package main

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

// GenerateScanGridSVG creates printable calibration grid SVG files.
// Returns the list of generated file paths.
func GenerateScanGridSVG(cfg *ScanHelperConfig, outputDir string) ([]string, error) {
	if cfg == nil {
		return nil, fmt.Errorf("no scan helper config")
	}

	os.MkdirAll(outputDir, 0755)

	pageW := cfg.PageWidth
	pageH := cfg.PageHeight
	grid := cfg.GridSpacing
	if grid <= 0 {
		grid = 10
	}

	margin := 15.0 // mm margin for printer bleed
	markerSize := 5.0

	var files []string

	for row := 0; row < cfg.PagesTall; row++ {
		for col := 0; col < cfg.PagesWide; col++ {
			filename := fmt.Sprintf("scan_grid_%dx%d.svg", col+1, row+1)
			if cfg.PagesWide == 1 && cfg.PagesTall == 1 {
				filename = "scan_grid.svg"
			}
			path := filepath.Join(outputDir, filename)

			svg, err := renderGridPage(pageW, pageH, margin, grid, markerSize, col, row, cfg.PagesWide, cfg.PagesTall)
			if err != nil {
				return files, err
			}

			if err := os.WriteFile(path, []byte(svg), 0644); err != nil {
				return files, fmt.Errorf("write %s: %v", filename, err)
			}
			files = append(files, path)
		}
	}

	return files, nil
}

func renderGridPage(pageW, pageH, margin, gridSpacing, markerSize float64, col, row, totalCols, totalRows int) (string, error) {
	var b strings.Builder

	b.WriteString(fmt.Sprintf(`<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" version="1.1"
     width="%.1fmm" height="%.1fmm"
     viewBox="0 0 %.1f %.1f">
`, pageW, pageH, pageW, pageH))

	// White background
	b.WriteString(fmt.Sprintf(`<rect x="0" y="0" width="%.1f" height="%.1f" fill="white"/>
`, pageW, pageH))

	// Printable area
	areaX := margin
	areaY := margin
	areaW := pageW - 2*margin
	areaH := pageH - 2*margin

	// Thin border around printable area
	b.WriteString(fmt.Sprintf(`<rect x="%.2f" y="%.2f" width="%.2f" height="%.2f" fill="none" stroke="#ccc" stroke-width="0.3"/>
`, areaX, areaY, areaW, areaH))

	// Grid lines
	b.WriteString(`<g stroke="#ddd" stroke-width="0.15">` + "\n")
	for x := areaX; x <= areaX+areaW+0.01; x += gridSpacing {
		b.WriteString(fmt.Sprintf(`  <line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f"/>`, x, areaY, x, areaY+areaH))
		b.WriteString("\n")
	}
	for y := areaY; y <= areaY+areaH+0.01; y += gridSpacing {
		b.WriteString(fmt.Sprintf(`  <line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f"/>`, areaX, y, areaX+areaW, y))
		b.WriteString("\n")
	}
	b.WriteString("</g>\n")

	// Major grid lines every 5 cells
	majorSpacing := gridSpacing * 5
	b.WriteString(`<g stroke="#aaa" stroke-width="0.3">` + "\n")
	for x := areaX; x <= areaX+areaW+0.01; x += majorSpacing {
		b.WriteString(fmt.Sprintf(`  <line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f"/>`, x, areaY, x, areaY+areaH))
		b.WriteString("\n")
	}
	for y := areaY; y <= areaY+areaH+0.01; y += majorSpacing {
		b.WriteString(fmt.Sprintf(`  <line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f"/>`, areaX, y, areaX+areaW, y))
		b.WriteString("\n")
	}
	b.WriteString("</g>\n")

	// Corner registration marks (L-shaped fiducials)
	writeCornerMark(&b, areaX, areaY, markerSize, 1, 1)
	writeCornerMark(&b, areaX+areaW, areaY, markerSize, -1, 1)
	writeCornerMark(&b, areaX, areaY+areaH, markerSize, 1, -1)
	writeCornerMark(&b, areaX+areaW, areaY+areaH, markerSize, -1, -1)

	// Center crosshair
	cx, cy := pageW/2, pageH/2
	b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.3"/>`,
		cx-markerSize, cy, cx+markerSize, cy))
	b.WriteString("\n")
	b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.3"/>`,
		cx, cy-markerSize, cx, cy+markerSize))
	b.WriteString("\n")
	b.WriteString(fmt.Sprintf(`<circle cx="%.2f" cy="%.2f" r="1" fill="none" stroke="black" stroke-width="0.3"/>`,
		cx, cy))
	b.WriteString("\n")

	// Multi-page alignment markers (only if multiple pages)
	if totalCols > 1 || totalRows > 1 {
		writeAlignmentMarkers(&b, areaX, areaY, areaW, areaH, markerSize)

		// Page coordinate label
		b.WriteString(fmt.Sprintf(`<text x="%.2f" y="%.2f" font-family="monospace" font-size="3" fill="#999" text-anchor="end">Page %d,%d of %dx%d</text>`,
			areaX+areaW, areaY-2, col+1, row+1, totalCols, totalRows))
		b.WriteString("\n")
	}

	// Scale reference bar (10mm)
	refY := areaY + areaH + 5
	b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.5"/>`,
		areaX, refY, areaX+10, refY))
	b.WriteString("\n")
	b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.5"/>`,
		areaX, refY-1.5, areaX, refY+1.5))
	b.WriteString("\n")
	b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.5"/>`,
		areaX+10, refY-1.5, areaX+10, refY+1.5))
	b.WriteString("\n")
	b.WriteString(fmt.Sprintf(`<text x="%.2f" y="%.2f" font-family="monospace" font-size="2.5" fill="black" text-anchor="middle">10mm</text>`,
		areaX+5, refY+3.5))
	b.WriteString("\n")

	// Grid spacing label
	b.WriteString(fmt.Sprintf(`<text x="%.2f" y="%.2f" font-family="monospace" font-size="2" fill="#999">Grid: %.0fmm</text>`,
		areaX+15, refY+0.8, gridSpacing))
	b.WriteString("\n")

	b.WriteString("</svg>\n")
	return b.String(), nil
}

func writeCornerMark(b *strings.Builder, x, y, size, dx, dy float64) {
	// L-shaped corner mark
	b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.5"/>`,
		x, y, x+size*dx, y))
	b.WriteString("\n")
	b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.5"/>`,
		x, y, x, y+size*dy))
	b.WriteString("\n")
	// Small filled circle at corner
	b.WriteString(fmt.Sprintf(`<circle cx="%.2f" cy="%.2f" r="0.8" fill="black"/>`, x, y))
	b.WriteString("\n")
}

func writeAlignmentMarkers(b *strings.Builder, x, y, w, h, size float64) {
	// Edge midpoint crosses for stitching alignment
	edges := [][2]float64{
		{x + w/2, y},         // top center
		{x + w/2, y + h},     // bottom center
		{x, y + h/2},         // left center
		{x + w, y + h/2},     // right center
	}
	for _, e := range edges {
		b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.4"/>`,
			e[0]-size/2, e[1], e[0]+size/2, e[1]))
		b.WriteString("\n")
		b.WriteString(fmt.Sprintf(`<line x1="%.2f" y1="%.2f" x2="%.2f" y2="%.2f" stroke="black" stroke-width="0.4"/>`,
			e[0], e[1]-size/2, e[0], e[1]+size/2))
		b.WriteString("\n")
	}
}