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

// Five pcode — stack-based bytecode for FRB interpreter mode.
// Each opcode maps 1:1 to a Thread method call, making the pcode
// a direct serialization of what gengo generates as Go code.
//
// Format: [opcode:1byte] [operands:variable]
// Strings: [len:uint16 LE] [bytes]
// Numbers: int64 = 8 bytes LE, float64 = 8 bytes LE

package hbrt

// Opcode definitions
const (
	// Stack operations
	PcOpNop        byte = 0x00
	PcOpPushNil    byte = 0x01
	PcOpPushTrue   byte = 0x02
	PcOpPushFalse  byte = 0x03
	PcOpPushInt    byte = 0x04 // + int64 LE
	PcOpPushDouble byte = 0x05 // + float64 LE (8 bytes)
	PcOpPushString byte = 0x06 // + uint16 len + bytes
	PcOpPushLocal  byte = 0x07 // + uint16 index
	PcOpPopLocal   byte = 0x08 // + uint16 index
	PcOpPop        byte = 0x09
	PcOpDup        byte = 0x0A

	// Arithmetic
	PcOpPlus   byte = 0x10
	PcOpMinus  byte = 0x11
	PcOpMult   byte = 0x12
	PcOpDivide byte = 0x13
	PcOpMod    byte = 0x14
	PcOpPower  byte = 0x15
	PcOpNegate byte = 0x16

	// Comparison
	PcOpEqual    byte = 0x20
	PcOpNotEqual byte = 0x21
	PcOpLess     byte = 0x22
	PcOpGreater  byte = 0x23
	PcOpLessEq   byte = 0x24
	PcOpGreaterEq byte = 0x25
	PcOpInString byte = 0x26

	// Logical
	PcOpAnd byte = 0x28
	PcOpOr  byte = 0x29
	PcOpNot byte = 0x2A

	// String
	PcOpConcat byte = 0x2C // same as Plus for strings

	// Flow control
	PcOpJump      byte = 0x30 // + int32 LE (relative offset)
	PcOpJumpFalse byte = 0x31 // + int32 LE
	PcOpJumpTrue  byte = 0x32 // + int32 LE
	PcOpReturn    byte = 0x33
	PcOpRetValue  byte = 0x34

	// Frame
	PcOpFrame   byte = 0x38 // + uint16 params + uint16 locals
	PcOpEndProc byte = 0x39

	// Function calls
	PcOpPushSymbol byte = 0x40 // + uint16 string len + name
	PcOpPushNilArg byte = 0x41 // push NIL for function self
	PcOpFunction   byte = 0x42 // + uint16 nArgs
	PcOpDo         byte = 0x43 // + uint16 nArgs

	// Workarea field access — skips PushSymbol + Function dispatch
	// for `FieldGet(n)` where n is a literal. Emitted by genpc as a
	// peephole optimization. Operand: uint16 1-based field position.
	PcOpFieldGet byte = 0x46

	// `AllTrim(FieldGet(n))` peephole — fetch the field, trim the
	// result in place, push one string. Skips two Function dispatches
	// (FieldGet + AllTrim) and one intermediate string allocation
	// per invocation. Operand: uint16 1-based field position.
	PcOpFieldTrim byte = 0x47

	// Self / OOP
	PcOpPushSelf      byte = 0x48
	PcOpPushSelfField byte = 0x49 // + uint16 len + name
	PcOpSetSelfField  byte = 0x4A // + uint16 len + name
	PcOpSend          byte = 0x4B // + uint16 len + name + uint16 nArgs

	// Array / Hash
	PcOpArrayGen  byte = 0x50 // + uint16 count
	PcOpHashGen   byte = 0x51 // + uint16 count
	PcOpArrayPush byte = 0x52
	PcOpArrayPop  byte = 0x53

	// Block — operand layout:
	//   PcOpPushBlock + uint32 codeLen + body bytes
	//                 + uint16 nParams + uint16 nDetached
	//                 + nDetached × uint16 (source-local index per slot)
	// Each captured slot snapshots the current frame's Local(idx)
	// into the block's Detached[i] at creation time. Body accesses
	// captured values via PcOpPushDetached / PcOpPopDetached with the
	// 0-based slot index.
	PcOpPushBlock    byte = 0x58
	PcOpPushDetached byte = 0x59 // + uint16 0-based detached slot
	PcOpPopDetached  byte = 0x5A // + uint16 0-based detached slot

	// Local operations
	PcOpLocalAddInt byte = 0x60 // + uint16 index + int32 value
	PcOpInc         byte = 0x61
	PcOpDec         byte = 0x62

	// Special
	PcOpPopLogical byte = 0x70 // pop and store logical result
	PcOpPushBool   byte = 0x71 // + 1 byte (0 or 1)

	// Memvar lookup — runtime resolution of an unresolved identifier.
	// Used by the macro evaluator and the debugger's expression evaluator:
	// at compile time we don't know which LOCAL frame an identifier
	// refers to, so we emit this op with the name and resolve at runtime
	// via t.Memvars (PRIVATE/PUBLIC). Pushes NIL if the name isn't set.
	PcOpPushMemvar byte = 0x72 // + uint16 len + name

	// Line info (for debugging)
	PcOpLine byte = 0xFE // + uint16 lineNo
	PcOpHalt byte = 0xFF
)

// PcodeFunc represents a pcode-compiled function.
type PcodeFunc struct {
	Name   string
	Code   []byte   // bytecode
	Params int      // number of parameters
	Locals int      // number of locals
}

// PcodeModule represents a compiled pcode module (multiple functions).
type PcodeModule struct {
	Name    string
	Funcs   map[string]*PcodeFunc
	Strings []string // string constant pool
	// Warnings captures compile-time diagnostics from genpc — most
	// commonly "AST node X not supported in pcode mode". Surfaced
	// by the build pipeline so users learn their PRG isn't fully
	// pcode-compilable instead of seeing silent wrong results from
	// no-op fallbacks. Empty slice = clean compile.
	Warnings []string
}