337 lines
8.7 KiB
Go
337 lines
8.7 KiB
Go
package state
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import (
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"fmt"
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"log"
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"strings"
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)
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type IndexError struct {
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}
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func(err *IndexError) Error() string {
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return fmt.Sprintf("already at first index")
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}
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// State holds the command stack, error condition of a unique execution session.
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//
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// It also holds cached values for all results of executed symbols.
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//
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// Cached values are linked to the command stack level it which they were loaded. When they go out of scope they are freed.
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//
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// Values must be mapped to a level in order to be available for retrieval and count towards size
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//
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// It can hold a single argument, which is freed once it is read
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//
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// Symbols are loaded with individual size limitations. The limitations apply if a load symbol is updated. Symbols may be added with a 0-value for limits, called a "sink." If mapped, the sink will consume all net remaining size allowance unused by other symbols. Only one sink may be mapped per level.
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//
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// Symbol keys do not count towards cache size limitations.
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//
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// 8 first flags are reserved.
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type State struct {
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Code []byte // Pending bytecode to execute
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ExecPath []string // Command symbols stack
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BitSize uint32 // size of (32-bit capacity) bit flag byte array
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SizeIdx uint16
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Flags []byte // Error state
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Moves uint32 // Number of times navigation has been performed
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input []byte // Last input
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}
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// number of bytes necessary to represent a bitfield of the given size.
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func toByteSize(BitSize uint32) uint8 {
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if BitSize == 0 {
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return 0
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}
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n := BitSize % 8
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if n > 0 {
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BitSize += (8 - n)
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}
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return uint8(BitSize / 8)
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}
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// Retrieve the state of a state flag
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func getFlag(bitIndex uint32, bitField []byte) bool {
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byteIndex := bitIndex / 8
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localBitIndex := bitIndex % 8
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b := bitField[byteIndex]
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return (b & (1 << localBitIndex)) > 0
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}
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// NewState creates a new State object with BitSize number of error condition states in ADDITION to the 8 builtin flags.
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func NewState(BitSize uint32) State {
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st := State{
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BitSize: BitSize + 8,
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}
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byteSize := toByteSize(BitSize + 8)
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if byteSize > 0 {
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st.Flags = make([]byte, byteSize)
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} else {
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st.Flags = []byte{}
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}
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return st
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}
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// SetFlag sets the flag at the given bit field index
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//
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// Returns true if bit state was changed.
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//
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// Fails if bitindex is out of range.
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func(st *State) SetFlag(bitIndex uint32) (bool, error) {
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if bitIndex + 1 > st.BitSize {
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return false, fmt.Errorf("bit index %v is out of range of bitfield size %v", bitIndex, st.BitSize)
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}
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r := getFlag(bitIndex, st.Flags)
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if r {
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return false, nil
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}
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byteIndex := bitIndex / 8
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localBitIndex := bitIndex % 8
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b := st.Flags[byteIndex]
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st.Flags[byteIndex] = b | (1 << localBitIndex)
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return true, nil
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}
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// ResetFlag resets the flag at the given bit field index.
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//
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// Returns true if bit state was changed.
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//
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// Fails if bitindex is out of range.
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func(st *State) ResetFlag(bitIndex uint32) (bool, error) {
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if bitIndex + 1 > st.BitSize {
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return false, fmt.Errorf("bit index %v is out of range of bitfield size %v", bitIndex, st.BitSize)
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}
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r := getFlag(bitIndex, st.Flags)
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if !r {
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return false, nil
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}
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byteIndex := bitIndex / 8
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localBitIndex := bitIndex % 8
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b := st.Flags[byteIndex]
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st.Flags[byteIndex] = b & (^(1 << localBitIndex))
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return true, nil
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}
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// GetFlag returns the state of the flag at the given bit field index.
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//
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// Fails if bit field index is out of range.
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func(st *State) GetFlag(bitIndex uint32) (bool, error) {
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if bitIndex + 1 > st.BitSize {
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return false, fmt.Errorf("bit index %v is out of range of bitfield size %v", bitIndex, st.BitSize)
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}
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return getFlag(bitIndex, st.Flags), nil
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}
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// FlagBitSize reports the amount of bits available in the bit field index.
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func(st *State) FlagBitSize() uint32 {
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return st.BitSize
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}
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// FlagBitSize reports the amount of bits available in the bit field index.
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func(st *State) FlagByteSize() uint8 {
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return uint8(len(st.Flags))
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}
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// MatchFlag matches the current state of the given flag.
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//
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// The flag is specified given its bit index in the bit field.
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//
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// If invertMatch is set, a positive result will be returned if the flag is not set.
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func(st *State) MatchFlag(sig uint32, invertMatch bool) (bool, error) {
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r, err := st.GetFlag(sig)
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if err != nil {
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return false, err
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}
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if invertMatch {
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if !r {
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return true, nil
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}
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} else if r {
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return true, nil
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}
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return false, nil
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}
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// GetIndex scans a byte slice in same order as in storage, and returns the index of the first set bit.
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//
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// If the given byte slice is too small for the bit field bitsize, the check will terminate at end-of-data without error.
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func(st *State) GetIndex(flags []byte) bool {
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var globalIndex uint32
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if st.BitSize == 0 {
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return false
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}
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if len(flags) == 0 {
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return false
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}
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var byteIndex uint8
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var localIndex uint8
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l := uint8(len(flags))
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var i uint32
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for i = 0; i < st.BitSize; i++ {
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testVal := flags[byteIndex] & (1 << localIndex)
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if (testVal & st.Flags[byteIndex]) > 0 {
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return true
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}
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globalIndex += 1
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if globalIndex % 8 == 0 {
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byteIndex += 1
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localIndex = 0
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if byteIndex > (l - 1) {
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return false
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}
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} else {
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localIndex += 1
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}
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}
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return false
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}
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// Where returns the current active rendering symbol.
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func(st *State) Where() (string, uint16) {
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if len(st.ExecPath) == 0 {
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return "", 0
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}
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l := len(st.ExecPath)
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return st.ExecPath[l-1], st.SizeIdx
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}
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// Next moves to the next sink page index.
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func(st *State) Next() (uint16, error) {
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if len(st.ExecPath) == 0 {
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return 0, fmt.Errorf("state root node not yet defined")
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}
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st.SizeIdx += 1
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s, idx := st.Where()
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log.Printf("next page for %s: %v", s, idx)
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st.Moves += 1
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return st.SizeIdx, nil
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}
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// Previous moves to the next sink page index.
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//
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// Fails if try to move beyond index 0.
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func(st *State) Previous() (uint16, error) {
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if len(st.ExecPath) == 0 {
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return 0, fmt.Errorf("state root node not yet defined")
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}
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if st.SizeIdx == 0 {
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return 0, &IndexError{} // ("already at first index")
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}
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st.SizeIdx -= 1
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s, idx := st.Where()
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log.Printf("previous page for %s: %v", s, idx)
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st.Moves += 1
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return st.SizeIdx, nil
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}
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// Sides informs the caller which index page options will currently succeed.
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//
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// Two values are returned, for the "next" and "previous" options in that order. A false value means the option is not available in the current state.
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func(st *State) Sides() (bool, bool) {
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if len(st.ExecPath) == 0 {
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return false, false
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}
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next := true
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log.Printf("sides %v", st.SizeIdx)
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if st.SizeIdx == 0 {
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return next, false
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}
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return next, true
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}
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// Top returns true if currently at topmode node.
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//
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// Fails if first Down() was never called.
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func(st *State) Top() (bool, error) {
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if len(st.ExecPath) == 0 {
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return false, fmt.Errorf("state root node not yet defined")
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}
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return len(st.ExecPath) == 1, nil
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}
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// Down adds the given symbol to the command stack.
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//
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// Clears mapping and sink.
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func(st *State) Down(input string) error {
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st.ExecPath = append(st.ExecPath, input)
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st.SizeIdx = 0
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st.Moves += 1
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return nil
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}
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// Up removes the latest symbol to the command stack, and make the previous symbol current.
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//
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// Frees all symbols and associated values loaded at the previous stack level. Cache capacity is increased by the corresponding amount.
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//
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// Clears mapping and sink.
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//
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// Fails if called at top frame.
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func(st *State) Up() (string, error) {
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l := len(st.ExecPath)
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if l == 0 {
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return "", fmt.Errorf("exit called beyond top frame")
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}
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log.Printf("execpath before %v", st.ExecPath)
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st.ExecPath = st.ExecPath[:l-1]
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sym := ""
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if len(st.ExecPath) > 0 {
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sym = st.ExecPath[len(st.ExecPath)-1]
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}
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st.SizeIdx = 0
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log.Printf("execpath after %v", st.ExecPath)
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st.Moves += 1
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return sym, nil
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}
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// Depth returns the current call stack depth.
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func(st *State) Depth() uint8 {
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return uint8(len(st.ExecPath)-1)
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}
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// Appendcode adds the given bytecode to the end of the existing code.
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func(st *State) AppendCode(b []byte) error {
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st.Code = append(st.Code, b...)
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log.Printf("code changed to 0x%x", b)
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return nil
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}
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// SetCode replaces the current bytecode with the given bytecode.
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func(st *State) SetCode(b []byte) {
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log.Printf("code set to 0x%x", b)
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st.Code = b
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}
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// Get the remaning cached bytecode
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func(st *State) GetCode() ([]byte, error) {
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b := st.Code
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st.Code = []byte{}
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return b, nil
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}
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// GetInput gets the most recent client input.
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func(st *State) GetInput() ([]byte, error) {
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if st.input == nil {
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return nil, fmt.Errorf("no input has been set")
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}
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return st.input, nil
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}
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// SetInput is used to record the latest client input.
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func(st *State) SetInput(input []byte) error {
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l := len(input)
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if l > 255 {
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return fmt.Errorf("input size %v too large (limit %v)", l, 255)
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}
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st.input = input
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return nil
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}
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func(st *State) Reset() error {
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return nil
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}
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func(st State) String() string {
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return fmt.Sprintf("moves %v idx %v path: %s", st.Moves, st.SizeIdx, strings.Join(st.ExecPath, "/"))
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}
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