package mesh

import (
	"fmt"
	"math"
	"strings"
)

// View is an orthographic camera basis: Right/Up span the screen plane,
// Toward points from the scene toward the viewer (bigger depth = closer).
type View struct {
	Name              string
	Axes              string // human-readable axis legend
	Right, Up, Toward Vec3
}

var Views = map[string]View{
	"front": {"front", "X→right Y↑up (seen from +Z)", Vec3{1, 0, 0}, Vec3{0, 1, 0}, Vec3{0, 0, 1}},
	"back":  {"back", "-X→right Y↑up (seen from -Z)", Vec3{-1, 0, 0}, Vec3{0, 1, 0}, Vec3{0, 0, -1}},
	"side":  {"side", "-Z→right Y↑up (seen from +X)", Vec3{0, 0, -1}, Vec3{0, 1, 0}, Vec3{1, 0, 0}},
	"top":   {"top", "X→right Z↓down-screen (seen from above, +Y)", Vec3{1, 0, 0}, Vec3{0, 0, -1}, Vec3{0, 1, 0}},
	"iso": {"iso", "isometric from (+X +Y +Z)",
		Vec3{1, 0, -1}.Norm(), Vec3{-1, 2, -1}.Norm(), Vec3{1, 1, 1}.Norm()},
}

// ViewOrder is the canonical ordering for multi-view output.
var ViewOrder = []string{"front", "side", "top", "iso", "back"}

const shadeRamp = " .:-=+*#%@"

// charAspect compensates terminal cells being ~2x taller than wide.
const charAspect = 0.5

// RenderASCII draws the mesh from the given view into a text block of
// the given character width. Triangles are z-buffer rasterized and
// shaded by how much each face points toward the light (over the
// viewer's shoulder), so curvature and depth read as brightness.
func RenderASCII(m *Mesh, v View, width int) string {
	if width < 8 {
		width = 8
	}
	if len(m.Tris) == 0 {
		return "(empty mesh)\n"
	}

	// project all vertices into view space
	type pv struct{ x, y, z float64 }
	pts := make([]pv, len(m.Verts))
	minX, minY := math.Inf(1), math.Inf(1)
	maxX, maxY := math.Inf(-1), math.Inf(-1)
	for i, w := range m.Verts {
		p := pv{w.Dot(v.Right), w.Dot(v.Up), w.Dot(v.Toward)}
		pts[i] = p
		minX, maxX = math.Min(minX, p.x), math.Max(maxX, p.x)
		minY, maxY = math.Min(minY, p.y), math.Max(maxY, p.y)
	}
	spanX, spanY := maxX-minX, maxY-minY
	if spanX == 0 {
		spanX = 1e-9
	}
	if spanY == 0 {
		spanY = 1e-9
	}
	height := int(float64(width) * (spanY / spanX) * charAspect)
	if height < 1 {
		height = 1
	}
	if height > 4*width {
		height = 4 * width
	}
	sx := float64(width-1) / spanX
	sy := float64(height-1) / spanY

	depth := make([]float64, width*height)
	for i := range depth {
		depth[i] = math.Inf(-1)
	}
	shade := make([]float64, width*height)
	for i := range shade {
		shade[i] = -1
	}

	light := v.Toward.Mul(0.8).Add(v.Up.Mul(0.5)).Add(v.Right.Mul(0.3)).Norm()

	for ti, t := range m.Tris {
		n := m.FaceNormal(ti)
		// abs: downloaded models often have mixed winding; treat both
		// sides as lit so the silhouette never goes black
		lum := 0.15 + 0.85*math.Abs(n.Dot(light))

		a, b, c := pts[t[0]], pts[t[1]], pts[t[2]]
		ax, ay := (a.x-minX)*sx, (maxY-a.y)*sy
		bx, by := (b.x-minX)*sx, (maxY-b.y)*sy
		cx, cy := (c.x-minX)*sx, (maxY-c.y)*sy

		x0 := int(math.Floor(math.Min(ax, math.Min(bx, cx))))
		x1 := int(math.Ceil(math.Max(ax, math.Max(bx, cx))))
		y0 := int(math.Floor(math.Min(ay, math.Min(by, cy))))
		y1 := int(math.Ceil(math.Max(ay, math.Max(by, cy))))
		if x0 < 0 {
			x0 = 0
		}
		if y0 < 0 {
			y0 = 0
		}
		if x1 >= width {
			x1 = width - 1
		}
		if y1 >= height {
			y1 = height - 1
		}

		area := (bx-ax)*(cy-ay) - (by-ay)*(cx-ax)
		if area == 0 {
			continue
		}
		for py := y0; py <= y1; py++ {
			for px := x0; px <= x1; px++ {
				fx, fy := float64(px), float64(py)
				w0 := (bx-ax)*(fy-ay) - (by-ay)*(fx-ax)
				w1 := (cx-bx)*(fy-by) - (cy-by)*(fx-bx)
				w2 := (ax-cx)*(fy-cy) - (ay-cy)*(fx-cx)
				if !sameSide(w0, w1, w2, area) {
					continue
				}
				// barycentric depth: w2 tracks b, w0 tracks c
				l1 := w2 / area
				l2 := w0 / area
				l0 := 1 - l1 - l2
				z := l0*a.z + l1*b.z + l2*c.z
				idx := py*width + px
				if z > depth[idx] {
					depth[idx] = z
					shade[idx] = lum
				}
			}
		}
	}

	var sb strings.Builder
	mn, mx := m.BBox()
	size := mx.Sub(mn)
	fmt.Fprintf(&sb, "%s view — %s\nmodel %.3g x %.3g x %.3g (XYZ)\n",
		v.Name, v.Axes, size.X, size.Y, size.Z)
	ramp := []rune(shadeRamp)
	for py := 0; py < height; py++ {
		for px := 0; px < width; px++ {
			s := shade[py*width+px]
			if s < 0 {
				sb.WriteByte(' ')
				continue
			}
			i := int(s * float64(len(ramp)-1))
			if i >= len(ramp) {
				i = len(ramp) - 1
			}
			sb.WriteRune(ramp[i])
		}
		sb.WriteByte('\n')
	}
	return sb.String()
}

func sameSide(w0, w1, w2, area float64) bool {
	if area > 0 {
		return w0 >= 0 && w1 >= 0 && w2 >= 0
	}
	return w0 <= 0 && w1 <= 0 && w2 <= 0
}