/*
Copyright (c) 2017 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.

Author: Jared Roesch
*/
#include <string>
#include <fstream>
#include <iostream>
#include <iomanip>
#include <utility>
#include <system_error>

#if defined(LEAN_WINDOWS)
#include <unordered_map>
#include <windows.h>
#include <fcntl.h>
#include <io.h>
#include <tchar.h>
#include <stdio.h>
#include <strsafe.h>
#else
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>
#endif

#include "runtime/object.h"
#include "runtime/io.h"
#include "runtime/array_ref.h"
#include "runtime/string_ref.h"
#include "runtime/option_ref.h"
#include "runtime/pair_ref.h"
#include "runtime/buffer.h"

namespace lean {

enum stdio {
    PIPED,
    INHERIT,
    NUL,
};

#if defined(LEAN_WINDOWS)

static lean_external_class * g_win_handle_external_class = nullptr;

static void win_handle_finalizer(void * h) {
    lean_always_assert(CloseHandle(static_cast<HANDLE>(h)));
}

static void win_handle_foreach(void * /* mod */, b_obj_arg /* fn */) {
}

lean_object * wrap_win_handle(HANDLE h) {
    return lean_alloc_external(g_win_handle_external_class, static_cast<void *>(h));
}

extern "C" LEAN_EXPORT obj_res lean_io_process_child_wait(b_obj_arg, b_obj_arg child, obj_arg) {
    HANDLE h = static_cast<HANDLE>(lean_get_external_data(cnstr_get(child, 3)));
    DWORD exit_code;
    if (WaitForSingleObject(h, INFINITE) == WAIT_FAILED) {
        return io_result_mk_error((sstream() << GetLastError()).str());
    }
    if (!GetExitCodeProcess(h, &exit_code)) {
        return io_result_mk_error((sstream() << GetLastError()).str());
    }
    return lean_io_result_mk_ok(box_uint32(exit_code));
}

static FILE * from_win_handle(HANDLE handle, char const * mode) {
    int fd = _open_osfhandle(reinterpret_cast<intptr_t>(handle), _O_APPEND);
    return fdopen(fd, mode);
}

static void setup_stdio(SECURITY_ATTRIBUTES * saAttr, HANDLE * theirs, object ** ours, bool in, stdio cfg) {
    /* Setup stdio based on process configuration. */
    switch (cfg) {
    case stdio::INHERIT:
        lean_always_assert(DuplicateHandle(GetCurrentProcess(), *theirs,
                                           GetCurrentProcess(), theirs,
                                           0, TRUE, DUPLICATE_SAME_ACCESS));
        return;
    case stdio::PIPED: {
        HANDLE readh;
        HANDLE writeh;
        if (!CreatePipe(&readh, &writeh, saAttr, 0))
            throw std::system_error(GetLastError(), std::system_category());
        *ours = io_wrap_handle(in ? from_win_handle(writeh, "w") : from_win_handle(readh, "r"));
        *theirs = in ? readh : writeh;
        // Ensure the write handle to the pipe for STDIN is not inherited.
        lean_always_assert(SetHandleInformation(in ? writeh : readh, HANDLE_FLAG_INHERIT, 0));
        return;
    }
    case stdio::NUL:
        HANDLE hNul = CreateFile("NUL",
                                 in ? GENERIC_READ : GENERIC_WRITE,
                                 0, // TODO(WN): does NUL have to be shared?
                                 saAttr,
                                 OPEN_EXISTING,
                                 FILE_ATTRIBUTE_NORMAL,
                                 NULL);
        if (hNul == INVALID_HANDLE_VALUE)
            throw std::system_error(GetLastError(), std::system_category());
        *theirs = hNul;
        return;
    }
    lean_unreachable();
}

// This code is adapted from: https://msdn.microsoft.com/en-us/library/windows/desktop/ms682499(v=vs.85).aspx
static obj_res spawn(string_ref const & proc_name, array_ref<string_ref> const & args, stdio stdin_mode, stdio stdout_mode,
                     stdio stderr_mode, option_ref<string_ref> const & cwd, array_ref<pair_ref<string_ref, option_ref<string_ref>>> const & env) {
    HANDLE child_stdin  = GetStdHandle(STD_INPUT_HANDLE);
    HANDLE child_stdout = GetStdHandle(STD_OUTPUT_HANDLE);
    HANDLE child_stderr = GetStdHandle(STD_ERROR_HANDLE);

    SECURITY_ATTRIBUTES saAttr;

    // Set the bInheritHandle flag so pipe/NUL handles are inherited.
    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
    saAttr.bInheritHandle = TRUE;
    saAttr.lpSecurityDescriptor = NULL;

    object * parent_stdin  = box(0); setup_stdio(&saAttr, &child_stdin,  &parent_stdin,  true, stdin_mode);
    object * parent_stdout = box(0); setup_stdio(&saAttr, &child_stdout, &parent_stdout, false, stdout_mode);
    object * parent_stderr = box(0); setup_stdio(&saAttr, &child_stderr, &parent_stderr, false, stderr_mode);

    std::string command = proc_name.to_std_string();

    // This needs some thought, on Windows we must pass a command string
    // which is a valid command, that is a fully assembled command to be executed.
    //
    // We must escape the arguments to preseving spacing and other characters,
    // we might need to revisit escaping here.
    for (auto arg : args) {
        command += " \"";
        for (char const * c = arg.data(); *c != 0; c++) {
            if (*c == '"') {
                command += '\\';
            }
            command += *c;
        }
        command += "\"";
    }

    PROCESS_INFORMATION piProcInfo;
    STARTUPINFO siStartInfo;

    // Set up members of the PROCESS_INFORMATION structure.
    ZeroMemory(&piProcInfo, sizeof(PROCESS_INFORMATION));

    // Set up members of the STARTUPINFO structure.
    // This structure specifies the STDIN and STDOUT handles for redirection.

    ZeroMemory(&siStartInfo, sizeof(STARTUPINFO));
    siStartInfo.cb = sizeof(STARTUPINFO);
    siStartInfo.hStdInput = child_stdin;
    siStartInfo.hStdOutput = child_stdout;
    siStartInfo.hStdError = child_stderr;
    siStartInfo.dwFlags |= STARTF_USESTDHANDLES;

    std::unique_ptr<char[]> new_env(nullptr);

    if (env.size()) {
        auto * esp = GetEnvironmentStrings();

        std::unordered_map<std::string, std::string> new_env_vars; // C++17 gives us no-copy std::string_view for this, much better!
        for (auto & entry : env) {
            new_env_vars[entry.fst().data()] = entry.snd() ? entry.snd().get()->data() : std::string{};
        }
        static constexpr auto env_buf_size = 0x7fff; // according to MS docs 0x7fff is the max total size of env block
        new_env = std::make_unique<char[]>(env_buf_size);
        // First copy old evars not in new evars.
        char *new_envp = new_env.get(), *key_begin = esp;
        while (*key_begin) {
            char *key_end = strchr(key_begin, '=');
            char *entry_end = key_end + strlen(key_end);
            if (!new_env_vars.count({key_begin, key_end})) {
                new_envp = std::copy(key_begin, entry_end + 1, new_envp);
            }
            key_begin = entry_end + 1;
        }
        // Then copy new evars if nonempty
        for(const auto & ev : new_env_vars) {
          if (ev.second.empty()) continue;
          // Check if the destination buffer has enough room.
          if (new_envp + ev.first.length() + 1 + ev.second.length() + 1 > new_env.get() + env_buf_size - 1) break;
          new_envp = std::copy(ev.first.cbegin(), ev.first.cend(), new_envp);
          *new_envp++ = '=';
          new_envp = std::copy(ev.second.cbegin(), ev.second.cend(), new_envp);
          *new_envp++ = '\0';
        }
        *new_envp = '\0';

        FreeEnvironmentStrings(esp);
    }

    // Create the child process.
    bool bSuccess = CreateProcess(
        NULL,
        const_cast<char *>(command.c_str()), // command line
        NULL,                                // process security attributes
        NULL,                                // primary thread security attributes
        TRUE,                                // handles are inherited
        0,                                   // creation flags
        new_env.get(),                       // new environment
        cwd ? cwd.get()->data() : NULL,      // current directory
        &siStartInfo,                        // STARTUPINFO pointer
        &piProcInfo);                        // receives PROCESS_INFORMATION

    if (!bSuccess) {
        throw std::system_error(GetLastError(), std::system_category());
    }

    // Close handle to primary thread, we don't need it.
    CloseHandle(piProcInfo.hThread);

    if (stdin_mode  == stdio::PIPED) CloseHandle(child_stdin);
    if (stdout_mode == stdio::PIPED) CloseHandle(child_stdout);
    if (stderr_mode == stdio::PIPED) CloseHandle(child_stderr);

    object_ref r = mk_cnstr(0, parent_stdin, parent_stdout, parent_stderr, wrap_win_handle(piProcInfo.hProcess));
    return lean_io_result_mk_ok(r.steal());
}

extern "C" LEAN_EXPORT obj_res lean_io_process_child_take_stdin(b_obj_arg, obj_arg lchild, obj_arg) {
    object_ref child(lchild);
    object_ref child2 = mk_cnstr(0, object_ref(box(0)), cnstr_get_ref(child, 1), cnstr_get_ref(child, 2), cnstr_get_ref(child, 3));
    object_ref r = mk_cnstr(0, cnstr_get_ref(child, 0), child2);
    return lean_io_result_mk_ok(r.steal());
}

void initialize_process() {
    g_win_handle_external_class = lean_register_external_class(win_handle_finalizer, win_handle_foreach);
}
void finalize_process() {}

#else

extern "C" LEAN_EXPORT obj_res lean_io_process_child_wait(b_obj_arg, b_obj_arg child, obj_arg) {
    static_assert(sizeof(pid_t) == sizeof(uint32), "pid_t is expected to be a 32-bit type"); // NOLINT
    pid_t pid = cnstr_get_uint32(child, 3 * sizeof(object *));
    int status;
    if (waitpid(pid, &status, 0) == -1) {
        return io_result_mk_error(decode_io_error(errno, nullptr));
    }
    if (WIFEXITED(status)) {
        return lean_io_result_mk_ok(box_uint32(static_cast<unsigned>(WEXITSTATUS(status))));
    } else {
        lean_assert(WIFSIGNALED(status));
        // use bash's convention
        return lean_io_result_mk_ok(box_uint32(128 + static_cast<unsigned>(WTERMSIG(status))));
    }
}

struct pipe { int m_read_fd; int m_write_fd; };

static optional<pipe> setup_stdio(stdio cfg) {
    /* Setup stdio based on process configuration. */
    switch (cfg) {
    case stdio::INHERIT:
        /* We should need to do nothing in this case */
        return optional<pipe>();
    case stdio::PIPED:
        int fds[2];
#ifdef __APPLE__
        // this is inherently racy, but there is nothing we can do on MacOS
        if (::pipe(fds) == -1) { throw errno; }
        if (::fcntl(fds[0], F_SETFD, FD_CLOEXEC)) { throw errno; }
        if (::fcntl(fds[1], F_SETFD, FD_CLOEXEC)) { throw errno; }
#else
        if (::pipe2(fds, O_CLOEXEC) == -1) { throw errno; }
#endif
        return optional<pipe>(pipe { fds[0], fds[1] });
    case stdio::NUL:
        /* We should map /dev/null. */
        return optional<pipe>();
    }
    lean_unreachable();
}

static obj_res spawn(string_ref const & proc_name, array_ref<string_ref> const & args, stdio stdin_mode, stdio stdout_mode,
  stdio stderr_mode, option_ref<string_ref> const & cwd, array_ref<pair_ref<string_ref, option_ref<string_ref>>> const & env) {
    /* Setup stdio based on process configuration. */
    auto stdin_pipe  = setup_stdio(stdin_mode);
    auto stdout_pipe = setup_stdio(stdout_mode);
    auto stderr_pipe = setup_stdio(stderr_mode);

    int pid = fork();

    if (pid == 0) {
        for (auto & entry : env) {
            if (entry.snd()) {
                setenv(entry.fst().data(), entry.snd().get()->data(), true);
            } else {
                unsetenv(entry.fst().data());
            }
        }

        if (stdin_pipe) {
            dup2(stdin_pipe->m_read_fd, STDIN_FILENO);
            close(stdin_pipe->m_write_fd);
        } else if (stdin_mode == stdio::NUL) {
            int fd = open("/dev/null", O_RDONLY);
            dup2(fd, STDIN_FILENO);
        }

        if (stdout_pipe) {
            dup2(stdout_pipe->m_write_fd, STDOUT_FILENO);
            close(stdout_pipe->m_read_fd);
        } else if (stdout_mode == stdio::NUL) {
            int fd = open("/dev/null", O_WRONLY);
            dup2(fd, STDOUT_FILENO);
        }

        if (stderr_pipe) {
            dup2(stderr_pipe->m_write_fd, STDERR_FILENO);
            close(stderr_pipe->m_read_fd);
        } else if (stderr_mode == stdio::NUL) {
            int fd = open("/dev/null", O_WRONLY);
            dup2(fd, STDERR_FILENO);
        }

        if (cwd) {
            if (chdir(cwd.get()->data()) < 0) {
                std::cerr << "could not change directory to " << cwd.get()->data() << std::endl;
                exit(-1);
            }
        }

        buffer<char *> pargs;
        pargs.push_back(strdup(proc_name.data()));
        for (auto & arg : args)
            pargs.push_back(strdup(arg.data()));
        pargs.push_back(NULL);

        if (execvp(pargs[0], pargs.data()) < 0) {
            std::cerr << "could not execute external process '" << pargs[0] << "'" << std::endl;
            exit(-1);
        }
    } else if (pid == -1) {
        throw errno;
    }

    object * parent_stdin  = box(0);
    object * parent_stdout = box(0);
    object * parent_stderr = box(0);
    if (stdin_pipe) {
        close(stdin_pipe->m_read_fd);
        parent_stdin = io_wrap_handle(fdopen(stdin_pipe->m_write_fd, "w"));
    }

    if (stdout_pipe) {
        close(stdout_pipe->m_write_fd);
        parent_stdout = io_wrap_handle(fdopen(stdout_pipe->m_read_fd, "r"));
    }

    if (stderr_pipe) {
        close(stderr_pipe->m_write_fd);
        parent_stderr = io_wrap_handle(fdopen(stderr_pipe->m_read_fd, "r"));
    }

    object_ref r = mk_cnstr(0, parent_stdin, parent_stdout, parent_stderr, sizeof(pid_t));
    static_assert(sizeof(pid_t) == sizeof(uint32), "pid_t is expected to be a 32-bit type"); // NOLINT
    cnstr_set_uint32(r.raw(), 3 * sizeof(object *), pid);
    return lean_io_result_mk_ok(r.steal());
}

extern "C" LEAN_EXPORT obj_res lean_io_process_child_take_stdin(b_obj_arg, obj_arg lchild, obj_arg) {
    object_ref child(lchild);
    object_ref child2 = mk_cnstr(0, object_ref(box(0)), cnstr_get_ref(child, 1), cnstr_get_ref(child, 2), sizeof(pid_t));
    cnstr_set_uint32(child2.raw(), 3 * sizeof(object *), cnstr_get_uint32(child.raw(), 3 * sizeof(object *)));
    object_ref r = mk_cnstr(0, cnstr_get_ref(child, 0), child2);
    return lean_io_result_mk_ok(r.steal());
}

void initialize_process() {}
void finalize_process() {}

#endif

extern "C" lean_object* lean_mk_io_error_other_error(uint32_t, lean_object*);

extern "C" LEAN_EXPORT obj_res lean_io_process_spawn(obj_arg args_, obj_arg) {
    object_ref args(args_);
    object_ref stdio_cfg = cnstr_get_ref(args, 0);
    stdio stdin_mode  = static_cast<stdio>(cnstr_get_uint8(stdio_cfg.raw(), 0));
    stdio stdout_mode = static_cast<stdio>(cnstr_get_uint8(stdio_cfg.raw(), 1));
    stdio stderr_mode = static_cast<stdio>(cnstr_get_uint8(stdio_cfg.raw(), 2));
    if (stdin_mode == stdio::INHERIT) {
        std::cout.flush();
    }
    try {
        return spawn(
                cnstr_get_ref_t<string_ref>(args, 1),
                cnstr_get_ref_t<array_ref<string_ref>>(args, 2),
                stdin_mode,
                stdout_mode,
                stderr_mode,
                cnstr_get_ref_t<option_ref<string_ref>>(args, 3),
                cnstr_get_ref_t<array_ref<pair_ref<string_ref, option_ref<string_ref>>>>(args, 4));
    } catch (int err) {
        return lean_io_result_mk_error(decode_io_error(err, nullptr));
    } catch (std::system_error const & err) {
        // TODO: decode
        return lean_io_result_mk_error(lean_mk_io_error_other_error(err.code().value(), mk_string(err.code().message())));
    }
}

}