import { decodedMappings, traceSegment, TraceMap } from '@jridgewell/trace-mapping';
import { GenMapping, maybeAddSegment, setSourceContent, toDecodedMap, toEncodedMap } from '@jridgewell/gen-mapping';

const SOURCELESS_MAPPING = /* #__PURE__ */ SegmentObject('', -1, -1, '', null);
const EMPTY_SOURCES = [];
function SegmentObject(source, line, column, name, content) {
    return { source, line, column, name, content };
}
function Source(map, sources, source, content) {
    return {
        map,
        sources,
        source,
        content,
    };
}
/**
 * MapSource represents a single sourcemap, with the ability to trace mappings into its child nodes
 * (which may themselves be SourceMapTrees).
 */
function MapSource(map, sources) {
    return Source(map, sources, '', null);
}
/**
 * A "leaf" node in the sourcemap tree, representing an original, unmodified source file. Recursive
 * segment tracing ends at the `OriginalSource`.
 */
function OriginalSource(source, content) {
    return Source(null, EMPTY_SOURCES, source, content);
}
/**
 * traceMappings is only called on the root level SourceMapTree, and begins the process of
 * resolving each mapping in terms of the original source files.
 */
function traceMappings(tree) {
    // TODO: Eventually support sourceRoot, which has to be removed because the sources are already
    // fully resolved. We'll need to make sources relative to the sourceRoot before adding them.
    const gen = new GenMapping({ file: tree.map.file });
    const { sources: rootSources, map } = tree;
    const rootNames = map.names;
    const rootMappings = decodedMappings(map);
    for (let i = 0; i < rootMappings.length; i++) {
        const segments = rootMappings[i];
        for (let j = 0; j < segments.length; j++) {
            const segment = segments[j];
            const genCol = segment[0];
            let traced = SOURCELESS_MAPPING;
            // 1-length segments only move the current generated column, there's no source information
            // to gather from it.
            if (segment.length !== 1) {
                const source = rootSources[segment[1]];
                traced = originalPositionFor(source, segment[2], segment[3], segment.length === 5 ? rootNames[segment[4]] : '');
                // If the trace is invalid, then the trace ran into a sourcemap that doesn't contain a
                // respective segment into an original source.
                if (traced == null)
                    continue;
            }
            const { column, line, name, content, source } = traced;
            maybeAddSegment(gen, i, genCol, source, line, column, name);
            if (source && content != null)
                setSourceContent(gen, source, content);
        }
    }
    return gen;
}
/**
 * originalPositionFor is only called on children SourceMapTrees. It recurses down into its own
 * child SourceMapTrees, until we find the original source map.
 */
function originalPositionFor(source, line, column, name) {
    if (!source.map) {
        return SegmentObject(source.source, line, column, name, source.content);
    }
    const segment = traceSegment(source.map, line, column);
    // If we couldn't find a segment, then this doesn't exist in the sourcemap.
    if (segment == null)
        return null;
    // 1-length segments only move the current generated column, there's no source information
    // to gather from it.
    if (segment.length === 1)
        return SOURCELESS_MAPPING;
    return originalPositionFor(source.sources[segment[1]], segment[2], segment[3], segment.length === 5 ? source.map.names[segment[4]] : name);
}

function asArray(value) {
    if (Array.isArray(value))
        return value;
    return [value];
}
/**
 * Recursively builds a tree structure out of sourcemap files, with each node
 * being either an `OriginalSource` "leaf" or a `SourceMapTree` composed of
 * `OriginalSource`s and `SourceMapTree`s.
 *
 * Every sourcemap is composed of a collection of source files and mappings
 * into locations of those source files. When we generate a `SourceMapTree` for
 * the sourcemap, we attempt to load each source file's own sourcemap. If it
 * does not have an associated sourcemap, it is considered an original,
 * unmodified source file.
 */
function buildSourceMapTree(input, loader) {
    const maps = asArray(input).map((m) => new TraceMap(m, ''));
    const map = maps.pop();
    for (let i = 0; i < maps.length; i++) {
        if (maps[i].sources.length > 1) {
            throw new Error(`Transformation map ${i} must have exactly one source file.\n` +
                'Did you specify these with the most recent transformation maps first?');
        }
    }
    let tree = build(map, loader, '', 0);
    for (let i = maps.length - 1; i >= 0; i--) {
        tree = MapSource(maps[i], [tree]);
    }
    return tree;
}
function build(map, loader, importer, importerDepth) {
    const { resolvedSources, sourcesContent } = map;
    const depth = importerDepth + 1;
    const children = resolvedSources.map((sourceFile, i) => {
        // The loading context gives the loader more information about why this file is being loaded
        // (eg, from which importer). It also allows the loader to override the location of the loaded
        // sourcemap/original source, or to override the content in the sourcesContent field if it's
        // an unmodified source file.
        const ctx = {
            importer,
            depth,
            source: sourceFile || '',
            content: undefined,
        };
        // Use the provided loader callback to retrieve the file's sourcemap.
        // TODO: We should eventually support async loading of sourcemap files.
        const sourceMap = loader(ctx.source, ctx);
        const { source, content } = ctx;
        // If there is a sourcemap, then we need to recurse into it to load its source files.
        if (sourceMap)
            return build(new TraceMap(sourceMap, source), loader, source, depth);
        // Else, it's an an unmodified source file.
        // The contents of this unmodified source file can be overridden via the loader context,
        // allowing it to be explicitly null or a string. If it remains undefined, we fall back to
        // the importing sourcemap's `sourcesContent` field.
        const sourceContent = content !== undefined ? content : sourcesContent ? sourcesContent[i] : null;
        return OriginalSource(source, sourceContent);
    });
    return MapSource(map, children);
}

/**
 * A SourceMap v3 compatible sourcemap, which only includes fields that were
 * provided to it.
 */
class SourceMap {
    constructor(map, options) {
        const out = options.decodedMappings ? toDecodedMap(map) : toEncodedMap(map);
        this.version = out.version; // SourceMap spec says this should be first.
        this.file = out.file;
        this.mappings = out.mappings;
        this.names = out.names;
        this.sourceRoot = out.sourceRoot;
        this.sources = out.sources;
        if (!options.excludeContent) {
            this.sourcesContent = out.sourcesContent;
        }
    }
    toString() {
        return JSON.stringify(this);
    }
}

/**
 * Traces through all the mappings in the root sourcemap, through the sources
 * (and their sourcemaps), all the way back to the original source location.
 *
 * `loader` will be called every time we encounter a source file. If it returns
 * a sourcemap, we will recurse into that sourcemap to continue the trace. If
 * it returns a falsey value, that source file is treated as an original,
 * unmodified source file.
 *
 * Pass `excludeContent` to exclude any self-containing source file content
 * from the output sourcemap.
 *
 * Pass `decodedMappings` to receive a SourceMap with decoded (instead of
 * VLQ encoded) mappings.
 */
function remapping(input, loader, options) {
    const opts = typeof options === 'object' ? options : { excludeContent: !!options, decodedMappings: false };
    const tree = buildSourceMapTree(input, loader);
    return new SourceMap(traceMappings(tree), opts);
}

export { remapping as default };
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