package boolean

import (
  "bufio"
  "io"
  "fmt"
  "errors"
  "slices"
  "log/slog"
)

type TokenType int
type ExprType int

const (
  EXPR_NUMERIC_CONSTANT ExprType = iota
  EXPR_BOOLEAN_CONSTNAT

  TOKEN_ERR TokenType = iota
  TOKEN_UNARY_OPERATOR
  TOKEN_BINARY_OPERATOR
  TOKEN_AMBIGUOUS_OPERATOR
  TOKEN_LEFT_PAREN
  TOKEN_RIGHT_PAREN
  TOKEN_SYMBOL
  TOKEN_NUMERIC_LITERAL
  TOKEN_BOOLEAN_LITERAL
)

type Token struct {
  Text string
  Type TokenType
  Index uint
}

type TokenStream struct {
  Tokens []Token
  Position int
}
func (stream *TokenStream) Peek(n int) ([]Token, error) {
  if stream.Position >= len(stream.Tokens) {
    return nil, io.EOF
  }
  return stream.Tokens[stream.Position:stream.Position+n], nil
}
func (stream *TokenStream) Read(n int) ([]Token, error) {
  if stream.Position >= len(stream.Tokens) {
    return nil, io.EOF
  }
  ret := stream.Tokens[stream.Position:stream.Position+n]
  stream.Position += len(ret)
  return ret, nil
}

func NewTokenStream(tokens []Token) *TokenStream {
  return &TokenStream{
    Tokens: tokens,
    Position: 0,
  }
}

type OperatorTree struct {
  TokenType
  Next map[byte]OperatorTree
}

func SymbolValidStart(char byte) bool {
  if char >= 97 && char <= 122 {
    return true
  } else if char >= 65 && char <= 90 {
    return true
  } else if char == '_' {
    return true
  }
  return false
}

func SymbolValidCont(char byte) bool {
  if SymbolValidStart(char) {
    return true
  } else if char >= 48 && char <= 57 {
    return true
  } else if char == '-' {
    return true
  }
  return false
}

func NumericValid(char byte) bool {
  if char >= 48 && char <= 57 {
    return true
  }
  return false
}

var (
  Whitepace = []byte{' ', '\t', '\n', '\r'}
  OperatorTokens = map[byte]OperatorTree{
    '.': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: nil,
    },
    '~': {
      TokenType: TOKEN_UNARY_OPERATOR,
      Next: nil,
    },
    '&': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: nil,
    },
    '|': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: nil,
    },
    '^': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: nil,
    },
    '+': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: nil,
    },
    '*': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: map[byte]OperatorTree{
        '*': {
          TokenType: TOKEN_BINARY_OPERATOR,
          Next: nil,
        },
      },
    },
    '/': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: nil,
    },
    '-': {
      TokenType: TOKEN_AMBIGUOUS_OPERATOR,
      Next: nil,
    },
    '!': {
      TokenType: TOKEN_ERR,
      Next: map[byte]OperatorTree{
        '=': {
          TokenType: TOKEN_BINARY_OPERATOR,
          Next: nil,
        },
      },
    },
    '=': {
      TokenType: TOKEN_ERR,
      Next: map[byte]OperatorTree{
        '=': {
          TokenType: TOKEN_BINARY_OPERATOR,
          Next: nil,
        },
      },
    },
    '>': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: map[byte]OperatorTree{
        '=': {
          TokenType: TOKEN_BINARY_OPERATOR,
          Next: nil,
        },
      },
    },
    '<': {
      TokenType: TOKEN_BINARY_OPERATOR,
      Next: map[byte]OperatorTree{
        '=': {
          TokenType: TOKEN_BINARY_OPERATOR,
          Next: nil,
        },
      },
    },
  }
)

func TokenizeOperator(stream *bufio.Reader, node *OperatorTree, current string) (TokenType, string, error) {
  next_chars, err := stream.Peek(1)
  if errors.Is(err, io.EOF) {
    return node.TokenType, current, nil
  } else if err != nil {
    return TOKEN_ERR, current, fmt.Errorf("TokenizeOperator peek error: %w", err)
  }

  next_node, continues := node.Next[next_chars[0]]
  if continues == true {
    _, err := stream.ReadByte()
    if err != nil {
      return TOKEN_ERR, current, fmt.Errorf("TokenizeOperator consume error: %w", err)
    }
    return TokenizeOperator(stream, &next_node, current + string(next_chars))
  } else {
    return node.TokenType, current, nil
  }
}

func Tokenize(stream *bufio.Reader) (*TokenStream, error) {
  tokens := []Token{}
  var position uint = 0

  for true {
    char, err := stream.ReadByte()
    if errors.Is(err, io.EOF) {
      break
    } else if err != nil {
      return nil, fmt.Errorf("tokenize read error: %w", err)
    }

    if slices.Contains(Whitepace, char) {
      slog.Debug("tokenizer", "whitespace", char)
      position += 1
      continue
    } else if node, is_operator := OperatorTokens[char]; is_operator == true{
      token_type, string, err := TokenizeOperator(stream, &node, string(char))
      if err != nil {
        return nil, err
      }
      slog.Debug("tokenizer", "operator", string)
      tokens = append(tokens, Token{
        Type: token_type,
        Text: string,
        Index: position,
      })
      position += uint(len(string))
    } else if NumericValid(char) {
      literal := string(char)
      decimal := false

      for true {
        next_chars, err := stream.Peek(1)
        if errors.Is(err, io.EOF) {
          break
        } else if err != nil {
          return nil, fmt.Errorf("numeric peek error: %w", err)
        } else if NumericValid(next_chars[0]) {
          _, err := stream.ReadByte()
          if err != nil {
            return nil, fmt.Errorf("numeric read error: %w", err)
          }
          literal += string(next_chars)
        } else if next_chars[0] == '.' {
          if decimal == true {
            break
          }
          decimal = true
          _, err := stream.ReadByte()
          if err != nil {
            return nil, fmt.Errorf("numeric read error: %w", err)
          }
          literal += string(next_chars)
        } else {
          break
        }
      }
      slog.Debug("tokenizer", "numeric", literal)
      tokens = append(tokens, Token{
        Type: TOKEN_NUMERIC_LITERAL,
        Text: literal,
        Index: position,
      })
      position += uint(len(literal))
    } else if SymbolValidStart(char) {
      symbol := string(char)
      for true {
        next_chars, err := stream.Peek(1)
        if errors.Is(err, io.EOF) {
          break
        } else if err != nil {
          return nil, fmt.Errorf("symbol peek error: %w", err)
        } else if SymbolValidCont(next_chars[0]) == true {
          _, err := stream.ReadByte()
          if err != nil {
            return nil, fmt.Errorf("symbol read error: %w", err)
          }
          symbol += string(next_chars)
        } else {
          break
        }
      }
      slog.Debug("tokenizer", "symbol", symbol)
      token_type := TOKEN_SYMBOL
      switch symbol {
      case "TRUE":
        token_type = TOKEN_BOOLEAN_LITERAL
      case "FALSE":
        token_type = TOKEN_BOOLEAN_LITERAL
      }
      tokens = append(tokens, Token{
        Type: token_type,
        Text: symbol,
        Index: position,
      })
      position += uint(len(symbol))
    } else {
      switch char {
      case '(':
        tokens = append(tokens, Token{
          Type: TOKEN_LEFT_PAREN,
          Text: "(",
          Index: position,
        })
        position += 1
      case ')':
        tokens = append(tokens, Token{
          Type: TOKEN_RIGHT_PAREN,
          Text: ")",
          Index: position,
        })
        position += 1
      default:
        return nil, fmt.Errorf("tokenize unexpected character: %c", char)
      }
    }
  }

  return NewTokenStream(tokens), nil
}