// Author: simon
// Author: ynwdlxm@163.com
// Date: 2024/4/5 17:02
// Desc:

package binchunk

import (
    "encoding/binary"
    "math"
)

type reader struct {
    data []byte
}

func (r *reader) checkHeader() {
    if string(r.readBytes(4)) != LUA_SIGNATURE {
        panic("not a precompiled chunk!")
    } else if r.readByte() != LUAC_VERSION {
        panic("version mismatch!")
    } else if r.readByte() != LUAC_FORMAT {
        panic("format mismatch!")
    } else if string(r.readBytes(6)) != LUAC_DATA {
        panic("corrupted!")
    } else if r.readByte() != CINT_SIZE {
        panic("int size mismatch!")
    } else if r.readByte() != CSZIET_SIZE {
        panic("size_t size mismatch!")
    } else if r.readByte() != INSTRUCTION_SIZE {
        panic("instruction size mismatch!")
    } else if r.readByte() != LUA_INTEGER_SIZE {
        panic("lua_Integer size mismatch!")
    } else if r.readByte() != LUA_NUMBER_SIZE {
        panic("lua_number size mismatch!")
    } else if r.readLuaInteger() != LUAC_INT {
        panic("endianness mismatch!")
    } else if r.readLuaNumber() != LUAC_NUM {
        panic("float format mismatch")
    }
}

func (r *reader) readByte() byte {
    b := r.data[0]
    r.data = r.data[1:]
    return b
}
func (r *reader) readUint32() uint32 {
    i := binary.LittleEndian.Uint32(r.data)
    r.data = r.data[4:]
    return i
}
func (r *reader) readUint64() uint64 {
    i := binary.LittleEndian.Uint64(r.data)
    r.data = r.data[8:]
    return i
}
func (r *reader) readLuaInteger() int64 {
    return int64(r.readUint64())
}
func (r *reader) readLuaNumber() float64 {
    return math.Float64frombits(r.readUint64())
}
func (r *reader) readString() string {
    size := uint(r.readByte())
    if size == 0 {
        // NUll 字符串
        return ""
    }
    if size == 0XFF {
        // 长字符串
        size = uint(r.readUint64())
    }
    bytes := r.readBytes(size - 1)
    return string(bytes)
}
func (r *reader) readBytes(n uint) []byte {
    bytes := r.data[:n]
    r.data = r.data[n:]
    return bytes
}

func (r *reader) readProto(parentSource string) *Prototype {
    source := r.readString()
    if source == "" {
        source = parentSource
    }
    return &Prototype{
        Source:          source,
        LineDefined:     r.readUint32(),
        LastLineDefined: r.readUint32(),
        NumParams:       r.readByte(),
        IsVararg:        r.readByte(),
        MaxStackSize:    r.readByte(),
        Code:            r.readCode(),
        Constants:       r.readConstants(),
        Upvalues:        r.readUpvalues(),
        Protos:          r.readProtos(source),
        LineInfo:        r.readLineInfo(),
        LocVars:         r.readLocVars(),
        UpvalueNames:    r.readUpvalueNames(),
    }
}

func (r *reader) readCode() []uint32 {
    code := make([]uint32, r.readUint32())
    for i := range code {
        code[i] = r.readUint32()
    }
    return code
}

func (r *reader) readConstants() []interface{} {
    constants := make([]interface{}, r.readUint32())
    for i := range constants {
        constants[i] = r.readConstant()
    }
    return constants
}

func (r *reader) readConstant() interface{} {
    switch r.readByte() { // tag
    case TAG_NIL:
        return nil
    case TAG_BOOLEAN:
        return r.readByte() != 0
    case TAG_INTEGER:
        return r.readLuaInteger()
    case TAG_NUMBER:
        return r.readLuaNumber()
    case TAG_SHORT_STR:
        return r.readString()
    case TAG_LONG_STR:
        return r.readString()
    default:
        panic("corrupted!")
    }
}

func (r *reader) readUpvalues() []Upvalue {
    upvalues := make([]Upvalue, r.readUint32())
    for i := range upvalues {
        upvalues[i] = Upvalue{
            Instack: r.readByte(),
            Idx:     r.readByte(),
        }
    }

    return upvalues
}

func (r *reader) readProtos(parentSource string) []*Prototype {
    protos := make([]*Prototype, r.readUint32())
    for i := range protos {
        protos[i] = r.readProto(parentSource)
    }
    return protos
}

func (r *reader) readLineInfo() []uint32 {
    lineInfo := make([]uint32, r.readUint32())
    for i := range lineInfo {
        lineInfo[i] = r.readUint32()
    }

    return lineInfo
}

func (r *reader) readLocVars() []LocVar {
    locVars := make([]LocVar, r.readUint32())
    for i := range locVars {
        locVars[i] = LocVar{
            VarName: r.readString(),
            StartPC: r.readUint32(),
            EndPC:   r.readUint32(),
        }
    }

    return locVars
}

func (r *reader) readUpvalueNames() []string {
    names := make([]string, r.readUint32())
    for i := range names {
        names[i] = r.readString()
    }

    return names
}