#include <stdlib.h>
#include <string.h> // strcmp()

#include "scanner.h"
#include "scannerStructs.h"
#include "recognizeEq.h"

// checks if input is a number
int acceptNumber(List **list) {
    if (*list != NULL && (*list)->type == NUMBER) {
        *list = (*list)->next;
        return 1;
    }
    return 0;
}

// checks if input is an identifier
int acceptIdentifier(List **list) {
    if (*list != NULL && (*list)->type == IDENTIFIER) {
        *list = (*list)->next;
        return 1;
    }
    return 0;
}

// checks if input is a specified character
int acceptCharacter(char symbol, List **list) {
    if (*list != NULL && (*list)->type == SYMBOL && ((*list)->token).symbol == symbol) {
        char symbol = ((*list)->token).symbol;
        *list = (*list)->next;
        return symbol;
    }
    return 0;
}

// checks if input follows the grammar <nat> | [nat] <identifier> ['^' <nat>]
int acceptTerm(List **list) {
    if (acceptNumber(list)) {
        if (acceptIdentifier(list)) {
            if (acceptCharacter('^', list)) {
                if (!acceptNumber(list)) {
                    return 0;
                }
            }
            return 1;
        }
        return 1;
    }
    if (acceptIdentifier(list)) {
        if (acceptCharacter('^', list)) {
            if (!acceptNumber(list)) {
                return 0;
            }
        }
        return 1;
    }
    return 0;
}

// checks if input follows the grammar [-] <term> {'+' <term> || '-' <term>}
int acceptExpression(List **list) {
    if (acceptCharacter('-', list)) {
    }

    if (!acceptTerm(list)) {
        return 0;
    }

    while (acceptCharacter('+', list) || acceptCharacter('-', list)) {
        if (!acceptTerm(list)) {
            return 0;
        }
    }
    return 1;
}

// checks if input follows the grammar <expression> '=' <expression>
int acceptEquation(List **list) {
    if (!acceptExpression(list)) {
        return 0;
    }
    if (!acceptCharacter('=', list)) {
        return 0;
    }
    if (!acceptExpression(list)) {
        return 0;
    }
    if (*list != NULL) {
        return 0; // the list should be empty at this point
    }
    return 1;
}

// checks if the entire input is a valid equation
int isValidEquation(List *list) {
    return acceptEquation(&list);
}

// Returns maximum between two values
int getMax(int a, int b) {
    return (a > b ? a : b);
}

// returns 1 if there is exactly one variable
int isSingleVariableEquation(List *list) {
    char *str = NULL;
    int found = 0;
    while (list != NULL) {
        if (list->type == IDENTIFIER) {
            if (str == NULL) {
                str = list->token.identifier;
                found = 1;
            }
            if (strcmp(list->token.identifier, str)) {
                return 0;
            }
        }
        list = list->next;
    }
    return found;
}

// returns the highest degree of x as an int
int getDegree(List *list) {
    int maxFound = 1;
    while (list != NULL && list->next != NULL) {
        if (acceptCharacter('^', &list)) {
            maxFound = getMax(maxFound, (list->token).number);
        }
        list = list->next;
    }
    return maxFound;
}

// evaluates the entire input as an equation
double solveEquation(List *list) {
    int coefficient = 0, constant = 0;
    int sign = 1;
    int onLeftSide = 1;

    while (list != NULL) {
        switch (list->type) {
            case NUMBER:
                if (list->next != NULL && list->next->type == IDENTIFIER) {
                    if (onLeftSide) {
                        coefficient += sign * (list->token.number - 1);
                    } else {
                        coefficient -= sign * (list->token.number + 1);
                    }
                } else {
                    if (onLeftSide) {
                        constant += sign * list->token.number;
                    } else {
                        constant -= sign * list->token.number;
                    }
                }
                sign = 1;
                break;
            case IDENTIFIER:
                if (onLeftSide) {
                    coefficient += sign;
                } else {
                    coefficient -= sign;
                }
                break;
            case SYMBOL:
                if (list->token.symbol == '=') {
                    onLeftSide = 0;
                } else if (list->token.symbol == '-') {
                    sign = -1;
                }
                break;
        }
        list = list->next;
    }

    return (double)-constant / coefficient;
}