//! Parsing what people type into a cell (and numeric text in formulas).
//!
//! Recognises numbers with thousands separators, percentages, currency, scientific notation,
//! fractions (`1 1/2`), dates (`3/4/2026`, `2026-03-04`, `4-Mar-2026`, `Mar 4, 2026`), times
//! (`10:30`, `10:30:15 PM`) and date-times. Locale: en-US.

use crate::date::{DateSystem, MONTHS, serial_from_ymd, time_fraction};
use crate::value::{CellError, Value};

/// A parsed entry: its value and the number format Excel would apply automatically.
#[derive(Clone, Debug, PartialEq)]
pub struct Parsed {
    pub value: Value,
    pub format: Option<&'static str>,
}

/// Interprets typed cell input (not formulas). Text that isn't a number, date, boolean or error
/// stays text. A leading apostrophe forces text.
pub fn parse_input(s: &str, sys: DateSystem) -> Parsed {
    if s.is_empty() {
        return Parsed { value: Value::Empty, format: None };
    }
    if let Some(rest) = s.strip_prefix('\'') {
        return Parsed { value: Value::text(rest), format: None };
    }
    let t = s.trim();
    if t.eq_ignore_ascii_case("TRUE") {
        return Parsed { value: Value::Bool(true), format: None };
    }
    if t.eq_ignore_ascii_case("FALSE") {
        return Parsed { value: Value::Bool(false), format: None };
    }
    if let Some(e) = CellError::parse(t) {
        return Parsed { value: Value::Error(e), format: None };
    }
    if let Some((n, f)) = parse_numeric(t, sys) {
        return Parsed { value: Value::number(n), format: f };
    }
    Parsed { value: Value::text(s), format: None }
}

/// Numeric text as arithmetic coerces it ("1,000", "50%", "$3", "1/2/2020", "10:00").
pub fn parse_number_text(s: &str) -> Option<f64> {
    parse_numeric(s.trim(), DateSystem::D1900).map(|(n, _)| n)
}

fn parse_numeric(t: &str, sys: DateSystem) -> Option<(f64, Option<&'static str>)> {
    if t.is_empty() {
        return None;
    }
    // Parenthesised negatives: (100) = -100.
    if let Some(inner) = t.strip_prefix('(').and_then(|x| x.strip_suffix(')')) {
        return parse_numeric(inner.trim(), sys).map(|(n, f)| (-n, f));
    }
    if let Some(r) = parse_plain(t) {
        return Some(r);
    }
    if let Some(r) = parse_fraction(t) {
        return Some((r, Some("# ?/?")));
    }
    if let Some(r) = parse_datetime(t, sys) {
        return Some(r);
    }
    None
}

/// Signs, currency, thousands separators, percent, exponent.
fn parse_plain(t: &str) -> Option<(f64, Option<&'static str>)> {
    let mut s = t;
    let mut neg = false;
    let mut currency = false;
    let mut percent = false;
    if let Some(r) = s.strip_prefix('-') {
        neg = true;
        s = r.trim_start();
    } else if let Some(r) = s.strip_prefix('+') {
        s = r.trim_start();
    }
    if let Some(r) = s.strip_prefix('$') {
        currency = true;
        s = r.trim_start();
        if !neg && let Some(r2) = s.strip_prefix('-') {
            neg = true;
            s = r2;
        }
    }
    if let Some(r) = s.strip_suffix('%') {
        percent = true;
        s = r.trim_end();
    }
    if s.is_empty() {
        return None;
    }
    let has_sep = s.contains(',');
    let digits: String = if has_sep {
        // Thousands separators must be in groups of three before the decimal point.
        let (int, frac) = s.split_once('.').map_or((s, None), |(a, b)| (a, Some(b)));
        let groups: Vec<&str> = int.split(',').collect();
        let first = groups.first()?;
        if first.is_empty() || first.len() > 3 || groups.iter().skip(1).any(|g| g.len() != 3) {
            return None;
        }
        let mut d = groups.concat();
        if let Some(f) = frac {
            d.push('.');
            d.push_str(f);
        }
        d
    } else {
        s.to_string()
    };
    let b = digits.as_bytes();
    if !b.iter().all(|c| c.is_ascii_digit() || matches!(c, b'.' | b'e' | b'E' | b'+' | b'-')) {
        return None;
    }
    if !b.first().is_some_and(|c| c.is_ascii_digit() || *c == b'.') {
        return None;
    }
    let mut n: f64 = digits.parse().ok()?;
    if !n.is_finite() {
        return None;
    }
    let sci = digits.contains(['e', 'E']);
    if percent {
        n /= 100.0;
    }
    if neg {
        n = -n;
    }
    let fmt = if currency {
        Some(if digits.contains('.') { "\"$\"#,##0.00" } else { "\"$\"#,##0" })
    } else if percent {
        Some(if digits.contains('.') { "0.00%" } else { "0%" })
    } else if sci {
        Some("0.00E+00")
    } else if has_sep {
        Some(if digits.contains('.') { "#,##0.00" } else { "#,##0" })
    } else {
        None
    };
    Some((n, fmt))
}

/// `1/2` (only with a whole part, else it's a date), `1 1/2`, `0 3/4`.
fn parse_fraction(t: &str) -> Option<f64> {
    let (whole, frac) = t.split_once(' ')?;
    let neg = whole.starts_with('-');
    let w: f64 = whole.trim_start_matches('-').parse().ok()?;
    let (a, b) = frac.trim().split_once('/')?;
    let a: f64 = a.parse().ok()?;
    let b: f64 = b.parse().ok()?;
    if b == 0.0 || !w.is_finite() {
        return None;
    }
    let v = w + a / b;
    Some(if neg { -v } else { v })
}

fn month_from_name(s: &str) -> Option<u32> {
    let l = s.to_ascii_lowercase();
    if l.len() < 3 {
        return None;
    }
    MONTHS.iter().position(|m| m.to_ascii_lowercase().starts_with(&l)).map(|i| i as u32 + 1)
}

/// Time part: `h:mm`, `h:mm:ss`, `h:mm:ss.000`, `h AM`, with optional AM/PM.
fn parse_time(t: &str) -> Option<(f64, bool, bool)> {
    let t = t.trim();
    let lower = t.to_ascii_lowercase();
    let (body, ampm) = if let Some(b) = lower.strip_suffix("am").or_else(|| lower.strip_suffix('a')) {
        (b.trim().to_string(), Some(false))
    } else if let Some(b) = lower.strip_suffix("pm").or_else(|| lower.strip_suffix('p')) {
        (b.trim().to_string(), Some(true))
    } else {
        (lower.clone(), None)
    };
    let parts: Vec<&str> = body.split(':').collect();
    if parts.len() == 1 && ampm.is_none() {
        return None;
    }
    if parts.len() > 3 || parts.iter().any(|p| p.is_empty()) {
        return None;
    }
    let mut h: f64 = parts.first()?.parse().ok()?;
    let m: f64 = parts.get(1).map_or(Some(0.0), |p| p.parse().ok())?;
    let s: f64 = parts.get(2).map_or(Some(0.0), |p| p.parse().ok())?;
    if m >= 60.0 || s >= 60.0 || h < 0.0 || m < 0.0 || s < 0.0 {
        return None;
    }
    if let Some(pm) = ampm {
        if !(0.0..=12.0).contains(&h) {
            return None;
        }
        if h == 12.0 {
            h = 0.0;
        }
        if pm {
            h += 12.0;
        }
    } else if h >= 10000.0 {
        return None;
    }
    Some((time_fraction(h, m, s), parts.len() == 3, ampm.is_some()))
}

fn parse_date(t: &str, sys: DateSystem) -> Option<(f64, &'static str)> {
    let t = t.trim().trim_end_matches(',');
    let num = |s: &str| s.trim().parse::<i64>().ok();
    // ISO yyyy-mm-dd or yyyy/mm/dd
    let seps: &[char] = &['/', '-', '.'];
    let parts: Vec<&str> = t.split(seps).collect();
    if parts.len() == 3 {
        let (a, b, c) = (parts[0].trim(), parts[1].trim(), parts[2].trim());
        if a.len() == 4
            && let (Some(y), Some(m), Some(d)) = (num(a), num(b), num(c))
        {
            return valid_ymd(sys, y, m, d).map(|s| (s, "yyyy-mm-dd"));
        }
        if let (Some(m), Some(d), Some(y)) = (num(a), num(b), num(c)) {
            let y = if c.len() <= 2 { if y < 30 { 2000 + y } else { 1900 + y } } else { y };
            return valid_ymd(sys, y, m, d).map(|s| (s, "m/d/yyyy"));
        }
        // 4-Mar-2026
        if let (Some(d), Some(m), Some(y)) = (num(a), month_from_name(b), num(c)) {
            let y = if c.len() <= 2 { if y < 30 { 2000 + y } else { 1900 + y } } else { y };
            return valid_ymd(sys, y, m as i64, d).map(|s| (s, "d-mmm-yy"));
        }
    }
    if parts.len() == 2 {
        let (a, b) = (parts[0].trim(), parts[1].trim());
        // m/d in the current year is ambiguous without a clock; use month/day of 2026? Excel uses
        // the current year. We accept d-mmm / mmm-d only with month names, and m/d → current year.
        if let (Some(m), Some(d)) = (num(a), num(b)) {
            let y = current_year();
            if (1..=12).contains(&m) && (1..=31).contains(&d) {
                return valid_ymd(sys, y, m, d).map(|s| (s, "d-mmm"));
            }
            // m/yyyy
            if (1..=12).contains(&m) && b.len() == 4 {
                return valid_ymd(sys, d, m, 1).map(|s| (s, "mmm-yy"));
            }
        }
        if let (Some(d), Some(m)) = (num(a), month_from_name(b)) {
            return valid_ymd(sys, current_year(), m as i64, d).map(|s| (s, "d-mmm"));
        }
        if let (Some(m), Some(y)) = (month_from_name(a), num(b)) {
            let y = if b.len() <= 2 { if y < 30 { 2000 + y } else { 1900 + y } } else { y };
            return valid_ymd(sys, y, m as i64, 1).map(|s| (s, "mmm-yy"));
        }
    }
    // "Mar 4, 2026" / "March 4 2026" / "4 March 2026"
    let words: Vec<&str> = t.split([' ', ',']).filter(|w| !w.is_empty()).collect();
    if words.len() == 3 {
        if let (Some(m), Some(d), Some(y)) = (month_from_name(words[0]), num(words[1]), num(words[2])) {
            return valid_ymd(sys, y, m as i64, d).map(|s| (s, "d-mmm-yy"));
        }
        if let (Some(d), Some(m), Some(y)) = (num(words[0]), month_from_name(words[1]), num(words[2])) {
            return valid_ymd(sys, y, m as i64, d).map(|s| (s, "d-mmm-yy"));
        }
    }
    None
}

fn valid_ymd(sys: DateSystem, y: i64, m: i64, d: i64) -> Option<f64> {
    // Dates before 1900 stay text (`DATE()` would add 1900 to such a year).
    if !(1..=12).contains(&m) || d < 1 || y < 1900 {
        return None;
    }
    let max = crate::date::days_in_month_in(sys, y as i32, m as u32) as i64;
    if d > max {
        return None;
    }
    serial_from_ymd(sys, y, m, d)
}

/// The year used for dates typed without one. Fixed per process from the system clock when
/// available (wasm without clock falls back to 2026).
#[allow(clippy::disallowed_methods)] // the clock is read only off wasm
pub fn current_year() -> i64 {
    #[cfg(not(target_arch = "wasm32"))]
    {
        if let Ok(d) = std::time::SystemTime::now().duration_since(std::time::UNIX_EPOCH) {
            let days = (d.as_secs() / 86400) as i64;
            return crate::date::civil_from_days(days).0 as i64;
        }
    }
    2026
}

fn parse_datetime(t: &str, sys: DateSystem) -> Option<(f64, Option<&'static str>)> {
    if let Some((tf, secs, ampm)) = parse_time(t) {
        let f = match (secs, ampm) {
            // 24 hours or more: elapsed hours, so 25:00 shows as 25:00:00, not 1:00.
            _ if tf >= 1.0 => "[h]:mm:ss",
            (false, false) => "h:mm",
            (true, false) => "h:mm:ss",
            (false, true) => "h:mm AM/PM",
            (true, true) => "h:mm:ss AM/PM",
        };
        return Some((tf, Some(f)));
    }
    if let Some((d, f)) = parse_date(t, sys) {
        return Some((d, Some(f)));
    }
    // date + time: split at the last space(s) before a time-looking tail.
    for (i, _) in t.match_indices(' ') {
        let (a, b) = (t.get(..i)?, t.get(i + 1..)?);
        if let (Some((d, _)), Some((tf, _, _))) = (parse_date(a, sys), parse_time(b)) {
            return Some((d + tf, Some("m/d/yyyy h:mm")));
        }
    }
    None
}

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

    fn p(s: &str) -> Parsed {
        parse_input(s, DateSystem::D1900)
    }

    #[test]
    fn numbers() {
        assert_eq!(p("42").value, Value::Number(42.0));
        assert_eq!(p("-3.5").value, Value::Number(-3.5));
        assert_eq!(p("1,234").format, Some("#,##0"));
        assert_eq!(p("1,234").value, Value::Number(1234.0));
        assert_eq!(p("1,23").value, Value::text("1,23"));
        assert_eq!(p("12%").value, Value::Number(0.12));
        assert_eq!(p("$1,200.50").value, Value::Number(1200.5));
        assert_eq!(p("$1,200.50").format, Some("\"$\"#,##0.00"));
        assert_eq!(p("(100)").value, Value::Number(-100.0));
        assert_eq!(p("1e3").value, Value::Number(1000.0));
        assert_eq!(p("1 1/2").value, Value::Number(1.5));
        assert_eq!(p(".5").value, Value::Number(0.5));
    }

    #[test]
    fn texts_and_specials() {
        assert_eq!(p("hello").value, Value::text("hello"));
        assert_eq!(p("'123").value, Value::text("123"));
        assert_eq!(p("true").value, Value::Bool(true));
        assert_eq!(p("#N/A").value, Value::Error(CellError::NA));
        assert_eq!(p("e").value, Value::text("e"));
        assert_eq!(p("-").value, Value::text("-"));
        assert_eq!(p("1.2.3.4").value, Value::text("1.2.3.4"));
    }

    #[test]
    fn dates_and_times() {
        assert_eq!(p("10/7/2026").value, Value::Number(46302.0));
        assert_eq!(p("2026-10-07").value, Value::Number(46302.0));
        assert_eq!(p("7-Oct-2026").value, Value::Number(46302.0));
        assert_eq!(p("Oct 7, 2026").value, Value::Number(46302.0));
        assert_eq!(p("2/30/2026").value, Value::text("2/30/2026"));
        assert_eq!(p("7/4/1776").value, Value::text("7/4/1776"));
        assert_eq!(p("1776-07-04").value, Value::text("1776-07-04"));
        assert_eq!(p("4-Jul-1776").value, Value::text("4-Jul-1776"));
        assert_eq!(p("12/31/1899").value, Value::text("12/31/1899"));
        assert_eq!(p("1/1/1900").value, Value::Number(1.0));
        assert_eq!(p("12:00").value, Value::Number(0.5));
        assert_eq!(p("6:00 PM").value, Value::Number(0.75));
        assert_eq!(p("12:00 AM").value, Value::Number(0.0));
        assert_eq!(p("10/7/2026 18:00").value, Value::Number(46302.75));
        assert_eq!(p("25:00").value, Value::Number(25.0 / 24.0));
        assert_eq!(p("25:00").format, Some("[h]:mm:ss"));
        assert_eq!(p("23:59").format, Some("h:mm"));
    }

    #[test]
    fn fictitious_1900_02_29() {
        // Excel accepts 29 February 1900 (serial 60) and keeps 1 March 1900 at 61.
        assert_eq!(p("2/29/1900").value, Value::Number(60.0));
        assert_eq!(p("1900-02-29").value, Value::Number(60.0));
        assert_eq!(p("29-Feb-1900").value, Value::Number(60.0));
        assert_eq!(p("2/28/1900").value, Value::Number(59.0));
        assert_eq!(p("3/1/1900").value, Value::Number(61.0));
        assert_eq!(p("2/29/1901").value, Value::text("2/29/1901"));
        assert_eq!(p("2/30/1900").value, Value::text("2/30/1900"));
        // The 1904 system starts after it.
        assert_eq!(parse_input("2/29/1900", DateSystem::D1904).value, Value::text("2/29/1900"));
        assert_eq!(parse_input("2/29/1904", DateSystem::D1904).value, Value::Number(59.0));
    }
}