/* Semantic analyzer and type checker */
#include <stdlib.h>
#include <string.h>

#include "pre.h"
#include "sema.h"
#include "datatype.h"
#include "location.h"
#include "symbol.h"
#include "ast.h"
#include "state.h"
#include "messages.h"
#include "libs/stb_ds.h"

#define sema_error(ctx, loc, ...) do { 		\
		error((ctx)->cm, loc, __VA_ARGS__);	\
		(ctx)->ok = false;					\
	} while (0)
#define sema_warning(ctx, loc, ...) warning((ctx)->cm, loc, __VA_ARGS__)
#define sema_note(ctx, loc, ...) note((ctx)->cm, loc, __VA_ARGS__)
#define sema_is_stmt_terminal(s) (s->type == AST_RETURN || s->type == AST_BREAK)
#define sym_insert(syms, k, v) shput(syms, k, v)

enum SemaCtxFlags /* 64 bits */
{
	SctxInsideProc = BitPos(0),
	SctxInsideLoop = BitPos(1),
	SctxInsideIf = BitPos(2),
	SctxInTopLevel = BitPos(3),
	SctxInExpr = BitPos(4),
	SctxInDiscard = BitPos(5),
	SctxInStmtBlock = BitPos(6),
};

typedef struct {
	enum SymbolKind kind;
 	/* The data type associated with the symbol. */
	DataType *dtype;
	bool used;
	bool procparm; /* if its a proc parameter */
	Location loc;
} Symbol;

typedef HashMapStr(Symbol) SymbolEntry;

struct Scope
{
	Scope *prev; /* Previous scope in the stack */
	SymbolEntry *symbols; /* All the symbols in this scope */
};

typedef struct {
	bool ok;
} SemaStatus;

static const Symbol InvalidSymbol = {.kind = SymInvalid};
static const DataType *InvalidDataType = &(DataType){.kind = DtkInvalid};

static DataTypeCheck
datatype_struct_cmp(SemaCtx *sctx, DataType *s1, DataType *s2);
static DataTypeCheck
datatype_cmp(SemaCtx *sctx, DataType *dt1, DataType *dt2);
static DataType *
sema_expr(SemaCtx *sctx, Ast *expr, Location loc);
static void
sema_expr_list(SemaCtx *sctx, Vec(Ast *) exprs, Location loc);
static void
sema_node(SemaCtx *sctx, Ast *node);
static void
sema_stmts(SemaCtx *sctx, Vec(Ast *) stmts);
static DataType *
resolve_datatype(SemaCtx *sctx, const Str ident, Location loc);

static Scope *
make_scope(Scope *prev)
{
	Scope *sc = malloc(sizeof(*sc));
	sc->prev = prev;
	sc->symbols = nil;
	sh_new_arena(sc->symbols);
	shdefault(sc->symbols, InvalidSymbol);
	return sc;
}

static SemaCtx *
make_semactx(Compiler *cm, SemaCtx *prev)
{
	SemaCtx *smc = calloc(1, sizeof(*smc));
	smc->cm = cm;
	smc->prev = prev;
	return smc;
}

static DataType *
make_data_type(enum DataTypeKind kind, u16 size, bool builtin, bool sign)
{
	DataType *dt = calloc(1, sizeof(*dt));
	dt->kind = kind;
	dt->size = size;
	dt->builtin = builtin;
	dt->sign = sign;
	return dt;
}

static DataType *
make_proc_type(bool builtin, DataType *rettype, Vec(DataType *) argtypes)
{
	DataType *pdt = calloc(1, sizeof(*pdt));
	pdt->kind = DtkProc;
	pdt->builtin = builtin;
	pdt->proc.rettype = rettype;
	pdt->proc.argtypes = argtypes;
	return pdt;
}

static Vec(DataType *)
make_type_list_from_idents(SemaCtx *sctx, Vec(AstIdentTypePair) idents)
{
	if (idents == nil)
		return nil;

	Vec(DataType *) dts = nil;
	foreach (ident, idents)
		arrput(dts, resolve_datatype(sctx, ident.dtype, ident.dtype_loc));
	return dts;
}

static Vec(DataType *)
make_proc_args(DataType *a[], isize len)
{
	Vec(DataType *) args = nil;
	arrsetlen(args, len);
	memcpy(args, a, len);
	return args;
}

/* Pushes a new context frame. Note that this inherits the flags and scope of the
 * previous context frame.
 * XXX: could rather only push flags...
 */
static void
push_semactx(SemaCtx **sctx) 
{
	SemaCtx *tmp = make_semactx((*sctx)->cm, *sctx);
	tmp->flags = (*sctx)->flags;
	tmp->current_scope = (*sctx)->current_scope;
	tmp->top_scope = (*sctx)->top_scope;
	tmp->ok = (*sctx)->ok;
	*sctx = tmp;
}

/* Pops the current context frame. */
static void
pop_semactx(SemaCtx **sctx)
{
	SemaCtx *prev = (*sctx)->prev;
	compiler_assert((*sctx)->cm, prev != nil);
	prev->ok = (*sctx)->ok;
	free(*sctx);
	*sctx = prev;
}

static void
enter_scope(SemaCtx *sctx) 
{
	sctx->current_scope = make_scope(sctx->current_scope);
}

static void
exit_scope(SemaCtx *sctx)
{
	compiler_assert(sctx->cm, sctx->current_scope->prev != nil);
	sctx->current_scope = sctx->current_scope->prev;
}

Symbol *
sym_search_oncurrent(Scope *scope, const Str name)
{
	Symbol *sym = &shget(scope->symbols, name.s);
	if (sym->kind != SymInvalid)
		return sym;
	return nil;
}

/* Searches for a symbol in the current and previous scopes */
Symbol *
sym_search(Scope *scope, const Str name)
{
	Scope *sp = scope;
	Symbol *sym = nil;
	while (sp != nil && sym == nil) {
		sym = sym_search_oncurrent(sp, name);
		sp = sp->prev;
	}
	return sym;
}

/* Scans through the current scope for any unused var-like bindings
 * (including proc parameters)
 */
static void
sema_check_unused_vars(SemaCtx *sctx)
{
	/* Very simple, iterate over all bindings on this scope and report any that
	 * doesn't have the 'used' flag toggled. */
	const SymbolEntry *syms = sctx->current_scope->symbols;
	for (isize i = 0; i < shlen(syms); ++i) {
		const Symbol sym = syms[i].value;
		if (!sym.used && symbol_is_var_binding(sym.kind)) {
			const char *bind_kind_name = !sym.procparm ? "variable" : "proc parameter"; // SymbolKindStr[sym.kind] : "proc parameter";
			sema_warning(
				sctx, &sym.loc,
				"unused %s '%s'", bind_kind_name, syms[i].key
			);
		}
	}
}

static void
sema_check_dead_stmts(SemaCtx *sctx, Vec(Ast *) stmts)
{
	(void)sctx, (void)stmts;
	/* those who forsake the CFG are doomed to implement it badly without even
	 * noticing... */
}

static void
sema_match_proc_type(SemaCtx *sctx, Symbol *fsym, Str fident)
{
	if (fsym->dtype->kind != DtkProc) {
		sema_error(
			sctx, nil,
			"cannot call '%s' because has non-proc type '%s'",
			fident.s, "uh"
		);
		return;
	}
}

static DataType *
sema_proccall(SemaCtx *sctx, const AstProcCall *call, Location loc)
{
	Symbol *fsym = sym_search(sctx->current_scope, call->name);
	if (fsym == nil) {
		sema_error(sctx, &loc, "call to undeclared proc '%s'", call->name.s);
		return nil;
	}

	fsym->used = true;
	sema_match_proc_type(sctx, fsym, call->name);

	/* check call arguments */
	const isize proc_arglen = arrlen(fsym->dtype->proc.argtypes);
	if (call->args != nil) {
		compiler_assert(sctx->cm, call->args->type == AST_EXPRS);
		const isize call_arglen = arrlen(call->args->exprs);

		if (call_arglen != proc_arglen) {
			const char *at_most = call_arglen > proc_arglen ? "s at most" : "";
			sema_error(
				sctx, &loc,
				"argument length mismatch: given %li arguments to '%s' but it expects %li argument%s",
				call_arglen, call->name.s, proc_arglen, at_most
			);
			return nil;
		}
		sema_expr_list(sctx, call->args->exprs, loc); /* now sema-check the args */
	} else if (call->args == nil && proc_arglen != 0) {
		sema_error(sctx, &loc, "'%s' proc takes %li argument(s), but none given",
			  call->name.s, proc_arglen);
		return nil;
	}

	if (fsym->dtype->proc.rettype != sctx->builtintypes.void_t
		&& (~sctx->flags & SctxInDiscard)
		&& (~sctx->flags & SctxInExpr)) {
		sema_error(sctx, &loc, "result of function call with non-void type ignored");
		sema_note(sctx, &loc, "use 'discard' if this was intentional");
		return nil;
	}

	for (isize i = 0; i < proc_arglen; ++i) {
		;
	}
	return fsym->dtype;
}

/************ Semantic and type checking of expressions ************/
/* Type checking for expressions is done inside-out */

static DataType *
sema_expr_number(SemaCtx *sctx, AstNumber *num)
{
#define pow2(exp) (2 << (exp - 1))
	/* type rule axiom */
	num->type = sym_search_oncurrent(sctx->top_scope, Sl("u64"))->dtype;
	return num->type;
#undef pow2
}

static DataType *
sema_expr_strlit(SemaCtx *sctx, const Str *strlit)
{
	(void)sctx, (void)strlit;
	/* type rule axiom */
	return sym_search_oncurrent(sctx->top_scope, Sl("string"))->dtype;
}

static Symbol *
sema_expr_ident(SemaCtx *sctx, const Str ident)
{
	Symbol *ident_sym = sym_search(sctx->current_scope, ident);
	if (ident_sym == nil) {
		sema_error(sctx, nil, "undeclared identifier '%s'", ident.s);
		return nil;
	}
	if (ident_sym->kind == SymType) {
		sema_error(sctx, nil, "data type '%s' used as identifier in expression", ident.s);
		return nil;
	}
	ident_sym->used = true;
	return ident_sym;
}

static DataType *
sema_expr_unary(SemaCtx *sctx, AstUnary *unary, Location loc)
{
	Ast *expr = unary->atom;
	compiler_assert(sctx->cm, ast_node_is_expr(expr->type));
	//if (expr->type == AST_STRLIT) {
	//	sema_error(sctx, nil, "%s with a string literal makes no sense\n", TokenIdStr[unary->op]);
	//	return;
	//}

	//if (expr->type == AST_NUMBER) {
	//	if (unary->op == T_MINUS && !expr->number.type->sign) {
	//	}
	//}
	return sema_expr(sctx, expr, loc);
}

static DataType *
sema_binop(SemaCtx *sctx, const AstBinop *expr, Location loc)
{
	Symbol *opsym = sym_search_oncurrent(sctx->top_scope, expr->op);
	if (opsym == nil) {
		sema_error(sctx, nil, "no operator '%s'", expr->op.s);
		return nil;
	}
	if (arrlen(opsym->dtype->proc.argtypes) != 2) {
		sema_error(sctx, nil, "no binary operator for '%s'", expr->op.s);
		return nil;
	}

	DataType *ldt = sema_expr(sctx, expr->left, loc);
	DataType *rdt = sema_expr(sctx, expr->right, loc);
	/* Skip typechecking if either ldt or rdt have `InvalidDataType` and propagate
	 * it up the call stack. */
	if (ldt == InvalidDataType || rdt == InvalidDataType)
		return (DataType *)InvalidDataType;

	DataTypeCheck tchk;
	if (!(tchk = datatype_cmp(sctx, ldt, rdt)).ok) {
		sema_error(sctx, &loc, "type error: %s", tchk.msg.s);
		return nil;
	}
	return ldt;
}

static DataType *
sema_expr(SemaCtx *sctx, Ast *expr, Location loc)
{
	compiler_assert(sctx->cm, ast_node_is_expr(expr->type));
	push_semactx(&sctx);
	sctx->flags |= SctxInExpr;

	DataType *dt = nil;
	switch (expr->type) {
	case AST_BINEXPR:
		dt = sema_binop(sctx, &expr->bin, loc);
		break;
	case AST_UNARY:
		dt = sema_expr_unary(sctx, &expr->unary, loc);
		break;
	case AST_NUMBER:
		dt = sema_expr_number(sctx, &expr->number);
		break;
	case AST_STRLIT:
		dt = sema_expr_strlit(sctx, &expr->strlit);
		break;
	case AST_IDENT:
		dt = sema_expr_ident(sctx, expr->ident)->dtype;
		break;
	case AST_PROCCALL:
		dt = sema_proccall(sctx, &expr->call, expr->loc);
		break;
	default:
		unreachable();
	}

	pop_semactx(&sctx);
	return dt;
}

static void
sema_expr_list(SemaCtx *sctx, Vec(Ast *) exprs, Location loc)
{
	foreach (expr, exprs) {
		sema_expr(sctx, expr, loc);
	}
}

/************ Type checking ************/

/* Structurally compare two structural data types. */
static DataTypeCheck
datatype_struct_cmp(SemaCtx *sctx, DataType *s1, DataType *s2)
{
	compiler_assert(sctx->cm, s1->kind == DtkStruct && s2->kind == DtkStruct);
	const DataTypeCompound *s1s = &s1->compound;
	const DataTypeCompound *s2s = &s2->compound;

	if (s1s->packed != s2s->packed)
		return (DataTypeCheck){false, Sl("")};
	if (arrlen(s1s->fields) != arrlen(s2s->fields))
		return (DataTypeCheck){false, Sl("")};
	for (isize i = 0; i < arrlen(s1s->fields); ++i) {
		DataTypeCheck tchk;
		if (!(tchk = datatype_cmp(sctx, s1s->fields[i], s2s->fields[i])).ok)
			return tchk;
	}
	return (DataTypeCheck){.ok = true};
}

static DataTypeCheck
datatype_array_cmp(SemaCtx *sctx, DataType *a1, DataType *a2)
{
	DataTypeCheck tchk = {.ok = true};
	if (a1->array.len != a2->array.len)
		return (DataTypeCheck){false, Sl("")};
	if (!(tchk = datatype_cmp(sctx, a1->array.base, a2->array.base)).ok)
		return tchk;
	return tchk;
}

static DataTypeCheck
datatype_proc_cmp(SemaCtx *sctx, DataType *pc1, DataType *pc2)
{
	DataTypeCheck tchk = {.ok = true};

	if (pc1->proc.public != pc2->proc.public)
		return (DataTypeCheck){false, Sl("")};
	if (pc1->proc.extern_lnk != pc2->proc.extern_lnk)
		return (DataTypeCheck){false, Sl("")};
	if (pc1->proc.c_varargs != pc2->proc.c_varargs)
		return (DataTypeCheck){false, Sl("")};
	if (arrlen(pc1->proc.argtypes) != arrlen(pc2->proc.argtypes))
		return (DataTypeCheck){false, Sl("")};
	if (!(tchk = datatype_cmp(sctx, pc1->proc.rettype, pc2->proc.rettype)).ok)
		return tchk;

	for (isize i = 0; i < arrlen(pc1->proc.argtypes); ++i) {
		if (!(tchk = datatype_cmp(sctx, pc1->proc.argtypes[i], pc2->proc.argtypes[i])).ok)
			return tchk;
	}
	return tchk;
}

static DataTypeCheck
datatype_basic_cmp(SemaCtx *sctx, DataType *dt1, DataType *dt2)
{
	(void)sctx;
	if (dt1->size > dt2->size) /* if it has a size equal or less than dt2 */
		return (DataTypeCheck){false, Sl("")};
	if (dt1->sign != dt2->sign)
		return (DataTypeCheck){false, Strafmt("integers with different sign")};
	return (DataTypeCheck){.ok = true};
}

/* Compares two datatype objects, returning true if they are equal. */
static DataTypeCheck
datatype_cmp(SemaCtx *sctx, DataType *dt1, DataType *dt2)
{
	if (dt1 == nil || dt2 == nil)
		return (DataTypeCheck){false, Sl("")};
	/* TODO: return more information in case of a mismatch... */
	if (dt1 == dt2) /* shallow */
		return (DataTypeCheck){.ok = true};
	if (dt1->kind != dt2->kind)
		return (DataTypeCheck){.ok = false};

	switch (dt1->kind) {
	case DtkBasic:
		return datatype_basic_cmp(sctx, dt1, dt2);
	case DtkStruct:
	case DtkUnion:
		return datatype_struct_cmp(sctx, dt1, dt2);
	case DtkProc:
		return datatype_proc_cmp(sctx, dt1, dt2);
	case DtkArray:
		return datatype_array_cmp(sctx, dt1, dt2);
	case DtkBool:
	case DtkVoid:
		return (DataTypeCheck){.ok = true};
	}
	return (DataTypeCheck){.ok = false};
}

static DataType *
expr_get_datatype(SemaCtx *sctx, Ast *expr)
{
	compiler_assert(sctx->cm, ast_node_is_expr(expr->type));
	switch (expr->type) {
	case AST_BINEXPR:
		return expr->bin.type;
	case AST_UNARY:
		return expr->unary.type;
	case AST_NUMBER:
		return expr->number.type;
	case AST_STRLIT:
		return sym_search_oncurrent(sctx->top_scope, Sl("string"))->dtype;
	/* XXX: for these two we could attach the type in the ast... */
	case AST_IDENT:
		return sym_search(sctx->current_scope, expr->ident)->dtype;
	case AST_PROCCALL:
		return sym_search(sctx->current_scope, expr->call.name)->dtype->proc.rettype;
	default:
		unreachable();
	}
	return nil;
}

/* Search for the type in the symbol table, asserting that is a data type. */
static DataType *
resolve_datatype(SemaCtx *sctx, const Str ident, Location loc)
{
	Symbol *dtsym = sym_search(sctx->current_scope, ident);
	if (dtsym == nil) {
		sema_error(sctx, &loc, "no such type '%s'", ident.s);
		return (DataType *)InvalidDataType;
	}
	if (dtsym->kind != SymType) {
		sema_error(sctx, &loc, "'%s' is not a type but a %s", ident.s, SymbolKindStr[dtsym->kind]);
		return (DataType *)InvalidDataType;
	}
	return dtsym->dtype;
}

static void
sema_procdef(SemaCtx *sctx, AstProc *proc, Location loc)
{
	Symbol *sym_prev;
	if ((sym_prev = sym_search(sctx->current_scope, proc->name)) != nil) {
		sema_error(
			sctx, nil,
			"'%s' was already declared as a %s",
			proc->name.s, SymbolKindStr[sym_prev->kind]
		);
		sema_note(sctx, &sym_prev->loc, "'%s' previously declared here", proc->name.s);
		return;
	}

	if (Str_equal(proc->name, Sl("main"))) {
		sctx->main_defined = true;
		if (!proc->ispublic) {
			sema_error(sctx, &loc, "'main' has to be declared as a public proc");
		}
	}

	const Ast *rettype_node = proc->rettype;
	DataType *proc_rettype = nil;
	if (rettype_node != nil) {
		compiler_assert(sctx->cm, rettype_node->type == AST_IDENT);
		proc_rettype = resolve_datatype(sctx, proc->rettype->ident, rettype_node->loc);
		if (proc_rettype == InvalidDataType)
			return;
	} else {
		/* return type node is nil, we infer that as a `void` type */
		proc_rettype = sctx->builtintypes.void_t;	
	}

	Vec(DataType *) procargs = make_type_list_from_idents(sctx, proc->args);
	DataType *procdtype = make_proc_type(false, proc_rettype, procargs);
	procdtype->proc.public = proc->ispublic;
	Symbol proc_sym = {
		.kind = SymProc,
		.dtype = procdtype,
		.loc = loc
	};

	sym_insert(sctx->current_scope->symbols, proc->name.s, proc_sym);
	proc->type = procdtype;

	/* proc has no body at all */
	if (proc->body == nil)
		return;

	/* analyze the body */
	compiler_assert(sctx->cm, proc->body->type == AST_STMTS);
	push_semactx(&sctx);
	enter_scope(sctx);

	compiler_assert(sctx->cm, arrlen(proc->args) == arrlen(procargs));
	/* Inject proc parameters into the proc body top scope */
	for (isize i = 0; i < arrlen(proc->args); ++i) {
		DataType *argdtype = procargs[i];
		enum SymbolKind argsymkind = proc->args[i].kind;

		compiler_assert(sctx->cm, argdtype != nil);
		compiler_assert(sctx->cm, argsymkind == SymLet || argsymkind == SymVar);

		Symbol argsym = {
			.kind = argsymkind,
			.dtype = argdtype,
			.procparm = true,
			.loc = proc->args[i].ident_loc
		};
		sym_insert(sctx->current_scope->symbols, proc->args[i].ident.s, argsym);
	}
	sctx->flags |= SctxInsideProc;
	sema_stmts(sctx, proc->body->stmts);
	sema_check_unused_vars(sctx);
	exit_scope(sctx);
	pop_semactx(&sctx);
}

static void
sema_return(SemaCtx *sctx, Ast *ret_expr, Location loc)
{
	if (~sctx->flags & SctxInsideProc) {
		sema_error(sctx, &loc, "'return' outside of proc");
	}
	if (ret_expr != nil)
		sema_expr(sctx, ret_expr, ret_expr->loc);
}

static void
sema_break(SemaCtx *sctx, Ast *unused, Location loc)
{
	(void)unused;
	if (~sctx->flags & SctxInsideLoop) {
		sema_error(sctx, &loc, "'break' used outside of a loop");
	}
}

static void
sema_discard(SemaCtx *sctx, Ast *expr, Location loc)
{
	sctx->flags |= SctxInDiscard;
	sema_expr(sctx, expr, loc);
	sctx->flags &= ~SctxInDiscard;
}

static void
sema_attribute(SemaCtx *sctx, AstAttribute *attr)
{
	sema_node(sctx, attr->node);
}

static void
sema_var_decl(SemaCtx *sctx, AstVarDecl *decl, Location loc)
{
	compiler_assert(sctx->cm, symbol_is_var_binding(decl->kind));

	const Symbol *symp = sym_search(sctx->current_scope, decl->name);
	if (symp != nil && symp->kind != decl->kind) {
		switch (symp->kind) {
		case SymLet:
			sema_error(sctx, &symp->loc, "'%s' was already declared as 'let'", decl->name.s);
			return;
		case SymVar:
			sema_error(sctx, &symp->loc, "'%s' was already declared as 'var'", decl->name.s);
			return;
		case SymConst:
			sema_error(
				sctx, &symp->loc, 
				"declaration of '%s' shadows previously declared constant with the same name",
				decl->name.s
			);
			return;
		case SymType:
			sema_error(sctx, &symp->loc, "'%s' was already declared as a type", decl->name.s);
			return;
		default:
			break;
		}
		sema_note(sctx, &symp->loc, "'%s' was declared in this line", decl->name.s);
	}

	Ast *dexpr = decl->expr;
	if (dexpr != nil) {
		sema_expr(sctx, dexpr, loc); /* check the assignment expression */
	} else {
		sema_warning(sctx, &loc, "variable is unitialized");
	}

	if (decl->datatype == nil) {
		sema_error(sctx, nil, "we don't do type inference yet sorry");
		return;
	}

	compiler_assert(sctx->cm, decl->datatype->type == AST_IDENT);
 	DataType *dtype = resolve_datatype(sctx, decl->datatype->ident, decl->datatype->loc);
	/* Note that we ignore whether `resolve_datatype` return an invalid type,
	 * since we still want to insert the variable into the symbol table,
	 * otherwise we would have spurious "undeclared identifier" errors. */
	decl->type = dtype;

	Symbol sym = {
		.kind = decl->kind,
		.dtype = dtype,
		.loc = loc,
	};
	/* Insert the variable to the symbol table */
	sym_insert(sctx->current_scope->symbols, decl->name.s, sym);
}

static void
sema_var_assign(SemaCtx *sctx, AstVarAssign *assign, Location loc)
{
	sema_expr_ident(sctx, assign->name);
	sema_expr(sctx, assign->expr, loc);

	Symbol *decl = sym_search(sctx->current_scope, assign->name);
	if (decl == nil) {
		sema_error(sctx, &loc, "assign to undeclared variable '%s'", assign->name.s);
		return;
	}
	if (!symbol_is_var_binding(decl->kind)) {
		sema_error(
			sctx, &loc,
			"assign to non-variable symbol ('%s' is a '%s')",
			assign->name.s, SymbolKindStr[decl->kind]
		);
		return;
	}
	if (decl->kind != SymVar) {
		sema_error(
			sctx, &loc,
			"assign to immutable symbol ('%s' was declared as '%s')",
			assign->name.s, SymbolKindStr[decl->kind]
		);
		return;
	}
	//datatype_cmp(sctx, nil, decl->dtype);
}

static void
sema_ifstmtexpr(SemaCtx *sctx, AstIf *ift, Location loc)
{
	sema_expr(sctx, ift->cond, loc);
	sema_node(sctx, ift->true_body);
	sema_node(sctx, ift->false_body);

	const isize elifs_len = arrlen(ift->elifs);
	if (elifs_len > 0) {
		for (isize i = 0; i < elifs_len; ++i) {
			AstElif *elif = &ift->elifs[i];
			sema_expr(sctx, elif->cond, loc);
			sema_node(sctx, elif->body);
		}
	}
}

static void
sema_loop(SemaCtx *sctx, AstLoop *loop, Location loc)
{
	if (loop->precond != nil) {
		sema_expr(sctx, loop->precond, loc);
	}
	if (loop->postcond != nil) {
		sema_expr(sctx, loop->postcond, loc);
	}
	push_semactx(&sctx);
	sctx->flags |= SctxInsideLoop;
	sema_node(sctx, loop->body);
	pop_semactx(&sctx);
}

static void
sema_stmts(SemaCtx *sctx, Vec(Ast *) stmts)
{
	/* AST_STMTS imply the opening of a new scope */
	const isize stmts_len = arrlen(stmts);
	for (isize i = 0; i < stmts_len; ++i) {
		sema_node(sctx, stmts[i]);
		if (sema_is_stmt_terminal(stmts[i]) && i + 1 != stmts_len) {
			sema_warning(sctx, &stmts[i + 1]->loc, "dead code after 'return'");
		}
	}
}

static void
sema_stmt_block(SemaCtx *sctx, Vec(Ast *) stmts)
{
	enter_scope(sctx);
	sema_stmts(sctx, stmts);
	exit_scope(sctx);
	/* check for unused bindings declared in this scope */
	sema_check_unused_vars(sctx);
}

static void
sema_node(SemaCtx *sctx, Ast *node)
{
	if (node == nil)
		return;
	switch (node->type) {
	case AST_IF:
		sema_ifstmtexpr(sctx, &node->ifse, node->loc);
		break;
	case AST_LOOP:
		sema_loop(sctx, &node->loop, node->loc);
		break;
	case AST_STMTS:
		sema_stmt_block(sctx, node->stmts);
		break;
	case AST_PROCDEF:
		sema_procdef(sctx, &node->proc, node->loc);
		break;
	case AST_PROCCALL:
		sema_proccall(sctx, &node->call, node->loc);
		break;
	case AST_VARDECL:
		sema_var_decl(sctx, &node->var, node->loc);
		break;
	case AST_VARASSIGN:
		sema_var_assign(sctx, &node->varassgn, node->loc);
		break;
	case AST_RETURN:
		sema_return(sctx, node->ret, node->loc);
		break;
	case AST_BREAK:
		sema_break(sctx, nil, node->loc);
		break;
	case AST_DISCARD:
		sema_discard(sctx, node->discard.expr, node->loc);
		break;
	case AST_ATTRIBUTE:
		sema_attribute(sctx, &node->attribute);
		break;
	case AST_BINEXPR:
	case AST_UNARY:
	case AST_NUMBER:
	case AST_STRLIT:
	case AST_IDENT:
		sema_expr(sctx, node, node->loc);
		break;
	case AST_INVALID:
	case AST_EXPRS:
	case AST_PROCCALL_ARGS:
		unreachable();
	}
}

static void
sema_make_builtin_types(SemaCtx *sctx)
{
	typedef struct {
		const char *name;
		Symbol sym;
	} NameSym;

	DataType *void_type = make_data_type(DtkVoid, 0, true, false);
	DataType *str_type = make_data_type(DtkStruct, 0, false, false);
	DataType *puts_proto = make_data_type(DtkProc, 0, false, false);
	puts_proto->proc.rettype = void_type;
	puts_proto->proc.argtypes = make_proc_args((DataType *[]){str_type}, 1);
	puts_proto->proc.extern_lnk = true;

	NameSym builtin_basic_types[] = {
		{"void", {.kind = SymType, .dtype = void_type}},
		{"u64", {.kind = SymType, .dtype = make_data_type(DtkBasic, 8, true, false)}},
		{"i64", {.kind = SymType, .dtype = make_data_type(DtkBasic, 8, true, true)}},
		{"cint", {.kind = SymType, .dtype = make_data_type(DtkBasic, sizeof(int), true, true)}},
		{"string", {.kind = SymType, .dtype = str_type}},
		{"bool", {.kind = SymType, .dtype = make_data_type(DtkBool, 1, true, false)}},
	};
	DataType *u64_dt = builtin_basic_types[1].sym.dtype;
	DataType *bool_dt = builtin_basic_types[5].sym.dtype;

	NameSym builtin_procs[] = {
		{
			"+",
			{
				.kind = SymProc,
				.dtype = make_proc_type(
					true,
					u64_dt,
					make_proc_args((DataType *[]){u64_dt, u64_dt}, 2)
				)
			}
		},
		{
			"-",
			{
				.kind = SymProc,
				.dtype = make_proc_type(
					true,
					u64_dt,
					make_proc_args((DataType *[]){u64_dt, u64_dt}, 2)
				)
			}
		},
		{
			"==",
			{
				.kind = SymProc,
				.dtype = make_proc_type(
					true,
					bool_dt,
					make_proc_args((DataType *[]){u64_dt, u64_dt}, 2)
				)
			}
		},
	};

	for (isize i = 0; i < countof(builtin_basic_types); ++i) {
		const char *name = builtin_basic_types[i].name;
		Symbol sym = builtin_basic_types[i].sym;
		sym_insert(sctx->current_scope->symbols, name, sym);
	}
	for (isize i = 0; i < countof(builtin_procs); ++i) {
		sym_insert(sctx->current_scope->symbols,
			  builtin_procs[i].name, builtin_procs[i].sym);
	}

	sctx->builtintypes.tyu64 = builtin_basic_types[1].sym.dtype;
	sctx->builtintypes.void_t = void_type;

	Symbol puts_sym = {.kind = SymProc, .dtype = puts_proto};
	sym_insert(sctx->current_scope->symbols, "puts", puts_sym);
}

SemaCtx *
sema_new(Compiler *cm)
{
	SemaCtx *toplevel_context = make_semactx(cm, nil);
	toplevel_context->current_scope = make_scope(nil);

	sema_make_builtin_types(toplevel_context);
	toplevel_context->top_scope = toplevel_context->current_scope;
	toplevel_context->ok = true;
	return toplevel_context;
}

void
sema_destroy(SemaCtx *sctx)
{
	free(sctx);
}

void
sema(SemaCtx *sctx, Ast *program)
{
	/* Analyze toplevel */
	/* XXX: DRY it */
	compiler_assert(sctx->cm, program->type == AST_STMTS);
	for (isize i = 0; i < arrlen(program->stmts); ++i)
		sema_node(sctx, program->stmts[i]);

	if (!sctx->cm->opts.compile_only && !sctx->main_defined)
		sema_error(sctx, nil, "missing 'main' entrypoint proc");

	/* check unused local procedures */
	const SymbolEntry *syms = sctx->current_scope->symbols;
	for (isize i = 0; i < shlen(syms); ++i) {
		const Symbol fsym = syms[i].value;
		if (fsym.kind == SymProc
			&& !fsym.dtype->builtin
			&& !fsym.dtype->proc.public
			&& !fsym.dtype->proc.extern_lnk
			&& !fsym.used) {
			sema_warning(
				sctx, &fsym.loc,
				"defined proc '%s' is never called in this module", syms[i].key
			);
		}
	}
}