// Copyright 2015 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.

// This file implements support functionality for iimport.go.

package gcimporter

import (
	"fmt"
	"go/token"
	"go/types"
	"sync"
)

func errorf(format string, args ...interface{}) {
	panic(fmt.Sprintf(format, args...))
}

// deltaNewFile is a magic line delta offset indicating a new file.
// We use -64 because it is rare; see issue 20080 and CL 41619.
// -64 is the smallest int that fits in a single byte as a varint.
const deltaNewFile = -64

// Synthesize a token.Pos
type fakeFileSet struct {
	fset  *token.FileSet
	files map[string]*token.File
}

func (s *fakeFileSet) pos(file string, line, column int) token.Pos {
	// TODO(mdempsky): Make use of column.

	// Since we don't know the set of needed file positions, we
	// reserve maxlines positions per file.
	const maxlines = 64 * 1024
	f := s.files[file]
	if f == nil {
		f = s.fset.AddFile(file, -1, maxlines)
		s.files[file] = f
		// Allocate the fake linebreak indices on first use.
		// TODO(adonovan): opt: save ~512KB using a more complex scheme?
		fakeLinesOnce.Do(func() {
			fakeLines = make([]int, maxlines)
			for i := range fakeLines {
				fakeLines[i] = i
			}
		})
		f.SetLines(fakeLines)
	}

	if line > maxlines {
		line = 1
	}

	// Treat the file as if it contained only newlines
	// and column=1: use the line number as the offset.
	return f.Pos(line - 1)
}

var (
	fakeLines     []int
	fakeLinesOnce sync.Once
)

func chanDir(d int) types.ChanDir {
	// tag values must match the constants in cmd/compile/internal/gc/go.go
	switch d {
	case 1 /* Crecv */ :
		return types.RecvOnly
	case 2 /* Csend */ :
		return types.SendOnly
	case 3 /* Cboth */ :
		return types.SendRecv
	default:
		errorf("unexpected channel dir %d", d)
		return 0
	}
}

var predeclared = []types.Type{
	// basic types
	types.Typ[types.Bool],
	types.Typ[types.Int],
	types.Typ[types.Int8],
	types.Typ[types.Int16],
	types.Typ[types.Int32],
	types.Typ[types.Int64],
	types.Typ[types.Uint],
	types.Typ[types.Uint8],
	types.Typ[types.Uint16],
	types.Typ[types.Uint32],
	types.Typ[types.Uint64],
	types.Typ[types.Uintptr],
	types.Typ[types.Float32],
	types.Typ[types.Float64],
	types.Typ[types.Complex64],
	types.Typ[types.Complex128],
	types.Typ[types.String],

	// basic type aliases
	types.Universe.Lookup("byte").Type(),
	types.Universe.Lookup("rune").Type(),

	// error
	types.Universe.Lookup("error").Type(),

	// untyped types
	types.Typ[types.UntypedBool],
	types.Typ[types.UntypedInt],
	types.Typ[types.UntypedRune],
	types.Typ[types.UntypedFloat],
	types.Typ[types.UntypedComplex],
	types.Typ[types.UntypedString],
	types.Typ[types.UntypedNil],

	// package unsafe
	types.Typ[types.UnsafePointer],

	// invalid type
	types.Typ[types.Invalid], // only appears in packages with errors

	// used internally by gc; never used by this package or in .a files
	anyType{},

	// comparable
	types.Universe.Lookup("comparable").Type(),
}

type anyType struct{}

func (t anyType) Underlying() types.Type { return t }
func (t anyType) String() string         { return "any" }