#pragma once

#include <iostream>
#include <map>
#include <memory>

#include <nlohmann/json_fwd.hpp>

#include "util.hh"

namespace nix {

enum HashType : char;

class MultiCommand;

class Args
{
public:

    /* Parse the command line, throwing a UsageError if something goes
       wrong. */
    void parseCmdline(const Strings & cmdline);

    /* Return a short one-line description of the command. */
    virtual std::string description() { return ""; }

    virtual bool forceImpureByDefault() { return false; }

    /* Return documentation about this command, in Markdown format. */
    virtual std::string doc() { return ""; }

protected:

    static const size_t ArityAny = std::numeric_limits<size_t>::max();

    struct Handler
    {
        std::function<void(std::vector<std::string>)> fun;
        size_t arity;

        Handler() {}

        Handler(std::function<void(std::vector<std::string>)> && fun)
            : fun(std::move(fun))
            , arity(ArityAny)
        { }

        Handler(std::function<void()> && handler)
            : fun([handler{std::move(handler)}](std::vector<std::string>) { handler(); })
            , arity(0)
        { }

        Handler(std::function<void(std::string)> && handler)
            : fun([handler{std::move(handler)}](std::vector<std::string> ss) {
                handler(std::move(ss[0]));
              })
            , arity(1)
        { }

        Handler(std::function<void(std::string, std::string)> && handler)
            : fun([handler{std::move(handler)}](std::vector<std::string> ss) {
                handler(std::move(ss[0]), std::move(ss[1]));
              })
            , arity(2)
        { }

        Handler(std::vector<std::string> * dest)
            : fun([=](std::vector<std::string> ss) { *dest = ss; })
            , arity(ArityAny)
        { }

        Handler(std::string * dest)
            : fun([=](std::vector<std::string> ss) { *dest = ss[0]; })
            , arity(1)
        { }

        Handler(std::optional<std::string> * dest)
            : fun([=](std::vector<std::string> ss) { *dest = ss[0]; })
            , arity(1)
        { }

        template<class T>
        Handler(T * dest, const T & val)
            : fun([=](std::vector<std::string> ss) { *dest = val; })
            , arity(0)
        { }

        template<class I>
        Handler(I * dest)
            : fun([=](std::vector<std::string> ss) {
                *dest = string2IntWithUnitPrefix<I>(ss[0]);
              })
            , arity(1)
        { }

        template<class I>
        Handler(std::optional<I> * dest)
            : fun([=](std::vector<std::string> ss) {
                *dest = string2IntWithUnitPrefix<I>(ss[0]);
            })
            , arity(1)
        { }
    };

    /* Options. */
    struct Flag
    {
        typedef std::shared_ptr<Flag> ptr;

        std::string longName;
        std::set<std::string> aliases;
        char shortName = 0;
        std::string description;
        std::string category;
        Strings labels;
        Handler handler;
        std::function<void(size_t, std::string_view)> completer;

        static Flag mkHashTypeFlag(std::string && longName, HashType * ht);
        static Flag mkHashTypeOptFlag(std::string && longName, std::optional<HashType> * oht);
    };

    std::map<std::string, Flag::ptr> longFlags;
    std::map<char, Flag::ptr> shortFlags;

    virtual bool processFlag(Strings::iterator & pos, Strings::iterator end);

    /* Positional arguments. */
    struct ExpectedArg
    {
        std::string label;
        bool optional = false;
        Handler handler;
        std::function<void(size_t, std::string_view)> completer;
    };

    std::list<ExpectedArg> expectedArgs;

    virtual bool processArgs(const Strings & args, bool finish);

    virtual Strings::iterator rewriteArgs(Strings & args, Strings::iterator pos)
    { return pos; }

    std::set<std::string> hiddenCategories;

    /* Called after all command line flags before the first non-flag
       argument (if any) have been processed. */
    virtual void initialFlagsProcessed() {}

    /* Called after the command line has been processed if we need to generate
       completions. Useful for commands that need to know the whole command line
       in order to know what completions to generate. */
    virtual void completionHook() { }

public:

    void addFlag(Flag && flag);

    void removeFlag(const std::string & longName);

    void expectArgs(ExpectedArg && arg)
    {
        expectedArgs.emplace_back(std::move(arg));
    }

    /* Expect a string argument. */
    void expectArg(const std::string & label, std::string * dest, bool optional = false)
    {
        expectArgs({
            .label = label,
            .optional = optional,
            .handler = {dest}
        });
    }

    /* Expect 0 or more arguments. */
    void expectArgs(const std::string & label, std::vector<std::string> * dest)
    {
        expectArgs({
            .label = label,
            .handler = {dest}
        });
    }

    virtual nlohmann::json toJSON();

    friend class MultiCommand;

    MultiCommand * parent = nullptr;
};

/* A command is an argument parser that can be executed by calling its
   run() method. */
struct Command : virtual public Args
{
    friend class MultiCommand;

    virtual ~Command() { }

    virtual void run() = 0;

    typedef int Category;

    static constexpr Category catDefault = 0;

    virtual Category category() { return catDefault; }
};

typedef std::map<std::string, std::function<ref<Command>()>> Commands;

/* An argument parser that supports multiple subcommands,
   i.e. ‘<command> <subcommand>’. */
class MultiCommand : virtual public Args
{
public:
    Commands commands;

    std::map<Command::Category, std::string> categories;

    // Selected command, if any.
    std::optional<std::pair<std::string, ref<Command>>> command;

    MultiCommand(const Commands & commands);

    bool processFlag(Strings::iterator & pos, Strings::iterator end) override;

    bool processArgs(const Strings & args, bool finish) override;

    void completionHook() override;

    nlohmann::json toJSON() override;
};

Strings argvToStrings(int argc, char * * argv);

struct Completion {
    std::string completion;
    std::string description;

    bool operator<(const Completion & other) const;
};
class Completions : public std::set<Completion> {
public:
    void add(std::string completion, std::string description = "");
};
extern std::shared_ptr<Completions> completions;

enum CompletionType {
    ctNormal,
    ctFilenames,
    ctAttrs
};
extern CompletionType completionType;

std::optional<std::string> needsCompletion(std::string_view s);

void completePath(size_t, std::string_view prefix);

void completeDir(size_t, std::string_view prefix);

}