// Copyright 2013 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package interp

// Emulated functions that we cannot interpret because they are
// external or because they use "unsafe" or "reflect" operations.

import (
	"go/types"
	"math"
	"os"
	"runtime"
	"strings"
	"sync/atomic"
	"time"
	"unsafe"

	"golang.org/x/tools/go/ssa"
)

type externalFn func(fr *frame, args []value) value

// TODO(adonovan): fix: reflect.Value abstracts an lvalue or an
// rvalue; Set() causes mutations that can be observed via aliases.
// We have not captured that correctly here.

// Key strings are from Function.String().
var externals = make(map[string]externalFn)

func init() {
	// That little dot ۰ is an Arabic zero numeral (U+06F0), categories [Nd].
	for k, v := range map[string]externalFn{
		"(*sync.Pool).Get":                 ext۰sync۰Pool۰Get,
		"(*sync.Pool).Put":                 ext۰nop,
		"(reflect.Value).Bool":             ext۰reflect۰Value۰Bool,
		"(reflect.Value).CanAddr":          ext۰reflect۰Value۰CanAddr,
		"(reflect.Value).CanInterface":     ext۰reflect۰Value۰CanInterface,
		"(reflect.Value).Elem":             ext۰reflect۰Value۰Elem,
		"(reflect.Value).Field":            ext۰reflect۰Value۰Field,
		"(reflect.Value).Float":            ext۰reflect۰Value۰Float,
		"(reflect.Value).Index":            ext۰reflect۰Value۰Index,
		"(reflect.Value).Int":              ext۰reflect۰Value۰Int,
		"(reflect.Value).Interface":        ext۰reflect۰Value۰Interface,
		"(reflect.Value).IsNil":            ext۰reflect۰Value۰IsNil,
		"(reflect.Value).IsValid":          ext۰reflect۰Value۰IsValid,
		"(reflect.Value).Kind":             ext۰reflect۰Value۰Kind,
		"(reflect.Value).Len":              ext۰reflect۰Value۰Len,
		"(reflect.Value).MapIndex":         ext۰reflect۰Value۰MapIndex,
		"(reflect.Value).MapKeys":          ext۰reflect۰Value۰MapKeys,
		"(reflect.Value).NumField":         ext۰reflect۰Value۰NumField,
		"(reflect.Value).NumMethod":        ext۰reflect۰Value۰NumMethod,
		"(reflect.Value).Pointer":          ext۰reflect۰Value۰Pointer,
		"(reflect.Value).Set":              ext۰reflect۰Value۰Set,
		"(reflect.Value).String":           ext۰reflect۰Value۰String,
		"(reflect.Value).Type":             ext۰reflect۰Value۰Type,
		"(reflect.Value).Uint":             ext۰reflect۰Value۰Uint,
		"(reflect.error).Error":            ext۰reflect۰error۰Error,
		"(reflect.rtype).Bits":             ext۰reflect۰rtype۰Bits,
		"(reflect.rtype).Elem":             ext۰reflect۰rtype۰Elem,
		"(reflect.rtype).Field":            ext۰reflect۰rtype۰Field,
		"(reflect.rtype).In":               ext۰reflect۰rtype۰In,
		"(reflect.rtype).Kind":             ext۰reflect۰rtype۰Kind,
		"(reflect.rtype).NumField":         ext۰reflect۰rtype۰NumField,
		"(reflect.rtype).NumIn":            ext۰reflect۰rtype۰NumIn,
		"(reflect.rtype).NumMethod":        ext۰reflect۰rtype۰NumMethod,
		"(reflect.rtype).NumOut":           ext۰reflect۰rtype۰NumOut,
		"(reflect.rtype).Out":              ext۰reflect۰rtype۰Out,
		"(reflect.rtype).Size":             ext۰reflect۰rtype۰Size,
		"(reflect.rtype).String":           ext۰reflect۰rtype۰String,
		"bytes.init":                       ext۰nop, // avoid asm dependency
		"bytes.Equal":                      ext۰bytes۰Equal,
		"bytes.IndexByte":                  ext۰bytes۰IndexByte,
		"hash/crc32.haveSSE42":             ext۰crc32۰haveSSE42,
		"internal/cpu.cpuid":               ext۰cpu۰cpuid,
		"math.Abs":                         ext۰math۰Abs,
		"math.Exp":                         ext۰math۰Exp,
		"math.Float32bits":                 ext۰math۰Float32bits,
		"math.Float32frombits":             ext۰math۰Float32frombits,
		"math.Float64bits":                 ext۰math۰Float64bits,
		"math.Float64frombits":             ext۰math۰Float64frombits,
		"math.Ldexp":                       ext۰math۰Ldexp,
		"math.Log":                         ext۰math۰Log,
		"math.Min":                         ext۰math۰Min,
		"math.hasSSE4":                     ext۰math۰hasSSE4,
		"os.runtime_args":                  ext۰os۰runtime_args,
		"os.runtime_beforeExit":            ext۰nop,
		"os/signal.init":                   ext۰nop,
		"reflect.New":                      ext۰reflect۰New,
		"reflect.SliceOf":                  ext۰reflect۰SliceOf,
		"reflect.TypeOf":                   ext۰reflect۰TypeOf,
		"reflect.ValueOf":                  ext۰reflect۰ValueOf,
		"reflect.Zero":                     ext۰reflect۰Zero,
		"reflect.init":                     ext۰reflect۰Init,
		"reflect.valueInterface":           ext۰reflect۰valueInterface,
		"runtime.Breakpoint":               ext۰runtime۰Breakpoint,
		"runtime.Caller":                   ext۰runtime۰Caller,
		"runtime.Callers":                  ext۰runtime۰Callers,
		"runtime.FuncForPC":                ext۰runtime۰FuncForPC,
		"runtime.GC":                       ext۰runtime۰GC,
		"runtime.GOMAXPROCS":               ext۰runtime۰GOMAXPROCS,
		"runtime.Goexit":                   ext۰runtime۰Goexit,
		"runtime.Gosched":                  ext۰runtime۰Gosched,
		"runtime.init":                     ext۰nop,
		"runtime.KeepAlive":                ext۰nop,
		"runtime.NumCPU":                   ext۰runtime۰NumCPU,
		"runtime.NumGoroutine":             ext۰runtime۰NumGoroutine,
		"runtime.ReadMemStats":             ext۰runtime۰ReadMemStats,
		"runtime.SetFinalizer":             ext۰nop, // ignore
		"(*runtime.Func).Entry":            ext۰runtime۰Func۰Entry,
		"(*runtime.Func).FileLine":         ext۰runtime۰Func۰FileLine,
		"(*runtime.Func).Name":             ext۰runtime۰Func۰Name,
		"runtime.environ":                  ext۰runtime۰environ,
		"runtime.getgoroot":                ext۰runtime۰getgoroot,
		"strings.init":                     ext۰nop, // avoid asm dependency
		"strings.Count":                    ext۰strings۰Count,
		"strings.Index":                    ext۰strings۰Index,
		"strings.IndexByte":                ext۰strings۰IndexByte,
		"sync.runtime_Semacquire":          ext۰nop, // unimplementable
		"sync.runtime_Semrelease":          ext۰nop, // unimplementable
		"sync.runtime_Syncsemcheck":        ext۰nop, // unimplementable
		"sync.runtime_notifyListCheck":     ext۰nop,
		"sync.runtime_registerPoolCleanup": ext۰nop,
		"sync/atomic.AddInt32":             ext۰atomic۰AddInt32,
		"sync/atomic.AddUint32":            ext۰atomic۰AddUint32,
		"sync/atomic.CompareAndSwapInt32":  ext۰atomic۰CompareAndSwapInt32,
		"sync/atomic.CompareAndSwapUint32": ext۰atomic۰CompareAndSwapUint32,
		"sync/atomic.LoadInt32":            ext۰atomic۰LoadInt32,
		"sync/atomic.LoadUint32":           ext۰atomic۰LoadUint32,
		"sync/atomic.StoreInt32":           ext۰atomic۰StoreInt32,
		"sync/atomic.StoreUint32":          ext۰atomic۰StoreUint32,
		"sync/atomic.AddInt64":             ext۰atomic۰AddInt64,
		"sync/atomic.AddUint64":            ext۰atomic۰AddUint64,
		"sync/atomic.CompareAndSwapInt64":  ext۰atomic۰CompareAndSwapInt64,
		"sync/atomic.CompareAndSwapUint64": ext۰atomic۰CompareAndSwapUint64,
		"sync/atomic.LoadInt64":            ext۰atomic۰LoadInt64,
		"sync/atomic.LoadUint64":           ext۰atomic۰LoadUint64,
		"sync/atomic.StoreInt64":           ext۰atomic۰StoreInt64,
		"sync/atomic.StoreUint64":          ext۰atomic۰StoreUint64,
		"testing.callerEntry":              ext۰testing۰callerEntry,
		"testing.callerName":               ext۰testing۰callerName,
		"testing.runExample":               ext۰testing۰runExample,
		"time.Sleep":                       ext۰time۰Sleep,
		"time.now":                         ext۰time۰now,
	} {
		externals[k] = v
	}
}

// wrapError returns an interpreted 'error' interface value for err.
func wrapError(err error) value {
	if err == nil {
		return iface{}
	}
	return iface{t: errorType, v: err.Error()}
}

func ext۰nop(fr *frame, args []value) value { return nil }

func ext۰sync۰Pool۰Get(fr *frame, args []value) value {
	Pool := fr.i.prog.ImportedPackage("sync").Type("Pool").Object()
	_, newIndex, _ := types.LookupFieldOrMethod(Pool.Type(), false, Pool.Pkg(), "New")

	if New := (*args[0].(*value)).(structure)[newIndex[0]]; New != nil {
		return call(fr.i, fr, 0, New, nil)
	}
	return nil
}

func ext۰bytes۰Equal(fr *frame, args []value) value {
	// func Equal(a, b []byte) bool
	a := args[0].([]value)
	b := args[1].([]value)
	if len(a) != len(b) {
		return false
	}
	for i := range a {
		if a[i] != b[i] {
			return false
		}
	}
	return true
}

func ext۰bytes۰IndexByte(fr *frame, args []value) value {
	// func IndexByte(s []byte, c byte) int
	s := args[0].([]value)
	c := args[1].(byte)
	for i, b := range s {
		if b.(byte) == c {
			return i
		}
	}
	return -1
}

func ext۰crc32۰haveSSE42(fr *frame, args []value) value {
	return false
}

func ext۰math۰Float64frombits(fr *frame, args []value) value {
	return math.Float64frombits(args[0].(uint64))
}

func ext۰math۰Float64bits(fr *frame, args []value) value {
	return math.Float64bits(args[0].(float64))
}

func ext۰math۰Float32frombits(fr *frame, args []value) value {
	return math.Float32frombits(args[0].(uint32))
}

func ext۰math۰Abs(fr *frame, args []value) value {
	return math.Abs(args[0].(float64))
}

func ext۰math۰Exp(fr *frame, args []value) value {
	return math.Exp(args[0].(float64))
}

func ext۰math۰Float32bits(fr *frame, args []value) value {
	return math.Float32bits(args[0].(float32))
}

func ext۰math۰Min(fr *frame, args []value) value {
	return math.Min(args[0].(float64), args[1].(float64))
}

func ext۰math۰hasSSE4(fr *frame, args []value) value {
	return false
}

func ext۰math۰Ldexp(fr *frame, args []value) value {
	return math.Ldexp(args[0].(float64), args[1].(int))
}

func ext۰math۰Log(fr *frame, args []value) value {
	return math.Log(args[0].(float64))
}

func ext۰os۰runtime_args(fr *frame, args []value) value {
	return fr.i.osArgs
}

func ext۰runtime۰Breakpoint(fr *frame, args []value) value {
	runtime.Breakpoint()
	return nil
}

func ext۰runtime۰Caller(fr *frame, args []value) value {
	// func Caller(skip int) (pc uintptr, file string, line int, ok bool)
	skip := 1 + args[0].(int)
	for i := 0; i < skip; i++ {
		if fr != nil {
			fr = fr.caller
		}
	}
	var pc uintptr
	var file string
	var line int
	var ok bool
	if fr != nil {
		fn := fr.fn
		// TODO(adonovan): use pc/posn of current instruction, not start of fn.
		// (Required to interpret the log package's tests.)
		pc = uintptr(unsafe.Pointer(fn))
		posn := fn.Prog.Fset.Position(fn.Pos())
		file = posn.Filename
		line = posn.Line
		ok = true
	}
	return tuple{pc, file, line, ok}
}

func ext۰runtime۰Callers(fr *frame, args []value) value {
	// Callers(skip int, pc []uintptr) int
	skip := args[0].(int)
	pc := args[1].([]value)
	for i := 0; i < skip; i++ {
		if fr != nil {
			fr = fr.caller
		}
	}
	i := 0
	for fr != nil && i < len(pc) {
		pc[i] = uintptr(unsafe.Pointer(fr.fn))
		i++
		fr = fr.caller
	}
	return i
}

func ext۰runtime۰FuncForPC(fr *frame, args []value) value {
	// FuncForPC(pc uintptr) *Func
	pc := args[0].(uintptr)
	var fn *ssa.Function
	if pc != 0 {
		fn = (*ssa.Function)(unsafe.Pointer(pc)) // indeed unsafe!
	}
	var Func value
	Func = structure{fn} // a runtime.Func
	return &Func
}

func ext۰runtime۰environ(fr *frame, args []value) value {
	// This function also implements syscall.runtime_envs.
	return environ
}

func ext۰runtime۰getgoroot(fr *frame, args []value) value {
	return os.Getenv("GOROOT")
}

func ext۰strings۰Count(fr *frame, args []value) value {
	// Call compiled version to avoid asm dependency.
	return strings.Count(args[0].(string), args[1].(string))
}

func ext۰strings۰IndexByte(fr *frame, args []value) value {
	// Call compiled version to avoid asm dependency.
	return strings.IndexByte(args[0].(string), args[1].(byte))
}

func ext۰strings۰Index(fr *frame, args []value) value {
	// Call compiled version to avoid asm dependency.
	return strings.Index(args[0].(string), args[1].(string))
}

func ext۰runtime۰GOMAXPROCS(fr *frame, args []value) value {
	// Ignore args[0]; don't let the interpreted program
	// set the interpreter's GOMAXPROCS!
	return runtime.GOMAXPROCS(0)
}

func ext۰runtime۰Goexit(fr *frame, args []value) value {
	// TODO(adonovan): don't kill the interpreter's main goroutine.
	runtime.Goexit()
	return nil
}

func ext۰runtime۰GC(fr *frame, args []value) value {
	runtime.GC()
	return nil
}

func ext۰runtime۰Gosched(fr *frame, args []value) value {
	runtime.Gosched()
	return nil
}

func ext۰runtime۰NumCPU(fr *frame, args []value) value {
	return runtime.NumCPU()
}

func ext۰runtime۰NumGoroutine(fr *frame, args []value) value {
	return int(atomic.LoadInt32(&fr.i.goroutines))
}

func ext۰runtime۰ReadMemStats(fr *frame, args []value) value {
	// TODO(adonovan): populate args[0].(Struct)
	return nil
}

func ext۰atomic۰LoadUint32(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	return (*args[0].(*value)).(uint32)
}

func ext۰atomic۰StoreUint32(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	*args[0].(*value) = args[1].(uint32)
	return nil
}

func ext۰atomic۰LoadInt32(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	return (*args[0].(*value)).(int32)
}

func ext۰atomic۰StoreInt32(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	*args[0].(*value) = args[1].(int32)
	return nil
}

func ext۰atomic۰CompareAndSwapInt32(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	p := args[0].(*value)
	if (*p).(int32) == args[1].(int32) {
		*p = args[2].(int32)
		return true
	}
	return false
}

func ext۰atomic۰CompareAndSwapUint32(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	p := args[0].(*value)
	if (*p).(uint32) == args[1].(uint32) {
		*p = args[2].(uint32)
		return true
	}
	return false
}

func ext۰atomic۰AddInt32(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	p := args[0].(*value)
	newv := (*p).(int32) + args[1].(int32)
	*p = newv
	return newv
}

func ext۰atomic۰AddUint32(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	p := args[0].(*value)
	newv := (*p).(uint32) + args[1].(uint32)
	*p = newv
	return newv
}

func ext۰atomic۰LoadUint64(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	return (*args[0].(*value)).(uint64)
}

func ext۰atomic۰StoreUint64(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	*args[0].(*value) = args[1].(uint64)
	return nil
}

func ext۰atomic۰LoadInt64(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	return (*args[0].(*value)).(int64)
}

func ext۰atomic۰StoreInt64(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	*args[0].(*value) = args[1].(int64)
	return nil
}

func ext۰atomic۰CompareAndSwapInt64(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	p := args[0].(*value)
	if (*p).(int64) == args[1].(int64) {
		*p = args[2].(int64)
		return true
	}
	return false
}

func ext۰atomic۰CompareAndSwapUint64(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	p := args[0].(*value)
	if (*p).(uint64) == args[1].(uint64) {
		*p = args[2].(uint64)
		return true
	}
	return false
}

func ext۰atomic۰AddInt64(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	p := args[0].(*value)
	newv := (*p).(int64) + args[1].(int64)
	*p = newv
	return newv
}

func ext۰atomic۰AddUint64(fr *frame, args []value) value {
	// TODO(adonovan): fix: not atomic!
	p := args[0].(*value)
	newv := (*p).(uint64) + args[1].(uint64)
	*p = newv
	return newv
}

func ext۰cpu۰cpuid(fr *frame, args []value) value {
	return tuple{uint32(0), uint32(0), uint32(0), uint32(0)}
}

// Pretend: type runtime.Func struct { entry *ssa.Function }

func ext۰runtime۰Func۰FileLine(fr *frame, args []value) value {
	// func (*runtime.Func) FileLine(uintptr) (string, int)
	f, _ := (*args[0].(*value)).(structure)[0].(*ssa.Function)
	pc := args[1].(uintptr)
	_ = pc
	if f != nil {
		// TODO(adonovan): use position of current instruction, not fn.
		posn := f.Prog.Fset.Position(f.Pos())
		return tuple{posn.Filename, posn.Line}
	}
	return tuple{"", 0}
}

func ext۰runtime۰Func۰Name(fr *frame, args []value) value {
	// func (*runtime.Func) Name() string
	f, _ := (*args[0].(*value)).(structure)[0].(*ssa.Function)
	if f != nil {
		return f.String()
	}
	return ""
}

func ext۰runtime۰Func۰Entry(fr *frame, args []value) value {
	// func (*runtime.Func) Entry() uintptr
	f, _ := (*args[0].(*value)).(structure)[0].(*ssa.Function)
	return uintptr(unsafe.Pointer(f))
}

// This is a workaround for a bug in go/ssa/testmain.go: it creates
// InternalExamples even for Example functions with no Output comment.
// TODO(adonovan): fix (and redesign) testmain.go..
func ext۰testing۰runExample(fr *frame, args []value) value {
	// This is a stripped down runExample that simply calls the function.
	// It does not capture and compare output nor recover from panic.
	//
	// func runExample(eg testing.InternalExample) bool {
	//     eg.F()
	//     return true
	// }
	F := args[0].(structure)[1]
	call(fr.i, fr, 0, F, nil)
	return true
}

// These two internal functions must be faked to avoid calls to
// runtime.CallersFrames, which is hard to emulate. We are inching
// towards the point at which I blow away this entire package, or at
// least all tests that interpret the standard "testing" package.

func ext۰testing۰callerEntry(fr *frame, args []value) value {
	return uintptr(0) // bogus implementation for now
}

func ext۰testing۰callerName(fr *frame, args []value) value {
	return "<unknown>" // bogus implementation for now
}

func ext۰time۰now(fr *frame, args []value) value {
	nano := time.Now().UnixNano()
	return tuple{int64(nano / 1e9), int32(nano % 1e9), int64(0)}
}

func ext۰time۰Sleep(fr *frame, args []value) value {
	time.Sleep(time.Duration(args[0].(int64)))
	return nil
}

func valueToBytes(v value) []byte {
	in := v.([]value)
	b := make([]byte, len(in))
	for i := range in {
		b[i] = in[i].(byte)
	}
	return b
}