// SPDX-FileCopyrightText: 2024 Himbeer <himbeer@disroot.org>
//
// SPDX-License-Identifier: GPL-3.0-or-later

package main

import (
	"fmt"
	"io"
	"strconv"
	"strings"
)

var funcRegIndex int

func allocReg() string {
	defer func() { funcRegIndex++ }()
	return fmt.Sprintf("%%local%d", funcRegIndex)
}

func resetRegs() {
	funcRegIndex = 0
}

var globalRegIndex int
var stringLiterals = map[string]string{}

func allocGlobal() string {
	defer func() { globalRegIndex++ }()
	return fmt.Sprintf("$global%d", globalRegIndex)
}

func allocString(s string, w io.Writer) string {
	if reg, ok := stringLiterals[s]; ok {
		return reg
	}

	reg := allocGlobal()
	stringLiterals[s] = reg

	fmt.Fprintf(w, "data %s = { %q }", reg, s)

	return reg
}

type invalidToplevel struct {
	got expression
}

func (i invalidToplevel) Error() string {
	return fmt.Sprintf("%d: expected top-level declaration, got %s", i.got.line(), i.got)
}

func generate(root *rootExpr, w io.Writer, errs chan<- error) {
	defer wg.Done()

	for _, toplevel := range root.toplevels {
		if err := generateToplevel(toplevel, w); err != nil {
			errs <- err
		}
	}
}

func generateToplevel(toplevel expression, w io.Writer) error {
	switch expr := toplevel.(type) {
	case *functionExpr:
		return generateFunction(expr, w)
	}

	return invalidToplevel{got: toplevel}
}

func generateFunction(function *functionExpr, w io.Writer) error {
	resetRegs()

	if function.link != defaultLinkage {
		fmt.Fprintf(w, "%s ", function.link)
	}

	fmt.Fprintf(w, "function %s $%s", function.returnType, function.name)
	fmt.Fprintf(w, "(%s) {\n", function.params)
	fmt.Fprintln(w, "@start")
	if err := generateBlock(function.blk, w); err != nil {
		return err
	}
	fmt.Fprintf(w, "}\n")

	return nil
}

func generateBlock(blk *blockExpr, w io.Writer) error {
	for _, stmt := range blk.stmts {
		if err := generateStatement(stmt, w); err != nil {
			return err
		}
	}

	return nil
}

func generateStatement(stmt statementExpr, w io.Writer) error {
	switch s := stmt.(type) {
	case *returnStmt:
		return generateReturnStmt(s, w)
	}

	return nil
}

func generateReturnStmt(stmt *returnStmt, w io.Writer) error {
	value, err := stmt.value.generate(w)
	if err != nil {
		return err
	}

	fmt.Fprintln(w, "ret", value)

	return nil
}

func (e *equalityExpr) generate(w io.Writer) (string, error) {
	lhs, err := e.lhs.generate(w)
	if err != nil {
		return "", err
	}

	out := lhs
	for _, rhs := range e.rhs {
		out, err = rhs.generate(out, w)
		if err != nil {
			return "", err
		}
	}

	return out, nil
}

func (e *equalityRhs) generate(in string, w io.Writer) (string, error) {
	instruction := "c"

	switch e.op {
	case equalTo:
		instruction += "eq"
	case notEqualTo:
		instruction += "ne"
	}

	instruction += "w"

	rhs, err := e.value.generate(w)
	if err != nil {
		return "", err
	}

	out := allocReg()

	fmt.Fprintf(w, "%s =w %s %s, %s\n", out, instruction, in, rhs)
	return out, nil
}

func (c *comparisonExpr) generate(w io.Writer) (string, error) {
	lhs, err := c.lhs.generate(w)
	if err != nil {
		return "", err
	}

	out := lhs
	if c.rhs != nil {
		out, err = c.rhs.generate(out, w)
		if err != nil {
			return "", err
		}
	}

	return out, nil
}

func (c *comparisonRhs) generate(in string, w io.Writer) (string, error) {
	instruction := "cs"

	switch c.op {
	case lessThan:
		instruction += "lt"
	case lessThanOrEqualTo:
		instruction += "le"
	case greaterThan:
		instruction += "gt"
	case greaterThanOrEqualTo:
		instruction += "ge"
	}

	instruction += "w"

	rhs, err := c.value.generate(w)
	if err != nil {
		return "", err
	}

	out := allocReg()

	fmt.Fprintf(w, "%s =w %s %s, %s\n", out, instruction, in, rhs)
	return out, nil
}

func (t *termExpr) generate(w io.Writer) (string, error) {
	lhs, err := t.lhs.generate(w)
	if err != nil {
		return "", err
	}

	out := lhs
	for _, rhs := range t.rhs {
		out, err = rhs.generate(out, w)
		if err != nil {
			return "", err
		}
	}

	return out, nil
}

func (t *termRhs) generate(in string, w io.Writer) (string, error) {
	instruction := ""

	switch t.op {
	case shiftLeft:
		instruction += "shl"
	case shiftRight:
		instruction += "shr"
	}

	rhs, err := t.value.generate(w)
	if err != nil {
		return "", err
	}

	out := allocReg()

	fmt.Fprintf(w, "%s =w %s %s, %s\n", out, instruction, in, rhs)
	return out, nil
}

func (n *numeralExpr) generate(w io.Writer) (string, error) {
	lhs, err := n.lhs.generate(w)
	if err != nil {
		return "", err
	}

	out := lhs
	for _, rhs := range n.rhs {
		out, err = rhs.generate(out, w)
		if err != nil {
			return "", err
		}
	}

	return out, nil
}

func (n *numeralRhs) generate(in string, w io.Writer) (string, error) {
	instruction := ""

	switch n.op {
	case add:
		instruction += "add"
	case subtract:
		instruction += "sub"
	}

	rhs, err := n.value.generate(w)
	if err != nil {
		return "", err
	}

	out := allocReg()

	fmt.Fprintf(w, "%s =w %s %s, %s\n", out, instruction, in, rhs)
	return out, nil
}

func (f *factorExpr) generate(w io.Writer) (string, error) {
	lhs, err := f.lhs.generate(w)
	if err != nil {
		return "", err
	}

	out := lhs
	for _, rhs := range f.rhs {
		out, err = rhs.generate(out, w)
		if err != nil {
			return "", err
		}
	}

	return out, nil
}

func (f *factorRhs) generate(in string, w io.Writer) (string, error) {
	instruction := ""

	switch f.op {
	case multiply:
		instruction += "mul"
	case divide:
		instruction += "div"
	}

	rhs, err := f.value.generate(w)
	if err != nil {
		return "", err
	}

	out := allocReg()

	fmt.Fprintf(w, "%s =w %s %s, %s\n", out, instruction, in, rhs)
	return out, nil
}

func (u *unaryExpr) generate(w io.Writer) (string, error) {
	value, err := u.value.generate(w)
	if err != nil {
		return "", err
	}

	if u.op == unaryIdentity {
		return value, nil
	}

	instruction, rhs := "", ""

	switch u.op {
	case negate:
		instruction += "neg"
	case invertLogical:
		instruction += "ceqw"
		rhs = ", 0"
	case invertBits:
		instruction += "xor"
		rhs = ", 0xffffffff"
	}

	out := allocReg()

	fmt.Fprintf(w, "%s =w %s %s%s\n", out, instruction, value, rhs)
	return out, nil
}

func (g *groupingExpr) generate(w io.Writer) (string, error) {
	return g.inner.generate(w)
}

func (s *stringExpr) generate(w io.Writer) (string, error) {
	value := strings.Join(s.segments, "")
	out := allocString(value, w)
	return out, nil
}

func (n *numberExpr) generate(w io.Writer) (string, error) {
	base := 10
	switch {
	case strings.HasPrefix(n.s, "0x"):
		base = 16
	case strings.HasPrefix(n.s, "0o"):
		base = 8
	case strings.HasPrefix(n.s, "0b"):
		base = 2
	}

	s := n.s
	if base != 10 {
		s = s[2:]
	}

	num, err := strconv.ParseInt(s, base, 64)
	if err != nil {
		return "", err
	}

	return fmt.Sprintf("%d", num), nil
}