// Package raster converts rasters to Cloud-Optimized GeoTIFFs and reads their
// footprints using the GDAL command-line tools (gdal_translate, gdalinfo),
// which must be installed in the worker environment.
package raster

import (
	"context"
	"encoding/json"
	"fmt"
	"os/exec"
	"strings"
)

// GDALConverter shells out to GDAL.
type GDALConverter struct {
	compression string
}

// NewGDALConverter returns a converter using DEFLATE compression.
func NewGDALConverter() *GDALConverter {
	return &GDALConverter{compression: "DEFLATE"}
}

// ToCOG converts the source raster to a Cloud-Optimized GeoTIFF at dst. The COG
// driver builds internal tiling and overviews.
func (c *GDALConverter) ToCOG(ctx context.Context, src, dst string) error {
	cmd := exec.CommandContext(ctx, "gdal_translate",
		"-of", "COG",
		"-co", "COMPRESS="+c.compression,
		src, dst,
	)
	var stderr strings.Builder
	cmd.Stderr = &stderr
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("gdal_translate: %w: %s", err, strings.TrimSpace(stderr.String()))
	}
	return nil
}

// Footprint returns the raster's footprint as a GeoJSON polygon in EPSG:4326, or
// nil if the raster has no spatial reference.
func (c *GDALConverter) Footprint(ctx context.Context, src string) ([]byte, error) {
	out, err := exec.CommandContext(ctx, "gdalinfo", "-json", src).Output()
	if err != nil {
		return nil, fmt.Errorf("gdalinfo: %w", err)
	}

	var info struct {
		Wgs84Extent json.RawMessage `json:"wgs84Extent"`
	}
	if err := json.Unmarshal(out, &info); err != nil {
		return nil, fmt.Errorf("parse gdalinfo: %w", err)
	}
	if len(info.Wgs84Extent) == 0 || string(info.Wgs84Extent) == "null" {
		return nil, nil
	}
	return info.Wgs84Extent, nil
}