// Bitcoin Dev Kit
// Written in 2020 by Alekos Filini <alekos.filini@gmail.com>
//
// Copyright (c) 2020-2021 Bitcoin Dev Kit Developers
//
// This file is licensed under the Apache License, Version 2.0 <LICENSE-APACHE
// or http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your option.
// You may not use this file except in accordance with one or both of these
// licenses.

use bitcoin::blockdata::script::Script;
use bitcoin::secp256k1::{All, Secp256k1};

use miniscript::{MiniscriptKey, Satisfier, ToPublicKey};

// MSB of the nSequence. If set there's no consensus-constraint, so it must be disabled when
// spending using CSV in order to enforce CSV rules
pub(crate) const SEQUENCE_LOCKTIME_DISABLE_FLAG: u32 = 1 << 31;
// When nSequence is lower than this flag the timelock is interpreted as block-height-based,
// otherwise it's time-based
pub(crate) const SEQUENCE_LOCKTIME_TYPE_FLAG: u32 = 1 << 22;
// Mask for the bits used to express the timelock
pub(crate) const SEQUENCE_LOCKTIME_MASK: u32 = 0x0000FFFF;

// Threshold for nLockTime to be considered a block-height-based timelock rather than time-based
pub(crate) const BLOCKS_TIMELOCK_THRESHOLD: u32 = 500000000;

/// Trait to check if a value is below the dust limit
// we implement this trait to make sure we don't mess up the comparison with off-by-one like a <
// instead of a <= etc.
pub trait IsDust {
    /// Check whether or not a value is below dust limit
    fn is_dust(&self, script: &Script) -> bool;
}

impl IsDust for u64 {
    fn is_dust(&self, script: &Script) -> bool {
        *self <= script.dust_value().as_sat()
    }
}

pub struct After {
    pub current_height: Option<u32>,
    pub assume_height_reached: bool,
}

impl After {
    pub(crate) fn new(current_height: Option<u32>, assume_height_reached: bool) -> After {
        After {
            current_height,
            assume_height_reached,
        }
    }
}

pub(crate) fn check_nsequence_rbf(rbf: u32, csv: u32) -> bool {
    // This flag cannot be set in the nSequence when spending using OP_CSV
    if rbf & SEQUENCE_LOCKTIME_DISABLE_FLAG != 0 {
        return false;
    }

    let mask = SEQUENCE_LOCKTIME_TYPE_FLAG | SEQUENCE_LOCKTIME_MASK;
    let rbf = rbf & mask;
    let csv = csv & mask;

    // Both values should be represented in the same unit (either time-based or
    // block-height based)
    if (rbf < SEQUENCE_LOCKTIME_TYPE_FLAG) != (csv < SEQUENCE_LOCKTIME_TYPE_FLAG) {
        return false;
    }

    // The value should be at least `csv`
    if rbf < csv {
        return false;
    }

    true
}

pub(crate) fn check_nlocktime(nlocktime: u32, required: u32) -> bool {
    // Both values should be expressed in the same unit
    if (nlocktime < BLOCKS_TIMELOCK_THRESHOLD) != (required < BLOCKS_TIMELOCK_THRESHOLD) {
        return false;
    }

    // The value should be at least `required`
    if nlocktime < required {
        return false;
    }

    true
}

impl<Pk: MiniscriptKey + ToPublicKey> Satisfier<Pk> for After {
    fn check_after(&self, n: u32) -> bool {
        if let Some(current_height) = self.current_height {
            current_height >= n
        } else {
            self.assume_height_reached
        }
    }
}

pub struct Older {
    pub current_height: Option<u32>,
    pub create_height: Option<u32>,
    pub assume_height_reached: bool,
}

impl Older {
    pub(crate) fn new(
        current_height: Option<u32>,
        create_height: Option<u32>,
        assume_height_reached: bool,
    ) -> Older {
        Older {
            current_height,
            create_height,
            assume_height_reached,
        }
    }
}

impl<Pk: MiniscriptKey + ToPublicKey> Satisfier<Pk> for Older {
    fn check_older(&self, n: u32) -> bool {
        if let Some(current_height) = self.current_height {
            // TODO: test >= / >
            current_height as u64 >= self.create_height.unwrap_or(0) as u64 + n as u64
        } else {
            self.assume_height_reached
        }
    }
}

pub(crate) type SecpCtx = Secp256k1<All>;

#[cfg(test)]
mod test {
    use super::{
        check_nlocktime, check_nsequence_rbf, BLOCKS_TIMELOCK_THRESHOLD,
        SEQUENCE_LOCKTIME_TYPE_FLAG,
    };
    use crate::types::FeeRate;

    #[test]
    fn test_fee_from_btc_per_kb() {
        let fee = FeeRate::from_btc_per_kvb(1e-5);
        assert!((fee.as_sat_vb() - 1.0).abs() < 0.0001);
    }

    #[test]
    fn test_fee_from_sats_vbyte() {
        let fee = FeeRate::from_sat_per_vb(1.0);
        assert!((fee.as_sat_vb() - 1.0).abs() < 0.0001);
    }

    #[test]
    fn test_fee_default_min_relay_fee() {
        let fee = FeeRate::default_min_relay_fee();
        assert!((fee.as_sat_vb() - 1.0).abs() < 0.0001);
    }

    #[test]
    fn test_check_nsequence_rbf_msb_set() {
        let result = check_nsequence_rbf(0x80000000, 5000);
        assert!(!result);
    }

    #[test]
    fn test_check_nsequence_rbf_lt_csv() {
        let result = check_nsequence_rbf(4000, 5000);
        assert!(!result);
    }

    #[test]
    fn test_check_nsequence_rbf_different_unit() {
        let result = check_nsequence_rbf(SEQUENCE_LOCKTIME_TYPE_FLAG + 5000, 5000);
        assert!(!result);
    }

    #[test]
    fn test_check_nsequence_rbf_mask() {
        let result = check_nsequence_rbf(0x3f + 10_000, 5000);
        assert!(result);
    }

    #[test]
    fn test_check_nsequence_rbf_same_unit_blocks() {
        let result = check_nsequence_rbf(10_000, 5000);
        assert!(result);
    }

    #[test]
    fn test_check_nsequence_rbf_same_unit_time() {
        let result = check_nsequence_rbf(
            SEQUENCE_LOCKTIME_TYPE_FLAG + 10_000,
            SEQUENCE_LOCKTIME_TYPE_FLAG + 5000,
        );
        assert!(result);
    }

    #[test]
    fn test_check_nlocktime_lt_cltv() {
        let result = check_nlocktime(4000, 5000);
        assert!(!result);
    }

    #[test]
    fn test_check_nlocktime_different_unit() {
        let result = check_nlocktime(BLOCKS_TIMELOCK_THRESHOLD + 5000, 5000);
        assert!(!result);
    }

    #[test]
    fn test_check_nlocktime_same_unit_blocks() {
        let result = check_nlocktime(10_000, 5000);
        assert!(result);
    }

    #[test]
    fn test_check_nlocktime_same_unit_time() {
        let result = check_nlocktime(
            BLOCKS_TIMELOCK_THRESHOLD + 10_000,
            BLOCKS_TIMELOCK_THRESHOLD + 5000,
        );
        assert!(result);
    }
}