package com.intellectualcrafters.json;

import java.io.*;

/**
 * A JSONTokener takes a source string and extracts characters and tokens from it. It is used by the JSONObject and
 * JSONArray constructors to parse JSON source strings.
 *
 * @author JSON.org
 * @version 2014-05-03
 */
public class JSONTokener {
    private final Reader reader;
    private long character;
    private boolean eof;
    private long index;
    private long line;
    private char previous;
    private boolean usePrevious;

    /**
     * Construct a JSONTokener from a Reader.
     *
     * @param reader A reader.
     */
    public JSONTokener(final Reader reader) {
        this.reader = reader.markSupported() ? reader : new BufferedReader(reader);
        this.eof = false;
        this.usePrevious = false;
        this.previous = 0;
        this.index = 0;
        this.character = 1;
        this.line = 1;
    }

    /**
     * Construct a JSONTokener from an InputStream.
     *
     * @param inputStream The source.
     */
    public JSONTokener(final InputStream inputStream) throws JSONException {
        this(new InputStreamReader(inputStream));
    }

    /**
     * Construct a JSONTokener from a string.
     *
     * @param s A source string.
     */
    public JSONTokener(final String s) {
        this(new StringReader(s));
    }

    /**
     * Get the hex value of a character (base16).
     *
     * @param c A character between '0' and '9' or between 'A' and 'F' or between 'a' and 'f'.
     *
     * @return An int between 0 and 15, or -1 if c was not a hex digit.
     */
    public static int dehexchar(final char c) {
        if ((c >= '0') && (c <= '9')) {
            return c - '0';
        }
        if ((c >= 'A') && (c <= 'F')) {
            return c - ('A' - 10);
        }
        if ((c >= 'a') && (c <= 'f')) {
            return c - ('a' - 10);
        }
        return -1;
    }

    /**
     * Back up one character. This provides a sort of lookahead capability, so that you can test for a digit or letter
     * before attempting to parse the next number or identifier.
     */
    public void back() throws JSONException {
        if (this.usePrevious || (this.index <= 0)) {
            throw new JSONException("Stepping back two steps is not supported");
        }
        this.index -= 1;
        this.character -= 1;
        this.usePrevious = true;
        this.eof = false;
    }

    public boolean end() {
        return this.eof && !this.usePrevious;
    }

    /**
     * Determine if the source string still contains characters that next() can consume.
     *
     * @return true if not yet at the end of the source.
     */
    public boolean more() throws JSONException {
        this.next();
        if (this.end()) {
            return false;
        }
        this.back();
        return true;
    }

    /**
     * Get the next character in the source string.
     *
     * @return The next character, or 0 if past the end of the source string.
     */
    public char next() throws JSONException {
        int c;
        if (this.usePrevious) {
            this.usePrevious = false;
            c = this.previous;
        } else {
            try {
                c = this.reader.read();
            } catch (final IOException exception) {
                throw new JSONException(exception);
            }
            if (c <= 0) { // End of stream
                this.eof = true;
                c = 0;
            }
        }
        this.index += 1;
        if (this.previous == '\r') {
            this.line += 1;
            this.character = c == '\n' ? 0 : 1;
        } else if (c == '\n') {
            this.line += 1;
            this.character = 0;
        } else {
            this.character += 1;
        }
        this.previous = (char) c;
        return this.previous;
    }

    /**
     * Consume the next character, and check that it matches a specified character.
     *
     * @param c The character to match.
     *
     * @return The character.
     *
     * @throws JSONException if the character does not match.
     */
    public char next(final char c) throws JSONException {
        final char n = this.next();
        if (n != c) {
            throw this.syntaxError("Expected '" + c + "' and instead saw '" + n + "'");
        }
        return n;
    }

    /**
     * Get the next n characters.
     *
     * @param n The number of characters to take.
     *
     * @return A string of n characters.
     *
     * @throws JSONException Substring bounds error if there are not n characters remaining in the source string.
     */
    public String next(final int n) throws JSONException {
        if (n == 0) {
            return "";
        }
        final char[] chars = new char[n];
        int pos = 0;
        while (pos < n) {
            chars[pos] = this.next();
            if (this.end()) {
                throw this.syntaxError("Substring bounds error");
            }
            pos += 1;
        }
        return new String(chars);
    }

    /**
     * Get the next char in the string, skipping whitespace.
     *
     * @return A character, or 0 if there are no more characters.
     *
     * @throws JSONException
     */
    public char nextClean() throws JSONException {
        for (;;) {
            final char c = this.next();
            if ((c == 0) || (c > ' ')) {
                return c;
            }
        }
    }

    /**
     * Return the characters up to the next close quote character. Backslash processing is done. The formal JSON format
     * does not allow strings in single quotes, but an implementation is allowed to accept them.
     *
     * @param quote The quoting character, either <code>"</code> &nbsp;<small>(double quote)</small> or <code>'</code>
     *              &nbsp;<small>(single quote)</small>.
     *
     * @return A String.
     *
     * @throws JSONException Unterminated string.
     */
    public String nextString(final char quote) throws JSONException {
        char c;
        final StringBuilder sb = new StringBuilder();
        for (;;) {
            c = this.next();
            switch (c) {
                case 0:
                case '\n':
                case '\r':
                    throw this.syntaxError("Unterminated string");
                case '\\':
                    c = this.next();
                    switch (c) {
                        case 'b':
                            sb.append('\b');
                            break;
                        case 't':
                            sb.append('\t');
                            break;
                        case 'n':
                            sb.append('\n');
                            break;
                        case 'f':
                            sb.append('\f');
                            break;
                        case 'r':
                            sb.append('\r');
                            break;
                        case 'u':
                            sb.append((char) Integer.parseInt(this.next(4), 16));
                            break;
                        case '"':
                        case '\'':
                        case '\\':
                        case '/':
                            sb.append(c);
                            break;
                        default:
                            throw this.syntaxError("Illegal escape.");
                    }
                    break;
                default:
                    if (c == quote) {
                        return sb.toString();
                    }
                    sb.append(c);
            }
        }
    }

    /**
     * Get the text up but not including the specified character or the end of line, whichever comes first.
     *
     * @param delimiter A delimiter character.
     *
     * @return A string.
     */
    public String nextTo(final char delimiter) throws JSONException {
        final StringBuilder sb = new StringBuilder();
        for (;;) {
            final char c = this.next();
            if ((c == delimiter) || (c == 0) || (c == '\n') || (c == '\r')) {
                if (c != 0) {
                    this.back();
                }
                return sb.toString().trim();
            }
            sb.append(c);
        }
    }

    /**
     * Get the text up but not including one of the specified delimiter characters or the end of line, whichever comes
     * first.
     *
     * @param delimiters A set of delimiter characters.
     *
     * @return A string, trimmed.
     */
    public String nextTo(final String delimiters) throws JSONException {
        char c;
        final StringBuilder sb = new StringBuilder();
        for (;;) {
            c = this.next();
            if ((delimiters.indexOf(c) >= 0) || (c == 0) || (c == '\n') || (c == '\r')) {
                if (c != 0) {
                    this.back();
                }
                return sb.toString().trim();
            }
            sb.append(c);
        }
    }

    /**
     * Get the next value. The value can be a Boolean, Double, Integer, JSONArray, JSONObject, Long, or String, or the
     * JSONObject.NULL object.
     *
     * @return An object.
     *
     * @throws JSONException If syntax error.
     */
    public Object nextValue() throws JSONException {
        char c = this.nextClean();
        String string;
        switch (c) {
            case '"':
            case '\'':
                return this.nextString(c);
            case '{':
                this.back();
                return new JSONObject(this);
            case '[':
                this.back();
                return new JSONArray(this);
        }
        /*
         * Handle unquoted text. This could be the values true, false, or
         * null, or it can be a number. An implementation (such as this one)
         * is allowed to also accept non-standard forms.
         * Accumulate characters until we reach the end of the text or a
         * formatting character.
         */
        final StringBuilder sb = new StringBuilder();
        while ((c >= ' ') && (",:]}/\\\"[{;=#".indexOf(c) < 0)) {
            sb.append(c);
            c = this.next();
        }
        this.back();
        string = sb.toString().trim();
        if ("".equals(string)) {
            throw this.syntaxError("Missing value");
        }
        return JSONObject.stringToValue(string);
    }

    /**
     * Skip characters until the next character is the requested character. If the requested character is not found, no
     * characters are skipped.
     *
     * @param to A character to skip to.
     *
     * @return The requested character, or zero if the requested character is not found.
     */
    public char skipTo(final char to) throws JSONException {
        char c;
        try {
            final long startIndex = this.index;
            final long startCharacter = this.character;
            final long startLine = this.line;
            this.reader.mark(1000000);
            do {
                c = this.next();
                if (c == 0) {
                    this.reader.reset();
                    this.index = startIndex;
                    this.character = startCharacter;
                    this.line = startLine;
                    return c;
                }
            } while (c != to);
        } catch (final IOException exception) {
            throw new JSONException(exception);
        }
        this.back();
        return c;
    }

    /**
     * Make a JSONException to signal a syntax error.
     *
     * @param message The error message.
     *
     * @return A JSONException object, suitable for throwing
     */
    public JSONException syntaxError(final String message) {
        return new JSONException(message + this.toString());
    }

    /**
     * Make a printable string of this JSONTokener.
     *
     * @return " at {index} [character {character} line {line}]"
     */
    @Override
    public String toString() {
        return " at " + this.index + " [character " + this.character + " line " + this.line + "]";
    }
}