class DiffModule {
    constructor() {
        this.commands = {};
        this.terminal = null;
    }

    requirements() {
        return { met: true, missing: [] };
    }

    getHelpInfo() {
        return {
            'diff': 'Show differences between two VFS files or compare module source (usage: diff <file1> <file2> or diff --module <name>)',
        };
    }
    
    registerCommands() {
        this.commands['diff'] = (args) => this.diff(args);
    }
    async diff(args) {
        if (!args.length) return this.terminal.print('Usage: diff <file1> <file2>  or  diff --module <ModuleName>', 'warning');

        if (args[0] === '--module') {
            if (!args[1]) return this.terminal.print('Usage: diff --module <ModuleName>', 'warning');
            return this._diffModule(args[1]);
        }

        return this._diffFiles(args[0], args[1]);
    }
    _diffFiles(path1, path2) {
        let content1, content2;
        try {
            content1 = this.terminal.fs.readFile(path1);
            content2 = this.terminal.fs.readFile(path2);
        } catch (e) {
            return this.terminal.print(`Error reading files: ${e.message}`, 'error');
        }
        if (content1 === null || content1 === undefined) {
            return this.terminal.print(`File not found: ${path1}`, 'error');
        }
        if (content2 === null || content2 === undefined) {
            return this.terminal.print(`File not found: ${path2}`, 'error');
        }
        const lines1 = String(content1).split('\n');
        const lines2 = String(content2).split('\n');

        // Strip trailing empty line if file ends with newline
        if (lines1.length > 0 && lines1[lines1.length - 1] === '') lines1.pop();
        if (lines2.length > 0 && lines2[lines2.length - 1] === '') lines2.pop();

        if (lines1.length === 0 && lines2.length === 0) {
            return this.terminal.print('Both files are empty — no differences', 'info');
        }

        // Compute LCS-based diff
        const result = this._computeDiff(lines1, lines2);

        // Render output
        this.terminal.print(`--- ${path1}`, 'info');
        this.terminal.print(`+++ ${path2}`, 'info');

        if (result.length === 0) {
            return this.terminal.print('Files are identical', 'success');
        }

        const maxLineNum = Math.max(lines1.length, lines2.length);
        const lineNumWidth = String(maxLineNum).length;

        result.forEach(part => {
            if (part.type === 'same') {
                // Print up to 3 unchanged lines for context, then collapse
                if (part.lines.length <= 3) {
                    part.lines.forEach((line, i) => {
                        const ln = String(part.aStart + i + 1).padStart(lineNumWidth);
                        this.terminal.print(` ${ln} ${line}`, 'dim');
                    });
                } else {
                    // Show first line
                    this.terminal.print(` ${String(part.aStart + 1).padStart(lineNumWidth)} ${part.lines[0]}`, 'dim');
                    this.terminal.print(` ${' '.repeat(lineNumWidth)} ... ${part.lines.length - 2} more unchanged lines`, 'dim');
                    // Show last line
                    const lastIdx = part.lines.length - 1;
                    const ln = String(part.aStart + lastIdx + 1).padStart(lineNumWidth);
                    this.terminal.print(` ${ln} ${part.lines[lastIdx]}`, 'dim');
                }
            } else if (part.type === 'removed') {
                part.lines.forEach((line, i) => {
                    const ln = String(part.aStart + i + 1).padStart(lineNumWidth);
                    this.terminal.print(`-${ln} ${line}`, 'error');
                });
            } else if (part.type === 'added') {
                part.lines.forEach((line, i) => {
                    const ln = String(part.bStart + i + 1).padStart(lineNumWidth);
                    this.terminal.print(`+${ln} ${line}`, 'success');
                });
            }
        });
    }
    _computeDiff(a, b) {
        // Build LCS table
        const m = a.length;
        const n = b.length;
        const dp = Array.from({ length: m + 1 }, () => new Int32Array(n + 1));

        for (let i = 1; i <= m; i++) {
            for (let j = 1; j <= n; j++) {
                if (a[i - 1] === b[j - 1]) {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                } else {
                    dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
                }
            }
        }

        // Backtrack to build diff parts
        const parts = [];
        let i = m, j = n;
        let removed = [], added = [], same = [];
        const aStart = 0, bStart = 0;

        const flush = () => {
            if (same.length > 0) {
                parts.push({
                    type: 'same',
                    aStart: aStart + (parts.length > 0 ? parts.reduce((sum, p) => {
                        if (p.type === 'same') return sum + p.lines.length;
                        if (p.type === 'removed') return sum + p.lines.length;
                        return sum;
                    }, 0) : 0),
                    lines: same.splice(0)
                });
            }
            if (removed.length > 0 || added.length > 0) {
                if (removed.length > 0) {
                    const aIdx = parts.reduce((sum, p) => {
                        if (p.type === 'same') return sum + p.lines.length;
                        if (p.type === 'removed') return sum + p.lines.length;
                        return sum;
                    }, 0);
                    parts.push({ type: 'removed', aStart: aIdx, lines: removed.splice(0) });
                }
                if (added.length > 0) {
                    const bIdx = parts.reduce((sum, p) => {
                        if (p.type === 'same') return sum;
                        if (p.type === 'added') return sum + p.lines.length;
                        return sum;
                    }, 0);
                    parts.push({ type: 'added', bStart: bIdx, lines: added.splice(0) });
                }
            }
        };

        // Trace back through DP table
        const trace = [];
        while (i > 0 || j > 0) {
            if (i > 0 && j > 0 && a[i - 1] === b[j - 1]) {
                trace.push({ type: 'same', lineA: a[i - 1], lineB: b[j - 1] });
                i--; j--;
            } else if (j > 0 && (i === 0 || dp[i][j - 1] >= dp[i - 1][j])) {
                trace.push({ type: 'added', lineB: b[j - 1] });
                j--;
            } else {
                trace.push({ type: 'removed', lineA: a[i - 1] });
                i--;
            }
        }

        // Reverse trace to get forward order
        trace.reverse();

        // Build parts from trace
        let aIdx = 0, bIdx = 0;
        for (const entry of trace) {
            if (entry.type === 'same') {
                same.push(entry.lineA);
                aIdx++;
                bIdx++;
            } else if (entry.type === 'removed') {
                flush();
                removed.push(entry.lineA);
                aIdx++;
            } else if (entry.type === 'added') {
                flush();
                added.push(entry.lineB);
                bIdx++;
            }
        }
        flush();

        return parts;
    }
    async _diffModule(modName) {
        // Find module in registry
        const entry = this.terminal.moduleManager.moduleRegistry.find(m => m.name === modName);
        if (!entry) {
            return this.terminal.print(`Module "${modName}" not found in registry`, 'error');
        }

        const url = entry.url;
        if (!url) {
            return this.terminal.print(`No source URL for module "${modName}"`, 'warning');
        }

        // Fetch original source
        let originalSource;
        try {
            const resp = await fetch(url);
            if (!resp.ok) throw new Error(`HTTP ${resp.status}`);
            originalSource = await resp.text();
        } catch (e) {
            return this.terminal.print(`Failed to fetch original source: ${e.message}`, 'error');
        }

        // Read local edited version
        const localPath = `_mods/${modName}.js`;
        let localSource;
        let hasLocalEdit = false;
        try {
            localSource = this.terminal.fs.readFile(localPath);
            if (localSource === null || localSource === undefined) {
                hasLocalEdit = false;
            } else {
                hasLocalEdit = true;
            }
        } catch (e) {
            hasLocalEdit = false;
        }

        if (!hasLocalEdit) {
            // Try to read the module's currently loaded source
            const loadedModule = this.terminal.moduleManager.modules[modName];
            if (!loadedModule) {
                return this.terminal.print(`Module "${modName}" is not loaded and has no local edits`, 'info');
            }
            return this.terminal.print(`Module "${modName}" has no local edits — source matches original`, 'success');
        }

        // Compare original source vs local edit
        const lines1 = String(originalSource).split('\n');
        const lines2 = String(localSource).split('\n');

        // Strip trailing empty line if file ends with newline
        if (lines1.length > 0 && lines1[lines1.length - 1] === '') lines1.pop();
        if (lines2.length > 0 && lines2[lines2.length - 1] === '') lines2.pop();

        this.terminal.print(`--- ${url}`, 'info');
        this.terminal.print(`+++ ${localPath}`, 'info');

        if (lines1.length === lines2.length && lines1.every((l, i) => l === lines2[i])) {
            return this.terminal.print('No differences — local edit matches original', 'success');
        }

        const result = this._computeDiff(lines1, lines2);
        const maxLineNum = Math.max(lines1.length, lines2.length);
        const lineNumWidth = String(maxLineNum).length;

        result.forEach(part => {
            if (part.type === 'same') {
                if (part.lines.length <= 3) {
                    part.lines.forEach((line, i) => {
                        const ln = String(part.aStart + i + 1).padStart(lineNumWidth);
                        this.terminal.print(` ${ln} ${line}`, 'dim');
                    });
                } else {
                    this.terminal.print(` ${String(part.aStart + 1).padStart(lineNumWidth)} ${part.lines[0]}`, 'dim');
                    this.terminal.print(` ${' '.repeat(lineNumWidth)} ... ${part.lines.length - 2} more unchanged lines`, 'dim');
                    const lastIdx = part.lines.length - 1;
                    const ln = String(part.aStart + lastIdx + 1).padStart(lineNumWidth);
                    this.terminal.print(` ${ln} ${part.lines[lastIdx]}`, 'dim');
                }
            } else if (part.type === 'removed') {
                part.lines.forEach((line, i) => {
                    const ln = String(part.aStart + i + 1).padStart(lineNumWidth);
                    this.terminal.print(`-${ln} ${line}`, 'error');
                });
            } else if (part.type === 'added') {
                part.lines.forEach((line, i) => {
                    const ln = String(part.bStart + i + 1).padStart(lineNumWidth);
                    this.terminal.print(`+${ln} ${line}`, 'success');
                });
            }
        });
    }
}
if (typeof window.webx11 !== 'undefined' && window.webx11) {
    webx11.moduleManager.registerModule(new DiffModule(), 'https://webx11.duckdns.org/spaces/chatstudio/newos4/modules/diff.js');
}