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// Copyright (c) Cole Frederick. All rights reserved.
// The use and distribution terms for this software are covered by the
// Eclipse Public License 1.0 (https://opensource.org/licenses/eclipse-1.0.php)
// which can be found in the file epl-v10.html at the root of this distribution.
// By using this software in any fashion, you are agreeing to be bound by the terms of this license.
// You must not remove this notice, or any other, from this software.

use memory::*;

/// The Guide structure is hydrated from its in-memory representation, 64 bits in length.
/// The top 32 bits contain the hash, the bottom 32 bits tell if the number is arbitrary
/// precision, and if so, how many units hold the significant bits.

/// `Top 32 bits  [                    Hash  (32) ]`
/// `Bottom bits  [ Big? | Significant units (16) ]`
///


#[derive(Copy, Clone, Debug)]
pub struct Guide {
    pub hash: u32,

    pub is_big_bit: u32,
    pub unit_count: u32,

    pub prism: AnchoredLine,
    pub root: AnchoredLine,
}

impl Guide {
    pub fn units() -> u32 { if cfg!(target_pointer_width = "32") { 2 } else { 1 } }
    pub fn segment(&self) -> Segment { self.prism.segment() }
    pub fn set_hash(mut self, hash: u32) -> Guide {
        self.hash = hash;
        self
    }
    pub fn clear_hash(mut self) -> Guide {
        self.hash = 0;
        self
    }
    pub fn has_hash(&self) -> bool { self.hash != 0 }
    pub fn set_big(mut self) -> Guide {
        self.is_big_bit = 1;
        self
    }
    pub fn is_big(&self) -> bool { self.is_big_bit == 1 }
    pub fn set_count(mut self, count: u32) -> Guide {
        self.unit_count = count;
        self.clear_hash()
    }

    pub fn reroot(mut self) -> Guide {
        let root_offset = 1 /*prism*/ + Guide::units();
        self.root = self.prism.offset(root_offset as i32);
        self
    }

    pub fn hydrate(prism: AnchoredLine) -> Guide {
        if cfg!(target_pointer_width = "32") {
            Guide::hydrate_top_bot(prism, prism[1].into(), prism[2].into())
        } else {
            let g: u64 = prism[1].into();
            Guide::hydrate_top_bot(prism, (g >> 32) as u32, g as u32)
        }
    }

    pub fn hydrate_top_bot(prism: AnchoredLine, top: u32, bot: u32) -> Guide {
        let hash = top;
        let is_big_bit = (bot >> 31) & 1;
        let unit_count = bot & 0xFFFF;

        let root_offset = 1 /*prism*/ + Guide::units();
        let root = prism.offset(root_offset as i32);

        Guide { hash, is_big_bit, unit_count, prism, root }
    }

    pub fn new(prism: AnchoredLine) -> Guide {
        let root_offset = 1 /*prism*/ + Guide::units();
        Guide { hash: 0, is_big_bit: 0, unit_count: 0,
            prism, root: prism.offset(root_offset as i32) }
    }

    pub fn store_at(&self, mut prism: AnchoredLine) {
        let top: u32 = self.hash;
        let bot: u32 = (self.is_big_bit << 31) | self.unit_count;
        if cfg!(target_pointer_width = "32") {
            prism[1] = top.into();
            prism[2] = bot.into();
        } else {
            let g: u64 = ((top as u64) << 32) | (bot as u64);
            prism[1] = g.into();
        }
    }

    pub fn store(self) -> Guide {
        self.store_at(self.prism);
        self
    }

    pub fn store_hash(self) -> Guide {
        let prism = self.prism;
        let top: u32 = self.hash;
        let bot: u32 = (self.is_big_bit << 31) | self.unit_count;
        if cfg!(target_pointer_width = "32") {
            prism.store_hash(1, top.into());
            prism.store_hash(2, bot.into());
        } else {
            let g: u64 = ((top as u64) << 32) | (bot as u64);
            prism.store_hash(1, g.into());
        }
        self
    }
}