//! `GET /api/crime-records` — the individual police.uk crimes (last 7 years)
//! behind a selected hexagon or postcode, paginated. Display-only and
//! independent of the property filters, like the population figure: the records
//! are an attribute of the area, not of the filter-matching subset.

use std::str::FromStr;
use std::sync::Arc;

use axum::extract::{Query, State};
use axum::http::StatusCode;
use axum::response::{IntoResponse, Json};
use axum::Extension;
use rustc_hash::{FxHashMap, FxHashSet};
use serde::{Deserialize, Serialize};
use tracing::{info, warn};

use crate::auth::OptionalUser;
use crate::licensing::{check_license_bounds, check_license_point, resolve_share_code};
use crate::parsing::{cell_for_row_cached, h3_cell_bounds, needs_parent, validate_h3_resolution};
use crate::state::SharedState;
use crate::utils::normalize_postcode;

/// Default and hard-cap page sizes for the records list.
const DEFAULT_LIMIT: usize = 200;
const MAX_LIMIT: usize = 500;

#[derive(Deserialize)]
pub struct CrimeRecordsParams {
    /// Hexagon selection: H3 cell + resolution. Mutually exclusive with `postcode`.
    pub h3: Option<String>,
    pub resolution: Option<u8>,
    /// Postcode selection.
    pub postcode: Option<String>,
    pub offset: Option<usize>,
    pub limit: Option<usize>,
    /// Lower bound on `month_index` (`year*12 + month0`) to restrict to a recent
    /// window; omitted = all stored records (last 7 years).
    pub since: Option<u32>,
    /// Share-link code; grants scoped access for unlicensed users.
    pub share: Option<String>,
}

#[derive(Serialize)]
pub struct CrimeRecord {
    /// `"YYYY-MM"`.
    pub month: String,
    #[serde(rename = "type")]
    pub crime_type: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub location: Option<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub outcome: Option<String>,
    pub lat: f32,
    pub lon: f32,
}

#[derive(Serialize)]
pub struct CrimeRecordsResponse {
    pub records: Vec<CrimeRecord>,
    pub total: usize,
    pub offset: usize,
    pub truncated: bool,
}

fn format_month(month_index: u32) -> String {
    let year = month_index / 12;
    let month = month_index % 12 + 1;
    format!("{year:04}-{month:02}")
}

pub async fn get_crime_records(
    State(shared): State<Arc<SharedState>>,
    Extension(user): Extension<OptionalUser>,
    Extension(geo): Extension<crate::demo_zone::DemoZone>,
    Query(params): Query<CrimeRecordsParams>,
) -> Result<Json<CrimeRecordsResponse>, axum::response::Response> {
    let state = shared.load_state();
    let share_bounds = resolve_share_code(&state, params.share.as_deref()).await;
    let offset = params.offset.unwrap_or(0);
    let limit = params.limit.unwrap_or(DEFAULT_LIMIT).min(MAX_LIMIT);
    let since = params.since;

    // Resolve the selection to a set of postcodes, after a license check scoped
    // to the selection's geometry (bounds for a hexagon, point for a postcode).
    enum Selection {
        Hexagon { cell: u64, resolution: u8 },
        Postcode(String),
    }

    let selection = if let Some(h3) = params.h3.clone() {
        let cell = h3o::CellIndex::from_str(&h3).map_err(|error| {
            warn!(h3 = %h3, error = %error, "Invalid H3 cell index");
            (StatusCode::BAD_REQUEST, format!("Invalid H3 cell: {error}")).into_response()
        })?;
        let resolution = params.resolution.ok_or_else(|| {
            (StatusCode::BAD_REQUEST, "resolution is required with h3").into_response()
        })?;
        validate_h3_resolution(resolution).map_err(IntoResponse::into_response)?;
        let bounds = h3_cell_bounds(cell, 0.0);
        check_license_bounds(&user.0, bounds, geo.free_zone, share_bounds)?;
        Selection::Hexagon {
            cell: cell.into(),
            resolution,
        }
    } else if let Some(postcode) = params.postcode.clone() {
        let normalized = normalize_postcode(&postcode);
        let &pc_idx = state
            .postcode_data
            .postcode_to_idx
            .get(&normalized)
            .ok_or_else(|| {
                (StatusCode::NOT_FOUND, format!("Postcode not found: {normalized}")).into_response()
            })?;
        let (lat, lon) = state.postcode_data.centroids[pc_idx];
        check_license_point(&user.0, lat as f64, lon as f64, geo.free_zone, share_bounds)?;
        Selection::Postcode(normalized)
    } else {
        return Err((StatusCode::BAD_REQUEST, "h3 or postcode is required").into_response());
    };

    let result = tokio::task::spawn_blocking(move || -> Result<CrimeRecordsResponse, String> {
        // Distinct postcodes covered by the selection.
        let postcodes: Vec<String> = match selection {
            Selection::Postcode(pc) => vec![pc],
            Selection::Hexagon { cell, resolution } => {
                let h3_res = h3o::Resolution::try_from(resolution)
                    .map_err(|err| format!("Invalid H3 resolution {resolution}: {err}"))?;
                let need_parent = needs_parent(resolution);
                let h3o_cell = h3o::CellIndex::try_from(cell)
                    .map_err(|err| format!("Invalid H3 cell: {err}"))?;
                let (min_lat, min_lon, max_lat, max_lon) = h3_cell_bounds(h3o_cell, 0.001);
                let mut h3_cache: FxHashMap<u64, u64> = FxHashMap::default();
                let mut seen: FxHashSet<&str> = FxHashSet::default();
                let mut out: Vec<String> = Vec::new();
                state.grid.for_each_in_bounds(
                    min_lat,
                    min_lon,
                    max_lat,
                    max_lon,
                    |row_idx| {
                        let row = row_idx as usize;
                        if cell_for_row_cached(
                            row,
                            &state.h3_cells,
                            h3_res,
                            need_parent,
                            &mut h3_cache,
                        ) == cell
                        {
                            let pc = state.data.postcode(row);
                            if seen.insert(pc) {
                                out.push(pc.to_string());
                            }
                        }
                    },
                );
                out
            }
        };

        let pc_refs: Vec<&str> = postcodes.iter().map(String::as_str).collect();
        let indices = state.crime_records.gather(&pc_refs, since);
        let total = indices.len();
        let records: Vec<CrimeRecord> = indices
            .iter()
            .skip(offset)
            .take(limit)
            .map(|&idx| {
                let v = state.crime_records.view(idx);
                CrimeRecord {
                    month: format_month(v.month_index),
                    crime_type: v.crime_type.to_string(),
                    location: v.location.map(str::to_string),
                    outcome: v.outcome.map(str::to_string),
                    lat: v.lat,
                    lon: v.lon,
                }
            })
            .collect();
        let truncated = offset + records.len() < total;
        Ok(CrimeRecordsResponse {
            records,
            total,
            offset,
            truncated,
        })
    })
    .await
    .map_err(|error| (StatusCode::INTERNAL_SERVER_ERROR, error.to_string()).into_response())?
    .map_err(|error| (StatusCode::INTERNAL_SERVER_ERROR, error).into_response())?;

    info!(total = result.total, returned = result.records.len(), "GET /api/crime-records");
    Ok(Json(result))
}