import Foundation

enum RDEPUBJavaScriptBridgeMessage: String, CaseIterable {

    case progressionChanged = "ssReaderProgressionChanged"

    case selectionChanged = "ssReaderSelectionChanged"

    case internalLink = "ssReaderInternalLink"

    case externalLink = "ssReaderExternalLink"

    case javaScriptError = "ssReaderJSError"

    case fixedLayoutReady = "ssReaderFixedLayoutReady"

    case imageDidTap = "ssReaderImageDidTap"

    case footnoteDidTap = "ssReaderFootnoteDidTap"
}

enum RDEPUBJavaScriptBridge {

    static var messageNames: [String] {
        RDEPUBJavaScriptBridgeMessage.allCases.map(\.rawValue)
    }

    static var userScript: String {
        [
            RDEPUBAssetRepository.string(for: .rangyCoreScript),
            RDEPUBAssetRepository.string(for: .rangySerializerScript),
            RDEPUBAssetRepository.string(for: .cssInjectorScript),
            RDEPUBAssetRepository.string(for: .weReadAPIScript),
            RDEPUBAssetRepository.string(
                for: .bridgeScript,
                replacements: [
                    "PROGRESSION_CHANGED_MESSAGE": RDEPUBJavaScriptBridgeMessage.progressionChanged.rawValue,
                    "SELECTION_CHANGED_MESSAGE": RDEPUBJavaScriptBridgeMessage.selectionChanged.rawValue,
                    "INTERNAL_LINK_MESSAGE": RDEPUBJavaScriptBridgeMessage.internalLink.rawValue,
                    "EXTERNAL_LINK_MESSAGE": RDEPUBJavaScriptBridgeMessage.externalLink.rawValue,
                    "JAVASCRIPT_ERROR_MESSAGE": RDEPUBJavaScriptBridgeMessage.javaScriptError.rawValue,
                    "FIXED_LAYOUT_READY_MESSAGE": RDEPUBJavaScriptBridgeMessage.fixedLayoutReady.rawValue,
                    "IMAGE_DID_TAP_MESSAGE": RDEPUBJavaScriptBridgeMessage.imageDidTap.rawValue,
                    "FOOTNOTE_DID_TAP_MESSAGE": RDEPUBJavaScriptBridgeMessage.footnoteDidTap.rawValue
                ]
            )
        ].joined(separator: "\n\n")
    }

    static func applyPresentationScript(for request: RDEPUBReflowableRenderRequest) -> String {
        let style = escapedJavaScriptTemplateLiteral(RDEPUBStyleSheetBuilder.renderCSS(for: request.presentation))
        let pageStride = max(1, request.presentation.viewportSize.width)
        let searchScript = applySearchScript(for: request.searchPresentation)

        return """
        (function() {
            if (!window.WeReadApi) { return false; }
            window.WeReadApi.applySharedTheme({
                backgroundColor: \(javaScriptStringLiteral(request.presentation.themeBackgroundColor)),
                textColor: \(javaScriptStringLiteral(request.presentation.themeTextColor)),
                includeFrames: false
            });
            window.WeReadApi.applyPagination(`\(style)`);
            window.WeReadApi.setPageMetrics(\(request.totalPagesInChapter), \(pageStride));
            window.WeReadApi.clearHighlights();
            window.WeReadApi.setHighlights(\(jsonString(from: highlightsPayload(request.highlights), fallback: "[]")));
            if (\(jsonString(from: targetLocationPayload(request.targetLocation), fallback: "null")) !== null) {
                window.WeReadApi.scrollToLocation(
                    \(jsonString(from: targetLocationPayload(request.targetLocation), fallback: "null")),
                    \(request.pageIndex),
                    \(javaScriptStringLiteral(request.targetHighlightRangeInfo))
                );
            } else {
                window.WeReadApi.scrollToPage(\(request.pageIndex));
            }
            window.WeReadApi.reportProgression();
            return true;
        })();
        \(searchScript)
        """
    }

    static func applyFixedPresentationScript(for request: RDEPUBFixedRenderRequest) -> String {
        """
        (function() {
            if (!window.WeReadApi) { return false; }
            window.WeReadApi.applySharedTheme({
                backgroundColor: \(javaScriptStringLiteral(request.backgroundColorCSS)),
                textColor: null,
                includeFrames: true
            });
            return true;
        })();
        """
    }

    static func applySearchScript(for presentation: RDEPUBSearchPresentation?) -> String {
        let payload = jsonString(from: searchPayload(presentation), fallback: "null")
        return """
        (function() {
            if (!window.WeReadApi) { return false; }
            window.WeReadApi.setSearchPresentation(\(payload));
            return true;
        })();
        """
    }

    static func resolveDecorationsScript() -> String {
        """
        (function() {
            if (!window.WeReadApi) { return { highlights: [], search: [] }; }
            return window.WeReadApi.resolveDecorations();
        })();
        """
    }

    private static func escapedJavaScriptTemplateLiteral(_ string: String) -> String {
        string
            .replacingOccurrences(of: "\\", with: "\\\\")
            .replacingOccurrences(of: "`", with: "\\`")
    }

    private static func highlightsPayload(_ highlights: [RDEPUBHighlight]) -> [[String: String]] {
        highlights.compactMap { highlight in
            guard let rangeInfo = highlight.rangeInfo, !rangeInfo.isEmpty else { return nil }
            return [
                "id": highlight.id,
                "rangeInfo": rangeInfo,
                "color": highlight.color,
                "style": highlight.style.rawValue
            ]
        }
    }

    private static func targetLocationPayload(_ location: RDEPUBLocation?) -> [String: Any]? {
        guard let location else { return nil }
        return [
            "progression": location.progression,
            "lastProgression": location.lastProgression ?? location.progression,
            "fragment": location.fragment as Any
        ]
    }

    private static func searchPayload(_ presentation: RDEPUBSearchPresentation?) -> [String: Any]? {
        guard let presentation else { return nil }
        return [
            "keyword": presentation.keyword,
            "resources": presentation.resources.map { resource in
                [
                    "href": resource.href,
                    "matchCount": resource.matchCount,
                    "activeLocalMatchIndex": resource.activeLocalMatchIndex as Any
                ]
            }
        ]
    }

    private static func jsonString(from object: Any?, fallback: String) -> String {
        guard let object else { return fallback }
        guard JSONSerialization.isValidJSONObject(object),
              let data = try? JSONSerialization.data(withJSONObject: object, options: []),
              let string = String(data: data, encoding: .utf8) else {
            return fallback
        }
        return string
    }

    /// Encodes a string value as a safe JavaScript string literal.
    ///
    /// Uses JSON serialization to handle escaping of quotes, backslashes, control
    /// characters, and Unicode, then strips the array wrapper to produce a standalone
    /// JS string literal (including surrounding quotes).
    ///
    /// - Parameter value: The string to encode, or `nil` which produces the JS keyword `null`.
    /// - Returns: A JavaScript string literal safe for inline embedding in JS source.
    private static func javaScriptStringLiteral(_ value: String?) -> String {
        guard let value else { return "null" }
        guard JSONSerialization.isValidJSONObject([value]),
              let data = try? JSONSerialization.data(withJSONObject: [value], options: []),
              let arrayString = String(data: data, encoding: .utf8) else {
            return "null"
        }
        // JSON encodes ["value"] as `["value"]`. Drop the leading `[` and trailing `]`
        // to yield `"value"` — a valid JS string literal with all special characters escaped.
        return String(arrayString.dropFirst().dropLast())
    }
}