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// Copyright 2009 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.

// DWARF type information structures.
// The format is heavily biased toward C, but for simplicity
// the String methods use a pseudo-Go syntax.

package dwarf

import "strconv"

// A Type conventionally represents a pointer to any of the
// specific Type structures (CharType, StructType, etc.).
type Type interface {
        Common() *CommonType
        String() string
        Size() int64
}

// A CommonType holds fields common to multiple types.
// If a field is not known or not applicable for a given type,
// the zero value is used.
type CommonType struct {
        ByteSize int64  // size of value of this type, in bytes
        Name     string // name that can be used to refer to type
}

func (c *CommonType) Common() *CommonType { return c }

func (c *CommonType) Size() int64 { return c.ByteSize }

// Basic types

// A BasicType holds fields common to all basic types.
type BasicType struct {
        CommonType
        BitSize   int64
        BitOffset int64
}

func (b *BasicType) Basic() *BasicType { return b }

func (t *BasicType) String() string {
        if t.Name != "" {
                return t.Name
        }
        return "?"
}

// A CharType represents a signed character type.
type CharType struct {
        BasicType
}

// A UcharType represents an unsigned character type.
type UcharType struct {
        BasicType
}

// An IntType represents a signed integer type.
type IntType struct {
        BasicType
}

// A UintType represents an unsigned integer type.
type UintType struct {
        BasicType
}

// A FloatType represents a floating point type.
type FloatType struct {
        BasicType
}

// A ComplexType represents a complex floating point type.
type ComplexType struct {
        BasicType
}

// A BoolType represents a boolean type.
type BoolType struct {
        BasicType
}

// An AddrType represents a machine address type.
type AddrType struct {
        BasicType
}

// qualifiers

// A QualType represents a type that has the C/C++ "const", "restrict", or "volatile" qualifier.
type QualType struct {
        CommonType
        Qual string
        Type Type
}

func (t *QualType) String() string { return t.Qual + " " + t.Type.String() }

func (t *QualType) Size() int64 { return t.Type.Size() }

// An ArrayType represents a fixed size array type.
type ArrayType struct {
        CommonType
        Type          Type
        StrideBitSize int64 // if > 0, number of bits to hold each element
        Count         int64 // if == -1, an incomplete array, like char x[].
}

func (t *ArrayType) String() string {
        return "[" + strconv.FormatInt(t.Count, 10) + "]" + t.Type.String()
}

func (t *ArrayType) Size() int64 { return t.Count * t.Type.Size() }

// A VoidType represents the C void type.
type VoidType struct {
        CommonType
}

func (t *VoidType) String() string { return "void" }

// A PtrType represents a pointer type.
type PtrType struct {
        CommonType
        Type Type
}

func (t *PtrType) String() string { return "*" + t.Type.String() }

// A StructType represents a struct, union, or C++ class type.
type StructType struct {
        CommonType
        StructName string
        Kind       string // "struct", "union", or "class".
        Field      []*StructField
        Incomplete bool // if true, struct, union, class is declared but not defined
}

// A StructField represents a field in a struct, union, or C++ class type.
type StructField struct {
        Name       string
        Type       Type
        ByteOffset int64
        ByteSize   int64
        BitOffset  int64 // within the ByteSize bytes at ByteOffset
        BitSize    int64 // zero if not a bit field
}

func (t *StructType) String() string {
        if t.StructName != "" {
                return t.Kind + " " + t.StructName
        }
        return t.Defn()
}

func (t *StructType) Defn() string {
        s := t.Kind
        if t.StructName != "" {
                s += " " + t.StructName
        }
        if t.Incomplete {
                s += " /*incomplete*/"
                return s
        }
        s += " {"
        for i, f := range t.Field {
                if i > 0 {
                        s += "; "
                }
                s += f.Name + " " + f.Type.String()
                s += "@" + strconv.FormatInt(f.ByteOffset, 10)
                if f.BitSize > 0 {
                        s += " : " + strconv.FormatInt(f.BitSize, 10)
                        s += "@" + strconv.FormatInt(f.BitOffset, 10)
                }
        }
        s += "}"
        return s
}

// An EnumType represents an enumerated type.
// The only indication of its native integer type is its ByteSize
// (inside CommonType).
type EnumType struct {
        CommonType
        EnumName string
        Val      []*EnumValue
}

// An EnumValue represents a single enumeration value.
type EnumValue struct {
        Name string
        Val  int64
}

func (t *EnumType) String() string {
        s := "enum"
        if t.EnumName != "" {
                s += " " + t.EnumName
        }
        s += " {"
        for i, v := range t.Val {
                if i > 0 {
                        s += "; "
                }
                s += v.Name + "=" + strconv.FormatInt(v.Val, 10)
        }
        s += "}"
        return s
}

// A FuncType represents a function type.
type FuncType struct {
        CommonType
        ReturnType Type
        ParamType  []Type
}

func (t *FuncType) String() string {
        s := "func("
        for i, t := range t.ParamType {
                if i > 0 {
                        s += ", "
                }
                s += t.String()
        }
        s += ")"
        if t.ReturnType != nil {
                s += " " + t.ReturnType.String()
        }
        return s
}

// A DotDotDotType represents the variadic ... function parameter.
type DotDotDotType struct {
        CommonType
}

func (t *DotDotDotType) String() string { return "..." }

// A TypedefType represents a named type.
type TypedefType struct {
        CommonType
        Type Type
}

func (t *TypedefType) String() string { return t.Name }

func (t *TypedefType) Size() int64 { return t.Type.Size() }

func (d *Data) Type(off Offset) (Type, error) {
        if t, ok := d.typeCache[off]; ok {
                return t, nil
        }

        r := d.Reader()
        r.Seek(off)
        e, err := r.Next()
        if err != nil {
                return nil, err
        }
        if e == nil || e.Offset != off {
                return nil, DecodeError{"info", off, "no type at offset"}
        }

        // Parse type from Entry.
        // Must always set d.typeCache[off] before calling
        // d.Type recursively, to handle circular types correctly.
        var typ Type

        // Get next child; set err if error happens.
        next := func() *Entry {
                if !e.Children {
                        return nil
                }
                kid, err1 := r.Next()
                if err1 != nil {
                        err = err1
                        return nil
                }
                if kid == nil {
                        err = DecodeError{"info", r.b.off, "unexpected end of DWARF entries"}
                        return nil
                }
                if kid.Tag == 0 {
                        return nil
                }
                return kid
        }

        // Get Type referred to by Entry's AttrType field.
        // Set err if error happens.  Not having a type is an error.
        typeOf := func(e *Entry) Type {
                toff, ok := e.Val(AttrType).(Offset)
                if !ok {
                        // It appears that no Type means "void".
                        return new(VoidType)
                }
                var t Type
                if t, err = d.Type(toff); err != nil {
                        return nil
                }
                return t
        }

        switch e.Tag {
        case TagArrayType:
                // Multi-dimensional array.  (DWARF v2 §5.4)
                // Attributes:
                //      AttrType:subtype [required]
                //      AttrStrideSize: size in bits of each element of the array
                //      AttrByteSize: size of entire array
                // Children:
                //      TagSubrangeType or TagEnumerationType giving one dimension.
                //      dimensions are in left to right order.
                t := new(ArrayType)
                typ = t
                d.typeCache[off] = t
                if t.Type = typeOf(e); err != nil {
                        goto Error
                }
                t.StrideBitSize, _ = e.Val(AttrStrideSize).(int64)

                // Accumulate dimensions,
                ndim := 0
                for kid := next(); kid != nil; kid = next() {
                        // TODO(rsc): Can also be TagEnumerationType
                        // but haven't seen that in the wild yet.
                        switch kid.Tag {
                        case TagSubrangeType:
                                max, ok := kid.Val(AttrUpperBound).(int64)
                                if !ok {
                                        max = -2 // Count == -1, as in x[].
                                }
                                if ndim == 0 {
                                        t.Count = max + 1
                                } else {
                                        // Multidimensional array.
                                        // Create new array type underneath this one.
                                        t.Type = &ArrayType{Type: t.Type, Count: max + 1}
                                }
                                ndim++
                        case TagEnumerationType:
                                err = DecodeError{"info", kid.Offset, "cannot handle enumeration type as array bound"}
                                goto Error
                        }
                }
                if ndim == 0 {
                        // LLVM generates this for x[].
                        t.Count = -1
                }

        case TagBaseType:
                // Basic type.  (DWARF v2 §5.1)
                // Attributes:
                //      AttrName: name of base type in programming language of the compilation unit [required]
                //      AttrEncoding: encoding value for type (encFloat etc) [required]
                //      AttrByteSize: size of type in bytes [required]
                //      AttrBitOffset: for sub-byte types, size in bits
                //      AttrBitSize: for sub-byte types, bit offset of high order bit in the AttrByteSize bytes
                name, _ := e.Val(AttrName).(string)
                enc, ok := e.Val(AttrEncoding).(int64)
                if !ok {
                        err = DecodeError{"info", e.Offset, "missing encoding attribute for " + name}
                        goto Error
                }
                switch enc {
                default:
                        err = DecodeError{"info", e.Offset, "unrecognized encoding attribute value"}
                        goto Error

                case encAddress:
                        typ = new(AddrType)
                case encBoolean:
                        typ = new(BoolType)
                case encComplexFloat:
                        typ = new(ComplexType)
                case encFloat:
                        typ = new(FloatType)
                case encSigned:
                        typ = new(IntType)
                case encUnsigned:
                        typ = new(UintType)
                case encSignedChar:
                        typ = new(CharType)
                case encUnsignedChar:
                        typ = new(UcharType)
                }
                d.typeCache[off] = typ
                t := typ.(interface {
                        Basic() *BasicType
                }).Basic()
                t.Name = name
                t.BitSize, _ = e.Val(AttrBitSize).(int64)
                t.BitOffset, _ = e.Val(AttrBitOffset).(int64)

        case TagClassType, TagStructType, TagUnionType:
                // Structure, union, or class type.  (DWARF v2 §5.5)
                // Attributes:
                //      AttrName: name of struct, union, or class
                //      AttrByteSize: byte size [required]
                //      AttrDeclaration: if true, struct/union/class is incomplete
                // Children:
                //      TagMember to describe one member.
                //              AttrName: name of member [required]
                //              AttrType: type of member [required]
                //              AttrByteSize: size in bytes
                //              AttrBitOffset: bit offset within bytes for bit fields
                //              AttrBitSize: bit size for bit fields
                //              AttrDataMemberLoc: location within struct [required for struct, class]
                // There is much more to handle C++, all ignored for now.
                t := new(StructType)
                typ = t
                d.typeCache[off] = t
                switch e.Tag {
                case TagClassType:
                        t.Kind = "class"
                case TagStructType:
                        t.Kind = "struct"
                case TagUnionType:
                        t.Kind = "union"
                }
                t.StructName, _ = e.Val(AttrName).(string)
                t.Incomplete = e.Val(AttrDeclaration) != nil
                t.Field = make([]*StructField, 0, 8)
                for kid := next(); kid != nil; kid = next() {
                        if kid.Tag == TagMember {
                                f := new(StructField)
                                if f.Type = typeOf(kid); err != nil {
                                        goto Error
                                }
                                if loc, ok := kid.Val(AttrDataMemberLoc).([]byte); ok {
                                        b := makeBuf(d, "location", 0, loc, d.addrsize)
                                        if b.uint8() != opPlusUconst {
                                                err = DecodeError{"info", kid.Offset, "unexpected opcode"}
                                                goto Error
                                        }
                                        f.ByteOffset = int64(b.uint())
                                        if b.err != nil {
                                                err = b.err
                                                goto Error
                                        }
                                }
                                f.Name, _ = kid.Val(AttrName).(string)
                                f.ByteSize, _ = kid.Val(AttrByteSize).(int64)
                                f.BitOffset, _ = kid.Val(AttrBitOffset).(int64)
                                f.BitSize, _ = kid.Val(AttrBitSize).(int64)
                                t.Field = append(t.Field, f)
                        }
                }

        case TagConstType, TagVolatileType, TagRestrictType:
                // Type modifier (DWARF v2 §5.2)
                // Attributes:
                //      AttrType: subtype
                t := new(QualType)
                typ = t
                d.typeCache[off] = t
                if t.Type = typeOf(e); err != nil {
                        goto Error
                }
                switch e.Tag {
                case TagConstType:
                        t.Qual = "const"
                case TagRestrictType:
                        t.Qual = "restrict"
                case TagVolatileType:
                        t.Qual = "volatile"
                }

        case TagEnumerationType:
                // Enumeration type (DWARF v2 §5.6)
                // Attributes:
                //      AttrName: enum name if any
                //      AttrByteSize: bytes required to represent largest value
                // Children:
                //      TagEnumerator:
                //              AttrName: name of constant
                //              AttrConstValue: value of constant
                t := new(EnumType)
                typ = t
                d.typeCache[off] = t
                t.EnumName, _ = e.Val(AttrName).(string)
                t.Val = make([]*EnumValue, 0, 8)
                for kid := next(); kid != nil; kid = next() {
                        if kid.Tag == TagEnumerator {
                                f := new(EnumValue)
                                f.Name, _ = kid.Val(AttrName).(string)
                                f.Val, _ = kid.Val(AttrConstValue).(int64)
                                n := len(t.Val)
                                if n >= cap(t.Val) {
                                        val := make([]*EnumValue, n, n*2)
                                        copy(val, t.Val)
                                        t.Val = val
                                }
                                t.Val = t.Val[0 : n+1]
                                t.Val[n] = f
                        }
                }

        case TagPointerType:
                // Type modifier (DWARF v2 §5.2)
                // Attributes:
                //      AttrType: subtype [not required!  void* has no AttrType]
                //      AttrAddrClass: address class [ignored]
                t := new(PtrType)
                typ = t
                d.typeCache[off] = t
                if e.Val(AttrType) == nil {
                        t.Type = &VoidType{}
                        break
                }
                t.Type = typeOf(e)

        case TagSubroutineType:
                // Subroutine type.  (DWARF v2 §5.7)
                // Attributes:
                //      AttrType: type of return value if any
                //      AttrName: possible name of type [ignored]
                //      AttrPrototyped: whether used ANSI C prototype [ignored]
                // Children:
                //      TagFormalParameter: typed parameter
                //              AttrType: type of parameter
                //      TagUnspecifiedParameter: final ...
                t := new(FuncType)
                typ = t
                d.typeCache[off] = t
                if t.ReturnType = typeOf(e); err != nil {
                        goto Error
                }
                t.ParamType = make([]Type, 0, 8)
                for kid := next(); kid != nil; kid = next() {
                        var tkid Type
                        switch kid.Tag {
                        default:
                                continue
                        case TagFormalParameter:
                                if tkid = typeOf(kid); err != nil {
                                        goto Error
                                }
                        case TagUnspecifiedParameters:
                                tkid = &DotDotDotType{}
                        }
                        t.ParamType = append(t.ParamType, tkid)
                }

        case TagTypedef:
                // Typedef (DWARF v2 §5.3)
                // Attributes:
                //      AttrName: name [required]
                //      AttrType: type definition [required]
                t := new(TypedefType)
                typ = t
                d.typeCache[off] = t
                t.Name, _ = e.Val(AttrName).(string)
                t.Type = typeOf(e)
        }

        if err != nil {
                goto Error
        }

        {
                b, ok := e.Val(AttrByteSize).(int64)
                if !ok {
                        b = -1
                }
                typ.Common().ByteSize = b
        }
        return typ, nil

Error:
        // If the parse fails, take the type out of the cache
        // so that the next call with this offset doesn't hit
        // the cache and return success.
        delete(d.typeCache, off)
        return nil, err
}