#include "RemoveLeftRecursion.h"
#include <string.h>
#include <stdlib.h>

const char *VoidSymbol = "$"; // "ε"
const char *Postfix = "'";

char rule_table[20][256];
char ruleNameArr[20][64];

int main(int argc, char *argv[])
{
	//
	// 调用 InitRules 函数初始化文法
	//

	Rule *pHead = InitRules();

	//
	// 输出消除左递归之前的文法
	//
	printf("Before Remove Left Recursion:\n");
	PrintRule(pHead);

	//
	// 调用 RemoveLeftRecursion 函数对文法消除左递归
	//
	RemoveLeftRecursion(pHead);

	//
	// 输出消除左递归之后的文法
	//
	printf("\nAfter Remove Left Recursion:\n");
	PrintRule(pHead);

	FreeRule(pHead);

	return 0;
}

/*
功能：
	将一个 Symbol 添加到 Select 的末尾。

参数：
	pSelect -- Select 指针。
	pNewSymbol -- Symbol 指针。
*/
void AddSymbolToSelect(RuleSymbol *pSelect, RuleSymbol *pNewSymbol)
{
	while (pSelect->pNextSymbol != NULL)
	{
		pSelect = pSelect->pNextSymbol;
	}
	pSelect->pNextSymbol = pNewSymbol;
}

/*
功能：
	将一个 Select 加入到文法末尾。当 Select 为 NULL 时就将一个ε终结符加入到文法末尾。

参数：
	pRule -- 文法指针。
	pNewSelect -- Select 指针。
*/
void AddSelectToRule(Rule *pRule, RuleSymbol *pNewSelect)
{

	if (pNewSelect == NULL)
	{
		pNewSelect = CreateSymbol();
		pNewSelect->isToken = 1;
		strcpy(pNewSelect->TokenName, VoidSymbol);
	}
	RuleSymbol **ppSelect = &(pRule->pFirstSymbol);
	while (*ppSelect != NULL)
	{
		ppSelect = &((*ppSelect)->pOther);
	}
	*ppSelect = pNewSelect;
}

/*
功能：
	消除左递归。

参数：
	pHead -- 文法链表的头指针。
*/
void RemoveLeftRecursion(Rule *pHead)
{
	RuleSymbol *pSelect; // Select 游标
	Rule *pNewRule;		 // Rule 指针

	pNewRule = CreateRule(pHead->RuleName); // 创建新 Rule
	strcat(pNewRule->RuleName, Postfix);

	pSelect = pHead->pFirstSymbol; // 初始化 Select 游标
	RuleSymbol **pSelectPrePtr = &pHead->pFirstSymbol;
	while (pSelect != NULL) // 循环处理所有的 Select
	{
		if (0 == pSelect->isToken && pSelect->pRule == pHead) // Select 存在左递归
		{
			// 移除包含左递归的 Select，将其转换为右递归后添加到新 Rule 的末尾，并移动游标

			*pSelectPrePtr = pSelect->pOther;
			pSelect->pOther = NULL;
			RuleSymbol *pOldSymbol = pSelect;
			pSelect = pSelect->pNextSymbol;
			free(pOldSymbol);
			AddSelectToRule(pNewRule, pSelect);
			RuleSymbol *pNewSymbol = CreateSymbol();
			pNewSymbol->isToken = 0;
			pNewSymbol->pRule = pNewRule;
			AddSymbolToSelect(pSelect, pNewSymbol);

			pSelect = *pSelectPrePtr;
		}
		else // Select 不存在左递归
		{
			// 在没有左递归的 Select 末尾添加指向新 Rule 的非终结符，并移动游标

			RuleSymbol *pNewSymbol = CreateSymbol();
			pNewSymbol->isToken = 0;
			pNewSymbol->pRule = pNewRule;
			AddSymbolToSelect(pSelect, pNewSymbol);

			pSelectPrePtr = &((*pSelectPrePtr)->pOther);
			pSelect = *pSelectPrePtr;
		}
	}

	// 在新 Rule 的最后加入ε(用 '$' 代替)
	AddSelectToRule(pNewRule, NULL);
	// 将新 Rule 插入文法链表
	Rule **ppRule = &(pHead->pNextRule);
	while (*ppRule != NULL)
	{
		ppRule = &((*ppRule)->pNextRule);
	}
	*ppRule = pNewRule;

	return;
}

/*
功能：
	使用给定的数据初始化文法链表

返回值：
	Rule 指针
*/
typedef struct _SYMBOL
{
	int isToken;
	//char Name[MAX_STR_LENGTH];
} SYMBOL;

typedef struct _RULE_ENTRY
{
	char RuleName[MAX_STR_LENGTH];
	SYMBOL Selects[64][64];
} RULE_ENTRY;

/*
功能：
	初始化文法链表。
	
返回值：
	文法的头指针。
*/
Rule *InitRules()
{
	/* A -> Aa | bA | c | Ad */

	int nRuleCount = 0;
	for (int i = 0; i < 20; i++)
	{
		gets(rule_table[i]);
		int length = strlen(rule_table[i]);
		if (length == 0)
		{
			break;
		}

		for (int j = 0; j < length; j++)
		{
			if (rule_table[i][j] == ' ')
			{
				ruleNameArr[i][j] = '\0';
				break;
			}
			ruleNameArr[i][j] = rule_table[i][j];
		}

		nRuleCount++;
	}

	Rule *pHead, *pRule;
	RuleSymbol **pSymbolPtr1, **pSymbolPtr2;

	int i, k;

	Rule **pRulePtr = &pHead;
	for (i = 0; i < nRuleCount; i++)
	{
		*pRulePtr = CreateRule(ruleNameArr[i]);
		pRulePtr = &(*pRulePtr)->pNextRule;
	}

	pRule = pHead;
	for (i = 0; i < nRuleCount; i++)
	{
		pSymbolPtr1 = &pRule->pFirstSymbol;

		int start = 0;
		for (int j = 0; rule_table[i][j] != '\0'; j++)
		{
			if (rule_table[i][j] == ' '
				&& rule_table[i][j + 1] == '-'
				&& rule_table[i][j + 2] == '>'
				&& rule_table[i][j + 3] == ' ')
			{
				start = j + 4;
				break;
			}
		}

		for (k = start; rule_table[i][k] != '\0'; k++)
		{
			if (rule_table[i][k] == '|')
			{
				pSymbolPtr1 = &(*pSymbolPtr1)->pOther;
				pSymbolPtr2 = pSymbolPtr1;
				continue;
			}
			if (rule_table[i][k] == ' ')
			{
				continue;
			}
			if (k == start)
			{
				pSymbolPtr2 = pSymbolPtr1;
			}

			*pSymbolPtr2 = CreateSymbol();

			char tokenName[MAX_STR_LENGTH] = {};
			tokenName[0] = rule_table[i][k];
			tokenName[1] = '\0';
			(*pSymbolPtr2)->isToken = 1;
			for (int m = 0; m < nRuleCount; m++)
			{
				if (strcmp(tokenName, ruleNameArr[m]) == 0)
				{
					(*pSymbolPtr2)->isToken = 0;
					(*pSymbolPtr2)->pRule = FindRule(pHead, tokenName);
					if (NULL == (*pSymbolPtr2)->pRule)
					{
						printf("Init rules error, miss rule \"%s\"\n", tokenName);
						exit(1);
					}
				}
			}
			if ((*pSymbolPtr2)->isToken == 1)
			{
				strcpy((*pSymbolPtr2)->TokenName, tokenName);
			}

			pSymbolPtr2 = &(*pSymbolPtr2)->pNextSymbol;
		}

		pRule = pRule->pNextRule;
	}

	return pHead;
}

/*
功能：
	创建一个新的 Rule。

参数：
	pRuleName -- 文法的名字。
	
返回值：
	Rule 指针
*/
Rule *CreateRule(const char *pRuleName)
{
	Rule *pRule = (Rule *)malloc(sizeof(Rule));

	strcpy(pRule->RuleName, pRuleName);
	pRule->pFirstSymbol = NULL;
	pRule->pNextRule = NULL;

	return pRule;
}

/*
功能：
	创建一个新的 Symbol。
	
返回值：
	RuleSymbol 指针
*/
RuleSymbol *CreateSymbol()
{
	RuleSymbol *pSymbol = (RuleSymbol *)malloc(sizeof(RuleSymbol));

	pSymbol->pNextSymbol = NULL;
	pSymbol->pOther = NULL;
	pSymbol->isToken = -1;
	pSymbol->TokenName[0] = '\0';
	pSymbol->pRule = NULL;

	return pSymbol;
}

/*
功能：
	根据 RuleName 在文法链表中查找名字相同的文法。

参数：
	pHead -- 文法链表的头指针。
	RuleName -- 文法的名字。
	
返回值：
	如果存在名字相同的文法返回 Rule 指针，否则返回 NULL
*/
Rule *FindRule(Rule *pHead, const char *RuleName)
{
	Rule *pRule;
	for (pRule = pHead; pRule != NULL; pRule = pRule->pNextRule)
	{
		if (0 == strcmp(pRule->RuleName, RuleName))
		{
			break;
		}
	}

	return pRule;
}

/*
功能：
	输出文法。

参数：
	pHead -- 文法链表的头指针。
*/
void PrintRule(Rule *pHead)
{
	while (pHead != NULL)
	{
		printf("%s->", pHead->RuleName);
		RuleSymbol *pSelect = pHead->pFirstSymbol;
		while (pSelect != NULL)
		{
			RuleSymbol *pSymbol = pSelect;
			while (pSymbol != NULL)
			{
				if (pSymbol->isToken)
				{
					printf("%s", pSymbol->TokenName);
				}
				else
				{
					printf("%s", pSymbol->pRule->RuleName);
				}
				pSymbol = pSymbol->pNextSymbol;
			}
			pSelect = pSelect->pOther;
			if (pSelect != NULL)
			{
				printf("|");
			}
		}
		printf("\n");
		pHead = pHead->pNextRule;
	}
}
void FreeSymbol(RuleSymbol *pSymbol)
{
	if (pSymbol)
	{
		FreeSymbol(pSymbol->pNextSymbol);
		FreeSymbol(pSymbol->pOther);
		free(pSymbol);
	}
}

void FreeRule(Rule *pHead)
{
	if (pHead)
	{
		FreeRule(pHead->pNextRule);
		FreeSymbol(pHead->pFirstSymbol);
		free(pHead);
	}
}