#pragma once

#include <string>
#include <functional>
#include <memory>
#include <vector>
#include <unordered_map>
#include <filesystem>

namespace lumacs {

class EditorCore; // Forward declaration

/// @brief Result of command execution.
struct CommandResult {
    bool success;
    std::string message;
    
    CommandResult(bool s = true, std::string msg = "") 
        : success(s), message(std::move(msg)) {}
};

/// @brief Function signature for executable commands.
/// Takes a vector of string arguments and returns a CommandResult.
using CommandFunction = std::function<CommandResult(const std::vector<std::string>&)>;

/// @brief Metadata and implementation of a named command.
struct Command {
    std::string name;             ///< Unique command name (e.g., "find-file").
    std::string description;      ///< Human-readable help text.
    CommandFunction function;     ///< The implementation function.
    std::vector<std::string> aliases; ///< Alternative names.
    bool interactive;             ///< Whether this command can be called interactively (M-x).
    
    Command(std::string n, std::string desc, CommandFunction func, 
            std::vector<std::string> alias = {}, bool inter = true)
        : name(std::move(n)), description(std::move(desc)), 
          function(std::move(func)), aliases(std::move(alias)), interactive(inter) {}
};

/// @brief A possible completion match for user input.
struct CompletionCandidate {
    std::string text;       ///< The completion text.
    int score;              ///< Matching score (higher is better).
    std::string description;///< Extra info (e.g., file type, command desc).
    
    CompletionCandidate(std::string t, int s = 0, std::string desc = "")
        : text(std::move(t)), score(s), description(std::move(desc)) {}
        
    bool operator<(const CompletionCandidate& other) const {
        if (score != other.score) return score > other.score; // Higher score first
        return text < other.text; // Alphabetical for same score
    }
};

/// @brief Provider function for generating completions.
using CompletionProvider = std::function<std::vector<CompletionCandidate>(const std::string& input)>;

/// @brief Utility class for filesystem completions.
class FileSystemCompletionProvider {
public:
    /// @brief Complete paths (files and directories) relative to CWD or absolute.
    std::vector<CompletionCandidate> complete_path(const std::string& input) const;
    
    /// @brief Complete directory paths only.
    std::vector<CompletionCandidate> complete_directory(const std::string& input) const;
    
    /// @brief Complete files, optionally filtered by extension.
    std::vector<CompletionCandidate> complete_file(const std::string& input, const std::vector<std::string>& extensions = {}) const;
    
private:
    bool is_absolute_path(const std::string& path) const;
    std::string normalize_path(const std::string& path) const;
    int calculate_path_score(const std::string& candidate, const std::string& input) const;
};

/// @brief Central registry for commands and completion logic.
/// 
/// The CommandSystem manages:
/// - Registration of named commands.
/// - Execution of commands by name.
/// - Parsing of command strings.
/// - Autocompletion providers for different contexts (M-x, Find File, etc.).
class CommandSystem {
public:
    explicit CommandSystem(EditorCore& core);
    ~CommandSystem() = default;

    // === Command Registration ===

    /// @brief Register a command object.
    void register_command(std::unique_ptr<Command> command);

    /// @brief Helper to register a command.
    void register_command(const std::string& name, const std::string& description,
                         CommandFunction function, const std::vector<std::string>& aliases = {},
                         bool interactive = true);
    
    // === Command Execution ===

    /// @brief Execute a named command with arguments.
    /// @return Result indicating success/failure and message.
    CommandResult execute(const std::string& command_name, const std::vector<std::string>& args = {});

    /// @brief Parse and execute a raw command string (e.g., "find-file src/main.cpp").
    CommandResult execute_string(const std::string& command_string);
    
    // === Command Lookup ===

    /// @brief Check if a command exists.
    bool has_command(const std::string& name) const;

    /// @brief Get a command by name.
    std::shared_ptr<Command> get_command(const std::string& name) const;

    /// @brief Get names of all registered commands.
    std::vector<std::string> get_all_command_names() const;

    /// @brief Get names of commands marked as interactive.
    std::vector<std::string> get_interactive_command_names() const;
    
    // === Completion System ===

    /// @brief Get completions for command names (M-x).
    std::vector<CompletionCandidate> complete_command(const std::string& input) const;

    /// @brief Get completions for buffer names (C-x b).
    std::vector<CompletionCandidate> complete_buffer_name(const std::string& input) const;

    /// @brief Get completions for file paths (C-x C-f).
    std::vector<CompletionCandidate> complete_file_path(const std::string& input) const;

    /// @brief Get completions for theme names.
    std::vector<CompletionCandidate> complete_theme_name(const std::string& input) const;
    
    /// @brief Register a custom completion provider for a command argument.
    void register_completion_provider(const std::string& command_name, CompletionProvider provider);

    /// @brief Get completions for a specific command's arguments.
    std::vector<CompletionCandidate> get_completions(const std::string& command_name, const std::string& input) const;
    
    // === Utilities ===

    /// @brief Calculate fuzzy match score between candidate and input.
    static int fuzzy_match_score(const std::string& candidate, const std::string& input);

    /// @brief Check if candidate matches input fuzzily.
    static bool fuzzy_match(const std::string& candidate, const std::string& input);
    
private:
    EditorCore& core_;
    std::unordered_map<std::string, std::shared_ptr<Command>> commands_;
    std::unordered_map<std::string, CompletionProvider> completion_providers_;
    FileSystemCompletionProvider fs_provider_;
    
    void register_builtin_commands();
    std::vector<std::string> parse_command_string(const std::string& command_string) const;
};

} // namespace lumacs