#[cfg(not(target_arch = "wasm32"))]
use crate::comp;
use crate::{uid::Uid, DamageSource};
use serde::{Deserialize, Serialize};

#[cfg(not(target_arch = "wasm32"))]
use specs::{Component, DerefFlaggedStorage};
#[cfg(not(target_arch = "wasm32"))]
use specs_idvs::IdvStorage;
use std::ops::Mul;

/// Specifies what and how much changed current health
#[derive(Clone, Copy, Debug, Serialize, Deserialize, PartialEq)]
pub struct HealthChange {
    pub amount: f32,
    pub by: Option<Uid>,
    pub cause: Option<DamageSource>,
}

impl HealthChange {
    pub fn damage_by(&self) -> Option<Uid> { self.cause.is_some().then_some(self.by).flatten() }
}

#[derive(Clone, Copy, Debug, Serialize, Deserialize)]
/// Health is represented by u32s within the module, but treated as a float by
/// the rest of the game.
// As a general rule, all input and output values to public functions should be
// floats rather than integers.
pub struct Health {
    // Current and base_max are scaled by 256 within this module compared to what is visible to
    // outside this module. The scaling is done to allow health to function as a fixed point while
    // still having the advantages of being an integer. The scaling of 256 was chosen so that max
    // health could be u16::MAX - 1, and then the scaled health could fit inside an f32 with no
    // precision loss
    /// Current health is how much health the entity currently has. Current
    /// health *must* be lower than or equal to maximum health.
    current: u32,
    /// Base max is the amount of health the entity has without considering
    /// temporary modifiers such as buffs
    base_max: u32,
    /// Maximum is the amount of health the entity has after temporary modifiers
    /// are considered
    maximum: u32,
    // Time since last change and what the last change was
    // TODO: Remove the time since last change, either convert to time of last change or just emit
    // an outcome where appropriate. Is currently just used for frontend.
    pub last_change: (f64, HealthChange),
    pub is_dead: bool,
}

impl Health {
    /// Used when comparisons to health are needed outside this module.
    // This value is chosen as anything smaller than this is more precise than our
    // units of health.
    pub const HEALTH_EPSILON: f32 = 0.5 / Self::MAX_SCALED_HEALTH as f32;
    /// Maximum value allowed for health before scaling
    const MAX_HEALTH: u16 = u16::MAX - 1;
    /// The maximum value allowed for current and maximum health
    /// Maximum value is (u16:MAX - 1) * 256, which only requires 24 bits. This
    /// can fit into an f32 with no loss to precision
    // Cast to u32 done as u32::from cannot be called inside constant
    const MAX_SCALED_HEALTH: u32 = Self::MAX_HEALTH as u32 * Self::SCALING_FACTOR_INT;
    /// The amount health is scaled by within this module
    const SCALING_FACTOR_FLOAT: f32 = 256.;
    const SCALING_FACTOR_INT: u32 = Self::SCALING_FACTOR_FLOAT as u32;

    /// Returns the current value of health casted to a float
    pub fn current(&self) -> f32 { self.current as f32 / Self::SCALING_FACTOR_FLOAT }

    /// Returns the base maximum value of health casted to a float
    pub fn base_max(&self) -> f32 { self.base_max as f32 / Self::SCALING_FACTOR_FLOAT }

    /// Returns the maximum value of health casted to a float
    pub fn maximum(&self) -> f32 { self.maximum as f32 / Self::SCALING_FACTOR_FLOAT }

    /// Returns the fraction of health an entity has remaining
    pub fn fraction(&self) -> f32 { self.current() / self.maximum().max(1.0) }

    /// Updates the maximum value for health
    pub fn update_maximum(&mut self, modifiers: comp::stats::StatsModifier) {
        let maximum = modifiers
            .compute_maximum(self.base_max())
            .mul(Self::SCALING_FACTOR_FLOAT)
            // NaN does not need to be handled here as rust will automatically change to 0 when casting to u32
            .clamp(0.0, Self::MAX_SCALED_HEALTH as f32) as u32;
        self.maximum = maximum;
        // Clamp the current health to enforce the current <= maximum invariant.
        self.current = self.current.min(self.maximum);
    }

    #[cfg(not(target_arch = "wasm32"))]
    pub fn new(body: comp::Body, level: u16) -> Self {
        let health = u32::from(
            body.base_health()
                .saturating_add(body.base_health_increase().saturating_mul(level)),
        ) * Self::SCALING_FACTOR_INT;
        Health {
            current: health,
            base_max: health,
            maximum: health,
            last_change: (0.0, HealthChange {
                amount: 0.0,
                by: None,
                cause: None,
            }),
            is_dead: false,
        }
    }

    // TODO: Delete this once stat points will be a thing
    #[cfg(not(target_arch = "wasm32"))]
    pub fn update_max_hp(&mut self, body: comp::Body, level: u16) {
        let old_max = self.base_max;
        self.base_max = u32::from(
            body.base_health()
                .saturating_add(body.base_health_increase().saturating_mul(level)),
        ) * Self::SCALING_FACTOR_INT;
        self.current = (self.current + self.base_max - old_max).min(self.maximum);
    }

    #[cfg(not(target_arch = "wasm32"))]
    pub fn change_by(&mut self, change: HealthChange) {
        self.current = (((self.current() + change.amount).clamp(0.0, f32::from(Self::MAX_HEALTH))
            * Self::SCALING_FACTOR_FLOAT) as u32)
            .min(self.maximum);
        self.last_change = (0.0, change);
    }

    pub fn should_die(&self) -> bool { self.current == 0 }

    pub fn kill(&mut self) {
        self.current = 0;
        self.is_dead = true;
    }

    #[cfg(not(target_arch = "wasm32"))]
    pub fn revive(&mut self) {
        self.current = self.maximum;
        self.is_dead = false;
    }

    // Function only exists for plugin tests, do not use anywhere else
    // TODO: Remove somehow later
    #[deprecated]
    pub fn empty() -> Self {
        Health {
            current: 0,
            base_max: 0,
            maximum: 0,
            last_change: (0.0, HealthChange {
                amount: 0.0,
                by: None,
                cause: None,
            }),
            is_dead: false,
        }
    }
}

#[cfg(not(target_arch = "wasm32"))]
impl Component for Health {
    type Storage = DerefFlaggedStorage<Self, IdvStorage<Self>>;
}