/*
 * Copyright (c) 2024 The GoPlus Authors (goplus.org). All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package ssa

import (
	"bytes"
	"fmt"
	"go/constant"
	"go/token"
	"go/types"
	"log"
	"unsafe"

	"github.com/goplus/llvm"
)

// -----------------------------------------------------------------------------

type Expr struct {
	impl llvm.Value
	Type
}

/*
// TypeOf returns the type of the expression.
func (v Expr) TypeOf() types.Type {
	return v.t
}
*/

// Do evaluates the delay expression and returns the result.
func (v Expr) Do() Expr {
	if vt := v.Type; vt.kind == vkDelayExpr {
		return vt.t.(delayExprTy)()
	}
	return v
}

// DelayExpr returns a delay expression.
func DelayExpr(f func() Expr) Expr {
	return Expr{Type: &aType{t: delayExprTy(f), kind: vkDelayExpr}}
}

type delayExprTy func() Expr

func (p delayExprTy) Underlying() types.Type {
	panic("don't call")
}

func (p delayExprTy) String() string {
	return "delayExpr"
}

// -----------------------------------------------------------------------------

func llvmValues(vals []Expr) []llvm.Value {
	ret := make([]llvm.Value, len(vals))
	for i, v := range vals {
		ret[i] = v.impl
	}
	return ret
}

// -----------------------------------------------------------------------------

// Null returns a null constant expression.
func (p Program) Null(t Type) Expr {
	return Expr{llvm.ConstNull(t.ll), t}
}

// CStringVal returns a c-style string constant expression.
func (p Program) CStringVal(v string) Expr {
	t := p.CString()
	return Expr{llvm.ConstString(v, true), t}
}

// StringVal returns string constant expression.
func (p Program) StringVal(v string) Expr {
	t := p.String()
	cstr := llvm.ConstString(v, true)
	// TODO(xsw): cstr => gostring
	return Expr{cstr, t}
}

// BoolVal returns a boolean constant expression.
func (p Program) BoolVal(v bool) Expr {
	t := p.Bool()
	var bv uint64
	if v {
		bv = 1
	}
	ret := llvm.ConstInt(t.ll, bv, v)
	return Expr{ret, t}
}

// IntVal returns an integer constant expression.
func (p Program) IntVal(v uint64, t Type) Expr {
	ret := llvm.ConstInt(t.ll, v, false)
	return Expr{ret, t}
}

// Val returns a constant expression.
func (p Program) Val(v interface{}) Expr {
	switch v := v.(type) {
	case int:
		return p.IntVal(uint64(v), p.Int())
	case uintptr:
		return p.IntVal(uint64(v), p.Uintptr())
	case bool:
		return p.BoolVal(v)
	case float64:
		t := p.Float64()
		ret := llvm.ConstFloat(t.ll, v)
		return Expr{ret, t}
	}
	panic("todo")
}

// Const returns a constant expression.
func (b Builder) Const(v constant.Value, typ Type) Expr {
	prog := b.Prog
	if v == nil {
		return prog.Null(typ)
	}
	switch t := typ.t.(type) {
	case *types.Basic:
		kind := t.Kind()
		switch {
		case kind == types.Bool:
			return prog.BoolVal(constant.BoolVal(v))
		case kind >= types.Int && kind <= types.Uintptr:
			if v, exact := constant.Uint64Val(v); exact {
				return prog.IntVal(v, typ)
			}
		case kind == types.String:
			return prog.StringVal(constant.StringVal(v))
		}
	}
	panic("todo")
}

// -----------------------------------------------------------------------------

const (
	mathOpBase = token.ADD
	mathOpLast = token.REM
)

var mathOpToLLVM = []llvm.Opcode{
	int(token.ADD-mathOpBase)<<2 | vkSigned:   llvm.Add,
	int(token.ADD-mathOpBase)<<2 | vkUnsigned: llvm.Add,
	int(token.ADD-mathOpBase)<<2 | vkFloat:    llvm.FAdd,

	int(token.SUB-mathOpBase)<<2 | vkSigned:   llvm.Sub,
	int(token.SUB-mathOpBase)<<2 | vkUnsigned: llvm.Sub,
	int(token.SUB-mathOpBase)<<2 | vkFloat:    llvm.FSub,

	int(token.MUL-mathOpBase)<<2 | vkSigned:   llvm.Mul,
	int(token.MUL-mathOpBase)<<2 | vkUnsigned: llvm.Mul,
	int(token.MUL-mathOpBase)<<2 | vkFloat:    llvm.FMul,

	int(token.QUO-mathOpBase)<<2 | vkSigned:   llvm.SDiv,
	int(token.QUO-mathOpBase)<<2 | vkUnsigned: llvm.UDiv,
	int(token.QUO-mathOpBase)<<2 | vkFloat:    llvm.FDiv,

	int(token.REM-mathOpBase)<<2 | vkSigned:   llvm.SRem,
	int(token.REM-mathOpBase)<<2 | vkUnsigned: llvm.URem,
	int(token.REM-mathOpBase)<<2 | vkFloat:    llvm.FRem,
}

func mathOpIdx(op token.Token, x valueKind) int {
	return int(op-mathOpBase)<<2 | x
}

// ADD SUB MUL QUO REM          + - * / %
func isMathOp(op token.Token) bool {
	return op >= mathOpBase && op <= mathOpLast
}

const (
	logicOpBase = token.AND
	logicOpLast = token.AND_NOT
)

var logicOpToLLVM = []llvm.Opcode{
	token.AND - logicOpBase: llvm.And,
	token.OR - logicOpBase:  llvm.Or,
	token.XOR - logicOpBase: llvm.Xor,
	token.SHL - logicOpBase: llvm.Shl,
	token.SHR - logicOpBase: llvm.AShr, // Arithmetic Shift Right
}

// AND OR XOR SHL SHR AND_NOT   & | ^ << >> &^
func isLogicOp(op token.Token) bool {
	return op >= logicOpBase && op <= logicOpLast
}

const (
	predOpBase = token.EQL
	predOpLast = token.GEQ
)

var intPredOpToLLVM = []llvm.IntPredicate{
	token.EQL - predOpBase: llvm.IntEQ,
	token.NEQ - predOpBase: llvm.IntNE,
	token.LSS - predOpBase: llvm.IntSLT,
	token.LEQ - predOpBase: llvm.IntSLE,
	token.GTR - predOpBase: llvm.IntSGT,
	token.GEQ - predOpBase: llvm.IntSGE,
}

var uintPredOpToLLVM = []llvm.IntPredicate{
	token.EQL - predOpBase: llvm.IntEQ,
	token.NEQ - predOpBase: llvm.IntNE,
	token.LSS - predOpBase: llvm.IntULT,
	token.LEQ - predOpBase: llvm.IntULE,
	token.GTR - predOpBase: llvm.IntUGT,
	token.GEQ - predOpBase: llvm.IntUGE,
}

var floatPredOpToLLVM = []llvm.FloatPredicate{
	token.EQL - predOpBase: llvm.FloatOEQ,
	token.NEQ - predOpBase: llvm.FloatONE,
	token.LSS - predOpBase: llvm.FloatOLT,
	token.LEQ - predOpBase: llvm.FloatOLE,
	token.GTR - predOpBase: llvm.FloatOGT,
	token.GEQ - predOpBase: llvm.FloatOGE,
}

// EQL NEQ LSS LEQ GTR GEQ      == != < <= < >=
func isPredOp(op token.Token) bool {
	return op >= predOpBase && op <= predOpLast
}

// The BinOp instruction yields the result of binary operation (x op y).
// op can be:
// ADD SUB MUL QUO REM          + - * / %
// AND OR XOR SHL SHR AND_NOT   & | ^ << >> &^
// EQL NEQ LSS LEQ GTR GEQ      == != < <= < >=
func (b Builder) BinOp(op token.Token, x, y Expr) Expr {
	if debugInstr {
		log.Printf("BinOp %d, %v, %v\n", op, x.impl, y.impl)
	}
	switch {
	case isMathOp(op): // op: + - * / %
		kind := x.kind
		switch kind {
		case vkString, vkComplex:
			panic("todo")
		}
		idx := mathOpIdx(op, kind)
		if llop := mathOpToLLVM[idx]; llop != 0 {
			return Expr{llvm.CreateBinOp(b.impl, llop, x.impl, y.impl), x.Type}
		}
	case isLogicOp(op): // op: & | ^ << >> &^
		if op == token.AND_NOT {
			panic("todo")
		}
		kind := x.kind
		llop := logicOpToLLVM[op-logicOpBase]
		if op == token.SHR && kind == vkUnsigned {
			llop = llvm.LShr // Logical Shift Right
		}
		return Expr{llvm.CreateBinOp(b.impl, llop, x.impl, y.impl), x.Type}
	case isPredOp(op): // op: == != < <= < >=
		tret := b.Prog.Bool()
		kind := x.kind
		switch kind {
		case vkSigned:
			pred := intPredOpToLLVM[op-predOpBase]
			return Expr{llvm.CreateICmp(b.impl, pred, x.impl, y.impl), tret}
		case vkUnsigned, vkPtr:
			pred := uintPredOpToLLVM[op-predOpBase]
			return Expr{llvm.CreateICmp(b.impl, pred, x.impl, y.impl), tret}
		case vkFloat:
			pred := floatPredOpToLLVM[op-predOpBase]
			return Expr{llvm.CreateFCmp(b.impl, pred, x.impl, y.impl), tret}
		case vkString, vkComplex, vkBool:
			panic("todo")
		}
	}
	panic("todo")
}

// The UnOp instruction yields the result of (op x).
// ARROW is channel receive.
// MUL is pointer indirection (load).
// XOR is bitwise complement.
// SUB is negation.
// NOT is logical negation.
func (b Builder) UnOp(op token.Token, x Expr) Expr {
	switch op {
	case token.MUL:
		return b.Load(x)
	}
	if debugInstr {
		log.Printf("UnOp %v, %v\n", op, x.impl)
	}
	panic("todo")
}

// Load returns the value at the pointer ptr.
func (b Builder) Load(ptr Expr) Expr {
	if debugInstr {
		log.Printf("Load %v\n", ptr.impl)
	}
	telem := b.Prog.Elem(ptr.Type)
	return Expr{llvm.CreateLoad(b.impl, telem.ll, ptr.impl), telem}
}

// Store stores val at the pointer ptr.
func (b Builder) Store(ptr, val Expr) Builder {
	if debugInstr {
		log.Printf("Store %v, %v\n", ptr.impl, val.impl)
	}
	b.impl.CreateStore(val.impl, ptr.impl)
	return b
}

// The FieldAddr instruction yields the address of Field of *struct X.
//
// The field is identified by its index within the field list of the
// struct type of X.
//
// Dynamically, this instruction panics if X evaluates to a nil
// pointer.
//
// Type() returns a (possibly named) *types.Pointer.
//
// Pos() returns the position of the ast.SelectorExpr.Sel for the
// field, if explicit in the source. For implicit selections, returns
// the position of the inducing explicit selection. If produced for a
// struct literal S{f: e}, it returns the position of the colon; for
// S{e} it returns the start of expression e.
//
// Example printed form:
//
//	t1 = &t0.name [#1]
func (b Builder) FieldAddr(x Expr, idx int) Expr {
	if debugInstr {
		log.Printf("FieldAddr %v, %d\n", x.impl, idx)
	}
	prog := b.Prog
	tstruc := prog.Elem(x.Type)
	telem := prog.Field(tstruc, idx)
	pt := prog.Pointer(telem)
	return Expr{llvm.CreateStructGEP(b.impl, tstruc.ll, x.impl, idx), pt}
}

// The IndexAddr instruction yields the address of the element at
// index `idx` of collection `x`.  `idx` is an integer expression.
//
// The elements of maps and strings are not addressable; use Lookup (map),
// Index (string), or MapUpdate instead.
//
// Dynamically, this instruction panics if `x` evaluates to a nil *array
// pointer.
//
// Example printed form:
//
//	t2 = &t0[t1]
func (b Builder) IndexAddr(x, idx Expr) Expr {
	if debugInstr {
		log.Printf("IndexAddr %v, %v\n", x.impl, idx.impl)
	}
	prog := b.Prog
	telem := prog.Index(x.Type)
	pt := prog.Pointer(telem)
	indices := []llvm.Value{idx.impl}
	return Expr{llvm.CreateInBoundsGEP(b.impl, telem.ll, x.impl, indices), pt}
}

// The Alloc instruction reserves space for a variable of the given type,
// zero-initializes it, and yields its address.
//
// If heap is false, Alloc zero-initializes the same local variable in
// the call frame and returns its address; in this case the Alloc must
// be present in Function.Locals. We call this a "local" alloc.
//
// If heap is true, Alloc allocates a new zero-initialized variable
// each time the instruction is executed. We call this a "new" alloc.
//
// When Alloc is applied to a channel, map or slice type, it returns
// the address of an uninitialized (nil) reference of that kind; store
// the result of MakeSlice, MakeMap or MakeChan in that location to
// instantiate these types.
//
// Example printed form:
//
//	t0 = local int
//	t1 = new int
func (b Builder) Alloc(t *types.Pointer, heap bool) (ret Expr) {
	if debugInstr {
		log.Printf("Alloc %v, %v\n", t, heap)
	}
	prog := b.Prog
	telem := t.Elem()
	if heap {
		pkg := b.fn.pkg
		size := unsafe.Sizeof(telem)
		ret = b.Call(pkg.rtFunc("Alloc"), prog.Val(size))
	} else {
		ret.impl = llvm.CreateAlloca(b.impl, prog.Type(telem).ll)
	}
	// TODO(xsw): zero-initialize
	ret.Type = prog.Type(t)
	return
}

// The ChangeType instruction applies to X a value-preserving type
// change to Type().
//
// Type changes are permitted:
//   - between a named type and its underlying type.
//   - between two named types of the same underlying type.
//   - between (possibly named) pointers to identical base types.
//   - from a bidirectional channel to a read- or write-channel,
//     optionally adding/removing a name.
//   - between a type (t) and an instance of the type (tσ), i.e.
//     Type() == σ(X.Type()) (or X.Type()== σ(Type())) where
//     σ is the type substitution of Parent().TypeParams by
//     Parent().TypeArgs.
//
// This operation cannot fail dynamically.
//
// Type changes may to be to or from a type parameter (or both). All
// types in the type set of X.Type() have a value-preserving type
// change to all types in the type set of Type().
//
// Example printed form:
//
//	t1 = changetype *int <- IntPtr (t0)
func (b Builder) ChangeType(t Type, x Expr) (ret Expr) {
	if debugInstr {
		log.Printf("ChangeType %v, %v\n", t.t, x.impl)
	}
	typ := t.t
	switch typ.(type) {
	default:
		ret.impl = b.impl.CreateBitCast(x.impl, t.ll, "bitCast")
		ret.Type = b.Prog.Type(typ)
		return
	}
}

// The Convert instruction yields the conversion of value X to type
// Type().  One or both of those types is basic (but possibly named).
//
// A conversion may change the value and representation of its operand.
// Conversions are permitted:
//   - between real numeric types.
//   - between complex numeric types.
//   - between string and []byte or []rune.
//   - between pointers and unsafe.Pointer.
//   - between unsafe.Pointer and uintptr.
//   - from (Unicode) integer to (UTF-8) string.
//
// A conversion may imply a type name change also.
//
// Conversions may to be to or from a type parameter. All types in
// the type set of X.Type() can be converted to all types in the type
// set of Type().
//
// This operation cannot fail dynamically.
//
// Conversions of untyped string/number/bool constants to a specific
// representation are eliminated during SSA construction.
//
// Pos() returns the ast.CallExpr.Lparen, if the instruction arose
// from an explicit conversion in the source.
//
// Example printed form:
//
//	t1 = convert []byte <- string (t0)
func (b Builder) Convert(t Type, x Expr) (ret Expr) {
	typ := t.t
	ret.Type = b.Prog.Type(typ)
	switch und := typ.Underlying().(type) {
	case *types.Basic:
		kind := und.Kind()
		switch {
		case kind >= types.Int && kind <= types.Uintptr:
			ret.impl = castInt(b.impl, x.impl, t.ll)
			return
		case kind == types.UnsafePointer:
			ret.impl = castPtr(b.impl, x.impl, t.ll)
			return
		}
	case *types.Pointer:
		ret.impl = castPtr(b.impl, x.impl, t.ll)
		return
	}
	panic("todo")
}

func castInt(b llvm.Builder, x llvm.Value, t llvm.Type) llvm.Value {
	xt := x.Type()
	if xt.TypeKind() == llvm.PointerTypeKind {
		return llvm.CreatePtrToInt(b, x, t)
	}
	if xt.IntTypeWidth() <= t.IntTypeWidth() {
		return llvm.CreateIntCast(b, x, t)
	}
	return llvm.CreateTrunc(b, x, t)
}

func castPtr(b llvm.Builder, x llvm.Value, t llvm.Type) llvm.Value {
	if x.Type().TypeKind() == llvm.PointerTypeKind {
		return llvm.CreatePointerCast(b, x, t)
	}
	return llvm.CreateIntToPtr(b, x, t)
}

// MakeInterface constructs an instance of an interface type from a
// value of a concrete type.
//
// Use Program.MethodSets.MethodSet(X.Type()) to find the method-set
// of X, and Program.MethodValue(m) to find the implementation of a method.
//
// To construct the zero value of an interface type T, use:
//
//	NewConst(constant.MakeNil(), T, pos)
//
// Pos() returns the ast.CallExpr.Lparen, if the instruction arose
// from an explicit conversion in the source.
//
// Example printed form:
//
//	t1 = make interface{} <- int (42:int)
//	t2 = make Stringer <- t0
func (b Builder) MakeInterface(inter types.Type, x Expr, mayDelay bool) (ret Expr) {
	if debugInstr {
		log.Printf("MakeInterface %v, %v\n", inter, x.impl)
	}
	t := inter.Underlying().(*types.Interface)
	isAny := t.Empty()
	fnDo := func() Expr {
		pkg := b.fn.pkg
		switch x.kind {
		case vkSigned, vkUnsigned, vkFloat:
			fn := pkg.rtFunc("MakeAnyInt")
			return b.InlineCall(fn, x)
		case vkString:
			fn := pkg.rtFunc("MakeAnyString")
			return b.InlineCall(fn, x)
		}
		panic("todo")
	}
	if mayDelay && isAny {
		return DelayExpr(fnDo)
	}
	return fnDo()
}

// The TypeAssert instruction tests whether interface value X has type
// AssertedType.
//
// If !CommaOk, on success it returns v, the result of the conversion
// (defined below); on failure it panics.
//
// If CommaOk: on success it returns a pair (v, true) where v is the
// result of the conversion; on failure it returns (z, false) where z
// is AssertedType's zero value.  The components of the pair must be
// accessed using the Extract instruction.
//
// If Underlying: tests whether interface value X has the underlying
// type AssertedType.
//
// If AssertedType is a concrete type, TypeAssert checks whether the
// dynamic type in interface X is equal to it, and if so, the result
// of the conversion is a copy of the value in the interface.
//
// If AssertedType is an interface, TypeAssert checks whether the
// dynamic type of the interface is assignable to it, and if so, the
// result of the conversion is a copy of the interface value X.
// If AssertedType is a superinterface of X.Type(), the operation will
// fail iff the operand is nil.  (Contrast with ChangeInterface, which
// performs no nil-check.)
//
// Type() reflects the actual type of the result, possibly a
// 2-types.Tuple; AssertedType is the asserted type.
//
// Depending on the TypeAssert's purpose, Pos may return:
//   - the ast.CallExpr.Lparen of an explicit T(e) conversion;
//   - the ast.TypeAssertExpr.Lparen of an explicit e.(T) operation;
//   - the ast.CaseClause.Case of a case of a type-switch statement;
//   - the Ident(m).NamePos of an interface method value i.m
//     (for which TypeAssert may be used to effect the nil check).
//
// Example printed form:
//
//	t1 = typeassert t0.(int)
//	t3 = typeassert,ok t2.(T)
func (b Builder) TypeAssert(x Expr, assertedTyp Type, commaOk bool) (ret Expr) {
	if debugInstr {
		log.Printf("TypeAssert %v, %v, %v\n", x.impl, assertedTyp.t, commaOk)
	}
	switch assertedTyp.kind {
	case vkSigned, vkUnsigned, vkFloat:
		pkg := b.fn.pkg
		fnName := "I2Int"
		if commaOk {
			fnName = "CheckI2Int"
		}
		fn := pkg.rtFunc(fnName)
		var kind types.BasicKind
		switch t := assertedTyp.t.(type) {
		case *types.Basic:
			kind = t.Kind()
		default:
			panic("todo")
		}
		typ := b.InlineCall(pkg.rtFunc("Basic"), b.Prog.Val(int(kind)))
		return b.InlineCall(fn, x, typ)
	}
	panic("todo")
}

// -----------------------------------------------------------------------------

// TODO(xsw): make inline call
func (b Builder) InlineCall(fn Expr, args ...Expr) (ret Expr) {
	return b.Call(fn, args...)
}

// The Call instruction represents a function or method call.
//
// The Call instruction yields the function result if there is exactly
// one.  Otherwise it returns a tuple, the components of which are
// accessed via Extract.
//
// Example printed form:
//
//	t2 = println(t0, t1)
//	t4 = t3()
//	t7 = invoke t5.Println(...t6)
func (b Builder) Call(fn Expr, args ...Expr) (ret Expr) {
	if debugInstr {
		var b bytes.Buffer
		fmt.Fprint(&b, "Call ", fn.impl.Name())
		for _, arg := range args {
			fmt.Fprint(&b, ", ", arg.impl)
		}
		log.Println(b.String())
	}
	switch t := fn.t.(type) {
	case *types.Signature:
		ret.Type = b.Prog.retType(t)
	default:
		panic("todo")
	}
	ret.impl = llvm.CreateCall(b.impl, fn.ll, fn.impl, llvmValues(args))
	return
}

// A Builtin represents a specific use of a built-in function, e.g. len.
//
// Builtins are immutable values.  Builtins do not have addresses.
//
// `fn` indicates the function: one of the built-in functions from the
// Go spec (excluding "make" and "new").
func (b Builder) BuiltinCall(fn string, args ...Expr) (ret Expr) {
	panic("todo")
}

// -----------------------------------------------------------------------------