import os
import json
from datetime import datetime

from reportlab.lib.pagesizes import A4
from reportlab.lib.styles import getSampleStyleSheet, ParagraphStyle
from reportlab.lib.units import cm
from reportlab.lib import colors
from reportlab.lib.enums import TA_CENTER, TA_LEFT, TA_RIGHT
from reportlab.platypus import (
    SimpleDocTemplate, Paragraph, Spacer, Table, TableStyle, HRFlowable
)


def _styles():
    base = getSampleStyleSheet()
    custom = {
        'title': ParagraphStyle(
            'DocTitle', parent=base['Title'],
            fontSize=16, spaceAfter=6, alignment=TA_CENTER, textColor=colors.HexColor('#1a3a5c'),
        ),
        'subtitle': ParagraphStyle(
            'Subtitle', parent=base['Normal'],
            fontSize=10, spaceAfter=4, alignment=TA_CENTER, textColor=colors.HexColor('#555555'),
        ),
        'section': ParagraphStyle(
            'Section', parent=base['Heading2'],
            fontSize=11, spaceBefore=12, spaceAfter=4,
            textColor=colors.HexColor('#1a3a5c'), borderPad=2,
        ),
        'normal': base['Normal'],
        'small': ParagraphStyle(
            'Small', parent=base['Normal'], fontSize=8, textColor=colors.grey,
        ),
        'footer': ParagraphStyle(
            'Footer', parent=base['Normal'],
            fontSize=8, alignment=TA_CENTER, textColor=colors.grey,
        ),
        'signature_label': ParagraphStyle(
            'SigLabel', parent=base['Normal'], fontSize=9, alignment=TA_CENTER,
        ),
        'right': ParagraphStyle(
            'Right', parent=base['Normal'], alignment=TA_RIGHT,
        ),
    }
    return custom


def _header_table(company_name, company_address, doc_type_label, doc_id, created_at, styles):
    left_data = [
        [Paragraph(f'<b>{company_name}</b>', styles['normal'])],
        [Paragraph(company_address or '', styles['small'])],
    ]
    right_data = [
        [Paragraph(f'<b>{doc_type_label}</b>', styles['right'])],
        [Paragraph(f'Doc #: {doc_id}', styles['right'])],
        [Paragraph(f'Date: {created_at.strftime("%d/%m/%Y") if created_at else ""}', styles['right'])],
    ]
    table = Table(
        [[Table(left_data, colWidths=[9 * cm]), Table(right_data, colWidths=[8 * cm])]],
        colWidths=[9 * cm, 8 * cm],
    )
    table.setStyle(TableStyle([('VALIGN', (0, 0), (-1, -1), 'TOP')]))
    return table


def _field_table(rows, styles):
    """rows: list of (label, value) tuples."""
    data = [[Paragraph(f'<b>{label}</b>', styles['normal']), Paragraph(str(value or '—'), styles['normal'])]
            for label, value in rows]
    t = Table(data, colWidths=[5 * cm, 12 * cm])
    t.setStyle(TableStyle([
        ('BACKGROUND', (0, 0), (0, -1), colors.HexColor('#eaf0f8')),
        ('GRID', (0, 0), (-1, -1), 0.4, colors.HexColor('#cccccc')),
        ('VALIGN', (0, 0), (-1, -1), 'TOP'),
        ('TOPPADDING', (0, 0), (-1, -1), 4),
        ('BOTTOMPADDING', (0, 0), (-1, -1), 4),
        ('LEFTPADDING', (0, 0), (-1, -1), 6),
    ]))
    return t


def _signature_block(styles):
    data = [
        [Paragraph('Issued by (IT Dept.)', styles['signature_label']),
         Paragraph('Received by (Employee)', styles['signature_label'])],
        [Spacer(1, 1.5 * cm), Spacer(1, 1.5 * cm)],
        [HRFlowable(width='95%'), HRFlowable(width='95%')],
        [Paragraph('Name / Signature / Date', styles['signature_label']),
         Paragraph('Name / Signature / Date', styles['signature_label'])],
    ]
    t = Table(data, colWidths=[8.5 * cm, 8.5 * cm])
    t.setStyle(TableStyle([
        ('VALIGN', (0, 0), (-1, -1), 'MIDDLE'),
        ('ALIGN', (0, 0), (-1, -1), 'CENTER'),
    ]))
    return t


def generate_paperwork_pdf(doc, app):
    """
    Generate a PDF for a Paperwork document and save it to PDF_FOLDER.
    Returns the filename (not the full path).
    """
    pdf_dir = os.path.join(app.root_path, '..', app.config['PDF_FOLDER'])
    os.makedirs(pdf_dir, exist_ok=True)

    filename = f'doc_{doc.id}_{datetime.utcnow().strftime("%Y%m%d_%H%M%S")}.pdf'
    filepath = os.path.join(pdf_dir, filename)

    page_doc = SimpleDocTemplate(
        filepath, pagesize=A4,
        rightMargin=2 * cm, leftMargin=2 * cm,
        topMargin=2 * cm, bottomMargin=2.5 * cm,
        title=doc.title,
    )

    styles = _styles()
    company_name = app.config.get('COMPANY_NAME', '')
    company_address = app.config.get('COMPANY_ADDRESS', '')

    user = doc.user
    asset = doc.asset
    assignment = doc.assignment

    # Load extra template fields
    extra_fields = {}
    if doc.template_data:
        try:
            raw = json.loads(doc.template_data)
            extra_fields = {k.replace('td_', '').replace('_', ' ').title(): v
                            for k, v in raw.items()}
        except (json.JSONDecodeError, TypeError):
            pass

    story = []

    # ── Header ──────────────────────────────────────────────────────────────
    story.append(_header_table(company_name, company_address,
                               doc.doc_type_label, doc.id, doc.created_at, styles))
    story.append(Spacer(1, 0.3 * cm))
    story.append(HRFlowable(width='100%', thickness=1.5, color=colors.HexColor('#1a3a5c')))
    story.append(Spacer(1, 0.4 * cm))

    # ── Title ────────────────────────────────────────────────────────────────
    story.append(Paragraph(doc.title, styles['title']))
    story.append(Spacer(1, 0.5 * cm))

    # ── User section ─────────────────────────────────────────────────────────
    story.append(Paragraph('Employee Information', styles['section']))
    user_rows = [
        ('Windows ID', user.windows_id),
        ('Full Name', user.display_name),
        ('Email', user.display_email),
        ('Department', user.department or '—'),
        ('Job Title', user.job_title or '—'),
        ('Location', user.location or '—'),
    ]
    story.append(_field_table(user_rows, styles))
    story.append(Spacer(1, 0.4 * cm))

    # ── Asset section ─────────────────────────────────────────────────────────
    if asset:
        story.append(Paragraph('Asset Information', styles['section']))
        asset_rows = [
            ('Asset Type', asset.asset_type),
            ('Brand / Model', f'{asset.brand or ""} {asset.model or ""}'.strip() or '—'),
            ('Serial Number', asset.serial_number),
            ('Service Tag', asset.service_tag or '—'),
            ('Asset Tag', asset.asset_tag or '—'),
            ('Operating System', asset.operating_system or '—'),
        ]
        if asset.ram_gb:
            asset_rows.append(('RAM', f'{asset.ram_gb} GB'))
        if asset.storage_gb:
            asset_rows.append(('Storage', f'{asset.storage_gb} GB'))
        story.append(_field_table(asset_rows, styles))
        story.append(Spacer(1, 0.4 * cm))

    # ── Assignment section ────────────────────────────────────────────────────
    if assignment:
        story.append(Paragraph('Assignment Details', styles['section']))
        assign_rows = [
            ('Assigned Date', str(assignment.assigned_date) if assignment.assigned_date else '—'),
            ('Returned Date', str(assignment.returned_date) if assignment.returned_date else 'Currently assigned'),
        ]
        story.append(_field_table(assign_rows, styles))
        story.append(Spacer(1, 0.4 * cm))

    # ── Extra / custom fields ─────────────────────────────────────────────────
    if extra_fields:
        story.append(Paragraph('Additional Information', styles['section']))
        story.append(_field_table(list(extra_fields.items()), styles))
        story.append(Spacer(1, 0.4 * cm))

    # ── Notes ─────────────────────────────────────────────────────────────────
    if doc.notes:
        story.append(Paragraph('Notes', styles['section']))
        story.append(Paragraph(doc.notes, styles['normal']))
        story.append(Spacer(1, 0.4 * cm))

    # Type-specific clauses
    if doc.document_type == 'assignment':
        story.append(Paragraph('Terms & Conditions', styles['section']))
        clause = (
            'By signing below the employee acknowledges receipt of the above equipment in good '
            'working condition and agrees to: (1) use it solely for company business, '
            '(2) report any damage or loss immediately to the IT department, and '
            '(3) return it upon request or at the end of employment.'
        )
        story.append(Paragraph(clause, styles['normal']))
        story.append(Spacer(1, 0.4 * cm))

    if doc.document_type == 'return':
        story.append(Paragraph('Return Confirmation', styles['section']))
        clause = (
            'By signing below both parties confirm that the above equipment has been returned '
            'to the IT department and has been inspected for completeness and condition.'
        )
        story.append(Paragraph(clause, styles['normal']))
        story.append(Spacer(1, 0.4 * cm))

    # ── Signatures ────────────────────────────────────────────────────────────
    story.append(Paragraph('Signatures', styles['section']))
    story.append(Spacer(1, 0.3 * cm))
    story.append(_signature_block(styles))
    story.append(Spacer(1, 0.5 * cm))

    # ── Footer ────────────────────────────────────────────────────────────────
    story.append(HRFlowable(width='100%', thickness=0.5, color=colors.grey))
    story.append(Spacer(1, 0.2 * cm))
    story.append(Paragraph(
        f'Generated by IT Asset Management System · {datetime.utcnow().strftime("%d/%m/%Y %H:%M")} UTC',
        styles['footer'],
    ))

    page_doc.build(story)
    return filename