#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stdbool.h>

#include "com.h"
#include "mem.h"
#include "chunk.h"
#include "ast.h"
#include "util.h"
#include "prs.h"
#include "lib.h"


#define BYTECODE(C) (C->ch->bc)

Chunk chunk_new(State *S) {
	return (Chunk){ 0 };
}

Compiler compiler_new(Compiler *outer, Chunk *ch) {
	return (Compiler){
		.S = outer->S,
		.ch = ch,
		.stack_cur = 0,
		.scope = NULL,
	};
}

static void compile_byte(Compiler *C, uint8_t byte);
static void compile_opcode(Compiler *C, Op opcode);
static size_t compile_constant(Compiler *C, Val v);

static int stack_effect_of(Op opcode) {
	switch (opcode) {
	case OP_LOADK:
	case OP_GETGLOBAL:
	case OP_GETLOCAL:
	case OP_NIL:
	case OP_TRUE:
	case OP_FALSE:
	case OP_ARRNEW:
		return 1;
	case OP_SKIP:
	case OP_REDO:
	case OP_SETGLOBAL:
	case OP_SETLOCAL:
	case OP_RET:
	case OP_HALT:
		return 0;
	case OP_DROP:
	case OP_0BRANCH:
	case OP_ADD:
	case OP_SUB:
	case OP_MUL:
	case OP_DIV:
	case OP_CMP:
	case OP_EQU:
	case OP_MOD:
	case OP_ARRAPPEND:
		return -1;
	case OP_SETIDX:
		return -2;

	// these ones depend on their argument. handle them specifically
	case OP_CALL:
	case OP_TAILCALL:
	case OP_ENDSCOPE:
		return 0;

	default:
		ERROR("unknown stack effect of opcode %d",opcode); 
	}
}


// compile that byte directly
static void compile_byte(Compiler *C, uint8_t byte) {
	Chunk *ch = C->ch;
	if (ch->bc.len == ch->bc.cap) {
		size_t newsz = (ch->bc.cap == 0 ? 8 : ch->bc.cap * 2);
		ch->bc.d = RENEW_ARR(C->S, ch->bc.d, uint8_t, ch->bc.cap, newsz);
		ch->bc.cap = newsz;
	}
	size_t ix = ch->bc.len;
	ch->bc.d[ix] = byte;
	ch->bc.len ++;
}
// compile an opcode, keeping track of its stack effect
static void compile_opcode(Compiler *C, Op opcode) {
	int stack_effect = stack_effect_of(opcode);
	C->stack_cur += stack_effect;
	compile_byte(C, opcode);
}
// add a new constant to the constant table, and return its index
// (but return the index of any existing identical constant instead of
//  inserting a duplicate)
static size_t compile_constant(Compiler *C, Val v) {
	Chunk *ch = C->ch;
	for (int i = 0; i < ch->consts.len; i ++)
		if (val_equal(v, ch->consts.d[i])) return i;

	if (ch->consts.len == ch->consts.cap) {
		size_t newsz = (ch->consts.cap == 0 ? 8 : ch->consts.cap *2);
		ch->consts.d = RENEW_ARR(C->S, ch->consts.d, Val, ch->consts.cap, newsz);
		ch->consts.cap = newsz;
	}

	size_t ix = ch->consts.len;
	ch->consts.d[ix] = v;
	ch->consts.len ++;
	return ix;
}

// len is 1 + number of args
static void compile_call_instr(Compiler *C, uint8_t len) {
	compile_opcode(C, OP_CALL);
	compile_byte(C, len);
	C->stack_cur -= len - 1;
}

static void compile_tailcall_instr(Compiler *C, uint8_t len) {
	compile_opcode(C, OP_TAILCALL);
	compile_byte(C, len);
	C->stack_cur -= len - 1;
}

static void compile_endscope_instr(Compiler *C, uint8_t nlocals) {
	if (nlocals > 0) {
		compile_opcode(C, OP_ENDSCOPE);
		compile_byte(C, nlocals);
		C->stack_cur -= nlocals;
	}
}

static size_t placeholder(Compiler *C) {
	size_t old_ix = BYTECODE(C).len;
	compile_byte(C, 0x00);
	compile_byte(C, 0x00);
	return old_ix;
}
static void patch(Compiler *C, size_t addr, uint16_t val) {
	BYTECODE(C).d[addr] = val & 0xff;
	BYTECODE(C).d[addr+1] = (val & 0xff00) >> 8;
}

// ----

enum flags {
	F_toplevel = 1,
	F_tail = 2,
};

static void compile_node(Compiler *C, AstNode a, int flags);
static void begin_scope(Compiler *C);
static void end_scope(Compiler *C);

typedef void (*form_compiler)(Compiler *C, AstVec l, Op op, int flags);

static void compile_body(Compiler *C, AstVec l, int startat, int flags) {
	begin_scope(C);
	for (int i = startat; i < l.len - 1; i++) {
		compile_node(C, l.vals[i], F_toplevel);
		compile_opcode(C, OP_DROP);
	}
	compile_node(C, l.vals[l.len - 1], F_toplevel | (flags & F_tail));
	end_scope(C);
}

void single_form(Compiler *C, AstVec l, Op op) {
	compile_node(C, l.vals[1], 0);
	compile_opcode(C, op);
}

static Local *locate_local(Compiler *C, char *name);

void set_form(Compiler *C, AstVec l, Op _, int flags) {
	AstNode target = l.vals[1];
	if (target.ty == AST_IDENT)  {
		// set variable, local or global
		char *name = target.as.str;

		Local *loc = locate_local(C, name);
		if (loc != NULL) {
			compile_node(C, l.vals[2], 0);
			compile_opcode(C, OP_SETLOCAL);
			compile_byte(C, loc->slot);
		} else {
			// write global
			ObjString *o = objstring_copy_cstr(C->S, name);
			compile_node(C, l.vals[2], 0);
			compile_opcode(C, OP_SETGLOBAL);
			compile_byte(C, compile_constant(C, VAL_OBJ(o)));
		}
	} else if (target.ty == AST_LIST) {
		AstVec pair = target.as.list;
		CHECK(pair.len == 2, "can only set to (arr, ix) 2-pair");
		// (value arr ix) <- TOS
		compile_node(C, l.vals[2], 0);
		compile_node(C, pair.vals[0], 0);
		compile_node(C, pair.vals[1], 0);
		compile_opcode(C, OP_SETIDX);
	}
}

void do_form(Compiler *C, AstVec l, Op _, int flags) {
	compile_body(C, l, 1, flags);
}

void if_form(Compiler *C, AstVec l, Op _, int flags) {
	// (if cond if-true if-false)
	// cond
	// 0branch ->A
	// if-true
	// skip ->B
	// A: if-false
	// B:

	// never toplevel
	int downflags = flags & ~F_toplevel;

	int orig_stack_cur = C->stack_cur;

	compile_node(C, l.vals[1], 0);
	compile_opcode(C, OP_0BRANCH);
	size_t ph_a = placeholder(C);
	compile_node(C, l.vals[2], downflags);
	compile_opcode(C, OP_SKIP);

	size_t ph_b = placeholder(C);
	size_t dest_a = BYTECODE(C).len;
	int stack_cur_a = C->stack_cur;
	C->stack_cur = orig_stack_cur;

	compile_node(C, l.vals[3], downflags);
	size_t dest_b = BYTECODE(C).len;

	int stack_cur_b = C->stack_cur;

	patch(C, ph_a, dest_a - ph_a - 2);
	patch(C, ph_b, dest_b - ph_b - 2);

	CHECK(stack_cur_a == stack_cur_b, "this should never happen");
	CHECK(stack_cur_a == orig_stack_cur + 1, "this should never happen");
}

void while_form(Compiler *C, AstVec l, Op _, int flags) {
	// (while cond body ...)
	// A:
	// cond
	// 0branch ->B
	// body ....
	// redo ->A
	// B:
	// nil   (while loop always returns nil)
	size_t dest_a = BYTECODE(C).len;
	compile_node(C, l.vals[1], 0);
	compile_opcode(C, OP_0BRANCH);
	size_t ph_b = placeholder(C);
	compile_body(C, l, 2, flags & ~F_tail);
	compile_opcode(C, OP_DROP);
	compile_opcode(C, OP_REDO);
	size_t ph_a = placeholder(C);
	size_t dest_b = BYTECODE(C).len;
	compile_opcode(C, OP_NIL);

	patch(C, ph_a, ph_a - dest_a + 2);
	patch(C, ph_b, dest_b - ph_b - 2);
}

void arith_form(Compiler *C, AstVec l, Op op, int flags) {
	compile_node(C, l.vals[1], 0);
	compile_node(C, l.vals[2], 0);
	compile_opcode(C, op);
}


static void begin_scope(Compiler *C) {
	Scope *sc = malloc(sizeof(Scope));
	CHECK(sc != NULL, "memory fail");
	memset(sc, 0, sizeof(Scope));
	sc->outer = C->scope;
	C->scope = sc;
}
static void end_scope(Compiler *C) {
	Scope *sc = C->scope;
	CHECK(sc != NULL, "attempt to end nonexistent scope");
	C->scope = sc->outer;
	// printf("ending scope with %d locals, named: \n", sc->nlocals);
	// for (int i = 0; i < sc->nlocals; i++) {
	// 	Local loc = sc->locals[i];
	// 	printf("\t%3d  %s\n",loc.slot, loc.name);
	// }

	compile_endscope_instr(C, sc->nlocals);

	free(sc);
}
static void declare_local(Compiler *C, char *name) {
	Scope *sc = C->scope;
	CHECK(sc != NULL, "can't declare local outside of scope");
	Local *l = &sc->locals[sc->nlocals++];
	l->name = name;
	// -1 because local is expected to be already on the stack
	// ie sitting just below where stack_cur points
	l->slot = C->stack_cur - 1;
	// printf("declaring local %s at %d, stack_cur is %d\n",l->name, l->slot, C->stack_cur);
}
static Local *locate_local(Compiler *C, char *name) {
	for (Scope *sc = C->scope; sc != NULL; sc = sc->outer) {
		for (int i = 0; i < sc->nlocals; i++) {
			Local *loc = &sc->locals[i];
			if (0 == strcmp(loc->name, name)) 
				return loc;
		}
	}
	return NULL;
}

void let_form(Compiler *C, AstVec l, Op _, int flags) {
	CHECK(l.vals[1].ty == AST_LIST, "let's first argument must be list");
	AstVec bindlist = l.vals[1].as.list;
	CHECK(bindlist.len % 2 == 0, "unmatched binding in let");
	int nbinds = bindlist.len / 2;

	begin_scope(C);

	for (int i = 0; i < nbinds; i++) {
		int ix = i * 2;
		AstNode name = bindlist.vals[ix];
		AstNode expr = bindlist.vals[ix+1];
		CHECK(name.ty == AST_IDENT, "binding name must be identifier");
		compile_node(C, expr, 0);
		declare_local(C, name.as.str);
	}

	compile_body(C, l, 2, flags);

	end_scope(C);
}

void def_form(Compiler *C, AstVec l, Op _, int flags) {
	CHECK(l.vals[1].ty == AST_IDENT, "def's first argument must be ident");
	CHECK(flags & F_toplevel, "def only allowed at top level");
	compile_node(C, l.vals[2], 0);
	declare_local(C, l.vals[1].as.str);
	// whatever is calling us will compile an OP_DROP next
	// or, well. not if we're in tail position. but i can't see
	// any circumstance where you'd want that anyway
	compile_opcode(C, OP_NIL);
}

void fn_form(Compiler *C, AstVec l, Op _, int flags) {
	// (fn (arg arg arg) body ...)
	CHECK(l.vals[1].ty == AST_LIST, "fn's first argument must be list");
	AstVec arglist = l.vals[1].as.list;
	CHECK(arglist.len <= 255, "maximum 255 args for function");
	uint8_t arity = arglist.len;

	ObjFunc *func = objfunc_new(C->S, arity);
	Compiler subcompiler = compiler_new(C, &func->ch);

	Compiler *SC = &subcompiler;
	begin_scope(SC);
	// when called, stack slot 0 contains the function itself,
	// stack slots 1..n contain passed arguments
	SC->stack_cur ++;
	declare_local(SC, "__func__");
	for (int i = 0; i < arity; i++) {
		AstNode argname = arglist.vals[i];
		CHECK(argname.ty == AST_IDENT, "argument name must be identifier");
		SC->stack_cur ++;
		declare_local(SC, argname.as.str);
	}

	compile_body(SC, l, 2, F_tail);

	end_scope(SC);
	compile_opcode(SC, OP_RET);

	compile_opcode(C, OP_LOADK);
	compile_byte(C, compile_constant(C, VAL_OBJ(func)));
}

typedef struct {
	char *name;
	int min_params;
	bool ellipsis;
	form_compiler action;
	Op op;
} BuiltinForm;

static BuiltinForm builtin_forms[] = {
	{ "set",   2, false, set_form, 0 },
	{ "do",    1,  true, do_form, 0 },
	{ "if",    3, false, if_form, 0 },
	{ "while", 2,  true, while_form, 0 },
	{ "fn",    2,  true, fn_form, 0 },
	{ "let",   2,  true, let_form, 0 },
	{ "def",   2, false, def_form, 0 },
#define ARITH_OP(str, op) \
	{ str, 2, false, arith_form, op },
	ARITH_OP("+", OP_ADD)
	ARITH_OP("-", OP_SUB)
	ARITH_OP("*", OP_MUL)
	ARITH_OP("/", OP_DIV)
	ARITH_OP("=", OP_EQU)
	ARITH_OP("<", OP_CMP)
	ARITH_OP("%", OP_MOD)
#undef ARITH_OP
	{ 0 },
};

typedef struct {
	char *name;
	Op op;
} BuiltinIdent;
static BuiltinIdent builtin_idents[] = {
	{ "true", OP_TRUE },
	{ "false", OP_FALSE },
	{ "nil", OP_NIL },
	{ 0 },
};



static void compile_node(Compiler *C, AstNode a, int flags) {
	switch (a.ty) {
	case AST_IDENT:;
		char *ident = a.as.str;
		bool found_builtin = false;
		for (BuiltinIdent *b = builtin_idents; b->name != NULL; b++) {
			if (0 == strcmp(b->name, ident)) {
				compile_opcode(C, b->op);
				found_builtin = true;
				break;
			}
		}
		if (!found_builtin) {
			Local *loc = locate_local(C, ident);
			if (loc != NULL) {
				compile_opcode(C, OP_GETLOCAL);
				compile_byte(C, loc->slot);
			} else {
				// read global
				ObjString *o = objstring_copy_cstr(C->S, a.as.str);
				compile_opcode(C, OP_GETGLOBAL);
				compile_byte(C, compile_constant(C, VAL_OBJ(o)));
			}
		}
		break;
	case AST_NUM:
		compile_opcode(C, OP_LOADK);
		compile_byte(C, compile_constant(C, VAL_NUM(a.as.num)));
		break;
	case AST_STRING: {
		ObjString *o = objstring_copy_cstr(C->S, a.as.str);
		compile_opcode(C, OP_LOADK);
		compile_byte(C, compile_constant(C, VAL_OBJ(o)));
		break;
	}
	case AST_ARR: {
		compile_opcode(C, OP_ARRNEW);
		AstVec v = a.as.list;
		for (int i = 0; i < v.len; i++) {
			compile_node(C, v.vals[i], 0);
			compile_opcode(C, OP_ARRAPPEND);
		}
		break;
	}

	case AST_LIST: {
		AstVec l = a.as.list;

		CHECK(l.len > 0, "can't handle empty list");

		BuiltinForm *form = NULL;

		if (l.vals[0].ty == AST_IDENT) {
			char *head = l.vals[0].as.str;
			for (BuiltinForm *b = builtin_forms; b->name != NULL; b++) {
				if (0 == strcmp(b->name, head)) {
					form = b;
					break;
				}
			}
		}

		if (form != NULL) {
			size_t nparams = l.len - 1;
			if (form->ellipsis) 
				CHECK(nparams >= form->min_params, "%s requires at least %d parameters",
					form->name, form->min_params);
			else 
				CHECK(nparams == form->min_params, "%s requires exactly %d parameters",
					form->name, form->min_params);

			form->action(C, l, form->op, flags);
		} else {
			// function call
			// (f a b c )
			if (l.len > 255) {
				fprintf(stderr, "can't have more than 255 args in a function call\n");
				exit(1);
			}
			for (int i = 0; i < l.len; i++) {
				compile_node(C, l.vals[i], 0);
			}
			if (flags & F_tail) {
				compile_tailcall_instr(C, l.len);
			} else {
				compile_call_instr(C, l.len);
			}
		}

		break;
	}
	}
}

int main(int argc, char **argv) {
	State st = state_new();
	State *S = &st;
	Chunk ch = chunk_new(S);

	S->do_disasm = false;
	S->do_trace = false;

	char *infile_names[16];
	int infile_name_n = 0;
	for (int i = 1; i < argc; i++) {
		if (argv[i][0] != '-') {
			infile_names[infile_name_n++] = argv[i];
			CHECK(infile_name_n < 16, "input file count exceeded");
			continue;
		}
		switch (argv[i][1]) {
		case 'D': 
			CHECK(strlen(argv[i]) > 1, "unknown option a");
			switch (argv[i][2]) {
				case 'l': S->do_disasm = true; break;
				case 't': S->do_trace = true; break;
				default: ERROR("unknown option b");
			}
		break;
		default: ERROR("unknown option c");
		}
	}

	Compiler com = (Compiler){ 0 };
	com.S = S;
	com.ch = &ch;

	if (infile_name_n == 0) infile_names[infile_name_n++] = "-";

	for (int i = 0; i < infile_name_n; i++) {
		char *fname = infile_names[i];
		FILE *infile = NULL;
		if (0 == strcmp(fname, "-")) 
			infile = stdin;
		else
			infile = fopen(fname, "r");

		if (infile == NULL) {
			perror("fopen");
			exit(1);
		}

		AstNode an;
		memset(&an, 0, sizeof an);
		pcc_context_t *parser = pcc_create(infile);
		while (pcc_parse(parser, &an)) {
			compile_node(&com, an, 0);
			astnode_free(&an);
		}
		pcc_destroy(parser);
	}



	compile_opcode(&com, OP_HALT);

	Thread th = thread_new(S);
	th.ch = &ch;
	S->th = &th;

	load_stdlib(S);

	return runvm(S);
}
#undef CHECK
#undef ER