffer.concat(chunks).toString('utf8')));
      req.on('error', reject);
    });
  }

  private async handleRequest(req: http.IncomingMessage, res: http.ServerResponse): Promise<void> {
    const method = req.method || 'GET';
    const requestPath = req.url || '/';
    const upstreamBase = new URL(this.config.upstreamBaseUrl);
    const fullUpstreamUrl = new URL(requestPath, upstreamBase);

    this.log(`${method} ${requestPath} → ${fullUpstreamUrl.href}`);

    // Debug/status endpoint (no upstream call). Does not expose prompt content.
    if (method.toUpperCase() === 'GET' && requestPath === '/__ccs/reasoning') {
      res.writeHead(200, { 'Content-Type': 'application/json' });
      res.end(
        JSON.stringify({
          counts: this.counts,
          recent: this.recent,
          modelMap: this.config.modelMap,
          defaultEffort: this.config.defaultEffort,
        })
      );
      return;
    }

    // Only buffer+rewrite JSON bodies; otherwise just proxy as-is.
    const contentType = String(req.headers['content-type'] || '');
    const isJson = contentType.includes('application/json');
    const shouldRewrite = isJson && ['POST', 'PUT', 'PATCH'].includes(method.toUpperCase());

    try {
      if (!shouldRewrite) {
        await this.forwardRaw(req, res, fullUpstreamUrl);
        return;
      }

      const rawBody = await this.readBody(req);
      let parsed: unknown;
      try {
        parsed = rawBody.length ? JSON.parse(rawBody) : {};
      } catch {
        res.writeHead(400, { 'Content-Type': 'application/json' });
        res.end(JSON.stringify({ error: 'Invalid JSON in request body' }));
        return;
      }

      const originalModel =
        isRecord(parsed) && typeof parsed.model === 'string' ? parsed.model : null;

      // Support "model aliases" like `gpt-5.2-codex-xhigh` by translating to:
      // - upstream model: `gpt-5.2-codex`
      // - reasoning.effort: `xhigh`
      //
      // This allows tier→effort mapping without inventing upstream model IDs.
      const suffixParsed = originalModel ? parseModelEffortSuffix(originalModel) : null;
      const upstreamModel = suffixParsed?.upstreamModel ?? originalModel;
      const effort =
        suffixParsed?.effort ??
        getEffortForModel(originalModel, this.modelEffort, this.config.defaultEffort);

      const withUpstreamModel =
        upstreamModel && isRecord(parsed) ? { ...parsed, model: upstreamModel } : parsed;
      const rewritten = injectReasoningEffortIntoBody(withUpstreamModel, effort);

      this.record(originalModel, upstreamModel, effort, requestPath);
      this.trace(
        `[${new Date().toISOString()}] model=${originalModel ?? 'null'} upstreamModel=${
          upstreamModel ?? 'null'
        } effort=${effort} path=${requestPath}`
      );

      await this.forwardJson(req, res, fullUpstreamUrl, rewritten);
    } catch (error) {
      const err = error as Error;
      if (!res.headersSent) {
        res.writeHead(502, { 'Content-Type': 'application/json' });
      }
      res.end(JSON.stringify({ error: err.message }));
    }
  }

  private buildForwardHeaders(
    originalHeaders: http.IncomingHttpHeaders,
    bodyString?: string
  ): http.OutgoingHttpHeaders {
    const headers: http.OutgoingHttpHeaders = {};

    // RFC 7230 hop-by-hop headers that should not be forwarded
    const hopByHop = new Set([
      'host',
      'content-length',
      'connection',
      'transfer-encoding',
      'keep-alive',
      'proxy-authenticate',
      'proxy-authorization',
      'te',
      'trailer',
      'upgrade',
    ]);

    for (const [key, value] of Object.entries(originalHeaders)) {
      if (!value) continue;
      const lower = key.toLowerCase();
      if (hopByHop.has(lower)) continue;
      headers[key] = value;
    }

    if (bodyString !== undefined) {
      headers['Content-Type'] = headers['Content-Type'] || 'application/json';
      headers['Content-Length'] = Buffer.byteLength(bodyString);
    }

    return headers;
  }

  private forwardRaw(
    originalReq: http.IncomingMessage,
    clientRes: http.ServerResponse,
    upstreamUrl: URL
  ): Promise<void> {
    return new Promise((resolve, reject) => {
      const upstreamReq = http.request(
        {
          protocol: upstreamUrl.protocol,
          hostname: upstreamUrl.hostname,
          port: upstreamUrl.port,
          path: upstreamUrl.pathname + upstreamUrl.search,
          method: originalReq.method,
          timeout: this.config.timeoutMs,
          headers: this.buildForwardHeaders(originalReq.headers),
        },
        (upstreamRes) => {
          clientRes.writeHead(upstreamRes.statusCode || 200, upstreamRes.headers);
          upstreamRes.pipe(clientRes);
          upstreamRes.on('end', () => resolve());
          upstreamRes.on('error', reject);
        }
      );

      upstreamReq.on('timeout', () => upstreamReq.destroy(new Error('Upstream request timeout')));
      upstreamReq.on('error', reject);
      originalReq.pipe(upstreamReq);
    });
  }

  private forwardJson(
    originalReq: http.IncomingMessage,
    clientRes: http.ServerResponse,
    upstreamUrl: URL,
    body: unknown
  ): Promise<void> {
    return new Promise((resolve, reject) => {
      const bodyString = JSON.stringify(body);
      const upstreamReq = http.request(
        {
          protocol: upstreamUrl.protocol,
          hostname: upstreamUrl.hostname,
          port: upstreamUrl.port,
          path: upstreamUrl.pathname + upstreamUrl.search,
          method: originalReq.method,
          timeout: this.config.timeoutMs,
          headers: this.buildForwardHeaders(originalReq.headers, bodyString),
        },
        (upstreamRes) => {
          clientRes.writeHead(upstreamRes.statusCode || 200, upstreamRes.headers);
          upstreamRes.pipe(clientRes);
          upstreamRes.on('end', () => resolve());
          upstreamRes.on('error', reject);
        }
      );

      upstreamReq.on('timeout', () => upstreamReq.destroy(new Error('Upstream request timeout')));
      upstreamReq.on('error', reject);
      upstreamReq.write(bodyString);
      upstreamReq.end();
    });
  }
}