import type { ExtensionAPI, ExtensionContext } from "@earendil-works/pi-coding-agent";
import { writeFile } from "node:fs/promises";
import { join } from "node:path";

// ── Types ──────────────────────────────────────────────────────────

type TutorMode = "bilingual" | "english-only";
type Difficulty = "A2" | "B1" | "B2" | "C1";

interface TutorState {
  mode: TutorMode;
  strictMode: boolean;
  difficulty: Difficulty;
}

// ── Constants ──────────────────────────────────────────────────────

const STATE_TYPE = "english-tutor-state";
const DIFFICULTIES: Difficulty[] = ["A2", "B1", "B2", "C1"];

const DEFAULT_STATE: TutorState = {
  mode: "bilingual",
  strictMode: false,
  difficulty: "B1",
};

// ── CEFR Guidelines ────────────────────────────────────────────────

const CEFR_GUIDELINES: Record<Difficulty, string> = {
  A2: `- Use simple sentences (8–15 words)
- Stick to common vocabulary (top 1000–1500 words)
- Use only basic tenses: present simple, past simple, present continuous
- Avoid idioms, phrasal verbs, passive voice, complex clauses
- Define any word above A2 level in simple English`,

  B1: `- Use moderate sentences (12–20 words) with connectors (because, however, although)
- Use everyday vocabulary with some topic-specific terms
- Add present perfect, type-1 conditionals, and basic modals (should, might)
- Introduce 1–2 common phrasal verbs at a time
- Explain less common vocabulary`,

  B2: `- Use natural conversational English with varied sentence length
- Broader vocabulary including professional and academic terms
- Full grammar range: all conditionals, passive voice, relative clauses
- Use phrasal verbs and common idioms naturally
- Express opinions, agreement/disagreement, and hypotheticals`,

  C1: `- Use native-like fluency with sophisticated vocabulary
- Complex sentence structures with subtle meaning distinctions
- Idiomatic expressions, humor, wordplay, and cultural references
- Academic, professional, and literary language as appropriate
- Fine shades of meaning: "reluctant" vs "hesitant" vs "unwilling"`,
};

// ── Helpers ────────────────────────────────────────────────────────

function hasChinese(text: string): boolean {
  return /[\u4e00-\u9fff\u3400-\u4dbf]/.test(text);
}

function extractText(content: unknown): string {
  if (typeof content === "string") return content;
  if (Array.isArray(content)) {
    return (content as Array<{ type: string; text?: string }>)
      .filter((c) => c.type === "text" && c.text)
      .map((c) => c.text!)
      .join("\n");
  }
  return "";
}

function loadState(ctx: ExtensionContext): TutorState {
  for (const entry of ctx.sessionManager.getEntries()) {
    if (entry.type === "custom" && entry.customType === STATE_TYPE) {
      const data = entry.data as Partial<TutorState> | undefined;
      if (data) return { ...DEFAULT_STATE, ...data };
    }
  }
  return { ...DEFAULT_STATE };
}

function buildPrompt(mode: TutorMode, difficulty: Difficulty): string {
  const cefr = CEFR_GUIDELINES[difficulty];

  if (mode === "bilingual") {
    return `
## 🇬🇧🇨🇳 English Tutor — BILINGUAL MODE (active until mode changes)

You are an English conversation tutor. Follow these rules STRICTLY for EVERY response.

### MAIN RESPONSE FORMAT
Every response MUST include BOTH languages in clearly separated sections:

Your natural English response here (conversational, friendly, at CEFR ${difficulty}).

---
你的中文翻译（自然的中文，帮助用户理解英文部分）

### DIFFICULTY: ${difficulty}
${cefr}

### CORRECTIONS (when user makes an error)
Add after your main response, ONLY for significant errors:
💡 "user's phrase" → "corrected phrase" — brief reason in Chinese

### VOCABULARY (every 3–4 exchanges, suggest 1 word)
📝 "word" (中文释义) — example sentence showing natural usage

### CRITICAL RULES
- ALWAYS provide BOTH languages for the main response
- NEVER skip the Chinese translation in bilingual mode
- Be encouraging and supportive — build confidence, not anxiety
- If the user writes in Chinese, gently encourage: "Try saying this in English! I can help you find the right words."
- Keep responses concise: 3–8 sentences per language
`.trim();
  }

  return `
## 🇬🇧 English Tutor — ENGLISH-ONLY MODE (active until mode changes)

You are an English conversation tutor. Follow these rules STRICTLY for EVERY response.

### RESPONSE RULES
- Respond ONLY in English — NO Chinese, not even a single character
- Use natural, conversational English at CEFR ${difficulty}

### DIFFICULTY: ${difficulty}
${cefr}

### CORRECTIONS (when user makes an error)
Add after your main response, ONLY for significant errors:
💡 "user's phrase" → "corrected phrase" — brief reason in simple English

### VOCABULARY (every 3–4 exchanges, suggest 1 word)
📝 "word" — simple English definition + example sentence

### CRITICAL RULES
- NEVER use Chinese — not for definitions, not for explanations
- If the user writes in Chinese, gently remind in English: "Please try in English! If you're stuck, tell me what you want to say and I'll help you express it."
- Be encouraging and supportive
- Keep responses concise: 3–8 sentences
`.trim();
}

// ── Extension Entry ────────────────────────────────────────────────

export default function (pi: ExtensionAPI) {
  let state: TutorState = { ...DEFAULT_STATE };

  // ── Persist state helper ──
  function save() {
    pi.appendEntry(STATE_TYPE, state);
  }

  // ── UI helpers ──
  function updateStatus(ctx: ExtensionContext) {
    const modeLabel = state.mode === "bilingual" ? "🇬🇧🇨🇳 双语" : "🇬🇧 纯英";
    const strictIcon = state.strictMode ? "🔒" : "🔓";
    ctx.ui.setStatus("english-tutor", `${strictIcon} ${modeLabel} | ${state.difficulty}`);
  }

  function updateWidget(ctx: ExtensionContext) {
    const modeLabel = state.mode === "bilingual" ? "中英双语" : "纯英文";
    const strictLabel = state.strictMode ? "严格" : "宽松";
    ctx.ui.setWidget("english-tutor", [
      `🇬🇧 English Tutor | ${modeLabel} | ${state.difficulty} | ${strictLabel}`,
      `Ctrl+Shift+E 切换模式 | Ctrl+Shift+S 严格切换 | /english help`,
    ], { placement: "aboveEditor" });
  }

  // ── Session Start ────────────────────────────────────────────────
  pi.on("session_start", async (_event, ctx) => {
    state = loadState(ctx);
    updateStatus(ctx);
    updateWidget(ctx);
    ctx.ui.notify(
      `🇬🇧 English Tutor loaded — ${state.mode} | ${state.difficulty} | ${state.strictMode ? "strict" : "gentle"}`,
      "info",
    );
  });

  // ── Input Guard ──────────────────────────────────────────────────
  pi.on("input", async (event, ctx) => {
    // Skip if no Chinese characters
    if (!hasChinese(event.text)) return { action: "continue" };

    // Skip if this is a slash command (starts with /)
    if (event.text.trim().startsWith("/")) return { action: "continue" };

    if (state.strictMode) {
      const words = event.text.match(/[\u4e00-\u9fff]+/g)?.slice(0, 3).join(", ") ?? "";
      ctx.ui.notify(
        `🚫 Strict mode: please use English! (detected: ${words}...) Use /english strict off to allow Chinese`,
        "error",
      );
      return { action: "handled" };
    }

    // Gentle mode: remind but allow
    ctx.ui.notify(
      "💡 Try English! Not sure how? Just ask: 'How do I say... in English?'",
      "warning",
    );
    return { action: "continue" };
  });

  // ── System Prompt Injection ──────────────────────────────────────
  pi.on("before_agent_start", async (event, _ctx) => {
    return {
      systemPrompt: event.systemPrompt + "\n\n" + buildPrompt(state.mode, state.difficulty),
    };
  });

  // ── /english Command ─────────────────────────────────────────────
  pi.registerCommand("english", {
    description: "English tutor controls: mode, strict, difficulty, stats, export",
    handler: async (args, ctx) => {
      const parts = (args ?? "").trim().split(/\s+/);
      const sub = parts[0]?.toLowerCase() ?? "";
      const val = parts.slice(1).join(" ");

      const showHelp = () => {
        ctx.ui.notify(
          [
            "/english mode <bilingual|english-only>  — switch response mode",
            "/english strict <on|off>                — toggle strict input",
            "/english difficulty <A2|B1|B2|C1>      — set CEFR level",
            "/english stats                          — show current settings",
            "/english export                         — export study report",
          ].join("\n"),
          "info",
        );
      };

      switch (sub) {
        // ── Mode ──
        case "mode": {
          if (val === "bilingual" || val === "english-only" || val === "en") {
            const normalized = val === "en" ? "english-only" : val as TutorMode;
            state.mode = normalized;
            save();
            updateStatus(ctx);
            updateWidget(ctx);
            const label = normalized === "bilingual" ? "🇬🇧🇨🇳 Bilingual (中英双语)" : "🇬🇧 English Only (纯英文)";
            ctx.ui.notify(`✅ Mode switched to: ${label}`, "info");
          } else {
            ctx.ui.notify("Usage: /english mode bilingual | english-only", "warning");
          }
          break;
        }

        // ── Strict ──
        case "strict": {
          if (val === "on") {
            state.strictMode = true;
            save();
            updateStatus(ctx);
            updateWidget(ctx);
            ctx.ui.notify("🔒 Strict mode ON — Chinese input will be BLOCKED", "info");
          } else if (val === "off") {
            state.strictMode = false;
            save();
            updateStatus(ctx);
            updateWidget(ctx);
            ctx.ui.notify("🔓 Strict mode OFF — Chinese input allowed with reminder", "info");
          } else {
            ctx.ui.notify("Usage: /english strict on | off", "warning");
          }
          break;
        }

        // ── Difficulty ──
        case "difficulty":
        case "level": {
          const upper = val.toUpperCase();
          if (DIFFICULTIES.includes(upper as Difficulty)) {
            state.difficulty = upper as Difficulty;
            save();
            updateStatus(ctx);
            updateWidget(ctx);
            ctx.ui.notify(`📚 Difficulty set to: ${state.difficulty}`, "info");
          } else {
            ctx.ui.notify("Usage: /english difficulty A2 | B1 | B2 | C1", "warning");
          }
          break;
        }

        // ── Stats ──
        case "stats":
        case "status": {
          const modeLabel = state.mode === "bilingual" ? "Bilingual (中英双语)" : "English Only (纯英文)";
          const lines = [
            `Mode:       ${modeLabel}`,
            `Difficulty: ${state.difficulty}`,
            `Strict:     ${state.strictMode ? "ON (Chinese blocked)" : "OFF (Chinese allowed)"}`,
            `Shortcuts:  Ctrl+Shift+E (mode), Ctrl+Shift+S (strict)`,
          ];
          ctx.ui.notify(lines.join("\n"), "info");
          break;
        }

        // ── Export ──
        case "export": {
          const entries = ctx.sessionManager.getEntries();
          const messages: string[] = [];
          let userCount = 0;
          let aiCount = 0;

          for (const entry of entries) {
            if (entry.type !== "message") continue;
            const { role, content } = entry.message;
            const text = extractText(content);
            if (!text) continue;

            if (role === "user") {
              messages.push(`### 👤 You\n\n${text}\n`);
              userCount++;
            } else if (role === "assistant") {
              messages.push(`### 🤖 AI Tutor\n\n${text}\n`);
              aiCount++;
            }
          }

          const date = new Date().toISOString().split("T")[0];
          const modeLabel = state.mode === "bilingual" ? "Bilingual (中英双语)" : "English Only (纯英文)";

          const report = [
            `# 📚 English Study Report — ${date}`,
            "",
            "## Session Info",
            `- **Mode:** ${modeLabel}`,
            `- **Difficulty:** ${state.difficulty}`,
            `- **Your messages:** ${userCount}`,
            `- **AI responses:** ${aiCount}`,
            "",
            "---",
            "",
            "## Conversation",
            "",
            ...messages,
            "",
            "---",
            "",
            "*Generated by pi-english-tutor • Happy learning! 🎉*",
          ].join("\n");

          const exportPath = join(ctx.cwd, `english-study-${date}.md`);
          await writeFile(exportPath, report, "utf-8");
          ctx.ui.notify(`📄 Report exported: ${exportPath}`, "info");
          break;
        }

        // ── Help / unknown ──
        default:
          showHelp();
          break;
      }
    },
  });

  // ── Keyboard Shortcuts ───────────────────────────────────────────
  pi.registerShortcut("ctrl+shift+e", {
    description: "Toggle English tutor mode (bilingual / english-only)",
    handler: async (ctx) => {
      state.mode = state.mode === "bilingual" ? "english-only" : "bilingual";
      save();
      updateStatus(ctx);
      updateWidget(ctx);
      const label = state.mode === "bilingual" ? "🇬🇧🇨🇳 Bilingual" : "🇬🇧 English Only";
      ctx.ui.notify(`🔄 ${label}`, "info");
    },
  });

  pi.registerShortcut("ctrl+shift+s", {
    description: "Toggle strict input mode",
    handler: async (ctx) => {
      state.strictMode = !state.strictMode;
      save();
      updateStatus(ctx);
      updateWidget(ctx);
      ctx.ui.notify(`🔒 Strict mode: ${state.strictMode ? "ON" : "OFF"}`, "info");
    },
  });
}