# All files / router/src/core hashNavigation.ts

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98.18% Branches 54/55
94.11% Functions 16/17
88.11% Lines 215/244

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     import { signal, computed, effect, batch } from '@preact/signals';

    import type {
        NavigationResult,
        NavigationState,
        NavigationHistoryEntry,
        NavigationOptions,
        HashNavigation
    } from '#src/types';
    import {
        createHistoryEntry,
        createNavigationResult,
        getHash,
        createHash
    } from '#src/helpers';

    /**
     * Implementation of hash-based router core using Preact signals
     * and following the Navigation API interface, while using window.history for compatibility
     */
    export const createHashNavigation = (): HashNavigation => {
        // Internal signals to manage router state
        const _currentURL = signal<string>(window.location.href);
        const _entries = signal<NavigationHistoryEntry[]>([createHistoryEntry(window.location.href)]);
        const _currentIndex = signal<number>(0);
        const _navigations = signal<Map<string, NavigationResult>>(new Map());

        // Storage for active subscriptions
        const _subscriptions = new Set<VoidFunction>();

        // Public computed signals that reflect the router state
        const currentEntry = computed(() => _entries.value[_currentIndex.value]);
        const entries = computed(() => [..._entries.value]);
        const canGoBack = computed(() => _currentIndex.value > 0);
        const canGoForward = computed(() => _currentIndex.value < _entries.value.length - 1);

        // Initialize the router state from the current location
        const initializeFromLocation = (): void => {
            // Try to get existing state from the history API
            const state = window.history.state ?? currentEntry.value.state;

            const initialEntry = createHistoryEntry(_currentURL.value, state);

            // Using batch to update multiple signals at once
            batch(() => {
                _currentURL.value = initialEntry.url as string;
                _entries.value = [initialEntry];
                _currentIndex.value = 0;
            });
        };

        // Handle hash change events from the window
        const handleHashChange = (event: HashChangeEvent): void => {
            // This is triggered by the browser, so we need to update our state
            const newUrl = event.newURL;
            const state = window.history.state;

            // Check if this is a navigation we already know about
            const existingEntryIndex = _entries.value.findIndex((entry) => entry.url === newUrl);

            if(existingEntryIndex >= 0) {
                // If we already have this entry, just update the index
                _currentIndex.value = existingEntryIndex;

                // Update state if it has changed
                const existingEntry = _entries.value[existingEntryIndex];

                if(JSON.stringify(existingEntry.state) !== JSON.stringify(state)) {
                    const updatedEntries = [..._entries.value];

                    updatedEntries[existingEntryIndex] = {
                        ...existingEntry,
                        state,
                    };
                    _entries.value = updatedEntries;
                }
            } else {
                // Otherwise, create a new entry
                const newEntry = createHistoryEntry(newUrl, state, _entries.value.length);
                const newEntries = [..._entries.value];

                // If we navigated from a point in history, remove the forward entries
                if(_currentIndex.value < _entries.value.length - 1) {
                    newEntries.splice(_currentIndex.value + 1);
                }

                newEntries.push(newEntry);

                // Using batch to update multiple signals at once
                batch(() => {
                    _entries.value = newEntries;
                    _currentIndex.value = newEntries.length - 1;
                });
            }
        };

        // Helper function to update navigation state
        const updateNavigationState = (
            destination: NavigationHistoryEntry,
            newCurrentIndex: number,
            newUrl?: string
        ): NavigationResult => {
            // Create a navigation result
            const result = createNavigationResult(destination);

            // Store the navigation for potential future reference
            const navigations = new Map(_navigations.value);

            navigations.set(destination.key, result);

            // Using batch to update multiple signals at once
            batch(() => {
                if(newUrl) {
                    _currentURL.value = newUrl;
                }
                _currentIndex.value = newCurrentIndex;
                _navigations.value = navigations;
            });

            return result;
        };

        // Handle entry state updates
        const updateEntryState = (
            entryIndex: number,
            newState: NavigationState | null | undefined
        ): NavigationHistoryEntry => {
            const newEntries = [..._entries.value];
            const entry = newEntries[entryIndex];

            // Create updated entry with new state
            const updatedEntry = {
                ...entry,
                state: newState,
            };

            // Update our entries array
            newEntries[entryIndex] = updatedEntry;
            _entries.value = newEntries;

            return updatedEntry;
        };

        const updateEntryUrl = (
            entryIndex: number,
            newUrl: string
        ): NavigationHistoryEntry => {
            const newEntries = [..._entries.value];
            const entry = newEntries[entryIndex];

            // Create updated entry with new url
            const updatedEntry = {
                ...entry,
                url : newUrl,
                hash: getHash(newUrl),
            };

            // Update our entries array
            newEntries[entryIndex] = updatedEntry;
            _entries.value = newEntries;

            return updatedEntry;
        };

        const updateCurrentEntryHash = (hash: string) => {
            return updateEntryUrl(
                _currentIndex.value,
                new URL(`#${createHash(hash)}`, window.location.href).href
            );
        };

        /**
         * Subscribe to navigation changes with current and previous history entries
         * and current hash route
         * @param callback - Callback function called when navigation changes
         * @returns Unsubscribe function
         */
        const subscribe = (
            callback: (
                entry: NavigationHistoryEntry,
                prevEntry: NavigationHistoryEntry | null,
                hash: string
            ) => void
        ): VoidFunction => {
            // Get the current entry before setting up the effect
            const current = currentEntry.value;

            // Track the previous entry for change detection
            // Initialize with current to avoid double call
            let previousEntry: NavigationHistoryEntry | null = current;

            // Call the callback with the current value on initial subscription
            callback(current, null, current.hash);

            // Create an effect that tracks changes in the currentEntry signal
            const unsubscribe = effect(() => {
                const entry = currentEntry.value;
                const currentHash = entry.hash;

                // Call the callback with current and previous entries
                if(previousEntry !== entry) {
                    callback(entry, previousEntry, currentHash);
                    previousEntry = entry;
                }
            });

            // Create a complete unsubscribe function that also removes the subscription from storage
            const completeUnsubscribe = () => {
                unsubscribe();
                _subscriptions.delete(completeUnsubscribe);
            };

            // Save the subscription in storage
            _subscriptions.add(completeUnsubscribe);

            // Return the unsubscribe function
            return completeUnsubscribe;
        };

        // Public API methods
        const navigate = (hash: string, options: NavigationOptions = {}): NavigationResult => {
            // Create full URL by resolving against current location
            const originalHash = currentEntry.value.hash;
            const fullUrl = new URL(`#${createHash(hash)}`, window.location.href).href;

            // Only navigate if the hash part actually changed
            if(originalHash !== hash) {
                // Create a new destination with state from options
                const destination = createHistoryEntry(fullUrl, options.state as NavigationState, _entries.value.length);

                // Use history pushState to update the URL without reloading
                window.history.pushState(options.state || null, '', fullUrl);

                // Update our internal state
                const newEntries = [..._entries.value];

                // If we navigated from a point in history, remove the forward entries
                if(_currentIndex.value < _entries.value.length - 1) {
                    newEntries.splice(_currentIndex.value + 1);
                }

                newEntries.push(destination);

                // Using batch to update multiple signals at once
                batch(() => {
                    _entries.value = newEntries;
                    _currentIndex.value = newEntries.length - 1;
                    _currentURL.value = fullUrl;
                });

                // Update navigation state
                return updateNavigationState(destination, newEntries.length - 1);
            } else {
                // If hash didn't change, check if state changed
                const currentEntryValue = currentEntry.value;

                if(options.state && JSON.stringify(currentEntryValue.state) !== JSON.stringify(options.state)) {
                    // Update state without changing URL
                    window.history.replaceState(options.state, '', fullUrl);

                    const updatedEntry = updateEntryState(_currentIndex.value, options.state as NavigationState);

                    // Create and return a navigation result for the updated entry
                    return createNavigationResult(updatedEntry);
                }

                // If nothing changed, return a result that resolves immediately with current entry
                return createNavigationResult(currentEntryValue);
            }
        };

        const traverseTo = (key: string, options: NavigationOptions = {}): NavigationResult | null => {
            const entryIndex = _entries.value.findIndex((entry) => entry.key === key);

            if(entryIndex === -1) {
                return null;
            }

            const destination = _entries.value[entryIndex];
            const delta = entryIndex - _currentIndex.value;

            // Handle potential state update if options include state
            let updatedDestination = destination;

            if(options.state) {
                // Update history state and our entries
                window.history.replaceState(options.state, '', destination.url);
                updatedDestination = updateEntryState(entryIndex, options.state as NavigationState);
            }

            // Use history.go to navigate through history
            window.history.go(delta);

            // Update navigation state
            return updateNavigationState(updatedDestination, entryIndex, updatedDestination.url);
        };

        const back = (options: NavigationOptions = {}): NavigationResult | null => {
            if(!canGoBack.value) {
                window.history.back();
                return null;
            }

            const prevIndex = _currentIndex.value - 1;
            let destination = _entries.value[prevIndex];

            // Handle potential state update if options include state
            if(options.state) {
                // Update history state before going back
                window.history.replaceState(options.state, '', destination.url);
                destination = updateEntryState(prevIndex, options.state as NavigationState);
            }

            // Use history.back to navigate back
            window.history.back();

            // Update navigation state
            return updateNavigationState(destination, prevIndex, destination.url);
        };

        const forward = (options: NavigationOptions = {}): NavigationResult | null => {
            if(!canGoForward.value) {
                return null;
            }

            const nextIndex = _currentIndex.value + 1;
            let destination = _entries.value[nextIndex];

            // Handle potential state update if options include state
            if(options.state) {
                // Update history state before going forward
                window.history.replaceState(options.state, '', destination.url);
                destination = updateEntryState(nextIndex, options.state as NavigationState);
            }

            // Use history.forward to navigate forward
            window.history.forward();

            // Update navigation state
            return updateNavigationState(destination, nextIndex, destination.url);
        };

        const reload = (options: NavigationOptions = {}): NavigationResult => {
            const currentEntryValue = currentEntry.value;

            // Create a new destination to represent the reload, potentially with updated state
            const state = options.state !== undefined ? options.state : currentEntryValue.state;
            const destination = createHistoryEntry(currentEntryValue.url, state, currentEntryValue.index);

            // Update history state if new state is provided
            if(options.state !== undefined) {
                window.history.replaceState(options.state, '', currentEntryValue.url);
                updateEntryState(_currentIndex.value, options.state as NavigationState);
            }

            // Actually reload the current hash route
            window.location.hash = getHash(currentEntryValue.url);

            // Update navigation state
            const result = createNavigationResult(destination);

            // Store the navigation for potential future reference
            const navigations = new Map(_navigations.value);

            navigations.set(destination.key, result);
            _navigations.value = navigations;

            return result;
        };

        const updateCurrentEntry = (options: NavigationOptions = {}): void => {
            const currentIndex = _currentIndex.value;

            // Update the history state
            window.history.replaceState(options.state || null, '', window.location.hash);

            // Update entry state
            updateEntryState(currentIndex, options.state as NavigationState || null);
        };

        // Set up effect to synchronize URL with current entry
        const unsubscribe = effect(() => {
            const currentEntryValue = currentEntry.value;

            if(currentEntryValue && getHash(_currentURL.value) !== getHash(currentEntryValue.url as string)) {
                _currentURL.value = currentEntryValue.url as string;
            }
        });

        const create = () => {
            // Initialize and set up event listeners
            initializeFromLocation();
            window.addEventListener('hashchange', handleHashChange);
        };

        const destroy = (): void => {
            window.removeEventListener('hashchange', handleHashChange);

            // Cancel all active subscriptions
            _subscriptions.forEach((unsub) => unsub());
            _subscriptions.clear();

            // Cancel internal synchronization effect
            unsubscribe();
        };

        // Return the public API
        return {
            // Public signals
            currentEntry,
            entries,
            canGoBack,
            canGoForward,

            // Navigation methods
            navigate,
            traverseTo,
            back,
            forward,
            reload,
            updateCurrentEntry,

            // Subscription method
            subscribe,

            // Service methods
            updateCurrentEntryHash,

            // Init
            create,
            // Cleanup
            destroy,
        };
    };

    // Export a singleton instance for convenience
    export const hashNavigation = createHashNavigation();