// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

package lint

import (
	"fmt"
	"strings"

	"sourcedock.dev/petrbalvin/gasm-sdk/ast"
)

// scanAddressing flags the two pseudo-register spellings the language
// reference (docs/asm/OPERANDS.md) calls its sharpest edge: a numeric offset
// against FP names no symbol, and a negative numeric offset against SP
// addresses the hardware stack pointer rather than the virtual frame.
func scanAddressing(t *ast.Text, cfg Config) []Diagnostic {
	var out []Diagnostic
	for _, s := range t.Body {
		in, ok := s.(*ast.Instr)
		if !ok {
			continue
		}
		for _, op := range in.Operands {
			if op.Kind != ast.OpAddr {
				continue
			}
			// FP is a pseudo-register, never a base register of a memory
			// operand; a Base of FP only arises from the numeric form
			// 0(FP), which the parser routes through memory parsing.  The
			// toolchain rejects it with "cannot reference FP without a
			// symbol" and gasm with "unknown base register FP".
			if strings.EqualFold(op.Addr.Base, "FP") && !cfg.Disable[CodeUnnamedFPRef] {
				out = append(out, Diagnostic{
					Pos:      op.Pos,
					Severity: Error,
					Code:     CodeUnnamedFPRef,
					Message:  "FP is referenced without a symbol; the assembler requires name+offset(FP)",
				})
				continue
			}
			// A numeric offset against (SP) addresses the hardware stack
			// pointer.  Positive offsets are the deliberate runtime idiom
			// for reading caller frames, but a negative offset is exactly
			// the local-frame spelling with the name missing: x-8(SP) and
			// -8(SP) are one character apart and mean different registers.
			// Only the negative form is flagged, which keeps the rule
			// silent across GOROOT's 140-odd deliberate hardware-SP
			// references (all positive) while catching the mistyped local.
			if strings.EqualFold(op.Addr.Base, "SP") && op.Addr.Sym == nil &&
				op.Addr.HasOff && op.Addr.Offset < 0 && !cfg.Disable[CodeHardwareSP] {
				out = append(out, Diagnostic{
					Pos:      op.Pos,
					Severity: Warning,
					Code:     CodeHardwareSP,
					Message: fmt.Sprintf("%d(SP) addresses the hardware stack pointer, not the virtual frame; "+
						"a frame local is spelled x%d(SP)", op.Addr.Offset, op.Addr.Offset),
				})
			}
		}
	}
	return out
}