const express = require("express");
const fs = require("fs/promises");
const path = require("path");
const crypto = require("crypto");

const app = express();
const PORT = process.env.PORT || 5180;
const DB_PATH = path.join(__dirname, "data", "shaders.json");

app.use(express.json({ limit: "1mb" }));
app.use(express.static(__dirname));

async function ensureDb() {
  await fs.mkdir(path.dirname(DB_PATH), { recursive: true });
  try {
    await fs.access(DB_PATH);
  } catch {
    await fs.writeFile(DB_PATH, "[]", "utf8");
  }
}

async function readDb() {
  await ensureDb();
  const raw = await fs.readFile(DB_PATH, "utf8");
  return JSON.parse(raw);
}

async function writeDb(list) {
  await ensureDb();
  await fs.writeFile(DB_PATH, JSON.stringify(list, null, 2), "utf8");
}

function extractFunctionSection(code) {
  const endMarker = code.indexOf("void ANGLE__0_main");
  const end = endMarker >= 0 ? endMarker : code.length;
  const firstFn = code.search(
    /(metal::float[234](x2)?|float|void)\s+[A-Za-z_][A-Za-z0-9_]*\s*\([^)]*\)\s*\{/m
  );
  if (firstFn < 0 || firstFn >= end) return "";
  return code.slice(firstFn, end);
}

function isAngleLike(code) {
  return (
    code.includes("_umainImage") &&
    (code.includes("ANGLE_") ||
      code.includes("metal::") ||
      code.includes("[[function_constant") ||
      code.includes("float2") ||
      code.includes("float3"))
  );
}

function extractFunctionBlocks(code) {
  const blocks = [];
  const sig = /(?:^|\n)\s*(?:void|float|vec[234]|mat[234]|float[234](?:x[234])?)\s+([A-Za-z_][A-Za-z0-9_]*)\s*\([^;]*\)\s*\{/g;
  let m;
  while ((m = sig.exec(code)) !== null) {
    const name = m[1];
    if (name === "main0" || name === "ANGLE__0_main") continue;
    let i = code.indexOf("{", m.index);
    if (i < 0) continue;
    let depth = 0;
    let end = -1;
    for (let p = i; p < code.length; p++) {
      const ch = code[p];
      if (ch === "{") depth++;
      else if (ch === "}") {
        depth--;
        if (depth === 0) {
          end = p + 1;
          break;
        }
      }
    }
    if (end > i) {
      blocks.push(code.slice(m.index, end));
      sig.lastIndex = end;
    }
  }
  return blocks;
}

function convertAngleLikeToGlsl(code) {
  let s = code;
  const cut = s.indexOf("fragment ANGLE_FragmentOut");
  if (cut > 0) s = s.slice(0, cut);

  s = s
    .replace(/metal::fast::normalize/g, "normalize")
    .replace(/metal::/g, "")
    .replace(/\[\[[^\]]+\]\]/g, "")
    .replace(/\bthread\b/g, "")
    .replace(/\bconstant\b/g, "")
    .replace(/\bprecise::tanh\b/g, "tanh")
    .replace(/\bfloat2x2\b/g, "mat2")
    .replace(/\bfloat3x3\b/g, "mat3")
    .replace(/\bfloat4x4\b/g, "mat4")
    .replace(/\bfloat2\b/g, "vec2")
    .replace(/\bfloat3\b/g, "vec3")
    .replace(/\bfloat4\b/g, "vec4")
    .replace(/\bint2\b/g, "ivec2")
    .replace(/\bint3\b/g, "ivec3")
    .replace(/\bint4\b/g, "ivec4")
    .replace(/\buint2\b/g, "uvec2")
    .replace(/\buint3\b/g, "uvec3")
    .replace(/\buint4\b/g, "uvec4")
    .replace(/\buint32_t\b/g, "uint")
    .replace(/\bANGLE_userUniforms\._uiResolution\b/g, "iResolution")
    .replace(/\bANGLE_userUniforms\._uiTime\b/g, "iTime")
    .replace(/\bANGLE_userUniforms\._uiMouse\b/g, "iMouse")
    .replace(/\bANGLE_userUniforms\./g, "")
    .replace(/ANGLE_texture\([^)]*\)/g, "vec4(0.0)")
    .replace(/ANGLE_texelFetch\([^)]*\)/g, "vec4(0.0)")
    .replace(/\bANGLE_mod\(/g, "mod(")
    .replace(/\bANGLE_out\(([^)]+)\)/g, "$1")
    .replace(/\bANGLE_swizzle_ref\(([^)]+)\)/g, "$1")
    .replace(/\bANGLE_elem_ref\(([^)]+)\)/g, "$1")
    .replace(/\bANGLE_addressof\(([^)]+)\)/g, "$1")
    .replace(/\bANGLE_UserUniforms\s*&\s*ANGLE_userUniforms\s*,?/g, "")
    .replace(/\bANGLE_TextureEnvs\s*&\s*ANGLE_textureEnvs\s*,?/g, "")
    .replace(/\bANGLE_NonConstGlobals\s*&\s*ANGLE_nonConstGlobals\s*,?/g, "")
    .replace(/\(\s*,/g, "(")
    .replace(/,\s*,/g, ",")
    .replace(/,\s*\)/g, ")")
    .replace(/(\d+\.\d+|\d+)f\b/g, "$1")
    .replace(/;\s*;/g, ";");

  s = s.replace(/void\s+_umainImage\s*\([^)]*\)/g, "void _umainImage(out vec4 _ufragColor, vec2 _ufragCoord)");

  const blocks = extractFunctionBlocks(s).filter((b) =>
    /(ANGLE_sc|ANGLE_sd|_u|mainImage|ANGLE_loopForwardProgress|_umainImage)/.test(b)
  );

  if (!blocks.length || !s.includes("_umainImage")) return "";

  const hasMainImage = blocks.some((b) => /void\s+mainImage\s*\(/.test(b));
  const withoutDupLoop = [];
  let seenLoop = false;
  for (const b of blocks) {
    if (/void\s+ANGLE_loopForwardProgress\s*\(/.test(b)) {
      if (seenLoop) continue;
      seenLoop = true;
      withoutDupLoop.push("void ANGLE_loopForwardProgress() {}");
      continue;
    }
    withoutDupLoop.push(b);
  }
  if (!hasMainImage) {
    withoutDupLoop.push("void mainImage(out vec4 fragColor, in vec2 fragCoord) { _umainImage(fragColor, fragCoord); }");
  }

  return withoutDupLoop.join("\n\n");
}

function normalizeIncomingCode(code) {
  if (!code || typeof code !== "string") return { error: "code 不能为空", normalized: "" };
  if (isAngleLike(code)) {
    const converted = convertAngleLikeToGlsl(code);
    if (!converted) {
      return { error: "自动解构失败：请检查粘贴内容是否完整。", normalized: "" };
    }
    return { error: "", normalized: converted };
  }
  if (!code.includes("mainImage")) {
    return { error: "code 必须包含 mainImage", normalized: "" };
  }
  return { error: "", normalized: code };
}

async function autoNormalizeStoredShaders() {
  const shaders = await readDb();
  let changed = false;
  const next = shaders.map((item) => {
    const code = String(item.code || "");
    if (isAngleLike(code) || code.includes("struct ANGLE_") || item.sourceFormat === "angle-metal-auto-converted") {
      const { error, normalized } = normalizeIncomingCode(code);
      if (!error && normalized) {
        changed = true;
        return {
          ...item,
          code: normalized,
          updatedAt: new Date().toISOString(),
          sourceFormat: "angle-metal-auto-converted",
        };
      }
    }
    return item;
  });
  if (changed) await writeDb(next);
}

app.get("/api/shaders", async (_req, res) => {
  try {
    let shaders = await readDb();
    // Runtime safeguard: always return normalized code for display layer.
    shaders = shaders.map((item) => {
      const { error, normalized } = normalizeIncomingCode(String(item.code || ""));
      if (error || !normalized) return item;
      if (normalized === item.code) return item;
      return { ...item, code: normalized, sourceFormat: "angle-metal-auto-converted" };
    });
    res.json(shaders);
  } catch {
    res.status(500).json({ error: "读取失败" });
  }
});

app.post("/api/shaders", async (req, res) => {
  const { name, author = "unknown", code } = req.body || {};
  if (!name || typeof name !== "string") {
    return res.status(400).json({ error: "name 必填" });
  }
  const { error: parseError, normalized } = normalizeIncomingCode(code);
  if (parseError) {
    return res.status(400).json({ error: parseError });
  }

  try {
    const shaders = await readDb();
    const item = {
      id: crypto.randomUUID(),
      name: name.trim(),
      author: String(author || "unknown").trim() || "unknown",
      code: normalized,
      views: Math.floor(3000 + Math.random() * 22000),
      likes: Math.floor(40 + Math.random() * 700),
      createdAt: new Date().toISOString(),
      sourceFormat: isAngleLike(code) ? "angle-metal-auto-converted" : "glsl",
    };
    shaders.unshift(item);
    await writeDb(shaders);
    res.status(201).json(item);
  } catch {
    res.status(500).json({ error: "保存失败" });
  }
});

app.delete("/api/shaders/:id", async (req, res) => {
  try {
    const shaders = await readDb();
    const next = shaders.filter((it) => it.id !== req.params.id);
    if (next.length === shaders.length) {
      return res.status(404).json({ error: "未找到该 shader" });
    }
    await writeDb(next);
    res.status(204).end();
  } catch {
    res.status(500).json({ error: "删除失败" });
  }
});

ensureDb().then(() => {
  autoNormalizeStoredShaders().catch(() => {});
  app.listen(PORT, () => {
    console.log(`Server running: http://localhost:${PORT}`);
  });
});