import luaparse from "luaparse"
import {
  LuaClosure,
  LuaCoroutine,
  LuaError,
  LuaTable,
  NativeFunction,
  getMetatable,
  shortSrc,
  typeName,
} from "v8lua/src/runtime.js"
import { Call, Frame } from "./evaluate.js"

const boundaryError = "attempt to yield across metamethod/C-call boundary"

export class VM {
  globals = new LuaTable()
  main = { frames: [], barriers: 0 }
  thread = this.main
  hook = null // v8lua native library callbacks do not run debug hooks.

  compile(source, chunkname) {
    let proto
    try {
      proto = luaparse.parse(source, {
        luaVersion: "5.1",
        encodingMode: "pseudo-latin1",
        locations: true,
        comments: false,
        onCreateNode(node) {
          if (node.type === "FunctionDeclaration" && node.parameters.at(-1)?.type === "VarargLiteral") {
            node.legacyArg = !usesVarargs(node.body)
          }
        },
      })
    } catch (e) {
      if (!(e instanceof SyntaxError)) throw e
      throw new LuaError(`${shortSrc(chunkname)}:${e.line}: ${e.message}`)
    }
    const chunk = new LuaClosure(proto, null, chunkname, this)
    chunk.env = this.thread.env ?? this.globals
    chunk.chunkname = chunkname
    return chunk
  }

  // A synchronous library or metamethod callback may run Lua but cannot yield
  // to its caller. Resuming a *different* thread starts with its own barriers.
  atomic(code) {
    const thread = this.thread
    thread.barriers++
    try {
      const result = code.next()
      if (!result.done) throw new Error("unexpected suspension across VM boundary")
      return result.value
    } finally {
      thread.barriers--
    }
  }

  *invoke(fn, args) {
    const thread = this.thread
    const frames = thread.frames
    const base = frames.length
    let call = new Call(fn, args)
    let values
    try {
      for (;;) {
        if (call) {
          let { fn, args } = call
          if (!(fn instanceof LuaClosure || fn instanceof NativeFunction)) {
            const handler = getMetatable(fn)?.get("__call")
            if (!(handler instanceof LuaClosure || handler instanceof NativeFunction))
              throw new LuaError(`attempt to call a ${typeName(fn)} value`)
            args = [fn, ...args]
            fn = handler
          }
          if (fn instanceof LuaClosure) {
            if (frames.length > base && frames.at(-1).tail) frames.pop()
            if (frames.length >= 20000) throw new LuaError("stack overflow")
            frames.push(new Frame(this, fn, args))
            values = undefined
          } else if (fn === this.yieldFn) {
            if (thread === this.main || thread.barriers) throw new LuaError(boundaryError)
            values = yield args
          } else {
            values = this.atomic(fn.fn(this, args)) ?? []
          }
          call = undefined
        }

        if (frames.length === base) return values
        const frame = frames.at(-1)
        if (frame.tail) {
          frames.pop() // a tail-called native just returned
          continue
        }
        const step = frame.code.next(values)
        if (step.value instanceof Call) {
          frame.tail = step.done
          call = step.value
          continue
        }
        if (!step.done) throw new Error("invalid Lua frame suspension")
        values = step.value ?? []
        frames.pop()
      }
    } catch (e) {
      const err = e instanceof RangeError ? new LuaError("stack overflow") : e
      if (err instanceof LuaError && !err.positioned && frames.length > base) {
        const frame = frames.at(-1)
        if (typeof err.luaMessage === "string")
          err.message = err.luaMessage = `${shortSrc(frame.closure.chunkname)}:${frame.line}: ${err.luaMessage}`
        err.positioned = true
      }
      throw err
    } finally {
      frames.length = base
    }
  }

  create(fn) {
    if (!(fn instanceof LuaClosure)) throw new LuaError("Lua function expected")
    const thread = new LuaCoroutine(fn)
    thread.frames = []
    thread.barriers = 0
    thread.env = this.thread.env ?? this.globals
    return thread
  }

  resume(thread, args) {
    if (!(thread instanceof LuaCoroutine)) throw new LuaError("thread expected")
    if (thread.status !== "suspended") return [false, `cannot resume ${thread.status} coroutine`]
    const parent = this.thread
    parent.status = "normal"
    thread.status = "running"
    this.thread = thread
    try {
      thread.it ??= this.invoke(thread.fn, args)
      const result = thread.it.next(args)
      thread.status = result.done ? "dead" : "suspended"
      return [true, ...result.value]
    } catch (e) {
      thread.status = "dead"
      if (e instanceof LuaError) return [false, e.luaMessage]
      throw e
    } finally {
      this.thread = parent
      parent.status = "running"
      if (thread.status === "dead") thread.it = thread.fn = null
    }
  }
}

// Lua 5.1 compatibility: a vararg function gets a local arg table only
// when it doesn't use `...` itself. Nested function bodies don't count.
function usesVarargs(node) {
  if (node === null || typeof node !== "object" || node.type === "FunctionDeclaration") return false
  return node.type === "VarargLiteral" || Object.values(node).some(usesVarargs)
}