// |reftest| skip

// A little pattern-matching library.
var Match =

(function() {

    function Pattern(template) {
        // act like a constructor even as a function
        if (!(this instanceof Pattern))
            return new Pattern(template);

        this.template = template;
    }

    Pattern.prototype = {
        match: function(act) {
            return match(act, this.template);
        },

        matches: function(act) {
            try {
                return this.match(act);
            }
            catch (e) {
                if (!(e instanceof MatchError))
                    throw e;
                return false;
            }
        },

        assert: function(act, message) {
            try {
                return this.match(act);
            }
            catch (e) {
                if (!(e instanceof MatchError))
                    throw e;
                throw new Error((message || "failed match") + ": " + e.message);
            }
        },

        toString: () => "[object Pattern]"
    };

    Pattern.ANY = new Pattern;
    Pattern.ANY.template = Pattern.ANY;

    Pattern.NUMBER = new Pattern;
    Pattern.NUMBER.match = function (act) {
      if (typeof act !== 'number') {
        throw new MatchError("Expected number, got: " + quote(act));
      }
    }

    Pattern.NATURAL = new Pattern
    Pattern.NATURAL.match = function (act) {
      if (typeof act !== 'number' || act !== Math.floor(act) || act < 0) {
        throw new MatchError("Expected natural number, got: " + quote(act));
      }
    }

    class ObjectWithExactly extends Pattern {
      constructor(template) {
        super(template);
      }

      match(actual) {
        return matchObjectWithExactly(actual, this.template)
      }
    }

    Pattern.OBJECT_WITH_EXACTLY = function (template) {
      return new ObjectWithExactly(template);
    }

    var quote = JSON.stringify;

    class MatchError extends Error {
        toString() {
            return "match error: " + this.message;
        }
    };

    Pattern.MatchError = MatchError;

    function isAtom(x) {
        return (typeof x === "number") ||
            (typeof x === "string") ||
            (typeof x === "boolean") ||
            (x === null) ||
            (x === undefined) ||
            (typeof x === "object" && x instanceof RegExp) ||
            (typeof x === "bigint");
    }

    function isObject(x) {
        return (x !== null) && (typeof x === "object");
    }

    function isFunction(x) {
        return typeof x === "function";
    }

    function isArrayLike(x) {
        return isObject(x) && ("length" in x);
    }

    function matchAtom(act, exp) {
        if ((typeof exp) === "number" && isNaN(exp)) {
            if ((typeof act) !== "number" || !isNaN(act))
                throw new MatchError("expected NaN, got: " + quote(act));
            return true;
        }

        if (exp === null) {
            if (act !== null)
                throw new MatchError("expected null, got: " + quote(act));
            return true;
        }

        if (exp instanceof RegExp) {
            if (!(act instanceof RegExp) || exp.source !== act.source)
                throw new MatchError("expected " + quote(exp) + ", got: " + quote(act));
            return true;
        }

        switch (typeof exp) {
        case "string":
        case "undefined":
            if (act !== exp)
                throw new MatchError("expected " + quote(exp) + ", got " + quote(act));
            return true;
        case "boolean":
        case "number":
        case "bigint":
            if (exp !== act)
                throw new MatchError("expected " + exp + ", got " + quote(act));
            return true;
        }

        throw new Error("bad pattern: " + JSON.stringify(exp));
    }

    // Match an object having at least the expected properties.
    function matchObjectWithAtLeast(act, exp) {
        if (!isObject(act))
            throw new MatchError("expected object, got " + quote(act));

        for (var key in exp) {
            if (!(key in act))
                throw new MatchError("expected property " + quote(key) + " not found in " + quote(act));
            try {
                match(act[key], exp[key]);
            } catch (inner) {
                if (!(inner instanceof MatchError)) {
                    throw inner;
                }
                inner.message = `matching property "${String(key)}":\n${inner.message}`;
                throw inner;
            }
        }

        return true;
    }

    // Match an object having all the expected properties and no more.
    function matchObjectWithExactly(act, exp) {
        matchObjectWithAtLeast(act, exp);

        for (var key in act) {
            if (!(key in exp)) {
                throw new MatchError("unexpected property " + quote(key));
            }
        }

        return true;
    }

    function matchFunction(act, exp) {
        if (!isFunction(act))
            throw new MatchError("expected function, got " + quote(act));

        if (act !== exp)
            throw new MatchError("expected function: " + exp +
                                 "\nbut got different function: " + act);
    }

    function matchArray(act, exp) {
        if (!isObject(act) || !("length" in act))
            throw new MatchError("expected array-like object, got " + quote(act));

        var length = exp.length;
        if (act.length !== exp.length)
            throw new MatchError("expected array-like object of length " + length + ", got " + quote(act));

        for (var i = 0; i < length; i++) {
            if (i in exp) {
                if (!(i in act))
                    throw new MatchError("expected array property " + i + " not found in " + quote(act));
                try {
                    match(act[i], exp[i]);
                } catch (inner) {
                    if (!(inner instanceof MatchError)) {
                        throw inner;
                    }
                    inner.message = `matching array element [${i}]:\n${inner.message}`;
                    throw inner;
                }
            }
        }

        return true;
    }

    function match(act, exp) {
        if (exp === Pattern.ANY)
            return true;

        if (exp instanceof Pattern)
            return exp.match(act);

        if (isAtom(exp))
            return matchAtom(act, exp);

        if (isArrayLike(exp))
            return matchArray(act, exp);

        if (isFunction(exp))
            return matchFunction(act, exp);

        if (isObject(exp))
            return matchObjectWithAtLeast(act, exp);

        throw new Error("bad pattern: " + JSON.stringify(exp));
    }

    return { Pattern: Pattern,
             MatchError: MatchError };

})();