/// SPDX-License-Identifier: GPL-3.0-or-later
/// SPDX-FileCopyrightText: Copyright © 2016-2021 Tony Garnock-Jones <tonyg@leastfixedpoint.com>

import { canonicalString, is, Record, RecordConstructorInfo, Value } from '@preserves/core';
import { AnyValue } 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.ctor.label) + '/' + v.ctor.arity;
        case 'arr':
            return '' + v.ctor.arity;
        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 walk(p: P.Pattern) {
        switch (p._variant) {
            case 'DCompound':
                p.value.members.forEach((v, k) => {
                    path.push(k);
                    walk(v);
                    path.pop();
                });
                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.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;
                for (const [stepIndex, pp] of p.value.members.entries()) {
                    const vv = step(v, stepIndex);
                    if (vv === void 0) return false;
                    if (!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':
                for (const pp of p.value.members.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': return P.Pattern.DCompound({
                _variant: p.value._variant,
                ctor: p.value.ctor,
                members: p.value.members.mapEntries(e => [e[0], walk(e[1])]),
            } as P.DCompound);
        }
    }
    return walk(p);
}