use regex::Regex;
use serde::{Deserialize, Serialize};

use crate::{RenameContext, RenameRule};

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub enum MoveTarget {
    None,
    Position(usize),
    Start,
    End,
}

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub enum SelectionMode {
    Chars,
    Words,
    Regex,
}

impl Default for SelectionMode {
    fn default() -> Self {
        SelectionMode::Chars
    }
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct MovePartsRule {
    pub source_from: usize,
    pub source_length: usize,
    pub target: MoveTarget,
    pub separator: String,
    pub copy_mode: bool,
    pub enabled: bool,
    #[serde(default)]
    pub selection_mode: SelectionMode,
    #[serde(default)]
    pub regex_pattern: Option<String>,
    #[serde(default)]
    pub regex_group: usize,
    #[serde(default)]
    pub swap_with_from: Option<usize>,
    #[serde(default)]
    pub swap_with_length: Option<usize>,
}

impl MovePartsRule {
    pub fn new() -> Self {
        Self {
            source_from: 0,
            source_length: 0,
            target: MoveTarget::None,
            separator: String::new(),
            copy_mode: false,
            enabled: true,
            selection_mode: SelectionMode::Chars,
            regex_pattern: None,
            regex_group: 0,
            swap_with_from: None,
            swap_with_length: None,
        }
    }
}

fn split_words(s: &str) -> Vec<(usize, usize)> {
    let mut spans = Vec::new();
    let chars: Vec<char> = s.chars().collect();
    let mut i = 0;
    while i < chars.len() {
        if chars[i].is_whitespace() || matches!(chars[i], '_' | '-' | '.') {
            i += 1;
            continue;
        }
        let start = i;
        while i < chars.len() && !chars[i].is_whitespace() && !matches!(chars[i], '_' | '-' | '.') {
            i += 1;
        }
        spans.push((start, i));
    }
    spans
}

impl RenameRule for MovePartsRule {
    fn apply(&self, filename: &str, _context: &RenameContext) -> String {
        // swap mode
        if let (Some(sw_from), Some(sw_len)) = (self.swap_with_from, self.swap_with_length) {
            return self.apply_swap(filename, sw_from, sw_len);
        }

        match self.selection_mode {
            SelectionMode::Chars => self.apply_chars(filename),
            SelectionMode::Words => self.apply_words(filename),
            SelectionMode::Regex => self.apply_regex(filename),
        }
    }

    fn display_name(&self) -> &str {
        "Move/Copy"
    }

    fn rule_type(&self) -> &str {
        "move_parts"
    }

    fn is_enabled(&self) -> bool {
        self.enabled
    }
}

impl MovePartsRule {
    fn apply_chars(&self, filename: &str) -> String {
        if self.target == MoveTarget::None || self.source_length == 0 {
            return filename.to_string();
        }

        let chars: Vec<char> = filename.chars().collect();
        if self.source_from >= chars.len() {
            return filename.to_string();
        }

        let end = (self.source_from + self.source_length).min(chars.len());
        let extracted: String = chars[self.source_from..end].iter().collect();

        let remaining: String = if self.copy_mode {
            filename.to_string()
        } else {
            let mut r = String::new();
            for (i, c) in chars.iter().enumerate() {
                if i < self.source_from || i >= end {
                    r.push(*c);
                }
            }
            r
        };

        self.place_at_target(&extracted, &remaining)
    }

    fn apply_words(&self, filename: &str) -> String {
        if self.target == MoveTarget::None || self.source_length == 0 {
            return filename.to_string();
        }

        let words = split_words(filename);
        if self.source_from >= words.len() {
            return filename.to_string();
        }

        let word_end = (self.source_from + self.source_length).min(words.len());
        let byte_start = words[self.source_from].0;
        let byte_end = words[word_end - 1].1;

        let chars: Vec<char> = filename.chars().collect();
        let extracted: String = chars[byte_start..byte_end].iter().collect();

        let remaining: String = if self.copy_mode {
            filename.to_string()
        } else {
            // remove extracted span, trimming adjacent separators
            let mut r = String::new();
            let mut skip_start = byte_start;
            let mut skip_end = byte_end;
            // extend skip to eat one adjacent separator
            if skip_end < chars.len() && (chars[skip_end].is_whitespace() || matches!(chars[skip_end], '_' | '-' | '.')) {
                skip_end += 1;
            } else if skip_start > 0 && (chars[skip_start - 1].is_whitespace() || matches!(chars[skip_start - 1], '_' | '-' | '.')) {
                skip_start -= 1;
            }
            for (i, c) in chars.iter().enumerate() {
                if i < skip_start || i >= skip_end {
                    r.push(*c);
                }
            }
            r
        };

        self.place_at_target(&extracted, &remaining)
    }

    fn apply_regex(&self, filename: &str) -> String {
        let pat = match &self.regex_pattern {
            Some(p) if !p.is_empty() => p,
            _ => return filename.to_string(),
        };
        let re = match Regex::new(pat) {
            Ok(r) => r,
            Err(_) => return filename.to_string(),
        };
        let caps = match re.captures(filename) {
            Some(c) => c,
            None => return filename.to_string(),
        };
        let full_match = match caps.get(0) {
            Some(m) => m,
            None => return filename.to_string(),
        };
        let extracted = match caps.get(self.regex_group) {
            Some(m) => m.as_str().to_string(),
            None => return filename.to_string(),
        };

        if self.target == MoveTarget::None {
            return filename.to_string();
        }

        // remove the full match from filename
        let remaining = if self.copy_mode {
            filename.to_string()
        } else {
            let mut r = String::new();
            r.push_str(&filename[..full_match.start()]);
            r.push_str(&filename[full_match.end()..]);
            r
        };

        self.place_at_target(&extracted, &remaining)
    }

    fn apply_swap(&self, filename: &str, sw_from: usize, sw_len: usize) -> String {
        let chars: Vec<char> = filename.chars().collect();
        let len = chars.len();

        let a_start = self.source_from;
        let a_end = (a_start + self.source_length).min(len);
        let b_start = sw_from;
        let b_end = (b_start + sw_len).min(len);

        if a_start >= len || b_start >= len || self.source_length == 0 || sw_len == 0 {
            return filename.to_string();
        }

        // ranges must not overlap
        if a_start < b_end && b_start < a_end {
            return filename.to_string();
        }

        // ensure first < second
        let (r1_start, r1_end, r2_start, r2_end) = if a_start < b_start {
            (a_start, a_end, b_start, b_end)
        } else {
            (b_start, b_end, a_start, a_end)
        };

        let part1: String = chars[r1_start..r1_end].iter().collect();
        let part2: String = chars[r2_start..r2_end].iter().collect();

        let mut result = String::new();
        let before: String = chars[..r1_start].iter().collect();
        let mid: String = chars[r1_end..r2_start].iter().collect();
        let after: String = chars[r2_end..].iter().collect();
        result.push_str(&before);
        result.push_str(&part2);
        result.push_str(&mid);
        result.push_str(&part1);
        result.push_str(&after);
        result
    }

    fn place_at_target(&self, extracted: &str, remaining: &str) -> String {
        match &self.target {
            MoveTarget::None => remaining.to_string(),
            MoveTarget::Start => {
                if self.separator.is_empty() {
                    format!("{}{}", extracted, remaining)
                } else {
                    format!("{}{}{}", extracted, self.separator, remaining)
                }
            }
            MoveTarget::End => {
                if self.separator.is_empty() {
                    format!("{}{}", remaining, extracted)
                } else {
                    format!("{}{}{}", remaining, self.separator, extracted)
                }
            }
            MoveTarget::Position(pos) => {
                let rem_chars: Vec<char> = remaining.chars().collect();
                let p = (*pos).min(rem_chars.len());
                let before: String = rem_chars[..p].iter().collect();
                let after: String = rem_chars[p..].iter().collect();
                format!("{}{}{}", before, extracted, after)
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn move_to_end() {
        let rule = MovePartsRule {
            source_from: 0,
            source_length: 3,
            target: MoveTarget::End,
            separator: "_".into(),
            copy_mode: false,
            ..MovePartsRule::new()
        };
        let ctx = RenameContext::dummy(0);
        assert_eq!(rule.apply("abcdef", &ctx), "def_abc");
    }

    #[test]
    fn copy_to_start() {
        let rule = MovePartsRule {
            source_from: 3,
            source_length: 3,
            target: MoveTarget::Start,
            separator: "-".into(),
            copy_mode: true,
            ..MovePartsRule::new()
        };
        let ctx = RenameContext::dummy(0);
        assert_eq!(rule.apply("abcdef", &ctx), "def-abcdef");
    }
}