import { NextResponse } from "next/server";
import { z } from "zod";
import type {
  ParsedCommand,
  ResolvedChatContext,
  WorkPackage,
} from "@/lib/work-package-types";
import { SIMULATED_EXECUTION_DISCLAIMER } from "@/lib/work-package-types";
import { runMockAgent } from "@/lib/mock-agent";
import type { ChatResponse } from "@/lib/board-actions";
import {
  buildExecutionPrompt,
  buildRealExecutionResponse,
  REAL_AUTOMATION_DISCLAIMER,
} from "@/lib/automation-agent";
import { generateLlmText } from "@/lib/llm-client";
import {
  DEFAULT_LLM_BASE_URL,
  DEFAULT_LLM_MODEL,
  isLlmConfigReady,
  normalizeLlmConfig,
} from "@/lib/llm-config";
import { compactTracePreview } from "@/lib/chat-trace";
import { recoverInvalidLlmResponse } from "@/lib/llm-response";
import {
  buildResolvedContext,
  buildThinkingSummary,
} from "@/lib/chat-request-context";
import { readFile } from "node:fs/promises";
import path from "node:path";

const ChatMessageSchema = z.object({
  role: z.enum(["user", "assistant", "system"]),
  content: z.string(),
});

const ParsedCommandSchema = z.object({
  referencedPackageName: z.string().optional(),
  mode: z.enum(["ask", "plan", "change", "execute"]).optional(),
  instruction: z.string(),
});

const OutputTypeSchema = z.enum([
  "text",
  "table",
  "code",
  "image_prompt",
  "design_brief",
  "test_case",
  "checklist",
  "risk_table",
  "bom",
  "sbom",
  "feature_list",
]);

const WorkPackageOutputSchema = z.object({
  id: z.string(),
  title: z.string(),
  type: OutputTypeSchema,
  content: z.string(),
  createdAt: z.string(),
  sourceTaskId: z.string().nullable().optional(),
  executionMode: z.enum(["simulated", "real"]),
  disclaimer: z.string(),
});

const BoardActionSchema = z.object({
  type: z.enum(["none", "create", "update", "append_output", "replace_all"]),
  workPackageId: z.string().nullable(),
  fields: z.record(z.string(), z.unknown()).optional(),
  output: WorkPackageOutputSchema.optional(),
});

const LlmJsonSchema = z.object({
  assistantMessage: z.string(),
  boardAction: BoardActionSchema,
});

const ChatRequestSchema = z.object({
  messages: z.array(ChatMessageSchema),
  workPackages: z.array(z.any()),
  selectedWorkPackageId: z.string().nullable().optional(),
  parsedCommand: ParsedCommandSchema.optional(),
  llmConfig: z
    .object({
      apiKey: z.string().optional(),
      baseUrl: z.string().optional(),
      model: z.string().optional(),
    })
    .optional(),
});

function summarizeThinking(args: {
  context: ResolvedChatContext;
  model?: string;
  note?: string;
}) {
  return buildThinkingSummary(args);
}

function withRouteMetadata(
  payload: ChatResponse,
  args: {
    context: ResolvedChatContext;
    model?: string;
    note?: string;
  },
): ChatResponse {
  return {
    ...payload,
    resolvedContext: args.context,
    thinkingSummary: summarizeThinking(args),
  };
}

function guardBoardActionForContext(args: {
  payload: z.infer<typeof LlmJsonSchema>;
  context: ResolvedChatContext;
}) {
  const { payload, context } = args;
  const action = payload.boardAction;
  if (!action) {
    return { payload, note: undefined as string | undefined };
  }

  if (context.boardMutationPolicy === "none" && action.type !== "none") {
    return {
      payload: {
        ...payload,
        boardAction: { type: "none", workPackageId: null },
      },
      note: "Blocked a board update for an ask-only request.",
    };
  }

  if (context.boardMutationPolicy !== "selected_package_only") {
    return { payload, note: undefined as string | undefined };
  }

  const invalidScopedTarget =
    action.type === "replace_all" ||
    action.type === "create" ||
    ((action.type === "update" || action.type === "append_output") &&
      action.workPackageId !== context.workPackageId);

  if (invalidScopedTarget) {
    return {
      payload: {
        ...payload,
        boardAction: { type: "none", workPackageId: null },
      },
      note: "Blocked a board update that targeted a different work package.",
    };
  }

  return { payload, note: undefined as string | undefined };
}

function safeJsonParse(text: string): unknown {
  try {
    return JSON.parse(text);
  } catch {
    // Try extracting the first JSON object.
    const start = text.indexOf("{");
    const end = text.lastIndexOf("}");
    if (start !== -1 && end !== -1 && end > start) {
      const slice = text.slice(start, end + 1);
      return JSON.parse(slice);
    }
    throw new Error("Invalid JSON");
  }
}

async function loadSystemPrompt(): Promise<string> {
  // Prefer repo root prompt; fall back to the planning pack copy.
  const rootPrompt = path.join(process.cwd(), "prompts/work-package-system-prompt.md");
  try {
    return await readFile(rootPrompt, "utf8");
  } catch {
    const packPrompt = path.join(
      process.cwd(),
      "agentic_pm_demo_codex_plans/prompts/work-package-system-prompt.md",
    );
    return await readFile(packPrompt, "utf8");
  }
}

function ensureExecuteDisclaimer(payload: z.infer<typeof LlmJsonSchema>) {
  const out = payload.boardAction?.output;
  if (!out) return payload;
  if (!out.disclaimer) {
    out.disclaimer =
      out.executionMode === "real"
        ? REAL_AUTOMATION_DISCLAIMER
        : SIMULATED_EXECUTION_DISCLAIMER;
  }
  return payload;
}

function resolveLlmConfig(
  llmConfig?: { apiKey?: string; baseUrl?: string; model?: string } | null,
) {
  if (isLlmConfigReady(llmConfig)) {
    return normalizeLlmConfig(llmConfig);
  }

  const fromEnv = normalizeLlmConfig({
    apiKey: process.env.LLM_API_KEY,
    baseUrl: process.env.LLM_API_BASE_URL || DEFAULT_LLM_BASE_URL,
    model: process.env.LLM_MODEL || DEFAULT_LLM_MODEL,
  });

  return isLlmConfigReady(fromEnv) ? fromEnv : null;
}

function latestUserText(messages: Array<{ role: string; content: string }>) {
  return [...messages].reverse().find((message) => message.role === "user")?.content;
}

function buildMockFallbackResponse(args: {
  messages: Array<{ role: "user" | "assistant" | "system"; content: string }>;
  workPackages: WorkPackage[];
  selectedWorkPackageId?: string | null;
  parsedCommand?: ParsedCommand;
}) {
  const { messages, workPackages, selectedWorkPackageId, parsedCommand } = args;
  if (!parsedCommand?.mode) {
    return undefined;
  }

  return runMockAgent({
    messages: messages.map((message, index) => ({
      id: `fallback-msg-${index}`,
      role: message.role === "system" ? "assistant" : message.role,
      content: message.content,
      createdAt: new Date().toISOString(),
    })),
    workPackages,
    selectedWorkPackageId: selectedWorkPackageId ?? undefined,
    parsedCommand,
  });
}

export async function POST(req: Request) {
  const json = await req.json().catch(() => null);
  const parsedReq = ChatRequestSchema.safeParse(json);
  if (!parsedReq.success) {
    return NextResponse.json(
      { assistantMessage: "Bad request.", boardAction: { type: "none", workPackageId: null } },
      { status: 400 },
    );
  }

  const {
    messages,
    workPackages,
    selectedWorkPackageId,
    parsedCommand,
    llmConfig,
  } = parsedReq.data;

  const resolvedConfig = resolveLlmConfig(llmConfig);
  const currentWorkPackages = workPackages as WorkPackage[];
  const selectedWp =
    currentWorkPackages.find((wp) => wp.id === selectedWorkPackageId) ?? null;
  const mockContext = buildResolvedContext({
    parsedCommand: parsedCommand as ParsedCommand | undefined,
    shouldAutomateBoard: !parsedCommand?.mode,
    selectedWorkPackage: selectedWp,
    provider: "mock",
  });
  const liveContext = buildResolvedContext({
    parsedCommand: parsedCommand as ParsedCommand | undefined,
    shouldAutomateBoard: !parsedCommand?.mode,
    selectedWorkPackage: selectedWp,
    provider: "live",
  });

  // Mock-first: if no key is present, stay local.
  if (!resolvedConfig) {
    const resp = runMockAgent({
      messages: messages.map((message, index) => ({
        id: `server-msg-${index}`,
        role: message.role === "system" ? "assistant" : message.role,
        content: message.content,
        createdAt: new Date().toISOString(),
      })),
      workPackages: workPackages as WorkPackage[],
      selectedWorkPackageId: selectedWorkPackageId ?? undefined,
      parsedCommand: parsedCommand as ParsedCommand | undefined,
    });
    return NextResponse.json(
      withRouteMetadata(
        {
          ...resp,
          trace: {
            provider: "mock",
            model: "mock-agent",
            requestPreview: compactTracePreview(
              latestUserText(messages) || "No user message.",
            ),
            responsePreview: compactTracePreview(resp.assistantMessage),
          },
        } satisfies ChatResponse,
        {
          context: mockContext,
        },
      ),
    );
  }

  const systemPrompt = await loadSystemPrompt();
  const userText = latestUserText(messages) || "";

  if (parsedCommand?.mode === "execute") {
    const targetPackage =
      selectedWp ??
      currentWorkPackages.find(
        (wp) =>
          wp.title.toLowerCase() ===
            parsedCommand.referencedPackageName?.toLowerCase() ||
          wp.shortName.toLowerCase() ===
            parsedCommand.referencedPackageName?.toLowerCase(),
      );

    if (!targetPackage) {
      return NextResponse.json(
        {
          assistantMessage: "No matching work package was found for execution.",
          boardAction: { type: "none", workPackageId: null },
        } satisfies ChatResponse,
        { status: 200 },
      );
    }

    try {
      const llmResult = await generateLlmText({
        config: resolvedConfig,
        systemPrompt:
          "You are an expert product development PM and systems engineer. Generate complete, practical, package-specific deliverables in markdown.",
        userPrompt: buildExecutionPrompt({
          workPackage: targetPackage,
          workPackages: currentWorkPackages,
          productIdea: userText,
          instruction: parsedCommand.instruction,
        }),
        temperature: 0.2,
        maxTokens: 2800,
      });

      return NextResponse.json(
        withRouteMetadata(
          {
            ...buildRealExecutionResponse({
              workPackage: targetPackage,
              generatedContent: llmResult.text,
              instruction: parsedCommand.instruction,
              productIdea: userText,
            }),
            trace: {
              provider: "live",
              model: resolvedConfig.model,
              endpoint: llmResult.endpoint,
              requestPreview: llmResult.requestPreview,
              responsePreview: llmResult.responsePreview,
            },
          } satisfies ChatResponse,
          {
            context: liveContext,
            model: resolvedConfig.model,
          },
        ),
        { status: 200 },
      );
    } catch (err) {
      return NextResponse.json(
        withRouteMetadata(
          {
            assistantMessage: `Live execution failed. (No board changes applied.)\n\n${String(err)}`,
            boardAction: { type: "none", workPackageId: null },
            trace: {
              provider: "live",
              model: resolvedConfig.model,
              responsePreview: compactTracePreview(String(err)),
            },
          } satisfies ChatResponse,
          {
            context: liveContext,
            model: resolvedConfig.model,
            note: "Provider call failed; preserving the package-scoped fallback.",
          },
        ),
        { status: 200 },
      );
    }
  }

  const contextBlock = JSON.stringify(
    {
      selectedWorkPackageId: selectedWorkPackageId ?? null,
      selectedWorkPackage: selectedWp,
      parsedCommand: parsedCommand ?? null,
      workPackages: currentWorkPackages,
    },
    null,
    2,
  );

  const conversationBlock = messages
    .map((message) => `${message.role.toUpperCase()}: ${message.content}`)
    .join("\n\n");

  try {
    const llmResult = await generateLlmText({
      config: resolvedConfig,
      systemPrompt,
      userPrompt: [
        "Return JSON ONLY that matches the required contract.",
        "Use the context to decide whether and how the board should change.",
        `Context:\n${contextBlock}`,
        `Conversation:\n${conversationBlock}`,
      ].join("\n\n"),
      temperature: 0.2,
      maxTokens: 2200,
      responseFormat: "json_object",
    });

    if (!llmResult.text) {
      return NextResponse.json(
        withRouteMetadata(
          {
            assistantMessage: "LLM returned an empty response.",
            boardAction: { type: "none", workPackageId: null },
            trace: {
              provider: "live",
              model: resolvedConfig.model,
              endpoint: llmResult.endpoint,
              requestPreview: llmResult.requestPreview,
            },
          } satisfies ChatResponse,
          {
            context: liveContext,
            model: resolvedConfig.model,
            note: "Provider returned an empty response; no board mutation was applied.",
          },
        ),
        { status: 200 },
      );
    }

    let parsedJson: unknown;
    try {
      parsedJson = safeJsonParse(llmResult.text);
    } catch {
      const recovered = recoverInvalidLlmResponse({
        rawText: llmResult.text,
        parsedCommand: parsedCommand as ParsedCommand | undefined,
        fallbackResponse: buildMockFallbackResponse({
          messages,
          workPackages: currentWorkPackages,
          selectedWorkPackageId,
          parsedCommand: parsedCommand as ParsedCommand | undefined,
        }),
      });
      return NextResponse.json(
        withRouteMetadata(
          {
            ...recovered,
            trace: {
              provider: "live",
              model: resolvedConfig.model,
              endpoint: llmResult.endpoint,
              requestPreview: llmResult.requestPreview,
              responsePreview: llmResult.responsePreview,
            },
          } satisfies ChatResponse,
          {
            context: liveContext,
            model: resolvedConfig.model,
            note:
              parsedCommand?.mode === "ask"
                ? "Provider returned non-JSON output; preserving assistant text and skipping board mutation."
                : "Provider returned non-JSON output; preserving the package-scoped fallback.",
          },
        ),
        { status: 200 },
      );
    }

    const validated = LlmJsonSchema.safeParse(parsedJson);
    if (!validated.success) {
      const recovered = recoverInvalidLlmResponse({
        rawText: llmResult.text,
        parsedCommand: parsedCommand as ParsedCommand | undefined,
        fallbackResponse: buildMockFallbackResponse({
          messages,
          workPackages: currentWorkPackages,
          selectedWorkPackageId,
          parsedCommand: parsedCommand as ParsedCommand | undefined,
        }),
      });
      return NextResponse.json(
        withRouteMetadata(
          {
            ...recovered,
            trace: {
              provider: "live",
              model: resolvedConfig.model,
              endpoint: llmResult.endpoint,
              requestPreview: llmResult.requestPreview,
              responsePreview: llmResult.responsePreview,
            },
          } satisfies ChatResponse,
          {
            context: liveContext,
            model: resolvedConfig.model,
            note:
              parsedCommand?.mode === "ask"
                ? "Provider returned invalid JSON; preserving assistant text and skipping board mutation."
                : "Provider returned invalid JSON; preserving the package-scoped fallback.",
          },
        ),
        { status: 200 },
      );
    }

    const payload = ensureExecuteDisclaimer(validated.data);
    const guarded = guardBoardActionForContext({
      payload,
      context: liveContext,
    });
    const guardedResponse: ChatResponse = {
      assistantMessage: guarded.payload.assistantMessage,
      boardAction: guarded.payload.boardAction as ChatResponse["boardAction"],
      trace: {
        provider: "live",
        model: resolvedConfig.model,
        endpoint: llmResult.endpoint,
        requestPreview: llmResult.requestPreview,
        responsePreview: llmResult.responsePreview,
      },
    };

    return NextResponse.json(
      withRouteMetadata(guardedResponse, {
        context: liveContext,
        model: resolvedConfig.model,
        note: guarded.note,
      }),
    );
  } catch (err) {
    const fallback = buildMockFallbackResponse({
      messages,
      workPackages: currentWorkPackages,
      selectedWorkPackageId,
      parsedCommand: parsedCommand as ParsedCommand | undefined,
    });

    if (fallback) {
      return NextResponse.json(
        withRouteMetadata(
          {
            ...fallback,
            trace: {
              provider: "live",
              model: resolvedConfig.model,
              responsePreview: compactTracePreview(String(err)),
            },
          } satisfies ChatResponse,
          {
            context: liveContext,
            model: resolvedConfig.model,
            note: "Provider call failed; preserving the package-scoped fallback.",
          },
        ),
        { status: 200 },
      );
    }

    return NextResponse.json(
      withRouteMetadata(
        {
          assistantMessage: `Network or parsing error calling LLM. (No board changes applied.)\n\n${String(err)}`,
          boardAction: { type: "none", workPackageId: null },
          trace: {
            provider: "live",
            model: resolvedConfig.model,
            responsePreview: compactTracePreview(String(err)),
          },
        } satisfies ChatResponse,
        {
          context: liveContext,
          model: resolvedConfig.model,
          note: "Provider call failed; no safe board fallback was available.",
        },
      ),
      { status: 200 },
    );
  }
}