import Foundation

enum RDAILocatorBuilder {
    static func makeLocator(
        document: RDAIDocumentDescriptor,
        snapshot: RDAIResourceSnapshot,
        range: RDAITextRange
    ) -> RDAILocator? {
        let matchingRuns = snapshot.locatorRuns.filter { $0.textRange.intersects(range) }
        guard let first = matchingRuns.first else { return nil }
        let anchor = mergedAnchor(matchingRuns) ?? first.anchor
        return RDAILocator(
            documentIdentifier: document.identifier,
            resourceIdentifier: snapshot.descriptor.identifier,
            textRange: range,
            anchor: anchor,
            sourceHash: snapshot.sourceHash
        )
    }

    private static func mergedAnchor(_ runs: [RDAILocatorRun]) -> RDAIAnchor? {
        guard !runs.isEmpty else { return nil }
        let anchors = runs.compactMap { run -> RDAIPDFAnchor? in
            if case .pdf(let anchor) = run.anchor { return anchor }
            return nil
        }
        guard anchors.count == runs.count,
              let first = anchors.first,
              anchors.allSatisfy({ $0.pageIndex == first.pageIndex && $0.textSource == first.textSource }) else {
            return nil
        }
        var rects: [RDAINormalizedRect] = []
        for rect in anchors.flatMap(\.rects) where !rects.contains(rect) {
            rects.append(rect)
        }
        let readingOrder = anchors.compactMap(\.readingOrder).min()
        return .pdf(RDAIPDFAnchor(
            pageIndex: first.pageIndex,
            rects: rects,
            textSource: first.textSource,
            readingOrder: readingOrder
        ))
    }
}