fhirPath.ts

import { ParseConformance } from './parseConformance';

interface PathStructure {
    name?: string;
    params?: StatementStructure[];
}

interface StatementStructure {
    resourceType?: string;
    value?: string;
    path?: [string | PathStructure];
    left?: StatementStructure;
    right?: StatementStructure;
    op?: string;
}

export class FhirPath {
    private parser: any;
    readonly resources: any;
    readonly operators = ['=', '!', '&', '<', '>', '~'];

    private findClosingParenIndex(string, startIndex) {
        let parenLevel = 0;

        for (let i = startIndex; i < string.length; i++) {
            if (string[i] === '(') {
                parenLevel++;
            } else if (string[i] === ')') {
                if (parenLevel > 0) {
                    parenLevel--;
                } else {
                    return i;
                }
            }
        }
    }

    private findClosingQuoteIndex(string, startIndex) {
        for (let i = startIndex; i < string.length; i++) {
            if (string[i] === '\'') {
                if (string[i-1] === '\\') {
                    continue;
                }
                return i;
            }
        }
    }

    /**
     * Constructs a new instance of the FhirPath class with one or mores resources
     * @classdesc Handles evaluation of FhirPath against one or more resources. See {@link http://build.fhir.org/fhirpath.html} for more information.
     * @param {Resource|Array<Resource>} resources One or more resources that the class should evaluate FhirPath against
     * @param {ParseConformance} parser The conformance parser to use when needing to reference definitions of resources
     * @class
     */
    constructor(resources, parser) {
        this.resources = resources instanceof Array ? resources : [resources];
        this.parser = parser ? parser : new ParseConformance(true);
    }
    /**
     * Attempts to resolve the resource reference using this resources.
     * If no resource is found in the resources provided to the FhirPath class, calls the resolve event.
     * @param {string} reference The resource reference string to resolve
     * @return {Resource}
     * @fires FhirPath#resolve
     * @private
     */
    private internalResolve(reference) {
        const regex = /^([A-z]+)\/(.+?)$/;
        const match = reference.trim().match(regex);

        function find(resources, resourceType, id) {
            for (let i = 0; i < resources.length; i++) {
                const resource = resources[i];

                if (resource.resourceType === 'Bundle') {
                    // recursively search through resources in the bundle
                    const childResources = resource.entry.map(e => e.resource);
                    const found = find(childResources, resourceType, id);

                    if (found) {
                        return found;
                    }
                }

                if (resource.resourceType.toLowerCase() !== resourceType.toLowerCase()) {
                    continue;
                }

                if (resource.id.toLowerCase() !== id.toLowerCase()) {
                    continue;
                }

                return resource;
            }
        }

        if (match) {
            const found = find(this.resources, match[1], match[2]);

            if (found) {
                return found;
            }
        }

        return this.resolve(reference);
    }

    /**
     * A callback which is executed when a reference needs to be resolved to a resource.
     * This should be overridden by the caller of the FhirPath class.
     * @param {string} reference The reference that needs to be resolved
     * @returns Should return a Resource instance
     * @event
     */
    public resolve(reference) {
        return;
    }

    /**
     * Gets a list of all resource type names from the ParseConformance class loaded with the FhirPath class.
     * @returns {string[]}
     * @private
     */
    private getResourceTypes() {
        const self = this;
        const keys = Object.keys(this.parser.parsedStructureDefinitions);
        return keys.filter(key => self.parser.parsedStructureDefinitions[key]._kind === 'resource');
    }

    /**
     * Parses the specified path into a structure
     * @param {string} fhirPath
     * @returns {Array}
     * @private
     */
    public parse(fhirPath): StatementStructure[] {
        const statements = [];
        let ns: StatementStructure = {};          // newStatement

        const fhirPathSplit = fhirPath.split('.');
        const resourceTypes = this.getResourceTypes();

        if (fhirPathSplit.length > 0 && resourceTypes.indexOf(fhirPathSplit[0]) >= 0) {
            ns.resourceType = fhirPathSplit[0];
            fhirPath = fhirPath.substring(fhirPathSplit[0].length+1);
        }

        for (let i = 0; i < fhirPath.length; i++) {
            const char = fhirPath[i];

            if (char === '\'') {
                if (i === 0) {
                    const closingQuoteIndex = this.findClosingQuoteIndex(fhirPath, i+1);
                    ns.value = fhirPath.substring(i+1, closingQuoteIndex);
                    i = closingQuoteIndex;
                }
            } else if (char === '(') {
                if (ns.path && ns.path.length > 0) {     // Paren is used for function
                    const fn: PathStructure = {
                        name: (<string>ns.path.pop()).toLowerCase()
                    };
                    ns.path.push(fn);

                    // set the params for the function
                    const closingParenIndex = this.findClosingParenIndex(fhirPath, i+1);
                    const fnParams = fhirPath.substring(i+1, closingParenIndex);
                    fn.params = this.parse(fnParams);
                    i = closingParenIndex;
                }
                // TODO
            } else if (char === '\'') {
                // TODO?
            } else if (char === ' ') {
                // TODO?
            } else if (this.operators.indexOf(char) >= 0) {
                const left = ns;
                let rightPath = fhirPath.substring(i+1);
                let operator = char;

                // Double-operator
                if (this.operators.indexOf(rightPath[0]) >= 0) {
                    operator += rightPath[0];
                    rightPath = rightPath.substring(1);
                }

                ns = {
                    left: left,
                    right: this.parse(rightPath.trim())[0],           // TODO: Should right ever be an array? Don't think so
                    op: operator
                }

                if (ns.left.path && ns.left.path.length > 0) {
                    ns.left.path[ns.left.path.length-1] = (<string>ns.left.path[ns.left.path.length-1]).trim();
                }
                if (ns.right.path && ns.right.path.length > 0) {
                    ns.right.path[ns.right.path.length-1] = (<string>ns.right.path[ns.right.path.length-1]).trim();
                }
                break;
            } else if (char === '.') {
                ns.path.push('');
            } else {
                if (!ns.hasOwnProperty('path')) {
                    ns.path = [''];
                }

                ns.path[ns.path.length-1] += char;
            }
        }

        statements.push(ns);

        return statements;
    }


    private getValue(current, paths): any {
        if (current === undefined || current == null) {
            return current;
        }

        if (!paths || paths.length === 0) {
            return current;
        }

        const nextPath = paths[0];
        const nextPaths = paths.slice(1);

        if (current instanceof Array) {
            if (typeof nextPath === 'string') {
                let ret = [];

                nextPaths.unshift(nextPath);

                for (let i = 0; i < current.length; i++) {
                    const currentRet = this.getValue(current[i], nextPaths);

                    if (currentRet instanceof Array) {
                        ret = ret.concat(currentRet);
                    } else if (currentRet !== undefined && currentRet !== null) {
                        ret.push(currentRet);
                    }
                }

                return ret;
            } else if (nextPath.name === 'first') {
                return this.getValue(current[0], nextPaths);
            } else if (nextPath.name === 'last') {
                return this.getValue(current[current.length - 1], nextPaths);
            } else if (nextPath.name === 'where') {
                if (!nextPath.params || nextPath.params.length === 0) {
                    throw new Error('Expected .where() to have a parameter');
                }

                const filtered = [];

                for (let i = 0; i < current.length; i++) {
                    const paramsClone = JSON.parse(JSON.stringify(nextPath.params));
                    const results = this.internalEvaluate(current[i], paramsClone);

                    if (typeof results === 'boolean' && results === true) {
                        filtered.push(current[i]);
                    } else if (results instanceof Array && results.length === 1 && results[0]) {
                        filtered.push(current[i]);
                    }
                }

                return this.getValue(filtered, nextPaths);
            } else {
                throw new Error('Unsupported function for arrays ' + nextPath.name);
            }
        } else {
            if (typeof nextPath === 'string') {
                return this.getValue(current[nextPath], nextPaths);
            } else if (nextPath.name === 'resolve') {
                const reference = typeof current === 'string' ? current : current.reference;
                const resource = this.internalResolve(reference);
                return this.getValue(resource, nextPaths);
            } else if (nextPath.name === 'startswith') {
                if (!nextPath.params || nextPath.params.length !== 1) {
                    throw new Error('Expected a single parameter to startsWith()');
                }

                if (typeof current !== 'string') {
                    throw new Error('startsWith() must be used on string types');
                }

                const paramValue = nextPath.params[0].value || this.getValue(current, nextPath.params[0].path);

                if (!paramValue || current.indexOf(paramValue) !== 0) {
                    return false;
                }

                return true;
            } else {
                throw new Error('Unsupported function for objects ' + nextPath.name);
            }
        }
    }

    /**
     * Evaluates the given statements against the specified single resource.
     * @param {Resource} resource
     * @param statements
     * @returns {*}
     * @private
     */
    private internalEvaluate(resource, statements) {
        let ret = [];

        for (let i = 0; i < statements.length; i++) {
            const statement = statements[i];

            if (statement.path) {
                statement.value = this.getValue(resource, statement.path);
            }

            if (statement.left && statement.left.path) {
                statement.left.value = this.getValue(resource, statement.left.path);
            }

            if (statement.right && statement.right.path) {
                statement.right.value = this.getValue(resource, statement.right.path);
            }

            if (statement.op) {
                if (!statement.left || !statement.right) {
                    return false;
                }

                switch (statement.op) {
                    case '=':
                    case '==':
                        return statement.left.value === statement.right.value;
                    case '!=':
                        return statement.left.value !== statement.right.value;
                }
            } else {
                if (statement.value instanceof Array) {
                    ret = ret.concat(statement.value);
                } else {
                    ret.push(statement.value);
                }
            }
        }

        return ret;
    }

    /**
     * Determines if the statements specified should result in an array being returned
     * @param statements
     * @returns {boolean}
     * @private
     */
    private shouldReturnArray(statements) {
        // TODO: Make this more intelligent.
        // It could instead determine if the last actual path represents
        // an array, based on the definitions stored in ParseConformance class.
        if (statements.length === 1) {
            const statementHasWhereFn = (statements[0].path || []).filter(nextPath => nextPath.name === 'where');

            if (statementHasWhereFn.length > 0) {
                return true;
            }
        }

        return false;
    }

    /**
     * Evaluates the given fhirPath string against the resources passed in the constructor of the class
     * In the event of an operator comparison, returns a boolean
     * In the event of a path evaluation, returns the value of the given path (for each of the resources)
     * @param {string} fhirPath The FhirPath string to evaluate against the resources provided to the FhirPath class
     * @returns {obj|Array} The result of the evaluation. Can be either an object, boolean or array of results
     */
    public evaluate(fhirPath) {
        if (!fhirPath) {
            return;
        }

        const statements = this.parse(fhirPath);
        let ret = [];

        for (let r = 0; r < this.resources.length; r++) {
            const resource = this.resources[r];
            ret = ret.concat(this.internalEvaluate(resource, statements));
        }

        if (this.resources.length === 1 && ret.length === 1 && !this.shouldReturnArray(statements)) {
            return ret[0];
        }

        return ret;
    }
}