// The `GSUB` table contains ligatures, among other things.
// https://www.microsoft.com/typography/OTSPEC/gsub.htm

import check from '../check';
import { Parser } from '../parse';

const subtableParsers = new Array(9); // subtableParsers[0] is unused

// https://www.microsoft.com/typography/OTSPEC/GSUB.htm#SS
subtableParsers[1] = function parseLookup1() {
    const start = this.offset + this.relativeOffset;
    const substFormat = this.parseUShort();
    if (substFormat === 1) {
        return {
            substFormat: 1,
            coverage: this.parsePointer(Parser.coverage),
            deltaGlyphId: this.parseUShort(),
        };
    } else if (substFormat === 2) {
        return {
            substFormat: 2,
            coverage: this.parsePointer(Parser.coverage),
            substitute: this.parseOffset16List(),
        };
    }
    check.assert(
        false,
        '0x' + start.toString(16) + ': lookup type 1 format must be 1 or 2.'
    );
};

// https://www.microsoft.com/typography/OTSPEC/GSUB.htm#MS
subtableParsers[2] = function parseLookup2() {
    const substFormat = this.parseUShort();
    check.argument(
        substFormat === 1,
        'GSUB Multiple Substitution Subtable identifier-format must be 1'
    );
    return {
        substFormat: substFormat,
        coverage: this.parsePointer(Parser.coverage),
        sequences: this.parseListOfLists(),
    };
};

// https://www.microsoft.com/typography/OTSPEC/GSUB.htm#AS
subtableParsers[3] = function parseLookup3() {
    const substFormat = this.parseUShort();
    check.argument(
        substFormat === 1,
        'GSUB Alternate Substitution Subtable identifier-format must be 1'
    );
    return {
        substFormat: substFormat,
        coverage: this.parsePointer(Parser.coverage),
        alternateSets: this.parseListOfLists(),
    };
};

// https://www.microsoft.com/typography/OTSPEC/GSUB.htm#LS
subtableParsers[4] = function parseLookup4() {
    const substFormat = this.parseUShort();
    check.argument(
        substFormat === 1,
        'GSUB ligature table identifier-format must be 1'
    );
    return {
        substFormat: substFormat,
        coverage: this.parsePointer(Parser.coverage),
        ligatureSets: this.parseListOfLists(function () {
            return {
                ligGlyph: this.parseUShort(),
                components: this.parseUShortList(this.parseUShort() - 1),
            };
        }),
    };
};

const lookupRecordDesc = {
    sequenceIndex: Parser.uShort,
    lookupListIndex: Parser.uShort,
};

// https://www.microsoft.com/typography/OTSPEC/GSUB.htm#CSF
subtableParsers[5] = function parseLookup5() {
    const start = this.offset + this.relativeOffset;
    const substFormat = this.parseUShort();

    if (substFormat === 1) {
        return {
            substFormat: substFormat,
            coverage: this.parsePointer(Parser.coverage),
            ruleSets: this.parseListOfLists(function () {
                const glyphCount = this.parseUShort();
                const substCount = this.parseUShort();
                return {
                    input: this.parseUShortList(glyphCount - 1),
                    lookupRecords: this.parseRecordList(
                        substCount,
                        lookupRecordDesc
                    ),
                };
            }),
        };
    } else if (substFormat === 2) {
        return {
            substFormat: substFormat,
            coverage: this.parsePointer(Parser.coverage),
            classDef: this.parsePointer(Parser.classDef),
            classSets: this.parseListOfLists(function () {
                const glyphCount = this.parseUShort();
                const substCount = this.parseUShort();
                return {
                    classes: this.parseUShortList(glyphCount - 1),
                    lookupRecords: this.parseRecordList(
                        substCount,
                        lookupRecordDesc
                    ),
                };
            }),
        };
    } else if (substFormat === 3) {
        const glyphCount = this.parseUShort();
        const substCount = this.parseUShort();
        return {
            substFormat: substFormat,
            coverages: this.parseList(
                glyphCount,
                Parser.pointer(Parser.coverage)
            ),
            lookupRecords: this.parseRecordList(substCount, lookupRecordDesc),
        };
    }
    check.assert(
        false,
        '0x' + start.toString(16) + ': lookup type 5 format must be 1, 2 or 3.'
    );
};

// https://www.microsoft.com/typography/OTSPEC/GSUB.htm#CC
subtableParsers[6] = function parseLookup6() {
    const start = this.offset + this.relativeOffset;
    const substFormat = this.parseUShort();
    if (substFormat === 1) {
        return {
            substFormat: 1,
            coverage: this.parsePointer(Parser.coverage),
            chainRuleSets: this.parseListOfLists(function () {
                return {
                    backtrack: this.parseUShortList(),
                    input: this.parseUShortList(this.parseShort() - 1),
                    lookahead: this.parseUShortList(),
                    lookupRecords: this.parseRecordList(lookupRecordDesc),
                };
            }),
        };
    } else if (substFormat === 2) {
        return {
            substFormat: 2,
            coverage: this.parsePointer(Parser.coverage),
            backtrackClassDef: this.parsePointer(Parser.classDef),
            inputClassDef: this.parsePointer(Parser.classDef),
            lookaheadClassDef: this.parsePointer(Parser.classDef),
            chainClassSet: this.parseListOfLists(function () {
                return {
                    backtrack: this.parseUShortList(),
                    input: this.parseUShortList(this.parseShort() - 1),
                    lookahead: this.parseUShortList(),
                    lookupRecords: this.parseRecordList(lookupRecordDesc),
                };
            }),
        };
    } else if (substFormat === 3) {
        return {
            substFormat: 3,
            backtrackCoverage: this.parseList(Parser.pointer(Parser.coverage)),
            inputCoverage: this.parseList(Parser.pointer(Parser.coverage)),
            lookaheadCoverage: this.parseList(Parser.pointer(Parser.coverage)),
            lookupRecords: this.parseRecordList(lookupRecordDesc),
        };
    }
    check.assert(
        false,
        '0x' + start.toString(16) + ': lookup type 6 format must be 1, 2 or 3.'
    );
};

// https://www.microsoft.com/typography/OTSPEC/GSUB.htm#ES
subtableParsers[7] = function parseLookup7() {
    // Extension Substitution subtable
    const substFormat = this.parseUShort();
    check.argument(
        substFormat === 1,
        'GSUB Extension Substitution subtable identifier-format must be 1'
    );
    const extensionLookupType = this.parseUShort();
    const extensionParser = new Parser(
        this.data,
        this.offset + this.parseULong()
    );
    return {
        substFormat: 1,
        lookupType: extensionLookupType,
        extension: subtableParsers[extensionLookupType].call(extensionParser),
    };
};

// https://www.microsoft.com/typography/OTSPEC/GSUB.htm#RCCS
subtableParsers[8] = function parseLookup8() {
    const substFormat = this.parseUShort();
    check.argument(
        substFormat === 1,
        'GSUB Reverse Chaining Contextual Single Substitution Subtable identifier-format must be 1'
    );
    return {
        substFormat: substFormat,
        coverage: this.parsePointer(Parser.coverage),
        backtrackCoverage: this.parseList(Parser.pointer(Parser.coverage)),
        lookaheadCoverage: this.parseList(Parser.pointer(Parser.coverage)),
        substitutes: this.parseUShortList(),
    };
};

// https://www.microsoft.com/typography/OTSPEC/gsub.htm
function parseGsubTable(data, start) {
    start = start || 0;
    const p = new Parser(data, start);
    const tableVersion = p.parseVersion(1);
    check.argument(
        tableVersion === 1 || tableVersion === 1.1,
        'Unsupported GSUB table version.'
    );
    if (tableVersion === 1) {
        return {
            version: tableVersion,
            scripts: p.parseScriptList(),
            features: p.parseFeatureList(),
            lookups: p.parseLookupList(subtableParsers),
        };
    } else {
        return {
            version: tableVersion,
            scripts: p.parseScriptList(),
            features: p.parseFeatureList(),
            lookups: p.parseLookupList(subtableParsers),
            variations: p.parseFeatureVariationsList(),
        };
    }
}

export default { parse: parseGsubTable };