s2-tools/dist/readers/shapefile/dbf.js

A collection of geospatial tools primarily designed for WGS84, Web Mercator, and S2.

import { toReader } from '..';
/** A DBF data class to parse the data from a DBF */
export class DataBaseFile {
    reader;
    #header;
    #rows;
    /**
     * @param input - the input data structure to parse
     * @param encoding - the encoding of the raw data. defaults to 'utf-8'
     */
    constructor(input, encoding) {
        this.reader = toReader(input);
        if (encoding !== undefined)
            this.reader.setStringEncoding(encoding);
        this.#parseHeader();
        this.#rows = this.#parseRowHeader();
    }
    /**
     * Create a copy of the header data
     * @returns - a copy of the header
     */
    getHeader() {
        return { ...this.#header };
    }
    /**
     * Get the properties for the given index
     * @param index - the index of the properties data we want
     * @returns - the properties for the given index
     */
    getProperties(index) {
        const { records, recLen } = this.#header;
        if (index > records)
            return undefined;
        const offset = ((this.#rows.length + 1) << 5) + 2 + index * recLen;
        return this.#parseProperties(offset);
    }
    /**
     * Get all the properties in the DBF
     * @returns - an array of Properties
     */
    getAllProperties() {
        const { records } = this.#header;
        const res = [];
        for (let i = 0; i < records; i++) {
            const properties = this.getProperties(i);
            if (properties !== undefined)
                res.push(properties);
        }
        return res;
    }
    /**
     * Parse the header and store it in the class
     */
    #parseHeader() {
        const { reader } = this;
        this.#header = {
            lastUpdated: new Date(reader.getUint8(1) + 1900, reader.getUint8(2), reader.getUint8(3)),
            records: reader.getUint32(4, true),
            headerLen: reader.getUint16(8, true),
            recLen: reader.getUint16(10, true),
        };
    }
    /**
     * Parses the row header and builds an array of keys that each property may have
     * @returns - an array of Rows that describe keys in each property
     */
    #parseRowHeader() {
        const { reader } = this;
        const { headerLen } = this.#header;
        const len = headerLen - 1;
        const res = [];
        let offset = 32;
        while (offset < len) {
            res.push({
                name: reader.parseString(offset, 11),
                dataType: String.fromCharCode(reader.getUint8(offset + 11)),
                len: reader.getUint8(offset + 16),
                decimal: reader.getUint8(offset + 17),
            });
            if (reader.getUint8(offset + 32) === 13) {
                break;
            }
            else {
                offset += 32;
            }
        }
        return res;
    }
    /**
     * Parse the properties starting from the given offset
     * @param offset - offset of the row
     * @returns - a Properties object
     */
    #parseProperties(offset) {
        const properties = {};
        for (const header of this.#rows) {
            const value = this.#parseValue(offset, header.len, header.dataType);
            offset += header.len;
            if (typeof value !== 'undefined')
                properties[header.name] = value;
        }
        return properties;
    }
    /**
     * Parse the value at the given offset
     * @param offset - offset of the value
     * @param len - length of the value
     * @param type - the type of the value
     * @returns - the value as a string, number or boolean
     */
    #parseValue(offset, len, type) {
        const { reader } = this;
        const textData = reader.parseString(offset, len);
        switch (type) {
            case 'N':
            case 'F':
            case 'O':
                return parseFloat(textData);
            case 'D':
                return new Date(parseFloat(textData.slice(0, 4)), parseInt(textData.slice(4, 6)) - 1, parseFloat(textData.slice(6, 8))).getUTCDate();
            case 'L':
                return textData.toLowerCase() === 'y' || textData.toLowerCase() === 't';
            default:
                return textData;
        }
    }
}
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