/*
 * Peppermint C89 interpreter.
 *
 * This implements the language behavior present in the original TypeScript
 * front end: let bindings, integer/real literals, strings, arithmetic,
 * comments, and @argv/@env/@exit builtins.
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define PM_NAME_MAX 128
#define PM_TEXT_MAX 4096
#define PM_MAX_VARS 256

typedef enum {
    PM_NONE,
    PM_INT,
    PM_REAL,
    PM_STRING
} PMType;

typedef struct {
    PMType type;
    long integer;
    double real;
    char *text;
} PMValue;

typedef struct {
    char name[PM_NAME_MAX];
    PMValue value;
} PMVariable;

typedef struct {
    const char *source;
    const char *filename;
    long line;
    int argc;
    char **argv;
    PMVariable vars[PM_MAX_VARS];
    int var_count;
    int stopped;
} PMContext;

static void pm_free_value(PMValue *value)
{
    if (value->type == PM_STRING && value->text != NULL) {
        free(value->text);
    }
    value->type = PM_NONE;
    value->text = NULL;
    value->integer = 0L;
    value->real = 0.0;
}

static char *pm_copy_text(const char *start, size_t length)
{
    char *result;
    result = (char *)malloc(length + 1U);
    if (result == NULL) {
        return NULL;
    }
    memcpy(result, start, length);
    result[length] = '\0';
    return result;
}

static void pm_error(PMContext *context, const char *message)
{
    fprintf(stderr, "%s:%ld: %s\n", context->filename, context->line, message);
}

static void pm_skip_space(PMContext *context, const char **cursor)
{
    const char *p;
    (void)context;
    p = *cursor;
    for (;;) {
        while (*p == ' ' || *p == '\t' || *p == '\r') {
            p++;
        }
        if (*p == '#') {
            while (*p != '\0' && *p != '\n') {
                p++;
            }
        } else {
            break;
        }
    }
    *cursor = p;
}

static int pm_is_identifier_start(int c)
{
    return isalpha((unsigned char)c) || c == '_';
}

static int pm_is_identifier_char(int c)
{
    return isalnum((unsigned char)c) || c == '_';
}

static int pm_match(PMContext *context, const char **cursor, const char *word)
{
    const char *p;
    size_t length;
    (void)context;
    p = *cursor;
    length = strlen(word);
    if (strncmp(p, word, length) == 0 &&
        !pm_is_identifier_char((unsigned char)p[length])) {
        *cursor = p + length;
        return 1;
    }
    return 0;
}

static int pm_make_none(PMValue *value)
{
    value->type = PM_NONE;
    value->integer = 0L;
    value->real = 0.0;
    value->text = NULL;
    return 1;
}

static int pm_make_integer(PMValue *value, long number)
{
    pm_make_none(value);
    value->type = PM_INT;
    value->integer = number;
    return 1;
}

static int pm_make_real(PMValue *value, double number)
{
    pm_make_none(value);
    value->type = PM_REAL;
    value->real = number;
    return 1;
}

static int pm_make_string(PMValue *value, const char *start, size_t length)
{
    pm_make_none(value);
    value->text = pm_copy_text(start, length);
    if (value->text == NULL) {
        return 0;
    }
    value->type = PM_STRING;
    return 1;
}

static int pm_copy_value(PMValue *destination, const PMValue *source)
{
    pm_free_value(destination);
    destination->type = source->type;
    destination->integer = source->integer;
    destination->real = source->real;
    destination->text = NULL;
    if (source->type == PM_STRING) {
        if (source->text == NULL) {
            return 1;
        }
        destination->text = pm_copy_text(source->text, strlen(source->text));
        if (destination->text == NULL) {
            destination->type = PM_NONE;
            return 0;
        }
    }
    return 1;
}

static PMVariable *pm_find_variable(PMContext *context, const char *name)
{
    int i;
    for (i = 0; i < context->var_count; i++) {
        if (strcmp(context->vars[i].name, name) == 0) {
            return &context->vars[i];
        }
    }
    return NULL;
}

static int pm_set_variable(PMContext *context, const char *name,
                           const PMValue *value)
{
    PMVariable *variable;
    variable = pm_find_variable(context, name);
    if (variable == NULL) {
        if (context->var_count >= PM_MAX_VARS || strlen(name) >= PM_NAME_MAX) {
            pm_error(context, "too many or oversized variables");
            return 0;
        }
        variable = &context->vars[context->var_count];
        strcpy(variable->name, name);
        pm_make_none(&variable->value);
        context->var_count++;
    }
    return pm_copy_value(&variable->value, value);
}

static int pm_parse_expression(PMContext *context, const char **cursor,
                               PMValue *value);

static int pm_parse_string(PMContext *context, const char **cursor,
                           PMValue *value)
{
    const char *p;
    const char *start;
    char buffer[PM_TEXT_MAX];
    size_t length;
    p = *cursor;
    p++;
    start = p;
    length = 0U;
    while (*p != '\0' && *p != '"') {
        if (*p == '\\' && p[1] != '\0') {
            p++;
            if (*p == 'n') {
                if (length < PM_TEXT_MAX - 1U) buffer[length++] = '\n';
            } else if (*p == 'r') {
                if (length < PM_TEXT_MAX - 1U) buffer[length++] = '\r';
            } else if (*p == 't') {
                if (length < PM_TEXT_MAX - 1U) buffer[length++] = '\t';
            } else {
                if (length < PM_TEXT_MAX - 1U) buffer[length++] = *p;
            }
            p++;
        } else {
            if (length < PM_TEXT_MAX - 1U) buffer[length++] = *p;
            p++;
        }
    }
    (void)start;
    if (*p != '"') {
        pm_error(context, "string not closed");
        return 0;
    }
    buffer[length] = '\0';
    if (!pm_make_string(value, buffer, length)) {
        pm_error(context, "out of memory");
        return 0;
    }
    *cursor = p + 1;
    return 1;
}

static int pm_parse_primary(PMContext *context, const char **cursor,
                            PMValue *value)
{
    const char *p;
    char name[PM_NAME_MAX];
    size_t length;
    char *end;
    long integer;
    double real;
    PMVariable *variable;
    p = *cursor;
    pm_skip_space(context, &p);
    if (*p == '"') {
        if (!pm_parse_string(context, &p, value)) return 0;
        *cursor = p;
        return 1;
    }
    if (*p == '(') {
        p++;
        if (!pm_parse_expression(context, &p, value)) return 0;
        pm_skip_space(context, &p);
        if (*p != ')') {
            pm_error(context, "expected ')' ");
            pm_free_value(value);
            return 0;
        }
        *cursor = p + 1;
        return 1;
    }
    if (isdigit((unsigned char)*p) || (*p == '.' && isdigit((unsigned char)p[1]))) {
        real = strtod(p, &end);
        if (end == p) {
            pm_error(context, "invalid number");
            return 0;
        }
        if (strchr(p, '.') != NULL && strchr(p, '.') < end) {
            pm_make_real(value, real);
        } else {
            integer = strtol(p, &end, 10);
            pm_make_integer(value, integer);
        }
        *cursor = end;
        return 1;
    }
    if (pm_is_identifier_start((unsigned char)*p)) {
        length = 0U;
        while (pm_is_identifier_char((unsigned char)p[length])) {
            if (length < PM_NAME_MAX - 1U) name[length] = p[length];
            length++;
        }
        if (length >= PM_NAME_MAX) {
            pm_error(context, "identifier too long");
            return 0;
        }
        name[length] = '\0';
        variable = pm_find_variable(context, name);
        if (variable == NULL) {
            pm_error(context, "unknown identifier");
            return 0;
        }
        if (!pm_copy_value(value, &variable->value)) {
            pm_error(context, "out of memory");
            return 0;
        }
        *cursor = p + length;
        return 1;
    }
    pm_error(context, "expected expression");
    return 0;
}

static int pm_numeric(const PMValue *value, double *number)
{
    if (value->type == PM_INT) {
        *number = (double)value->integer;
        return 1;
    }
    if (value->type == PM_REAL) {
        *number = value->real;
        return 1;
    }
    return 0;
}

static int pm_apply_operator(PMContext *context, PMValue *left, char operator,
                             PMValue *right)
{
    double a;
    double b;
    double result;
    int integer_result;
    char *text;
    size_t left_length;
    size_t right_length;
    if (operator == '+' && left->type == PM_STRING && right->type == PM_STRING) {
        left_length = strlen(left->text);
        right_length = strlen(right->text);
        text = (char *)malloc(left_length + right_length + 1U);
        if (text == NULL) {
            pm_error(context, "out of memory");
            return 0;
        }
        memcpy(text, left->text, left_length);
        memcpy(text + left_length, right->text, right_length + 1U);
        pm_free_value(left);
        left->type = PM_STRING;
        left->text = text;
        return 1;
    }
    if (!pm_numeric(left, &a) || !pm_numeric(right, &b)) {
        pm_error(context, "arithmetic requires numeric values");
        return 0;
    }
    if (operator == '+') result = a + b;
    else if (operator == '-') result = a - b;
    else if (operator == '*') result = a * b;
    else if (operator == '/') {
        if (b == 0.0) {
            pm_error(context, "division by zero");
            return 0;
        }
        result = a / b;
    } else if (operator == '%') {
        long ia;
        long ib;
        if (left->type != PM_INT || right->type != PM_INT || b == 0.0) {
            pm_error(context, "modulo requires nonzero integers");
            return 0;
        }
        ia = left->integer;
        ib = right->integer;
        pm_free_value(left);
        pm_make_integer(left, ia % ib);
        return 1;
    } else {
        pm_error(context, "unknown operator");
        return 0;
    }
    integer_result = left->type == PM_INT && right->type == PM_INT && operator != '/';
    pm_free_value(left);
    if (integer_result) {
        pm_make_integer(left, (long)result);
    } else {
        pm_make_real(left, result);
    }
    return 1;
}

static int pm_parse_expression(PMContext *context, const char **cursor,
                               PMValue *value)
{
    const char *p;
    PMValue right;
    char operator;
    p = *cursor;
    pm_make_none(value);
    if (!pm_parse_primary(context, &p, value)) return 0;
    for (;;) {
        pm_skip_space(context, &p);
        operator = *p;
        if (operator != '+' && operator != '-' && operator != '*' &&
            operator != '/' && operator != '%') break;
        p++;
        pm_make_none(&right);
        if (!pm_parse_primary(context, &p, &right)) {
            pm_free_value(value);
            return 0;
        }
        if (!pm_apply_operator(context, value, operator, &right)) {
            pm_free_value(value);
            pm_free_value(&right);
            return 0;
        }
        pm_free_value(&right);
    }
    *cursor = p;
    return 1;
}

static void pm_print_value(const PMValue *value)
{
    if (value->type == PM_STRING) printf("%s\n", value->text);
    else if (value->type == PM_INT) printf("%ld\n", value->integer);
    else if (value->type == PM_REAL) printf("%g\n", value->real);
    else printf("None\n");
}

static void pm_builtin(PMContext *context, const char **cursor)
{
    const char *p;
    const char *start;
    char name[PM_NAME_MAX];
    char *end;
    long index;
    size_t length;
    p = *cursor + 1;
    start = p;
    while (pm_is_identifier_char((unsigned char)*p)) p++;
    length = (size_t)(p - start);
    if (length >= PM_NAME_MAX) {
        pm_error(context, "builtin name too long");
        return;
    }
    memcpy(name, start, length);
    name[length] = '\0';
    if (strcmp(name, "exit") == 0) {
        context->stopped = 1;
        *cursor = p;
        return;
    }
    if (strcmp(name, "argv") == 0) {
        if (*p == ':') {
            index = strtol(p + 1, &end, 10);
            if (end == p + 1 || index < 0L || index >= context->argc) {
                printf("None\n");
            } else {
                printf("%s\n", context->argv[index]);
            }
            p = end;
        } else {
            int i;
            for (i = 0; i < context->argc; i++) {
                if (i != 0) putchar(' ');
                fputs(context->argv[i], stdout);
            }
            putchar('\n');
        }
    } else if (strcmp(name, "env") == 0) {
        const char *key;
        const char *result;
        key = NULL;
        if (*p == ':') {
            p++;
            start = p;
            while (pm_is_identifier_char((unsigned char)*p)) p++;
            length = (size_t)(p - start);
            if (length >= PM_NAME_MAX) length = PM_NAME_MAX - 1U;
            memcpy(name, start, length);
            name[length] = '\0';
            key = name;
        }
        result = key == NULL ? NULL : getenv(key);
        printf("%s\n", result == NULL || result[0] == '\0' ? "None" : result);
    } else {
        pm_error(context, "unknown builtin");
    }
    *cursor = p;
}

static int pm_run(PMContext *context)
{
    const char *p;
    PMValue value;
    char name[PM_NAME_MAX];
    size_t length;
    p = context->source;
    context->line = 1L;
    while (*p != '\0' && !context->stopped) {
        pm_skip_space(context, &p);
        if (*p == '\n') {
            context->line++;
            p++;
            continue;
        }
        if (*p == '\0') break;
        if (*p == '@') {
            pm_builtin(context, &p);
        } else if (pm_match(context, &p, "let")) {
            pm_skip_space(context, &p);
            length = 0U;
            while (pm_is_identifier_char((unsigned char)p[length])) {
                if (length < PM_NAME_MAX - 1U) name[length] = p[length];
                length++;
            }
            if (length == 0U || length >= PM_NAME_MAX) {
                pm_error(context, "expected variable name");
                return 0;
            }
            name[length] = '\0';
            p += length;
            pm_skip_space(context, &p);
            if (p[0] != ':' || p[1] != '=') {
                pm_error(context, "expected ':='");
                return 0;
            }
            p += 2;
            pm_make_none(&value);
            if (!pm_parse_expression(context, &p, &value)) return 0;
            if (!pm_set_variable(context, name, &value)) {
                pm_free_value(&value);
                return 0;
            }
            pm_free_value(&value);
        } else {
            pm_make_none(&value);
            if (!pm_parse_expression(context, &p, &value)) return 0;
            pm_print_value(&value);
            pm_free_value(&value);
        }
        while (*p == ' ' || *p == '\t' || *p == '\r') p++;
        if (*p == '\n') {
            context->line++;
            p++;
        } else if (*p != '\0' && *p != '#') {
            pm_error(context, "unexpected characters");
            return 0;
        }
    }
    return 1;
}

static char *pm_read_file(const char *filename)
{
    FILE *file;
    long size;
    char *data;
    size_t count;
    file = fopen(filename, "rb");
    if (file == NULL) return NULL;
    if (fseek(file, 0L, SEEK_END) != 0) { fclose(file); return NULL; }
    size = ftell(file);
    if (size < 0L || fseek(file, 0L, SEEK_SET) != 0) { fclose(file); return NULL; }
    data = (char *)malloc((size_t)size + 1U);
    if (data == NULL) { fclose(file); return NULL; }
    count = fread(data, 1U, (size_t)size, file);
    fclose(file);
    data[count] = '\0';
    return data;
}

int main(int argc, char **argv)
{
    PMContext context;
    char *source;
    int i;
    int result;
    if (argc < 2) {
        fprintf(stderr, "usage: peppermint <file.ppm> [args...]\n");
        return 2;
    }
    source = pm_read_file(argv[1]);
    if (source == NULL) {
        fprintf(stderr, "peppermint: cannot read %s\n", argv[1]);
        return 2;
    }
    context.source = source;
    context.filename = argv[1];
    context.argc = argc - 2;
    context.argv = argv + 2;
    context.var_count = 0;
    context.stopped = 0;
    for (i = 0; i < PM_MAX_VARS; i++) pm_make_none(&context.vars[i].value);
    result = pm_run(&context) ? 0 : 1;
    for (i = 0; i < context.var_count; i++) pm_free_value(&context.vars[i].value);
    free(source);
    return result;
}