import hashlib
from datetime import date
from io import BytesIO

from django.utils import timezone


def generate_coa_pdf(qc, batch, spec_version="", issuer="IXG Ltd"):
    """Generate the IXG Quality Summary cover sheet PDF for an approved QC result.

    This is a companion to (never a replacement for) the independent laboratory
    certificate, which remains the authoritative source document.

    Returns (pdf_bytes, sha256_hex).
    """
    from reportlab.lib import colors
    from reportlab.lib.pagesizes import A4
    from reportlab.lib.styles import ParagraphStyle, getSampleStyleSheet
    from reportlab.lib.units import mm
    from reportlab.platypus import Paragraph, SimpleDocTemplate, Spacer, Table, TableStyle

    styles = getSampleStyleSheet()
    title_style = ParagraphStyle(
        "TitleX", parent=styles["Title"], fontSize=16, leading=20,
        textColor=colors.HexColor("#1A3D2B"),
    )
    sub_style = ParagraphStyle(
        "SubX", parent=styles["Normal"], fontSize=9, leading=12,
        textColor=colors.HexColor("#4B5563"),
    )
    cell_style = ParagraphStyle("CellX", parent=styles["Normal"], fontSize=9, leading=11)

    issued = date.today()
    reference = f"{batch.batch_reference}-COA-V{1}"

    rows = [
        ["Batch reference", batch.batch_reference],
        ["Product", "Unrefined Shea Butter"],
        ["Origin", batch.origin_facility],
        ["Grade", batch.grade or "-"],
        ["Weight", f"{batch.weight_kg} kg" if batch.weight_kg is not None else "-"],
        ["Harvest date", batch.harvest_date.isoformat() if batch.harvest_date else "-"],
        ["Specification", spec_version or "-"],
        ["Lab reference", qc.lab_reference or "-"],
        ["Tested by", qc.tested_by or "-"],
        ["Quality approved by", (qc.verified_by.full_name or qc.verified_by.email) if qc.verified_by else "-"],
        ["Quality approved on", qc.approved_at.isoformat() if qc.approved_at else "-"],
        ["Issued by", issuer],
        ["Issue date", issued.isoformat()],
    ]
    body = [
        ["Parameter", "Result", "Unit", "Result status"],
        ["FFA", f"{qc.ffa_percentage}", "%", "Within specification" if float(qc.ffa_percentage) <= 3 else "Outside specification"],
        ["Moisture", f"{qc.moisture_percentage}", "%", "Within specification" if float(qc.moisture_percentage) <= 0.1 else "Outside specification"],
        ["Peroxide value", f"{qc.peroxide_value}", "meq O2/kg", "Within specification" if float(qc.peroxide_value) <= 10 else "Outside specification"],
        ["Visual grade", qc.visual_grade, "-", "Within specification" if qc.visual_grade != "Fail" else "Outside specification"],
    ]

    pdf = BytesIO()
    doc = SimpleDocTemplate(pdf, pagesize=A4, leftMargin=20 * mm, rightMargin=20 * mm, topMargin=18 * mm, bottomMargin=18 * mm)
    elements = []

    elements.append(Paragraph("IXG Ltd &mdash; Quality Summary", title_style))
    elements.append(Spacer(1, 2 * mm))
    elements.append(Paragraph(
        "Companion document to the independent laboratory Certificate of Analysis. "
        "The independent laboratory certificate remains the authoritative source document.",
        sub_style,
    ))
    elements.append(Spacer(1, 6 * mm))

    header_table = Table([[Paragraph(f"Reference: {reference}", sub_style)]], colWidths=[120 * mm])
    elements.append(header_table)
    elements.append(Spacer(1, 4 * mm))

    meta = Table([[Paragraph(c, cell_style) for c in row] for row in rows], colWidths=[55 * mm, 115 * mm])
    meta.setStyle(TableStyle([
        ("BACKGROUND", (0, 0), (0, -1), colors.HexColor("#EAF3EF")),
        ("GRID", (0, 0), (-1, -1), 0.4, colors.HexColor("#CCD3CF")),
        ("VALIGN", (0, 0), (-1, -1), "TOP"),
        ("TOPPADDING", (0, 0), (-1, -1), 3),
        ("BOTTOMPADDING", (0, 0), (-1, -1), 3),
    ]))
    elements.append(meta)
    elements.append(Spacer(1, 6 * mm))

    elements.append(Paragraph("Results vs Specification", styles["Heading3"]))
    elements.append(Spacer(1, 2 * mm))
    result_table = Table(body, colWidths=[55 * mm, 35 * mm, 30 * mm, 50 * mm], repeatRows=1)
    result_table.setStyle(TableStyle([
        ("BACKGROUND", (0, 0), (-1, 0), colors.HexColor("#1A3D2B")),
        ("TEXTCOLOR", (0, 0), (-1, 0), colors.white),
        ("GRID", (0, 0), (-1, -1), 0.4, colors.HexColor("#CCD3CF")),
        ("FONTSIZE", (0, 0), (-1, -1), 9),
        ("ROWBACKGROUNDS", (0, 1), (-1, -1), [colors.white, colors.HexColor("#F7F6F2")]),
    ]))
    elements.append(result_table)
    elements.append(Spacer(1, 6 * mm))

    elements.append(Paragraph(
        "This summary is derived from the structured QC record on the IXG platform. "
        "The independent laboratory certificate remains the authoritative source document.",
        sub_style,
    ))

    doc.build(elements)
    data = pdf.getvalue()
    digest = hashlib.sha256(data).hexdigest()
    return data, digest


def write_coa_file(qc, batch, pdf_bytes):
    """Persist the generated PDF under media/ixg-documents/{batch_id}/ and return (file_url, file_name)."""
    import os
    import uuid as uuid_mod
    from django.conf import settings

    batch_dir = os.path.join(settings.MEDIA_ROOT, "ixg-documents", str(batch.id))
    os.makedirs(batch_dir, exist_ok=True)
    filename = f"coa-{uuid_mod.uuid4().hex[:8]}-{batch.batch_reference}.pdf"
    filepath = os.path.join(batch_dir, filename)
    with open(filepath, "wb") as f:
        f.write(pdf_bytes)
    return f"/media/ixg-documents/{batch.id}/{filename}", filename