#include "block.h"
#include "expr/expr.h"
#include "iterate.h"

struct cond_group_parser_state {
	struct parser_state s_base;
	bool s_inline;
	unsigned int s_prev_token;

	struct ivy_ast_cond_node *s_cur_branch;
	b_queue s_branches;

	struct ivy_ast_node *s_prev_node;
};

static void init_state(struct ivy_parser *ctx, struct parser_state *sp, uintptr_t arg)
{
	struct cond_group_parser_state *state
		= (struct cond_group_parser_state *)sp;
	state->s_prev_node = (struct ivy_ast_node *)arg;
}

static enum ivy_status flush_current_branch(struct cond_group_parser_state *state)
{
	if (!state->s_cur_branch) {
		return IVY_ERR_INTERNAL_FAILURE;
	}

	b_queue_push_back(&state->s_branches, &state->s_cur_branch->n_base.n_entry);

	state->s_cur_branch
		= (struct ivy_ast_cond_node *)ast_node_create(IVY_AST_COND);

	if (!state->s_cur_branch) {
		return IVY_ERR_NO_MEMORY;
	}

	return IVY_OK;
}

struct token_parse_result parse_if(struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct cond_group_parser_state *state
		= parser_get_state(ctx, struct cond_group_parser_state);

	if (state->s_cur_branch) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	state->s_cur_branch
		= (struct ivy_ast_cond_node *)ast_node_create(IVY_AST_COND);
	if (!state->s_cur_branch) {
		return PARSE_RESULT(IVY_ERR_NO_MEMORY, 0);
	}

	if (state->s_prev_node) {
		/* this is an inline if-else */
		state->s_inline = true;
		state->s_cur_branch->n_body = state->s_prev_node;
		state->s_prev_node = NULL;
	} else {
		state->s_inline = false;
	}

	struct expr_parser_state *expr
		= (struct expr_parser_state *)parser_push_state(
			ctx, IVY_AST_EXPR, 0);

	state->s_prev_token = IVY_KW_IF;
	expr->s_subexpr_depth = 1;

	return PARSE_RESULT(IVY_OK, 0);
}

struct token_parse_result parse_elif(struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct cond_group_parser_state *state
		= parser_get_state(ctx, struct cond_group_parser_state);

	if (!state->s_cur_branch) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_inline) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_prev_token != IVY_KW_THEN) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	state->s_cur_branch->n_body = state->s_prev_node;
	state->s_prev_node = NULL;

	enum ivy_status status = flush_current_branch(state);
	if (status != IVY_OK) {
		return PARSE_RESULT(status, 0);
	}

	struct expr_parser_state *expr
		= (struct expr_parser_state *)parser_push_state(
			ctx, IVY_AST_EXPR, 0);

	state->s_prev_token = IVY_KW_ELIF;
	expr->s_subexpr_depth = 1;

	return PARSE_RESULT(IVY_OK, 0);
}

static struct token_parse_result parse_then(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct cond_group_parser_state *state
		= parser_get_state(ctx, struct cond_group_parser_state);

	if (!state->s_cur_branch) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_inline) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (state->s_prev_token != IVY_KW_IF && state->s_prev_token != IVY_KW_ELIF) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	/* previous component was the if-condition. */
	if (!state->s_prev_node) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	state->s_cur_branch->n_cond = state->s_prev_node;
	state->s_prev_node = NULL;

	/* next component will be a block. */
	struct block_parser_state *block
		= (struct block_parser_state *)parser_push_state(
			ctx, IVY_AST_BLOCK, 0);
	/* set the sub-expression depth to be non-zero so the expression parser doesn't consume the expression separator. */
	block_add_terminator(block, IVY_KW_ELIF);
	block_add_terminator(block, IVY_KW_ELSE);
	block_add_terminator(block, IVY_KW_END);

	state->s_prev_token = IVY_KW_THEN;
	return PARSE_RESULT(IVY_OK, 0);
}

static struct token_parse_result parse_else(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	enum ivy_status status;
	struct cond_group_parser_state *state
		= parser_get_state(ctx, struct cond_group_parser_state);

	if (!state->s_cur_branch) {
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	if (!state->s_inline) {
		/* previous component was either an expression or a block, and is the if branch body. */
		if (!state->s_prev_node) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		if (state->s_prev_token != IVY_KW_THEN) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		state->s_cur_branch->n_body = state->s_prev_node;
		state->s_prev_node = NULL;

		status = flush_current_branch(state);
		if (status != IVY_OK) {
			return PARSE_RESULT(status, 0);
		}

		/* next component should be a block. */
	} else {
		/* previous component was the if-condition. */
		if (!state->s_prev_node) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		if (state->s_prev_token != IVY_KW_IF) {
			return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
		}

		state->s_cur_branch->n_cond = state->s_prev_node;
		state->s_prev_node = NULL;

		status = flush_current_branch(state);
		if (status != IVY_OK) {
			return PARSE_RESULT(status, 0);
		}

		/* next component will be an expression. */
		struct expr_parser_state *expr
			= (struct expr_parser_state *)parser_push_state(
				ctx, IVY_AST_EXPR, 0);
		/* set the sub-expression depth to be non-zero so the expression
		 * parser doesn't consume the expression separator. */
		expr->s_subexpr_depth = 1;
	}

	state->s_prev_token = IVY_KW_ELSE;
	return PARSE_RESULT(IVY_OK, 0);
}

static struct token_parse_result parse_expr_begin(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct cond_group_parser_state *state
		= parser_get_state(ctx, struct cond_group_parser_state);

	if (state->s_prev_token != IVY_KW_ELSE
	    && state->s_prev_token != IVY_KW_THEN) {
		/* expression can only follow else and then keywords. */
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	struct block_parser_state *block
		= (struct block_parser_state *)parser_push_state(
			ctx, IVY_AST_BLOCK, 0);
	block_add_terminator(block, IVY_KW_END);
	return PARSE_RESULT(IVY_OK, PARSE_REPEAT_TOKEN);
}

static enum ivy_status finalise_cond_group(struct cond_group_parser_state *state)
{
	struct ivy_ast_cond_group_node *group
		= (struct ivy_ast_cond_group_node *)state->s_base.s_node;

	if (state->s_inline) {
		/* we have just reached the end of either the 'if' or the 'else' expression. */
		if (!state->s_cur_branch) {
			/* not currently parsing a conditional branch. */
			return IVY_ERR_BAD_SYNTAX;
		}

		if (!state->s_prev_node) {
			/* else expression is empty. */
			return IVY_ERR_BAD_SYNTAX;
		}

		if (state->s_prev_token == IVY_KW_ELSE) {
			/* this is the else expression, s_prev_node is the else body. */
			state->s_cur_branch->n_body = state->s_prev_node;
		} else if (state->s_prev_token == IVY_KW_IF) {
			/* this is the if expression, s_prev_node is the if condition. */
			state->s_cur_branch->n_cond = state->s_prev_node;
		}

		state->s_prev_node = NULL;
		flush_current_branch(state);

		group->n_branches = state->s_branches;
		state->s_branches = B_QUEUE_INIT;
		return IVY_OK;
	} else {
		/* we have just reached the 'end' keyword. */
		if (!state->s_cur_branch) {
			/* not currently parsing a conditional branch. */
			return IVY_ERR_BAD_SYNTAX;
		}

		if (!state->s_prev_node) {
			/* else expression is empty. */
			return IVY_ERR_BAD_SYNTAX;
		}

		state->s_cur_branch->n_body = state->s_prev_node;
		state->s_prev_node = NULL;
		flush_current_branch(state);

		group->n_branches = state->s_branches;
		state->s_branches = B_QUEUE_INIT;
		return IVY_OK;
	}
}

static struct token_parse_result parse_punct_terminator(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct cond_group_parser_state *state
		= parser_get_state(ctx, struct cond_group_parser_state);

	if (!state->s_inline) {
		/* only inline conditional can be ended with punctuation. */
		return PARSE_RESULT(IVY_ERR_BAD_SYNTAX, 0);
	}

	enum ivy_status status = finalise_cond_group(state);
	if (status != IVY_OK) {
		return PARSE_RESULT(status, 0);
	}

	parser_pop_state(ctx, STATE_ADD_NODE_TO_PARENT);
	return PARSE_RESULT(IVY_OK, PARSE_REPEAT_TOKEN);
}

static struct token_parse_result parse_end(
	struct ivy_parser *ctx, struct ivy_token *tok)
{
	struct cond_group_parser_state *state
		= parser_get_state(ctx, struct cond_group_parser_state);

	enum ivy_status status = finalise_cond_group(state);
	if (status != IVY_OK) {
		return PARSE_RESULT(status, 0);
	}

	int flags = 0;
	if (state->s_inline) {
		flags = PARSE_REPEAT_TOKEN;
	}

	parser_pop_state(ctx, STATE_ADD_NODE_TO_PARENT);
	return PARSE_RESULT(IVY_OK, flags);
}

static enum ivy_status add_child(
	struct parser_state *parent, struct ivy_ast_node *child)
{
	struct cond_group_parser_state *state
		= (struct cond_group_parser_state *)parent;

	if (state->s_prev_node) {
		return IVY_ERR_BAD_SYNTAX;
	}

	state->s_prev_node = child;
	return IVY_OK;
}

static void cond_group_collect_children(
	struct ivy_ast_node *node, struct ivy_ast_node_iterator *iterator)
{
	struct ivy_ast_cond_group_node *group
		= (struct ivy_ast_cond_group_node *)node;

	b_queue_entry *entry = b_queue_first(&group->n_branches);
	while (entry) {
		struct ivy_ast_node *branch
			= b_unbox(struct ivy_ast_node, entry, n_entry);
		ast_node_iterator_enqueue_node(iterator, node, branch);
		entry = b_queue_next(entry);
	}
}

static void cond_collect_children(
	struct ivy_ast_node *node, struct ivy_ast_node_iterator *iterator)
{
	struct ivy_ast_cond_node *cond = (struct ivy_ast_cond_node *)node;

	if (cond->n_cond) {
		ast_node_iterator_enqueue_node(iterator, node, cond->n_cond);
	}

	if (cond->n_body) {
		ast_node_iterator_enqueue_node(iterator, node, cond->n_body);
	}
}

struct ast_node_type cond_group_node_ops = {
	.n_init_state = init_state,
	.n_add_child = add_child,
	.n_collect_children = cond_group_collect_children,
	.n_state_size = sizeof(struct cond_group_parser_state),
	.n_node_size = sizeof(struct ivy_ast_cond_group_node),
	.n_keyword_parsers = {
		KW_PARSER(IF, parse_if),
		KW_PARSER(THEN, parse_then),
		KW_PARSER(ELIF, parse_elif),
		KW_PARSER(ELSE, parse_else),
		KW_PARSER(END, parse_end),
	},
	.n_symbol_parsers = {
		SYM_PARSER(DOT, parse_punct_terminator),
		SYM_PARSER(COMMA, parse_punct_terminator),
		SYM_PARSER(RIGHT_PAREN, parse_punct_terminator),
		SYM_PARSER(BANG, parse_punct_terminator),
	},
	.n_expr_parser = {
		.expr_begin = parse_expr_begin,
	},
};

struct ast_node_type cond_node_ops = {
	.n_collect_children = cond_collect_children,
	.n_state_size = sizeof(struct parser_state),
	.n_node_size = sizeof(struct ivy_ast_cond_node),
};