//! Cell selection: one or more ranges with an active cell.

use gridcraft_core::{CellRef, MAX_COLS, MAX_ROWS, RangeRef};
use gridcraft_model::Sheet;
use serde::{Deserialize, Serialize};

#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
pub struct Selection {
    /// The active (white) cell.
    pub active: CellRef,
    /// Where a Shift-extension is anchored.
    pub anchor: CellRef,
    /// Selected areas; the last one contains the active cell. Never empty.
    pub ranges: Vec<RangeRef>,
}

impl Default for Selection {
    fn default() -> Self {
        Selection::at(CellRef::default())
    }
}

impl Selection {
    pub fn at(c: CellRef) -> Selection {
        Selection { active: c, anchor: c, ranges: vec![RangeRef::cell(c)] }
    }
    pub fn range(r: RangeRef) -> Selection {
        Selection { active: r.start, anchor: r.start, ranges: vec![r] }
    }
    /// The current (last) area.
    pub fn current(&self) -> RangeRef {
        self.ranges.last().copied().unwrap_or(RangeRef::cell(self.active))
    }
    /// Bounding range of all areas.
    pub fn bounds(&self) -> RangeRef {
        let mut it = self.ranges.iter();
        let first = it.next().copied().unwrap_or(RangeRef::cell(self.active));
        it.fold(first, |a, b| a.union(b))
    }
    pub fn contains(&self, c: CellRef) -> bool {
        self.ranges.iter().any(|r| r.contains(c))
    }
    pub fn is_single_cell(&self) -> bool {
        self.ranges.len() == 1 && self.current().is_single()
    }
    /// Extends the current area from the anchor to `to` (Shift+click / Shift+arrows).
    pub fn extend_to(&mut self, to: CellRef) {
        let r = RangeRef::new(self.anchor, to);
        if let Some(last) = self.ranges.last_mut() {
            *last = r;
        } else {
            self.ranges.push(r);
        }
    }
    /// The A1 text of all areas (`A1:B2,D4`).
    pub fn a1(&self) -> String {
        self.ranges.iter().map(|r| r.a1()).collect::<Vec<_>>().join(",")
    }
    /// Expands areas so merged cells are included whole.
    pub fn expand_merges(&mut self, sheet: &Sheet) {
        for r in self.ranges.iter_mut() {
            let mut cur = *r;
            loop {
                let mut grown = cur;
                for m in &sheet.merges {
                    if m.intersects(&grown) {
                        grown = grown.union(m);
                    }
                }
                if grown == cur {
                    break;
                }
                cur = grown;
            }
            *r = cur;
        }
    }
    /// Moves the active cell within the selection (Enter/Tab inside a multi-cell selection).
    pub fn cycle(&mut self, forward: bool, by_row: bool) {
        let r = self.current();
        if r.is_single() && self.ranges.len() == 1 {
            return;
        }
        let a = self.active;
        let (mut row, mut col) = (a.row as i64, a.col as i64);
        let step: i64 = if forward { 1 } else { -1 };
        if by_row {
            col += step;
            if col > r.end.col as i64 {
                col = r.start.col as i64;
                row += 1;
            } else if col < r.start.col as i64 {
                col = r.end.col as i64;
                row -= 1;
            }
            if row > r.end.row as i64 {
                row = r.start.row as i64;
            } else if row < r.start.row as i64 {
                row = r.end.row as i64;
            }
        } else {
            row += step;
            if row > r.end.row as i64 {
                row = r.start.row as i64;
                col += 1;
            } else if row < r.start.row as i64 {
                row = r.end.row as i64;
                col -= 1;
            }
            if col > r.end.col as i64 {
                col = r.start.col as i64;
            } else if col < r.start.col as i64 {
                col = r.end.col as i64;
            }
        }
        self.active = CellRef::new(row.clamp(0, MAX_ROWS as i64 - 1) as u32, col.clamp(0, MAX_COLS as i64 - 1) as u32);
    }
}

/// Ctrl+arrow: jump to the edge of the current data region (Excel's End mode).
pub fn jump(sheet: &Sheet, from: CellRef, dr: i64, dc: i64) -> CellRef {
    if dr == 0 && dc == 0 {
        // No direction: nowhere to go (the search below would never advance).
        return from;
    }
    let filled = |c: CellRef| sheet.value_ref(c).is_some_and(|v| !v.is_empty());
    let Some(mut cur) = from.offset(dr, dc) else { return from };
    let here = filled(from);
    let next = filled(cur);
    if here && next {
        // Move to the last filled cell of the run.
        while let Some(n) = cur.offset(dr, dc) {
            if !filled(n) {
                break;
            }
            cur = n;
        }
        return cur;
    }
    // Move to the next filled cell, or the sheet edge. Use the used range to avoid walking a
    // million empty cells.
    let used = sheet.used_range();
    loop {
        if filled(cur) {
            return cur;
        }
        let beyond = match used {
            Some(u) => {
                (dr > 0 && cur.row > u.end.row)
                    || (dc > 0 && cur.col > u.end.col)
                    || (dr < 0 && cur.row < u.start.row)
                    || (dc < 0 && cur.col < u.start.col)
            }
            None => true,
        };
        if beyond {
            let r = if dr > 0 {
                MAX_ROWS - 1
            } else if dr < 0 {
                0
            } else {
                cur.row
            };
            let c = if dc > 0 {
                MAX_COLS - 1
            } else if dc < 0 {
                0
            } else {
                cur.col
            };
            return CellRef::new(r, c);
        }
        match cur.offset(dr, dc) {
            Some(n) => cur = n,
            None => return cur,
        }
    }
}

/// The contiguous data region around `c` (Ctrl+A / Ctrl+Shift+8, AutoSum, sort, tables).
pub fn current_region(sheet: &Sheet, c: CellRef) -> RangeRef {
    let filled = |c: CellRef| sheet.cell(c).is_some_and(|x| !x.value.is_empty() || x.formula.is_some()) || sheet.spill.contains_key(&c);
    // Whether a row (or column) has a filled cell between two columns (rows), inclusive.
    let row_has = |row: u32, a: u32, b: u32| (a..=b).any(|col| filled(CellRef::new(row, col)));
    let col_has = |col: u32, a: u32, b: u32| (a..=b).any(|row| filled(CellRef::new(row, col)));
    let (mut r0, mut r1, mut c0, mut c1) = (c.row, c.row, c.col, c.col);
    // Grow one side at a time while the line next to it (diagonals included) has data. Each
    // pass scans only the lines next to the region, so tall regions take linear time.
    loop {
        let before = (r0, r1, c0, c1);
        let (lo_c, hi_c) = (c0.saturating_sub(1), (c1 + 1).min(MAX_COLS - 1));
        while r0 > 0 && row_has(r0 - 1, lo_c, hi_c) {
            r0 -= 1;
        }
        while r1 + 1 < MAX_ROWS && row_has(r1 + 1, lo_c, hi_c) {
            r1 += 1;
        }
        let (lo_r, hi_r) = (r0.saturating_sub(1), (r1 + 1).min(MAX_ROWS - 1));
        while c0 > 0 && col_has(c0 - 1, lo_r, hi_r) {
            c0 -= 1;
        }
        while c1 + 1 < MAX_COLS && col_has(c1 + 1, lo_r, hi_r) {
            c1 += 1;
        }
        if (r0, r1, c0, c1) == before {
            break;
        }
    }
    RangeRef::new(CellRef::new(r0, c0), CellRef::new(r1, c1))
}

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

    #[test]
    fn jumps() {
        let mut s = Sheet::new("S");
        for r in 0..5 {
            s.set_value(CellRef::new(r, 0), Value::Number(1.0));
        }
        s.set_value(CellRef::new(10, 0), Value::Number(1.0));
        assert_eq!(jump(&s, CellRef::new(0, 0), 1, 0), CellRef::new(4, 0));
        // Without a direction it stays put (it used to loop forever from a blank cell).
        assert_eq!(jump(&s, CellRef::new(7, 0), 0, 0), CellRef::new(7, 0));
        assert_eq!(jump(&s, CellRef::new(4, 0), 1, 0), CellRef::new(10, 0));
        assert_eq!(jump(&s, CellRef::new(10, 0), 1, 0), CellRef::new(MAX_ROWS - 1, 0));
        assert_eq!(jump(&s, CellRef::new(0, 0), 0, 1), CellRef::new(0, MAX_COLS - 1));
        assert_eq!(jump(&s, CellRef::new(0, 0), -1, 0), CellRef::new(0, 0));
    }

    #[test]
    fn regions() {
        let mut s = Sheet::new("S");
        for r in 2..5 {
            for c in 1..4 {
                s.set_value(CellRef::new(r, c), Value::Number(1.0));
            }
        }
        assert_eq!(current_region(&s, CellRef::new(3, 2)).a1(), "B3:D5");
        assert_eq!(current_region(&s, CellRef::new(5, 4)).a1(), "B3:E6");
        assert_eq!(current_region(&s, CellRef::new(20, 20)).a1(), "U21");
        // Taller than 10,000 rows: it used to stop growing after 10,000 steps.
        let mut s = Sheet::new("S");
        for r in 0..20_000 {
            s.set_value(CellRef::new(r, 0), Value::Number(r as f64));
            s.set_value(CellRef::new(r, 1), Value::Number(1.0));
        }
        assert_eq!(current_region(&s, CellRef::new(5, 0)).a1(), "A1:B20000");
    }

    #[test]
    fn cycling() {
        let mut sel = Selection::range(RangeRef::parse("A1:B2").unwrap());
        sel.cycle(true, false);
        assert_eq!(sel.active.a1(), "A2");
        sel.cycle(true, false);
        assert_eq!(sel.active.a1(), "B1");
        sel.cycle(true, true);
        assert_eq!(sel.active.a1(), "A2");
    }
}