package evalop

import (
	"go/ast"
	"go/constant"

	"github.com/go-delve/delve/pkg/dwarf/godwarf"
)

// Op is a stack machine opcode
type Op interface {
	depthCheck() (npop, npush int)
}

// PushCurg pushes the current goroutine on the stack.
type PushCurg struct {
}

func (*PushCurg) depthCheck() (npop, npush int) { return 0, 1 }

// PushFrameoff pushes the frame offset for the current frame on the stack.
type PushFrameoff struct {
}

func (*PushFrameoff) depthCheck() (npop, npush int) { return 0, 1 }

// PushThreadID pushes the ID of the current thread on the stack.
type PushThreadID struct {
}

func (*PushThreadID) depthCheck() (npop, npush int) { return 0, 1 }

// PushRangeParentOffset pushes the frame offset of the range-over-func closure body parent.
type PushRangeParentOffset struct {
}

func (*PushRangeParentOffset) depthCheck() (npop, npush int) { return 0, 1 }

// PushConst pushes a constant on the stack.
type PushConst struct {
	Value constant.Value
}

func (*PushConst) depthCheck() (npop, npush int) { return 0, 1 }

// PushLocal pushes the local variable with the given name on the stack.
type PushLocal struct {
	Name  string
	Frame int64
}

func (*PushLocal) depthCheck() (npop, npush int) { return 0, 1 }

// PushIdent pushes a local or global variable or a predefined identifier
// (true, false, etc) or the value of a register on the stack.
type PushIdent struct {
	Name string
}

func (*PushIdent) depthCheck() (npop, npush int) { return 0, 1 }

// PushPackageVarOrSelect pushes the value of Name.Sel on the stack, which
// could either be a global variable (with the package name specified), or a
// field of a local variable.
type PushPackageVarOrSelect struct {
	Name, Sel    string
	NameIsString bool
}

func (*PushPackageVarOrSelect) depthCheck() (npop, npush int) { return 0, 1 }

// PushNil pushes an untyped nil on the stack.
type PushNil struct {
}

func (*PushNil) depthCheck() (npop, npush int) { return 0, 1 }

// PushLen pushes the length of the variable at the top of the stack into
// the stack.
type PushLen struct {
}

func (*PushLen) depthCheck() (npop, npush int) { return 1, 2 }

// Select replaces the topmost stack variable v with v.Name.
type Select struct {
	Name string
}

func (*Select) depthCheck() (npop, npush int) { return 1, 1 }

// TypeAssert replaces the topmost stack variable v with v.(DwarfType).
type TypeAssert struct {
	DwarfType godwarf.Type
	Node      *ast.TypeAssertExpr
}

func (*TypeAssert) depthCheck() (npop, npush int) { return 1, 1 }

// PointerDeref replaces the topmost stack variable v with *v.
type PointerDeref struct {
	Node *ast.StarExpr
}

func (*PointerDeref) depthCheck() (npop, npush int) { return 1, 1 }

// Unary applies the given unary operator to the topmost stack variable.
type Unary struct {
	Node *ast.UnaryExpr
}

func (*Unary) depthCheck() (npop, npush int) { return 1, 1 }

// AddrOf replaces the topmost stack variable v with &v.
type AddrOf struct {
	Node *ast.UnaryExpr
}

func (*AddrOf) depthCheck() (npop, npush int) { return 1, 1 }

// TypeCast replaces the topmost stack variable v with (DwarfType)(v).
type TypeCast struct {
	DwarfType godwarf.Type
	Node      *ast.CallExpr
}

func (*TypeCast) depthCheck() (npop, npush int) { return 1, 1 }

// Reslice implements a reslice operation.
// If HasHigh is set it pops three variables, low, high and v, and pushes
// v[low:high].
// Otherwise it pops two variables, low and v, and pushes v[low:].
// If TrustLen is set when the variable resulting from the reslice is loaded it will be fully loaded.
type Reslice struct {
	HasHigh  bool
	TrustLen bool
	Node     *ast.SliceExpr
}

func (op *Reslice) depthCheck() (npop, npush int) {
	if op.HasHigh {
		return 3, 1
	} else {
		return 2, 1
	}
}

// Index pops two variables, idx and v, and pushes v[idx].
type Index struct {
	Node *ast.IndexExpr
}

func (*Index) depthCheck() (npop, npush int) { return 2, 1 }

// Jump looks at the topmost stack variable and if it satisfies the
// condition specified by When it jumps to the stack machine instruction at
// Target+1.
// If Pop is set the topmost stack variable is also popped.
type Jump struct {
	When   JumpCond
	Pop    bool
	Target int
	Node   ast.Expr
}

func (jmpif *Jump) depthCheck() (npop, npush int) {
	switch jmpif.When {
	case JumpIfTrue, JumpIfFalse, JumpIfAllocStringChecksFail:
		if jmpif.Pop {
			return 1, 0
		} else {
			return 1, 1
		}
	}
	return 0, 0
}

// JumpCond specifies a condition for the Jump instruction.
type JumpCond uint8

const (
	JumpIfFalse JumpCond = iota
	JumpIfTrue
	JumpIfAllocStringChecksFail
	JumpAlways
	JumpIfPinningDone
)

// Binary pops two variables from the stack, applies the specified binary
// operator to them and pushes the result back on the stack.
type Binary struct {
	Node *ast.BinaryExpr
}

func (*Binary) depthCheck() (npop, npush int) { return 2, 1 }

// BoolToConst pops the topmost variable from the stack, which must be a
// boolean variable, and converts it to a constant.
type BoolToConst struct {
}

func (*BoolToConst) depthCheck() (npop, npush int) { return 1, 1 }

// Pop removes the topmost variable from the stack.
type Pop struct {
}

func (*Pop) depthCheck() (npop, npush int) { return 1, 0 }

// Roll removes the n-th element of the stack and pushes it back in at the top
type Roll struct {
	N int
}

func (*Roll) depthCheck() (npop, npush int) { return 1, 1 }

// BuiltinCall pops len(Args) argument from the stack, calls the specified
// builtin on them and pushes the result back on the stack.
type BuiltinCall struct {
	Name string
	Args []ast.Expr
}

func (bc *BuiltinCall) depthCheck() (npop, npush int) {
	return len(bc.Args), 1
}

// CallInjectionStart starts call injection by calling
// runtime.debugCallVn.
type CallInjectionStart struct {
	id      int  // identifier for all the call injection instructions that belong to the same sequence, this only exists to make reading listings easier
	HasFunc bool // target function already pushed on the stack
	Node    *ast.CallExpr
}

func (*CallInjectionStart) depthCheck() (npop, npush int) { return 0, 1 }

// CallInjectionSetTarget starts the call injection, after
// runtime.debugCallVn set up the stack for us, by copying the entry point
// of the function, setting the closure register and copying the receiver.
type CallInjectionSetTarget struct {
	id int
}

func (*CallInjectionSetTarget) depthCheck() (npop, npush int) { return 1, 0 }

// CallInjectionCopyArg copies one argument for call injection.
type CallInjectionCopyArg struct {
	id      int
	ArgNum  int
	ArgExpr ast.Expr
}

func (*CallInjectionCopyArg) depthCheck() (npop, npush int) { return 1, 0 }

// CallInjectionComplete resumes target execution so that the injected call can run.
// If DoPinning is true it stops after the call is completed without undoing
// the call injection frames so that address pinning for the return value
// can be performed, see CallInjectionComplete2.
type CallInjectionComplete struct {
	id        int
	DoPinning bool
}

func (op *CallInjectionComplete) depthCheck() (npop, npush int) {
	if op.DoPinning {
		return 0, 0
	} else {
		return 0, 1
	}
}

// CallInjectionComplete2 if DoPinning was passed to CallInjectionComplete
// this will finish the call injection protocol and push the evaluation
// result on the stack.
type CallInjectionComplete2 struct {
	id int
}

func (*CallInjectionComplete2) depthCheck() (npop, npush int) { return 0, 1 }

// CallInjectionStartSpecial starts call injection for a function with a
// name and arguments known at compile time.
type CallInjectionStartSpecial struct {
	id     int
	FnName string
	ArgAst []ast.Expr
}

func (*CallInjectionStartSpecial) depthCheck() (npop, npush int) { return 0, 1 }

// ConvertAllocToString pops two variables from the stack, a constant string
// and the return value of runtime.mallocgc (mallocv), copies the contents
// of the string at the address in mallocv and pushes on the stack a new
// string value that uses the backing storage of mallocv.
type ConvertAllocToString struct {
}

func (*ConvertAllocToString) depthCheck() (npop, npush int) { return 2, 1 }

// SetValue pops to variables from the stack, lhv and rhv, and sets lhv to
// rhv.
type SetValue struct {
	lhe, Rhe ast.Expr
}

func (*SetValue) depthCheck() (npop, npush int) { return 2, 0 }

// SetDebugPinner pops one variable from the stack and uses it as the saved debug pinner.
type SetDebugPinner struct {
}

func (*SetDebugPinner) depthCheck() (npop, npush int) { return 1, 0 }

// PushDebugPinner pushes the debug pinner on the stack.
type PushDebugPinner struct {
}

func (*PushDebugPinner) depthCheck() (npop, npush int) { return 0, 1 }

// PushPinAddress pushes an address to pin on the stack (as an
// unsafe.Pointer) and removes it from the list of addresses to pin.
type PushPinAddress struct {
}

func (*PushPinAddress) depthCheck() (npop, npush int) { return 0, 1 }