// KnowledgeBasePage.js
// Full-page knowledge base library — browse, search, filter, and read
// articles inline. Upload and delete require editor/admin role.
// Reuses existing KnowledgeBaseViewer and KnowledgeBaseModal components.

import React, { useState, useEffect, useCallback, useMemo } from 'react';
import {
    BookOpen, Search, Upload, RefreshCw, Loader,
    AlertCircle, FileText, File, Trash2, X,
} from 'lucide-react';
import { useAuth } from '../../contexts/AuthContext';
import KnowledgeBaseModal from '../KnowledgeBaseModal';
import KnowledgeBaseViewer from '../KnowledgeBaseViewer';

const API_BASE  = process.env.REACT_APP_API_BASE || 'http://localhost:3001/api';
const GREEN     = '#10B981';

// ---------------------------------------------------------------------------
// Static config
// ---------------------------------------------------------------------------
const CATEGORY_COLORS = {
    General:   '#94A3B8',
    Policy:    '#0EA5E9',
    Procedure: GREEN,
    Guide:     '#F59E0B',
    Reference: '#8B5CF6',
};

const FILE_EXT_COLORS = {
    pdf:  '#EF4444',
    md:   '#10B981',
    txt:  '#94A3B8',
    doc:  '#0EA5E9',
    docx: '#0EA5E9',
    xls:  '#10B981',
    xlsx: '#10B981',
    ppt:  '#F97316',
    pptx: '#F97316',
    html: '#8B5CF6',
};

const CATEGORY_ORDER = ['Procedure', 'Guide', 'Policy', 'Reference', 'General'];

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------
function extOf(filename) {
    return (filename || '').split('.').pop().toLowerCase();
}

function extColor(filename) {
    return FILE_EXT_COLORS[extOf(filename)] || '#64748B';
}

function fmtSize(bytes) {
    if (!bytes) return '';
    if (bytes < 1024)        return `${bytes} B`;
    if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
    return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
}

function fmtDate(str) {
    if (!str) return '';
    return new Date(str).toLocaleDateString('en-US', { year: 'numeric', month: 'short', day: 'numeric' });
}

function catColor(cat) {
    return CATEGORY_COLORS[cat] || '#94A3B8';
}

// ---------------------------------------------------------------------------
// ArticleCard
// ---------------------------------------------------------------------------
function ArticleCard({ article, selected, onSelect, onDelete, canDelete }) {
    const color    = catColor(article.category);
    const fileColor = extColor(article.file_name);
    const ext      = extOf(article.file_name).toUpperCase();

    return (
        <div
            onClick={() => onSelect(article)}
            style={{
                background: selected
                    ? `linear-gradient(135deg,rgba(16,185,129,0.1) 0%,rgba(15,23,42,0.98) 100%)`
                    : 'linear-gradient(135deg,rgba(30,41,59,0.95) 0%,rgba(15,23,42,0.98) 100%)',
                border: `1.5px solid ${selected ? GREEN : 'rgba(16,185,129,0.12)'}`,
                borderRadius: '0.5rem',
                padding: '1rem',
                cursor: 'pointer',
                transition: 'all 0.15s',
                position: 'relative',
                display: 'flex',
                flexDirection: 'column',
                gap: '0.5rem',
            }}
            onMouseEnter={e => { if (!selected) e.currentTarget.style.borderColor = 'rgba(16,185,129,0.35)'; }}
            onMouseLeave={e => { if (!selected) e.currentTarget.style.borderColor = 'rgba(16,185,129,0.12)'; }}
        >
            {/* File type badge + delete button */}
            <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center' }}>
                <span style={{
                    fontFamily: 'monospace', fontSize: '0.58rem', fontWeight: '700',
                    color: fileColor, padding: '0.15rem 0.4rem',
                    background: `${fileColor}15`, borderRadius: '0.2rem',
                    border: `1px solid ${fileColor}30`,
                }}>
                    {ext}
                </span>
                {canDelete && (
                    <button
                        onClick={e => { e.stopPropagation(); onDelete(article); }}
                        title="Delete article"
                        style={{
                            background: 'none', border: 'none', cursor: 'pointer',
                            color: '#334155', padding: '0.15rem',
                            borderRadius: '0.2rem', display: 'flex', alignItems: 'center',
                        }}
                        onMouseEnter={e => { e.currentTarget.style.color = '#EF4444'; }}
                        onMouseLeave={e => { e.currentTarget.style.color = '#334155'; }}
                    >
                        <Trash2 style={{ width: '12px', height: '12px' }} />
                    </button>
                )}
            </div>

            {/* Title */}
            <div style={{
                fontFamily: 'monospace', fontSize: '0.82rem', fontWeight: '700',
                color: selected ? GREEN : '#E2E8F0',
                lineHeight: 1.3,
            }}>
                {article.title}
            </div>

            {/* Description */}
            {article.description && (
                <div style={{
                    fontSize: '0.7rem', color: '#475569',
                    lineHeight: 1.45, display: '-webkit-box',
                    WebkitLineClamp: 2, WebkitBoxOrient: 'vertical',
                    overflow: 'hidden',
                }}>
                    {article.description}
                </div>
            )}

            {/* Footer — category + date */}
            <div style={{ display: 'flex', alignItems: 'center', justifyContent: 'space-between', marginTop: 'auto', paddingTop: '0.375rem', borderTop: '1px solid rgba(255,255,255,0.04)' }}>
                <span style={{
                    fontFamily: 'monospace', fontSize: '0.6rem', fontWeight: '600',
                    color, padding: '0.15rem 0.4rem',
                    background: `${color}12`, borderRadius: '0.2rem',
                    border: `1px solid ${color}25`,
                    textTransform: 'uppercase', letterSpacing: '0.04em',
                }}>
                    {article.category}
                </span>
                <div style={{ display: 'flex', gap: '0.5rem', alignItems: 'center' }}>
                    {article.file_size && (
                        <span style={{ fontFamily: 'monospace', fontSize: '0.6rem', color: '#334155' }}>
                            {fmtSize(article.file_size)}
                        </span>
                    )}
                    <span style={{ fontFamily: 'monospace', fontSize: '0.6rem', color: '#334155' }}>
                        {fmtDate(article.created_at)}
                    </span>
                </div>
            </div>
        </div>
    );
}

// ---------------------------------------------------------------------------
// Empty state
// ---------------------------------------------------------------------------
function EmptyState({ hasFilter, onClear }) {
    return (
        <div style={{
            gridColumn: '1 / -1',
            display: 'flex', flexDirection: 'column', alignItems: 'center',
            justifyContent: 'center', padding: '4rem 2rem',
            border: '1px dashed rgba(16,185,129,0.15)', borderRadius: '0.5rem',
            color: '#334155',
        }}>
            <BookOpen style={{ width: '36px', height: '36px', marginBottom: '1rem', opacity: 0.4 }} />
            <div style={{ fontFamily: 'monospace', fontSize: '0.8rem', marginBottom: '0.375rem' }}>
                {hasFilter ? 'No articles match your search' : 'No articles yet'}
            </div>
            {hasFilter ? (
                <button onClick={onClear} style={{
                    background: 'none', border: 'none', cursor: 'pointer',
                    color: GREEN, fontFamily: 'monospace', fontSize: '0.72rem',
                    marginTop: '0.375rem',
                }}>
                    Clear filters
                </button>
            ) : (
                <div style={{ fontFamily: 'monospace', fontSize: '0.7rem', color: '#475569' }}>
                    Upload a document to get started
                </div>
            )}
        </div>
    );
}

// ---------------------------------------------------------------------------
// Main page
// ---------------------------------------------------------------------------
export default function KnowledgeBasePage() {
    const { canWrite } = useAuth();

    const [articles,     setArticles]     = useState([]);
    const [loading,      setLoading]      = useState(true);
    const [error,        setError]        = useState(null);
    const [search,       setSearch]       = useState('');
    const [activeCategory, setActiveCategory] = useState('All');
    const [selected,     setSelected]     = useState(null);
    const [showUpload,   setShowUpload]   = useState(false);

    // -------------------------------------------------------------------------
    // Fetch
    // -------------------------------------------------------------------------
    const fetchArticles = useCallback(async () => {
        setLoading(true);
        setError(null);
        try {
            const res = await fetch(`${API_BASE}/knowledge-base`, { credentials: 'include' });
            if (!res.ok) throw new Error('Failed to load articles');
            const data = await res.json();
            setArticles(data);
        } catch (err) {
            setError(err.message);
        } finally {
            setLoading(false);
        }
    }, []);

    useEffect(() => { fetchArticles(); }, [fetchArticles]);

    // -------------------------------------------------------------------------
    // Delete
    // -------------------------------------------------------------------------
    const handleDelete = useCallback(async (article) => {
        if (!window.confirm(`Delete "${article.title}"? This cannot be undone.`)) return;
        try {
            const res = await fetch(`${API_BASE}/knowledge-base/${article.id}`, {
                method: 'DELETE', credentials: 'include',
            });
            if (!res.ok) throw new Error('Delete failed');
            setArticles(prev => prev.filter(a => a.id !== article.id));
            if (selected?.id === article.id) setSelected(null);
        } catch (err) {
            alert(`Failed to delete: ${err.message}`);
        }
    }, [selected]);

    // -------------------------------------------------------------------------
    // Filtering
    // -------------------------------------------------------------------------
    const filtered = useMemo(() => {
        const q = search.trim().toLowerCase();
        return articles.filter(a => {
            const matchesCat = activeCategory === 'All' || a.category === activeCategory;
            const matchesSearch = !q ||
                a.title.toLowerCase().includes(q) ||
                (a.description || '').toLowerCase().includes(q);
            return matchesCat && matchesSearch;
        });
    }, [articles, activeCategory, search]);

    // Category tab counts (always from full list, not filtered by search)
    const categoryCounts = useMemo(() => {
        const counts = { All: articles.length };
        CATEGORY_ORDER.forEach(cat => {
            counts[cat] = articles.filter(a => a.category === cat).length;
        });
        return counts;
    }, [articles]);

    const activeTabs = ['All', ...CATEGORY_ORDER.filter(c => categoryCounts[c] > 0)];

    const clearFilters = () => { setSearch(''); setActiveCategory('All'); };

    const hasFilter = search.trim() !== '' || activeCategory !== 'All';

    // -------------------------------------------------------------------------
    // Render
    // -------------------------------------------------------------------------
    return (
        <div style={{ display: 'flex', flexDirection: 'column', gap: '1.25rem', paddingBottom: '2rem' }}>

            {/* ── Page header ─────────────────────────────────────────── */}
            <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'flex-start' }}>
                <div>
                    <h2 style={{
                        fontFamily: 'monospace', fontSize: '1.5rem', fontWeight: '700',
                        color: GREEN, textTransform: 'uppercase', letterSpacing: '0.1em',
                        textShadow: `0 0 16px ${GREEN}40`, marginBottom: '0.25rem',
                    }}>
                        Knowledge Base
                    </h2>
                    <div style={{ fontSize: '0.72rem', color: '#475569', fontFamily: 'monospace' }}>
                        {loading ? '…' : `${articles.length} article${articles.length !== 1 ? 's' : ''}`}
                        {articles.length > 0 && activeCategory !== 'All' && (
                            <span style={{ marginLeft: '0.5rem', color: '#334155' }}>
                                · {categoryCounts[activeCategory] || 0} in {activeCategory}
                            </span>
                        )}
                    </div>
                </div>

                <div style={{ display: 'flex', gap: '0.5rem', flexShrink: 0 }}>
                    <button
                        onClick={fetchArticles}
                        title="Refresh"
                        style={{
                            background: 'none', border: `1px solid rgba(16,185,129,0.25)`,
                            borderRadius: '0.375rem', padding: '0.5rem', cursor: 'pointer', color: '#475569',
                        }}
                        onMouseEnter={e => { e.currentTarget.style.color = GREEN; e.currentTarget.style.borderColor = `${GREEN}60`; }}
                        onMouseLeave={e => { e.currentTarget.style.color = '#475569'; e.currentTarget.style.borderColor = 'rgba(16,185,129,0.25)'; }}
                    >
                        <RefreshCw style={{ width: '16px', height: '16px' }} />
                    </button>
                    {canWrite() && (
                        <button
                            onClick={() => setShowUpload(true)}
                            style={{
                                display: 'flex', alignItems: 'center', gap: '0.4rem',
                                background: `${GREEN}18`, border: `1px solid ${GREEN}`,
                                color: GREEN, padding: '0.5rem 1rem',
                                fontFamily: 'monospace', fontSize: '0.75rem', fontWeight: '600',
                                textTransform: 'uppercase', letterSpacing: '0.05em',
                                cursor: 'pointer', borderRadius: '0.375rem',
                            }}
                        >
                            <Upload style={{ width: '14px', height: '14px' }} />
                            Upload Article
                        </button>
                    )}
                </div>
            </div>

            {/* ── Search + category tabs ───────────────────────────────── */}
            <div style={{ display: 'flex', gap: '0.75rem', alignItems: 'center', flexWrap: 'wrap' }}>

                {/* Search */}
                <div style={{ position: 'relative', flexShrink: 0 }}>
                    <Search style={{
                        position: 'absolute', left: '0.625rem', top: '50%', transform: 'translateY(-50%)',
                        width: '13px', height: '13px', color: '#334155', pointerEvents: 'none',
                    }} />
                    <input
                        value={search}
                        onChange={e => setSearch(e.target.value)}
                        placeholder="Search articles…"
                        style={{
                            paddingLeft: '2rem', paddingRight: search ? '2rem' : '0.625rem',
                            paddingTop: '0.4rem', paddingBottom: '0.4rem',
                            background: 'rgba(15,23,42,0.8)',
                            border: '1px solid rgba(16,185,129,0.2)',
                            borderRadius: '0.375rem', color: '#E2E8F0',
                            outline: 'none', fontFamily: 'monospace', fontSize: '0.75rem',
                            width: '220px',
                        }}
                        onFocus={e => e.target.style.borderColor = `${GREEN}60`}
                        onBlur={e => e.target.style.borderColor = 'rgba(16,185,129,0.2)'}
                    />
                    {search && (
                        <button
                            onClick={() => setSearch('')}
                            style={{
                                position: 'absolute', right: '0.5rem', top: '50%', transform: 'translateY(-50%)',
                                background: 'none', border: 'none', cursor: 'pointer', color: '#334155', padding: 0,
                            }}
                        >
                            <X style={{ width: '12px', height: '12px' }} />
                        </button>
                    )}
                </div>

                {/* Category tabs */}
                <div style={{ display: 'flex', gap: '0.3rem', flexWrap: 'wrap' }}>
                    {activeTabs.map(cat => {
                        const isActive = activeCategory === cat;
                        const color    = cat === 'All' ? GREEN : catColor(cat);
                        return (
                            <button
                                key={cat}
                                onClick={() => setActiveCategory(cat)}
                                style={{
                                    padding: '0.35rem 0.75rem',
                                    fontFamily: 'monospace', fontSize: '0.7rem', fontWeight: '600',
                                    textTransform: 'uppercase', letterSpacing: '0.05em',
                                    cursor: 'pointer', borderRadius: '0.25rem',
                                    border: isActive ? `1px solid ${color}` : '1px solid transparent',
                                    background: isActive ? `${color}15` : 'transparent',
                                    color: isActive ? color : '#475569',
                                    transition: 'all 0.12s',
                                }}
                                onMouseEnter={e => { if (!isActive) { e.currentTarget.style.color = '#94A3B8'; e.currentTarget.style.borderColor = 'rgba(255,255,255,0.1)'; }}}
                                onMouseLeave={e => { if (!isActive) { e.currentTarget.style.color = '#475569'; e.currentTarget.style.borderColor = 'transparent'; }}}
                            >
                                {cat}
                                <span style={{ marginLeft: '0.35rem', opacity: 0.6, fontWeight: '400' }}>
                                    {categoryCounts[cat] ?? 0}
                                </span>
                            </button>
                        );
                    })}
                </div>
            </div>

            {/* ── Error state ──────────────────────────────────────────── */}
            {error && (
                <div style={{
                    display: 'flex', alignItems: 'center', gap: '0.5rem',
                    padding: '0.875rem 1rem',
                    background: 'rgba(239,68,68,0.08)', border: '1px solid rgba(239,68,68,0.3)',
                    borderRadius: '0.5rem', color: '#F87171',
                    fontFamily: 'monospace', fontSize: '0.78rem',
                }}>
                    <AlertCircle style={{ width: '15px', height: '15px', flexShrink: 0 }} />
                    {error}
                    <button
                        onClick={fetchArticles}
                        style={{ marginLeft: 'auto', background: 'none', border: 'none', cursor: 'pointer', color: '#F87171', fontFamily: 'monospace', fontSize: '0.72rem' }}
                    >
                        Retry
                    </button>
                </div>
            )}

            {/* ── Loading state ────────────────────────────────────────── */}
            {loading && (
                <div style={{ display: 'flex', justifyContent: 'center', padding: '3rem' }}>
                    <Loader style={{ width: '28px', height: '28px', color: GREEN, animation: 'spin 1s linear infinite' }} />
                </div>
            )}

            {/* ── Article grid ─────────────────────────────────────────── */}
            {!loading && !error && (
                <div style={{
                    display: 'grid',
                    gridTemplateColumns: 'repeat(auto-fill, minmax(240px, 1fr))',
                    gap: '0.875rem',
                }}>
                    {filtered.length === 0 ? (
                        <EmptyState hasFilter={hasFilter} onClear={clearFilters} />
                    ) : (
                        filtered.map(article => (
                            <ArticleCard
                                key={article.id}
                                article={article}
                                selected={selected?.id === article.id}
                                onSelect={a => setSelected(selected?.id === a.id ? null : a)}
                                onDelete={handleDelete}
                                canDelete={canWrite()}
                            />
                        ))
                    )}
                </div>
            )}

            {/* ── Inline viewer ────────────────────────────────────────── */}
            {selected && (
                <div style={{ marginTop: '0.25rem' }}>
                    <KnowledgeBaseViewer
                        article={selected}
                        onClose={() => setSelected(null)}
                    />
                </div>
            )}

            {/* ── Upload modal ─────────────────────────────────────────── */}
            {showUpload && (
                <KnowledgeBaseModal
                    onClose={() => setShowUpload(false)}
                    onUpdate={() => { fetchArticles(); setShowUpload(false); }}
                />
            )}
        </div>
    );
}