#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Sanity-check the coordinates and CRS of georeferenced LAS/LAZ point clouds.

Role in the pipeline:
    A verification utility that confirms the HoliCity (London) tiles have been
    georeferenced correctly before tiling. It inspects each LAS/LAZ file's header
    and bounding box, reprojects the bbox center to WGS84, and checks whether that
    center falls within an approximate London bounding box.

Behavior:
    - Recursively scans a directory for .las/.laz files.
    - Reads header stats (EPSG, bbox, point count, point format, scale, offset)
      and detects degenerate "near (0,0)" coordinates.
    - If the file has an EPSG, reprojects its center to WGS84 and flags whether it
      lies in the London region.
    - If no EPSG is present, tries a list of candidate CRSs (BNG / UTM 30N / Web
      Mercator / WGS84) and reports the first one whose center lands in London.
    - Emits a per-file status (OK / WARN / BAD / ERR) plus a hint, printed as a
      table and optionally exported to CSV.

Inputs:  directory of .las/.laz files (CLI: -d/--dir), optional CSV path (-o/--output).
Outputs: a console report table and an optional CSV file. No files are modified.
External tools: laspy, numpy, pyproj.
"""

import os
import sys
import csv
import math
import argparse
from pathlib import Path

import laspy
import numpy as np
from pyproj import CRS, Transformer

# ----------- Tunable parameters -----------
# London region (WGS84)
LON_MIN, LON_MAX = -0.6, 0.4
LAT_MIN, LAT_MAX = 51.2, 51.8

# Common candidate CRSs (used to guess when no EPSG is present)
CANDIDATE_EPSGS = [
    27700,   # OSGB36 / British National Grid
    32630,   # WGS84 / UTM zone 30N
    3857,    # Web Mercator
    4326,    # WGS84 (lat/lon)
]

# Rough "plausible ranges" for the UK / London (quick sanity check; approximate only)
RANGE_HINTS = {
    27700: {"E": (0, 700000), "N": (0, 1300000), "name": "OSGB36 / BNG"},
    32630: {"E": (160000, 840000), "N": (5550000, 5900000), "name": "UTM 30N"},
    3857: {"X": (-500000, 500000), "Y": (6200000, 7300000), "name": "WebMerc"},
    4326: {"Lon": (-10, 10), "Lat": (45, 60), "name": "WGS84 deg"},
}
# Approximate reference for the center of London (used only for printed hints)
LONDON_WGS84 = (-0.1, 51.51)

# --------------------------------

def in_london(lon, lat):
    return (LON_MIN <= lon <= LON_MAX) and (LAT_MIN <= lat <= LAT_MAX)

def safe_epsg_str(epsg):
    try:
        return f"EPSG:{int(epsg)}"
    except Exception:
        return "None"

def read_stats(path: Path, sample_n: int = 200000):
    """Read the bbox and center point; for large clouds only the header bbox is read; sample some points for QC if needed."""
    with laspy.open(str(path)) as f:
        hdr = f.header
        mins = np.array(getattr(hdr, "mins", getattr(hdr, "min", (0, 0, 0))), dtype=float)
        maxs = np.array(getattr(hdr, "maxs", getattr(hdr, "max", (0, 0, 0))), dtype=float)
        epsg = None
        try:
            epsg = hdr.epsg
        except Exception:
            pass

        # Center point (the bbox midpoint is sufficient)
        cx = (mins[0] + maxs[0]) * 0.5
        cy = (mins[1] + maxs[1]) * 0.5
        cz = (mins[2] + maxs[2]) * 0.5

        # Check whether everything sits near (0,0)
        zeroish = (abs(cx) < 1e-6 and abs(cy) < 1e-6) or \
                  (abs(mins[0]) < 1e-6 and abs(maxs[0]) < 1e-6 and
                   abs(mins[1]) < 1e-6 and abs(maxs[1]) < 1e-6)

        return {
            "epsg": epsg,
            "mins": mins, "maxs": maxs,
            "center": (cx, cy, cz),
            "zeroish": zeroish,
            "point_count": int(getattr(hdr, "point_count", 0)),
            "point_format": str(getattr(hdr.point_format, "id", hdr.point_format)),
            "scale": tuple(hdr.scales),
            "offset": tuple(hdr.offsets),
        }

def transform_to_wgs84(x, y, epsg):
    """Reproject (x,y) from the given EPSG to WGS84 lon/lat. Return None on failure."""
    try:
        src = CRS.from_epsg(int(epsg))
        dst = CRS.from_epsg(4326)
        tr = Transformer.from_crs(src, dst, always_xy=True)
        lon, lat = tr.transform(x, y)
        return lon, lat
    except Exception:
        return None

def guess_and_transform_to_wgs84(x, y, candidates=CANDIDATE_EPSGS):
    """When no EPSG is set, try each candidate CRS in turn; return the first projection that falls within the London region, along with its epsg."""
    tried = []
    for epsg in candidates:
        res = transform_to_wgs84(x, y, epsg)
        if res is None: 
            tried.append((epsg, None))
            continue
        lon, lat = res
        tried.append((epsg, (lon, lat)))
        if in_london(lon, lat):
            return (lon, lat), epsg, tried
    return None, None, tried

def range_hint_text(epsg, mins, maxs):
    h = RANGE_HINTS.get(int(epsg)) if epsg is not None else None
    if not h:
        return ""
    if epsg in (27700, 32630):
        E = (mins[0], maxs[0]); N = (mins[1], maxs[1])
        return f"RangeHint {h['name']}: E∈{h['E']} vs {E}, N∈{h['N']} vs {N}"
    elif epsg == 3857:
        X = (mins[0], maxs[0]); Y = (mins[1], maxs[1])
        return f"RangeHint {h['name']}: X∈{h['X']} vs {X}, Y∈{h['Y']} vs {Y}"
    elif epsg == 4326:
        Lon = (mins[0], maxs[0]); Lat = (mins[1], maxs[1])
        return f"RangeHint {h['name']}: Lon∈{h['Lon']} vs {Lon}, Lat∈{h['Lat']} vs {Lat}"
    return ""

def analyze_file(path: Path):
    size_mb = path.stat().st_size / (1024 * 1024)
    stats = read_stats(path)
    epsg = stats["epsg"]
    cx, cy, cz = stats["center"]
    mins, maxs = stats["mins"], stats["maxs"]

    result = {
        "file": str(path.name),
        "size_mb": f"{size_mb:.2f}",
        "epsg": safe_epsg_str(epsg),
        "pt_fmt": stats["point_format"],
        "pts": stats["point_count"],
        "scale": stats["scale"],
        "offset": stats["offset"],
        "center_xy": (cx, cy),
        "center_wgs84": None,
        "in_london": False,
        "status": "",
        "hint": "",
    }

    # 0) All-zero / near-zero
    if stats["zeroish"]:
        result["status"] = "BAD"
        result["hint"] = "Coordinates near (0,0); likely unassigned or wrong projection. Check the coordinate transform and EPSG write."
        return result

    # 1) Has EPSG: project and check directly
    if epsg is not None:
        wgs = transform_to_wgs84(cx, cy, int(epsg))
        if wgs is None:
            result["status"] = "WARN"
            result["hint"] = f"Could not project the center from {safe_epsg_str(epsg)} to WGS84; the EPSG may be invalid."
            return result
        lon, lat = wgs
        result["center_wgs84"] = (round(lon, 6), round(lat, 6))
        result["in_london"] = in_london(lon, lat)
        if result["in_london"]:
            result["status"] = "OK"
            result["hint"] = f"Center is within the London region; {range_hint_text(int(epsg), mins, maxs)}"
        else:
            result["status"] = "WARN"
            result["hint"] = f"Center is outside the London region ({lon:.5f},{lat:.5f}); if it should be in London, the EPSG or translation may be wrong. {range_hint_text(int(epsg), mins, maxs)}"
        return result

    # 2) No EPSG: try to guess and check whether it lands in London
    guessed, gepsg, tried = guess_and_transform_to_wgs84(cx, cy)
    if guessed is not None:
        lon, lat = guessed
        result["center_wgs84"] = (round(lon, 6), round(lat, 6))
        result["in_london"] = True
        result["status"] = "WARN"
        result["hint"] = (f"No EPSG written, but {safe_epsg_str(gepsg)} is inferred to fall in the London region. "
                          f"Suggest writing {safe_epsg_str(gepsg)} and retrying.")
    else:
        result["status"] = "BAD"
        tried_text = "; ".join(
            f"EPSG:{e} -> {('None' if v is None else f'({v[0]:.5f},{v[1]:.5f})')}" for e, v in tried
        )
        result["hint"] = ("No EPSG written, and none of the common candidate CRSs project the center into the London region. "
                          "Check whether a wrong translation/rotation/unit was used, or whether a different EPSG is needed. "
                          f"Attempts: {tried_text}")
    return result

def print_table(rows):
    headers = ["file","size_mb","epsg","pt_fmt","pts","center_xy","center_wgs84","in_london","status","hint"]
    colw = {h: max(len(h), max((len(str(r[h])) for r in rows), default=0)) for h in headers}
    sep = " | "
    print(sep.join(h.ljust(colw[h]) for h in headers))
    print("-" * (sum(colw.values()) + len(sep)*(len(headers)-1)))
    for r in rows:
        print(sep.join(str(r[h]).ljust(colw[h]) for h in headers))

def main():
    ap = argparse.ArgumentParser(description="Check whether LAS/LAZ files have correct coordinates and CRS, and whether they fall within the London region.")
    ap.add_argument("-d","--dir", default=".", help="Directory to scan (default: current directory)")
    ap.add_argument("-o","--output", default=None, help="CSV export path (optional)")
    args = ap.parse_args()

    root = Path(args.dir).resolve()
    if not root.exists():
        print(f"Directory does not exist: {root}", file=sys.stderr); sys.exit(1)

    files = []
    for p in root.rglob("*"):
        if p.is_file() and p.suffix.lower() in (".las",".laz"):
            files.append(p)

    if not files:
        print("No .las/.laz files found"); return

    rows = []
    for p in sorted(files):
        try:
            rows.append(analyze_file(p))
        except Exception as e:
            rows.append({
                "file": p.name, "size_mb":"?", "epsg":"?", "pt_fmt":"?", "pts":"?",
                "center_xy":"?", "center_wgs84":"?", "in_london":"?", "status":"ERR",
                "hint": f"Parse failed: {e}"
            })

    print(f"Scan directory: {root}\n")
    print_table(rows)

    if args.output:
        out = Path(args.output).resolve()
        out.parent.mkdir(parents=True, exist_ok=True)
        with out.open("w", newline="", encoding="utf-8") as f:
            writer = csv.DictWriter(f, fieldnames=list(rows[0].keys()))
            writer.writeheader()
            writer.writerows(rows)
        print(f"\nCSV written: {out}")

if __name__ == "__main__":
    main()