#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include "parser.h"

/* Vrátí ukazatel na aktuální token */
static const struct token *get_token(const struct parser *parser) {
    return lex_token(&parser->lexer);
}

/* Vrátí 1, pokud aktuální token je typu <type> */
static int token_is(const struct parser *parser, enum token_type type) {
    return get_token(parser)->type == type;
}

/* Vrátí hodnotu tokenu, který je konstanta */
static double token_num(const struct parser *parser) {
    return get_token(parser)->val.num;
}

/* Vrátí index funkce tokenu, který reprezentuje funkci */
static size_t token_fn_idx(const struct parser *parser) {
    return get_token(parser)->val.fn_idx;
}

/* Načte další token */
static void next_token(struct parser *parser) {
    lex_next(&parser->lexer);
}

/* Vrátí 1, pokud je aktuální token typu <type> a načte další */
static int accept_token(struct parser *parser, enum token_type type) {
    if (token_is(parser, type)) {
        next_token(parser);
        return 1;
    }
    return 0;
}

/* Nastaví chybu při alokaci */
static void error_bad_alloc(struct parser *parser) {
    error_set(&parser->eb, ERR_BAD_ALLOC);
    error_printf(&parser->eb, "Out of memory\n");
}

/* Vyhodí chybu při neočekávaném tokenu */
static void error_expected_tokens(struct parser *parser, size_t num_tokens, ...) {
    size_t i;
    va_list ap;

    enum token_type got = get_token(parser)->type;

    if (got == TOK_ERROR) {
        error_set(&parser->eb, lex_get_error(&parser->lexer));
        error_printf(&parser->eb, "%s", lex_get_error_text(&parser->lexer));
        return;
    }

    error_set(&parser->eb, ERR_INVALID_FUNCTION);
    error_printf(&parser->eb, "Syntax error - expected ");

    va_start(ap, num_tokens);
    for (i = 0; i < num_tokens; ++i) {
        enum token_type tok = va_arg(ap, enum token_type);

        if (i > 0)
            error_printf(&parser->eb, ", ");

        error_printf(&parser->eb, "%s", lex_token_str(tok));
    }
    va_end(ap);

    error_printf(&parser->eb, " - but got %s\n", lex_token_str(got));

    lex_print_position(&parser->lexer, &parser->eb);
}

static struct expr_node *parse_expression(struct parser *parser);
static int parse_n_expressions(struct parser *parser, struct expr_node **out_nodes, size_t n);

/* Zpracuje výraz obalený závorkami */
static struct expr_node *parse_bracketed(struct parser *parser) {
    struct expr_node *node;

    if (!accept_token(parser, TOK_LEFT_PAREN)) {
        error_expected_tokens(parser, 1, TOK_LEFT_PAREN);
        return NULL;
    }

    if (!(node = parse_expression(parser)))
        return NULL;

    if (!accept_token(parser, TOK_RIGHT_PAREN)) {
        error_expected_tokens(parser, 1, TOK_RIGHT_PAREN);
        node_free(node);
        return NULL;
    }

    return node;
}

static struct expr_node *parse_function(struct parser *parser) {
        struct expr_node *node;
        struct expr_node *arg_nodes[MAX_MATH_FUNCTION_ARGS];
        size_t i;
        size_t fn_idx = token_fn_idx(parser);
        const struct math_function *fn = &fns_get()[fn_idx];
        
        next_token(parser);

        if (!accept_token(parser, TOK_LEFT_PAREN)) {
            error_expected_tokens(parser, 1, TOK_LEFT_PAREN);
            return NULL;
        }

        if (!parse_n_expressions(parser, arg_nodes, fn->num_args))
            return NULL;

        if (!(node = node_create_fn(fn_idx, arg_nodes))) {
            error_bad_alloc(parser);
            
            for (i = 0; i < fn->num_args; ++i)
                node_free(arg_nodes[i]);
            
            return NULL;
        }

        if (!accept_token(parser, TOK_RIGHT_PAREN)) {
            error_expected_tokens(parser, 1, TOK_RIGHT_PAREN);
            node_free(node);
            return NULL;
        }

        return node;
}

/* Zpracuje část výrazu, která už má nejvyšší precedenci (číselnou konstantu, proměnnou, funkci, nebo výraz obalený závorkami) */
static struct expr_node *parse_factor(struct parser *parser) {
    struct expr_node *node;

    if (token_is(parser, TOK_NUMBER)) {
        double val = token_num(parser);
        next_token(parser);
        if (!(node = node_create_const(val))) {
            error_bad_alloc(parser);
            return NULL;
        }

        return node;
    }

    if (accept_token(parser, TOK_VARIABLE)) {
        if (!(node = node_create_x())) {
            error_bad_alloc(parser);
            return NULL;
        }
        return node;
    }

    if (token_is(parser, TOK_FUNCTION)) {
        return parse_function(parser);
    }

    if (token_is(parser, TOK_LEFT_PAREN)) {
        return parse_bracketed(parser);
    }

    error_expected_tokens(parser, 4, TOK_NUMBER, TOK_VARIABLE, TOK_FUNCTION, TOK_LEFT_PAREN);
    return NULL;
}

static struct expr_node *parse_unary(struct parser *parser);

/* Zpracuje umocnění */
static struct expr_node *parse_power(struct parser *parser) {
    struct expr_node *node, *new_node, *inner;

    if (!(node = parse_factor(parser)))
        return NULL;

    if (accept_token(parser, TOK_POWER)) {
        if (!(inner = parse_unary(parser))) {
            node_free(node);
            return NULL;
        }

        if (!(new_node = node_create_pow(node, inner))) {
            error_bad_alloc(parser);
            node_free(node);
            node_free(inner);
            return NULL;
        }

        return new_node;
    }

    return node;
}

/* Zpracuje unární mínus, resp. plus */
static struct expr_node *parse_unary(struct parser *parser) {
    if (accept_token(parser, TOK_MINUS)) {
        struct expr_node *node, *inner;
        
        if (!(inner = parse_power(parser)))
            return NULL;

        if (!(node = node_create_neg(inner))) {
            error_bad_alloc(parser);
            node_free(inner);
            return NULL;
        }

        return node;
    }

    accept_token(parser, TOK_PLUS);
    return parse_power(parser);
}

/* Zpracuje součin nebo dělení */
static struct expr_node *parse_term(struct parser *parser) {
    struct expr_node *node, *new_node, *inner;

    if (!(node = parse_unary(parser)))
        return NULL;

    while (1) {
        struct expr_node *(*create_node)(struct expr_node *left, struct expr_node *right);

        if (accept_token(parser, TOK_MULTIPLY))
            create_node = node_create_mult;
        else if (accept_token(parser, TOK_DIVIDE))
            create_node = node_create_div;
        else
            break;

        if (!(inner = parse_unary(parser))) {
            node_free(node);
            return NULL;
        }

        if (!(new_node = create_node(node, inner))) {
            error_bad_alloc(parser);
            node_free(node);
            node_free(inner);
            return NULL;
        }

        node = new_node;
    }

    return node;
}

/* Zpracuje sčítání nebo odečítání */
static struct expr_node *parse_expression(struct parser *parser) {
    struct expr_node *node, *new_node, *inner;

    if (!(node = parse_term(parser)))
        return NULL;

    while (1) {
        struct expr_node *(*create_node)(struct expr_node *left, struct expr_node *right);

        if (accept_token(parser, TOK_PLUS))
            create_node = node_create_add;
        else if (accept_token(parser, TOK_MINUS))
            create_node = node_create_sub;
        else
            break;

        if (!(inner = parse_term(parser))) {
            node_free(node);
            return NULL;
        }

        if (!(new_node = create_node(node, inner))) {
            error_bad_alloc(parser);
            node_free(node);
            node_free(inner);
            return NULL;
        }

        node = new_node;
    }

    return node;
}

/* Zpracuje n výrazů */
static int parse_n_expressions(struct parser *parser, struct expr_node **out_nodes, size_t n) {
    size_t i;

    for (i = 0; i < n; ++i) {
        struct expr_node *node;
        if (!(node = parse_expression(parser)))
            break;

        out_nodes[i] = node;

        if (i < n - 1)
            accept_token(parser, TOK_COMMA);
    }

    if (i != n) {
        while (i) {
            --i;
            node_free(out_nodes[i]);
            out_nodes[i] = NULL;
        }

        return 0;
    }

    return 1;
}

int parser_parse_n(struct parser *parser, const char *str, const char *variable_name, struct expr_node **out_nodes, size_t n) {
    error_buffer_init(&parser->eb);
    lex_init(&parser->lexer, str, variable_name);

    if (!parse_n_expressions(parser, out_nodes, n)) {
        return 0;
    }

    if (!token_is(parser, TOK_EOF)) {
        size_t i;
        error_expected_tokens(parser, 1, TOK_EOF);
        
        for (i = 0; i < n; ++i) {
            node_free(out_nodes[i]);
            out_nodes[i] = NULL;
        }
        
        return 0;
    }

    return 1;
}

struct expr_node *parser_parse(struct parser *parser, const char *str, const char *variable_name) {
    struct expr_node *out_node = NULL;
    parser_parse_n(parser, str, variable_name, &out_node, 1);
    return out_node;
}

enum error_code parser_get_error(const struct parser *parser) {
    return error_get(&parser->eb);
}

const char *parser_get_error_text(const struct parser *parser) {
    return error_get_text(&parser->eb);
}