/*
 * sccash - Simple C Cash
 * A lightweight CLI currency converter for USD, JPY, and EUR
 * Compile: gcc -o sccash sccash.c
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define RATE_USD_JPY 159.67
#define RATE_USD_EUR 0.866
#define RATE_EUR_JPY 184.20

typedef enum {
    CURRENCY_USD,
    CURRENCY_JPY,
    CURRENCY_EUR,
    CURRENCY_INVALID
} Currency;

const char* currency_names[] = {"USD", "JPY", "EUR"};

Currency parse_currency(const char* input) {
    char upper[4] = {0};
    int i;
    for (i = 0; i < 3 && input[i]; i++) {
        upper[i] = toupper(input[i]);
    }
    
    if (strcmp(upper, "USD") == 0) return CURRENCY_USD;
    if (strcmp(upper, "JPY") == 0) return CURRENCY_JPY;
    if (strcmp(upper, "EUR") == 0) return CURRENCY_EUR;
    return CURRENCY_INVALID;
}

double convert_to_usd(double amount, Currency from) {
    switch (from) {
        case CURRENCY_USD: return amount;
        case CURRENCY_JPY: return amount / RATE_USD_JPY;
        case CURRENCY_EUR: return amount / RATE_USD_EUR;
        default: return 0.0;
    }
}

double convert_from_usd(double usd_amount, Currency to) {
    switch (to) {
        case CURRENCY_USD: return usd_amount;
        case CURRENCY_JPY: return usd_amount * RATE_USD_JPY;
        case CURRENCY_EUR: return usd_amount * RATE_USD_EUR;
        default: return 0.0;
    }
}

double convert_currency(double amount, Currency from, Currency to) {
    double usd_amount;
    if (from == to) return amount;
    usd_amount = convert_to_usd(amount, from);
    return convert_from_usd(usd_amount, to);
}

void print_table_header(void) {
    printf("+--------+---------------+--------+----------------+\n");
    printf("|  FROM  |    AMOUNT     |   TO   |  CONVERTED     |\n");
    printf("+--------+---------------+--------+----------------+\n");
}

void print_table_row(const char* from, double amount, const char* to, double converted) {
    printf("| %-6s | %13.2f | %-6s | %14.2f |\n", from, amount, to, converted);
}

void print_table_footer(void) {
    printf("+--------+---------------+--------+----------------+\n");
}

void print_all_conversions(double amount, Currency from) {
    int i;
    printf("\n");
    print_table_header();
    
    for (i = 0; i < 3; i++) {
        if (i != from) {
            Currency to = (Currency)i;
            double result = convert_currency(amount, from, to);
            print_table_row(currency_names[from], amount, currency_names[to], result);
        }
    }
    
    print_table_footer();
    printf("\nExchange Rates (as of March 26, 2026):\n");
    printf("  1 USD = %.2f JPY\n", RATE_USD_JPY);
    printf("  1 USD = %.3f EUR\n", RATE_USD_EUR);
    printf("  1 EUR = %.2f JPY\n", RATE_EUR_JPY);
    printf("\n");
}

void interactive_mode(void) {
    char from_input[10], to_input[10];
    char show_all[10];
    double amount, result;
    Currency from, to;
    
    printf("\n=== sccash - Simple C Cash ===\n\n");
    printf("Available currencies: USD, JPY, EUR\n\n");
    
    printf("Enter amount: ");
    if (scanf("%lf", &amount) != 1 || amount < 0) {
        fprintf(stderr, "Error: Invalid amount\n");
        return;
    }
    
    printf("Convert from (USD/JPY/EUR): ");
    scanf("%9s", from_input);
    from = parse_currency(from_input);
    
    if (from == CURRENCY_INVALID) {
        fprintf(stderr, "Error: Invalid currency '%s'\n", from_input);
        return;
    }
    
    printf("Convert to (USD/JPY/EUR): ");
    scanf("%9s", to_input);
    to = parse_currency(to_input);
    
    if (to == CURRENCY_INVALID) {
        fprintf(stderr, "Error: Invalid currency '%s'\n", to_input);
        return;
    }
    
    if (from == to) {
        printf("\nResult: %.2f %s (same currency)\n", amount, currency_names[from]);
        return;
    }
    
    result = convert_currency(amount, from, to);
    
    printf("\n");
    print_table_header();
    print_table_row(currency_names[from], amount, currency_names[to], result);
    print_table_footer();
    printf("\n");
    
    printf("Show all conversions? (y/n): ");
    scanf("%9s", show_all);
    if (show_all[0] == 'y' || show_all[0] == 'Y') {
        print_all_conversions(amount, from);
    }
}

void cli_mode(int argc, char* argv[]) {
    double amount, result;
    Currency from, to;
    
    if (argc < 4) {
        fprintf(stderr, "Usage: %s <amount> <from> <to>\n", argv[0]);
        fprintf(stderr, "  amount: numeric value to convert\n");
        fprintf(stderr, "  from:   source currency (USD, JPY, EUR)\n");
        fprintf(stderr, "  to:     target currency (USD, JPY, EUR)\n\n");
        fprintf(stderr, "Example: %s 100 USD JPY\n", argv[0]);
        fprintf(stderr, "Or run without arguments for interactive mode\n");
        exit(1);
    }
    
    amount = atof(argv[1]);
    if (amount <= 0) {
        fprintf(stderr, "Error: Invalid amount '%s'\n", argv[1]);
        exit(1);
    }
    
    from = parse_currency(argv[2]);
    to = parse_currency(argv[3]);
    
    if (from == CURRENCY_INVALID) {
        fprintf(stderr, "Error: Invalid source currency '%s'\n", argv[2]);
        fprintf(stderr, "Available: USD, JPY, EUR\n");
        exit(1);
    }
    
    if (to == CURRENCY_INVALID) {
        fprintf(stderr, "Error: Invalid target currency '%s'\n", argv[3]);
        fprintf(stderr, "Available: USD, JPY, EUR\n");
        exit(1);
    }
    
    result = convert_currency(amount, from, to);
    
    printf("\n");
    print_table_header();
    print_table_row(currency_names[from], amount, currency_names[to], result);
    print_table_footer();
    printf("\n");
}

int main(int argc, char* argv[]) {
    if (argc == 1) {
        interactive_mode();
    } else {
        cli_mode(argc, argv);
    }
    
    return 0;
}