import { Injectable } from "@nestjs/common";
import { RoomService, USER_SPEAKER_ID, type Room } from "./room.service.js";
import { SpeakingRightService } from "./speaking-right.service.js";
import { RoomGenerationService } from "./room-generation.service.js";
import { PrismaService } from "../prisma/prisma.service.js";
import { SELF_CHAT_MAX_TURNS, STALL_CHECK_WINDOW, TOPIC_TWIST_LINES, SELF_CHAT_WRAP_UP_LINES } from "./constants.js";

function normalize(text: string): string {
  return text.trim().toLowerCase();
}

// 偵測最近幾輪是否開始空轉：內容高度重複，或字數持續下降（話越講越少，快聊不下去了）。
function isStalling(recentContents: string[]): boolean {
  if (recentContents.length < STALL_CHECK_WINDOW) {
    return false;
  }
  const window = recentContents.slice(-STALL_CHECK_WINDOW);
  const normalized = window.map(normalize);
  const uniqueCount = new Set(normalized).size;
  if (uniqueCount === 1) {
    return true; // 完全重複
  }
  const lengths = window.map((text) => text.length);
  const isMonotonicDecline = lengths.every((length, index) => index === 0 || length <= lengths[index - 1]);
  return isMonotonicDecline && lengths[0] > lengths[lengths.length - 1];
}

export interface SelfChatAdvanceResult {
  ended: boolean;
  turn?: { characterId: string; content: string };
  reason?: "topic-exhausted" | "turn-cap" | "stalled-out";
}

// K-6 角色自聊：話題種子驅動、發言權機制沿用 K-4、空轉偵測注入轉折或收尾、輪數硬上限。
@Injectable()
export class SelfChatService {
  private readonly twistCounts = new Map<string, number>();

  constructor(
    private readonly prisma: PrismaService,
    private readonly room: RoomService,
    private readonly speakingRight: SpeakingRightService,
    private readonly generation: RoomGenerationService,
  ) {}

  async start(userId: string, characterIds: string[], topicSeed: string, now: Date = new Date()) {
    const room = this.room.create(userId, characterIds, "SELF_CHAT", topicSeed);
    this.twistCounts.set(room.id, 0);
    return room;
  }

  async advance(roomId: string, now: Date = new Date()): Promise<SelfChatAdvanceResult> {
    const room = this.room.get(roomId);
    if (room.mode !== "SELF_CHAT" || room.status !== "ACTIVE") {
      return { ended: true, reason: "topic-exhausted" };
    }

    if (room.turnCounter >= SELF_CHAT_MAX_TURNS) {
      return this.wrapUp(room, now);
    }

    const lastTurn = room.turns.at(-1);
    const triggerSpeakerId = lastTurn?.speakerId ?? "__SEED__";
    const triggerContent = lastTurn?.content ?? room.topicSeed ?? "今天過得怎麼樣？";
    const triggerLabel = lastTurn?.speakerLabel ?? "話題";

    const recentContents = room.turns.slice(-STALL_CHECK_WINDOW).map((turn) => turn.content);
    const twistCount = this.twistCounts.get(room.id) ?? 0;
    if (isStalling(recentContents)) {
      if (twistCount >= 2) {
        return this.wrapUp(room, now);
      }
      return this.injectTwist(room, twistCount, now);
    }

    const candidates = await this.speakingRight.decideSpeakers(room, triggerSpeakerId, triggerContent, now);
    const speakerId = candidates[0]?.characterId ?? [...room.participants.keys()][0];
    if (!speakerId) {
      return this.wrapUp(room, now);
    }

    const character = await this.prisma.client.character.findUniqueOrThrow({ where: { id: speakerId } });
    const alias = await this.prisma.client.characterAlias.findFirst({ where: { characterId: speakerId } });
    const speakerLabel = alias?.nickname || alias?.formalName || character.id;

    const reply = await this.generation.generateReply(room, speakerId, triggerSpeakerId, triggerLabel, triggerContent, {
      now,
    });
    this.room.addTurn(roomId, speakerId, speakerLabel, reply.text, now);

    return { ended: false, turn: { characterId: speakerId, content: reply.text } };
  }

  // 使用者插話：切換為群聊模式，插話內容本身視為使用者的第一則群聊訊息。
  async interject(roomId: string): Promise<Room> {
    return this.room.switchToGroup(roomId);
  }

  private async injectTwist(room: Room, twistCount: number, now: Date): Promise<SelfChatAdvanceResult> {
    const speakerId = [...room.participants.keys()][twistCount % room.participants.size];
    const character = await this.prisma.client.character.findUniqueOrThrow({ where: { id: speakerId } });
    const alias = await this.prisma.client.characterAlias.findFirst({ where: { characterId: speakerId } });
    const speakerLabel = alias?.nickname || alias?.formalName || character.id;
    const line = TOPIC_TWIST_LINES[twistCount % TOPIC_TWIST_LINES.length];

    this.room.addTurn(room.id, speakerId, speakerLabel, line, now);
    this.twistCounts.set(room.id, twistCount + 1);
    return { ended: false, turn: { characterId: speakerId, content: line } };
  }

  private async wrapUp(room: Room, now: Date): Promise<SelfChatAdvanceResult> {
    const speakerId = [...room.participants.keys()][0];
    if (speakerId) {
      const character = await this.prisma.client.character.findUniqueOrThrow({ where: { id: speakerId } });
      const alias = await this.prisma.client.characterAlias.findFirst({ where: { characterId: speakerId } });
      const speakerLabel = alias?.nickname || alias?.formalName || character.id;
      const line = SELF_CHAT_WRAP_UP_LINES[room.turnCounter % SELF_CHAT_WRAP_UP_LINES.length];
      this.room.addTurn(room.id, speakerId, speakerLabel, line, now);
    }
    this.twistCounts.delete(room.id);
    this.room.end(room.id);
    return {
      ended: true,
      reason: room.turnCounter >= SELF_CHAT_MAX_TURNS ? "turn-cap" : "stalled-out",
    };
  }
}