//! 有限布局盒子的尺寸策略。区分 auto、固定值和 fill，并处理 min/max 对约束与最终尺寸的限制。
//! margin、border、padding 的空间分配由布局层结合本模块完成；场景世界范围不被当成无限布局盒子。
//!
//! Native border-box sizing. An unbounded axis cannot resolve `fill`.
use crate::{layout::Size, ui_bridge::MAX_DIMENSION};
use anyhow::Result;
use endor_core::{Value, VmError};

#[derive(Debug, Clone, Copy, Default, PartialEq)]
/// 一个布局轴的尺寸策略：随内容、固定值或占用有限可用空间。
pub enum Dimension {
    #[default]
    Auto,
    Fixed(f32),
    Fill,
}

impl Dimension {
    /// 把内部尺寸策略投影为相应的源属性表示。
    pub fn value(self) -> Value {
        match self {
            Self::Auto => Value::Text("auto".into()),
            Self::Fill => Value::Text("fill".into()),
            Self::Fixed(value) => Value::Number((value as f64).into()),
        }
    }

    /// 把外部源码或属性表示转换为内部枚举/结构，并反馈不支持的输入。
    pub fn parse(value: &Value) -> Result<Self, VmError> {
        match value {
            Value::Text(text) if text == "auto" => Ok(Self::Auto),
            Value::Text(text) if text == "fill" => Ok(Self::Fill),
            Value::Number(_) => Ok(Self::Fixed(crate::scroll::coordinate(value).and_then(
                |n| {
                    if n >= 0.0 {
                        Ok(n)
                    } else {
                        Err(VmError::InvalidArgument(
                            "box dimensions must be nonnegative",
                        ))
                    }
                },
            )?)),
            _ => Err(VmError::InvalidArgument(
                "box dimension expects auto, fill or a nonnegative number",
            )),
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq)]
/// border-box 尺寸策略与双轴上下限，实际求解仍要结合父级约束。
pub struct Sizing {
    pub width: Dimension,
    pub height: Dimension,
    pub min_width: f32,
    pub min_height: f32,
    pub max_width: f32,
    pub max_height: f32,
}

impl Default for Sizing {
    /// 建立类型约定的初始值，供尚未发布或尚未交互的状态使用。
    fn default() -> Self {
        Self {
            width: Dimension::Auto,
            height: Dimension::Auto,
            min_width: 0.0,
            min_height: 0.0,
            max_width: MAX_DIMENSION as f32,
            max_height: MAX_DIMENSION as f32,
        }
    }
}

impl Sizing {
    /// Constrain descendants using the actual finite box before wrapping text.
    /// 根据固定/auto/fill 与 min/max 规则细化父级提供的可用约束。
    pub fn available(self, mut constraints: [f32; 4]) -> [f32; 4] {
        constraints[2] = constraints[2].min(self.max_width);
        constraints[3] = constraints[3].min(self.max_height);
        if let Dimension::Fixed(width) = self.width {
            constraints[2] = constraints[2].min(width.max(self.min_width));
        }
        if let Dimension::Fixed(height) = self.height {
            constraints[3] = constraints[3].min(height.max(self.min_height));
        }
        constraints[0] = constraints[0].min(constraints[2]);
        constraints[1] = constraints[1].min(constraints[3]);
        constraints
    }

    /// 结合内容期望尺寸、轴策略和父级约束求最终盒子尺寸；无界轴不能解析 fill。
    pub fn resolve(self, intrinsic: Size, constraints: [f32; 4]) -> Result<Size> {
        /// 针对单个尺寸轴应用约束与边界规则，供双轴尺寸求解复用。
        fn axis(
            policy: Dimension,
            intrinsic: f32,
            min: f32,
            max: f32,
            available: f32,
        ) -> Result<f32> {
            let value = match policy {
                Dimension::Auto => intrinsic,
                Dimension::Fixed(value) => value,
                Dimension::Fill => {
                    if available >= MAX_DIMENSION as f32 {
                        return Err(VmError::InvalidArgument(
                            "fill requires a finite parent allocation on this axis",
                        )
                        .into());
                    }
                    available
                }
            };
            Ok(value.clamp(min, max).min(available))
        }
        Ok(Size {
            width: axis(
                self.width,
                intrinsic.width,
                self.min_width,
                self.max_width,
                constraints[2],
            )?,
            height: axis(
                self.height,
                intrinsic.height,
                self.min_height,
                self.max_height,
                constraints[3],
            )?,
        })
    }
}