php_repl.c

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <termios.h>
#include <unistd.h>
#include <ctype.h>
#include <string.h>

#define FG_MAGENTA "\x1B[35m"
#define FG_RESET "\x1B[0m"

/**
 * Represents the REPL state which `render' will observe
 */
struct s_php_repl_state {
    char *line;
    int column;
    int history_index;
    bool complete;
    char *command;
    char **history;
};

/**
 * REPL interface and essential functions to share state
 */
typedef struct s_php_repl {
    struct s_php_repl_state state;
    void (*start)(struct s_php_repl *self);
    void (*render)(struct s_php_repl *self);
    void (*handle_read)(struct s_php_repl *self);
    void (*tick)(struct s_php_repl *self, char chr);
} php_repl;

/**
 * Disables the canonical mode for the terminal and returns the old
 * configuration to be restored later
 *
 * @static
 * @return struct termios
 */
static struct termios disable_canonical_mode() {
    struct termios old_term, new_term;
    tcgetattr(STDIN_FILENO, &old_term);
    new_term = old_term;
    new_term.c_lflag &= ~ICANON;
    new_term.c_lflag &= ~ECHO;
    tcsetattr(STDIN_FILENO, TCSANOW, &new_term);
    return old_term;
}

/**
 * Receives and sets a terminal configuration
 *
 * @static
 * @param struct termios term
 * @return void
 */
static void restore_canonical_mode(struct termios term) {
    tcsetattr(STDIN_FILENO, TCSANOW, &term);
}

/**
 * Emits the ANSI escape code to clear the current line
 *
 * @static
 * @return void
 */
static void console_clear_line() {
    printf("\e[2K");
}

/**
 * Emits the ANSI escape code to reset the cursor for up to 1024 chars
 *
 * @static
 * @return void
 */
static void console_reset_cursor() {
    printf("\e[1024D");
}

/**
 * Sets the initial state for the REPL
 *
 * @param php_repl *self
 * @return void
 */
static void php_repl_start(php_repl *self) {
    struct s_php_repl_state state;
    state.line = malloc(1);
    state.column = 0;
    state.history_index = 0;
    state.complete = true;
    state.command = NULL;
    state.history = NULL;
    self->state = state;
}

/**
 * CLI renderer for the current line based on the state. Yes, we are using the React
 * model with C, sorry
 *
 * @param php_repl *repl
 * @return void
 */
static void php_repl_render(php_repl *repl) {
    struct s_php_repl_state state = repl->state;
    char *line = state.line;
    int column = state.column;

    console_clear_line();
    console_reset_cursor();

    printf(FG_MAGENTA);
    printf("php> ");
    printf(FG_RESET);

    printf("%s", state.line);
}

/**
 * Handles terminal ticks and events using a char stream
 *
 * @param php_repl *repl
 * @param char chr
 * @return void
 */
static void php_repl_tick(php_repl *repl, char chr) {
    if (iscntrl(chr)) {
        return;
    }

    struct s_php_repl_state state = repl->state;
    char *line = state.line;
    int column = state.column;

    // Insert chat at specific index
    char *buffer = malloc(sizeof(line) + sizeof(char));
    char holder[1] = { chr };
    strncpy(buffer, line, column);
    int size = strlen(buffer);
    strcpy(buffer + size, holder);
    strcpy(buffer + size + 1, line + column);

    repl->state.line = malloc(sizeof(buffer));
    repl->state.line = buffer;
    repl->state.column++;
    repl->render(repl);
}

/**
 * Main loop for the line. Ends when the ENTER key is pressed
 *
 * @param php_repl *repl
 * @return void
 */
static void php_repl_handle_read(php_repl *repl) {
    struct termios checkpoint = disable_canonical_mode();
    char current;

    do {
        current = getchar();
        repl->tick(repl, current);
    } while (current != 0xA);

    restore_canonical_mode(checkpoint);
}

/**
 * Initializes the REPL functions
 *
 * @param php_repl *repl
 * @return void
 */
static void php_repl_init(php_repl *repl) {
    repl->start = &php_repl_start;
    repl->render = &php_repl_render;
    repl->tick = &php_repl_tick;
    repl->handle_read = &php_repl_handle_read;
}

/**
 * Entry point for testing purposes
 *
 * @param int argc
 * @param char **argv
 * @return int
 */
int main(int argc, char **argv) {
    php_repl repl;
    php_repl_init(&repl);
    repl.start(&repl);
    repl.render(&repl);
    repl.handle_read(&repl);
    return 0;
}