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
    // the mesh, reads ALL painted channel values at the hit texel (albedo, metallic,
    // smoothness, occlusion, emission) and adopts them into the brush properties - with every
    // opacity/alpha forced to 1 so re-painting reproduces the picked look at full strength.
    // The values are read through ReadCanonical(), which already converts both backends (GPU
    // RenderTextures / CPU Texture2D mirrors) into the same canonical material layout, so the
    // pick matches what is stored without any new colour-space handling.

    [Header("Brush - pipette (eyedropper)")]
    [Tooltip("Pipette mode: a click samples ALL channel values at the hit point (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, finds the hit texel UV and copies every painted channel
    /// value there into the brush (albedo color, metallic, smoothness, occlusion, emission
    /// color), forcing all opacities/alphas to 1. Reads regardless of which channels are
    /// currently toggled for painting.
    /// </summary>
    private void PickAtScreen(Vector2 screenPos)
    {
        if (!TryRaycastPaintMesh(screenPos, out RaycastHit hit)) return;
        if (_verts == null || _uvs == null || _tris == null || hit.triangleIndex < 0) return;

        int t = hit.triangleIndex;
        if (t * 3 + 2 >= _tris.Length) return;
        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;

        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);

        // "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;

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