/**
 * @file sh.c
 * @brief ClaudeOS shell.
 *
 * A simple interactive shell that reads commands from stdin,
 * supports built-in commands (cd, exit, help, env), and
 * executes external programs via fork+exec.
 */

#include "syscalls.h"

/** Maximum command line length. */
#define CMD_MAX 256

/** Read a line from stdin with echo and basic line editing.
 *  Returns length of the line (excluding newline). */
static int readline(char *buf, int maxlen) {
    int pos = 0;
    while (pos < maxlen - 1) {
        char c;
        int n = read(0, &c, 1);
        if (n <= 0) {
            /* No data yet: yield CPU and retry */
            yield();
            continue;
        }

        if (c == '\n' || c == '\r') {
            putchar('\n');
            break;
        } else if (c == '\b' || c == 127) {
            /* Backspace */
            if (pos > 0) {
                pos--;
                puts("\b \b"); /* Move back, overwrite with space, move back */
            }
        } else if (c >= 32) {
            /* Printable character */
            buf[pos++] = c;
            putchar(c);
        }
    }
    buf[pos] = '\0';
    return pos;
}

/** Skip leading whitespace, return pointer to first non-space. */
static char *skip_spaces(char *s) {
    while (*s == ' ' || *s == '\t') s++;
    return s;
}

/** Find the next space or end of string. */
static char *find_space(char *s) {
    while (*s && *s != ' ' && *s != '\t') s++;
    return s;
}

/** Built-in: cd <path> */
static void builtin_cd(char *arg) {
    if (!arg || !*arg) {
        arg = "/";
    }

    /* Update CWD environment variable */
    setenv("CWD", arg);
    /* Verify it was set */
    char cwd[128];
    if (getenv("CWD", cwd, sizeof(cwd)) >= 0) {
        puts("cd: ");
        puts(cwd);
        putchar('\n');
    }
}

/** Built-in: env - print all known env vars. */
static void builtin_env(void) {
    char buf[128];
    if (getenv("CWD", buf, sizeof(buf)) >= 0) {
        puts("CWD=");
        puts(buf);
        putchar('\n');
    }
    if (getenv("PATH", buf, sizeof(buf)) >= 0) {
        puts("PATH=");
        puts(buf);
        putchar('\n');
    }
    if (getenv("TEST", buf, sizeof(buf)) >= 0) {
        puts("TEST=");
        puts(buf);
        putchar('\n');
    }
}

/** Built-in: help */
static void builtin_help(void) {
    puts("ClaudeOS Shell\n");
    puts("Built-in commands:\n");
    puts("  cd <path>  - change working directory\n");
    puts("  env        - show environment variables\n");
    puts("  help       - show this message\n");
    puts("  exit       - exit the shell\n");
    puts("External commands are loaded from initrd.\n");
}

/** Execute an external command via fork+exec. */
static void run_command(const char *cmd) {
    int32_t pid = fork();
    if (pid < 0) {
        puts("sh: fork failed\n");
        return;
    }

    if (pid == 0) {
        /* Child: exec the command */
        int32_t ret = exec(cmd);
        if (ret < 0) {
            puts("sh: ");
            puts(cmd);
            puts(": not found\n");
            exit(127);
        }
        /* exec doesn't return on success */
        exit(1);
    }

    /* Parent: wait for child */
    waitpid(pid);
}

int main(void) {
    puts("ClaudeOS Shell v0.1\n");
    puts("Type 'help' for available commands.\n\n");

    char cmd[CMD_MAX];

    for (;;) {
        /* Print prompt with CWD */
        char cwd[128];
        if (getenv("CWD", cwd, sizeof(cwd)) < 0) {
            strcpy(cwd, "/");
        }
        puts(cwd);
        puts("$ ");

        /* Read command */
        int len = readline(cmd, CMD_MAX);
        if (len == 0) continue;

        /* Parse command and arguments */
        char *line = skip_spaces(cmd);
        if (*line == '\0') continue;

        char *arg_start = find_space(line);
        char *arg = (char *)0;
        if (*arg_start) {
            *arg_start = '\0';
            arg = skip_spaces(arg_start + 1);
            if (*arg == '\0') arg = (char *)0;
        }

        /* Check built-in commands */
        if (strcmp(line, "exit") == 0) {
            puts("Goodbye!\n");
            exit(0);
        } else if (strcmp(line, "cd") == 0) {
            builtin_cd(arg);
        } else if (strcmp(line, "env") == 0) {
            builtin_env();
        } else if (strcmp(line, "help") == 0) {
            builtin_help();
        } else {
            /* External command */
            run_command(line);
        }
    }

    return 0;
}