"""DataTools Fix Missing Values — Streamlit page."""

from __future__ import annotations

import io
import json
import sys
from pathlib import Path

import pandas as pd
import streamlit as st

_project_root = Path(__file__).resolve().parent.parent.parent.parent
if str(_project_root) not in sys.path:
    sys.path.insert(0, str(_project_root))

from src.gui.components import (
    back_to_home_link,
    render_sticky_footer,
    render_tool_header,
    hide_streamlit_chrome,
    html_download_button,
    pickup_or_upload,
    require_feature_or_render_upgrade,
)
from src.i18n import t
from src.core.missing import (
    DEFAULT_SENTINELS,
    MissingOptions,
    PRESETS,
    handle_missing,
    profile_missing,
)
from src.license import FeatureFlag

hide_streamlit_chrome()
render_sticky_footer()
back_to_home_link()
from src.audit import log_page_open
log_page_open("4_Missing_Values")
require_feature_or_render_upgrade(FeatureFlag.MISSING_HANDLER)


# ---------------------------------------------------------------------------
# Header
# ---------------------------------------------------------------------------

render_tool_header("04_missing_handler")


# ---------------------------------------------------------------------------
# File upload
# ---------------------------------------------------------------------------

uploaded = pickup_or_upload(
    label="Import CSV or Excel file",
    key="missing_file_upload",
    types=["csv", "tsv", "xlsx", "xls"],
)

if uploaded is None:
    st.info("Import a CSV, TSV, or Excel file to begin.")
    st.stop()


@st.cache_data(show_spinner=False)
def _read_uploaded(name: str, data: bytes) -> pd.DataFrame:
    """Read the uploaded bytes into a DataFrame.

    Unlike the text cleaner, we do *not* force ``dtype=str`` here: missing-
    value handling is more useful when numeric columns are typed correctly
    (so mean / median / interpolate work without manual coercion).
    Sentinel strings are still detected because they survive in object
    columns where any cell is non-numeric.
    """
    suffix = Path(name).suffix.lower()
    bio = io.BytesIO(data)
    if suffix in (".xlsx", ".xls"):
        return pd.read_excel(bio)
    for enc in ("utf-8", "utf-8-sig", "latin-1"):
        try:
            bio.seek(0)
            sep = "\t" if suffix == ".tsv" else ","
            return pd.read_csv(bio, encoding=enc, sep=sep, on_bad_lines="warn")
        except UnicodeDecodeError:
            continue
    bio.seek(0)
    return pd.read_csv(bio, encoding="latin-1")


try:
    df = _read_uploaded(uploaded.name, uploaded.getvalue())
except Exception as e:
    from src.core.errors import format_for_user
    st.error(
        f"**Could not read `{uploaded.name}`**\n\n"
        f"```\n{format_for_user(e)}\n```"
    )
    st.stop()

# Collapse the input preview + options once the user has clicked
# Handle Missing Values so the Results section below is the primary
# visual focus. The user can re-expand to re-inspect the source rows
# or tweak strategy and rerun.
_has_result = st.session_state.get("missing_result") is not None

with st.expander(f"Preview: {uploaded.name}", expanded=not _has_result):
    st.caption(f"{len(df)} rows, {len(df.columns)} columns")
    st.dataframe(df.head(10), width="stretch")

st.divider()

# ---------------------------------------------------------------------------
# Options (Missingness profile + Strategy)
# ---------------------------------------------------------------------------
#
# Wrapped in an outer expander whose default state mirrors the preview
# expander above: open before a result exists, folded once the user has
# clicked Handle Missing Values. The Missingness profile lives inside
# this expander too — after a run the Results section shows a richer
# before-vs-after comparison that supersedes the static input profile,
# so keeping it tucked away with the controls cleanly pushes Results
# to the top of the visible area.

with st.expander("Options", expanded=not _has_result):
    st.subheader("Missingness profile")

    initial_profile = profile_missing(df, MissingOptions())
    prof_df = initial_profile.to_dataframe()

    m1, m2, m3, m4 = st.columns(4)
    m1.metric("Rows", initial_profile.rows_total)
    m2.metric("Cells missing", initial_profile.cells_missing)
    m3.metric("% cells missing", f"{initial_profile.cells_missing_pct:.1f}%")
    m4.metric("Complete rows", initial_profile.rows_complete)

    st.dataframe(prof_df, width="stretch", hide_index=True)

    if initial_profile.cells_missing == 0:
        st.success("No missing values or disguised nulls detected. Nothing to handle.")

    st.divider()

    st.subheader("Strategy")

    preset_label = st.radio(
        "Preset",
        [
            "detect-only (standardize sentinels to NaN, no fill or drop)",
            "safe-fill (numeric → median, categorical → mode)",
            "drop-incomplete (drop any row with missing)",
        ],
        index=0,
        help=(
            "detect-only: replace 'N/A', '-', 'NULL', etc. with real NaN, then stop. "
            "safe-fill: also fill — numeric columns with median, others with mode. "
            "drop-incomplete: also drop every row that has any missing cell."
        ),
    )
    preset_key = preset_label.split(" ", 1)[0]
    options = MissingOptions.from_preset(preset_key)

    with st.expander("Advanced options"):
        col_a, col_b = st.columns(2)

        with col_a:
            st.markdown("**Detection**")
            options.standardize_sentinels = st.checkbox(
                "Standardize disguised nulls to NaN",
                value=options.standardize_sentinels,
                help="Replace 'N/A', '-', 'NULL', whitespace-only cells, etc. with real NaN.",
            )
            sentinels_text = st.text_input(
                "Sentinel values (comma-separated)",
                value=", ".join(options.sentinels),
                disabled=not options.standardize_sentinels,
                help="Matched case-insensitively after stripping whitespace.",
            )
            options.sentinels = [
                s.strip() for s in sentinels_text.split(",") if s.strip()
            ]

        with col_b:
            st.markdown("**Strategy override**")
            strat_options = [
                "(use preset)",
                "none", "drop_row", "drop_col", "drop_both",
                "mean", "median", "mode", "constant",
                "ffill", "bfill", "interpolate",
            ]
            strat_choice = st.selectbox(
                "Global strategy",
                strat_options,
                index=0,
                help=(
                    "drop_row / drop_col use the thresholds below. "
                    "mean / median / interpolate are numeric only — non-numeric "
                    "columns fall back to the categorical strategy."
                ),
            )
            if strat_choice != "(use preset)":
                options.strategy = strat_choice  # type: ignore[assignment]

            cat_strat = st.selectbox(
                "Categorical fallback (for non-numeric columns)",
                ["mode", "constant", "ffill", "bfill", "none"],
                index=0,
            )
            options.categorical_strategy = cat_strat  # type: ignore[assignment]

            if options.strategy == "constant" or cat_strat == "constant":
                fill_val = st.text_input(
                    "Constant fill value",
                    value="",
                    help="Used when strategy = constant. Leave blank to fill with empty string.",
                )
                options.fill_value = fill_val

        st.markdown("**Drop thresholds**")
        col_c, col_d = st.columns(2)
        with col_c:
            options.row_drop_threshold = st.slider(
                "Row drop threshold (drop rows with ≥ this fraction missing across selected cols)",
                0.0, 1.0, options.row_drop_threshold, 0.05,
            )
        with col_d:
            options.col_drop_threshold = st.slider(
                "Column drop threshold (drop columns with ≥ this fraction missing)",
                0.0, 1.0, options.col_drop_threshold, 0.05,
            )

        st.markdown("**Scope**")
        selected_cols = st.multiselect(
            "Columns to handle (default: all)",
            options=list(df.columns),
            default=list(df.columns),
        )
        skip_cols = st.multiselect(
            "Columns to skip",
            options=list(df.columns),
            default=[],
        )
        options.columns = selected_cols if selected_cols else None
        options.skip_columns = list(skip_cols)

        st.markdown("**Per-column strategy overrides** (optional)")
        st.caption(
            "Set a different strategy for specific columns. Leave any row blank to "
            "use the global strategy."
        )
        per_col_overrides: dict[str, str] = {}
        only_missing_cols = [
            r.column for r in initial_profile.columns if r.has_missing
        ]
        if only_missing_cols:
            edit_df = pd.DataFrame({
                "column": only_missing_cols,
                "strategy": ["" for _ in only_missing_cols],
            })
            edited = st.data_editor(
                edit_df,
                width="stretch",
                hide_index=True,
                column_config={
                    "column": st.column_config.TextColumn("Column", disabled=True),
                    "strategy": st.column_config.SelectboxColumn(
                        "Override",
                        options=[
                            "", "drop_row", "drop_col",
                            "mean", "median", "mode", "constant",
                            "ffill", "bfill", "interpolate",
                        ],
                    ),
                },
                key="missing_per_col_editor",
            )
            for _, row in edited.iterrows():
                if row["strategy"]:
                    per_col_overrides[row["column"]] = row["strategy"]
            options.column_strategies = per_col_overrides  # type: ignore[assignment]

# ---------------------------------------------------------------------------
# Run
# ---------------------------------------------------------------------------

st.divider()

if st.button("Handle Missing Values", type="primary", width="stretch"):
    with st.spinner("Handling..."):
        try:
            result = handle_missing(df, options)
        except (ValueError, OSError) as e:
            from src.core.errors import format_for_user
            st.error(format_for_user(e))
            st.stop()
    st.session_state["missing_result"] = result
    from src.audit import log_event
    log_event("tool_run", "Fix Missing Values run", page="4_Missing_Values")
    st.session_state["missing_input_name"] = uploaded.name
    st.session_state["missing_options"] = options.to_dict()
    # One-shot flag picked up on the next pass to scroll the parent
    # document to the Results anchor (see scroll snippet below).
    st.session_state["_missing_scroll_to_results"] = True
    # Force a second rerun so the preview and options expanders see
    # the new result on the NEXT script pass and collapse themselves.
    # Without this they stay expanded until the user touches any
    # other widget.
    st.rerun()

result = st.session_state.get("missing_result")
if result is None:
    st.info("Choose a strategy and click **Handle Missing Values** to run.")
    st.stop()

# ---------------------------------------------------------------------------
# Results
# ---------------------------------------------------------------------------

# Anchor target for the auto-scroll snippet at the end of this block.
# A bare ``<div id="...">`` survives Streamlit's HTML sanitizer (only
# ``<script>`` is stripped), and a 1px-tall div doesn't visually shift
# anything. Placed before the subheader so the scrolled-to viewport
# starts a few pixels above the section heading rather than below it.
st.markdown(
    '<div id="missing-results-anchor" style="height:1px"></div>',
    unsafe_allow_html=True,
)

st.subheader("Results")

m1, m2, m3, m4 = st.columns(4)
m1.metric("Sentinels → NaN", result.sentinels_standardized)
m2.metric("Cells filled", result.cells_filled)
m3.metric("Rows dropped", result.rows_dropped)
m4.metric("Columns dropped", len(result.columns_dropped))

if result.columns_dropped:
    st.warning(f"Dropped columns: {', '.join(result.columns_dropped)}")

st.markdown("**Missingness — before vs. after**")
before = result.profile_before.to_dataframe().set_index("column")[
    ["missing", "missing_pct"]
].rename(columns={"missing": "before_missing", "missing_pct": "before_pct"})
after = result.profile_after.to_dataframe().set_index("column")[
    ["missing", "missing_pct"]
].rename(columns={"missing": "after_missing", "missing_pct": "after_pct"})
combined = before.join(after, how="outer").fillna(0)
st.dataframe(combined, width="stretch")

if result.strategy_per_column:
    st.markdown("**Strategy applied per column**")
    strat_df = pd.DataFrame(
        [{"column": c, "strategy": s} for c, s in result.strategy_per_column.items()]
    )
    st.dataframe(strat_df, width="stretch", hide_index=True)

if not result.changes.empty:
    st.markdown("**Audit (first 50 changes)**")
    audit_view = result.changes.head(50).copy()
    audit_view["row"] = audit_view["row"].apply(lambda x: "—" if x == -1 else x + 1)
    st.dataframe(audit_view, width="stretch", hide_index=True)
    if len(result.changes) > 50:
        st.caption(f"… and {len(result.changes) - 50} more (download the full audit below).")

st.markdown("**Handled preview (first 10 rows)**")
st.dataframe(result.handled_df.head(10), width="stretch")

# ---------------------------------------------------------------------------
# Downloads
# ---------------------------------------------------------------------------
#
# Rendered via ``html_download_button`` (raw <a download> anchor) rather
# than ``st.download_button``. The latter has a long-standing bug where
# the second and third download_buttons rendered in the same script pass
# fail to fire — only the first one's click reaches the browser save
# dialog. The HTML helper bypasses the widget system entirely and works
# uniformly across all browsers. The empty-changes case still renders a
# disabled button (rather than vanishing) so the layout stays steady and
# the user understands why nothing's available.

st.divider()
stem = Path(st.session_state.get("missing_input_name", "input")).stem

handled_bytes = result.handled_df.to_csv(index=False).encode("utf-8-sig")
changes_bytes = (
    result.changes.to_csv(index=False).encode("utf-8-sig")
    if not result.changes.empty
    else b""
)
config_bytes = json.dumps(
    st.session_state.get("missing_options", {}), indent=2, default=str,
).encode("utf-8")

dl_a, dl_b, dl_c = st.columns(3)
with dl_a:
    html_download_button(
        "Download handled CSV",
        handled_bytes,
        file_name=f"{stem}_missing.csv",
        mime="text/csv",
    )
with dl_b:
    html_download_button(
        "Download changes audit",
        changes_bytes,
        file_name=f"{stem}_missing_changes.csv",
        mime="text/csv",
        disabled=result.changes.empty,
        help="No changes to audit." if result.changes.empty else None,
    )
with dl_c:
    html_download_button(
        "Download config JSON",
        config_bytes,
        file_name="missing_config.json",
        mime="application/json",
    )



# ---------------------------------------------------------------------------
# Post-run auto-scroll
# ---------------------------------------------------------------------------
#
# When the user clicks Handle Missing Values, the preview + options
# collapse but Streamlit by itself doesn't scroll — the Results section
# is at the bottom of a tall script so the user has to find it. Inject
# a tiny component-html iframe that calls ``scrollIntoView`` on the
# parent's Results anchor. Streamlit's main page is same-origin with
# component iframes so ``window.parent.document`` access is allowed.
#
# The flag is one-shot (``pop`` removes it) so re-renders triggered by
# unrelated widgets in the Results section don't yank the viewport
# back to the top of Results.
if st.session_state.pop("_missing_scroll_to_results", False):
    st.iframe(
        """
        <script>
          const doc = window.parent.document;
          const target = doc.getElementById('missing-results-anchor');
          if (target) target.scrollIntoView({behavior: 'smooth', block: 'start'});
        </script>
        """,
        height=1,
    )