// Copyright 2026 Dolphin Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later

#pragma once

#include <charconv>
#include <cstddef>
#include <optional>
#include <string>
#include <string_view>
#include <utility>
#include <vector>

#include <fmt/format.h>

#include "Common/CommonTypes.h"

// StarletBootstrapProbe's --ipc-script <file>: the probe stands in for Broadway (StarOS
// docs/contracts/hollywood-ipc-injection.md). A script is data: whole words stored in one range
// of PPC memory, the registers Broadway writes and reads, every wait bounded. It knows nothing of
// the code under test and answers nothing for it: what it reads back, the ARM code wrote.
namespace StarletBootstrapProbe
{
// The one range a script may store to or expect from: the 128 KiB below Broadway's boundary.
constexpr u32 IPC_RANGE_BASE = 0x135E0000;
// Exclusive.
constexpr u32 IPC_RANGE_END = 0x13600000;
constexpr u64 SCRIPT_MAX_BYTES = 64 * 1024;
constexpr size_t SCRIPT_MAX_STEPS = 256;
constexpr u64 SCRIPT_MAX_CYCLES = u64{1} << 30;

// Exit status of a run whose script is refused before StarOS starts (1: failed expectation,
// 2: usage, 3: Dolphin alert, 4: refused package file).
constexpr int SCRIPT_EXIT_STATUS = 5;

// The registers, as offsets from Hollywood's register page.
constexpr u32 IPC_PPCMSG = 0x00;
constexpr u32 IPC_PPCCTRL = 0x04;
constexpr u32 IPC_ARMMSG = 0x08;
// PPCCTRL's bits a write means: X1, Y2, Y1, X2, IY1, IY2.
constexpr u32 IPC_PPCCTRL_BITS = 0x3F;

enum class StepKind
{
  Store,
  PpcMsg,
  PpcCtrl,
  Wait,
  ExpectArmMsg,
  Expect,
  Run
};

struct ScriptStep
{
  StepKind kind;
  int line;
  u32 first;
  u32 second;
  u64 cycles;
};

// What a script reaches: PPC memory and the registers, nothing of the code under test.
class ScriptBus
{
public:
  virtual ~ScriptBus() = default;
  virtual void StoreWord(u32 address, u32 word) = 0;
  virtual u32 LoadWord(u32 address) = 0;
  virtual void WriteRegister(u32 offset, u32 value) = 0;
  virtual u32 ReadRegister(u32 offset) = 0;
};

// A number, hexadecimal with 0x or decimal, whole: nothing else.
inline std::optional<u64> ParseScriptNumber(std::string_view text)
{
  const bool hexadecimal = text.starts_with("0x");
  if (hexadecimal)
    text.remove_prefix(2);
  if (text.empty())
    return std::nullopt;
  u64 value = 0;
  const auto [end, status] =
      std::from_chars(text.data(), text.data() + text.size(), value, hexadecimal ? 16 : 10);
  if (status != std::errc{} || end != text.data() + text.size())
    return std::nullopt;
  return value;
}

// Whether a whole word at `address` lies in the range.
constexpr bool InIPCRange(u64 address)
{
  return address >= IPC_RANGE_BASE && address + 4 <= IPC_RANGE_END && address % 4 == 0;
}

// The script's steps, or nullopt with the reason in `error`. Nothing is run.
inline std::optional<std::vector<ScriptStep>> ParseScript(std::string_view text, std::string* error)
{
  const auto refuse = [error](int line, std::string_view why) {
    *error = fmt::format("line {}: {}", line, why);
    return std::nullopt;
  };
  std::vector<ScriptStep> steps;
  int line_number = 0;
  while (!text.empty())
  {
    ++line_number;
    const size_t end = text.find('\n');
    std::string_view line = text.substr(0, end);
    text = end == std::string_view::npos ? std::string_view{} : text.substr(end + 1);
    line = line.substr(0, line.find('#'));

    std::vector<std::string_view> words;
    while (!line.empty())
    {
      const size_t start = line.find_first_not_of(" \t\r");
      if (start == std::string_view::npos)
        break;
      line.remove_prefix(start);
      const size_t stop = line.find_first_of(" \t\r");
      words.push_back(line.substr(0, stop));
      line = stop == std::string_view::npos ? std::string_view{} : line.substr(stop);
    }
    if (words.empty())
      continue;
    if (steps.size() == SCRIPT_MAX_STEPS)
      return refuse(line_number, fmt::format("more than {} steps", SCRIPT_MAX_STEPS));

    std::vector<u64> numbers;
    for (size_t index = 1; index < words.size(); ++index)
    {
      const std::optional<u64> number = ParseScriptNumber(words[index]);
      if (!number)
        return refuse(line_number, fmt::format("not a number: {}", words[index]));
      numbers.push_back(*number);
    }
    const auto operands = [&numbers](size_t count) { return numbers.size() == count; };
    const auto word = [&numbers](size_t index) { return numbers[index] <= 0xFFFFFFFF; };
    const auto cycles = [&numbers](size_t index) {
      return numbers[index] != 0 && numbers[index] <= SCRIPT_MAX_CYCLES;
    };
    const std::string_view name = words[0];
    ScriptStep step{StepKind::Run, line_number, 0, 0, 0};
    if (name == "store" || name == "expect")
    {
      if (!operands(2) || !word(1))
        return refuse(line_number, "takes an address and a word");
      if (!InIPCRange(numbers[0]))
        return refuse(line_number, "the address is not a whole word of the range");
      step.kind = name == "store" ? StepKind::Store : StepKind::Expect;
      step.first = static_cast<u32>(numbers[0]);
      step.second = static_cast<u32>(numbers[1]);
    }
    else if (name == "ppcmsg" || name == "expect-armmsg")
    {
      // A register's value, in or out of the range: nothing is accessed through it here.
      if (!operands(1) || !word(0))
        return refuse(line_number, "takes one word");
      step.kind = name == "ppcmsg" ? StepKind::PpcMsg : StepKind::ExpectArmMsg;
      step.first = static_cast<u32>(numbers[0]);
    }
    else if (name == "ppcctrl")
    {
      if (!operands(1) || numbers[0] > IPC_PPCCTRL_BITS)
        return refuse(line_number, "takes PPCCTRL's six bits");
      step.kind = StepKind::PpcCtrl;
      step.first = static_cast<u32>(numbers[0]);
    }
    else if (name == "wait")
    {
      if (!operands(3) || !word(0) || !word(1) || !cycles(2))
        return refuse(line_number, "takes a mask, a value and a bound in cycles");
      step.kind = StepKind::Wait;
      step.first = static_cast<u32>(numbers[0]);
      step.second = static_cast<u32>(numbers[1]);
      step.cycles = numbers[2];
    }
    else if (name == "run")
    {
      if (!operands(1) || !cycles(0))
        return refuse(line_number, "takes a number of cycles");
      step.kind = StepKind::Run;
      step.cycles = numbers[0];
    }
    else
    {
      return refuse(line_number, fmt::format("unknown step: {}", name));
    }
    steps.push_back(step);
  }
  return steps;
}

// Runs a script's steps in order, between the probe's slices.
class ScriptRunner
{
public:
  explicit ScriptRunner(std::vector<ScriptStep> steps) : m_steps(std::move(steps)) {}

  // `elapsed` ARM cycles went by: every step that can run now does, up to one that must wait.
  void Advance(ScriptBus& bus, u64 elapsed)
  {
    m_waited += elapsed;
    while (m_failure.empty() && m_next < m_steps.size())
    {
      const ScriptStep& step = m_steps[m_next];
      switch (step.kind)
      {
      case StepKind::Store:
        bus.StoreWord(step.first, step.second);
        break;
      case StepKind::PpcMsg:
        bus.WriteRegister(IPC_PPCMSG, step.first);
        break;
      case StepKind::PpcCtrl:
        bus.WriteRegister(IPC_PPCCTRL, step.first);
        break;
      case StepKind::Wait:
      {
        const u32 seen = bus.ReadRegister(IPC_PPCCTRL);
        if ((seen & step.first) != step.second)
        {
          if (m_waited >= step.cycles)
            Fail(step, fmt::format("PPCCTRL reads {:#x} after {} cycles", seen, m_waited));
          return;
        }
        break;
      }
      case StepKind::ExpectArmMsg:
      {
        const u32 seen = bus.ReadRegister(IPC_ARMMSG);
        if (seen != step.first)
          return Fail(step, fmt::format("ARMMSG reads {:#x}, not {:#x}", seen, step.first));
        break;
      }
      case StepKind::Expect:
      {
        const u32 seen = bus.LoadWord(step.first);
        if (seen != step.second)
        {
          return Fail(step, fmt::format("the word at {:#x} reads {:#x}, not {:#x}", step.first,
                                        seen, step.second));
        }
        break;
      }
      case StepKind::Run:
        if (m_waited < step.cycles)
          return;
        break;
      }
      ++m_next;
      m_waited = 0;
    }
  }

  bool Done() const { return m_next == m_steps.size(); }
  bool Failed() const { return !m_failure.empty(); }
  const std::string& Failure() const { return m_failure; }
  // The line of the step it stands on.
  int Line() const { return Done() ? 0 : m_steps[m_next].line; }

private:
  void Fail(const ScriptStep& step, const std::string& why)
  {
    m_failure = fmt::format("line {}: {}", step.line, why);
  }

  std::vector<ScriptStep> m_steps;
  size_t m_next = 0;
  u64 m_waited = 0;
  std::string m_failure;
};
}  // namespace StarletBootstrapProbe