using System;
using UnityEngine;

public partial class MeshPainter
{
    // --- Pipette (eyedropper) ---
    //
    // A sampling MODE rather than a paint channel: while active, a left-click raycasts onto
    // ANY surface (not just the paint mesh) and reads every channel value at the hit point
    // (albedo, metallic, smoothness, occlusion, emission) into the brush properties - with
    // every opacity/alpha forced to 1 so re-painting reproduces the picked look at full
    // strength.
    //
    // Two read paths, chosen by what was hit:
    //   - Our own paint mesh: read texel-exact from the painted maps via ReadCanonical(),
    //     which converts both backends (GPU RenderTextures / CPU Texture2D mirrors) into the
    //     same canonical layout, so the pick matches what is stored bit-for-bit.
    //   - Any foreign object: read texel-exact from its material maps at the hit UV
    //     (BaseMap/MetallicGloss/Occlusion/Emission) combined with the material scalars, per
    //     the URP/Lit conventions, falling back to scalar properties where a map is absent or
    //     the collider carries no UV (non-MeshCollider).

    [Header("Brush - pipette (eyedropper)")]
    [Tooltip("Pipette mode: a click samples ALL channel values at the hit point on ANY surface " +
             "(albedo, metallic, smoothness, occlusion, emission) and adopts them into the brush " +
             "(all alphas set to 1) instead of painting. Held button picks only once.")]
    public bool pipette = false;

    /// <summary>
    /// Raised after a successful pick, once the brush has adopted the sampled values and all four
    /// paint-channel flags have been enabled. The in-game HUD listens to re-sync its widgets.
    /// </summary>
    public event Action Picked;

    private bool _pickHeld; // edge tracking so a held button picks once, not every frame

    /// <summary>
    /// Raycasts at a screen position against ANY collider, samples every channel value at the hit
    /// (texel-exact where possible) and copies it into the brush, forcing all opacities/alphas to
    /// 1 and enabling every paint channel. Reads regardless of which channels are currently toggled.
    /// </summary>
    private void PickAtScreen(Vector2 screenPos)
    {
        if (!TryRaycastAny(screenPos, out RaycastHit hit)) return;

        bool ok = (hit.collider == _collider)
            ? PickFromPaintTextures(hit)
            : PickFromForeignMaterial(hit);
        if (!ok) return;

        // "Set all alpha values to 1": full-strength adoption across every opacity control.
        metallicSmoothnessOpacity = 1f;
        occlusionOpacity = 1f;

        // Picking a whole material implies repainting all of it, so enable every channel.
        paintAlbedo = true;
        paintMetallicSmoothness = true;
        paintOcclusion = true;
        paintEmission = true;

        // A pick is a one-shot action: leave pipette mode automatically so the next click paints.
        pipette = false;

        // Let listeners (the in-game HUD) refresh their widgets to the adopted values + flags.
        Picked?.Invoke();
    }

    /// <summary>
    /// Picks from our own painted maps at the hit texel (bit-exact, backend-agnostic).
    /// </summary>
    private bool PickFromPaintTextures(RaycastHit hit)
    {
        if (_verts == null || _uvs == null || _tris == null || hit.triangleIndex < 0) return false;

        int t = hit.triangleIndex;
        if (t * 3 + 2 >= _tris.Length) return false;
        int i0 = _tris[t * 3], i1 = _tris[t * 3 + 1], i2 = _tris[t * 3 + 2];

        // UV at the hit via barycentric interpolation of the cached UVs - same UV space the
        // brush paints into, so the sampled texel is exactly the one that would be painted.
        Vector3 bc = hit.barycentricCoordinate;
        Vector2 uv = _uvs[i0] * bc.x + _uvs[i1] * bc.y + _uvs[i2] * bc.z;

        int px = Mathf.Clamp(Mathf.FloorToInt(uv.x * textureSize), 0, textureSize - 1);
        int py = Mathf.Clamp(Mathf.FloorToInt(uv.y * textureSize), 0, textureSize - 1);
        int idx = py * textureSize + px;

        // ReadCanonical gives material layout for either backend:
        //   albedo   -> sRGB RGB
        //   MSO      -> R = metallic, G = occlusion, A = smoothness (linear data)
        //   emission -> sRGB RGB
        Color32[] alb = ReadCanonical(MAP_ALBEDO);
        Color32[] mso = ReadCanonical(MAP_MSO);
        Color32[] em = ReadCanonical(MAP_EM);
        if (idx < 0 || idx >= alb.Length || idx >= mso.Length || idx >= em.Length) return false;

        Color32 a = alb[idx];
        Color32 m = mso[idx];
        Color32 e = em[idx];

        // sRGB bytes map straight back into the gamma-space brush colours (round-trips exactly).
        brushColor = new Color(a.r / 255f, a.g / 255f, a.b / 255f, 1f);
        metallic = m.r / 255f;
        occlusion = m.g / 255f;
        smoothness = m.a / 255f;
        emissionColor = new Color(e.r / 255f, e.g / 255f, e.b / 255f, 1f);
        return true;
    }

    /// <summary>
    /// Picks from a foreign object's material at the hit UV: texel-exact texture samples
    /// (where the surface has a MeshCollider and the map exists) combined with the material
    /// scalars per the URP/Lit conventions, with scalar fallbacks everywhere else.
    /// </summary>
    private bool PickFromForeignMaterial(RaycastHit hit)
    {
        Collider col = hit.collider;
        if (!col) return false;
        Renderer rend = col.GetComponent<Renderer>();
        if (!rend) rend = col.GetComponentInParent<Renderer>();
        if (!rend) return false;
        Material mat = rend.sharedMaterial;
        if (!mat) return false;

        // textureCoord is only meaningful for a MeshCollider; other collider shapes carry no UV,
        // so we fall back to the material's uniform scalar values for those.
        bool hasUv = col is MeshCollider;
        Vector2 uv = hasUv ? hit.textureCoord : Vector2.zero;

        // --- Albedo: BaseMap (sRGB) * BaseColor ---
        Color baseCol = GetColorProp(mat, "_BaseColor", "_Color", Color.white);
        Texture baseTex = GetTexProp(mat, "_BaseMap", "_MainTex");
        Color albedo = baseCol;
        if (hasUv && baseTex)
            albedo = SampleTexel(baseTex, ApplyST(mat, "_BaseMap", "_MainTex", uv), true) * baseCol;
        brushColor = new Color(Mathf.Clamp01(albedo.r), Mathf.Clamp01(albedo.g), Mathf.Clamp01(albedo.b), 1f);

        // --- Metallic / Smoothness: MetallicGloss map (linear) ---
        // URP/Lit: metallic = map.r ; smoothness = map.a * _Smoothness (or _Metallic/_Glossiness scalars).
        float metallicVal = GetFloatProp(mat, "_Metallic", null, 0f);
        float smoothVal = GetFloatProp(mat, "_Smoothness", "_Glossiness", 0.5f);
        Texture mgTex = GetTexProp(mat, "_MetallicGlossMap", null);
        if (hasUv && mgTex)
        {
            Color mg = SampleTexel(mgTex, ApplyST(mat, "_MetallicGlossMap", null, uv), false);
            metallicVal = mg.r;
            smoothVal = mg.a * smoothVal;
        }
        metallic = Mathf.Clamp01(metallicVal);
        smoothness = Mathf.Clamp01(smoothVal);

        // --- Occlusion: OcclusionMap.g (linear), lerp(1, g, strength) ---
        float occStrength = GetFloatProp(mat, "_OcclusionStrength", null, 1f);
        float occ = 1f;
        Texture occTex = GetTexProp(mat, "_OcclusionMap", null);
        if (hasUv && occTex)
            occ = Mathf.Lerp(1f, SampleTexel(occTex, ApplyST(mat, "_OcclusionMap", null, uv), false).g, occStrength);
        occlusion = Mathf.Clamp01(occ);

        // --- Emission: EmissionMap (sRGB) * EmissionColor ---
        Color emColor = GetColorProp(mat, "_EmissionColor", null, Color.black);
        Texture emTex = GetTexProp(mat, "_EmissionMap", null);
        Color emCol = emColor;
        if (hasUv && emTex)
            emCol = SampleTexel(emTex, ApplyST(mat, "_EmissionMap", null, uv), true) * emColor;
        emissionColor = new Color(Mathf.Clamp01(emCol.r), Mathf.Clamp01(emCol.g), Mathf.Clamp01(emCol.b), 1f);

        return true;
    }

    // --- Material read helpers (name-tolerant: URP and legacy Standard) ---

    private static Color GetColorProp(Material m, string nameA, string nameB, Color fallback)
    {
        if (m.HasProperty(nameA)) return m.GetColor(nameA);
        if (nameB != null && m.HasProperty(nameB)) return m.GetColor(nameB);
        return fallback;
    }

    private static float GetFloatProp(Material m, string nameA, string nameB, float fallback)
    {
        if (m.HasProperty(nameA)) return m.GetFloat(nameA);
        if (nameB != null && m.HasProperty(nameB)) return m.GetFloat(nameB);
        return fallback;
    }

    private static Texture GetTexProp(Material m, string nameA, string nameB)
    {
        if (m.HasProperty(nameA)) { Texture t = m.GetTexture(nameA); if (t) return t; }
        if (nameB != null && m.HasProperty(nameB)) { Texture t = m.GetTexture(nameB); if (t) return t; }
        return null;
    }

    private static Vector2 ApplyST(Material m, string nameA, string nameB, Vector2 uv)
    {
        string prop = m.HasProperty(nameA) ? nameA : (nameB != null && m.HasProperty(nameB) ? nameB : null);
        if (prop == null) return uv;
        Vector2 s = m.GetTextureScale(prop);
        Vector2 o = m.GetTextureOffset(prop);
        return new Vector2(uv.x * s.x + o.x, uv.y * s.y + o.y);
    }

    /// <summary>
    /// Samples a single texel from a texture at a UV (texel-exact). Uses GetPixelBilinear when the
    /// texture is CPU-readable; otherwise blits it to a temporary RenderTexture and reads back the
    /// one texel, so it works regardless of the texture's "Read/Write" import flag. <paramref
    /// name="srgb"/> selects the colour space so the returned value matches the readable path
    /// (gamma for colour maps, linear for data maps).
    /// </summary>
    private static Color SampleTexel(Texture tex, Vector2 uv, bool srgb)
    {
        Texture2D t2d = tex as Texture2D;
        if (t2d != null && t2d.isReadable)
            return t2d.GetPixelBilinear(uv.x, uv.y);

        int w = Mathf.Max(1, tex.width), h = Mathf.Max(1, tex.height);
        var rw = srgb ? RenderTextureReadWrite.sRGB : RenderTextureReadWrite.Linear;
        RenderTexture rt = RenderTexture.GetTemporary(w, h, 0, RenderTextureFormat.ARGB32, rw);
        RenderTexture prev = RenderTexture.active;
        Graphics.Blit(tex, rt);
        RenderTexture.active = rt;

        var tmp = new Texture2D(1, 1, TextureFormat.RGBA32, false, !srgb);
        int px = Mathf.Clamp(Mathf.FloorToInt(Mathf.Repeat(uv.x, 1f) * w), 0, w - 1);
        int py = Mathf.Clamp(Mathf.FloorToInt(Mathf.Repeat(uv.y, 1f) * h), 0, h - 1);
        tmp.ReadPixels(new Rect(px, py, 1, 1), 0, 0, false);
        tmp.Apply(false);
        Color c = tmp.GetPixel(0, 0);

        RenderTexture.active = prev;
        RenderTexture.ReleaseTemporary(rt);
        if (Application.isPlaying) Destroy(tmp); else DestroyImmediate(tmp);
        return c;
    }
}