// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

// Runtime macro compiler for Five.
// Implements &variable and &(expression) — runtime code compilation.
//
// Harbour has a full macro compiler (src/macro/macro.y) that parses
// and compiles expressions at runtime. Five uses a simplified approach:
// parse the expression string, then evaluate it using the existing
// lexer/parser/evaluator infrastructure.
//
// Usage:
//   LOCAL cField := "salary"
//   ? &cField              → evaluates variable named "salary"
//   ? &(cField + "_new")   → evaluates variable named "salary_new"
//
// Reference: /mnt/d/harbour-core/src/macro/
package hbrt

import (
	"strconv"
	"strings"
)

// MacroCompile compiles and evaluates a macro expression string.
// Returns the result value.
//
// For simple variable references (&cVar):
//   Looks up the variable name in memvars/locals.
//
// For complex expressions (&(expr)):
//   Would need full expression parser — simplified for now.
func (t *Thread) MacroCompile(expr string) Value {
	expr = strings.TrimSpace(expr)
	if expr == "" {
		return MakeNil()
	}

	// Simple case: expression is a variable name
	// Look up in memvars first, then try as function call
	if isSimpleIdent(expr) {
		// Try calling as a function (memvar lookup deferred to MacroEval)
		sym := t.vm.FindSymbol(strings.ToUpper(expr))
		if sym != nil && sym.Func != nil {
			t.PushSymbol(sym)
			t.PushNil()
			t.Function(0)
			return t.pop()
		}
		return MakeString(expr) // return as string if not found
	}

	// Complex expression: try parsing as number, then as function call
	// Full runtime expression parser would be needed for complete macro support.
	// This handles common patterns: &("literal"), &(numericExpr)

	// Try numeric (use stdlib strconv)
	if len(expr) > 0 && (expr[0] >= '0' && expr[0] <= '9' || expr[0] == '-' || expr[0] == '+') {
		if strings.Contains(expr, ".") {
			if f, err := strconv.ParseFloat(expr, 64); err == nil {
				return MakeDoubleAuto(f)
			}
		} else {
			if n, err := strconv.ParseInt(expr, 10, 64); err == nil {
				return MakeNumInt(n)
			}
		}
	}

	// Try string literal
	if len(expr) >= 2 && (expr[0] == '"' && expr[len(expr)-1] == '"' || expr[0] == '\'' && expr[len(expr)-1] == '\'') {
		return MakeString(expr[1 : len(expr)-1])
	}

	// Try .T./.F.
	upper := strings.ToUpper(expr)
	if upper == ".T." {
		return MakeBool(true)
	}
	if upper == ".F." {
		return MakeBool(false)
	}

	// Return as string (field name, variable name, etc.)
	return MakeString(expr)
}

// macroEvalHook is installed by hbrtl at init time. It handles the
// real work: parse the source via compiler/parser, compile to pcode
// via compiler/genpc, execute with ExecPcode. We can't call those
// directly from hbrt because genpc imports hbrt — the hook pattern
// keeps hbrt's core independent of the compiler packages.
//
// Stack contract matches MacroPush: pops the source string value,
// pushes the evaluated result.
var macroEvalHook func(*Thread)

// SetMacroEvalHook wires in the full macro evaluator. Called by
// hbrtl.init(). Without the hook installed, MacroPush falls back to
// the legacy stub that only resolves bare identifier names.
func SetMacroEvalHook(fn func(*Thread)) {
	macroEvalHook = fn
}

// MacroPush compiles a macro and pushes the result on stack.
// Harbour: HB_P_MACROPUSH
//
// Stack: [sourceString] → [result]. The caller emits the expression
// that yields the source string first — gengo produces
// `emitExpr(e.Expr); t.MacroPush()` for &<expr>.
func (t *Thread) MacroPush() {
	if macroEvalHook != nil {
		macroEvalHook(t)
		return
	}
	// Fallback: legacy simple-ident lookup. Kept so hbrt tests (which
	// don't init hbrtl) still function for trivial cases.
	exprVal := t.pop()
	result := t.MacroCompile(exprVal.AsString())
	t.push(result)
}

// parseFloat and parseInt64 removed — using strconv.ParseFloat/ParseInt instead.

// isSimpleIdent checks if string is a valid simple identifier.
func isSimpleIdent(s string) bool {
	if len(s) == 0 {
		return false
	}
	ch := s[0]
	if !((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '_') {
		return false
	}
	for i := 1; i < len(s); i++ {
		ch = s[i]
		if !((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9') || ch == '_') {
			return false
		}
	}
	return true
}