#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdalign.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>

#include "alloc.h"
#include "common.h"
#include "errors.h"
#include "lexer.h"
#include "parser.h"
#include "strview.h"

#if DEBUG
#	define AST_DFLT_CAP (8)
#	define AUX_DFLT_CAP (8)
#else
#	define AST_DFLT_CAP (2048)
#	define AUX_DFLT_CAP (128)
#endif
#define SIZE_WDTH (sizeof(size_t) * CHAR_BIT)

typedef idx_t parsefn(ast_t *, aux_t *, lexemes_t)
	__attribute__((nonnull));
static parsefn parseblk, parsefunc, parseproto, parsestmt, parsetype;
static idx_t parsedecl(ast_t *, aux_t *, lexemes_t, bool)
	__attribute__((nonnull));
static idx_t parseexpr(ast_t *, aux_t *, lexemes_t, int)
	__attribute__((nonnull));

static ast_t mkast(void);

/* Return a new index in AST where a node can be stored.  This function
   automatically resizes AST if it runs out of capacity. */
static idx_t astalloc(ast_t *ast)
	__attribute__((nonnull));

/* Resize AST to the next power-of-2 capacity */
static void astresz(ast_t *ast)
	__attribute__((nonnull));

/* TODO: Make thread-local? */
static size_t toksidx;

static int prectbl[_LEX_LAST_ENT] = {
	['+'] = 1,
	['-'] = 1,
	['*'] = 2,
	['/'] = 2,
	['%'] = 2,
};

idx_t
fwdnode(ast_t ast, idx_t i)
{
	while (likely(i < ast.len)) {
		switch (ast.kinds[i]) {
		case ASTBLK:
			i = ast.kids[i].lhs == AST_EMPTY ? i + 1 : ast.kids[i].rhs;
			break;
		case ASTDECL:
			i = ast.kids[i].rhs == AST_EMPTY ? i + 1 : ast.kids[i].rhs;
			break;
		case ASTRET:
			if (ast.kids[i].rhs == AST_EMPTY)
				return i + 1;
			i = ast.kids[i].rhs;
			break;
		case ASTBINADD:
		case ASTBINSUB:
		case ASTCDECL:
		case ASTFN:
		case ASTUNNEG:
			i = ast.kids[i].rhs;
			break;
		case ASTIDENT:
		case ASTNUMLIT:
		case ASTTYPE:
			return i + 1;
		case ASTFNPROTO:
			assert("analyzer: Not reachable");
			__builtin_unreachable();
		}
	}

	return i;
}

ast_t
parsetoks(lexemes_t toks, aux_t *aux)
{
	ast_t ast = mkast();
	aux->len = 0;
	aux->cap = AUX_DFLT_CAP;
	aux->buf = bufalloc(NULL, aux->cap, sizeof(*aux->buf));

	for (;;) {
		(void)parsedecl(&ast, aux, toks, true);
		if (toks.kinds[toksidx] == LEXEOF)
			break;
	}

	return ast;
}

idx_t
parseblk(ast_t *ast, aux_t *aux, lexemes_t toks)
{
	idx_t i = astalloc(ast);
	ast->lexemes[i] = toksidx;
	ast->kinds[i] = ASTBLK;
	ast->kids[i].lhs = AST_EMPTY;
	ast->kids[i].rhs = i;

	if (toks.kinds[toksidx++] != LEXLBRACE)
		err("parser: Expected left brace");

	if (toks.kinds[toksidx] != LEXRBRACE) {
		idx_t stmt = parsestmt(ast, aux, toks);
		ast->kids[i].lhs = ast->kids[i].rhs = stmt;
	}

	while (toks.kinds[toksidx] != LEXRBRACE) {
		idx_t stmt = parsestmt(ast, aux, toks);
		ast->kids[i].rhs = stmt;
	}

	toksidx++; /* Eat rbrace */
	return i;
}

idx_t
parsedecl(ast_t *ast, aux_t *aux, lexemes_t toks, bool toplvl)
{
	idx_t i = astalloc(ast), j = aux->len++;

	if (aux->len > aux->cap) {
		aux->cap *= 2;
		aux->buf = bufalloc(aux->buf, aux->cap, sizeof(*aux->buf));
	}

	/* TODO: Support ‘static’ as a keyword */
	aux->buf[j].decl.isstatic = toplvl;
	aux->buf[j].decl.isundef  = false;
	if (toplvl && toks.kinds[toksidx] == LEXIDENT
	    && strview_eq(SV("pub"), toks.strs[toksidx]))
	{
		aux->buf[j].decl.ispub = true;
		ast->lexemes[i] = ++toksidx;
	} else {
		aux->buf[j].decl.ispub = false;
		ast->lexemes[i] = toksidx;
	}

	if (toks.kinds[toksidx++] != LEXIDENT)
		err("parser: Expected identifier");
	if (toks.kinds[toksidx++] != LEXCOLON)
		err("parser: Expected colon");

	aux->buf[j].decl.type = toks.kinds[toksidx] == LEXIDENT
	                          ? parsetype(ast, aux, toks)
	                          : AST_EMPTY;
	ast->kids[i].lhs = j;

	switch (toks.kinds[toksidx++]) {
	case LEXSEMI:
		if (aux->buf[j].decl.type == AST_EMPTY)
			err("parser: No type provided in non-assigning declaration");
		ast->kinds[i] = ASTDECL;
		ast->kids[i].rhs = AST_EMPTY;
		return i;
	case LEXCOLON:
		ast->kinds[i] = ASTCDECL;
		break;
	case LEXEQ:
		ast->kinds[i] = ASTDECL;
		break;
	default:
		err("parser: Expected colon, equals, or semicolon");
	}

	idx_t rhs;
	bool func = false;

	switch (toks.kinds[toksidx]) {
	case LEXLPAR:
		func = true;
		if (ast->kinds[i] == ASTDECL)
			err("Cannot assign function to mutable variable");
		rhs = parsefunc(ast, aux, toks);
		break;
	case LEXELIP:
		toksidx++;
		if (ast->kinds[i] == ASTCDECL)
			err("parser: Cannot assign to ‘…’ in constant declaration");
		rhs = AST_EMPTY;
		aux->buf[j].decl.isundef = true;
		break;
	default:
		rhs = parseexpr(ast, aux, toks, 1);
	}

	ast->kids[i].rhs = rhs;
	if (!func && toks.kinds[toksidx++] != LEXSEMI)
		err("parser: Expected semicolon");

	return i;
}

idx_t
parsefunc(ast_t *ast, aux_t *aux, lexemes_t toks)
{
	idx_t i = astalloc(ast);
	ast->lexemes[i] = toksidx;

	assert(toks.kinds[toksidx] == LEXLPAR);

	ast->kinds[i] = ASTFN;
	idx_t lhs = parseproto(ast, aux, toks);
	idx_t rhs = parseblk(ast, aux, toks);
	ast->kids[i].lhs = lhs;
	ast->kids[i].rhs = rhs;

	return i;
}

idx_t
parseexprunit(ast_t *ast, lexemes_t toks)
{
	idx_t i = astalloc(ast);

	/* Unary plus is kind of a fake syntactic construct.  We just pretend
	   like it doesn’t exist, but allow it in the syntax to be consistent
	   with unary negation. */
	while (toks.kinds[toksidx] == LEXPLUS)
		toksidx++;

	ast->lexemes[i] = toksidx;

	switch (toks.kinds[toksidx++]) {
	case LEXNUM:
		ast->kinds[i] = ASTNUMLIT;
		break;
	case LEXIDENT:
		ast->kinds[i] = ASTIDENT;
		break;
	case LEXMINUS:
		ast->kinds[i] = ASTUNNEG;
		ast->kids[i].rhs = parseexprunit(ast, toks);
		break;
	default:
		err("parser: Invalid expression leaf");
	}
	return i;
}

idx_t
parseexprinc(ast_t *ast, aux_t *aux, lexemes_t toks, idx_t lhs, int minprec)
{
	uint8_t op = toks.kinds[toksidx];
	int nxtprec = prectbl[op];
	if (nxtprec != 0)
		toksidx++;
	if (nxtprec < minprec)
		return lhs;
	idx_t i = astalloc(ast);
	idx_t rhs = parseexpr(ast, aux, toks, nxtprec);
	ast->kinds[i] = op;
	ast->lexemes[i] = toksidx - 1;
	ast->kids[i].lhs = lhs;
	ast->kids[i].rhs = rhs;
	return i;
}

idx_t
parseexpr(ast_t *ast, aux_t *aux, lexemes_t toks, int minprec)
{
	idx_t lhs = parseexprunit(ast, toks);

	for (;;) {
		idx_t rhs = parseexprinc(ast, aux, toks, lhs, minprec);
		if (rhs == lhs)
			break;
		lhs = rhs;
	}

	return lhs;
}

idx_t
parseproto(ast_t *ast, aux_t *aux, lexemes_t toks)
{
	idx_t i = astalloc(ast);
	ast->lexemes[i] = toksidx;
	ast->kinds[i] = ASTFNPROTO;
	ast->kids[i].lhs = AST_EMPTY;

	if (toks.kinds[toksidx++] != LEXLPAR)
		err("parser: Expected left parenthesis");
	if (toks.kinds[toksidx++] != LEXRPAR)
		err("parser: Expected right parenthesis");

	idx_t rhs = toks.kinds[toksidx] == LEXIDENT ? parsetype(ast, aux, toks)
	                                             : AST_EMPTY;
	ast->kids[i].rhs = rhs;
	return i;
}

idx_t
parsestmt(ast_t *ast, aux_t *aux, lexemes_t toks)
{
	idx_t i;

	if (toks.kinds[toksidx] != LEXIDENT)
		err("parser: Expected identifier");

	strview_t sv = toks.strs[toksidx];
	if (strview_eq(SV("return"), sv)) {
		i = astalloc(ast);
		ast->lexemes[i] = toksidx++;
		ast->kinds[i] = ASTRET;

		idx_t rhs = toks.kinds[toksidx] != LEXSEMI ? parseexpr(ast, aux, toks, 1)
		                                            : AST_EMPTY;
		ast->kids[i].rhs = rhs;
		if (toks.kinds[toksidx++] != LEXSEMI)
			err("parser: Expected semicolon");
	} else if (toks.kinds[toksidx + 1] == LEXCOLON) {
		i = parsedecl(ast, aux, toks, false);
	} else {
		err("parser: Invalid statement");
	}

	return i;
}

idx_t
parsetype(ast_t *ast, aux_t *aux, lexemes_t toks)
{
	(void)aux;

	idx_t i = astalloc(ast);
	ast->kinds[i] = ASTTYPE;
	ast->lexemes[i] = toksidx;

	if (toks.kinds[toksidx++] != LEXIDENT)
		err("parser: Expected type");

	return i;
}

ast_t
mkast(void)
{
	ast_t soa;

	static_assert(AST_DFLT_CAP * sizeof(*soa.kinds) % alignof(idx_t) == 0,
	              "Additional padding is required to properly align LEXEMES");
	static_assert(AST_DFLT_CAP * (sizeof(*soa.kinds) + sizeof(*soa.lexemes))
	                      % alignof(pair_t)
	                  == 0,
	              "Additional padding is required to properly align KIDS");

	soa.len = 0;
	soa.cap = AST_DFLT_CAP;

	soa.kinds = bufalloc(NULL, soa.cap, AST_SOA_BLKSZ);
	soa.lexemes = (void *)((char *)soa.kinds + soa.cap * sizeof(*soa.kinds));
	soa.kids = (void *)((char *)soa.lexemes + soa.cap * sizeof(*soa.lexemes));

	return soa;
}

void
astresz(ast_t *soa)
{
	size_t ncap, pad1, pad2, newsz;
	ptrdiff_t lexemes_off, kids_off;

	lexemes_off = (char *)soa->lexemes - (char *)soa->kinds;
	kids_off = (char *)soa->kids - (char *)soa->kinds;

	/* The capacity is always going to be a power of 2, so checking for
	   overflow becomes pretty trivial */
	if (unlikely((soa->cap >> (SIZE_WDTH - 1)) != 0)) {
		errno = ENOMEM;
		err("%s:", __func__);
	}
	ncap = soa->cap << 1;

	/* Ensure that soa->lexemes is properly aligned */
	pad1 = alignof(idx_t) - ncap % alignof(idx_t);
	if (pad1 == alignof(idx_t))
		pad1 = 0;

	/* Ensure that soa->kids is properly aligned */
	pad2 = alignof(pair_t)
	     - (ncap * (1 + sizeof(idx_t)) + pad1) % alignof(pair_t);
	if (pad2 == alignof(pair_t))
		pad2 = 0;

	newsz = ncap * AST_SOA_BLKSZ + pad1 + pad2;
	soa->kinds = bufalloc(soa->kinds, newsz, 1);
	soa->lexemes = (void *)((char *)soa->kinds + ncap * sizeof(*soa->kinds)
	                        + pad1);
	soa->kids = (void *)((char *)soa->lexemes + ncap * sizeof(*soa->lexemes)
	                     + pad2);

	memmove(soa->kids, (char *)soa->kinds + kids_off,
	        soa->len * sizeof(*soa->kids));
	memmove(soa->lexemes, (char *)soa->kinds + lexemes_off,
	        soa->len * sizeof(*soa->lexemes));

	soa->cap = ncap;
}

idx_t
astalloc(ast_t *soa)
{
	if (unlikely(soa->len == soa->cap))
		astresz(soa);
	return soa->len++;
}