// State management module
const StateManager = (function() {
    class StateManager {
        constructor() {
            this.history = [];
            this.settings = {
                theme: 'dark',
                mode: 'standard', // 'standard' or 'rpn'
                historyLimit: 50
            };
            this.loadFromStorage();
        }

        // Add a calculation to history
        addToHistory(expression, result) {
            const entry = {
                id: Date.now().toString(),
                expression: expression,
                result: result,
                timestamp: new Date()
            };

            this.history.unshift(entry); // Add to beginning of array

            // Limit history size
            if (this.history.length > this.settings.historyLimit) {
                this.history = this.history.slice(0, this.settings.historyLimit);
            }

            this.saveToStorage();
        }

        // Get calculation history
        getHistory() {
            return [...this.history]; // Return a copy to prevent external modification
        }

        // Get settings
        getSettings() {
            return { ...this.settings }; // Return a copy
        }

        // Update settings
        updateSettings(newSettings) {
            this.settings = { ...this.settings, ...newSettings };
            this.saveToStorage();
        }

        // Toggle calculator mode (standard/RPN)
        toggleMode() {
            this.settings.mode = this.settings.mode === 'standard' ? 'rpn' : 'standard';
            this.saveToStorage();
            return this.settings.mode;
        }

        // Get current mode
        getMode() {
            return this.settings.mode;
        }

        // Clear history
        clearHistory() {
            this.history = [];
            this.saveToStorage();
        }

        // Save state to localStorage
        saveToStorage() {
            try {
                const stateData = {
                    history: this.history,
                    settings: this.settings
                };
                localStorage.setItem('geekCalculatorState', JSON.stringify(stateData));
            } catch (error) {
                console.error('Failed to save state to localStorage:', error);
            }
        }

        // Load state from localStorage
        loadFromStorage() {
            try {
                const stateData = localStorage.getItem('geekCalculatorState');
                if (stateData) {
                    const parsedData = JSON.parse(stateData);
                    this.history = Array.isArray(parsedData.history) ? parsedData.history : [];
                    this.settings = parsedData.settings || this.settings;
                }
            } catch (error) {
                console.error('Failed to load state from localStorage:', error);
                // If loading fails, keep default state
            }
        }

        // Get the last calculation result
        getLastResult() {
            if (this.history.length > 0) {
                return this.history[0].result; // First item is the most recent
            }
            return null;
        }

        // Re-run a specific calculation from history
        rerunCalculation(id) {
            const entry = this.history.find(item => item.id === id);
            if (entry) {
                return {
                    expression: entry.expression,
                    result: entry.result
                };
            }
            return null;
        }
    }

    return { StateManager };
})();