type Token = {
  type: string;
  value: string;
};

const tokenize = (input: string): Token[] => {
    let current = 0;
    let tokens: Token[] = [];

    while (current < input.length) {
      let char = input[current];

      if (char === '\\') {
        current++;
        continue;
      }

      if (char === '{') {
        tokens.push({
          type: 'brace',
          value: '{',
        });

        current++;
        continue;
      }

      if (char === '}') {
        tokens.push({
          type: 'brace',
          value: '}',
        });

        current++;
        continue;
      }

      if (char === '[') {
        tokens.push({
          type: 'paren',
          value: '[',
        });

        current++;
        continue;
      }

      if (char === ']') {
        tokens.push({
          type: 'paren',
          value: ']',
        });

        current++;
        continue;
      }

      if (char === ':') {
        tokens.push({
          type: 'separator',
          value: ':',
        });

        current++;
        continue;
      }

      if (char === ',') {
        tokens.push({
          type: 'delimiter',
          value: ',',
        });

        current++;
        continue;
      }

      if (char === '"') {
        let value = '';
        let danglingQuote = false;

        char = input[++current];

        while (char !== '"') {
          if (current === input.length) {
            danglingQuote = true;
            break;
          }

          if (char === '\\') {
            current++;
            if (current === input.length) {
              danglingQuote = true;
              break;
            }
            value += char + input[current];
            char = input[++current];
          } else {
            value += char;
            char = input[++current];
          }
        }

        char = input[++current];

        if (!danglingQuote) {
          tokens.push({
            type: 'string',
            value,
          });
        }
        continue;
      }

      let WHITESPACE = /\s/;
      if (char && WHITESPACE.test(char)) {
        current++;
        continue;
      }

      let NUMBERS = /[0-9]/;
      if ((char && NUMBERS.test(char)) || char === '-' || char === '.') {
        let value = '';

        if (char === '-') {
          value += char;
          char = input[++current];
        }

        while ((char && NUMBERS.test(char)) || char === '.') {
          value += char;
          char = input[++current];
        }

        tokens.push({
          type: 'number',
          value,
        });
        continue;
      }

      let LETTERS = /[a-z]/i;
      if (char && LETTERS.test(char)) {
        let value = '';

        while (char && LETTERS.test(char)) {
          if (current === input.length) {
            break;
          }
          value += char;
          char = input[++current];
        }

        if (value == 'true' || value == 'false' || value === 'null') {
          tokens.push({
            type: 'name',
            value,
          });
        } else {
          // unknown token, e.g. `nul` which isn't quite `null`
          current++;
          continue;
        }
        continue;
      }

      current++;
    }

    return tokens;
  },
  strip = (tokens: Token[]): Token[] => {
    if (tokens.length === 0) {
      return tokens;
    }

    let lastToken = tokens[tokens.length - 1]!;

    switch (lastToken.type) {
      case 'separator':
        tokens = tokens.slice(0, tokens.length - 1);
        return strip(tokens);
        break;
      case 'number':
        let lastCharacterOfLastToken = lastToken.value[lastToken.value.length - 1];
        if (lastCharacterOfLastToken === '.' || lastCharacterOfLastToken === '-') {
          tokens = tokens.slice(0, tokens.length - 1);
          return strip(tokens);
        }
      case 'string':
        let tokenBeforeTheLastToken = tokens[tokens.length - 2];
        if (tokenBeforeTheLastToken?.type === 'delimiter') {
          tokens = tokens.slice(0, tokens.length - 1);
          return strip(tokens);
        } else if (tokenBeforeTheLastToken?.type === 'brace' && tokenBeforeTheLastToken.value === '{') {
          tokens = tokens.slice(0, tokens.length - 1);
          return strip(tokens);
        }
        break;
      case 'delimiter':
        tokens = tokens.slice(0, tokens.length - 1);
        return strip(tokens);
        break;
    }

    return tokens;
  },
  unstrip = (tokens: Token[]): Token[] => {
    let tail: string[] = [];

    tokens.map((token) => {
      if (token.type === 'brace') {
        if (token.value === '{') {
          tail.push('}');
        } else {
          tail.splice(tail.lastIndexOf('}'), 1);
        }
      }
      if (token.type === 'paren') {
        if (token.value === '[') {
          tail.push(']');
        } else {
          tail.splice(tail.lastIndexOf(']'), 1);
        }
      }
    });

    if (tail.length > 0) {
      tail.reverse().map((item) => {
        if (item === '}') {
          tokens.push({
            type: 'brace',
            value: '}',
          });
        } else if (item === ']') {
          tokens.push({
            type: 'paren',
            value: ']',
          });
        }
      });
    }

    return tokens;
  },
  generate = (tokens: Token[]): string => {
    let output = '';

    tokens.map((token) => {
      switch (token.type) {
        case 'string':
          output += '"' + token.value + '"';
          break;
        default:
          output += token.value;
          break;
      }
    });

    return output;
  },
  partialParse = (input: string): unknown => JSON.parse(generate(unstrip(strip(tokenize(input)))));

export { partialParse };