#pragma once

#include <map>
#include <set>
#include <tuple>
#include <utility>

#include <fcntl.h>
#include <kernel/errno.h>
#include <kernel/event/evtqueue.hpp>
#include <kernel/interrupt.h>
#include <kernel/mm.hpp>
#include <kernel/signal.hpp>
#include <kernel/task.h>
#include <kernel/tty.hpp>
#include <kernel/vfs.hpp>
#include <stdint.h>
#include <sys/types.h>
#include <types/allocator.hpp>
#include <types/cplusplus.hpp>
#include <types/hash_map.hpp>
#include <types/status.h>
#include <types/string.hpp>
#include <types/types.h>

class process;
struct thread;

class proclist;
class readyqueue;

inline process* volatile current_process;
inline thread* volatile current_thread;
inline proclist* procs;
inline readyqueue* readythds;

inline tss32_t tss;

struct process_attr {
    uint16_t system : 1;
    uint16_t zombie : 1 = 0;
};

struct thread_attr {
    uint32_t system : 1;
    uint32_t ready : 1;
    uint32_t wait : 1;
};

struct thread {
private:
    void alloc_kstack(void);
    void free_kstack(uint32_t p);

public:
    uint32_t* esp;
    uint32_t pkstack;
    process* owner;
    thread_attr attr;

    explicit inline thread(process* _owner, bool system)
        : owner { _owner }
        , attr {
            .system = system,
            .ready = 1,
            .wait = 0,
        }
    {
        alloc_kstack();
    }

    constexpr thread(thread&& val)
        : esp { std::exchange(val.esp, nullptr) }
        , pkstack { std::exchange(val.pkstack, 0) }
        , owner { std::exchange(val.owner, nullptr) }
        , attr { std::exchange(val.attr, {}) } { }

    inline thread(const thread& val)
        : owner { val.owner }
        , attr { val.attr }
    {
        alloc_kstack();
    }

    inline thread(const thread& thd, process* new_parent)
        : thread { thd }
    {
        owner = new_parent;
    }

    constexpr ~thread()
    {
        if (pkstack)
            free_kstack(pkstack);
    }
};

class thdlist {
public:
    using list_type = types::list<thread>;

private:
    list_type thds;

public:
    constexpr thdlist(const thdlist& obj) = delete;
    constexpr thdlist(thdlist&& obj) = delete;

    constexpr thdlist& operator=(const thdlist& obj) = delete;
    constexpr thdlist& operator=(thdlist&& obj) = delete;

    constexpr thdlist(thdlist&& obj, process* new_parent)
        : thds { std::move(obj.thds) }
    {
        for (auto& thd : thds)
            thd.owner = new_parent;
    }

    explicit constexpr thdlist(void) = default;

    // implementation is below
    constexpr ~thdlist();

    template <typename... Args>
    constexpr thread& Emplace(Args&&... args)
    {
        return *thds.emplace_back(std::forward<Args>(args)...);
    }

    constexpr size_t size(void) const
    {
        return thds.size();
    }

    constexpr list_type& underlying_list(void)
    {
        return thds;
    }
};

class process {
public:
    class filearr {
    public:
        using container_type = types::list<fs::file>;
        using array_type = std::map<int, container_type::iterator_type>;

    private:
        inline static container_type* files;
        array_type arr;

    public:
        inline static void init_global_file_container(void)
        {
            files = new container_type;
        }

    private:
        // iter should not be nullptr
        constexpr void _close(container_type::iterator_type iter)
        {
            if (iter->ref == 1) {
                if (iter->type == fs::file::types::pipe) {
                    assert(iter->flags.read | iter->flags.write);
                    if (iter->flags.read)
                        iter->ptr.pp->close_read();
                    else
                        iter->ptr.pp->close_write();

                    if (iter->ptr.pp->is_free())
                        delete iter->ptr.pp;
                }

                files->erase(iter);
            } else
                --iter->ref;
        }

        constexpr int _next_fd(void) const
        {
            int fd = 0;

            for (auto [ item_fd, iter_file ] : arr) {
                if (item_fd == fd)
                    ++fd;
            }

            return fd;
        }

    public:
        constexpr filearr(const filearr&) = delete;
        constexpr filearr& operator=(const filearr&) = delete;
        constexpr filearr& operator=(filearr&&) = delete;
        constexpr filearr(void) = default;
        constexpr filearr(filearr&& val)
            : arr { std::move(val.arr) }
        {
        }

        constexpr int dup(int old_fd)
        {
            return dup2(old_fd, _next_fd());
        }

        // TODO: the third parameter should be int flags
        //       determining whether the fd should be closed
        //       after exec() (FD_CLOEXEC)
        constexpr int dup2(int old_fd, int new_fd)
        {
            close(new_fd);

            auto iter = arr.find(old_fd);
            if (!iter)
                return -EBADF;

            auto [ _, iter_file ] = *iter;

            this->arr.insert(std::make_pair(new_fd, iter_file));
            ++iter_file->ref;
            return new_fd;
        }

        constexpr void dup_all(const filearr& orig)
        {
            for (auto [ fd, iter_file ] : orig.arr) {
                this->arr.insert(std::make_pair(fd, iter_file));
                ++iter_file->ref;
            }
        }

        constexpr fs::file* operator[](int i) const
        {
            auto iter = arr.find(i);
            if (!iter)
                return nullptr;
            return &iter->second;
        }

        int pipe(int pipefd[2])
        {
            // TODO: set read/write flags
            auto* pipe = new fs::pipe;

            auto iter = files->emplace_back(fs::file {
                fs::file::types::pipe,
                { .pp = pipe },
                nullptr,
                0,
                1,
                {
                    .read = 1,
                    .write = 0,
                },
            });
            int fd = _next_fd();
            arr.insert(std::make_pair(fd, iter));

            // TODO: use copy_to_user()
            pipefd[0] = fd;

            iter = files->emplace_back(fs::file {
                fs::file::types::pipe,
                { .pp = pipe },
                nullptr,
                0,
                1,
                {
                    .read = 0,
                    .write = 1,
                },
            });
            fd = _next_fd();
            arr.insert(std::make_pair(fd, iter));

            // TODO: use copy_to_user()
            pipefd[1] = fd;

            return 0;
        }

        // TODO: file opening permissions check
        int open(const char* filename, uint32_t flags)
        {
            auto* dentry = fs::vfs_open(filename);

            if (!dentry) {
                errno = ENOTFOUND;
                return -1;
            }

            // check whether dentry is a file if O_DIRECTORY is set
            if ((flags & O_DIRECTORY) && !dentry->ind->flags.in.directory) {
                errno = ENOTDIR;
                return -1;
            }

            auto iter = files->emplace_back(fs::file {
                fs::file::types::ind,
                { .ind = dentry->ind },
                dentry->parent,
                0,
                1,
                {
                    .read = !!(flags & (O_RDONLY | O_RDWR)),
                    .write = !!(flags & (O_WRONLY | O_RDWR)),
                },
            });

            int fd = _next_fd();
            arr.insert(std::make_pair(fd, iter));
            return fd;
        }

        constexpr void close(int fd)
        {
            auto iter = arr.find(fd);
            if (iter) {
                _close(iter->second);
                arr.erase(iter);
            }
        }

        constexpr void close_all(void)
        {
            for (auto&& [ fd, file ] : arr)
                close(fd);
        }

        constexpr ~filearr()
        {
            close_all();
        }
    };

    struct wait_obj {
        pid_t pid;
        int code;
    };

public:
    mutable kernel::mm_list mms;
    thdlist thds;
    kernel::cond_var cv_wait;
    types::list<wait_obj> waitlist;
    process_attr attr;
    filearr files;
    types::string<> pwd;
    kernel::signal_list signals;

    pid_t pid;
    pid_t ppid;
    pid_t pgid;
    pid_t sid;

    tty* control_tty;
    std::set<pid_t> children;

public:
    // if waitlist is not empty or mutex in cv_wait
    // is locked, its behavior is undefined
    constexpr process(process&& val)
        : mms(std::move(val.mms))
        , thds { std::move(val.thds), this }
        , attr { val.attr }
        , files(std::move(val.files))
        , pwd(std::move(val.pwd))
        , pid(val.pid)
        , ppid(val.ppid)
        , pgid(val.pgid)
        , sid(val.sid)
        , control_tty(val.control_tty)
        , children(std::move(val.children))
    {
        if (current_process == &val)
            current_process = this;
    }

    process(const process&);

    // this function is used for system initialization
    // DO NOT use this after the system is on
    explicit process(pid_t ppid);

    constexpr bool is_system(void) const
    { return attr.system; }
    constexpr bool is_zombie(void) const
    { return attr.zombie; }

private:
    static inline pid_t max_pid;

    static inline pid_t alloc_pid(void)
    {
        return ++max_pid;
    }
};

class proclist final {
public:
    using list_type = std::map<pid_t, process>;
    using iterator = list_type::iterator;
    using const_iterator = list_type::const_iterator;

private:
    list_type m_procs;

public:
    template <typename... Args>
    iterator emplace(Args&&... args)
    {
        process _proc(std::forward<Args>(args)...);
        auto pid = _proc.pid;
        auto ppid = _proc.ppid;
        auto [ iter, inserted ] =
            m_procs.insert(std::make_pair(pid, std::move(_proc)));
        
        assert(inserted);

        if (ppid) {
            bool success = false;
            std::tie(std::ignore, success) = find(ppid).children.insert(pid);
            assert(success);
        }

        return iter;
    }

    constexpr void remove(pid_t pid)
    {
        make_children_orphans(pid);

        auto proc_iter = m_procs.find(pid);

        auto ppid = proc_iter->second.ppid;
        find(ppid).children.erase(pid);

        m_procs.erase(proc_iter);
    }

    constexpr bool try_find(pid_t pid) const
    { return !!m_procs.find(pid); }

    // if process doesn't exist, the behavior is undefined
    constexpr process& find(pid_t pid)
    {
        auto iter = m_procs.find(pid);
        assert(!!iter);
        return iter->second;
    }

    constexpr bool has_child(pid_t pid)
    {
        auto& proc = find(pid);
        return !proc.children.empty();
    }

    constexpr void make_children_orphans(pid_t pid)
    {
        auto& children = find(pid).children;
        auto& init_children = find(1).children;

        for (auto item : children) {
            init_children.insert(item);
            find(item).ppid = 1;
        }

        children.clear();
    }

    // the process MUST exist, or the behavior is undefined
    void send_signal(pid_t pid, kernel::sig_t signal)
    {
        auto proc = this->find(pid);
        proc.signals.set(signal);
    }
    void send_signal_grp(pid_t pgid, kernel::sig_t signal)
    {
        for (auto& [ pid, proc ] : m_procs) {
            if (proc.pgid == pgid)
                proc.signals.set(signal);
        }
    }

    void kill(pid_t pid, int exit_code);
};

class readyqueue final {
public:
    using list_type = types::list<thread*>;
    using iterator_type = list_type::iterator_type;
    using const_iterator_type = list_type::const_iterator_type;

private:
    list_type m_thds;

private:
    readyqueue(const readyqueue&) = delete;
    readyqueue(readyqueue&&) = delete;
    readyqueue& operator=(const readyqueue&) = delete;
    readyqueue& operator=(readyqueue&&) = delete;

    ~readyqueue() = delete;

public:
    constexpr explicit readyqueue(void) = default;

    constexpr void push(thread* thd)
    {
        m_thds.push_back(thd);
    }

    constexpr thread* pop(void)
    {
        auto iter = m_thds.begin();
        while (!((*iter)->attr.ready))
            iter = m_thds.erase(iter);
        auto* ptr = *iter;
        m_thds.erase(iter);
        return ptr;
    }

    constexpr thread* query(void)
    {
        auto* thd = this->pop();
        this->push(thd);
        return thd;
    }

    constexpr void remove_all(thread* thd)
    {
        auto iter = m_thds.find(thd);
        while (iter != m_thds.end()) {
            m_thds.erase(iter);
            iter = m_thds.find(thd);
        }
    }
};

void NORETURN init_scheduler(void);
/// @return true if returned normally, false if being interrupted
bool schedule(void);
void NORETURN schedule_noreturn(void);

constexpr uint32_t push_stack(uint32_t** stack, uint32_t val)
{
    --*stack;
    **stack = val;
    return val;
}

// class thdlist
constexpr thdlist::~thdlist()
{
    for (auto iter = thds.begin(); iter != thds.end(); ++iter)
        readythds->remove_all(&iter);
}

void k_new_thread(void (*func)(void*), void* data);

void NORETURN freeze(void);
void NORETURN kill_current(int exit_code);

void check_signal(void);