precision highp float;

// Textures
uniform sampler2D u_currentImage;
uniform sampler2D u_nextImage;

// Transition
uniform float u_blend;           // 0=current, 1=next
uniform int u_transitionMode;    // 0=crossfade, 1=dissolve, 2=glitch_cut, 3=melt_morph

// Shader params (from escalation engine, all 0-1)
uniform float u_morphSpeed;
uniform float u_shaderSeverity;
uniform float u_noiseLevel;
uniform float u_time;

// Scare flash
uniform float u_flashIntensity;  // 0=none, 1=full
uniform int u_flashType;         // 0=white, 1=inversion, 2=face_flash

// Vignette and overlay
uniform float u_vignetteStrength;
uniform vec3 u_colorTint;        // palette color shift

varying vec2 v_uv;

// --- Noise functions ---

float hash(vec2 p) {
    return fract(sin(dot(p, vec2(127.1, 311.7))) * 43758.5453);
}

float noise(vec2 p) {
    vec2 i = floor(p);
    vec2 f = fract(p);
    float a = hash(i);
    float b = hash(i + vec2(1.0, 0.0));
    float c = hash(i + vec2(0.0, 1.0));
    float d = hash(i + vec2(1.0, 1.0));
    vec2 u = f * f * (3.0 - 2.0 * f);
    return mix(a, b, u.x) + (c - a) * u.y * (1.0 - u.x) + (d - b) * u.x * u.y;
}

// --- Effect functions ---

vec2 meshWarp(vec2 uv, float severity, float time) {
    float freq = 3.0 + severity * 8.0;
    float amp = 0.002 + severity * 0.03;
    uv.x += sin(uv.y * freq + time * 0.5) * amp;
    uv.y += cos(uv.x * freq + time * 0.7) * amp;
    return uv;
}

vec3 chromaticAberration(sampler2D tex, vec2 uv, float severity) {
    float offset = 0.001 + severity * 0.015;
    float r = texture2D(tex, uv + vec2(offset, 0.0)).r;
    float g = texture2D(tex, uv).g;
    float b = texture2D(tex, uv - vec2(offset, 0.0)).b;
    return vec3(r, g, b);
}

vec2 meltEffect(vec2 uv, float severity, float time) {
    float melt = severity * 0.05 * noise(vec2(uv.x * 10.0, time * 0.3));
    uv.y += melt;
    return uv;
}

vec2 glitchEffect(vec2 uv, float severity, float time) {
    float glitchLine = step(0.98 - severity * 0.15, hash(vec2(floor(uv.y * 50.0), floor(time * 8.0))));
    uv.x += glitchLine * (hash(vec2(time, uv.y)) - 0.5) * severity * 0.1;
    return uv;
}

float scanlines(vec2 uv, float time) {
    return 0.95 + 0.05 * sin(uv.y * 800.0 + time * 2.0);
}

float filmGrain(vec2 uv, float time, float amount) {
    return 1.0 - amount * 0.5 * (hash(uv * 1000.0 + time) - 0.5);
}

float vignette(vec2 uv, float strength) {
    vec2 center = uv - 0.5;
    float dist = length(center);
    return 1.0 - smoothstep(0.3, 0.9, dist) * strength;
}

float pulse(float time, float severity) {
    return 1.0 + sin(time * (1.0 + severity * 3.0)) * severity * 0.1;
}

// --- Transition functions ---

vec3 transitionCrossfade(vec2 uv, float blend) {
    vec3 a = texture2D(u_currentImage, uv).rgb;
    vec3 b = texture2D(u_nextImage, uv).rgb;
    return mix(a, b, blend);
}

vec3 transitionDissolve(vec2 uv, float blend) {
    vec3 a = texture2D(u_currentImage, uv).rgb;
    vec3 b = texture2D(u_nextImage, uv).rgb;
    // Dissolve through black
    float mid = 0.5;
    if (blend < mid) {
        return a * (1.0 - blend / mid);
    } else {
        return b * ((blend - mid) / (1.0 - mid));
    }
}

vec3 transitionGlitchCut(vec2 uv, float blend, float time) {
    // Hard cut with glitch artifacts
    float threshold = 0.5 + 0.1 * sin(time * 20.0);
    vec3 img = blend < threshold
        ? texture2D(u_currentImage, uv).rgb
        : texture2D(u_nextImage, uv).rgb;
    // Add RGB split at transition point
    if (abs(blend - threshold) < 0.1) {
        img = chromaticAberration(blend < threshold ? u_currentImage : u_nextImage, uv, 0.8);
    }
    return img;
}

vec3 transitionMeltMorph(vec2 uv, float blend, float time) {
    vec2 meltUV = uv;
    meltUV.y += blend * 0.1 * noise(vec2(uv.x * 5.0, time));
    vec3 a = texture2D(u_currentImage, meltUV).rgb;
    vec3 b = texture2D(u_nextImage, uv).rgb;
    return mix(a, b, smoothstep(0.3, 0.7, blend));
}

// --- Main ---

void main() {
    vec2 uv = v_uv;
    float severity = u_shaderSeverity;

    // Apply distortion effects
    uv = meshWarp(uv, severity * u_morphSpeed, u_time);
    uv = meltEffect(uv, severity * 0.5, u_time);
    uv = glitchEffect(uv, severity, u_time);

    // Clamp UV to prevent sampling outside texture
    uv = clamp(uv, 0.0, 1.0);

    // Image transition
    vec3 color;
    if (u_transitionMode == 0) {
        color = transitionCrossfade(uv, u_blend);
    } else if (u_transitionMode == 1) {
        color = transitionDissolve(uv, u_blend);
    } else if (u_transitionMode == 2) {
        color = transitionGlitchCut(uv, u_blend, u_time);
    } else {
        color = transitionMeltMorph(uv, u_blend, u_time);
    }

    // Chromatic aberration on composited image
    if (severity > 0.1) {
        vec3 aberrated = chromaticAberration(u_currentImage, uv, severity);
        color = mix(color, aberrated, severity * 0.3);
    }

    // Color tint / palette shift
    color = mix(color, color * u_colorTint, severity * 0.3);

    // Pulse brightness
    color *= pulse(u_time, severity);

    // Film grain / noise
    color *= filmGrain(v_uv, u_time, u_noiseLevel);

    // Scanlines
    color *= scanlines(v_uv, u_time);

    // Vignette
    color *= vignette(v_uv, 0.5 + severity * 0.5);

    // Flash effects
    if (u_flashIntensity > 0.0) {
        if (u_flashType == 0) {
            // White-out
            color = mix(color, vec3(1.0), u_flashIntensity);
        } else if (u_flashType == 1) {
            // Inversion
            color = mix(color, 1.0 - color, u_flashIntensity);
        } else {
            // Face flash (red tint)
            color = mix(color, vec3(1.0, 0.0, 0.0), u_flashIntensity * 0.7);
        }
    }

    gl_FragColor = vec4(color, 1.0);
}