import { Reader, Annotated, Dictionary, is, peel, preserves, Record, strip, Tuple, Position, position, ReaderOptions, stringify, isCompound } from '@preserves/core';
import { Input, Pattern, Schema, Alternative, Definition, CompoundPattern, SimplePattern } from './meta';
import * as M from './meta';
import { SchemaSyntaxError } from './error';

const positionTable = new WeakMap<Input & object, Position>();

export function recordPosition<X extends Input & object>(v: X, pos: Position | null): X {
    if (pos === null) { console.error('Internal error in Schema reader: null source position for', v); }
    if (pos !== null) positionTable.set(v, pos);
    return v;
}

export function refPosition(v: Input & object): Position | null {
    return positionTable.get(v) ?? null;
}

function splitBy<T>(items: Array<T>, separator: T): Array<Array<T>> {
    const groups: Array<Array<T>> = [];
    let group: Array<T> = [];
    function finish() {
        if (group.length > 0) {
            groups.push(group);
            group = [];
        }
    }
    for (const item of items) {
        if (is(item, separator)) {
            finish();
        } else {
            group.push(item);
        }
    }
    finish();
    return groups;
}

function invalidClause(clause: Array<Input>): never {
    throw new SchemaSyntaxError(preserves`Invalid Schema clause: ${clause}`,
                                position(clause[0] ?? false));
}

function invalidPattern(name: string, item: Input, pos: Position | null): never {
    throw new SchemaSyntaxError(`Invalid pattern in ${name}: ${stringify(item)}`, pos);
}

export type SchemaReaderOptions = {
    readInclude?(includePath: string): string;
};

function _readSchema(source: string, options?: ReaderOptions<never>): Array<Input> {
    return new Reader<never>(source, {
        ... options ?? {},
        includeAnnotations: true
    }).readToEnd();
}

export function readSchema(source: string,
                           options?: ReaderOptions<never> & SchemaReaderOptions): Schema
{
    return parseSchema(_readSchema(source, options), options ?? {});
}

export function parseSchema(toplevelTokens: Array<Input>,
                            options: ReaderOptions<never> & SchemaReaderOptions): Schema
{
    let version: M.Version | undefined = void 0;
    let pointer: M.PointerName = false;
    let definitions = new Dictionary<never, Definition>();

    function process(toplevelTokens: Array<Input>): void {
        const toplevelClauses = splitBy(peel(toplevelTokens) as Array<Input>, M.DOT);
        for (const clause of toplevelClauses) {
            if (!Array.isArray(clause)) {
                invalidClause(clause);
            } else if (clause.length >= 2 && is(clause[1], M.EQUALS)) {
                const pos = position(clause[0]);
                const name = peel(clause[0]);
                if (typeof name !== 'symbol') invalidClause(clause);
                if (!M.isValidToken(name.description!)) {
                    throw new SchemaSyntaxError(preserves`Invalid definition name: ${name}`, pos);
                }
                if (definitions.has(name)) {
                    throw new SchemaSyntaxError(preserves`Duplicate definition: ${clause}`, pos);
                }
                definitions.set(name, parseDefinition(name, clause.slice(2)));
            } else if (clause.length === 2 && is(clause[0], M.$version)) {
                version = M.asVersion(peel(clause[1]));
            } else if (clause.length === 2 && is(clause[0], M.$pointer)) {
                const pos = position(clause[1]);
                const stx = peel(clause[1]);
                const quasiName = 'pointer name specification';
                pointer = M.asPointerName((stx === false) ? stx
                    : (typeof stx === 'symbol') ? parseRef(quasiName, pos, stx)
                    : invalidPattern(quasiName, stx, pos));
            } else if (clause.length === 2 && is(clause[0], M.INCLUDE)) {
                const pos = position(clause[1]);
                const path = peel(clause[1]);
                if (typeof path !== 'string') {
                    throw new SchemaSyntaxError(preserves`Invalid include: ${clause}`, pos);
                }
                if (options.readInclude === void 0) {
                    throw new SchemaSyntaxError(preserves`Cannot include files in schema`, pos);
                }
                process(_readSchema(options.readInclude(path), options));
            } else {
                invalidClause(clause);
            }
        }
    }

    process(toplevelTokens);

    if (version === void 0) {
        throw new SchemaSyntaxError("Schema: missing version declaration.", null);
    }

    return M.asSchema(Record(M.$schema, [new Dictionary<never>([
        [M.$version, version],
        [M.$pointer, pointer],
        [M.$definitions, definitions],
    ])]));
}

function parseDefinition(name: symbol, body: Array<Input>): Definition {
    let nextAnonymousAlternativeNumber = 0;
    function alternativeName([input, p]: readonly [Array<Input>, Alternative])
    : [symbol, Alternative]
    {
        const n = findName(input) || findName(input[0]);
        if (n !== false) {
            return [n, p];
        }
        if (p.label === M.$rec && p[0].label === M.$lit && typeof p[0][0] === 'symbol') {
            return [p[0][0], p];
        }
        if (p.label === M.$ref) {
            return [p[1], p];
        }
        if (p.label === M.$lit && typeof p[0] === 'symbol') {
            return [p[0], p];
        }
        return [Symbol.for('_anonymous' + nextAnonymousAlternativeNumber++), p];
    }

    return parseOp(body,
                   M.ORSYM,
                   p => [p, parseOp(p,
                                    M.ANDSYM,
                                    p => parsePattern(name, p),
                                    ps => Record(M.$and, [ps]),
                                    p => p as Alternative)] as const,
                   ps => Record(M.$or, [ps.map(alternativeName)]),
                   p => p[1] as Definition);
}

function parsePattern(name: symbol, body0: Array<Input>): Pattern {
    function parseSimple<A>(item0: Input, kf: () => A): SimplePattern | A {
        const pos = position(item0);
        const item = peel(item0);
        function complain(): never { invalidPattern(stringify(name), item, pos); }
        if (typeof item === 'symbol') {
            return parseRef(stringify(name), pos, item);
        } else if (Record.isRecord<Input, Tuple<Input>, never>(item)) {
            const label = item.label;
            if (Record.isRecord<Input, [], never>(label)) {
                if (label.length !== 0) complain();
                switch (label.label) {
                    case M.$lit:
                        if (item.length !== 1) complain();
                        return Record(M.$lit, [item[0]]);
                    default:
                        return kf();
                }
            } else {
                return kf();
            }
        } else if (isCompound(item)) {
            return kf();
        } else {
            return Record(M.$lit, [strip(item)]);
        }
    }

    function parseCompound(item0: Input): CompoundPattern {
        const pos = position(item0);
        const item = peel(item0);
        function complain(): never { invalidPattern(stringify(name), item, pos); }

        const walkSimple = (b: Input): SimplePattern => parseSimple(b, () => {
            throw new SchemaSyntaxError(`Compound patterns not accepted here`, position(b));
        });
        const walk = (b: Input): Pattern => parsePattern(name, [b]);

        function _maybeNamed<R>(recur: (b: Input) => R): (b: Input) => M.NamedSimplePattern_ | R {
            return (b: Input) => {
                const name = findName(b);
                if (name === false) return recur(b);
                return Record(M.$named, [name, parseSimple(b, () => {
                    throw new SchemaSyntaxError(`Named patterns must be Simple patterns`, position(b));
                })]);
            };
        }
        const maybeNamed = _maybeNamed(walk);
        const maybeNamedSimple = _maybeNamed(walkSimple);

        if (Record.isRecord<Input, Tuple<Input>, never>(item)) {
            const label = item.label;
            if (Record.isRecord<Input, [], never>(label)) {
                if (label.length !== 0) complain();
                switch (label.label) {
                    case M.$rec:
                        if (item.length !== 2) complain();
                        return Record(M.$rec, [walk(item[0]), walk(item[1])]);
                    default:
                        complain();
                }
            } else {
                return Record(M.$rec, [Record(M.$lit, [label]), Record(M.$tuple, [item.map(maybeNamed)])]);
            }
        } else if (Array.isArray(item)) {
            if (is(item[item.length - 1], M.DOTDOTDOT)) {
                if (item.length < 2) complain();
                return Record(M.$tuple_STAR_, [
                    item.slice(0, item.length - 2).map(maybeNamed),
                    maybeNamedSimple(item[item.length - 2]),
                ]);
            } else {
                return Record(M.$tuple, [item.map(maybeNamed)]);
            }
        } else if (Dictionary.isDictionary<never, Input>(item)) {
            if (item.size === 2 && item.has(M.DOTDOTDOT)) {
                const v = item.clone();
                v.delete(M.DOTDOTDOT);
                const [[kp, vp]] = v.entries();
                return Record(M.$dictof, [walkSimple(kp), walkSimple(vp)]);
            } else {
                return Record(M.$dict, [item.mapEntries<M.NamedSimplePattern, Input, never>(
                    ([k, vp]) => [strip(k), maybeNamedSimple(vp)])]);
            }
        } else if (Set.isSet<never>(item)) {
            if (item.size !== 1) complain();
            const [vp] = item.entries();
            return Record(M.$setof, [walkSimple(vp)]);
        } else {
            complain();
        }
    }

    const body = peel(body0) as Array<Input>;
    if (body.length !== 1) {
        invalidPattern(stringify(name), body, body.length > 0 ? position(body[0]) : position(body));
    }
    return parseSimple(body[0], () => parseCompound(body[0]));
}

function parseOp<Each, Combined>(body: Array<Input>,
                                 op: Input,
                                 each: (p: Array<Input>) => Each,
                                 combineN: (ps: Array<Each>) => Combined,
                                 finish1: (p: Each) => Combined): Combined
{
    const pieces = splitBy(body, op).map(each);
    return (pieces.length === 1) ? finish1(pieces[0]) : combineN(pieces);
}

function findName(x: Input): symbol | false {
    if (!Annotated.isAnnotated<never>(x)) return false;
    for (const a0 of x.annotations) {
        const a = peel(a0);
        if (typeof a === 'symbol') return a;
    }
    return false;
}

function parseRef(name: string, pos: Position | null, item: symbol): SimplePattern {
    const s = item.description;
    if (s === void 0) invalidPattern(name, item, pos);
    if (s[0] === '=') return Record(M.$lit, [Symbol.for(s.slice(1))]);
    const pieces = s.split('.');
    return recordPosition(Record(M.$ref, [
        pieces.slice(0, pieces.length - 1).map(Symbol.for),
        Symbol.for(pieces[pieces.length - 1])
    ]), pos);
}