use std::path::PathBuf;

use crate::{
    checksum::Checksum,
    model::{DownloadFile, PieceIndex, PieceState},
};

use super::model::{ControlFileError, ControlFileVersion, ControlMetadata};

/// Encodes normalized metadata into the simplified text control-file format.
#[must_use]
pub fn encode_control_metadata(metadata: &ControlMetadata) -> String {
    let mut lines = Vec::new();
    lines.push(format!(
        "version={}.{}",
        metadata.version.major(),
        metadata.version.minor()
    ));
    lines.push(format!("files={}", metadata.files.len()));
    for file in &metadata.files {
        lines.push(format!(
            "file={}|{}|{}",
            file.path.display(),
            file.length,
            file.piece_length
        ));
    }
    lines.push(format!("checksums={}", metadata.checksums.len()));
    for checksum in &metadata.checksums {
        lines.push(format!("checksum={}", encode_checksum(checksum)));
    }
    lines.push(format!("completed_length={}", metadata.completed_length));
    lines.push(format!("retry_count={}", metadata.retry_count));
    if let Some(value) = &metadata.last_error {
        lines.push(format!("last_error={}", escape_control_field(value)));
    }
    if let Some(value) = metadata.last_error_at_unix_ms {
        lines.push(format!("last_error_at_unix_ms={value}"));
    }
    if let Some(value) = metadata.last_retry_at_unix_ms {
        lines.push(format!("last_retry_at_unix_ms={value}"));
    }
    if let Some(value) = metadata.next_retry_at_unix_ms {
        lines.push(format!("next_retry_at_unix_ms={value}"));
    }
    if let Some(value) = metadata.consecutive_failure_count {
        lines.push(format!("consecutive_failure_count={value}"));
    }
    if let Some(value) = metadata.active_segment_count {
        lines.push(format!("active_segment_count={value}"));
    }
    if let Some(value) = metadata.resume_verified_at_unix_ms {
        lines.push(format!("resume_verified_at_unix_ms={value}"));
    }
    if let Some(value) = metadata.resume_generation {
        lines.push(format!("resume_generation={value}"));
    }
    lines.push(format!("pieces={}", metadata.piece_states.len()));
    for (index, state) in &metadata.piece_states {
        lines.push(format!("piece={}|{}", index.0, encode_piece_state(*state)));
    }
    lines.join("\n")
}

/// Decodes the simplified control-file text format.
///
/// # Errors
///
/// Returns [`ControlFileError`] when the encoded text is malformed.
#[expect(
    clippy::too_many_lines,
    reason = "text control metadata decoding keeps legacy and current field handling in one ordered parser"
)]
pub fn decode_control_metadata(content: &str) -> Result<ControlMetadata, ControlFileError> {
    let mut version = ControlFileVersion::CURRENT;
    let mut files = Vec::new();
    let mut checksums = Vec::new();
    let mut piece_states = Vec::new();
    let mut completed_length = 0_u64;
    let mut retry_count = 0_u32;
    let mut last_error = None;
    let mut last_error_at_unix_ms = None;
    let mut last_retry_at_unix_ms = None;
    let mut next_retry_at_unix_ms = None;
    let mut consecutive_failure_count = None;
    let mut active_segment_count = None;
    let mut resume_verified_at_unix_ms = None;
    let mut resume_generation = None;

    for line in content.lines() {
        if let Some(raw) = line.strip_prefix("version=") {
            let mut parts = raw.split('.');
            let major = parts
                .next()
                .ok_or_else(|| ControlFileError::Parse("missing version major".to_owned()))?
                .parse::<u16>()
                .map_err(|_| ControlFileError::Parse("invalid version major".to_owned()))?;
            let minor = parts
                .next()
                .ok_or_else(|| ControlFileError::Parse("missing version minor".to_owned()))?
                .parse::<u16>()
                .map_err(|_| ControlFileError::Parse("invalid version minor".to_owned()))?;
            version = ControlFileVersion::from_parts(major, minor);
            continue;
        }
        if let Some(raw) = line.strip_prefix("file=") {
            let mut parts = raw.split('|');
            let path = parts
                .next()
                .ok_or_else(|| ControlFileError::Parse("missing file path".to_owned()))?;
            let length = parts
                .next()
                .ok_or_else(|| ControlFileError::Parse("missing file length".to_owned()))?
                .parse::<u64>()
                .map_err(|_| ControlFileError::Parse("invalid file length".to_owned()))?;
            let piece_length = parts
                .next()
                .ok_or_else(|| ControlFileError::Parse("missing file piece_length".to_owned()))?
                .parse::<u64>()
                .map_err(|_| ControlFileError::Parse("invalid file piece_length".to_owned()))?;
            files.push(DownloadFile {
                path: PathBuf::from(path),
                length,
                piece_length,
            });
            continue;
        }
        if let Some(raw) = line.strip_prefix("checksum=") {
            checksums.push(decode_checksum(raw)?);
            continue;
        }
        if let Some(raw) = line.strip_prefix("completed_length=") {
            completed_length = raw
                .parse::<u64>()
                .map_err(|_| ControlFileError::Parse("invalid completed_length".to_owned()))?;
            continue;
        }
        if let Some(raw) = line.strip_prefix("retry_count=") {
            retry_count = raw
                .parse::<u32>()
                .map_err(|_| ControlFileError::Parse("invalid retry_count".to_owned()))?;
            continue;
        }
        if let Some(raw) = line.strip_prefix("last_error=") {
            last_error = Some(unescape_control_field(raw));
            continue;
        }
        if let Some(raw) = line.strip_prefix("last_error_at_unix_ms=") {
            last_error_at_unix_ms = Some(raw.parse::<u64>().map_err(|_| {
                ControlFileError::Parse("invalid last_error_at_unix_ms".to_owned())
            })?);
            continue;
        }
        if let Some(raw) = line.strip_prefix("last_retry_at_unix_ms=") {
            last_retry_at_unix_ms = Some(raw.parse::<u64>().map_err(|_| {
                ControlFileError::Parse("invalid last_retry_at_unix_ms".to_owned())
            })?);
            continue;
        }
        if let Some(raw) = line.strip_prefix("next_retry_at_unix_ms=") {
            next_retry_at_unix_ms = Some(raw.parse::<u64>().map_err(|_| {
                ControlFileError::Parse("invalid next_retry_at_unix_ms".to_owned())
            })?);
            continue;
        }
        if let Some(raw) = line.strip_prefix("consecutive_failure_count=") {
            consecutive_failure_count = Some(raw.parse::<u32>().map_err(|_| {
                ControlFileError::Parse("invalid consecutive_failure_count".to_owned())
            })?);
            continue;
        }
        if let Some(raw) = line.strip_prefix("active_segment_count=") {
            active_segment_count =
                Some(raw.parse::<u32>().map_err(|_| {
                    ControlFileError::Parse("invalid active_segment_count".to_owned())
                })?);
            continue;
        }
        if let Some(raw) = line.strip_prefix("resume_verified_at_unix_ms=") {
            resume_verified_at_unix_ms = Some(raw.parse::<u64>().map_err(|_| {
                ControlFileError::Parse("invalid resume_verified_at_unix_ms".to_owned())
            })?);
            continue;
        }
        if let Some(raw) = line.strip_prefix("resume_generation=") {
            resume_generation =
                Some(raw.parse::<u64>().map_err(|_| {
                    ControlFileError::Parse("invalid resume_generation".to_owned())
                })?);
            continue;
        }
        if let Some(raw) = line.strip_prefix("piece=") {
            let mut parts = raw.split('|');
            let index = parts
                .next()
                .ok_or_else(|| ControlFileError::Parse("missing piece index".to_owned()))?
                .parse::<u32>()
                .map_err(|_| ControlFileError::Parse("invalid piece index".to_owned()))?;
            let state = parts
                .next()
                .ok_or_else(|| ControlFileError::Parse("missing piece state".to_owned()))
                .and_then(decode_piece_state)?;
            piece_states.push((PieceIndex(index), state));
        }
    }

    Ok(ControlMetadata {
        version,
        files,
        checksums,
        piece_states,
        completed_length,
        retry_count,
        last_error,
        last_error_at_unix_ms,
        last_retry_at_unix_ms,
        next_retry_at_unix_ms,
        consecutive_failure_count,
        active_segment_count,
        resume_verified_at_unix_ms,
        resume_generation,
    })
}

/// Encodes a piece state for the text control-file format.
const fn encode_piece_state(state: PieceState) -> &'static str {
    match state {
        PieceState::Pending => "pending",
        PieceState::InFlight => "in-flight",
        PieceState::Verified => "verified",
        PieceState::Failed => "failed",
    }
}

/// Decodes a piece state from the text control-file format.
fn decode_piece_state(raw: &str) -> Result<PieceState, ControlFileError> {
    match raw {
        "pending" => Ok(PieceState::Pending),
        "in-flight" => Ok(PieceState::InFlight),
        "verified" => Ok(PieceState::Verified),
        "failed" => Ok(PieceState::Failed),
        _ => Err(ControlFileError::Parse("invalid piece state".to_owned())),
    }
}

/// Encodes a checksum into the text control-file format.
fn encode_checksum(checksum: &Checksum) -> String {
    match checksum {
        Checksum::Sha1(value) => format!("sha1:{value}"),
        Checksum::Sha256(value) => format!("sha256:{value}"),
        Checksum::Md5(value) => format!("md5:{value}"),
        Checksum::Adler32(value) => format!("adler32:{value}"),
        Checksum::Crc32(value) => format!("crc32:{value}"),
    }
}

/// Decodes a checksum from the text control-file format.
fn decode_checksum(raw: &str) -> Result<Checksum, ControlFileError> {
    let mut parts = raw.splitn(2, ':');
    let algorithm = parts
        .next()
        .ok_or_else(|| ControlFileError::Parse("missing checksum algorithm".to_owned()))?;
    let value = parts
        .next()
        .ok_or_else(|| ControlFileError::Parse("missing checksum value".to_owned()))?
        .to_owned();

    match algorithm {
        "sha1" => Ok(Checksum::Sha1(value)),
        "sha256" => Ok(Checksum::Sha256(value)),
        "md5" => Ok(Checksum::Md5(value)),
        "adler32" => Ok(Checksum::Adler32(value)),
        "crc32" => Ok(Checksum::Crc32(value)),
        _ => Err(ControlFileError::Parse(
            "unsupported checksum algorithm".to_owned(),
        )),
    }
}

/// Escapes free-form text fields embedded in a control file.
fn escape_control_field(raw: &str) -> String {
    raw.replace('\\', "\\\\")
        .replace('\t', "\\t")
        .replace('\n', "\\n")
        .replace('\r', "\\r")
        .replace(';', "\\s")
        .replace(',', "\\c")
        .replace('=', "\\e")
}

/// Reverses [`escape_control_field`] for text control-file fields.
fn unescape_control_field(raw: &str) -> String {
    let mut out = String::new();
    let mut chars = raw.chars();
    while let Some(ch) = chars.next() {
        if ch == '\\' {
            match chars.next() {
                Some('t') => out.push('\t'),
                Some('n') => out.push('\n'),
                Some('r') => out.push('\r'),
                Some('s') => out.push(';'),
                Some('c') => out.push(','),
                Some('e') => out.push('='),
                Some('\\') | None => out.push('\\'),
                Some(other) => {
                    out.push('\\');
                    out.push(other);
                }
            }
        } else {
            out.push(ch);
        }
    }
    out
}