use std::{cmp::Ordering, fmt::Display, ops::Range, str::FromStr};

use anyhow::Context;
use rayon::prelude::*;
use serde::{Deserialize, Serialize};

/// Represents a position in the genome using 0-based coordinates.
///
/// This struct encapsulates a genomic position, consisting of a contig (chromosome)
/// identifier and a position within that contig.
///
/// # Fields
/// * `contig` - An 8-bit unsigned integer representing the contig/chromosome
/// * `position` - A 32-bit unsigned integer representing the 0-based position within the contig
///
/// # Derives
/// This struct derives the following traits:
/// * `Debug` for easier debugging and logging
/// * `PartialEq` and `Eq` for equality comparisons
/// * `Clone` for creating deep copies
/// * `Serialize` and `Deserialize` for serialization (e.g., to JSON or other formats)
/// * `Hash` for use in hash-based collections
/// * `Default` for creating a default instance
///
/// # Note
/// The position is 0-based, meaning the first position in a contig is represented as 0.
///
/// # Usage
/// This struct is typically used to precisely locate genomic features or variants
/// within a reference genome.
///
/// # Example
/// ```
/// let position = GenomePosition {
///     contig: 1,  // Representing chromosome 1
///     position: 1000,  // 1001st base pair in the chromosome (remember it's 0-based)
/// };
/// ```
#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize, Hash, Default)]
pub struct GenomePosition {
    pub contig: u8,
    pub position: u32,
}

impl GenomePosition {
    /// Returns the contig (chromosome) identifier as a human-readable string.
    ///
    /// This method converts the internal numeric representation of the contig
    /// to a string format commonly used in genomics, such as "chr1", "chrX", etc...
    ///
    /// # Returns
    /// A `String` representing the contig identifier.
    ///
    /// # Examples
    ///
    /// ```
    /// let pos = GenomePosition { contig: 1, position: 1000 };
    /// assert_eq!(pos.contig(), "chr1");
    ///
    /// let pos_x = GenomePosition { contig: 23, position: 500 };
    /// assert_eq!(pos_x.contig(), "chrX");
    /// ```
    ///
    /// # Note
    /// This method uses the `num_to_contig` function to perform the conversion.
    /// Special cases like X, Y chromosomes and mitochondrial DNA are handled appropriately.
    pub fn contig(&self) -> String {
        num_to_contig(self.contig)
    }
}

/// Implements the `Display` trait for `GenomePosition`.
///
/// This implementation allows a `GenomePosition` to be formatted as a string
/// in the form "contig:position", where contig is the string representation
/// of the chromosome (e.g., "chr1", "chrX") and position is the 0-based position.
///
/// # Example
/// ```
/// let pos = GenomePosition { contig: 1, position: 1000 };
/// assert_eq!(format!("{}", pos), "chr1:1000");
/// ```
impl Display for GenomePosition {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}:{}", self.contig(), self.position)
    }
}

/// Implements the `FromStr` trait for `GenomePosition`.
///
/// This allows creating a `GenomePosition` from a string in the format "contig:position".
///
/// # Errors
/// Returns an `anyhow::Error` if:
/// - The input string doesn't contain a ':' character
/// - The contig part can't be converted to a numeric representation
/// - The position part can't be parsed as a `u32`
///
/// # Example
/// ```
/// use std::str::FromStr;
/// let pos = GenomePosition::from_str("chr1:1000").unwrap();
/// assert_eq!(pos.contig, 1);
/// assert_eq!(pos.position, 1000);
/// ```
impl FromStr for GenomePosition {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> anyhow::Result<Self> {
        let (c, p) = s
            .split_once(":")
            .ok_or(anyhow::anyhow!("Can't split {s}"))?;
        Ok(Self {
            contig: contig_to_num(c),
            position: p.parse()?,
        })
    }
}

/// Implements `TryFrom<(&str, &str)>` for `GenomePosition`.
///
/// This allows creating a `GenomePosition` from a tuple of two string slices,
/// where the first represents the contig and the second represents the position.
///
/// # Errors
/// Returns an `anyhow::Error` if:
/// - The contig part can't be converted to a numeric representation
/// - The position part can't be parsed as a `u32`
///
/// # Example
/// ```
/// use std::convert::TryFrom;
/// let pos = GenomePosition::try_from(("chr1", "1000")).unwrap();
/// assert_eq!(pos.contig, 1);
/// assert_eq!(pos.position, 1000);
/// ```
impl TryFrom<(&str, &str)> for GenomePosition {
    type Error = anyhow::Error;

    fn try_from((c, p): (&str, &str)) -> anyhow::Result<Self> {
        Ok(GenomePosition {
            contig: contig_to_num(c),
            position: p.parse().context(format!("Can't parse {p} into u32."))?,
        })
    }
}

/// Implements conversion from `VcfPosition` to `GenomePosition`.
///
/// This conversion adjusts for the difference between 1-based VCF coordinates
/// and 0-based genomic coordinates. It also handles the special case of
/// position 0 in VCF, which represents a variant inside telomeres.
///
/// # Note
/// This implementation assumes that `VcfPosition` uses 1-based coordinates.
///
/// # Example
/// ```
/// let vcf_pos = VcfPosition { contig: 1, position: 1001 };
/// let genome_pos: GenomePosition = vcf_pos.into();
/// assert_eq!(genome_pos.contig, 1);
/// assert_eq!(genome_pos.position, 1000);
/// ```
impl From<VcfPosition> for GenomePosition {
    fn from(value: VcfPosition) -> Self {
        let position = if value.position == 0 {
            // position 0 is a variant inside telomeres
            0
        } else {
            value.position - 1
        };
        Self {
            contig: value.contig,
            position,
        }
    }
}

/// Implements conversion from `GenomePosition` to `(String, String)`.
///
/// This conversion creates a tuple where the first element is the string
/// representation of the contig (e.g., "chr1", "chrX") and the second
/// element is the string representation of the position.
///
/// # Example
/// ```
/// let pos = GenomePosition { contig: 1, position: 1000 };
/// let (contig, position): (String, String) = pos.into();
/// assert_eq!(contig, "chr1");
/// assert_eq!(position, "1000");
/// ```
impl From<GenomePosition> for (String, String) {
    fn from(val: GenomePosition) -> Self {
        (num_to_contig(val.contig), val.position.to_string())
    }
}

/// Implements `PartialOrd` for `GenomePosition`.
///
/// This implementation allows `GenomePosition` instances to be compared
/// and ordered based first on their contig, then on their position.
impl PartialOrd for GenomePosition {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

/// Implements `Ord` for `GenomePosition`.
///
/// This implementation defines a total ordering for `GenomePosition` instances.
/// Positions are first compared by their contig, and if the contigs are equal,
/// then by their position.
///
/// # Example
/// ```
/// let pos1 = GenomePosition { contig: 1, position: 1000 };
/// let pos2 = GenomePosition { contig: 1, position: 2000 };
/// let pos3 = GenomePosition { contig: 2, position: 500 };
/// assert!(pos1 < pos2);
/// assert!(pos2 < pos3);
/// ```
impl Ord for GenomePosition {
    fn cmp(&self, other: &Self) -> Ordering {
        match self.contig.cmp(&other.contig) {
            Ordering::Equal => self.position.cmp(&other.position),
            other => other,
        }
    }
}

/// Converts a contig (chromosome) identifier string to its numeric representation.
///
/// # Arguments
/// * `contig` - A string slice representing the contig identifier (e.g., "chr1", "chrX")
///
/// # Returns
/// A `u8` representing the numeric value of the contig:
/// * 1-22 for autosomes
/// * 23 for X chromosome
/// * 24 for Y chromosome
/// * 25 for mitochondrial DNA
/// * `u8::MAX` (255) for any unrecognized input
///
/// # Examples
/// ```
/// assert_eq!(contig_to_num("chr1"), 1);
/// assert_eq!(contig_to_num("chrX"), 23);
/// assert_eq!(contig_to_num("chrM"), 25);
/// assert_eq!(contig_to_num("chr_unknown"), u8::MAX);
/// ```
///
/// # Note
/// This function assumes the input string starts with "chr" for standard chromosomes.
/// The "chr" prefix is trimmed before parsing numeric values.
pub fn contig_to_num(contig: &str) -> u8 {
    match contig {
        "chrX" => 23,
        "chrY" => 24,
        "chrM" => 25,
        c => c.trim_start_matches("chr").parse().unwrap_or(u8::MAX),
    }
}

/// Converts a numeric contig (chromosome) representation to its string identifier.
///
/// # Arguments
/// * `num` - A `u8` representing the numeric value of the contig
///
/// # Returns
/// A `String` representing the contig identifier:
/// * "chr1" to "chr22" for autosomes
/// * "chrX" for 23
/// * "chrY" for 24
/// * "chrM" for 25
/// * "chr{num}" for any other input
///
/// # Examples
/// ```
/// assert_eq!(num_to_contig(1), "chr1");
/// assert_eq!(num_to_contig(23), "chrX");
/// assert_eq!(num_to_contig(25), "chrM");
/// ```
///
/// # Note
/// This function always prepends "chr" to the output string.
pub fn num_to_contig(num: u8) -> String {
    match num {
        23 => "chrX".to_string(),
        24 => "chrY".to_string(),
        25 => "chrM".to_string(),
        c => format!("chr{c}"),
    }
}

/// Represents a position in a VCF (Variant Call Format) file using 1-based coordinates.
///
/// This struct encapsulates a genomic position as represented in VCF files, consisting of a contig (chromosome)
/// identifier and a position within that contig.
///
/// # Fields
/// * `contig` - An 8-bit unsigned integer representing the contig/chromosome
/// * `position` - A 32-bit unsigned integer representing the 1-based position within the contig
///
/// # Derives
/// This struct derives the following traits:
/// * `Debug` for easier debugging and logging
/// * `PartialEq` and `Eq` for equality comparisons
/// * `Clone` for creating deep copies
/// * `Serialize` and `Deserialize` for serialization (e.g., to JSON or other formats)
///
/// # Note
/// The position is 1-based, as per VCF file format specifications.
#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
pub struct VcfPosition {
    pub contig: u8,
    pub position: u32,
}

/// Implements `TryFrom<(&str, &str)>` for `VcfPosition`.
///
/// This allows creating a `VcfPosition` from a tuple of two string slices,
/// where the first represents the contig and the second represents the position.
///
/// # Errors
/// Returns an `anyhow::Error` if:
/// - The contig part can't be converted to a numeric representation
/// - The position part can't be parsed as a `u32`
///
/// # Example
/// ```
/// use std::convert::TryFrom;
/// let pos = VcfPosition::try_from(("chr1", "1000")).unwrap();
/// assert_eq!(pos.contig, 1);
/// assert_eq!(pos.position, 1000);
/// ```
impl TryFrom<(&str, &str)> for VcfPosition {
    type Error = anyhow::Error;

    fn try_from((c, p): (&str, &str)) -> anyhow::Result<Self> {
        Ok(VcfPosition {
            contig: contig_to_num(c),
            position: p.parse().context(format!("Can't parse {p} into u32."))?,
        })
    }
}

/// Implements conversion from `GenomePosition` to `VcfPosition`.
///
/// This conversion adjusts for the difference between 0-based genomic coordinates
/// and 1-based VCF coordinates.
///
/// # Example
/// ```
/// let genome_pos = GenomePosition { contig: 1, position: 999 };
/// let vcf_pos: VcfPosition = genome_pos.into();
/// assert_eq!(vcf_pos.contig, 1);
/// assert_eq!(vcf_pos.position, 1000);
/// ```
impl From<GenomePosition> for VcfPosition {
    fn from(value: GenomePosition) -> Self {
        Self {
            contig: value.contig,
            position: value.position + 1,
        }
    }
}

/// Implements conversion from `VcfPosition` to `(String, String)`.
///
/// This conversion creates a tuple where the first element is the string
/// representation of the contig (e.g., "chr1", "chrX") and the second
/// element is the string representation of the position.
///
/// # Example
/// ```
/// let pos = VcfPosition { contig: 1, position: 1000 };
/// let (contig, position): (String, String) = pos.into();
/// assert_eq!(contig, "chr1");
/// assert_eq!(position, "1000");
/// ```
impl From<VcfPosition> for (String, String) {
    fn from(val: VcfPosition) -> Self {
        (num_to_contig(val.contig), val.position.to_string())
    }
}

/// Represents a range in the genome using 0-based, half-open coordinates [start, end).
///
/// This struct encapsulates a genomic range, consisting of a contig (chromosome)
/// identifier and a range of positions within that contig.
///
/// # Fields
/// * `contig` - An 8-bit unsigned integer representing the contig/chromosome
/// * `range` - A `Range<u32>` representing the start (inclusive) and end (exclusive) positions
///
/// # Derives
/// This struct derives the following traits:
/// * `Debug` for easier debugging and logging
/// * `PartialEq` and `Eq` for equality comparisons
/// * `Clone` for creating deep copies
/// * `Serialize` and `Deserialize` for serialization (e.g., to JSON or other formats)
///
/// # Note
/// The range is 0-based and half-open, meaning the start position is included but the end position is not.
/// This is consistent with many programming languages and bioinformatics tools.
#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
pub struct GenomeRange {
    pub contig: u8,
    pub range: Range<u32>,
}

/// Implements `TryFrom<(&str, &str, &str)>` for `GenomeRange`.
///
/// This allows creating a `GenomeRange` from a tuple of three string slices,
/// where the first represents the contig, the second the start position,
/// and the third the end position.
///
/// # Errors
/// Returns an `anyhow::Error` if:
/// - The contig part can't be converted to a numeric representation
/// - Either the start or end position can't be parsed as a `u32`
///
/// # Example
/// ```
/// use std::convert::TryFrom;
/// let range = GenomeRange::try_from(("chr1", "1000", "2000")).unwrap();
/// assert_eq!(range.contig, 1);
/// assert_eq!(range.range.start, 1000);
/// assert_eq!(range.range.end, 2000);
/// ```
impl TryFrom<(&str, &str, &str)> for GenomeRange {
    type Error = anyhow::Error;

    fn try_from((c, s, e): (&str, &str, &str)) -> anyhow::Result<Self> {
        Ok(Self {
            contig: contig_to_num(c),
            range: Range {
                start: s.parse().context(format!("Can't parse {s} into u32."))?,
                end: e.parse().context(format!("Can't parse {e} into u32."))?,
            },
        })
    }
}

impl GenomeRange {
    /// Creates a `GenomeRange` from 1-based inclusive start and end positions.
    ///
    /// This method is useful when working with data sources that use 1-based coordinates
    /// and inclusive ranges. It converts the input to the 0-based, half-open format used by `GenomeRange`.
    ///
    /// # Arguments
    /// * `contig` - A string slice representing the contig/chromosome
    /// * `start` - A string slice representing the 1-based inclusive start position
    /// * `end` - A string slice representing the 1-based inclusive end position
    ///
    /// # Returns
    /// A `Result` containing the `GenomeRange` if successful, or an `anyhow::Error` if parsing fails.
    ///
    /// # Errors
    /// Returns an `anyhow::Error` if:
    /// - The contig can't be converted to a numeric representation
    /// - Either the start or end position can't be parsed as a `u32`
    ///
    /// # Example
    /// ```
    /// let range = GenomeRange::from_1_inclusive("chr1", "1000", "2000").unwrap();
    /// assert_eq!(range.contig, 1);
    /// assert_eq!(range.range.start, 999);  // Converted to 0-based
    /// assert_eq!(range.range.end, 2000);   // End is exclusive in 0-based
    /// ```
    pub fn from_1_inclusive(contig: &str, start: &str, end: &str) -> anyhow::Result<Self> {
        Ok(Self {
            contig: contig_to_num(contig),
            range: Range {
                start: start
                    .parse::<u32>()
                    .context(format!("Can't parse {start} into u32."))?
                    - 1,
                end: end
                    .parse()
                    .context(format!("Can't parse {end} into u32."))?,
            },
        })
    }
}

/// Finds overlaps between a list of genome positions and a list of genome ranges in parallel.
///
/// This function uses Rayon for parallel processing, dividing the positions into chunks
/// and processing them concurrently.
///
/// # Arguments
/// * `positions` - A slice of references to `GenomePosition`s
/// * `ranges` - A slice of references to `GenomeRange`s
///
/// # Returns
/// A `Vec<usize>` containing the indices of positions that overlap with any range.
///
/// # Performance
/// This function is optimized for scenarios where both `positions` and `ranges` are sorted
/// by contig and position/range start. It uses this ordering to avoid unnecessary comparisons.
///
/// # Example
/// ```
/// let positions = vec![
///     &GenomePosition { contig: 1, position: 100 },
///     &GenomePosition { contig: 1, position: 200 },
///     &GenomePosition { contig: 2, position: 150 },
/// ];
/// let ranges = vec![
///     &GenomeRange { contig: 1, range: 50..150 },
///     &GenomeRange { contig: 2, range: 100..200 },
/// ];
/// let overlaps = overlaps_par(&positions, &ranges);
/// assert_eq!(overlaps, vec!);
/// ```
pub fn overlaps_par(positions: &[&GenomePosition], ranges: &[&GenomeRange]) -> Vec<usize> {
    let chunk_size = (positions.len() / rayon::current_num_threads()).max(1);

    positions
        .par_chunks(chunk_size)
        .enumerate()
        .flat_map(|(chunk_idx, chunk)| {
            let mut result = Vec::new();
            let mut range_idx = ranges.partition_point(|r| r.contig < chunk[0].contig);

            for (pos_idx, pos) in chunk.iter().enumerate() {
                while range_idx < ranges.len() && ranges[range_idx].contig < pos.contig {
                    range_idx += 1;
                }

                if range_idx < ranges.len() && ranges[range_idx].contig == pos.contig {
                    while range_idx < ranges.len()
                        && ranges[range_idx].contig == pos.contig
                        && ranges[range_idx].range.end <= pos.position
                    {
                        range_idx += 1;
                    }

                    if range_idx < ranges.len()
                        && ranges[range_idx].contig == pos.contig
                        && ranges[range_idx].range.contains(&pos.position)
                    {
                        result.push(chunk_idx * chunk_size + pos_idx);
                    }
                }
            }
            result
        })
        .collect()
}

/// A parallel version of the overlap finding function that works with any types
/// implementing `GetGenomePosition` and `GetGenomeRange` traits.
///
/// This function first converts the input slices to vectors of `GenomePosition` and `GenomeRange`,
/// then calls `overlaps_par`.
///
/// # Arguments
/// * `a` - A slice of items implementing `GetGenomePosition`
/// * `b` - A slice of items implementing `GetGenomeRange`
///
/// # Returns
/// A `Vec<usize>` containing the indices of positions that overlap with any range.
///
/// # Example
/// ```
/// struct MyPosition(GenomePosition);
/// impl GetGenomePosition for MyPosition {
///     fn position(&self) -> &GenomePosition { &self.0 }
/// }
///
/// struct MyRange(GenomeRange);
/// impl GetGenomeRange for MyRange {
///     fn range(&self) -> &GenomeRange { &self.0 }
/// }
///
/// let positions = vec![
///     MyPosition(GenomePosition { contig: 1, position: 100 }),
///     MyPosition(GenomePosition { contig: 1, position: 200 }),
/// ];
/// let ranges = vec![
///     MyRange(GenomeRange { contig: 1, range: 50..150 }),
/// ];
/// let overlaps = par_overlaps(&positions, &ranges);
/// assert_eq!(overlaps, vec!);
/// ```
pub fn par_overlaps(a: &[impl GetGenomePosition], b: &[impl GetGenomeRange]) -> Vec<usize> {
    let a: Vec<_> = a.iter().map(|e| e.position()).collect();
    let b: Vec<_> = b.iter().map(|e| e.range()).collect();
    overlaps_par(&a, &b)
}

/// A trait for types that can provide a reference to a `GenomePosition`.
///
/// Implement this trait for types that contain or can compute a `GenomePosition`.
pub trait GetGenomePosition {
    // Returns a reference to the `GenomePosition` for this item.
    fn position(&self) -> &GenomePosition;
}

/// A trait for types that can provide a reference to a `GenomeRange`.
///
/// Implement this trait for types that contain or can compute a `GenomeRange`.
pub trait GetGenomeRange {
    /// Returns a reference to the `GenomeRange` for this item.
    fn range(&self) -> &GenomeRange;
}