static/problem.js

/* global problemIdx, datasetSlug, datasetName, hasGroundTruth, hasTasks */

function badgeClass(source) {
    return 'badge-' + source.toLowerCase().replace(/[^a-z0-9]/g, '');
}

async function loadProblem() {
    try {
        const response = await fetch(`/api/${datasetSlug}/problem/${problemIdx}`);
        const problem = await response.json();

        if (problem.error) {
            document.getElementById('problem-content').innerHTML =
                '<div class="card"><p style="color: red;">Error: ' + problem.error + '</p></div>';
            return;
        }

        renderProblem(problem);
    } catch (error) {
        document.getElementById('problem-content').innerHTML =
            '<div class="card"><p style="color: red;">Error loading problem: ' + error.message + '</p></div>';
    }
}

function renderProblem(problem) {
    const container = document.getElementById('problem-content');

    // Main problem info card (shared by all datasets)
    let html = `
        <div class="card">
            <div class="problem-header">
                <h2>${escapeHtml(problem.entry_point)}</h2>
                <span class="badge ${badgeClass(problem.source)}">${escapeHtml(problem.source)}</span>
            </div>
            <div class="problem-meta">
                <div class="meta-item">
                    <span class="meta-label">Task ID:</span>
                    <span class="meta-value">${escapeHtml(problem.task_id)}</span>
                </div>
                <div class="meta-item">
                    <span class="meta-label">Index:</span>
                    <span class="meta-value">${problem.idx}</span>
                </div>
                <div class="meta-item">
                    <span class="meta-label">Dataset:</span>
                    <span class="meta-value">${escapeHtml(datasetName)}</span>
                </div>
                ${problem.inputs.length > 0 ? `
                <div class="meta-item">
                    <span class="meta-label">Test Inputs:</span>
                    <span class="meta-value">${problem.inputs.length}</span>
                </div>` : ''}
            </div>
        </div>
    `;

    // --- BigOBench view (problem description + per-solution code & complexity) ---
    if (problem.solutions && problem.solutions.length > 0) {
        // Problem description
        if (problem.description) {
            html += `
                <div class="card">
                    <h2>Problem Statement</h2>
                    <pre class="code-block" style="white-space: pre-wrap;">${escapeHtml(problem.description)}</pre>
                </div>
            `;
        }

        // Each solution: code + complexity/language badges
        problem.solutions.forEach((sol, i) => {
            html += `
                <div class="card">
                    <h2>Solution ${i + 1} <span style="font-size:0.8rem;color:#7f8c8d;font-weight:400;">${escapeHtml(sol.solution_id)}</span></h2>
                    <div class="complexity-badges" style="margin-bottom: 15px;">
            `;
            if (sol.language) {
                html += `
                        <div class="complexity-item">
                            <span class="complexity-label">Language</span>
                            <span class="badge badge-info">${escapeHtml(sol.language)}</span>
                        </div>`;
            }
            if (sol.time_complexity) {
                html += `
                        <div class="complexity-item">
                            <span class="complexity-label">Time</span>
                            <span class="complexity-value">${escapeHtml(sol.time_complexity)}</span>
                        </div>`;
            }
            if (sol.space_complexity) {
                html += `
                        <div class="complexity-item">
                            <span class="complexity-label">Space</span>
                            <span class="complexity-value">${escapeHtml(sol.space_complexity)}</span>
                        </div>`;
            }
            html += `
                    </div>
                    <div class="code-with-tasks">
                        ${sol.highlighted_code}
                    </div>
                </div>
            `;
        });

        // Navigation hint
        html += `
            <div class="navigation-hint">
                <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
                or return to the list view to filter by dataset source or search by name.
            </div>
        `;

        container.innerHTML = html;
        window.currentProblem = problem;
        return;
    }

    // --- DebugBench before/after view (buggy → fixed) ---
    if (problem.buggy_code !== undefined && problem.fixed_code !== undefined) {
        // Problem description
        if (problem.description) {
            html += `
                <div class="card">
                    <h2>Problem Statement</h2>
                    <pre class="code-block" style="white-space: pre-wrap;">${escapeHtml(problem.description)}</pre>
                </div>
            `;
        }

        // Bug info
        html += `
            <div class="card">
                <h2>Bug Information</h2>
                <div class="bug-info">
                    <span class="bug-category">${escapeHtml(problem.bug_category || '')}</span>
                    <span class="bug-subtype">${escapeHtml(problem.bug_subtype || '')}</span>
                </div>
                <p style="margin-top: 10px;">${escapeHtml(problem.bug_explanation || '')}</p>
        `;
        if (problem.difficulty) {
            html += `<p style="margin-top: 8px; color: #7f8c8d;">Difficulty: <strong>${escapeHtml(problem.difficulty)}</strong></p>`;
        }
        html += `</div>`;

        // Unified diff view of buggy → fixed
        const unifiedDiff = computeUnifiedDiff(problem.buggy_code, problem.fixed_code);
        html += `
            <div class="card">
                <h2>Changes</h2>
                <div class="diff-view">${renderComputedDiff(unifiedDiff)}</div>
            </div>
        `;

        // Side-by-side buggy/fixed code
        html += `
            <div class="card">
                <h2>Full Code Comparison</h2>
                <div class="diff-container">
                    <div class="diff-panel">
                        <h3><span class="diff-label-buggy">Before</span></h3>
                        <div class="code-with-tasks">${problem.buggy_highlighted_code}</div>
                    </div>
                    <div class="diff-panel">
                        <h3><span class="diff-label-fixed">After</span></h3>
                        <div class="code-with-tasks">${problem.fixed_highlighted_code}</div>
                    </div>
                </div>
            </div>
        `;

        // Examples
        if (problem.examples && problem.examples.length > 0) {
            html += `<div class="card"><h2>Examples</h2>`;
            problem.examples.forEach((ex, i) => {
                html += `<pre class="code-block" style="margin-bottom: 10px; white-space: pre-wrap;">${escapeHtml(ex)}</pre>`;
            });
            html += `</div>`;
        }

        html += `
            <div class="navigation-hint">
                <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
                or return to the list view to filter by dataset source or search by name.
            </div>
        `;

        container.innerHTML = html;
        window.currentProblem = problem;
        return;
    }

    // --- HumanEval-X / HumanEvalPack multi-language view ---
    if (problem.lang_solutions && problem.lang_solutions.length > 0) {
        // Check if this is HumanEvalPack (has buggy_code in solutions)
        const hasBuggy = problem.lang_solutions.some(sol => sol.buggy_code);

        // Bug info (HumanEvalPack only)
        if (hasBuggy && (problem.bug_type || problem.failure_symptoms)) {
            html += `
                <div class="card">
                    <h2>Bug Information</h2>
                    <div class="bug-info">
                        ${problem.bug_type ? `<span class="bug-category">${escapeHtml(problem.bug_type)}</span>` : ''}
                        ${problem.failure_symptoms ? `<span class="bug-subtype">${escapeHtml(problem.failure_symptoms)}</span>` : ''}
                    </div>
                </div>
            `;
        }

        // Language tabs with code panels
        html += `
            <div class="card">
                <h2>Source Code</h2>
        `;

        // Buggy/Canonical toggle for HumanEvalPack
        if (hasBuggy) {
            html += `
                <div class="lang-tabs" id="code-mode-tabs" style="margin-bottom: 10px;">
                    <button class="lang-tab active" onclick="toggleCodeMode('canonical')">Canonical</button>
                    <button class="lang-tab" onclick="toggleCodeMode('buggy')">Buggy</button>
                </div>
            `;
        }

        html += `<div class="lang-tabs" id="lang-tabs">`;
        problem.lang_solutions.forEach((sol, i) => {
            const label = sol.language_label || sol.language;
            html += `<button class="lang-tab ${i === 0 ? 'active' : ''}" onclick="showLangTab(${i})">${escapeHtml(label)}</button>`;
        });
        html += `</div>`;

        problem.lang_solutions.forEach((sol, i) => {
            html += `
                <div class="lang-code-panel ${i === 0 ? 'active' : ''}" id="lang-panel-${i}">
                    <div class="code-with-tasks" id="lang-code-canonical-${i}">${sol.highlighted_code}</div>
                    ${sol.buggy_code ? `<div class="code-with-tasks" id="lang-code-buggy-${i}" style="display:none;">${sol.buggy_highlighted_code}</div>` : ''}
                </div>
            `;
        });
        html += `</div>`;

        // Test suite for current language
        html += `<div class="card" id="lang-test-container">`;
        if (problem.lang_solutions[0].test) {
            html += `<h2>Test Suite</h2><pre class="code-block">${escapeHtml(problem.lang_solutions[0].test)}</pre>`;
        }
        html += `</div>`;

        // Description
        if (problem.description) {
            html += `
                <div class="card">
                    <h2>Problem Description</h2>
                    <div style="padding: 10px; line-height: 1.6; white-space: pre-wrap;">${escapeHtml(problem.description)}</div>
                </div>
            `;
        }

        html += `
            <div class="navigation-hint">
                <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
                or return to the list view to filter by dataset source or search by name.
            </div>
        `;

        container.innerHTML = html;
        window.currentProblem = problem;
        window._currentCodeMode = 'canonical';
        return;
    }

    // --- SWE-bench / CommitBench diff view (unified diff patch) ---
    if (problem.patch !== undefined) {
        // GitHub links bar (SWE-bench variants)
        const ghLinks = [];
        if (problem.repo_url) ghLinks.push(`<a href="${escapeHtml(problem.repo_url)}" target="_blank" class="gh-link">Repository</a>`);
        if (problem.issue_url) ghLinks.push(`<a href="${escapeHtml(problem.issue_url)}" target="_blank" class="gh-link">Issue</a>`);
        if (problem.commit_url) ghLinks.push(`<a href="${escapeHtml(problem.commit_url)}" target="_blank" class="gh-link">Base Commit</a>`);
        if (ghLinks.length > 0) {
            html += `<div class="card gh-links-bar">${ghLinks.join('')}</div>`;
        }

        // Metadata badges (version, date)
        const metaBadges = [];
        if (problem.version) metaBadges.push(`<span class="badge badge-info">v${escapeHtml(problem.version)}</span>`);
        if (problem.created_at) metaBadges.push(`<span class="badge badge-info">${escapeHtml(problem.created_at.split('T')[0])}</span>`);
        if (problem.commit_hash) metaBadges.push(`<span class="badge badge-info">${escapeHtml(problem.commit_hash.substring(0, 12))}</span>`);
        if (problem.diff_languages) metaBadges.push(`<span class="badge badge-info">${escapeHtml(problem.diff_languages)}</span>`);
        if (metaBadges.length > 0) {
            html += `<div style="margin-bottom: 15px;">${metaBadges.join(' ')}</div>`;
        }

        // Problem statement (issue text / commit message)
        if (problem.description) {
            html += `
                <div class="card">
                    <h2>${problem.issue_url ? 'Issue Description' : 'Description'}</h2>
                    <div class="issue-statement">${escapeHtml(problem.description)}</div>
                </div>
            `;
        }

        // Render unified diff with per-file sections
        html += renderDiffFiles(problem.patch, 'Solution Patch');

        // Test patch if available
        if (problem.test_patch) {
            html += renderDiffFiles(problem.test_patch, 'Test Patch');
        }

        // Failing tests
        if (problem.fail_to_pass && problem.fail_to_pass.length > 0) {
            html += `<div class="card"><h2>Tests: Fail → Pass</h2><ul class="test-id-list">`;
            problem.fail_to_pass.forEach(t => {
                html += `<li>${escapeHtml(t)}</li>`;
            });
            html += `</ul></div>`;
        }

        // Hints
        if (problem.hints) {
            html += `
                <div class="card">
                    <h2>Hints</h2>
                    <div class="issue-statement">${escapeHtml(problem.hints)}</div>
                </div>
            `;
        }

        html += `
            <div class="navigation-hint">
                <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
                or return to the list view to filter by dataset source or search by name.
            </div>
        `;

        container.innerHTML = html;
        window.currentProblem = problem;
        return;
    }

    // --- SAFIM Fill-in-the-Middle view ---
    if (problem.fim_ground_truth !== undefined) {
        // Tab bar: "With Gap" | "Completed" | "Completion Only"
        html += `
            <div class="card">
                <h2>Fill-in-the-Middle</h2>
                <div class="lang-tabs" id="fim-tabs">
                    <button class="lang-tab" onclick="showFimTab(0)">With Gap</button>
                    <button class="lang-tab active" onclick="showFimTab(1)">Completed</button>
                    <button class="lang-tab" onclick="showFimTab(2)">Completion Only</button>
                </div>
                <div class="lang-code-panel" id="fim-panel-0">
                    <div class="code-with-tasks">${problem.highlighted_code}</div>
                </div>
                <div class="lang-code-panel active" id="fim-panel-1">
                    <div class="fim-merged-legend">
                        <span class="coverage-swatch" style="background:#ffffcc; border:1px solid #ccc;"></span>
                        Inserted completion (lines ${problem.fim_gt_start_line}&ndash;${problem.fim_gt_end_line})
                    </div>
                    <div class="code-with-tasks">${problem.fim_merged_highlighted}</div>
                </div>
                <div class="lang-code-panel" id="fim-panel-2">
                    <div class="fim-answer">${problem.fim_ground_truth_highlighted || escapeHtml(problem.fim_ground_truth)}</div>
                </div>
            </div>
        `;

        html += `
            <div class="navigation-hint">
                <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
                or return to the list view to filter by dataset source or search by name.
            </div>
        `;
        container.innerHTML = html;
        window.currentProblem = problem;
        return;
    }

    // --- Vulnerability view (BigVul, DiverseVul, PrimeVul) ---
    if (problem.vulnerable_code !== undefined || problem.is_vulnerable !== undefined) {
        // Vulnerability status and CWE info
        const isVuln = problem.is_vulnerable;
        html += `
            <div class="card">
                <h2>Vulnerability Information</h2>
                <div style="margin-bottom: 10px;">
                    <span class="vuln-status ${isVuln ? 'vuln-status-vulnerable' : 'vuln-status-patched'}">
                        ${isVuln ? 'Vulnerable' : 'Patched'}
                    </span>
                    ${problem.cwe_id ? `<span class="cwe-badge">${escapeHtml(problem.cwe_id)}</span>` : ''}
                    ${problem.cve_id ? `<span class="badge badge-info">${escapeHtml(problem.cve_id)}</span>` : ''}
                    ${problem.project ? `<span class="badge badge-info">${escapeHtml(problem.project)}</span>` : ''}
                </div>
                ${problem.description ? `<p style="margin-top: 10px; color: #555;">${escapeHtml(problem.description).substring(0, 500)}</p>` : ''}
            </div>
        `;

        // Show code with vuln/patched side-by-side if both available
        if (problem.vulnerable_code && problem.patched_code) {
            const vulnDiff = computeUnifiedDiff(problem.vulnerable_code, problem.patched_code);
            html += `
                <div class="card">
                    <h2>Changes</h2>
                    <div class="diff-view">${renderComputedDiff(vulnDiff)}</div>
                </div>
            `;
            html += `
                <div class="card">
                    <h2>Full Code Comparison</h2>
                    <div class="diff-container">
                        <div class="diff-panel">
                            <h3><span class="diff-label-buggy">Vulnerable</span></h3>
                            <div class="code-with-tasks">${problem.vulnerable_highlighted_code}</div>
                        </div>
                        <div class="diff-panel">
                            <h3><span class="diff-label-fixed">Patched</span></h3>
                            <div class="code-with-tasks">${problem.patched_highlighted_code}</div>
                        </div>
                    </div>
                </div>
            `;
        } else {
            // Single code view
            html += `
                <div class="card">
                    <h2>Source Code</h2>
                    <div class="code-with-tasks">${problem.highlighted_code}</div>
                </div>
            `;
        }

        html += `
            <div class="navigation-hint">
                <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
                or return to the list view to filter by dataset source or search by name.
            </div>
        `;
        container.innerHTML = html;
        window.currentProblem = problem;
        return;
    }

    // Source Code card
    html += `
        <div class="card">
            <h2>Source Code</h2>
            <div class="code-with-tasks" id="code-container">
                ${problem.highlighted_code}
            </div>
        </div>
    `;

    // --- Non-DREval (simple) view ---
    if (!hasTasks) {
        // GitHub / external links (e.g. LCA adapters)
        const simpleLinks = [];
        if (problem.repo_url) simpleLinks.push(`<a href="${escapeHtml(problem.repo_url)}" target="_blank" class="gh-link">Repository</a>`);
        if (problem.issue_url) simpleLinks.push(`<a href="${escapeHtml(problem.issue_url)}" target="_blank" class="gh-link">Issue</a>`);
        if (problem.commit_url) simpleLinks.push(`<a href="${escapeHtml(problem.commit_url)}" target="_blank" class="gh-link">Commit</a>`);
        if (simpleLinks.length > 0) {
            html += `<div class="card gh-links-bar">${simpleLinks.join('')}</div>`;
        }

        // Show description if available (e.g. LiveCodeBench, MBPP+, ClassEval)
        if (problem.description) {
            html += `
                <div class="card">
                    <h2>Problem Description</h2>
                    <div style="padding: 10px; line-height: 1.6; white-space: pre-wrap;">${escapeHtml(problem.description)}</div>
                </div>
            `;
        }

        // Show difficulty, contest date, tags, rating if available
        if (problem.difficulty || problem.contest_date || problem.tags || problem.cf_rating) {
            let metaHtml = '';
            if (problem.difficulty) {
                metaHtml += `<span class="badge badge-info">Difficulty: ${escapeHtml(problem.difficulty)}</span>`;
            }
            if (problem.cf_rating) {
                metaHtml += `<span class="badge badge-info">Rating: ${problem.cf_rating}</span>`;
            }
            if (problem.contest_date) {
                metaHtml += `<span class="badge badge-info">Date: ${escapeHtml(problem.contest_date.split('T')[0])}</span>`;
            }
            if (problem.tags && problem.tags.length > 0) {
                problem.tags.forEach(tag => {
                    metaHtml += `<span class="badge badge-info">${escapeHtml(tag)}</span>`;
                });
            }
            html += `<div style="margin-bottom: 15px;">${metaHtml}</div>`;
        }

        // Show inputs/outputs if available
        if (problem.inputs && problem.inputs.length > 0) {
            html += `<div class="card"><h2>Inputs &amp; Outputs</h2>`;
            problem.inputs.forEach((inp, i) => {
                const out = (problem.outputs && problem.outputs[i]) || '';
                html += `
                    <div class="io-section" style="margin-bottom: 15px;">
                        <div class="task-section">
                            <h3>Input ${i + 1}</h3>
                            <pre class="code-block">${escapeHtml(inp)}</pre>
                        </div>
                        <div class="task-section">
                            <h3>Output</h3>
                            <pre class="code-block">${escapeHtml(out)}</pre>
                        </div>
                    </div>
                `;
            });
            html += `</div>`;
        }

        // Show test suite if available
        if (problem.test) {
            html += `
                <div class="card">
                    <h2>Test Suite</h2>
                    <pre class="code-block">${escapeHtml(problem.test)}</pre>
                </div>
            `;
        }

        // Navigation hint
        html += `
            <div class="navigation-hint">
                <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
                or return to the list view to filter by dataset source or search by name.
            </div>
        `;

        container.innerHTML = html;
        window.currentProblem = problem;
        return;
    }

    // --- CRUXEval task view (tasks have given/predict fields, no task_items) ---
    if (problem.tasks.length > 0 && problem.tasks[0].given !== undefined) {
        // Task selector
        html += `
            <div class="card">
                <h2>Tasks</h2>
                <div class="task-selector" id="task-selector">
        `;
        problem.tasks.forEach((task, idx) => {
            html += `
                <button class="task-btn ${idx === 0 ? 'active' : ''}"
                        onclick="showCruxTask(${idx})">
                    ${escapeHtml(task.name)}
                </button>
            `;
        });
        html += `
                </div>
                <div id="task-content"></div>
            </div>
        `;

        // Navigation hint
        html += `
            <div class="navigation-hint">
                <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
                or return to the list view to filter by dataset source or search by name.
            </div>
        `;

        container.innerHTML = html;
        window.currentProblem = problem;
        showCruxTask(0);
        return;
    }

    // --- DREval (full) view with tasks, coverage, arrows ---
    // Rebuild html cleanly with coverage legend and SVG overlay
    html = `
        <div class="card">
            <div class="problem-header">
                <h2>${escapeHtml(problem.entry_point)}</h2>
                <span class="badge ${badgeClass(problem.source)}">${escapeHtml(problem.source)}</span>
            </div>
            <div class="problem-meta">
                <div class="meta-item">
                    <span class="meta-label">Task ID:</span>
                    <span class="meta-value">${escapeHtml(problem.task_id)}</span>
                </div>
                <div class="meta-item">
                    <span class="meta-label">Index:</span>
                    <span class="meta-value">${problem.idx}</span>
                </div>
                <div class="meta-item">
                    <span class="meta-label">Dataset:</span>
                    <span class="meta-value">${escapeHtml(datasetName)}</span>
                </div>
                <div class="meta-item">
                    <span class="meta-label">Test Inputs:</span>
                    <span class="meta-value">${problem.inputs.length}</span>
                </div>
            </div>
        </div>

        <div class="card">
            <h2>Source Code</h2>
            <div class="coverage-legend" id="coverage-legend">
                <strong>Coverage:</strong>
                <span class="coverage-legend-item">
                    <span class="coverage-swatch" style="background:#d4edda; border:1px solid #28a745;"></span>
                    Executed
                </span>
                <span class="coverage-legend-item">
                    <span class="coverage-swatch" style="background:#f8d7da; border:1px solid #dc3545;"></span>
                    Not executed
                </span>
            </div>
            <div class="code-with-tasks" id="code-container">
                ${problem.highlighted_code}
                <svg id="arrow-overlay" xmlns="http://www.w3.org/2000/svg">
                    <defs>
                        <marker id="arrowhead" markerWidth="8" markerHeight="6"
                                refX="8" refY="3" orient="auto">
                            <polygon points="0 0, 8 3, 0 6" class="exec-arrow-head"/>
                        </marker>
                    </defs>
                </svg>
            </div>
        </div>
    `;

    // Task selector
    html += `
        <div class="card">
            <h2>Test Cases & Tasks</h2>
            <p>Select a test input to view associated reasoning tasks:</p>
            <div class="task-selector" id="task-selector">
    `;

    problem.tasks.forEach((task, idx) => {
        html += `
            <button class="task-btn ${idx === 0 ? 'active' : ''}"
                    onclick="showTask(${idx})">
                Input ${task.input_idx + 1}
            </button>
        `;
    });

    html += `
            </div>
            <div id="task-content"></div>
        </div>
    `;

    // Navigation hint
    html += `
        <div class="navigation-hint">
            <strong>Tip:</strong> Use the Previous/Next buttons at the top to browse through problems,
            or return to the list view to filter by dataset source or search by name.
        </div>
    `;

    container.innerHTML = html;

    // Store problem data globally
    window.currentProblem = problem;

    // Show first task by default
    showTask(0);
}

function injectTaskMarkers(taskItems) {
    const codePre = document.querySelector('.source .code pre');

    // Save the pristine original innerHTML once, before any modification.
    if (codePre && !window._codePreOriginalHtml) {
        window._codePreOriginalHtml = codePre.innerHTML;
    }

    // Invalidate span cache (rebuilt lazily on next arrow draw)
    window._linenoSpanCache = null;

    // Store current task items so applyCoverage can re-add markers after wrapping.
    window._currentTaskItems = taskItems || [];

    // Reset code pre to original, then add markers from scratch.
    if (codePre && window._codePreOriginalHtml) {
        codePre.innerHTML = window._codePreOriginalHtml;
    }

    if (!taskItems || taskItems.length === 0) {
        return;
    }

    // Group tasks by line number
    const tasksByLine = {};
    taskItems.forEach(item => {
        if (!tasksByLine[item.lineno]) tasksByLine[item.lineno] = [];
        tasksByLine[item.lineno].push(item.var);
    });

    // Inject task marker badges into the code pre
    if (!codePre) return;
    const codeLines = codePre.innerHTML.split('\n');
    codePre.innerHTML = codeLines.map((line, idx) => {
        const lineNum = idx + 1;
        if (tasksByLine[lineNum] && line.trim() !== '') {
            const vars = tasksByLine[lineNum];
            return line + `<span class="task-marker" data-lineno="${lineNum}" data-vars="${escapeHtml(vars.join(', '))}">${escapeHtml(vars.join(', '))}</span>`;
        }
        return line;
    }).join('\n');

}

function applyCoverage(coverageSet, totalLines) {
    // Remove previous coverage classes from lineno spans.
    document.querySelectorAll('td.linenos .normal').forEach(el => {
        el.classList.remove('line-executed', 'line-not-executed');
    });

    if (!coverageSet) {
        const legend = document.getElementById('coverage-legend');
        if (legend) legend.style.display = 'none';
        return;
    }

    const legend = document.getElementById('coverage-legend');
    if (legend) legend.style.display = 'block';

    // Color lineno spans only.
    document.querySelectorAll('td.linenos .normal').forEach(span => {
        const lineNum = parseInt(span.textContent.trim());
        if (!isNaN(lineNum) && lineNum <= totalLines) {
            span.classList.add(coverageSet.has(lineNum) ? 'line-executed' : 'line-not-executed');
        }
    });
}

// Global map: lineno -> list of next line numbers (1-indexed; -1 = end of trace)
window._nextLinesMap = {};

async function loadAndApplyGroundTruth(problemIdx, inputIdx, taskItems) {
    // Show "loading" placeholders on all task items
    taskItems.forEach(item => {
        const el = document.getElementById(`gt-${item.lineno}-${item.var}`);
        if (el) { el.textContent = '…'; el.className = 'gt-answer loading'; }
    });

    // Clear next-lines data from previous input
    window._nextLinesMap = {};

    try {
        const resp = await fetch(`/api/${datasetSlug}/problem/${problemIdx}/ground_truth/${inputIdx}`);
        const gt = await resp.json();

        if (gt.status !== 'ok') {
            taskItems.forEach(item => {
                const el = document.getElementById(`gt-${item.lineno}-${item.var}`);
                if (el) { el.textContent = gt.status === 'error' ? '(exec error)' : '(unavailable)'; el.className = 'gt-answer'; }
            });
            applyCoverage(null, 0);
            return;
        }

        // Apply coverage highlighting
        const coverageSet = new Set(gt.coverage);
        applyCoverage(coverageSet, gt.total_lines);

        // Fill in variable answers
        const answerMap = {};
        gt.variable_answers.forEach(a => {
            answerMap[`${a.lineno}-${a.var}`] = a.answer_str;
        });
        taskItems.forEach(item => {
            const el = document.getElementById(`gt-${item.lineno}-${item.var}`);
            if (el) {
                const answer = answerMap[`${item.lineno}-${item.var}`] || '(not available)';
                el.textContent = answer;
                el.className = 'gt-answer';
            }
        });

        // Store next-lines data for arrow visualization
        if (gt.next_lines_answers) {
            gt.next_lines_answers.forEach(a => {
                window._nextLinesMap[a.lineno] = a.next_lines;
            });
        }

        // Attach hover handlers to task-marker spans now that we have next-lines data
        attachArrowHoverHandlers();

    } catch (e) {
        taskItems.forEach(item => {
            const el = document.getElementById(`gt-${item.lineno}-${item.var}`);
            if (el) { el.textContent = '(error)'; el.className = 'gt-answer'; }
        });
    }
}

// Cache of lineNum → DOM span, rebuilt whenever injectTaskMarkers runs.
window._linenoSpanCache = null;

function buildLinenoSpanCache(container) {
    const cache = {};
    container.querySelectorAll('td.linenos .normal').forEach(span => {
        const n = parseInt(span.textContent.trim());
        if (!isNaN(n)) cache[n] = span;
    });
    window._linenoSpanCache = cache;
}

/**
 * Get the bounding rect of the lineno span for a given 1-indexed line number,
 * relative to the code container element. Uses a cached span map.
 */
function getLinenoSpanRect(lineNum, container) {
    if (!window._linenoSpanCache) buildLinenoSpanCache(container);
    const span = window._linenoSpanCache[lineNum];
    if (!span) return null;
    const spanRect = span.getBoundingClientRect();
    const containerRect = container.getBoundingClientRect();
    return {
        top: spanRect.top - containerRect.top + container.scrollTop,
        bottom: spanRect.bottom - containerRect.top + container.scrollTop,
        left: spanRect.left - containerRect.left,
        right: spanRect.right - containerRect.left,
        width: spanRect.width,
        height: spanRect.height,
        midY: (spanRect.top + spanRect.bottom) / 2 - containerRect.top + container.scrollTop,
    };
}

/**
 * Draw arrows from sourceLine to each of the targetLines in the SVG overlay.
 * Lines are 1-indexed. -1 means "end of execution" (no arrow drawn).
 */
function drawArrows(sourceLineNum, targetLineNums) {
    const container = document.getElementById('code-container');
    const svg = document.getElementById('arrow-overlay');
    if (!container || !svg) return;

    // Remove previous arrows (but keep defs)
    svg.querySelectorAll('.arrow-path').forEach(el => el.remove());

    const srcRect = getLinenoSpanRect(sourceLineNum, container);
    if (!srcRect) return;

    // Update SVG height to match container
    svg.setAttribute('height', container.scrollHeight);

    targetLineNums.forEach(targetLineNum => {
        if (targetLineNum === -1) return;  // end of trace — no arrow

        const dstRect = getLinenoSpanRect(targetLineNum, container);
        if (!dstRect) return;

        // Start point: right edge of source lineno span, vertically centered
        const x1 = srcRect.right + 2;
        const y1 = srcRect.midY;

        // End point: right edge of target lineno span, vertically centered
        const x2 = dstRect.right + 2;
        const y2 = dstRect.midY;

        // Horizontal offset for the bezier control points — curves to the right
        const curveOffset = Math.max(30, Math.abs(y2 - y1) * 0.4);

        // Cubic bezier: both control points extend to the right of the lineno column
        const cx1 = x1 + curveOffset;
        const cy1 = y1;
        const cx2 = x2 + curveOffset;
        const cy2 = y2;

        const path = document.createElementNS('http://www.w3.org/2000/svg', 'path');
        path.setAttribute('d', `M ${x1} ${y1} C ${cx1} ${cy1}, ${cx2} ${cy2}, ${x2} ${y2}`);
        path.setAttribute('class', 'exec-arrow arrow-path');
        path.setAttribute('marker-end', 'url(#arrowhead)');
        svg.appendChild(path);
    });
}

/**
 * Clear all arrows from the SVG overlay.
 */
function clearArrows() {
    const svg = document.getElementById('arrow-overlay');
    if (svg) {
        svg.querySelectorAll('.arrow-path').forEach(el => el.remove());
    }
}

// AbortController for the current set of marker hover listeners.
let _markerListenersAbort = null;

/**
 * Attach mouseenter/mouseleave handlers to all .task-marker spans so that
 * hovering shows execution-flow arrows to next lines.
 */
function attachArrowHoverHandlers() {
    // Cancel any previously attached listeners without touching the DOM.
    if (_markerListenersAbort) _markerListenersAbort.abort();
    _markerListenersAbort = new AbortController();
    const { signal } = _markerListenersAbort;

    document.querySelectorAll('.task-marker').forEach(marker => {
        marker.addEventListener('mouseenter', () => {
            const lineNum = parseInt(marker.dataset.lineno);
            if (!lineNum) return;
            const nextLines = window._nextLinesMap[lineNum];
            if (nextLines && nextLines.length > 0) {
                drawArrows(lineNum, nextLines);
            }
        }, { signal });

        marker.addEventListener('mouseleave', () => {
            clearArrows();
        }, { signal });
    });
}

function showCruxTask(taskIdx) {
    const problem = window.currentProblem;
    const task = problem.tasks[taskIdx];

    // Update active button
    document.querySelectorAll('.task-btn').forEach((btn, idx) => {
        btn.classList.toggle('active', idx === taskIdx);
    });

    const givenLabel = task.given === 'input' ? 'Input (given)' : 'Output (given)';
    const predictLabel = task.predict === 'output' ? 'Output (predict)' : 'Input (predict)';
    const givenValue = task.given === 'input' ? task.input : task.output;
    const predictValue = task.predict === 'output' ? task.output : task.input;

    const html = `
        <div class="task-details">
            <div class="task-section">
                <p style="margin-bottom: 12px; color: #7f8c8d;">${escapeHtml(task.description)}</p>
            </div>
            <div class="io-section">
                <div class="task-section">
                    <h3>${escapeHtml(givenLabel)}</h3>
                    <pre class="code-block">${escapeHtml(givenValue)}</pre>
                </div>
                <div class="task-section">
                    <h3>${escapeHtml(predictLabel)}</h3>
                    <pre class="code-block crux-answer">${escapeHtml(predictValue)}</pre>
                </div>
            </div>
        </div>
    `;

    document.getElementById('task-content').innerHTML = html;
}

function showTask(taskIdx) {
    const problem = window.currentProblem;
    const task = problem.tasks[taskIdx];

    // Update active button
    const buttons = document.querySelectorAll('.task-btn');
    buttons.forEach((btn, idx) => {
        if (idx === taskIdx) {
            btn.classList.add('active');
        } else {
            btn.classList.remove('active');
        }
    });

    // Inject task markers into the code
    injectTaskMarkers(task.task_items);

    // Clear previous coverage while new one loads
    applyCoverage(null, 0);

    // Render task content
    const ioSection = task.test_class_code
        ? `<div class="io-section">
               <div class="task-section">
                   <h3>Input</h3>
                   <pre class="code-block">${escapeHtml(task.input)}</pre>
               </div>
           </div>
           <div class="task-section">
               <h3>Test Class &mdash; <code>${escapeHtml(task.test_class_name)}</code></h3>
               <pre class="code-block">${escapeHtml(task.test_class_code)}</pre>
           </div>`
        : `<div class="io-section">
               <div class="task-section">
                   <h3>Input</h3>
                   <pre class="code-block">${escapeHtml(task.input)}</pre>
               </div>
               <div class="task-section">
                   <h3>Expected Output</h3>
                   <pre class="code-block">${escapeHtml(task.output)}</pre>
               </div>
           </div>`;

    let html = `
        <div class="task-details">
            ${ioSection}
    `;

    // Show task items with ground truth answer placeholders
    if (task.task_items && task.task_items.length > 0) {
        html += `
            <div class="task-section">
                <h3>Reasoning Tasks</h3>
                <p style="margin-bottom: 10px; color: #7f8c8d;">
                    Variable state at each execution point (correct answer shown in
                    <span style="background:#17a2b8;color:white;padding:1px 6px;border-radius:3px;font-size:0.82rem;">teal</span>):
                </p>
                <ul class="task-items-list">
        `;

        task.task_items.forEach(item => {
            html += `
                <li>
                    <span class="line-ref">Line ${item.lineno}</span>
                    <span class="var-name">${escapeHtml(item.var)}</span>
                    <span class="gt-answer loading" id="gt-${item.lineno}-${item.var}">…</span>
                </li>
            `;
        });

        html += `
                </ul>
            </div>
        `;
    }

    // Show output prediction task if exists
    if (task.output_pred) {
        html += `
            <div class="task-section">
                <h3>Output Completion Task</h3>
                <p style="margin-bottom: 10px; color: #7f8c8d;">
                    The model needs to complete this test assertion:
                </p>
                <pre class="code-block">${escapeHtml(task.output_pred)}</pre>
            </div>
        `;
    }

    html += `</div>`;

    document.getElementById('task-content').innerHTML = html;

    // Fetch and apply ground truth (coverage + variable answers)
    if (hasGroundTruth && task.task_items) {
        loadAndApplyGroundTruth(problem.idx, task.input_idx, task.task_items);
    }
}

function showLangTab(idx) {
    // Only toggle tabs within the #lang-tabs container (not code-mode tabs)
    const langTabsContainer = document.getElementById('lang-tabs');
    if (langTabsContainer) {
        langTabsContainer.querySelectorAll('.lang-tab').forEach((tab, i) => {
            tab.classList.toggle('active', i === idx);
        });
    }
    document.querySelectorAll('.lang-code-panel').forEach((panel, i) => {
        panel.classList.toggle('active', i === idx);
    });
    // Re-apply the current code mode (canonical/buggy) to the newly visible panel
    if (window._currentCodeMode) {
        const problem = window.currentProblem;
        if (problem && problem.lang_solutions) {
            const sol = problem.lang_solutions[idx];
            if (sol) {
                const canonical = document.getElementById('lang-code-canonical-' + idx);
                const buggy = document.getElementById('lang-code-buggy-' + idx);
                if (canonical) canonical.style.display = window._currentCodeMode === 'canonical' ? '' : 'none';
                if (buggy) buggy.style.display = window._currentCodeMode === 'buggy' ? '' : 'none';
                // If buggy mode is selected but this language has no buggy code, fall back to canonical
                if (window._currentCodeMode === 'buggy' && !buggy && canonical) {
                    canonical.style.display = '';
                }
            }
        }
    }
    // Update test section
    const problem = window.currentProblem;
    if (problem && problem.lang_solutions) {
        const sol = problem.lang_solutions[idx];
        const testContainer = document.getElementById('lang-test-container');
        if (testContainer && sol && sol.test) {
            testContainer.innerHTML = `<h2>Test Suite</h2><pre class="code-block">${escapeHtml(sol.test)}</pre>`;
        } else if (testContainer) {
            testContainer.innerHTML = '';
        }
    }
}

function toggleCodeMode(mode) {
    window._currentCodeMode = mode;
    const problem = window.currentProblem;
    if (!problem || !problem.lang_solutions) return;

    // Update mode tabs
    const modeTabs = document.querySelectorAll('#code-mode-tabs .lang-tab');
    modeTabs.forEach(tab => {
        tab.classList.toggle('active', tab.textContent.trim().toLowerCase() === mode);
    });

    // Toggle visibility of canonical/buggy code in all panels
    problem.lang_solutions.forEach((sol, i) => {
        const canonical = document.getElementById('lang-code-canonical-' + i);
        const buggy = document.getElementById('lang-code-buggy-' + i);
        if (canonical) canonical.style.display = mode === 'canonical' ? '' : 'none';
        if (buggy) buggy.style.display = mode === 'buggy' ? '' : 'none';
    });
}

function showFimTab(idx) {
    const tabs = document.querySelectorAll('#fim-tabs .lang-tab');
    tabs.forEach((tab, i) => tab.classList.toggle('active', i === idx));
    for (let i = 0; i < 3; i++) {
        const panel = document.getElementById('fim-panel-' + i);
        if (panel) panel.classList.toggle('active', i === idx);
    }
}

/**
 * Split a unified diff into per-file sections and render each with a GitHub-style
 * file header bar. Returns an HTML string with one card per file.
 */
function renderDiffFiles(diffText, title) {
    if (!diffText) return '';
    // Split into per-file chunks by "diff --git" boundaries
    const files = [];
    let current = null;
    diffText.split('\n').forEach(line => {
        if (line.startsWith('diff --git')) {
            if (current) files.push(current);
            // Extract file path from "diff --git a/path b/path"
            const m = line.match(/^diff --git a\/(.+?) b\/(.+)/);
            const filePath = m ? m[2] : line;
            current = { path: filePath, lines: [line] };
        } else if (current) {
            current.lines.push(line);
        } else {
            // Lines before any diff header — create a default section
            if (!current) current = { path: '', lines: [] };
            current.lines.push(line);
        }
    });
    if (current) files.push(current);

    if (files.length === 0) return '';

    let html = '';
    if (files.length === 1 && !files[0].path) {
        // Single unnamed diff — render as before
        html += `<div class="card"><h2>${escapeHtml(title)}</h2><div class="diff-view">${renderDiff(diffText)}</div></div>`;
    } else {
        html += `<div class="card"><h2>${escapeHtml(title)}</h2>`;
        files.forEach(file => {
            const diffChunk = file.lines.join('\n');
            // Count additions/deletions
            let adds = 0, dels = 0;
            file.lines.forEach(l => {
                if (l.startsWith('+') && !l.startsWith('+++')) adds++;
                if (l.startsWith('-') && !l.startsWith('---')) dels++;
            });
            const statsHtml = `<span class="diff-file-stats"><span class="diff-stat-add">+${adds}</span> <span class="diff-stat-del">-${dels}</span></span>`;
            html += `
                <div class="diff-file-section">
                    <div class="diff-file-header">
                        <span class="diff-file-path">${escapeHtml(file.path)}</span>
                        ${statsHtml}
                    </div>
                    <div class="diff-view">${renderDiff(diffChunk)}</div>
                </div>
            `;
        });
        html += `</div>`;
    }
    return html;
}

/**
 * Render a unified diff with line numbers and file headers (GitHub-style).
 */
function renderDiff(diffText) {
    if (!diffText) return '';
    const lines = diffText.split('\n');
    let oldLine = 0, newLine = 0;
    const rows = [];

    lines.forEach(line => {
        if (line.startsWith('diff ')) {
            rows.push(`<tr class="diff-tr-header"><td class="diff-ln"></td><td class="diff-ln"></td><td class="diff-td-header">${escapeHtml(line)}</td></tr>`);
            return;
        }
        if (line.startsWith('---') || line.startsWith('+++')) {
            rows.push(`<tr class="diff-tr-header"><td class="diff-ln"></td><td class="diff-ln"></td><td class="diff-td-header">${escapeHtml(line)}</td></tr>`);
            return;
        }
        if (line.startsWith('@@')) {
            // Parse hunk header: @@ -oldStart,oldCount +newStart,newCount @@
            const m = line.match(/@@ -(\d+)(?:,\d+)? \+(\d+)(?:,\d+)? @@/);
            if (m) {
                oldLine = parseInt(m[1]);
                newLine = parseInt(m[2]);
            }
            rows.push(`<tr class="diff-tr-hunk"><td class="diff-ln"></td><td class="diff-ln"></td><td class="diff-td-hunk">${escapeHtml(line)}</td></tr>`);
            return;
        }
        if (line.startsWith('+')) {
            rows.push(`<tr class="diff-tr-add"><td class="diff-ln"></td><td class="diff-ln">${newLine}</td><td class="diff-td-add">${escapeHtml(line.substring(1))}</td></tr>`);
            newLine++;
        } else if (line.startsWith('-')) {
            rows.push(`<tr class="diff-tr-del"><td class="diff-ln">${oldLine}</td><td class="diff-ln"></td><td class="diff-td-del">${escapeHtml(line.substring(1))}</td></tr>`);
            oldLine++;
        } else if (line.startsWith(' ')) {
            rows.push(`<tr class="diff-tr-ctx"><td class="diff-ln">${oldLine}</td><td class="diff-ln">${newLine}</td><td class="diff-td-ctx">${escapeHtml(line.substring(1))}</td></tr>`);
            oldLine++;
            newLine++;
        } else if (line.trim() === '') {
            // Empty trailing line
        } else {
            rows.push(`<tr class="diff-tr-ctx"><td class="diff-ln">${oldLine}</td><td class="diff-ln">${newLine}</td><td class="diff-td-ctx">${escapeHtml(line)}</td></tr>`);
            oldLine++;
            newLine++;
        }
    });

    return `<table class="diff-table">${rows.join('')}</table>`;
}

/**
 * Simple line-by-line diff (LCS-based) between two code strings.
 * Returns an array of {type: 'context'|'add'|'del', line: string}.
 */
function computeUnifiedDiff(oldText, newText) {
    const oldLines = (oldText || '').split('\n');
    const newLines = (newText || '').split('\n');

    // LCS for line sequences
    const m = oldLines.length, n = newLines.length;
    // For very large files, just show both in full instead of computing LCS
    if (m * n > 500000) {
        const result = [];
        oldLines.forEach(l => result.push({type: 'del', line: l}));
        newLines.forEach(l => result.push({type: 'add', line: l}));
        return result;
    }

    const dp = Array.from({length: m + 1}, () => new Uint16Array(n + 1));
    for (let i = 1; i <= m; i++) {
        for (let j = 1; j <= n; j++) {
            if (oldLines[i - 1] === newLines[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
    const result = [];
    let i = m, j = n;
    while (i > 0 || j > 0) {
        if (i > 0 && j > 0 && oldLines[i - 1] === newLines[j - 1]) {
            result.push({type: 'context', line: oldLines[i - 1]});
            i--; j--;
        } else if (j > 0 && (i === 0 || dp[i][j - 1] >= dp[i - 1][j])) {
            result.push({type: 'add', line: newLines[j - 1]});
            j--;
        } else {
            result.push({type: 'del', line: oldLines[i - 1]});
            i--;
        }
    }
    result.reverse();

    // Compact: only show hunks with context (3 lines around changes)
    const contextSize = 3;
    const hasChange = result.map(r => r.type !== 'context');
    const show = new Uint8Array(result.length);
    for (let k = 0; k < result.length; k++) {
        if (hasChange[k]) {
            for (let c = Math.max(0, k - contextSize); c <= Math.min(result.length - 1, k + contextSize); c++) {
                show[c] = 1;
            }
        }
    }

    const compacted = [];
    let lastShown = -1;
    for (let k = 0; k < result.length; k++) {
        if (show[k]) {
            if (lastShown >= 0 && k - lastShown > 1) {
                compacted.push({type: 'separator', line: '...'});
            }
            compacted.push(result[k]);
            lastShown = k;
        }
    }

    return compacted.length > 0 ? compacted : result;
}

/**
 * Render the output of computeUnifiedDiff into diff HTML with line numbers.
 */
function renderComputedDiff(diffEntries) {
    let oldLine = 1, newLine = 1;
    const rows = diffEntries.map(entry => {
        if (entry.type === 'separator') {
            return `<tr class="diff-tr-hunk"><td class="diff-ln"></td><td class="diff-ln"></td><td class="diff-td-hunk">${escapeHtml(entry.line)}</td></tr>`;
        }
        if (entry.type === 'del') {
            const row = `<tr class="diff-tr-del"><td class="diff-ln">${oldLine}</td><td class="diff-ln"></td><td class="diff-td-del">${escapeHtml(entry.line)}</td></tr>`;
            oldLine++;
            return row;
        }
        if (entry.type === 'add') {
            const row = `<tr class="diff-tr-add"><td class="diff-ln"></td><td class="diff-ln">${newLine}</td><td class="diff-td-add">${escapeHtml(entry.line)}</td></tr>`;
            newLine++;
            return row;
        }
        // context
        const row = `<tr class="diff-tr-ctx"><td class="diff-ln">${oldLine}</td><td class="diff-ln">${newLine}</td><td class="diff-td-ctx">${escapeHtml(entry.line)}</td></tr>`;
        oldLine++;
        newLine++;
        return row;
    });
    return `<table class="diff-table">${rows.join('')}</table>`;
}

function escapeHtml(text) {
    if (text === null || text === undefined) return '';
    const div = document.createElement('div');
    div.textContent = text;
    return div.innerHTML;
}

loadProblem();