/// SPDX-License-Identifier: GPL-3.0-or-later
/// SPDX-FileCopyrightText: Copyright © 2016-2023 Tony Garnock-Jones <tonyg@leastfixedpoint.com>

import { canonicalString, Dictionary, is, Record, RecordConstructorInfo, Value } from '@preserves/core';
import { AnyValue, Ref } from './actor.js';
import * as P from '../gen/dataspacePatterns.js';

export type Path = Array<AnyValue>;

export type Shape = string;

export function classOfValue(v: any): Shape | null {
    if (Record.isRecord(v)) {
        return constructorInfoSignature(Record.constructorInfo(v));
    } else if (Array.isArray(v)) {
        return '' + v.length;
    } else if (Map.isMap(v)) {
        return '{}';
    } else {
        return null;
    }
}

export function classOfCtor(v: P.DCompound): Shape {
    switch (v._variant) {
        case 'rec':
            return canonicalString(v.label) + '/' + v.fields.length;
        case 'arr':
            return '' + v.items.length;
        case 'dict':
            return '{}';
    }
}

// Called by generated code in addition to functions in this module
export function constructorInfoSignature(ci: RecordConstructorInfo<Value>): string {
    return canonicalString(ci.label) + '/' + ci.arity;
}

export function step(v: AnyValue, index: AnyValue): AnyValue | undefined {
    if (Map.isMap(v)) {
        return v.get(index);
    } else {
        return (v as Array<AnyValue> /* includes Record! */)[index as number];
    }
}

export type PatternAnalysis = {
    constPaths: Array<Path>,
    constValues: Array<AnyValue>,
    capturePaths: Array<Path>,
};

export function analysePattern(p: P.Pattern): PatternAnalysis {
    const result: PatternAnalysis = {
        constPaths: [],
        constValues: [],
        capturePaths: [],
    };
    const path: Path = [];

    function walkKey(p: P.Pattern, key: AnyValue) {
        path.push(key);
        walk(p);
        path.pop();
    }

    function walk(p: P.Pattern) {
        switch (p._variant) {
            case 'DCompound':
                switch (p.value._variant) {
                    case 'rec': p.value.fields.forEach(walkKey); break;
                    case 'arr': p.value.items.forEach(walkKey); break;
                    case 'dict': p.value.entries.forEach(walkKey); break;
                }
                break;
            case 'DBind':
                result.capturePaths.push(path.slice());
                walk(p.value.pattern);
                break;
            case 'DDiscard':
                break;
            case 'DLit':
                result.constPaths.push(path.slice());
                result.constValues.push(P.fromAnyAtom(p.value.value));
                break;
        }
    }

    walk(p);
    return result;
}

export function match(p: P.Pattern, v: AnyValue): Array<AnyValue> | false {
    const captures: Array<AnyValue> = [];

    function walk(p: P.Pattern, v: AnyValue): boolean {
        switch (p._variant) {
            case 'DBind': {
                captures.push(v);
                return walk(p.value.pattern, v);
            }
            case 'DDiscard':
                return true;
            case 'DLit':
                return is(p.value.value, v);
            case 'DCompound': {
                const pcls = classOfCtor(p.value);
                const vcls = classOfValue(v);
                if (pcls !== vcls) return false;
                let items: Array<P.Pattern>;
                switch (p.value._variant) {
                    case 'dict':
                        for (const [stepIndex, pp] of p.value.entries.entries()) {
                            const vv = step(v, stepIndex);
                            if (vv === void 0 || !walk(pp, vv)) return false;
                        }
                        return true;
                    case 'rec': items = p.value.fields; break;
                    case 'arr': items = p.value.items; break;
                }
                let index = 0;
                for (const pp of items) {
                    const vv = step(v, index++);
                    if (vv === void 0 || !walk(pp, vv)) return false;
                }
                return true;
            }
        }
    }

    return walk(p, v) ? captures : false;
}

export function isCompletelyConcrete(p: P.Pattern): boolean {
    function walk(p: P.Pattern): boolean {
        switch (p._variant) {
            case 'DBind': return false;
            case 'DDiscard': return false;
            case 'DLit': return true;
            case 'DCompound': switch (p.value._variant) {
                case 'rec': return p.value.fields.every(isCompletelyConcrete);
                case 'arr': return p.value.items.every(isCompletelyConcrete);
                case 'dict': {
                    for (const pp of p.value.entries.values()) {
                        if (!walk(pp)) return false;
                    }
                    return true;
                }
            }
        }
    }
    return walk(p);
}

export function withoutCaptures(p: P.Pattern): P.Pattern {
    function walk(p: P.Pattern): P.Pattern {
        switch (p._variant) {
            case 'DBind': return walk(p.value.pattern);
            case 'DDiscard': return p;
            case 'DLit': return p;
            case 'DCompound':
                switch (p.value._variant) {
                    case 'rec':
                        return P.Pattern.DCompound(P.DCompound.rec({
                            label: p.value.label,
                            fields: p.value.fields.map(walk),
                        }));
                    case 'arr':
                        return P.Pattern.DCompound(P.DCompound.arr(p.value.items.map(walk)));
                    case 'dict':
                        return P.Pattern.DCompound(P.DCompound.dict(p.value.entries.mapEntries(
                            e => [e[0], walk(e[1])])));
                }
        }
    }
    return walk(p);
}

//---------------------------------------------------------------------------
// Constructor helpers

export function bind(p?: P.Pattern): P.Pattern {
    return P.Pattern.DBind(P.DBind(p ?? _));
}

export function discard(): P.Pattern {
    return P.Pattern.DDiscard(P.DDiscard());
}

export const _ = discard();

export function lit(v: AnyValue): P.Pattern {
    if (Array.isArray(v)) {
        if ('label' in v) {
            return P.Pattern.DCompound(P.DCompound.rec({
                label: v.label,
                fields: v.map(lit),
            }));
        } else {
            return P.Pattern.DCompound(P.DCompound.arr(v.map(lit)));
        }
    } else if (Map.isMap(v)) {
        return P.Pattern.DCompound(P.DCompound.dict(v.mapEntries(
            e => [e[0], lit(e[1])])));
    } else if (Set.isSet(v)) {
        throw new Error("Cannot express literal set in pattern");
    } else {
        return P.Pattern.DLit(P.DLit(P.asAnyAtom(v)));
    }
}

export function drop_lit(p: P.Pattern): AnyValue | null {
    const e = new Error();
    function walk(p: P.Pattern): AnyValue {
        switch (p._variant) {
            case 'DCompound':
                switch (p.value._variant) {
                    case 'rec': {
                        const v = [] as unknown as Record<AnyValue, AnyValue[], Ref>;
                        v.label = p.value.label;
                        p.value.fields.forEach(tt => v.push(walk(tt)));
                        return v;
                    }
                    case 'arr':
                        return p.value.items.map(walk);
                    case 'dict': {
                        const v = new Dictionary<Ref, AnyValue>();
                        p.value.entries.forEach((pp, key) => v.set(key, walk(pp)));
                        return v;
                    }
                }
            case 'DLit':
                return P.fromAnyAtom(p.value.value);
            default:
                throw e;
        }
    }
    try {
        return walk(p);
    } catch (ee) {
        if (ee == e) return null;
        throw ee;
    }
}

export function rec(label: AnyValue, ... fields: P.Pattern[]): P.Pattern {
    return P.Pattern.DCompound(P.DCompound.rec({ label, fields }));
}

export function arr(... patterns: P.Pattern[]): P.Pattern {
    return P.Pattern.DCompound(P.DCompound.arr(patterns));
}

export function dict(... entries: [AnyValue, P.Pattern][]): P.Pattern {
    return P.Pattern.DCompound(P.DCompound.dict(new Dictionary<Ref, P.Pattern>(entries)));
}